Applied Surface Science (v.252, #19)

Author Index (III-XII).

Preface by John Vickerman; Ian Gilmore (xix-xx).

This paper provides a personal perspective on the recent development of mass spectrometry, arguing that these developments are increasingly driven by the research demands of the life sciences. Within that context, the analytical requirements of proteomics (the determination of the protein constituents of a cell or organism) provide useful examples of the need for very high sensitivity, selectivity to match the required analytical outcomes, rigorous quantification (both relative and absolute) of individual components, and quantitative definition of cellular processes.
Keywords: Mass spectrometry; Post-genome science; Proteomics; Proteins; Peptides;

The physical mechanisms underlying the surface based mass spectrometry techniques of atomic SIMS, MALDI and cluster SIMS are discussed along with the relation of the physics to the measured quantities. In particular, there are at least two types of motion resulting from cluster bombardment in SIMS. One scenario involves the individual atoms in the cluster initiating collision cascades similar to atomic bombardment. The second mechanism involves a mesoscale motion of the cluster as a whole. This mesoscale motion can induce an organized flow of the ejected material in a plume.
Keywords: Molecular dynamics; Simulation; SIMS; MALDI; Cluster SIMS; C60;

This paper constitutes an attempt to rationalise impact-energy dependent yields of molecular secondary ions emitted from polymer samples under bombardment with atomic and molecular primary ions. The evaluation was based upon a comparison with sputtering yields calculated from linear-cascade sputtering theory, including threshold effects. To explore general trends, sputtering yields for carbon, silicon and silver were calculated under impact of normally incident C, F, S, Ga, Xe, Au, SF5, C11, C60 and Au5. The yields of carbon, for example, bombarded with C60 are larger than for Ga by factors of ∼5 and ∼10 at 10 and 100 keV, respectively. However, owing to the fact that the effective threshold energy for sputtering increases with the number of constituents of the projectile, the yields for molecular ion impact start to exceed the yields for atomic ions only at energies between 0.5 and 5 keV. The analysed experimental results relate to molecular ion emission from one monolayer (1 ML) and 9 ML films of polymethacrylate on silver bombarded with Xe and SF5 ions at energies E between 0.5 and 10 keV. Comparison of (initial) secondary ion yields S + (m/z 143) with calculated sputtering yields suggests that S + constitutes the sum of two contributions. The first, labelled S lo + , prevails at low energies and appears to reflect molecule ejection due to the mean effect of nuclear energy deposition (“ordinary” linear-cascade sputtering). The second contribution, S hi + , dominates at E  > 1.5 keV, increases with a high power of E, but does not correlate with the calculated sputtering yield. It is suggested that S hi + is a measure of those impact events which occasionally generate a very high energy density at the surface, thus providing optimum conditions for very efficient ejection of molecules that are located at the rim of the agitated area. The SF5/Xe secondary ion yield ratios are distinctly different for the two contributions, only about 0.3 for S lo + but ∼4 (1 ML) and ∼20 (9 ML) for S hi + . The pronounced secondary ion “yield enhancement” frequently reported in the literature for molecular versus atomic ion bombardment appears to be due to an enlargement of the S hi + contribution, more so the higher the impact energy and the more massive the projectile. The total (integrated) secondary ion yields, estimated by making use of the reported damage cross sections, were found to be the same for SF5 bombardment of the 1-ML and the 9-ML samples. This finding calls for more attention towards obtaining high secondary ion yields at minimum sample consumption.
Keywords: Yield enhancement; Sputtering yields; Polymer layers; Additivity of yields; Sample consumption;

Sputtering of thin benzene and polystyrene overlayers by keV Ga and C60 bombardment by B. Czerwiński; A. Delcorte; B.J. Garrison; R. Samson; N. Winograd; Z. Postawa (6419-6422).
The mechanisms of ion-stimulated desorption of thin organic overlayers deposited on metal substrates by mono- and polyatomic projectiles are examined using molecular dynamics (MD) computer simulations. A monolayer of polystyrene tetramers (PS4) physisorbed on Ag{1 1 1} is irradiated by 15 keV Ga and C60 projectiles at normal incidence. The results are compared with the data obtained for a benzene overlayer to investigate the differences in sputtering mechanisms of weakly and strongly bound organic molecules. The results indicate that the sputtering yield decreases with the increase of the binding energy and the average kinetic energy of parent molecules is shifted toward higher kinetic energy. Although the total sputtering yield of organic material is larger for 15 keV C60, the impact of this projectile leads to a significant fragmentation of ejected species. As a result, the yield of the intact molecules is comparable for C60 and Ga projectiles. Our data indicate that chemical analysis of the very thin organic films performed by detection of sputtered neutrals will not benefit from the use of C60 projectiles.
Keywords: Sputtering; Cluster bombardment; Organic overlayers; SIMS/SNMS;

Sputtering of amorphous ice induced by C60 and Au3 clusters by Michael F. Russo; Igor A. Wojciechowski; Barbara J. Garrison (6423-6425).
Molecular dynamics simulations were performed to study the behavior of cluster SIMS. Two predominant cluster ion beam sources, C60 and Au3, were chosen for comparison. An amorphous water ice substrate was bombarded with incident energy of 5 keV. The C60 cluster was observed to shatter upon impact creating a crater of damage approximately 8 nm deep. Although Au3 was also found to both break apart and form a damage crater, it continued along its initial trajectory causing damage roughly 10 nm deep into the sample and becoming completely imbedded. It is suggested that this difference in behavior is due to the large mass of Au relative to the substrate water molecule.
Keywords: Molecular dynamics; Cluster ion; Au3; C60;

Sputtering of clusters from nickel–aluminium by B.V. King; J.F. Moore; W.F. Calaway; I.V. Veryovkin; M.J. Pellin (6426-6428).
A NiAl(1 1 1) single crystal was bombarded with 15 keV Ar+, and the resulting secondary neutrals were analysed by laser postionisation secondary neutral mass spectrometry. By measuring the individual cluster photoion intensity as a function of laser power, the sputter yields of 33 individual clusters were determined. The yield of Al n clusters sputtered from NiAl falls with increasing cluster nuclearity as n −8.7 while Ni n and Al mn Ni n yields are proportional to n −5.9 and n −5.2, respectively. The distribution of thee yields of mixed Al mn Ni n clusters with n and m is found to diverge significantly from the expected distribution based on a random combinatorial approach, indicating that the energetics due to the chemical bonding in the clusters plays a significant role during cluster formation in the sputtering process.
Keywords: Sputtering; Laser SNMS; NiAl;

Quantitative fundamental SIMS studies using 18O implant standards by Peter Williams; Richard C. Sobers; Klaus Franzreb; Jan Lörinčík (6429-6432).
The use of dilute ‘minor-isotope’18O implant reference standards for quantification of surface oxygen levels during steady-state SIMS depth profiling is demonstrated. Some results of two types of quantitative fundamental SIMS studies with oxygen (16O) primary ion bombardment and/or oxygen flooding (O2 gas with natural isotopic abundance) are presented: (1) Determination of elemental useful ion yields, UY(X±), and sample sputter yields, Y, as a function of the oxygen fraction c O measured in the total flux emitted from the sputtered surface. Examples include new results for positive secondary ion emission of several elements (X = B, C, O, Al, Si, Cu, Ga, Ge, Cs) from variably oxidized SiC or Ge surfaces. (2) The dependence of exponential decay lengths λ(Au±) in sputter depth profiles of gold overlayers on silicon on the amount of oxygen present at the sputtered silicon surface. The latter study elucidates the (element-specific) effects of oxygen-induced surface segregation artifacts for sputter depth profiling through metal overlayers into silicon substrates.
Keywords: Useful ion yield; Sputter yield; Segregation; Oxygen; Implant standard;

The low energy mono-atomic secondary ion intensities of Ag over the transient regions from Ag under 1–5 keV Cs+ primary ion impact are compared. These energies are used since they appear to be above and below the collisional excitation threshold for 4d core hole formation. The lack of any work function dependence in both suggests that (a) Ag forms via resonance charge transfer of electrons from the broad 5s–5p band to Ag atoms bearing 4d core holes (Auger is disregarded for energetic reasons), and that (b) the route via which 4d core holes are formed, whether it be via collective oscillations or collisional excitation, is of minimal importance. The similarity in X-ray induced plasmon loss features from clean and Cs implanted Ag confers with these results.
Keywords: Secondary ion emission; Collective oscillations; Silver;

Coarse-grained molecular dynamics studies of cluster-bombarded benzene crystals by Edward J. Smiley; Zbigniew Postawa; Igor A. Wojciechowski; Nicholas Winograd; Barbara J. Garrison (6436-6439).
As high-energy cluster projectile beams become standard analysis probes for SIMS, simulating larger crystals is now a requirement for the modeling community due to the large sputtering yields. As crystals get larger, computer resources become a limitation. Even though computer technology has evolved to include large memory systems and fast processors, there are still issues with having sufficient resources to run a calculation. This manuscript reports a method of studying a full crystal of benzene after impact with a 500 eV C60 projectile using a coarse-grained model. The potentials developed for this model incorporate the C―H bond of benzene into a single coarse-grained bead. This coarse-grained method has several advantages over atomistic models—the amount of time to perform these calculations has been drastically reduced and the potentials for this sample are pair-wise additive potentials. A discussion is made as to how these results compare to those obtained with fully atomistic calculations using the AIREBO potential.
Keywords: Molecular dynamics; Simulation; Cluster; C60; SIMS;

In this work, a caesium/xenon co-sputtering gun was used to perform depth profiles of a RhSi layer with varying caesium beam concentration. The positive ion yields were monitored with respect to the varying work function of the solid and the intensities of the ions were plotted with respect to the caesium surface concentration. As expected by the tunneling model, all the M+ signals decrease exponentially with the increasing caesium beam concentration. Moreover, the heaviest ion yields decrease faster than the lighter ion ones. This phenomenon can be explained by the different velocities of the departing atoms, which has an important impact on the ionization processes. We then studied the variations of the MCs+ yields with respect to the caesium surface concentration and with respect to the nature of the departing atom. Finally, we applied models based on the tunneling model in order to fit our results.
Keywords: Ionization; Caesium; MCs; ToF-SIMS; Rh; Si; Depth profile;

Sputter yields in diamond bombarded by ultra low energy ions by B. Guzmán de la Mata; M.G. Dowsett; D. Twitchen (6444-6447).
Artificial diamond is an ideal material for high power, high voltage electronic devices, and for engineering use in extreme environments. Diamond process development requires parallel development in characterization techniques such as ultra low energy SIMS (uleSIMS), especially in the ability to depth profile for impurities and dopants at high depth resolution.As a contribution to the background knowledge required, we have measured the sputter yields of single crystal high pressure high temperature (HPHT) diamond using O2 +, Cs+ and Ar+ primary ions in the energy range 300 eV to 2 keV. We compare these with yields for silicon and GaAs. We show that the erosion rates with oxygen are ∼10 times what would be expected from ballistic processes and essentially energy independent in the measured range. This result agrees with the anomalously high sputter yield observed in the ion etching context. Conversely, positive ion yields for elements such as boron are very low in comparison with silicon. This points to a reactive ion etching process liberating CO or CO2 rather than sputtering as the principal erosion process.This is both problematic and beneficial for SIMS analysis. Oxygen can be used to reach buried structures in diamond efficiently, and the effects of the near-normal incidence beam are planarizing as they are in silicon. Conversely, since positive ion yields are low, alternative probes or strategies must be found for high sensitivity profiling of electropositive elements.
Keywords: Sputter yields; Diamond; uleSIMS; Oxygen bombardment; Caesium bombardment; Argon bombardment;

In this paper, the SIMS beam induced roughness (BIR) in monocrystalline Si in presence of initial surface or bulk defects of nanometric size is studied. We follow the development of the BIR by monitoring the increase of Si2+ and SiO2 + signals during SIMS sputtering. The topography of the crater bottoms is measured at different steps of the evolution of the roughness using an atomic force microscope (AFM). We show that in presence of nanometric sized defects on the surface or in the bulk, the BIR develops far more rapidly than usual. It appears as soon as the crater reaches the defects and, as reported on Si free from any treatment, the same morphology evidencing waves perpendicular to the sputtering beam develops rapidly. This study of the behaviour of the BIR in presence of voluntarily introduced defects allows us to better understand the basic physical phenomena involved in its apparition.
Keywords: RMS roughness; Cavities; Silicon; SIMS; Topography; AFM;

Determination of energy dependent ionization probabilities of sputtered particles by P. Mazarov; A.V. Samartsev; A. Wucher (6452-6455).
We present a novel method to determine the spectral ionization probability of sputtered species as a function of their emission velocity or energy. The technique is based on detection of neutral and ionic species in a reflectron time-of-flight mass spectrometer under otherwise identical experimental conditions. Using a pulsed ion extraction scheme in combination with sufficiently short primary ion pulses, the spectral ionization probability α + ( v ) can be determined without knowledge of possible energy discrimination effects in instrument transmission. Comparing the measured ionization probability with theoretical predictions, we find that none of the prevailing ionization models is capable of describing the experimental data over the whole velocity range studied.
Keywords: Kinetic energy distribution; Spectral ionization probability; Sputtering;

The low energy Si2 , Si3 and Si4 secondary ion signals resulting from Cs+ impact on Si appear to scale with the Cs uptake noted over the SIMS transient region in a manner consistent with the electron tunneling model. These populations, particularly Si3 and Si4 also exhibit a relative insensitivity to the presence of O (shown once sputter rate variations are accounted for). Profiles that more closely match the expected Si concentration gradient from a native oxide terminated Si wafer present within the SIMS transient region can also be obtained by simply dividing the Si3 or Si4 secondary ion intensities by the Si2 intensities. This suggests a possible alternative route for reducing transient effects present in the negative secondary ion populations from Si wafers.
Keywords: Secondary ion emission; Transient effects; Silicon;

Modeling the dissociation and ionization of a sputtered organic molecule by V. Solomko; M. Verstraete; A. Delcorte; B.J. Garrison; X. Gonze; P. Bertrand (6459-6462).
The evolution of an organic molecule after sputtering from a gold surface has been analyzed by classical molecular dynamics and ab initio calculations to gain insight into the ionization and fragmentation processes occurring in SIMS. The calculated ionization potential (6.2 eV) of the tetraphenylnaphthalene (TPN) molecule has been found to be close to the unimolecular dissociation energy (5.4 eV) of the most favorable reaction channel involving the loss of a phenyl ring. On the other hand, our calculations show that the internal energies of sputtered TPN molecules can be significantly larger than 5–6 eV. Therefore, it appears energetically possible to relax such excited molecules via both fragmentation and ionization.We propose to virtually decompose the TPN molecule into its basic fragments. The rationale is that, if the molecule is very excited, then separate parts (e.g. pendant phenyl rings) can interact with each other almost independently. The analysis of the molecular motion after emission shows that the oscillations along the phenyl-naphthalene bond direction, expected to induce the molecule fragmentation by the loss of a phenyl ring, are relatively small (they store only about 0.2 eV). On the other hand, the relative energy stored in the inter-phenyl interactions, modulated by their bending and responsible for ionization according to our hypothesis, oscillates over a range of 6–7 eV and favors ionization.
Keywords: Sputtering; Energy dissipation; Ionization; Fragmentation; Secondary ion mass spectrometry; Molecular dynamics simulations; First principles; Ion emission;

Bombardment induced surface chemistry on Si under keV C60 impact by Kristin D. Krantzman; David B. Kingsbury; Barbara J. Garrison (6463-6465).
Molecular dynamics simulations of the sputtering of Si by C60 keV bombardment are performed in order to understand the importance of chemical reactions between C atoms from the projectile and Si atoms in the target crystal. The simulations predict the formation of strong covalent bonds between the C and Si atoms, which result in nearly all of the C atoms remaining embedded in the surface after bombardment. At low incident kinetic energies, little sputtering of Si atoms is observed and there is a net deposition of solid material. As the incident kinetic energy is increased, the sputtering yield of Si atoms increases. At 15 keV, the yield of sputtered Si atoms is more than twice the number of C atoms deposited, and there is a net erosion of the solid material.
Keywords: ToF-SIMS; Cluster ion; C60 +; Sputtering; Si;

Molecular dynamics (MD) simulations of sputtering process with fluorine cluster impact onto silicon targets were performed. By iterating collisional simulations on a same target, accumulation of incident atoms and evolution of surface morphology were examined as well as emission process of precursors. When (F2)300 clusters were sequentially irradiated on Si(1 0 0) target at 6 keV of total incident energy, column-like surface structure covered with F atoms was formed. As the number of incident clusters increased, sputtering yield of Si atoms also increased because the target surface was well fluoridised to provide SiF x precursors. Size distribution of emitted particles showed that SiF2 was the major sputtered particle, but various types of silicon-fluoride compounds such like Si2F x , Si3F x and very large molecules consists of 100 atoms were also observed. This size distribution and kinetic energy distribution of desorbed materials were studied, which showed that the sputtering mechanism with reactive cluster ions is similar to that under thermal equilibrium condition at high-temperature.
Keywords: Molecular dynamics simulation; Fluorine; Cluster; Sputtering process; Surface morphology;

Kinetic energy distributions of neutral In monomers and In2 dimers sputtered from a polycrystalline indium surface under bombardment with 5 keV/atom Au1 and Au2 projectiles have been investigated by means of laser postionization time-of-flight mass spectrometry. Results show that 5 keV Au1 bombardment leads to results in full compliance with linear cascade sputtering theory. For polyatomic ion bombardment, we find a clear transition to a collisional spike dominated emission process. The spike contribution appears as a low-energy part in the sputtered flux which increases with increasing projectile nuclearity and energy. We show that, the velocity spectrum associated with the low-energy contribution is virtually identical for sputtered monomers and dimers. This finding has important implications with respect to the particle emission mechanism under polyatomic projectile bombardment.
Keywords: ToF-SNMS; Cluster emission; Sputtering; Kinetic energy distributions;

The emission of neutral and charged atoms and clusters from a polycrystalline indium surface under bombardment with 5 and 10 keV Au, Au2, Au3 and Au5 projectiles was investigated. Single photon laser postionization was utilized for the detection of sputtered neutral particles. Secondary ions were detected without the laser under otherwise exactly the same experimental conditions. The relative cluster yields were found to be enhanced under polyatomic projectile bombardment, more so the larger the number of atoms in the sputtered cluster. The ionization probability strongly increases with increasing cluster size, but is essentially independent of the projectile impact energy. At a fixed impact energy, the ionization probability of sputtered monomers was found to decrease with increasing number of constituent gold atoms per projectile, but there was no detectable effect for sputtered dimers and larger clusters.
Keywords: ToF-SNMS; Cluster emission; Sputtering; Ionization;

Deconvolution of very low primary energy SIMS depth profiles by B. Fares; B. Gautier; J.C. Dupuy; G. Prudon; P. Holliger (6478-6481).
In this paper, the deconvolution of SIMS profiles analysed at very low primary energy (0.5 keV/O2 +) is addressed. The depth resolution function (DRF) of the SIMS analysis in presence of roughness is established and a deconvolution procedure is implemented without or in presence of roughness on samples containing delta-doped layers of boron in silicon. It is shown that the deconvolution procedure can lead to a great improvement of the full width at half maximum (FWHM) of the measured peaks in the case where no roughness in detected in the crater bottom. In the case where it is present, the conditions required to use a deconvolution procedure are discussed, and the deconvolution is implemented using precise and restrictive assumptions.
Keywords: Roughness; Deconvolution; Depth resolution function (DRF); Delta-doped layers;

A brief review is given regarding the application of cluster ion beams as desorption probes in molecular SIMS. The general observation is that the efficiency of secondary ion formation, particularly that of complex molecular species, is significantly enhanced if polyatomic projectiles are employed instead of atomic species. Apart from the sensitivity increase, cluster bombardment also appears to allow for molecular depth profiling studies without the accompanying damage accumulation normally associated with atomic projectiles. A few fundamental aspects are addressed in an attempt to highlight the physics behind these observations. It appears that much of the benefit associated with cluster bombardment is connected to the fact that these projectiles give access to very high sputter yields which are not accessible with atomic primary ions.
Keywords: Cluster SIMS; Cluster bombardment; Polyatomic projectiles; Molecular secondary ion formation;

Molecular ion emission from single large cluster impacts by S.V. Verkhoturov; R.D. Rickman; C. Guillermier; G.J. Hager; J.E. Locklear; E.A. Schweikert (6490-6493).
We investigated the emission of the secondary ions stimulated by single impacts of 136 keV Au400 4+ projectiles. The study was carried out on targets of glycine, phenylalanine, and C60. In addition, a target of C60 was examined with 18 keV C60 + projectiles. The experiments were performed in the event-by-event bombardment/detection mode. The secondary ions were identified with linear time-of-flight mass spectrometer equipped with an 8-anode detector. The Au400 4+ projectile induces abundant multi-ion emission, for instance the average number of detected ions (atomic, fragment, molecular and cluster ions) emitted per event from glycine target is 12.5. The glycine intact molecular ion (Gly) yield is 1.14. The bombardment of a C60 target results in the efficient emission of multiple intact C60 (total yield is 0.15).
Keywords: Gold clusters; Secondary ion mass spectrometry; Intact molecules; Multi-ion emission; C60;

Stretching the limits of static SIMS with C60 + by A. Delcorte; C. Poleunis; P. Bertrand (6494-6497).
Pristine and Au-covered molecular films have been analyzed by ToF-SIMS (TRIFT™), using 15 keV Ga+ (FEI) and 15 keV C60 + (Ionoptika) primary ion sources. The use of C60 + leads to an enormous yield enhancement for gold clusters, especially when the amount of gold is low (2 nmol/cm2), i.e. a situation of relatively small nanoparticles well separated in space. It also allows us to extend significantly the traditional mass range of static SIMS. Under 15 keV C60 + ion bombardment, a series of clusters up to a mass of about 20,000 Da (Au100 : 19,700 Da) is detected. This large yield increase is attributed to the hydrocarbon matrix (low-atomic mass), because the yield increase observed for thick metallic films (Ag, Au) is much lower. The additional yield enhancement factors provided by the Au metallization procedure for organic ions (MetA-SIMS) have been measured under C60 + bombardment. They reach a factor of 2 for the molecular ion and almost an order of magnitude for Irganox fragments such as C4H9 +, C15H23O+ and C16H23O.
Keywords: Cluster SIMS; MetA-SIMS; C60; Metallization; Irganox; Gold clusters;

Cluster bombardment of molecular films has created new opportunities for SIMS research. To more quantitatively examine the interaction of cluster beams with organic materials, we have developed a reproducible platform consisting of a well-defined sugar film (trehalose) doped with peptides. Molecular depth profiles have been acquired with these systems using C60 + bombardment. In this study, we utilize this platform to determine the feasibility of examining buried interfaces for multi-layer systems. Using C60 + at 20 keV, several systems have been tested including Al/trehalose/Si, Al/trehalose/Al/Si, Ag/trehalose/Si and ice/trehalose/Si. The results show that there can be interactions between the layers during the bombardment process that prevent a simple interpretation of the depth profile. We find so far that the best results are obtained when the mass of the overlayer atoms is less than or nearly equal to the mass of the atoms in buried molecules. In general, these observations suggest that C60 + bombardment can be successfully applied to interface characterization of multi-layer systems if the systems are carefully chosen.
Keywords: Molecular depth profiling; Trehalose film; Multi-layer; Cluster ion; ToF-SIMS; C60 +;

Temperature-controlled depth profiling in polymeric materials using cluster secondary ion mass spectrometry (SIMS) by Christine M. Mahoney; Albert J. Fahey; Greg Gillen; Chang Xu; James D. Batteas (6502-6505).
Secondary ion mass spectrometry (SIMS) employing an SF5 + polyatomic primary ion source was used to depth profile through poly(methylmethacrylate) (PMMA), poly(lactic acid) (PLA) and polystyrene (PS) thin films at a series of temperatures from −125 °C to 150 °C. It was found that for PMMA, reduced temperature analysis produced depth profiles with increased secondary ion stability and reduced interfacial widths as compared to analysis at ambient temperature. Atomic force microscopy (AFM) images indicated that this improvement in interfacial width may be related to a decrease in sputter-induced topography. Depth profiling at higher temperatures was typically correlated with increased sputter rates. However, the improvements in interfacial widths and overall secondary ion stability were not as prevalent as was observed at low temperature. For PLA, improvements in signal intensities were observed at low temperatures, yet there was no significant change in secondary ion stability, interface widths or sputter rates. High temperatures yielded a significant decrease in secondary ion stability of the resulting profiles. PS films showed rapid degradation of characteristic secondary ion signals under all temperatures examined.
Keywords: Depth profiles; SIMS; TOF; Cluster; SF5 +; AFM; XPS; Polymers; Poly(methyl methacrylate); PMMA; Temperature; Poly(lactic acid); PLA; Polystyrene; PS; Glass transition;

Using polyatomic primary ions to probe an amino acid and a nucleic base in water ice by X.A. Conlan; G.X. Biddulph; N.P. Lockyer; J.C. Vickerman (6506-6508).
In this study on pure water ice, we show that protonated water species [H2O] n H+ are more prevalent than (H2O) n + ions after bombardment by Au+ monoatomic and Au3 + and C60 + polyatomic projectiles. This data also reveals significant differences in water cluster yields under bombardment by these three projectiles. The amino acid alanine and the nucleic base adenine in solution have been studied and have been shown to have an effect on the water cluster ion yields observed using an Au3 + ion beam.
Keywords: Nucleic base; Amino acid; Polyatomic ions; Water ice;

Chemical effects in C60 irradiation of polymers by R. Möllers; N. Tuccitto; V. Torrisi; E. Niehuis; A. Licciardello (6509-6512).
The C60 erosion behaviour of poly(methyl)methacrylate (PMMA), poly(α-methyl)styrene (PAMS) and polystyrene (PS) has been studied at various temperatures and compared with that under Ga+ irradiation. Strong variations of erosion yields are observed, indicating that chemical degradation mechanisms are operating. In particular, our results suggest that fast depolymerization mechanisms are important in leaving the surface of the sputter crater virtually undamaged. Since such mechanisms are connected with the chemical nature of the polymer, the possibility of performing molecular depth profiling of polymers with C60 appears to depend strongly on the chemical nature of the system under study.
Keywords: ToF-SIMS; Cluster SIMS; Fullerene ion beam; Depth profiling; Polymers; Radiation damage;

Molecular depth profiling of organic and biological materials by John S. Fletcher; Xavier A. Conlan; Nicholas P. Lockyer; John C. Vickerman (6513-6516).
Atomic depth profiling using secondary ion mass spectrometry, SIMS, is common in the field micro-electronics; however, the generation of molecular information as a function of sample depth is difficult due to the accumulation of damage both on and beneath the sample surface. The introduction of polyatomic ion beams such as SF5 and C60 have raised the possibility of overcoming this problem as they deposit the majority of their energy in the upper surface of the sample resulting in increased sputter yields but with a complimentary reduction in sub-surface damage accumulation. In this paper we report the depth profile analysis of the bio-polymer polycaprolactone, PCL, using the polyatomic ions A u 3 + and C 60 + and the monoatomic Au+. Results are compared to recent analysis of a similar sample using S F 5 + . C 60 + depth profiling of cellulose is also demonstrated, an experiment that has been reported as unsuccessful when attempted with S F 5 + implications for biological analysis are discussed.
Keywords: ToF-SIMS; Polyatomic ion beams; Molecular depth profiling;

A series of carbon-coated magnetic recording disks proved ideal for exploring sampling depth and ion formation trends as a function of variations in energy and cluster size (Au x ) of the primary ion beam, and variations in over coat thickness and type. Ion yield from the underlying metal layer increased with increasing energy and decreasing cluster size of the primary ions. The yields varied nearly linearly with over layer thickness. In contrast, M x Cs y depth profiles were unaffected by changes in the primary ion. The samples were fortuitously dosed with dinonyl phthalate, allowing a study similar to prior GSIMS work [I.S. Gilmore, M.P. Seah, J.E. Johnstone, in: A. Benninghoven, P. Bertrand, H.-N. Migeon, H.W. Werner (Eds.), Proceedings of the 12th International Conference on SIMS, Elsevier, Brussels, 2000, p. 801]. Ions prominent in the EI mass spectrum, including even electron ions, were more consistently enhanced at lower energies and higher cluster sizes than the primary (M  + H)+ ion. The total secondary ion count was inversely proportional to the film thickness. Secondary electrons, largely originating in the buried metal layer, may be inducing organic ion formation [A.M. Spool, Surf. Interface Anal. 36 (2004) 264].
Keywords: ToF-SIMS; Cluster ion depth profiling; Magnetic recording disks; Static SIMS;

Depth profiling using C60 + SIMS—Deposition and topography development during bombardment of silicon by Greg Gillen; James Batteas; Chris A. Michaels; Peter Chi; John Small; Eric Windsor; Albert Fahey; Jennifer Verkouteren; K.J. Kim (6521-6525).
A C60 + primary ion source has been coupled to an ion microscope secondary ion mass spectrometry (SIMS) instrument to examine sputtering of silicon with an emphasis on possible application of C60 + depth profiling for high depth resolution SIMS analysis of silicon semiconductor materials. Unexpectedly, C60 + SIMS depth profiling of silicon was found to be complicated by the deposition of an amorphous carbon layer which buries the silicon substrate. Sputtering of the silicon was observed only at the highest accessible beam energies (14.5 keV impact) or by using oxygen backfilling. C60 + SIMS depth profiling of As delta-doped test samples at 14.5 keV demonstrated a substantial (factor of 5) degradation in depth resolution compared to Cs+ SIMS depth profiling. This degradation is thought to result from the formation of an unusual platelet-like grain structure on the SIMS crater bottoms. Other unusual topographical features were also observed on silicon substrates after high primary ion dose C60 + bombardment.
Keywords: Fullerene ion source; Cluster bombardment; Depth profiling; Secondary ion mass spectrometer;

Fundamental studies of the cluster ion bombardment of water ice by Christopher Szakal; Joseph Kozole; Nicholas Winograd (6526-6528).
The fundamental sputtering properties of water ice are of interest for molecular depth profiling of biological samples in their native environment. We report on a method of studying amorphous water ice films of precise thicknesses in which pure water vapor is condensed onto a pre-cooled, silver-coated quartz crystal microbalance (QCM). This scheme allows for the determination of water ice sputter yields for any primary projectile as well as providing a means for studying escape depths of atoms and molecules beneath the deposited water ice layer. Specifically, we find a removal of approximately 2500 water molecule equivalents/20 keV C60 + projectile with an underlying silver ion escape depth of 7.0 Å.
Keywords: ToF-SIMS; Cluster ion; Water ice; Sputter yield; C60 +;

Influence of massive projectile size and energy on secondary ion yields from organic surfaces by C. Guillermier; S. Della Negra; R.D. Rickman; V. Pinnick; E.A. Schweikert (6529-6532).
We investigated the influence of the projectile size and energy using Au n q+ clusters (5 <  n  < 400, 1 <  q  < 4) impacting on a glycine target with a 19q–34q  keV energy range. We show that both CN fragment and Gly molecular ion yields are equivalent for projectiles with n  > 9 and increase with the energy per projectile atoms. A maximum yield of 0.5 (50%) for both CN and Gly was obtained with the Au400 4+ projectile at 136 keV total energy. For Gly, the yield enhancement is linear for Au n when n  > 5. Trends for the CN fragment are different. A nonlinear yield enhancement proportional to n 3 is observed for Au n when n  < 9.
Keywords: Secondary ion emission; Gold massive projectile; Ion yield;

Sputtering yields of PMMA films bombarded by keV C60 + ions by I.L. Bolotin; S.H. Tetzler; L. Hanley (6533-6536).
A quartz crystal microbalance (QCM) has been used to determine total-mass sputtering yields of PMMA films by 1–16 keV C60 +,2+ ion beams. Quantitative sputtering yields for PMMA are presented as mass loss per incident ion Y m . Mass-lost rate QCM data show that a 13 keV C60 cluster leads to emission equivalent to 800 PMMA molecules per ion. The power law obtained for the increase in sputtering yield with primary ion energy is in good agreement those predicted by “thermal spike” regime and MD models, when crater sizes are used to estimate sputtering.
Keywords: Sputtering yield; Polymers; PMMA; Cluster; C60; Secondary ion mass spectrometry;

3D molecular imaging SIMS by Greg Gillen; Albert Fahey; Matt Wagner; Christine Mahoney (6537-6541).
Thin monolayer and bilayer films of spin cast poly(methyl methacrylate) (PMMA), poly(2-hydroxyethyl methacrylate) (PHEMA), poly(lactic) acid (PLA) and PLA doped with several pharmaceuticals have been analyzed by dynamic SIMS using SF5 + polyatomic primary ion bombardment. Each of these systems exhibited minimal primary beam-induced degradation under cluster ion bombardment allowing molecular depth profiles to be obtained through the film. By combing secondary ion imaging with depth profiling, three-dimensional molecular image depth profiles have been obtained from these systems. In another approach, bevel cross-sections are cut in the samples with the SF5 + primary ion beam to produce a laterally magnified cross-section of the sample that does not contain the beam-induced damage that would be induced by conventional focussed ion beam (FIB) cross-sectioning. The bevel surface can then be examined using cluster SIMS imaging or other appropriate microanalysis technique.
Keywords: Beam-induced damage; Cluster bombardment; Depth profile; Secondary ion mass spectrometry;

Energy distributions of atomic and molecular ions sputtered by C60 + projectiles by A. Delcorte; C. Poleunis; P. Bertrand (6542-6546).
In the process of investigating the interaction of fullerene projectiles with adsorbed organic layers, we measured the kinetic energy distributions (KEDs) of fragment and parent ions sputtered from an overlayer of polystyrene (PS) oligomers cast on silver under 15 keV C60 + bombardment. These measurements have been conducted using our TRIFT™ spectrometer, recently equipped with the C60 + source developed by Ionoptika, Ltd. For atomic ions, the intensity corresponding to the high energy tail decreases in the following order: C+(E −0.4) > H+(E −1.5) > Ag+(E −3.5). In particular, the distribution of Ag+ is not broader than those of Ag2 + and Ag3 + clusters, in sharp contrast with 15 keV Ga+ bombardment. On the other hand, molecular ions (fragments and parent-like species) exhibit a significantly wider distribution using C60 + instead of Ga+ as primary ions. For instance, the KED of Ag-cationized PS oligomers resembles that of Ag+ and Ag n + clusters. A specific feature of fullerene projectiles is that they induce the direct desorption of positively charged oligomers, without the need of a cationizing metal atom. The energy spectrum of these PS+ ions is significantly narrower then that of Ag-cationized oligomers. For characteristic fragments of PS, such as C7H7 + and C15H13 + and polycyclic fragments, such as C9H7 + and C14H10 +, the high energy decay is steep (E −4  −  E −8). In addition, reorganized ions generally show more pronounced high energy tails than characteristic ions, similar to the case of monoatomic ion bombardment. This observation is consistent with the higher excitation energy needed for their formation. Finally, the fraction of hydrocarbon ions formed in the gas phase via unimolecular dissociation of larger species is slightly larger with gallium than with fullerene projectiles.
Keywords: Cluster SIMS; C60; Polystyrene; Silver; Kinetic energy distributions;

We investigated the enhancement of the secondary ion intensity in the TOF-SIMS spectra obtained by Au+ and Au3 + bombardment in comparison with Ga+ excitation using polymer samples with different molecular weight distributions. Since the polymer samples used in this experiment have a wide molecular weight distribution, the advantages of the gold cluster primary ion source over monoatomic ion could accurately be evaluated. It was observed that the degree of fragmentation decreased by the usage of cluster primary ion beam compared with monoatomic ion beam, which was observed as a shift of the intensity distribution in the spectra. It was also found out that the mass effect of Au+ and Ga+ as monoatomic primary ion, resulted in about 10–60 times of enhancement for both samples with different molecular distributions. On the other hand, the Au3 + bombardment caused intensity enhancement about 100–2600 compared with Ga+ bombardment, depending on the mass range of the detected secondary ion species. The cluster primary ion effect of Au3 +, compared with Au+, therefore, was estimated to be about 10–45.
Keywords: TOF-SIMS; Gold cluster ion; Intensity enhancement; Polyethylene glycol; Fragmentation; Molecular weight distribution;

High-intensity Si cluster ion emission from a silicon target bombarded with large Ar cluster ions by Satoshi Ninomiya; Takaaki Aoki; Toshio Seki; Jiro Matsuo (6550-6553).
Secondary ions emitted from Si targets were measured with a quadrupole mass spectrometer under large Ar cluster and monomer ion bombardment. Incident ion beams with energies from 7.5 to 25 keV were used and the mean size of the Ar cluster ion was about 1000 atoms/cluster. Si n + ions with n values up to n  = 8 were detected under Ar cluster ion bombardment, whereas Si cluster ions were scarcely detected under Ar monomer ion bombardment. These cluster ion yields showed the power law dependence on the cluster size.
Keywords: Ar cluster ion; Secondary ion; Low energy; Sputtering yield;

Characterization of drug-eluting stent (DES) materials with cluster secondary ion mass spectrometry (SIMS) by Christine M. Mahoney; Dinesh V. Patwardhan; M. Ken McDermott (6554-6557).
Secondary ion mass spectrometry (SIMS) employing an SF5 + polyatomic primary ion source was utilized to analyze several materials commonly used in drug-eluting stents (DES). Poly(ethylene-co-vinyl acetate) (PEVA), poly(lactic-co-glycolic acid) (PLGA) and various poly(urethanes) were successfully depth profiled using SF5 + bombardment. The resultant molecular depth profiles obtained from these polymeric films showed very little degradation in molecular signal as a function of increasing SF5 + primary ion dose when experiments were performed at low temperatures (signal was maintained for doses up to ∼5 × 1015 ions/cm2). Temperature was determined to be an important parameter in both the success of the depth profiles and the mass spectral analysis of the polymers. In addition to the pristine polymer films, paclitaxel (drug released in Taxus™ stent) containing PLGA films were also characterized, where it was confirmed that both drug and polymer signals could be monitored as a function of depth at lower paclitaxel concentrations (10 wt%).
Keywords: Depth profile; SIMS; Stents; Coronary; Drug-eluting; DES; Biomaterials; Cluster; SIMS; SF5 +; Polymers; Temperature; Paclitaxel;

Au-analyte adducts resulting from single massive gold cluster impacts by G.J. Hager; C. Guillermier; S.V. Verkhoturov; E.A. Schweikert (6558-6561).
Utilizing Au400 4+ primary ions produces large molecular ion yields, some in excess of unity, with minimal surface damage. A surprising observation is the occurrence of Au-analyte adducts as part of the ejecta desorbed by a single Au-cluster impact. We present data that demonstrate that Au and Au-adducts as secondary ions (e.g., AuCN, AuGly and AuCsI) are the result of the interaction between a single primary ion, Au400 4+ and the target atoms.
Keywords: Cluster-SIMS; Adducts; Massive Au clusters;

Polyethylene terephthalate (PET) bulk film analysis using C60 +, Au3 +, and Au+ primary ion beams by X.A. Conlan; I.S. Gilmore; A. Henderson; N.P. Lockyer; J.C. Vickerman (6562-6565).
The damage characteristics of polyethylene terephthalate (PET) have been studied under bombardment by C60 +, Au3 + and Au+ primary ions. The observed damage cross-sections for the three ion beams are not dramatically different. The secondary ion yields however were significantly enhanced by the polyatomic primary ions where the secondary ion yield of the [M + H]+ is on average 5× higher for C60 + than Au3 + and 8× higher for Au3 + than Au+. Damage accumulates under Au+ and Au3 + bombardment while C60 + bombardment shows a lack of damage accumulation throughout the depth profile of the PET thick film up to an ion dose of ∼1 × 1015 ions cm−2. These properties of C60 + bombardment suggest that the primary ion will be a useful molecular depth profiling tool.
Keywords: Polyethylene terephthalate; C60 +; Au3 +; Au+; Yield; Damage study;

In order to investigate the secondary cluster ion emission process of organo-metallic compounds under keV ion bombardment, self-assembled monolayers (SAMs) of alkanethiols on gold are ideal model systems. In this experimental study, we focussed on the influence of the primary ion species on the emission processes of gold–alkanethiolate cluster ions from a hexadecanethiol SAM on gold. For this purpose, we carried out time-of-flight secondary ion mass spectrometry (TOF-SIMS) measurements using the following primary ion species and acceleration voltages: Ar+, Xe+, SF5 + (10 kV), Bi+, Bi3 +(25 kV), Bi3 2+, Bi5 2+, Bi7 2+ (25 kV).It is well known that molecular ions M and gold–alkanethiolate cluster ions Au x M y with M = S-(CH2)15-CH3, x  − 3 ≤  y  ≤  x  + 1, x, y  > 0, show intense peaks in negative mass spectra. We derived yields Y SI exemplarily for the molecular ions M and the gold–hexadecanethiolate cluster ions Au y+1M y up to y  = 8 and found an exponentially decreasing behaviour for increasing y-values for the cluster ions.In contrast to the well-known increase in secondary ion yield for molecular secondary ions when moving from lighter to heavier (e.g. Ar+ to Xe+) or from monoatomic to polyatomic (e.g. Xe+ to SF5 +) primary ions, we find a distinctly different behaviour for the secondary cluster ions. For polyatomic primary ions, there is a decrease in secondary ion yield for the gold–hexadecanethiolate clusters whereas the relative decrease of the secondary ion yield ξ Y with increasing y remains almost constant for all investigated primary ions.
Keywords: ToF-SIMS; Alkanethiols; Cluster; SAM; Gold;

SSIMS analysis of organics, polymer blends and interfaces by Lu-Tao Weng; Chi-Ming Chan (6570-6574).
This paper gives a critical review on the applications of ToF SIMS in the areas of polymer additive characterization and in the study of polymer blends and interfaces. Polymer additives can readily be identified by ToF SIMS using their parent molecular ions or characteristic fragments. This analytical capability has been successfully applied to monitor the migration or segregation of additives during polymer processing. ToF SIMS is an ideal analytical tool for the study of polymer blends and interfaces because it is able to provide information on both surface composition and morphology. In combination with other analytical techniques such as AFM and XPS, ToF SIMS chemical imaging capability has opened up new horizons in the investigation of complex polymer blend systems. Finally the main advantages and limitations of ToF SIMS in these application areas are also discussed.
Keywords: ToF SIMS; Additives; Polymer blends; Interfaces; Surface composition; Morphology;

As analytical problems addressed using time-of-flight secondary ion mass spectrometry (ToF-SIMS) increase in chemical complexity, multivariate analysis (MVA) methods have become standard tools for simplifying the interpretation of ToF-SIMS spectra and images. MVA methods can significantly simplify ToF-SIMS datasets by providing a comprehensive description of the data using a small number of variables, typically in an automated fashion requiring minimal user intervention. However, successful and widespread application of MVA methods to SIMS data analysis is limited by a lack of understanding of the outputs of MVA methods and optimization of these methods for ToF-SIMS data analysis. Appropriate selection of data pre-processing and MVA tools are critical for accurate interpretation of ToF-SIMS spectra and images. As an example, an image dataset of a selectively ion-etched polymer film was analyzed to identify and characterize the chemically distinct regions in the image. Principal component analysis (PCA) and multivariate curve resolution (MCR) after pre-processing using normalization or Poisson-scaling were compared to identify the etched and non-etched regions of the image. The utility of each pre-processing and MVA method was examined, with MCR coupled with Poisson-scaling being the appropriate choice for identifying the different chemical phases present in the image. However, appropriate selection of data pre-processing and MVA methods generally depends on the specific dataset being analyzed and the goals of the analysis.
Keywords: ToF-SIMS; Multivariate analysis; Image analysis; Principal component analysis; Multivariate curve resolution;

Because of the requirements of large molecule characterization and high-lateral resolution SIMS imaging, the possibility of improving molecular ion yields by the use of specific sample preparation procedures has recently generated a renewed interest in the static SIMS community. In comparison with polyatomic projectiles, however, signal enhancement by a matrix might appear to some as the alchemist's versus the scientist's solution to the current problems of organic SIMS. In this contribution, I would like to discuss critically the pros and cons of matrix-enhanced SIMS procedures, in the new framework that includes polyatomic ion bombardment. This discussion is based on a short review of the experimental and theoretical developments achieved in the last decade with respect to the three following approaches: (i) blending the analyte with a low-molecular weight organic matrix (MALDI-type preparation procedure); (ii) mixing alkali/noble metal salts with the analyte; (iii) evaporating a noble metal layer on the analyte sample surface (organic molecules, polymers).
Keywords: Organic SIMS; Imaging SIMS; Matrix; ME-SIMS; MALDI; MetA-SIMS; Metal; Salt; Cluster ion;

Static ToF-SIMS analysis of plasma chemically deposited ethylene/allyl alcohol co-polymer films by U. Oran; S. Swaraj; J.F. Friedrich; W.E.S. Unger (6588-6590).
A plasma co-polymerization of ethylene as a “chain extending” monomer and allyl alcohol as a carrier monomer for hydroxyl groups was studied. The composition of the feed gas was systematically varied and the plasma co-polymers were analyzed in terms of their relative concentrations of OH functional groups by static Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) immediately after their preparation without any air contact, i.e., under so called “in situ” conditions.The relative OH group concentration involved in the –CH2–OH groups was derived from the normalized yields of the CH3O+ secondary fragment ion. The density of functional groups in the plasma co-polymers was found to vary non-linearly with respect to the mole percentage of the monomers in the feed gas.Co-polymerization phenomena, i.e. chemical interactions and recombination reactions taking place between monomer molecules in the plasma and/or during the deposition process, become evident in ToF-SIMS spectra.
Keywords: Plasma deposition; ToF-SIMS; Plasma co-polymerization; Ethylene; Allyl alcohol;

Mass accuracy—TOF-SIMS by F.M. Green; I.S. Gilmore; M.P. Seah (6591-6593).
A study is presented of the factors affecting the calibration of the mass scale for time-of-flight SIMS (TOF-SIMS). The effect of the ion kinetic energy, emission angle and other instrumental operating parameters on the measured peak position are determined. This shows clearly why molecular and atomic ions have different relative peak positions and the need for an aperture to restrict ions at large emission angles. A calibration protocol is developed which gives a fractional mass accuracy of better than 10 ppm for masses up to 140 u. The effects of extrapolation beyond the calibration range are discussed and a recommended procedure is given to ensure that accurate mass is achieved within a selectable uncertainty for large molecules.
Keywords: Static SIMS; Accurate mass; Identification; Calibration; TOF-SIMS; G-SIMS;

Diffusion study of multi-organic layers in OLEDs by ToF-SIMS by Wen-Yin Chen; Yong-Chien Ling; Bo-Jung Chen; Hung-Hsin Shih; Chien-Hong Cheng (6594-6596).
A model organic light-emitting diodes (OLEDs) with structure of tris(8-hydroxyquinoline) aluminum (Alq3)/N,N′-diphenyl-N,N′-bis[1-naphthy-(1,1′-diphenyl)]-4,4′-diamine (NPB)/indium tin oxide (ITO)-coated glass was fabricated for diffusion study by ToF-SIMS. The results demonstrate that ToF-SIMS is capable of delineating the structure of multi-organic layers in OLEDs and providing specific molecular information to aid deciphering the diffusion phenomena. Upon heat treatment, the solidity or hardness of the device was reduced. Complicated chemical reaction might occur at the NPB/ITO interface and results in the formation of a buffer layer, which terminates the upper diffusion of ions from underlying ITO.
Keywords: OLEDs; Diffusion; Interface; Heat treatment; ToF-SIMS;

3D-TOFSIMS characterization of black spots in polymer light emitting diodes by C.W.T. Bulle-Lieuwma; P. van de Weijer (6597-6600).
The occurrence and formation of black spots areas in PolyLED devices has been studied by time-of-flight SIMS (TOFSIMS). The composition, shape and position of the black spots is visualised by three-dimensional (3D)-TOFSIMS depth-profiling. It has been established that the formation of non-emissive spots is due to the growth of aluminium oxide clusters at the AlBa/polymer interface. Electron injection in the black spots is lost by the resulting local increase of the resistivity of the cathode.
Keywords: PolyLED devices; Black spots; Time-of-flight; Resistivity; Cathode;

G-SIMS is an easy to use method that considerably simplifies complex static SIMS spectra. The G-SIMS peaks relate directly to the parent molecular structure and so provide a library independent method for direct interpretation and identification. For larger molecules (>100 u) the mass alone may be insufficient to identify the molecule unambiguously. A development of G-SIMS, G-SIMS-fragmentation pathway mapping (FPM), solves this problem. G-SIMS-FPM allows the molecular structure to be re-assembled by following fragmentation pathways as the G-SIMS surface plasma temperature is varied. In this study, we develop the inclusion of negative secondary ion fragmentation data to provide a more complete analysis. This approach is exampled with data for complex molecules of Irganox 1010 and folic acid.
Keywords: Static SIMS; G-SIMS; Molecular structure; Identification; Interpretation;

SIMS studies of polymeric tertiary structures in monolayers: Polysiloxane helical coil structures by Rosamil Rey-Santos; Alan Piwowar; Leiddy Zoé Alvarado; Joseph A. Gardella (6605-6608).
A static SIMS study was performed using poly(dimethyl siloxane) (PDMS) as a model system to investigate the effects of tertiary structure on the ion formation mechanism and ion formation probability of fragments in the high mass region (>1000 Da). PDMS produced from anionic polymerization with a narrow polydispersity, can form well-ordered helically coiled monolayers using Langmuir–Blodgett methods at the air water interface, either in a hairpin configuration, if the endgroups are functional or as flat helically coiled chains. Reflection absorption Fourier transform infrared (RA-FTIR) spectroscopic analysis shows the changes in bonding between flat helically coiled PDMS and cast films from dilute solvents, which produces a random coil configuration. Differences between the model systems in infrared spectrum show evidence of changes in structure, producing variation in band formation. Also observed are changes in the band shape and relative peak area between the model systems. These polymeric changes translate into differences in the relative intensities of fragments formed in the repeating pattern of clusters in the high mass ToF-SIMS spectra of the ordered versus the random cast films. Both statistical chain break analysis and molecular mechanics simulations of structure are used to support the analysis.
Keywords: ToF-SIMS; PDMS; Polymeric tertiary structure;

SIMS depth profiling of polymer blends with protein based drugs by Christine M. Mahoney; Jinxiang Yu; Albert Fahey; Joseph A. Gardella (6609-6614).
We report the results of the surface and in-depth characterization of two component blend films of poly(l-lactic acid) (PLLA) and Pluronic surfactant [poly(ethylene oxide) (A) poly(propylene oxide) (B) ABA block copolymer]. These blend systems are of particular importance for protein drug delivery, where it is expected that the Pluronic surfactant will retain the activity of the protein drug and enhance the biocompatibility of the device. Angle dependant X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) employing an SF5 + polyatomic primary ion source were both used for monitoring the surfactant's concentration as a function of depth. The results show an increased concentration of surfactant at the surface, where the surface segregation initially increases with increasing bulk concentration and then remains constant above 5% (w/w) Pluronic. This surface segregated region is immediately followed by a depletion region with a homogeneous mixture in the bulk of the film. These results suggest the selection of the surfactant bulk concentration of the thin film matrices for drugs/proteins delivery should achieve a relatively homogeneous distribution of stabilizer/protein in the PLLA matrix. Analysis of three component blends of PLLA, Pluronic and insulin are also investigated. In the three component blends, ToF-SIMS imaging shows the spatial distribution of surfactant/protein mixtures. These data are reported also as depth profiles.
Keywords: ToF-SIMS; Drug delivery; AD-XPS; Depth profiling; PLLA; Pluronic;

Depth profiling of taxol-loaded poly(styrene-b-isobutylene-b-styrene) using Ga+ and C60 + ion beams by R.M. Braun; J. Cheng; E.E. Parsonage; J. Moeller; N. Winograd (6615-6618).
The surface of a triblock copolymer, containing a solid-phase drug, was investigated using 15 keV Ga+ and 20 keV C60 + ion beams. Overall, the results illustrate the successful use of a cluster ion beam for greatly enhancing the molecular ion and high-mass fragment ion intensities from the surface and bulk of the polymer system. The use of C60 + also established the ability to see through common overlayers like poly(dimethyl siloxane) which was not possible using atomic ion sources. Moreover, the use of C60 + allowed depth profiles to be obtained using primary ion dose densities in excess of 6 × 1014  C60 +/cm2. Resulting sputter craters possess relatively flat bottoms without the need for sample rotation and reached depths of ca. 2 μm. AFM results illustrate the more gentile removal of surface species using cluster ions. Specifically, phase contrast and topographic images suggest the relatively high ion doses do not significantly alter the phase distribution or surface topography of the polymer. However, a slight increase in rms roughness was noticed.
Keywords: TOF–SIMS; AFM; Cluster ion beam; Profiles; Stents;

Cluster ions have been recognized as a superb primary species in time of flight secondary ion mass spectroscopy (ToF–SIMS) compared with monatomic primary ions, as they significantly enhance the secondary ion yields from bulk samples. Self-assembled monolayers provide an important system for studying the fundamental mechanism involved in the yield enhancement.We used a gold cluster ion source to analyze a new type of self-assembled monolayer: a fluorocarbon-grafted polyethylene terephthalate. In addition to the structure details, which helped to understand the grafting mechanism, ToF–SIMS analysis revealed that fluorocarbon secondary ion yield enhancements by cluster ions were due to the enhanced sputter efficiency. A larger information depth may also be expected from the enhancement. Both mathematical definitions of damage cross-section and disappearance cross-section were revisited under a new context. Another cross-section parameter, sputter cross-section, was introduced to differentiate the beam induced sputter process from damage process.
Keywords: SIMS; Cluster ion; Polymer; Monolayer; Surface analysis; Sputter cross-section;

Matrix-enhanced cluster-SIMS by J.E. Locklear; C. Guillermier; S.V. Verkhoturov; E.A. Schweikert (6624-6627).
We have used 23 keV C60 + projectiles in the event-by-event bombardment and detection mode to investigate the emission of the gramicidin S [M  − H] ion embedded in a matrix of sinapic acid. We have observed an increase in the gramicidin S [M  − H] ion of approximately eight times by controlling the ratio of gramicidin S to sinapic acid. The maximum of the gramicidin S [M  − H] yield occurs at a matrix/analyte ratio of 10:1. This ratio is different from those typically used in matrix-assisted laser desorption/ionization.
Keywords: Matrix enhanced; Cluster-SIMS; C60;

S-SIMS and MetA-SIMS study of organic additives in thin polymer coatings by L. Adriaensen; F. Vangaever; J. Lenaerts; R. Gijbels (6628-6631).
In the present study a methodology for TOF-S-SIMS measurements is developed to gain information on the distribution of molecules on and in polymer coatings (thickness ∼100 μm). Experiments were carried out on model systems consisting of one or more additive-containing polyvinylbutyral coatings. Several organic additives were selected: carbocyanine dyes, basonyl blue and the pharmaceutical risperidone. The additives have been measured as pure compounds on a Si substrate to obtain good reference spectra. After optimisation of the sample preparation method, the coatings were embedded in epoxy resin and stored in an oven (60 °C) for 24 h. Cross-sections were made by means of a microtome. S-SIMS spectra were taken on the prepared cross-sections before and after Au was deposited on the sample surface. Compared to the untreated samples, the Au covered samples give rise to more intense secondary ion signals. Generally, signals of the intact cations were more intense than those of the fragment ions. Apart from mass spectra, images of the additive distribution in the coatings could also be acquired by recording structural ion signals. It was possible to make secondary ion images of the additive molecule ions with a (sub)-micrometer lateral resolution.
Keywords: S-SIMS; Risperidone; Basonyl blue; Carbocyanine dye; Cross section; Coating;

Chemical derivatization technique in ToF-SIMS for quantification analysis of surface amine groups by Tae Geol Lee; Jinmo Kim; Hyun Kyong Shon; Donggeun Jung; Dae Won Moon (6632-6635).
A chemical derivatization technique in ToF-SIMS along with principal component analysis (PCA) were used to perform a quantitative study of the surface amine density of the plasma-polymerized ethylenediamine (PPEDA) thin film. We used the scores on principal component (PC) 1 from a PCA of ToF-SIMS data for the PPEDA films and their chemical-derivatized surfaces for comparison with the surface amine densities. These surface amine densities were independently determined by UV–visible spectroscopy. Our work found a good linear relationship between the surface amine densities and the scores on PC 1 from a PCA of the ToF-SIMS data for the chemical-derivatized PPEDA surfaces, but not for the PPEDA thin films themselves. In addition to quantification, our PCA results provided insights into the surface chemical composition of each surface.
Keywords: Chemical derivatization; ToF-SIMS; PCA; PPEDA; UV–visible spectroscopy;

PLA-PMMA blends: A study by XPS and ToF-SIMS by D. Cossement; R. Gouttebaron; V. Cornet; P. Viville; M. Hecq; R. Lazzaroni (6636-6639).
This paper reports which are the possibilities of quantification by time of flight secondary ion mass spectrometry (ToF-SIMS) for some polymer blends. In order to assess the composition of the mixtures, we studied first different poly(l-lactide)/polymethylmethacrylate (PLA/PMMA) blends by X-ray photoelectron spectroscopy (XPS), this technique being quantitative. By XPS fitting of the C 1s level, we found a very good agreement of the measured concentrations with the initial compositions. Concerning ToF-SIMS data treatment, we used principal component analysis (PCA) on negative spectra allowing to discriminate one polymer from the other one. By partial least square regression (PLS), we found also a good agreement between the ToF-SIMS predicted and initial compositions. This shows that ToF-SIMS, in a similar way to XPS, can lead to quantitative results. In addition, the observed agreement between XPS (60–100 Å depth analyzed) and ToF-SIMS (10 Å depth analyzed) measurements show that there is no segregation of one of the two polymers onto the surface.
Keywords: XPS; ToF-SIMS; PLA/PMMA blends; PCA; PLS regression; Quantification;

In order to improve quantification of high mass ions, the influence of cluster composition on detection efficiencies has been studied using a TOF-SIMS IV with the extended capability of postaccelerating ions up to 20 keV. In this experimental study, we focus on the comparison of detection efficiencies for three types of negatively charged secondary cluster ions: gold–alkanethiolate-clusters (Au x M y ), gold–sulfur-clusters (Au x S y ) and gold-clusters (Au x ). The clusters were sputtered from self-assembled monolayers of hexadecanethiols on gold substrates using 10 keV Ar+ primary ions. The detection efficiencies were derived on the basis of a function for the secondary electron yield and a fourth-order approximated Poisson probability distribution for electron propagation and amplification within the microchannel plate.In addition to the well-known dependence of detection efficiencies on ion mass and energy, which has already been studied for positively charged ions, we were able to show a similar behaviour for the investigated negatively charged secondary ions. We have observed major variations among the three types of clusters at similar mass and energy as predicted in a theoretical approach. The observed differences are due to the different composition of the investigated clusters which has a major influence on the kinetic ion induced electron emission within the microchannel plate. For the first time it was possible to experimentally verify these predictions for detection efficiencies.
Keywords: ToF-SIMS; Detector efficiency; Microchannel plate; High mass ion detection; Ion-electron conversion;

Organic SIMS with single massive gold projectile: Ion yield enhancement by silver metallization by C. Guillermier; V. Pinnick; S.V. Verkhoturov; E.A. Schweikert (6644-6647).
The yield of CN from glycine rises from one CN per projectile impact to two when the sample is covered with a nominally 1 nm thick layer of silver. These yields were obtained for bombardment with Au400 4+ projectile with 136 keV impact energy. A multitude of CN-based clusters, e.g. Ag x O y (CN) z are produced concurrently. As a result, a total of three CN-based secondary ions are generated per projectile impact. The exceptionally high yield for CN is of interest for biological SIMS.
Keywords: Yield enhancement; Silver deposition; Massive gold projectile; Silver adduct ions;

Thin films of polystyrene (PS)/poly (methyl methacrylate) (PMMA) blends with different end groups were investigated using ToF-SIMS and AFM. PS with -OH and -NH2 end groups were blended in toluene solvent with pure PMMA homopolymer, and PMMA having anhydride end group. The ToF-SIMS spectra of PS-OH/PMMA resembled that of pure PS–PMMA blends showing an increase of PMMA intensity after annealing. On the contrary, the PS-NH2 blended with PMMA showed an increase in PS intensity on the surface after annealing. The ToF-SIMS spectra were similar to that of a pure PS–PMMA di-block copolymer. These results indicate copolymer formation at the surface. The PS-NH2 with PMMA-anhydride blend spectra showed very slight changes in spectra before and after annealing and the AFM images revealed spinodal bi-continuous structures on the surface before and after annealing. The copolymer formation is found to occur in the as-cast film itself and not after thermal treatment.
Keywords: ToF-SIMS; AFM; Blends; Thin films; End groups; Copolymer;

Empirical evaluation of metal deposition for the analysis of organic compounds with static secondary ion mass spectrometry (S-SIMS) by R. De Mondt; L. Adriaensen; F. Vangaever; J. Lenaerts; L. Van Vaeck; R. Gijbels (6652-6655).
Metal-assisted (MetA) SIMS using the deposition of a thin Au or Ag layer on non-conducting samples prior to analysis has been advocated as a means to improve the secondary ion (S.I.) yields of organic analytes. This study focuses on the influence of time and temperature on the yield enhancement in MetA-SIMS using thick layers of poly(vinylbutyral-co-vinylalcohol-co-vinylacetate) (PVB) containing dihydroxybenzophenone (DHBPh) or a cationic carbocyanine dye (CBC) and spin-coated layers of the cationic dye on Si. Pristine samples as well as Au- and Ag-coated ones were kept between −8 °C and 80 °C and analysed with S-SIMS at intervals of a few days over a period of 1 month. The yield enhancement was found to depend strongly on the kind of evaporated metal, the storage temperature and time between coating and analysis.
Keywords: MetA-SIMS; Polyvinylbutyral; S-SIMS; Organic additives;

The development of novel PP textiles requires materials of which the surface has well defined hydrophilic properties, for instance, by the use of additives before extrusion and drawing. The feasibility of static secondary ion mass spectrometry (S-SIMS) to provide detailed information on the molecular surface composition of materials in the form of 30 μm thick films has been explored. Extensive charge build-up during S-SIMS analysis prevents direct characterisation of such materials. Several methods have been used to circumvent the problem. Specifically, deposition of gold over the entire surface and pressing a slot grid into the material allow the commercial hydrophilic additive in PP to be detected. While the slot grid preserves the pristine surface composition, mass spectra from gold-coated samples reflect the occurrence of redistribution artefacts.
Keywords: S-SIMS; Polypropylene; Additives; Gold coating; Slot grid;

Static secondary ion mass spectrometry (S-SIMS) analysis of atmospheric plasma treated polypropylene films by Bart Boschmans; Myriam Vanneste; Luc Ruys; Eef Temmerman; Christophe Leys; Luc Van Vaeck (6660-6663).
Time-of-Flight (TOF) static secondary ion mass spectrometry (S-SIMS) was used to gain molecular information on the surface modifications introduced by plasma treatment of polypropylene (PP) films. A procedure using slotted electron microscopy grids was developed to deal with the charge build-up of samples with a thickness of about 30 μm. The surface composition was studied as a function of the plasma treatment time. A comparison of the mass spectra from untreated and treated PP showed significant differences of signal intensities of ions that could be specifically related to the presence of oxygen-containing species.
Keywords: TOF S-SIMS; Atmospheric plasma; Polypropylene; Charge build-up; Surface modification;

We have developed a highly sensitive analytical technique for detecting the distribution of surfactants existing on a polymer surface. We studied the chemical modification of surfactants with the hydroxyl group by using amine-containing compounds in the gaseous phase at 23 °C; then, we performed measurements by using time-of-flight secondary ion mass spectrometry (TOF-SIMS). We found that 4-(dimethylamino) phenyl isocyanate as a modification reagent is capable of modifying the hydroxyl group when 1,8-diazabicyclo[5,4,0]undec-7-ene (DBU) is used as a catalytic agent. We demonstrated this modification with stearyl alcohol on a polymer material surface. The signal sensitivity of stearyl alcohol after the modification increased considerably in comparison with that of the unmodified stearyl alcohol. Moreover, we confirmed that this modification method can be used for the distribution analysis of surfactants. The distribution conditions of traces of surfactants with the hydroxyl group can be observed clearly by using this modification method.
Keywords: TOF-SIMS; Chemical modification; Surfactant; Polymer; Signal enhancement; Imaging;

ToF-SIMS characterisation of diterpenoic acids after chromatographic separation by Andrej Oriňák; Renáta Oriňáková; Heinrich F. Arlinghaus; Guido Vering; Sebastian Hellweg; Valdir Cechinel-Filho (6668-6671).
Microcolumn liquid chromatography (μHPLC) coupled on-line with time of flight secondary ion mass spectrometry (ToF-SIMS) was applied for mixture of diterpenoic acids (abietic, gibberellic and kaurenoic) analysis. Chromatographic effluent, with analytes separated, was carried out directly onto different, ToF-SIMS compatible surface substrates, for further ToF-SIMS analysis. Silica gel Si60, aluminium backplate modified Si60, monolithic silica gel and Raman spectroscopy chromatographic thin layers were used as the deposition substrates in this experiment. By ToF-SIMS surface imaging the deposition trace picture has been obtained. Effluent deposition surface area was scanned for diterpenoic acid fragment mass values based on mass spectrometric library. Measured ToF-SIMS dataset of fragment abundance and intensities were used for preliminary fragmentation schemes construction. The lowest substrate background activity has been established for monolithic silica gel thin layer and aluminium backplate modified Si60 thin layer. In the case of Raman spectroscopy pre-treated thin layer or conventional chromatographic thin layer Si60, the both, high background signal intensity and impossibility to construct negative ions surface image, were observed. Diterpenoic acids studied serve the similar mass spectrum but ToF-SIMS coupled with liquid chromatographic separation brings new impact to the positive identification of analytes studied.
Keywords: μHPLC; ToF-SIMS; TLC-MS; Interfacing; SIMS imaging; Diterpenes;

Towards a fully optimised organic LED device: Analysis of surface synthesis using coupling reactions by ToF-SIMS by R. Pinna; F. Jamme; F.J.M. Rutten; E.F. Smith; M.R. Willis; D. Briggs; M.R.S. McCoustra (6672-6675).
Time-of-flight secondary ion mass spectrometry (ToF-SIMS) and polarisation–modulation reflection–absorption infrared spectroscopy (PM-RAIRS) have been used to monitor the surface synthesis of self-assembled aromatic π-conjugated molecular wires on gold substrates as a step towards a novel structure for organic electroluminescent devices (OLEDs). The wires have been synthesised using a series of Schiff's base coupling reactions in solution on a self-assembled monolayer of an aromatic thiolate anchor. ToF-SIMS and PM-RAIRS measurements have demonstrated that: (i) the anchor molecules self-assemble at the gold surface, (ii) the anchor molecules selectively react through imino coupling reactions with additional wire units with high efficiency and (iii) the wire-like structure is predominantly orientated normal to the surface.
Keywords: ToF-SIMS; PM-RAIRS; OLEDs; Molecular wires; Schiff's base;

G-SIMS of thermosetting polymers by P.N. Hawtin; M.-L. Abel; J.F. Watts; J. Powell (6676-6678).
In this study, the gentle SIMS (G-SIMS) concept has been applied to thermosetting polymers. The polymer chosen is an epoxy resin based adhesive, which is commercially available as a two-part mixture. The G-SIMS spectra have been used alongside the static SIMS (SSIMS) spectra to aid in the identification of ions characteristic of the individual components present in each part of the two-part formulation. The G-SIMS spectra are shown to provide information that is not readily available from the SSIMS spectra. G-SIMS has been shown to be a viable technique for mixtures and is of potential use in characterising thermosetting polymers.
Keywords: Gentle SIMS (G-SIMS); Static SIMS; Thermosetting polymers; Epoxy resin; Adhesive;

This paper examines the capabilities of cryogenic sample handling to examine composition and structure of hydrogel materials where siloxane components are central to the analysis. XPS analysis of multicomponent polymers with cryogenic sample handling following exposure to aqueous environments has revealed the composition and kinetics of near surface reorganization for siloxane and fluorocarbon containing polymers. In this study we report results from a ToF-SIMS protocol for cryogenic sample handling applied to the analysis of surface changes upon hydration/dehydration of hydrogel polymers. Comparison of results from angle dependent XPS and ToF-SIMS are discussed for a range of commercial soft contact lens materials. Both methods detected changes in surface chemistry between the hydrated (frozen) and dehydrated surfaces. Analysis of the hydrated surfaces detected polymer components indicative of the commercial formulation as well as ice clusters. Analysis of the dehydrated materials detected changes in surface chemistry relative to the hydrated surface in addition to loss of water due to sample dehydration. A quantitative standard additions method for ToF-SIMS data was used to determine submonolayer amounts of PDMS impurities at the surface of the hydrogels. ToF-SIMS analysis of a series of seven poly (allyl methacrylate-g-dimethylsiloxane), AMA-g-DMS, graft copolymers in the hydrated state revealed high mass oligomeric ion distributions for systems with bulk PDMS content greater than 25 wt.%. This marks the first time that detection of high mass oligomeric ion distributions from hydrated (frozen) surfaces has been reported. Analysis of the dehydrated surface detected formation of high mass oligomeric ion distributions for systems with PDMS bulk content greater than 15 wt.%, but only detected these ion distributions in wet (frozen) samples when the bulk concentration was greater than 25 wt.%.
Keywords: ToF-SIMS; Trace quantitative analysis; PDMS; Polymer reorganization;

Magnetic recording hard-disk drive may be attacked by many kinds of contaminations including vapours/gases. Vapour/gas contaminants are detrimental to magnetic heads, media and head–disk interfaces in hard-disk drive. Acrylic acid is a kind of gases released from drive components. In this study, the effects of acrylic acid vapour on the surface adsorption and corrosion of magnetic hard-disk media are investigated by TOF-SIMS. The related drive durability and failure property are discussed.
Keywords: Magnetic recording hard disk; Acrylic acid; Surface adsorption; Corrosion; TOF-SIMS;

Chemistry of metal atoms reacting with alkanethiol self-assembled monolayers by Z. Zhu; D.L. Allara; N. Winograd (6686-6688).
Time-of-flight secondary ion mass spectrometry (ToF-SIMS) is utilized to investigate the behavior of vapor-deposited K, Au and Ti atoms on several alkanethiol self-assembled monolayers (SAM). The goals are to acquire information about chemical reactions between metal atoms and surface organic functional groups, penetration of metal atoms through the SAMs, growth modes of metal overlayers on top of the SAMs and damage of organic molecules. It is found that appearance of new characteristic peaks and disappearance of initial peaks may indicate chemical reactions or decomposition of organic molecules. The relationship between metal dose and intensity of surface organic functional group-related peaks provides information about penetration or cluster-formation of metal atoms. In addition, removing the metal overlayers by chemical etching and then characterizing samples again is a complementary approach that can reveal valuable information about the location of the metal atoms.
Keywords: ToF-SIMS; SAM; Metal deposition; Interface;

Selective detection of organic compounds on modified polymer surfaces using TOF-SIMS in combination with derivatization by Moonhee Kwon; Yeonhee Lee; Youngsoo Kim; Seunghee Han; Haidong Kim (6689-6692).
This investigation encompasses work in the development of TOF-SIMS methodology for the characterization of compounds formed during polymer surface modification. TOF-SIMS was used in this study in combination with selective derivatization reactions with hydroxyl group specific reagents. Derivatization techniques with group specific reagents provide a means of identifying functional groups in a complex matrix, along with significant enhancement of detection limits. The study proceeded in three steps. First, derivatives of organic compounds as a model compound were monitored to determine the suitability for detecting oxygenated species. Second, useful derivatization reactions were tested on functional groups in the synthetic polymer chains. Third, the methods thus developed were applied to polymer surfaces treated by plasma source ion implantation (PSII). 2-Fluoro-1-methylpyridinium derivatives were useful for characterization of organic alcohols and phenolic compounds. Analysis of organic compounds derivatized by these methods on polymeric materials demonstrated clearly that analysis in the presence of a carbonaceous matrix is possible. The results yielded evidence for the formation of hydroxyl species as the polymer is modified by PSII technique.
Keywords: Derivatization; Hydroxyl groups; Polyimide; TOF-SIMS; Modification;

Surface spectroscopic imaging of PEG-PLA tissue engineering constructs with ToF-SIMS by G. Tsourapas; F.J.M. Rutten; D. Briggs; M.C. Davies; K.M. Shakesheff (6693-6696).
Poly(lactic acid) (PLA) has been studied extensively in the field of tissue engineering due to its well-established biodegradability and biocompatibility. To improve its non-fouling properties we entrapped poly(ethyl glycol) (PEG), into the surface, which was characterised by a combination of ToF-SIMS and XPS. Cell attachment was subsequently investigated as a function of the amount of entrapped PEG. XPS was instrumental in quantifying the amount of PEG entrapped at higher concentrations, whereas the significantly higher sensitivity and superior imaging capabilities of ToF-SIMS enabled a full characterisation of the PEG distribution at the low concentrations required for the desired non-fouling properties, which were well below the XPS quantification limit. It was found that pronounced segregation effects leading to the formation of PEG-enriched domains ranging between ca. 5 and several tens of microns across were present at all PEG concentrations investigated.
Keywords: ToF-SIMS; Imaging; Tissue engineering; Cell attachment; Isotopic substitution;

Mutual information theory for biomedical applications: Estimation of three protein-adsorbed dialysis membranes by Satoka Aoyagi; Azusa Takesawa; Akihiro C. Yamashita; Masahiro Kudo (6697-6701).
Protein-adsorbed dialysis membranes are evaluated with time-of-flight secondary ion mass spectrometry (TOF-SIMS) chemical imaging technique. Protein adsorption causing permeability change is one of big issues in the development of dialysis membranes. Bovine serum albumin adsorption onto three kinds of dialysis membranes has been evaluated with TOF-SIMS. In the present study three kinds of proteins, bovine serum albumin, α-chymotripsinogen A, and cytochrome C adsorbed onto hollow-fiber dialysis membranes, were measured by means of TOF-SIMS and then TOF-SIMS spectra were analyzed using mutual information. Then specific peaks of fragment ions related to α-chymotripsinogen A and bovine serum albumin were found, respectively. In this condition, however, specific peaks to cytochrome C were not able to find compared with other samples. Finally, chemical images of α-chymotripsinogen A and bovine serum albumin, respectively, adsorbed onto the membranes with co-existing proteins were obtained. The results of TOF-SIMS images of the proteins on the membranes show different tendency of adsorption depending on co-existing proteins. Further study is needed to study more detailed protein adsorption onto the membranes with co-existing proteins.
Keywords: Albumin; α-Chymotripsinogen A; Membrane adsorption; Membrane filtration;

The influence of the cholesterol microenvironment in tissue sections on molecular ionization efficiencies and distributions in ToF-SIMS by A.F. Maarten Altelaar; Jan van Minnen; Ron M.A. Heeren; Sander R. Piersma (6702-6705).
High-resolution images of cholesterol were obtained from Lymnaea stagnalis nervous tissue using metal-assisted (MetA) time-of-flight secondary ion mass spectrometry (ToF-SIMS). The spatial distributions of different pseudomolecular ions of cholesterol [M  − H]+, [M  − OH]+ and [2M  + Au]+, illustrate the influence of the tissue microenvironment on the ionization efficiencies of these ions. These biological matrix effects result in differences in localizations of molecular ions derived from the same molecular species.
Keywords: Metal-assisted; ToF-SIMS; Imaging; Cholesterol; Nervous tissue;

A sample preparation has been developed for NanoSIMS 50 analysis of biological samples, that does not require thin sectioning. The embedded sample was surfaced by a diamond knife and directly analyzed. This sample preparation technique is well adapted for the investigation of diffusible elements and an example of iodine-containing water-soluble molecule localization in human hair is shown. We compared the results with conventional thin wet sectioning.
Keywords: Sample preparation; NanoSIMS; Biological sample; Diffusible elements; Human hair;

Introduction of a cryosectioning-ToF-SIMS instrument for analysis of non-dehydrated biological samples by J. Möller; A. Beumer; D. Lipinsky; H.F. Arlinghaus (6709-6711).
Tof-SIMS and laser-SNMS are becoming increasingly important tools for analysing the elemental and molecular distribution in biological samples. We have developed the prototype of an in-vacuum cryosectioning instrument directly attached to a ToF-SIMS/laser-SNMS instrument, which allows preparing and analyzing frozen non-dehydrated biological samples. Due to unavoidable effects during the handling, storing, and preparation of frozen samples, even inside the vacuum, it must be ensured that the analyzed surface is from the sample and not a preparation artefact. To this effect, a model structure, similar to the biological samples and with a defined chemical composition, was analyzed under varying thermal treatment before and during analysis, respectively, in order to identify a balance between evaporating and subliming adsorbed materials and the effect of freeze-drying on the measured signal.
Keywords: Cryofractioning; Cryosectioning; Sample preparation; ToF-SIMS;

TOF-SIMS imaging of chlorhexidine-digluconate transport in frozen hydrated biofilms of the fungus Candida albicans by Bonnie J. Tyler; Srinath Rangaranjan; Jörg Möller; Andre’ Beumer; Heinrich F. Arlinghaus (6712-6715).
The diffusion of the anti-microbial chlorhexidine digluconate (CHG) has been studied in C. albicans biofilms by time-of-flight secondary-ion mass spectrometry (TOF-SIMS). C. albicans has been shown to become resistant to common anti-microbial agents, including CHG, when growing as a biofilm. Mass transport resistance within biofilms has commonly been suggested as a resistance mechanism, but measurement of transport for most anti-microbial agents in biofilms has proven extremely difficult because of the heterogeneity of the biofilms and the difficulty in detecting these agents within an intact biofilm. In this study, TOF-SIMS has been used to study the transport of CHG and glucose in a frozen hydrated biofilm. The TOF-SIMS images reveal a progression of CHG from the top of the biofilm to its base with time. Images suggest that there are channels within the biofilm and show preferential binding of CHG to cellular components of the biofilm. Additionally, both living and dead cells can be identified in the TOF-SIMS images by the sequestration of K+ and the presence of cell markers. This study demonstrates that TOF-SIMS has the unique potential to simultaneously observe the presence of an antimicrobial agent, concentration of nutrients, and the viability of the cell population.
Keywords: Spectral imaging; Biofilm; Multivariate statistical analysis; Maximum auto-correlation factors; Diffusion; Fungi; Drug resistance; Crogenic;

Investigating lipid interactions and the process of raft formation in cellular membranes using ToF-SIMS by Carolyn M. McQuaw; Audra G. Sostarecz; Leiliang Zheng; Andrew G. Ewing; Nicholas Winograd (6716-6718).
There is an increased interest in how lipids interact with each other, especially in the lateral separation of lipids into coexisting liquid phases as this is believed to be an attribute of raft formation in cell membranes. ToF-SIMS has shown itself to be an excellent tool for investigating cellular and model membrane systems and will be perhaps the most powerful one for investigating raft formation. Results from our laboratory show the capability of ToF-SIMS at identifying unequivocally the content of coexisting liquid lipid phases. Using supported lipid monolayers we find that the inclusion of dipalmitoylphosphatidylethanolamine (DPPE) to a homogeneous dipalmitoyl-phosphatidylcholine (DPPC)/cholesterol phase results in the formation of cholesterol-rich domains [A.G. Sostarecz, C.M. McQuaw, A.G. Ewing, N. Winograd, J. Am. Chem. Soc. 126 (2004) 13882]. Also, for DPPE/cholesterol systems a single homogeneous DPPE/cholesterol phase is formed at ∼50 mol% cholesterol, whereas DPPC/cholesterol systems form a single phase at 30 mol% cholesterol [C.M. McQuaw, A. Sostarecz, L. Zheng, A.G. Ewing, N. Winograd, Langmuir 21 (2005) 807]. Currently we are exploring the incorporation of sphingomyelin into phospholipid–cholesterol mixtures in an effort to gain a better understanding of its role in raft formation.
Keywords: ToF-SIMS imaging; Lipid rafts; Cholesterol domains;

ToF-SIMS studies of Bacillus using multivariate analysis with possible identification and taxonomic applications by C.E. Thompson; J. Ellis; J.S. Fletcher; R. Goodacre; A. Henderson; N.P. Lockyer; J.C. Vickerman (6719-6722).
In this paper we discuss the application of ToF-SIMS with an Au3 + primary ion beam, combined with principal components analysis (PCA) and discriminant function analysis (DFA) for the identification of individual strains of two Bacillus species. The ToF-SIMS PC-DFA methodology is capable of distinguishing bacteria at the strain level based on analysis of surface chemical species. By classifying the data using hierarchical cluster analysis (HCA) we are able to show quantitative separation of species and of these strains. This has taxonomic implications in the areas of rapid identification of pathogenic microbes isolated from the clinic, food and environment.
Keywords: ToF-SIMS; Bacillus; Multivariate analysis; Taxonomy; PCA; DFA;

7.87 eV postionization of peptides containing tryptophan or derivatized with fluorescein by L. Hanley; P.D. Edirisinghe; W.F. Calaway; I.V. Veryovkin; M.J. Pellin; J.F. Moore (6723-6726).
Chemical tags such as anthracene can be attached to a molecular analyte and serve as chromophores for 7.87 eV laser postionization by lowering the overall ionization potential of the tagged molecular complex. Fluorescein and tryptophan are demonstrated as two new tags for 7.87 eV laser postionization of various amino acids and peptides. Other molecular species that are efficient fluorescence probes should also serve as tags for 7.87 eV postionization since they display highest occupied molecular orbitals with extended π-conjugation that lead to ionization potentials below this photon energy and an ability to stabilize the net positive charge of the radical cations. This technique is demonstrated here for laser desorbed species, but is also applicable to keV ion sputtered neutrals. Overall, 7.87 eV laser postionization of derivatized species promises to expand the capabilities of mass spectrometric surface analysis.
Keywords: Vacuum ultraviolet; Postionization; Peptides; Laser desorption; ToF MS; Derivatization;

Suppression and enhancement of non-native molecules within biological systems by E.A. Jones; N.P. Lockyer; J.C. Vickerman (6727-6730).
With the aim of evaluating the potential of SIMS to provide molecular information from small molecules within biological systems, here we investigate the effect of different biological compounds as they act as matrices. The results highlight the fact that the chemical environment of a molecule can have a significant effect on its limit of detection. This has implications for the imaging of drugs and xenobiotics in tissue sections and other biological matrices.A 1:1 mixture of the organic acid 2,4,6-trihydroxyacetophenone and the dipeptide valine–valine demonstrates that almost complete suppression of the [M + H]+ ion of one compound can be caused by the presence of a compound of higher proton affinity. The significance of this is highlighted when two similar drug molecules, atropine (a neutral molecule) and ipratropium bromide (a quaternary nitrogen containing salt) are mixed with brain homogenate. The atropine [M + H]+ ion shows significant suppression whilst the [M − Br]+ of ipratopium bromide is detected at an intensity that can be rationalised by its decreased surface concentration.By investigating the effect of two abundant tissue lipids, cholesterol and dipalmitoylphosphatidyl choline (DPPC), on the atropine [M + H]+ signal detected in mixtures with these lipids we see that the DPPC has a strong suppressing effect, which may be attributed to gas phase proton transfer.
Keywords: SIMS ionisation; Suppression; Enhancement; Matrix effect;

A comparative study of secondary ion yield from model biological membranes using Au n + and C60 + primary ion sources by M.J. Baker; J.S. Fletcher; H. Jungnickel; N.P. Lockyer; J.C. Vickerman (6731-6733).
Au n + and C60 + primary ion sources have been used to acquire spectra from phospholipids, symmetric liposomes and asymmetric liposomes. We demonstrate that when using different ion beams different chemical information can be obtained. Symmetric and asymmetric liposomes, with 95% asymmetry, were produced and analysed with Au+, Au3 + and C60 + primary ion beams. C60 + gave the greatest yield from the symmetric liposome but after correcting for the yield effects on the data obtained from the asymmetric liposome it has been shown that C60 + is the most surface sensitive, providing the least information from the inner leaflet of the liposome. Au n + provides the greatest amount of information from the inner leaflet. The results present the possibility of designing ToF-SIMS experiments that selectively probe specific regions of a (bio)molecular surface.
Keywords: Phospholipids; Liposomes; Yield enhancement; Polyatomic ions; Depth information; Cluster ion beams;

A new analysis of the depolymerized fragments of lignin polymer in the plant cell walls using ToF-SIMS by K. Saito; T. Kato; H. Takamori; T. Kishimoto; A. Yamamoto; K. Fukushima (6734-6737).
High mass resolution ToF-SIMS spectra by Au+ primary ion bombardment were used to investigate exact structures of characteristic ions of lignin in plant cell walls. Previous study using Ga primary ion bombardment showed the characteristic peaks of guaiacyl lignin at m/z 137 ([C8H9O2]+) and 151 ([C8H7O3]+ and [C9H11O2]+), but it was unclear whether the peak at m/z 151 in the spectrum of lignin in situ in plant cell walls is actually a double-component, [C8H7O3]+ (151.0394) and [C9H11O2]+ (151.0758). This report achieved a higher mass resolution with lignin samples, showing that the peak at m/z 151 is dominated by the C6–C1 benzoyl ion, [C8H7O3]+, not the C6–C2 ion, [C9H11O2]+.
Keywords: Lignin; ToF-SIMS; High mass resolution; Wood; Plant cell walls;

Implantable biomaterials, such as Ti–6Al–4V alloy, are designed to replace a part of the human body and/or its associated functions. This system, containing the alloy onto which the osteoprogenitor cells are deposited, is formed through the grafting of linear RGD (Arginine–Glycine–Aspartic acid) peptides. Our preliminary work demonstrated that the bonding of the fibronectin cell attachment peptide RGD to a metallic surface is extremely successful in promoting the adhesion and the proliferation of osteoprogenitor cells. However, a fuller understanding of the relationship between surface coverage and the contribution of each layer is required, in order to optimize the efficiency of the RGD-modified surface through optimal RGD bonding. We have used the TOF-S-SIMS analysis of this new surface, previously studied by XPS, to follow each modification level.Functional groups for peptide immobilization are required at the metallic surface, and their presence has been identified by mass spectra. A relative quantification of immobilized RGD peptides is obtained by TOF-S-SIMS analysis. Molecular ion imaging informs us of the surface evolution throughout the modification process and offers a description of each group. A comparative analysis of the spectra has permitted us to correlate the presence of these species on the surface with their bioactivities.
Keywords: RGD peptides; TOF-S-SIMS; Imaging; Biomimetic materials; Ti–6Al–4V alloy; Osteoprogenitor;

Mass spectrometric characterization of DNA microarrays as a function of primary ion species by S. Hellweg; A. Jacob; J.D. Hoheisel; T. Grehl; H.F. Arlinghaus (6742-6745).
Recent studies have shown TOF-SIMS to be an appropriate method for the detailed examination of the immobilization process of PNA and its ability to hybridize to unlabeled complementary DNA fragments. Unlabeled single-stranded DNA was hybridized to Si wafer biosensor chips containing both complementary and non-complementary immobilized PNA sequences. The hybridization of complementary DNA could readily be identified by detecting phosphate-containing molecules from the DNA backbone. An unambiguous discrimination was achieved between complementary and non-complementary sequences.In order to optimize detection parameters, different primary ions were applied, including monoatomic ions (Bi+) as well as cluster ions (Bi2 +, Bi3 +, Bi4 +, Bi3 ++, Bi5 ++), and secondary ion yield behavior and formation efficiencies were studied. It was found that cluster primary ions resulted in a significantly increased yield of DNA-correlated fragments, enabling higher signal intensities and better secondary ion efficiencies.TOF-SIMS is undoubtedly a highly useful technique for identifying hybridized DNA on PNA biosensor chips. It is suitable for studying the complexity of the immobilization and hybridization processes and may provide a rapid method for DNA diagnostics. With the absence of the labeling procedure and the simultaneous increase of the phosphate signal as a result of increasing DNA sequence length, this technique comes to be especially useful for the direct analysis of genomic DNA.
Keywords: DNA; PNA; TOF-SIMS; Biosensor; Microarray; Cluster ions;

Direct ToF-SIMS analysis of organic halides and amines on TLC plates by Alexander A. Parent; Thomas M. Anderson; David J. Michaelis; Guilin Jiang; Paul B. Savage; Matthew R. Linford (6746-6749).
It has been reported that: “direct analysis of thin layer chromatography (TLC) plates with secondary ion mass spectrometry (SIMS) yields no satisfactory results” (J. Chromatogr. A 1084 (2005) 113–118). While this statement appears to be true in general, we have identified two important classes of compounds, organic halides and amines, that appear to yield to such direct analyses. For example, five organic halides with diverse structures were eluted on normal phase TLC plates. In all cases the halide signals in the negative ion time-of-flight secondary ion mass spectrometry (ToF-SIMS) spectra were notably stronger than the background signals. Similarly, a series of five organic amines with diverse structures were directly analyzed by positive ion ToF-SIMS. In all but one of the spectra characteristic, and sometimes even quasi-molecular ions, were observed. Most likely, the good halide ion yields are largely a function of the electronegativity of the halogens. We also propose that direct analysis of amines on normal phase silica gel is facilitated by the acidity, i.e., proton donation, of surface silanol groups.
Keywords: ToF-SIMS; TLC; Halide; Amine;

Surface structure and related chemistry understanding is a vital element in the design of high biocompatible materials since adsorption and adhesion of biological components are involved. These features are even more important in the case of nanostructured materials such as carbon nanotubes (CNTs) fibers. In our preliminary work we synthesised CNTs based fibers for medical applications. This new hybrid system combines polyvinyl alcohol (PVA) with CNTs and polylactic-co-glycolic acid (PLGA), a biodegradable copolymer. The surface properties of this material are investigated in order to guarantee a biocompatible response. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) was found to be an ideal tool for fiber characterisation owing to its capacity to provide chemical specificity combined with detection limits beyond the reach of techniques previously used. Complementary morphological information is provided by atomic force microscopy (AFM). The corroboration of both data enables us to define the chemistry and structure of this new formulation.
Keywords: Carbon nanotubes; PLGA; Fibers; Biocompatibility; TOF-SIMS; AFM;

ToF-SIMS imaging of gradient polyethylene and its amine-functionalized surfaces by Tae Geol Lee; Hyun Kyong Shon; Moon Suk Kim; Hai Bang Lee; Dae Won Moon (6754-6756).
A ToF-SIMS imaging technique has been used to obtain dye label-free chemical images of gradient polyethylene (PE) and its amine-functionalized surfaces. The gradient PE surface was prepared by a corona treatment with a power increase along the PE length and confirmed by ToF-SIMS. Amine reagents with varying molecular weights (MW 158, 600, 1200, 10,000 and 60,000) were successively reacted with a gradient PE surface and examined using ToF-SIMS. Our work found that the lower the molecular weight of amine reagent, the more gradient surface of amine surface density was generated. The amine-functionalized gradient surface can be used as a template surface for evaluating bioactive molecules on the gradient surface in just one experiment.
Keywords: Gradient polyethylene surface; ToF-SIMS; Amine-functionalized; Imaging;

Studies by imaging TOF-SIMS of bone mineralization on porous titanium implants after 1 week in bone by C. Eriksson; K. Börner; H. Nygren; K. Ohlson; U. Bexell; N. Billerdahl; M. Johansson (6757-6760).
Anodic oxidation was used to grow porous layers on titanium discs. Six different oxidation procedures were used producing six different surfaces. The implants were inserted in rat bone (tibia) for 7 days. After implant retrieval, mineralization (hydroxyapatite formation) on the implant surfaces was investigated using time-of-flight secondary ion mass spectrometry (TOF-SIMS). Bone tissue around the implants was sectioned and stained. The amount of bone in close apposition to the implant was calculated. The porosity showed great variation between the surfaces. Hydroxyapatite was detected on all surfaces. A slight positive correlation between porosity and mineralization was found, although the most porous surface was not the best mineralized one. Bone had formed around all implants after 7 days. The bone-to-metal contact for the porous implants did not differ significantly from the non-porous control. Porosity is known to influence cellular events. The results indicate that porosity could have an initial, positive influence on bone integration of implants, by stimulating the mineralization process. The methods used were found to be suitable tools for investigation of initial healing around implants in bone.
Keywords: TOF-SIMS; Porosity; Titanium oxide; Osseointegration; Hydroxyapatite; Bone;

Characterisation of human hair surfaces by means of static ToF-SIMS: A comparison between Ga+ and C60 + primary ions by Claude Poleunis; Emmanuel P. Everaert; Arnaud Delcorte; Patrick Bertrand (6761-6764).
This study deals with the secondary ion yield improvement induced by using C60 + primary ions instead of Ga+ ones to characterize human hair surfaces by ToF-SIMS. For that purpose, a bunch of hair fibres has been analysed with both ion sources. A high improvement is observed for the detection of amino acids with C60 + primary ions as compared to Ga+ ions. As an example, a yield enhancement factor greater than 3000 is found for the CNO peak. A similar gain is observed for the positive secondary ions characteristic of the amino acids. Most of the atomic ions, such as Ca+, O and S, constitute minor peaks with C60 + ions while they often dominate the spectrum in the case of Ga+ ions. However, with the C60 + source, a series of inorganic combination peaks with the elements Ca, S and O are observed in the positive spectra (i.e. HCaSO4 +), while they are marginal with the Ga+ source. For the mass range beyond 100 m/z and in both polarities, the hair fingerprints are similar with both sources. In average, for a comparable number of primary ions per spectrum, the C60 + ion source gives intensities between two and three orders of magnitude higher than the Ga+ one.
Keywords: C60 +; Amino acids; 18-Methyleicosanoic acid (18-MEA); Keratin; Surfactants; Static ToF-SIMS;

The focus of our current research aims at detailing and quantifying the presence of cations, primarily Ca and Mg, in mammalian cells and chromosomes throughout the different stages of the cell cycle, using our high resolution scanning ion microprobe, the UC-SIM. The 45 keV Ga+ probe of this instrument, typically ∼40 nm in diameter, carries a current of 30–40 pA, appropriate for surface SIMS studies, but limited in sample erosion rate for dynamic SIMS mapping over cell-size areas, of order 100 μm × 100 μm. Practical and reliable use of this probe toward the above SIMS goals requires a careful matching of the latter factors with the physical and chemical consequences of sample preparation protocols. We examine here how the preferred sample cryo-preservation methodologies such as freeze-fracture and lyophilization affect high resolution SIMS analysis, and, from this standpoint, develop and evaluate the advantages and disadvantages of fast alternate approaches to drying frozen samples. The latter include the use of methanol, ethanol, and methanol/acetic acid fixative. Methanol-dried freeze-fractured samples preserve histological morphology and yield Ca and Mg distributions containing reliable differential dynamical information, when compared with those following lyophilization.
Keywords: Cations; Mammalian cells; Chromosomes; SIMS; Imaging; Cryo-preservation;

Specific Mg2+ binding to AT-rich regions of chromatin in the evolution of eukaryotes by P.L. Strissel; K.L. Gavrilov; R. Levi-Setti; R. Strick (6770-6773).
At SIMS XIV, we reported SIMS evidence of specific Mg2+ binding to the AT-rich regions of human metaphase chromosomes represented by G-bands. Subsequent Mg2+-depletion experiments supported a direct role for Mg2+ in promoting and maintaining the higher order chromatin structure originating G-bands, possibly due to both Mg2+-DNA and Mg2+-protein interactions. An in-depth study, reported elsewhere, implicated also Ca2+ in the maintenance of chromatin ultrastructure in the scaffold of mammalian chromosomes, in association with topoisomerase II.We examine here the association of Mg2+ with AT-rich regions of chromatin in the chromosomes of the Indian muntjac deer (IMD), leading to conclusions similar to the above. To answer the question whether the presumed divalent cation role in the chromosomes of advanced eukaryotes had an evolutionary history to be traced back to earlier evolutionary stages, we have SIMS-mapped Ca2+ and Mg2+ in BrdU-labeled polytene chromosomes from the salivary gland of the Dipteran Drosophila melanogaster. Striking Ca2+ and Mg2+ SIMS banding patterns correlating with those of the Br label (a thymidine analogue) implicate unequivocally a close association of both these cations with the AT-rich regions of DNA for these primitive eukaryotes.
Keywords: Chromosomes; Chromatin; G-bands; SIMS imaging; Divalent cations; Eukaryote evolution;

Enhanced peptide molecular imaging using aqueous droplets by Y. Murayama; M. Komatsu; K. Kuge; H. Hashimoto (6774-6776).
A new method in time-of-flight secondary ion mass spectrometry (ToF-SIMS) imaging, the droplet-enhanced method, was developed for the molecular analysis of biomaterials. To facilitate the ionization of biomolecules, a small amount of aqueous solution containing a variety of protonation agents as ionization-enhancing agents was dropped onto peptide samples before ToF-SIMS measurement. Using trifluoroacetic acid (TFA) as an enhancing agent, protonated insulin (MW 5733) ions were detected as not only [M  + H]+ but also [M  + 2H]2+ and [M  + 3H]3+ from its film sample, using a Ga+ primary beam. TFA promoted the ionization of the large molecules much more effectively than did the other acids, and this peculiarity is related to both Na+ and Au3 + intensities. We also demonstrated the visualization of dot-patterned insulin drawn with our bubble jet (BJ) printing technology using insulin molecular ion signals.
Keywords: ToF-SIMS imaging; Peptide; Droplet-enhanced method; TFA; Bubble jet printing;

Localization of Na+ and K+ in rat cerebellum with imaging TOF-SIMS by Katrin Börner; Håkan Nygren; Per Malmberg; Elke Tallarek; Birgit Hagenhoff (6777-6781).
High pressure-frozen (HPF), freeze-fractured and freeze-dried rat cerebellum was analyzed with imaging TOF-SIMS equipped with a Bi-cluster ion source. Data were collected separately as spectra of high mass resolution mm  > 8000 and images of high lateral resolution <700 nm. Images were made showing the localization of the peaks m/z  = 22.99, and m/z  = 39.1.Topographical effects were noted due to the freeze fracture method. This effect was compensated by normalizing images of specific secondary ions to the intensity of total secondary ions and by making PCA analysis of the image. The results showed that potassium ions were localized in blood vessels and cortex cells and sodium ions were localized in blood vessels and cerebellar interstitial tissue and in the nuclei of some cells. The sodium ion concentration was found to be higher in blood vessels than in the interstitium.
Keywords: TOF-SIMS; High pressure freezing; Ion distribution; Sodium; Potassium;

Analysis of cardiac tissue by gold cluster ion bombardment by M. Aranyosiova; A. Chorvatova; D. Chorvat; Cs. Biro; D. Velic (6782-6785).
Specific molecules in cardiac tissue of spontaneously hypertensive rats are studied by using time-of-flight secondary ion mass spectrometry (TOF-SIMS). The investigation determines phospholipids, cholesterol, fatty acids and their fragments in the cardiac tissue, with special focus on cardiolipin. Cardiolipin is a unique phospholipid typical for cardiomyocyte mitochondrial membrane and its decrease is involved in pathologic conditions. In the positive polarity, the fragments of phosphatydilcholine are observed in the mass region of 700–850 u. Peaks over mass 1400 u correspond to intact and cationized molecules of cardiolipin. In animal tissue, cardiolipin contains of almost exclusively 18 carbon fatty acids, mostly linoleic acid. Linoleic acid at 279 u, other fatty acids, and phosphatidylglycerol fragments, as precursors of cardiolipin synthesis, are identified in the negative polarity. These data demonstrate that SIMS technique along with Au3 + cluster primary ion beam is a good tool for detection of higher mass biomolecules providing approximately 10 times higher yield in comparison with Au+.
Keywords: TOF-SIMS; Cardiac tissue; Cardiolipin; Au3 + cluster primary ions;

Hair dye distribution in human hair by ToF-SIMS by Bo-Jung Chen; Pei-Ling Lee; Wen-Yin Chen; Fu-Der Mai; Yong-Chien Ling (6786-6788).
A single hair sample preparation protocol modified from reported method was developed and used to prepare longitudinally sectioned hair for ToF-SIMS analysis. Preliminary results demonstrate that ToF-SIMS is capable of providing molecular distribution of fragment ions from intrinsic constituents as well as external chemicals like the hair dye ingredients used in this study. The observation of pPDA and H2PO4 penetrating into the internal region of hair might initiate a renewed interest in exposure study.
Keywords: Hair dye; ToF-SIMS; Hair; p-Phenylenediamine; Sample preparation;

Model multilayer structures for three-dimensional cell imaging by Joseph Kozole; Christopher Szakal; Michael Kurczy; Nicholas Winograd (6789-6792).
The prospects for SIMS three-dimensional analysis of biological materials were explored using model multilayer structures. The samples were analyzed in a ToF-SIMS spectrometer equipped with a 20 keV buckminsterfullerene (C60 +) ion source. Molecular depth information was acquired using a C60 + ion beam to etch through the multilayer structures at specified time intervals. Subsequent to each individual erosion cycle, static SIMS spectra were recorded using a pulsed C60 + ion probe. Molecular intensities in sequential mass spectra were monitored as a function of primary ion fluence. The resulting depth information was used to characterize C60 + bombardment of biological materials. Specifically, molecular depth profile studies involving dehydrated dipalmitoyl-phosphatidylcholine (DPPC) organic films indicate that cell membrane lipid materials do not experience significant chemical damage when bombarded with C60 + ion fluences greater than 1015  ions/cm2. Moreover, depth profile analyses of DPPC–sucrose frozen multilayer structures suggest that biomolecule information can be uncovered after the C60 + sputter removal of a 20 nm overlayer with no appreciable loss of underlying molecular signal. The experimental results support the potential for three-dimensional molecular mapping of biological materials using cluster SIMS.
Keywords: ToF-SIMS; Polyatomic projectile; C60 +; Molecular depth profiling; 3D imaging;

Dynamic SIMS analysis of cryo-prepared biological and geological specimens by M. Dickinson; P.J. Heard; J.H.A. Barker; A.C. Lewis; D. Mallard; G.C. Allen (6793-6796).
The modification of a dynamic magnetic sector secondary ion mass spectrometry (SIMS) instrument to permit the analysis of frozen biological and geological samples is described. The SIMS instrument used for this study combines SIMS analysis with the generation of ion-induced secondary electron images, allowing direct superposition of the SIMS image onto the image of cellular structures. Secondary ion maps have been acquired with sub-micron resolution, permitting the characterisation of sub-cellular elemental distributions in plant cells and human fibroblast cells, as well as the distribution of chemical impurities at grain boundaries in polar ice samples. This cryo-preparation technique clearly extends the applicability of SIMS analysis to a wide range of samples.
Keywords: Cryo; SIMS; Biological; Pteris vittata; Fibroblast cells; Polar ice;

G-SIMS of biodegradable homo-polyesters by R. Ogaki; F. Green; S. Li; M. Vert; M.R. Alexander; I.S. Gilmore; M.C. Davies (6797-6800).
Static SIMS (SSIMS) is a powerful surface analytical technique which can provide detailed molecular information from organic surfaces. However, often much of the acquired information is too rich in detail and the data analysis relies on analysts’ expertise and/or the limited number of materials in SSIMS libraries. Gilmore and Seah [Appl. Surf. Sci. 161 (2000) 465] recently developed a library independent technique, G-SIMS where extrapolation of the data to low surface plasma temperature reveals the un-degraded parent fragments from the SSIMS spectra. In this study, G-SIMS has been tested on biodegradable polyesters including: poly(glycolic acid) (PGA), poly(lactic acid) (PLA), poly(hydroxybutyrate) (PHB) and poly(caprolactone) (PCL). These materials are chosen to test G-SIMS capabilities on these structurally related compound series. The G-SIMS spectra derived from the SIMS spectra acquired from these polyesters yielded vital clues to fragmentation mechanisms as a function of molecular structure and highlight a powerful application of G-SIMS.
Keywords: Static SIMS; G-SIMS; Polyester; Fragmentation; Spectrum simplification;

Quantitative ToF-SIMS study of surface-immobilized streptavidin by Young-Pil Kim; Mi-Young Hong; Hyun Kyong Shon; Dae Won Moon; Hak-Sung Kim; Tae Geol Lee (6801-6804).
ToF-SIMS analysis with principal component analysis (PCA) has been used for quantitatively studying the interaction between streptavidin and biotin on a dendrimer surface. A poly(amidoamine) dendrimer surface was used as a model amine surface for biotinylation. The surface streptavidin density was systematically varied and independently quantified using the surface plasmon resonance (SPR) technique. A good linear correlation of streptavidin density was observed between the ToF-SIMS and SPR results.
Keywords: Quantification; Dendrimer; Streptavidin; ToF-SIMS; SPR; PCA;

TOF-SIMS investigation of the distribution of a cosmetic ingredient in the epidermis of the skin by Masayuki Okamoto; Noriyuki Tanji; Yasushi Katayama; Joji Okada (6805-6808).
In order to understand the mechanisms of the functions of a cosmetic ingredient, it is important to know the distribution of its agents in the epidermis of the skin. Imaging analysis of these agents by microscopic methods are quite difficult, and only a few studies have been reported to date. We analyzed the penetration of cosmetic ingredients into the skin using time-of-flight secondary ion mass spectrometry (TOF-SIMS).Pig skin treated with a cosmetic preparation was used as a model for the human epidermis. The sample was embedded in resin or glue and cross-sections were carefully cut using an ultramicrotome. After the appropriate sample preparation methods were determined, the synthetic pseudo-ceramides contained in the cosmetic preparation were detected as individual molecular ion peaks and it was revealed that these agents are able to penetrate the stratum corneum tissue. TOF-SIMS analysis detects these agents as separated masses and it is thus considered to be one of the most versatile methods of high resolution imaging analysis of such species.
Keywords: TOF-SIMS; Cosmetic ingredient; Synthetic pseudo-ceramides; Stratum corneum;

Imaging of single liver tumor cells intoxicated by heavy metals using ToF-SIMS by Fu-Der Mai; Bo-Jung Chen; Li-Chen Wu; Feng-Yin Li; Wen-Kang Chen (6809-6812).
Human liver tumor cells intoxicated with five different Cd, Cu, Cr, Hg and Zn metals were analyzed using imaging time-of-flight secondary ion mass spectrometry (ToF-SIMS) to visualize the metal distributions in a single cell basis. A protocol was developed by combining rapid freezing, freeze-fracture and imprinting for transferring the intoxicated cells to a silicon wafer. As shown in the ToF-SIMS images, the cellular morphology was preserved indicating that this protocol can be used to prepare a representative cell for ToF-SIMS imaging analysis. Among the five metal ions investigated in this study, only Cr and Cu ions show preferential diffusion into the cell after simulated intoxication while the signals of the other three ions are either too low to be detected or unable to be distinguished from background intensity.
Keywords: Liver cancer; Tumor cells; Heavy metals; ToF-SIMS; Imaging;

Study of the mechanism of diatom cell division by means of 29Si isotope tracing by J.-N. Audinot; C. Guignard; H.-N. Migeon; L. Hoffmann (6813-6815).
Diatoms are delicate unicellular organisms enclosed in a silica frustule, that is made up of two valves. Multiplication of the diatoms occurs by ordinary mitotic cell division. During cell division each cell produces two daughter cells, each of them keeping one of the two valves of the mother cell and producing a new valve by absorbing the silicon present in the environment.The NanoSIMS 50 allows ion imaging to be performed on diatoms in order to determine the site of fixation of silicon. The aim of this study was to observe and compare the mechanism of the construction of the new valve after cell division. To this end, different types of diatoms have been transferred in a culture medium enriched with 29Si and after several days, the distribution of the different isotopes of silicon has been determined by NanoSIMS50 imaging. The construction of new valves has been observed and the isotopic ratio has been determined.
Keywords: NanoSIMS; Isotope tracing; Diatoms; Biological sample; Silicon;

Bioaccumulation of chromium in aquatic macrophyte Borreria scabiosoides Cham. & Schltdl. by P.A. Mangabeira; M.S. Mielke; I. Arantes; L. Dutruch; D.da.C. Silva; F. Barbier; A.-A.F. de Almeida; A.H. Oliveira; M.I.G. Severo; L. Labejof; D.C. Rocha; T.S. Rosa; K.B. Santana; K.L. Gavrilov; P. Galle; R. Levi-Setti; M.F. Grenier-Loustalot (6816-6819).
The capacity of Borreria scabiosoides Cham. & Schltdl. growing in hydroponics solutions to remove Cr (III) from water was evaluated. This macrophytes efficiently removed Cr from water at concentrations of 25 and 50 mg/l Cr−1. High resolution imaging secondary ion mass-spectrometry (HRI-SIMS) measurements were performed using scanning ion microprobe at the University of Chicago (UC-SIM). The inductively coupled plasma sector type mass spectrometer (HR-ICP-MS) was used to analyse all samples. In general, plant roots exhibited higher metal concentrations than the aerial plants parts. Borreria shows promise for the removal and store Cr from contaminated wastewater. The ion images demonstrated that Cr is preferentially accumulated in cell walls and in some vacuoles of cortical roots cells. The number of Cr deposits are higher in cortical parenchyma, particularly in vacuoles and cell walls, compared to stellar tissue.
Keywords: Bioaccumulation; Aquatic macrophytes; SIMS; Borreria scabiosoides;

It is becoming clear that mass spectrometry is a powerful tool for the analysis and imaging of complex organic and biological systems. The discussion session “Meeting the Challenge of Molecule Specific Analysis and Imaging in Organic and Bio-Systems” will attempt to illustrate the challenges to be met in mass spectral imaging and analysis of biological samples. Some of these challenges will be discussed here including the issues of sensitivity needed to obtain high resolution images at the cellular and sub-cellular level, information that can be obtained with alternative techniques and where will they be better versus when SIMS will be better suited to the need, and finally the need for depth profiling and mechanisms to achieve this goal for cellular samples.
Keywords: Molecular imaging; Challenges; Single cell; Biological imaging;

Why don’t biologists use SIMS? by R.M.A. Heeren; L.A. McDonnell; E. Amstalden; S.L. Luxembourg; A.F.M. Altelaar; S.R. Piersma (6827-6835).
Secondary ion mass spectrometry is commonly used to study many different types of complex surfaces. Yet, compared with MALDI and ESI–MS, SIMS has not made a significant impact in biological or biomedical research. The key features of the technique, namely high spatial resolution, high detection efficiency of ions spanning a wide m/z range, surface sensitivity and the high scan rates seem to match ideally with several questions posed at the cellular level. To this date, SIMS has had only limited success in the biological arena. Why is this and what is needed to change this? This discussion paper will critically review the advances and the usefulness of SIMS in biomedical research and compare it to other approaches that offer spatially resolved molecular information available to a researcher with a biological interest. We will demonstrate that the type of information generated by the various incarnations of SIMS is strongly dependent on sample preparation and surface condition and these phenomena are only poorly understood. Modern approaches such as the cluster gun developments, ME-SIMS, gold coating and MALDI stigmatic imaging on a SIMS instrument might change the perception of SIMS being a tool for semiconductor manufacturers and physicists, and might persuade biologists to use these innovative mass spectrometric imaging tools.
Keywords: ME-SIMS; MALDI; Imaging mass spectrometry; Time-of-flight mass spectrometry; Biomolecules;

Improvements in SIMS continue by Nicholas Winograd; Zbigniew Postawa; Juan Cheng; Christopher Szakal; Joseph Kozole; Barbara J. Garrison (6836-6843).
Cluster ion bombardment is at the forefront of current ToF-SIMS research, particularly when examining the feasibility of molecular depth profiling and three-dimensional imaging applications. It has become increasingly clear that secondary ion emission after cluster projectile impact results from a radically different sputtering mechanism than the linear collision cascades that dominate after atomic ion bombardment. The new physics involved with cluster ion impacts dramatically change the traditional approaches toward sample analysis with the SIMS technique. Several new ion bombardment properties have emerged from experimental and theoretical work involving cluster ions such as Au3 +, Bi3 +, SF5 +, and C60 +—all of which are commercially available ion sources. These new properties lead to new rules for traditional static SIMS experiments, provoking new methodologies, and introducing new applications—especially where high mass sensitivity and high-resolution imaging of organic and biological materials are necessary. This paper aims to elucidate recent experimental and theoretical work on these new cluster ion properties and offers insights into how these special properties can be used for future experiments and applications.
Keywords: ToF-SIMS; Cluster ion; Au3 +; SF5 +; C60 +;

ToF-SIMS analysis of bio-systems: Are polyatomic primary ions the solution? by Emrys A. Jones; John S. Fletcher; Charlotte E. Thompson; Dean A. Jackson; Nicholas P. Lockyer; John C. Vickerman (6844-6854).
We discuss the potential of cluster ion beams for overcoming difficulties experienced within molecular analysis in conventional static secondary ion mass spectrometry (SIMS). Consideration of secondary ion yield, surface damage and molecular depth profiling is included. Examples of the greatly increased secondary ion yields from ‘real world’ samples such as bacterial membranes are illustrated, the increase in information then benefiting multivariate analysis techniques such as principal component analysis (PCA). The increased efficiency of secondary ion formation with cluster beams, in conjunction with the reduced subsurface damage associated with C60 bombardment is exemplified using a depth profile through a phospholipid layer, where molecular information is obtained even following doses of 2 × 1015  ions/cm2. This is developed further to the identification of molecular ions from the interior of etched cells. Challenges that cannot be solved solely by increased secondary ion yields and low sample damage have been considered and complications due to the influence of matrix effects along with the effect of salt concentration on the fate of molecular signals in depth profiles of biomaterials have been investigated.
Keywords: ToF-SIMS; Cluster ion beams; C60; Depth profiling; Bacteria; Cells; Matrix effects;

General discussion (6855-6859).

Information from complexity: Challenges of TOF-SIMS data interpretation by Daniel J. Graham; Matthew S. Wagner; David G. Castner (6860-6868).
Time-of-flight secondary ion mass spectrometry (TOF-SIMS) data are complex, even for the simplest systems. Yet it is within this complexity that information about sample composition, molecular orientation, surface order, chemical bonding, sample purity, etc., is contained. The challenge is how to easily extract this information from the spectra and images. Multivariate analysis (MVA) has shown promise in taming the complexity challenges presented by TOF-SIMS data while using all the information in the entire spectrum. The recent success of MVA methods such as principal component analysis (PCA) and partial least squares (PLS) in the spectroscopic and imaging analysis of organic and biological materials has led to a great increase in the interest of MVA processing of TOF-SIMS data. However, there is still a need to better understand what data to use to answer a given question, how to optimally process the data before applying MVA, and how to correctly interpret the MVA results. The challenges of TOF-SIMS data interpretation will only get more complex, especially for biological samples, further increasing the need for well-controlled MVA methodologies.
Keywords: Multivariate analysis; Principal component analysis; TOF-SIMS; Adsorbed proteins; Self-assembled monolayers;

Rapid discrimination of the causal agents of urinary tract infection using ToF-SIMS with chemometric cluster analysis by John S. Fletcher; Alexander Henderson; Roger M. Jarvis; Nicholas P. Lockyer; John C. Vickerman; Royston Goodacre (6869-6874).
Advances in time of flight secondary ion mass spectrometry (ToF-SIMS) have enabled this technique to become a powerful tool for the analysis of biological samples. Such samples are often very complex and as a result full interpretation of the acquired data can be extremely difficult. To simplify the interpretation of these information rich data, the use of chemometric techniques is becoming widespread in the ToF-SIMS community. Here we discuss the application of principal components-discriminant function analysis (PC-DFA) to the separation and classification of a number of bacterial samples that are known to be major causal agents of urinary tract infection. A large data set has been generated using three biological replicates of each isolate and three machine replicates were acquired from each biological replicate. Ordination plots generated using the PC-DFA are presented demonstrating strain level discrimination of the bacteria. The results are discussed in terms of biological differences between certain species and with reference to FT-IR, Raman spectroscopy and pyrolysis mass spectrometric studies of similar samples.
Keywords: ToF-SIMS; Chemometrics; Multivariate analysis; Urinary tract infection;

Processing TOF-SIMS images to obtain clear contrast between chemically distinct regions, distinguish between chemical and topographic effects and identify chemical species can be a formidable challenge, particularly when working with organic and biological molecules that have similar spectral features. Three multivariate statistical techniques, including principal components analysis (PCA), multivariate curve resolution (MCR), and maximum auto-correlation factors (MAF) have been explored to determine their utility for processing TOF-SIMS images. The methods have been exhaustively tested on synthetic images to allow quantitative assessment of their utility. The methods are compared here based on enhancement of image contrast, enhancement of image resolution, and isolation of pure component spectra. MAF, which includes information on the nearest neighbors to each pixel, shows clear advantages over PCA and MCR for enhancing image contrast and identifying sparse components in the matrix. However, MCR is better suited to identification of unknown compounds. No single method proves superior for all of these objectives so a simple strategy is presented for combining these methods to obtain optimal results.
Keywords: Spectral imaging; Principal component analysis; Multivariate statistical analysis; Poisson statistics; Maximum auto-correlation factors; Multivariate curve resolution;

Spatial statistics and interpolation methods for TOF SIMS imaging by Tammy M. Milillo; Joseph A. Gardella (6883-6890).
Multivariate statistical methods such as principal components analysis (PCA) and factor analysis (FA) have been applied to mass spectral data to extract higher quality information from ion intensities in the mass spectrum. This often leads to better image quality in the resulting image analysis of principal components or factors. This paper presents a second multivariate statistical approach by examining the spatial statistics of the two dimensional image data. Geographic information is analyzed using two and three dimensional spatial statistical methods focused on interpolating spatial distributions. Methods such as Kriging and inverse squared distance weighting are often used to develop spatial distributions of common surface features distributed over geographic distances of meters, kilometers, miles, etc. Geospatial statistics have not been widely applied to spatial chemical distributions of microscopic dimensions. In this paper, we compare ordinary Kriging and inverse squared distance weighting for the analysis of ToF SIMS image data. By selectively eliminating pixels from the original image, we evaluate the accuracy of images reconstructed from 50 to 0.5% of the original dataset. Accurate image reconstruction from small datasets can provide added speed to ToF SIMS image collection and analysis, a potential advantage for on-line ToF SIMS analysis.
Keywords: ToF SIMS; Imaging; Multivariate statistics; Geospatial statistics;

General discussion (6891-6894).

We describe some technical aspects of the application of multi-isotope imaging mass spectrometry (MIMS) to biological research, particularly the use of isotopic tags to localize and measure their incorporation into intracellular compartments. We touch on sample preparation, on image formation, on drift correction and on extraction of quantitative data from isotope ratio imaging. We insist on the wide variety of sample types that can be used, ranging from whole cells prepared directly on Si supports, to thin sections of cells and tissues on Si supports, to ultrathin TEM sections on carbon-coated grid. We attempt to dispel the myth of difficulties in sample preparation, which we view as a needless deterrent to the application of MIMS to the general biological community. We present protocols for the extraction of isotope ratio data from mass images. We illustrate the benefits of using sequential image plane acquisition followed by the application of an autocorrelation algorithm (nanotracking) to remove the effects of specimen drift. We insist on the advantages to display the isotope ratios as hue saturation intensity images.
Keywords: MIMS; Isotope ratios; Hue saturation intensity; Cells; 15N; Turnover;

High resolution SIMS imaging of cations in mammalian cell mitosis, and in Drosophila polytene chromosomes by R. Levi-Setti; K.L. Gavrilov; M.E. Neilly; R. Strick; P.L. Strissel (6907-6916).
The University of Chicago high resolution scanning ion microprobe (UC-SIM) was used to image, by Secondary Ion Mass Spectrometry (SIMS), the distribution of Ca2+ and Mg2+ in the chromosomes of Indian muntjac (IM) deer mitotic fibroblasts. This is part of a systematic study of the cation composition of mammalian cells and chromosomes throughout the cell cycle, after having shown that Ca2+ and Mg2+ appear to be important for chromosome condensation and structure at metaphase. We focus here on a detailed description of the metaphase–anaphase transition at narrow time intervals beyond the G2/M border, made possible by controlled cell synchronization procedures. High-density distributions of chromosome spreads showed progressive stages of mitosis, identified by their morphology, within the same UC-SIM field of view. Subtle differences in cation contents between successive mitotic stages could thus be quantified in identical experimental conditions. Preliminary results indicate maximal chromosomal concentrations of Ca2+ and Mg2+ at metaphase, and a progressive decrease of the same with advancing stages of anaphase. Ca2+ and Mg2+ distributions were also imaged in the polytene chromosomes of Drosophila melanogaster, whose DNA distribution had been previously studied by BrdU labeling. These cations may play a common role in mitosis from lower eukaryotes to mammals.
Keywords: Mitosis; Metaphase; Anaphase; Chromosomes; SIMS; Imaging;

Specimen preparation for NanoSIMS analysis of biological materials by C.R.M. Grovenor; K.E. Smart; M.R. Kilburn; B. Shore; J.R. Dilworth; B. Martin; C. Hawes; R.E.M. Rickaby (6917-6924).
In order to achieve reliable and reproducible analysis of biological materials by SIMS, it is critical both that the chosen specimen preparation method does not modify substantially the in vivo chemistry that is the focus of the study and that any chemical information obtained can be calibrated accurately by selection of appropriate standards. In Oxford, we have been working with our new Cameca NanoSIMS50 on two very distinct classes of biological materials; the first where the sample preparation problems are relatively undemanding – human hair – but calibration for trace metal analysis is a critical issue and, the second, marine coccoliths and hyperaccumulator plants where reliable specimen preparation by rapid freezing and controlled drying to preserve the distribution of diffusible species is the first and most demanding requirement, but worthwhile experiments on tracking key elements can still be undertaken even when it is clear that some redistribution of the most diffusible ions has occurred.
Keywords: NanoSIMS; Biological materials; Sample preparation;

Sub-cellular localisation of a 15N-labelled peptide vector using NanoSIMS imaging by Winfried Römer; Ting-Di Wu; Patricia Duchambon; Mohamed Amessou; Danièle Carrez; Ludger Johannes; Jean-Luc Guerquin-Kern (6925-6930).
Dynamic SIMS imaging is proposed to map sub-cellular distributions of isotopically labelled, exogenous compounds. NanoSIMS imaging allows the characterisation of the intracellular transport pathways of exogenous molecules, including peptide vectors employed in innovative therapies, using stable isotopes as molecular markers to detect the compound of interest. Shiga toxin B-subunit (STxB) was chosen as a representative peptide vector. The recombinant protein (15N-STxB) was synthesised in Escherichia coli using 15NH4Cl as sole nitrogen source resulting in 15N enrichment in the molecule.Using the NanoSIMS 50 ion microprobe (Cameca), different ion species (12C14N, 12C15N, 31P) originating from the same sputtered micro volume were simultaneously detected. High mass resolving power enabled the discrimination of 12C15N from its polyatomic isobars of mass 27. We imaged the membrane binding and internalisation of 15N-STxB in HeLa cells at spatial resolutions of less than 100 nm. Thus, the use of rare stable isotopes like 15N with dynamic SIMS imaging permits sub-cellular detection of isotopically labelled, exogenous molecules and imaging of their transport pathways at high mass and spatial resolution. Application of stable isotopes as markers can replace the large and chemically complex tags used for fluorescence microscopy, without altering the chemical and physical properties of the molecule.
Keywords: Dynamic SIMS imaging; Isotopic labelling; Shiga toxin; Retrograde transport; Correlative imaging;

General discussion (6931-6934).

Development towards label- and amplification-free genotyping of genomic DNA by O. Brandt; J. Feldner; S. Hellweg; M. Schröder; A. Stephan; H.F. Arlinghaus; J.D. Hoheisel; A. Jacob (6935-6940).
Peptide nucleic acid (PNA) microarrays have been used for the analysis of unlabelled DNA molecules by time-of-flight secondary mass spectrometry (ToF-SIMS). PNAs were synthesised with an automated system in multi-well plates followed by the spotting full-length molecules only onto derivatised silicon surfaces using a common split-pin contact printing instrument. After DNA hybridisation, phosphate specific signals were detected and visualised by ToF-SIMS imaging. Because phosphorus is entirely missing in PNAs but is an integral part of nucleic acids, specific signals were only detected on spots at which DNA bound to complementary PNA probes. Combining PNA microarrays with ToF-SIMS detection enables the sensitive analysis of DNA or RNA targets without the need for introducing labels like fluorescent groups.
Keywords: PNA; ToF-SIMS; Label-free detection; Microarray;

Mass spectrometric characterization of elements and molecules in cell cultures and tissues by H.F. Arlinghaus; C. Kriegeskotte; M. Fartmann; A. Wittig; W. Sauerwein; D. Lipinsky (6941-6948).
Time-of-flight secondary ion mass spectrometry (ToF-SIMS) and laser post-ionization secondary neutral mass spectrometry (laser-SNMS) have been used to image and quantify targeted compounds, intrinsic elements and molecules with subcellular resolution in single cells of both cell cultures and tissues. Special preparation procedures for analyzing cell cultures and tissue materials were developed. Cancer cells type MeWo, incubated with boronated compounds, were sandwiched between two substrates, cryofixed, freeze-fractured and freeze-dried. Also, after injection with boronated compounds, different types of mouse tissues were extracted, prepared on a special specimen carrier and plunged with high velocity into LN2-cooled propane for cryofixation. After trimming, these tissue blocks were freeze-dried.The measurements of the K/Na ratio demonstrated that for both cell cultures and tissue materials the special preparation techniques used were appropriate for preserving the chemical and structural integrity of the living cell. The boron images show inter- and intracellular boron signals with different intensities. Molecular images show distinct features partly correlated with the cell structure. A comparison between laser-SNMS and ToF-SIMS showed that especially laser-SNMS is particularly well-suited for identifying specific cell structures and imaging ultratrace element concentrations in tissues.
Keywords: ToF-SIMS; Laser-SNMS; Cell; Tissue; Sample preparation; BNCT;

Quantitative analysis of supported membrane composition using the NanoSIMS by Mary L. Kraft; Simon Foster Fishel; Carine Galli Marxer; Peter K. Weber; Ian D. Hutcheon; Steven G. Boxer (6950-6956).
We have improved methods reported earlier for sample preparation, imaging and quantifying components in supported lipid bilayers using high-resolution secondary ion mass spectrometry performed with the NanoSIMS 50. By selectively incorporating a unique stable isotope into each component of interest, a component-specific image is generated from the location and intensity of the unique secondary ion signals exclusively produced by each molecule. Up to five species can be simultaneously analyzed. Homogeneous supported lipid bilayers that systematically varied in their isotopic enrichment levels were freeze-dried and analyzed with the NanoSIMS 50. The molecule-specific secondary ion signal intensities had an excellent linear correlation to the isotopically labeled lipid content. Statistically indistinguishable calibration curves were obtained using different sample sets analyzed months apart. Fluid bilayers can be patterned using lithographic methods and the composition of each corralled region varied systematically by simple microfluidic methods. The resulting composition variations can be imaged and quantified. This approach opens the possibility of imaging and quantifying the composition of microdomains within membranes, including protein components, without using bulky labels and with very high lateral resolution and sensitivity.
Keywords: Lipid; Bilayer; SIMS; NanoSIMS; Mixture; Gradient; Compositional analysis;

Imaging lipid distributions in model monolayers by ToF-SIMS with selectively deuterated components and principal components analysis by Mark C. Biesinger; David J. Miller; Robert R. Harbottle; Fred Possmayer; N. Stewart McIntyre; Nils O. Petersen (6957-6965).
Time of flight secondary ion mass spectrometry (ToF-SIMS) provides the capability to image the distribution of molecular ions and their associated fragments that are emitted from monolayer films. ToF-SIMS can be applied to the analysis of monolayers of complex lipid mixtures that act as a model to understand the organization of cell membranes into solid-like domains called lipid rafts. The ability to determine the molecular distribution of lipids using ToF-SIMS in monolayer films is also important in studies of the function of pulmonary surfactant. One of the limitations of the use of ToF-SIMS to studies of complex lipid mixtures found in biological systems, arises from the similarity of the mass fragments that are emitted from the components of the lipid mixture. The use of selectively deuterated components in a mixture overcomes this limitation and results in an unambiguous assignment of specific lipids to particular surface domains. The use of deuterium labeling to identify specific lipids in a multi-component mixture can be done by the deuteration of a single lipid or by the addition of more than one lipid with selectively deuterated components. The incorporation of deuterium into the lipid chains does not alter the miscibility or phase behavior of these systems. The use of deuterium labeling to identify lipids and determine their distribution in monolayer films will be demonstrated using two biological systems. Principal components analysis (PCA) is used to further analyze these deuterated systems checking for the origin of the various mass fragments present.
Keywords: Lipid separations; Deuterated; Labeling; Monolayers; Principal components analysis (PCA);

Localization of lipids in freeze-dried mouse brain sections by imaging TOF-SIMS by Peter Sjövall; Björn Johansson; Jukka Lausmaa (6966-6974).
Imaging time-of-flight-secondary ion mass spectrometry (TOF-SIMS) was used to analyse the lateral distributions of lipids on the surface of freeze-dried mouse brain sections. Tissue sections (14 μm thick) were prepared by cryosectioning, placed on glass or Si substrates and desalinated by submersion in NH3HCOO solution. Immediately prior to analysis, the samples were freeze-dried by thawing the sample in vacuum. TOF-SIMS analysis was carried out using 25 keV Au3 + or Bi3 + primary ions, always keeping the accumulated ion dose below 4 × 1012  ions/cm2. Positive and negative ion images over the entire mouse brain section and of analysis areas down to 100 μm × 100 μm show characteristic distributions of various lipids. The signals from cholesterol and sulfatides are primarily located to white matter regions, while the phosphocholine and phosphatidylinositol signals are strongest in grey matter regions. By using two different staining methods, structures observed in the TOF-SIMS images could be identified as ribosome-rich regions and cell nuclei, respectively. Analysis of freeze-dried mouse brain sections at varying sample temperatures between −130 and 60 °C showed an abrupt increase in the cholesterol signal at T  > 0 °C, indicating extensive migration of cholesterol to the tissue surface under vacuum conditions.
Keywords: TOF-SIMS; Lipids; Tissue; Brain; Imaging;

Localization of cholesterol in rat cerebellum with imaging TOF-SIMS by Håkan Nygren; Katrin Börner; Per Malmberg; Birgit Hagenhoff (6975-6981).
Time-of-flight secondary ion mass spectrometry (TOF-SIMS) was utilized to address the issue of cholesterol localization in rat cerebellum, a subject not previously investigated.Rat cerebellum was prepared by three different procedures: (1) fixation in formaldehyde, freeze-protection by sucrose, freezing in liquid nitrogen and sectioning by cryoultramicrotomy and drying at room temperature or (2) freezing in liquid nitrogen, cryostat sectioning at −40 °C and drying at room temperature or (3) high-pressure freezing, freeze-fracturing and freeze-drying.The samples were analyzed in an imaging TOF-SIMS instrument equipped with a Bi1–7 +-source. The cholesterol signal (m/z 369 and 385), showed high intensity in the glial cells in white matter and lower intensity in Purkinje cells and in nuclei of granular layer cells. Specimen treated by procedure 1 showed some signs of diffusion of cholesterol in the tissue. Specimen treated by procedure 2 showed freeze-damage of the cells. Specimen treated by procedure 3 showed distinct localization of cholesterol in well preserved tissue. Thus, high-pressure freezing and freeze-fracturing was used for further characterization of the distribution of cholesterol in rat cerebellum.
Keywords: Cryofixation; Imaging mass spectrometry; High-pressure freezing; Bi-LMIG;

General discussion (6982-6985).

Owing to the sensitivity of Static SIMS to molecular structures and its selectivity to the outermost surface layers, this technique is very well suited to gain information about conformation and orientation of molecules at the surface. The aim of this presentation is to discuss critically and to illustrate these unique features of Static SIMS with selected applications.Firstly, the SIMS information depth and its dependence on the molecular fragment ion size are presented in order to justify the surface selectivity. This has been experimentally determined by looking at the substrate signal attenuation when depositing organic layers in a controlled manner on different materials as was done with Langmuir–Blodgett layers and polyelectrolyte ultra thin films. As illustrated for polymers, the surface selectivity allowed SIMS to be sensitive to tacticity of macrochains and orientation of mobile pendant groups. Based on these performances, Static SIMS has been used to study protein adsorption and highlighted modifications in protein conformation/orientation, depending on the substrate properties.Finally, the limitations of Static SIMS analyses are discussed. Indeed, for sample surfaces non-uniform at a nanoscale, which is beyond the limits of SIMS imaging, the chemical molecular information cannot be sufficient. It has to be complemented by surface morphology information in order to get a correct view of the system. This is illustrated by our recent study of very thin layers of block copolymers and polymer blends, forming nanostructures at the surface.
Keywords: ToF-SIMS; Protein adsorption; Amino acid; Conformation; Orientation; Sampling depth;

Characterisation of electrospun nanowebs with static secondary ion mass spectrometry (S-SIMS) by P. Van Royen; A.M. dos Santos; E. Schacht; L. Ruys; L. Van Vaeck (6992-6995).
Electrospinning (ES) uses the injection of a polymer solution in an electrical field to produce non-woven nanowebs of polymer fibres with diameters of 50–500 nm. The use of functionalised polymers or additives allows the surface composition of the nanostructured material to be tuned as a function of the application. Determination of the molecular composition in the outer monolayer at the surface of such nanoscale objects is an analytical challenge. This paper reports on the possibilities and limitations in the use of S-SIMS for the qualitative and quantitative characterisation of molecular components in nanofibres prepared from polycaprolactone (PCL) with and without cetyltrimethylammonium bromide (CTAB). Specifically, attention is given to the quality of the mass spectra in terms of mass resolution and mass accuracy, the detection of surface enrichment and the possibilities of imaging.
Keywords: S-SIMS; Electrospinning; Polycaprolactone;

TOF-SIMS study of photocatalytic decomposition reactions on nanocrystalline TiO2 films by Hubert Gnaser; Adam Orendorz; Christiane Ziegler; Elisabeth Rowlett; Wolfgang Bock (6996-6999).
Nanocrystalline TiO2 is known to be a very efficient photocatalyst. In order to elucidate the details of reaction pathways occurring on the surface, nanocrystalline TiO2 films (with 12 nm average crystallite size) were covered by methylene blue (MB) and studied, both in the pristine state and upon UV exposure, by TOF-SIMS. Distinct mass signals related to the MB parent molecule (m  = 284.1 amu) and from fragment ions are observed for the as-prepared samples. Upon irradiation with UV light under atmospheric conditions, the surface composition is pronouncedly changed, an observation ascribed to photocatalytic reactions induced by UV photons: the amount of the parent molecule is diminished whereas intermediate reaction products are identified to be present at the TiO2 surfaces. Eventually, the parent molecule and the characteristic fragment species disappear completely upon extended exposure to UV light.
Keywords: TOF-SIMS; Nanocrystalline TiO2; Photocatalysis; Methylene blue;

Supramolecular host–guest complexes based on cyclodextrin–diphenylhexatriene by L. Rabara; M. Aranyosiova; D. Velic (7000-7002).
Supramolecular host–guest complex cyclodextrin–diphenylhexatriene as a model of noncovalent binding is studied by means of time-of-flight secondary ion mass spectrometry. Cyclodextrin and diphenylhexatriene are in forms of β-cyclodextrin (C42H70O35) and 1,6-diphenyl-1,3,5-hexatriene (C18H16), respectively. The whole intact supramolecular host–guest 1:1 complex between cyclodextrin and diphenylhexatriene is observed in cationized forms with Na at 1389.5 m/z and with K at 1405.5 m/z. The focus is on the higher ratio complexes, where the complexes of cyclodextrin-diphenylhexatriene with ratios of 1:2 and 2:1 are observed in cationized forms with Na at 1622 and at 2524 m/z, and with K at 1638 and 2541 m/z, respectively. These complexes are assumed to be basic building blocks of cyclodextrin–diphenylhexatriene nanowire structure.
Keywords: Cyclodextrin; Diphenylhexatriene; Host–guest; SIMS; Nanowire;

Atomic distribution in quantum dots—A ToF-SIMS study by Wen-Yin Chen; Yong-Chien Ling; Bo-Jung Chen; Chiung-Chi Wang (7003-7005).
The atomic distribution in the monolayer of two different Mn-doped CdS quantum dots (QDs) was studied first time with ToF-SIMS. The model Cd:Mn QDs were immobilized on Au substrate by use of a self-assembled monolayer via 1,10-decanedithiol. Morphological analysis by SPM and TEM indicates larger particle size of in situ synthesizing CdS:Mn. ToF-SIMS depth profile and 3D-images reveal that Mn atoms reside on the surface of in situ synthesizing CdS:Mn and are uniformly embedded in capped CdS:Mn. The results obtained by SPM, TEM, and ToF-SIMS are comparable, indicating that ToF-SIMS might find potential applications in surface and interface study of semiconductor nanocrystals.
Keywords: ToF-SIMS; CdS; Immobilization; Depth profile; Image;

Characterization of individual atmospheric aerosol particles with SIMS and laser-SNMS by R.E. Peterson; A. Nair; S. Dambach; H.F. Arlinghaus; B.J. Tyler (7006-7009).
The surface chemistry of atmospheric aerosol particles is important in determining how these particles will effect human health, visibility, climate and precipitation chemistry. In previous work, it has been shown that ToF-SIMS can provide significant valuable information on both organic and inorganic constituents of the aerosol. It has been found, however, that ToF-SIMS with a Ga+ primary ion beam offers very low sensitivity to poly-aromatic hydrocarbons (PAHs) and heavy metals, two important classes of pollutants. In this work the utility of laser-SNMS for detection of these pollutants has been explored. Two laser systems, a 193 nm excimer laser and a 157 nm excimer laser have been utilized. Each approach has advantages. ToF-SIMS has the highest sensitivity to alkali metals and aliphatic hydrocarbons. The 193 nm laser provides very high sensitivity to lead and other metals. The 157 nm laser greatly enhances sensitivity to PAHs which has enabled detection of PAHs on the surface of individual particles.
Keywords: Spectral imaging; Particulate matter; PAH; Lead, Multivariate statistical analysis; Maximum auto-correlation factors;

Aerosol particles were collected in different environments in Poland—in Legnica, a middle size town situated close to big copper works and in a rural site in the suburbs of Kraków, the city three times bigger than Legnica. Bulk analysis of particulate matter collected on quartz-fibre filters was performed using spark source mass spectrometry (SSMS). Analysis of airborne particles from urban and rural environments revealed differences in partial concentration of 20 selected elements. In urban aerosol collected in Legnica we found more: Pb, Cr—20 times than in the rural environment, As, Sr—10 times, Co—7 times, Cl—5 times, V, Y—3 times, Ti, Mn, Cu, Se—2 times and Fe, Ni, Zn, Br, Zr, Mo almost 2 times more than in the rural environment.Secondary ion mass spectrometry (SIMS) depth profile analyses were performed for aerosol particles collected at Al-foils with the use of nine-stage rotating plates cascade impactor. SIMS results obtained with the use of 5 keV Ar+ ion sputtering show “core-shell” structure of urban and rural particles dependent of their grain size in the range of 300 nm to 15 μm. Ultra fine (300–500 nm diameter) rural particles have shell layers enriched in iron and manganese, while such enrichment is typical for coarse (5–10 μm diameter) urban particles.
Keywords: Airborne particles; Atmospheric aerosol; Core-shell structure; SIMS depth profiling;

Analysis of volatile nanoparticles emitted from diesel engine using TOF-SIMS and metal-assisted SIMS (MetA-SIMS) by Masae Inoue; Atsushi Murase; Masami Yamamoto; Shuichi Kubo (7014-7017).
Time-of-flight secondary ion mass spectrometry (TOF-SIMS) and metal-assisted SIMS (MetA-SIMS), which is TOF-SIMS analysis of metal-deposited sample surfaces, were applied to analyze small quantities of volatile nanoparticles emitted from a light-duty diesel engine under idling and deceleration conditions. We investigated nucleation materials, i.e., >C35 hydrocarbons, oxidation products, etc., which have lower volatility than the main components of volatile nanoparticles and control the formation of volatile nanoparticles.Oxygenated hydrocarbons were detected by TOF-SIMS in volatile nanoparticles under idling condition. Their relative intensities increased as particle diameter decreased. This resulted in the oxygenated hydrocarbons acting as nucleation materials for volatile nanoparticles under idling condition.High-molecular-weight hydrocarbons of greater than C35 were detected in volatile nanoparticles under deceleration condition by MetA-SIMS. It was concluded that the detected hydrocarbons originated in lubricants and acted as nucleation materials for volatile nanoparticles under deceleration condition.TOF-SIMS makes it possible to detect traces of low-volatility molecules due to its high-vacuum environment. MetA-SIMS is the only method of directly detecting high-molecular-weight hydrocarbons in small quantities of nanoparticles. TOF-SIMS and MetA-SIMS were proved to be useful tools for analyzing of the properties of volatile nanoparticles.
Keywords: TOF-SIMS; Metal-assisted SIMS (MetA-SIMS); Nucleation; Volatile nanoparticles; Diesel engine;

We have established a characterization method of a 100 nm sized core–shell latexes composed of styrene–butadiene co-polymer. The core–shell structure was revealed by TEM observation of the latex film after modification with OsO4 vapor. Pyrolysis gas chromatography combined with mass spectrometry (Py-GC/MS) of the latexes showed the average chemical composition of the core–shell latexes. TOF-SIMS of the latex film gave the characteristic peak for styrene and butadiene. The peak intensities changed in accordance with the chemical composition of the latexes. Surface composition of the latex film, which corresponds to the composition of the shell part of the latexes, was estimated from this peak intensity ratio. From the combined analysis of Py-GC/MS and TOF-SIMS of the latexes, we successfully evaluated the chemical composition of both the core part and the shell part of latexes individually.As the results of characterization of some core–shell latex, it was revealed that the high degree of cross-linking is needed to synthesize the tailored core–shell latex.
Keywords: Core–shell latex; TOF-SIMS; Pyrolysis-GC/MS; TEM; Composition quantification;

Characterization of individual complex particles in urban atmospheric environment by K. Suzuki; T. Takii; B. Tomiyasu; Y. Nihei (7022-7025).
The origins of carrier particles of complex particles (iron-rich particles) collected from the urban atmospheric environment near to road traffic and a railroad were investigated from the detailed surface information using FE-SEM/EDS and TOF-SIMS analyses. From the FE-SEM/EDS analyses, the iron-rich particles were classified into two typical types (spherical type and non-spherical type). From the TOF-SIMS measurements, the characteristic secondary ions of spherical type of iron-rich particles were 23Na+ and 39K+. The minor components of non-spherical type were Al, Ca and Ba. On the other hand, we carried out TOF-SIMS measurement to materials of rail origin and brake origin. From the comparison of these spectra pattern, it seemed that the spherical type of iron-rich particles was emitted from the rail origin. We concluded that the origin of non-spherical type of iron-rich particles were brake pad of vehicles.
Keywords: TOF-SIMS; Source apportionment; Iron-rich particle; Carrier particle; Adsorbed particle;

We obtained the detailed compositional information of diesel and gasoline exhaust particles, and discussed the possibility of the classification into each emission source. The intensities of Ca+ and hydrocarbons were relatively high in the TOF-SIMS spectrum of the gasoline exhaust particles. The secondary ions such as NH4 + and Si(CH3)3 + were strongly detected from the diesel exhaust particles. From TOF-SIMS images of each type of exhaust particles, Ca+ of the gasoline exhaust particles and Si(CH3)3 + of diesel exhaust particles were strongly detected from the large particles with diameter of 0.3 μm. From these results, the exhaust particles collected in the atmosphere near the traffic route can be classified by their origin by using TOF-SIMS information.
Keywords: TOF-SIMS; Source apportionment; Air environment; Diesel exhaust particle; Gasoline exhaust particle;

Study of coating distribution onto metallic hollow particles by Renáta Oriňáková; Andrej Oriňák; Heinrich F. Arlinghaus; Sebastian Hellweg; Miriam Kupková; Margita Kabátová (7030-7033).
Porous lightweight materials have found increasing interest for various applications. Regular structured cellular materials might be accessible by sintering the hollow metallic particles. The properties of the final product depend to a large extent on the properties of original hollow metallic particles. Therefore, the preparation of reliable hollow spheres of defined parameters represents an important step towards the cellular solids production by means of powder metallurgy route.Electrochemical deposition of metallic coatings on the surface of hollow spherical particles facilitates the required modification of the surface corresponding to high mechanical quality.The copper hollow spheres were created on porous iron powder particles by electroless deposition. The suitable matrix for the preparation of relatively light but mechanically strong porous materials was obtained by electrochemical plating of copper hollow micro-particles by Ni layer.In this study ToF-SIMS depth profiling and SEM/EDX analysis with elements mapping are used to investigate the distribution of the coating components across the surface and subsurface layer of coated hollow particles.
Keywords: ToF-SIMS; Depth profiling; Hollow spheres; Coating; Nickel; Copper;

Secondary ion statistics and determination of nanocluster (m  > 107  amu) ion registration efficiency by A.V. Novikov; S.N. Kirillov; I.A. Baranov; V.V. Obnorskii; S.V. Yarmiychuk (7034-7037).
The m/q spectra of gold nanocluster ions (NCI) (〈D〉 = 18.1 nm and 〈m〉 = 4.6 × 107  amu) desorbed from nanodispersed targets with 252Cf fission fragments were measured using a tandem time-of-flight mass spectrometer at acceleration of 38 kV. In parallel, the statistics of secondary ions (SI) emitted with NCI from various converters (Au and CsI) were measured and the registration efficiency (RE) of NCI was determined. It was shown that distribution of SI number is most adequately described by the geometric distribution. The resulting values of RE are less by a factor of 1.5–2 than those predicted by the Poisson distribution for the m/q range from 3.1 × 106 to 8.2 × 106  amu/e.
Keywords: Nanocluster; Statistics; Registration efficiency;

In this paper, ToF-SIMS was used to study the Pd–Rh interdiffusion which has a great interest in brachytherapy, a cancer treatment. The secondary ion mass spectrometry was used in the semi-quantitative MCs+ mode, by detecting the RhCs+ and the PdCs+ molecular ions under cesium bombardment. At first, different Rh x Pd y (from pure Rh to pure Pd) layers were deposited by PVD and were subsequently characterized by ToF-SIMS, RBS and PIXE. A linear relationship between the relative CsPd+ yields and the Pd concentration into the Rh matrices was found. Moreover, the total sputtering yield increases linearly with the Pd concentration. Those relationships permitted to calibrate the ToF-SIMS depth profiles of annealed Pd/Rh layers and were successfully used to quantify the Pd–Rh interdiffusion.
Keywords: ToF-SIMS; Cesium; MCs; Depth profile; Brachytherapy; RhPd; Quantification;

Secondary ionization mass spectrometric analysis of impurity element isotope ratios in nuclear reactor materials by D.C. Gerlach; J.B. Cliff; D.E. Hurley; B.D. Reid; W.W. Little; G.H. Meriwether; A.J. Wickham; T.A. Simmons (7041-7044).
During reactor operations and fuel burn up, some isotopic abundances change due to nuclear reactions and provide sensitive indicators of neutron fluence and fuel burnup. Secondary ion mass spectrometry (SIMS) analysis has been used to measure isotope ratios of selected impurity elements in irradiated nuclear reactor graphite. Direct SIMS measurements were made in graphite samples, following shaping and surface cleaning. Models predicting local fuel burnup based on isotopic measurements of B and Li isotopes by SIMS agreed well with U and Pu isotopic measurements obtained by thermal ionization mass spectrometry (TIMS).
Keywords: SIMS; Isotope ratios; Nuclear reactors; Graphite;

Application of SIMS analyses on oxygen transport in SOFC materials by N. Sakai; K. Yamaji; T. Horita; H. Kishimoto; M.E. Brito; H. Yokokawa; Y. Uchimoto (7045-7047).
The oxygen transport was investigated for modelled interface of striped metal electrode on a solid oxide electrolyte by oxygen tracer exchange and three dimensional imaging techniques by using a secondary ion mass spectrometry (SIMS). The gold or platinum electrode on yttrium stabilized zirconia (YSZ) electrolyte were stable, and acted as a blocking layer of 18O diffusion during the treatments in dry atmosphere at T  = 873 K in p(18O2) = 7 kPa. The oxygen flow via triple phase boundary was clearly observed for both electrodes. The treatment in humid atmosphere (T  = 773 K, p(18O2) = 7 kPa, p(H2 18O) = 2 kPa) raised the flux of oxygen diffusion through YSZ surface, however, it did not affect on the role of electrode on the oxygen transport properties.
Keywords: SOFC; Oxygen; Diffusion; Isotope exchange; Imaging; Depth profiling;

Characterisation of irradiated nuclear fuel with SIMS by L. Desgranges; Ch. Valot; B. Pasquet (7048-7050).
In addition to optical microscopy, SEM, EPMA and XRD, a shielded SIMS was designed and installed in our laboratory with the aim of providing information on the behaviour of nuclear fuel, in reactor and on also in storage conditions. For that purpose, the studies performed with SIMS on irradiated nuclear fuel were focused on three main axis: (1) the nuclear reactions occurring during in core irradiation which are characterised with isotopic ratio measurements, (2) the physical and chemical behaviour of fission products which is evidenced by isotopic cartography and (3) characterisation of fission gases, especially the gases filling bubbles in the UO2 ceramics, which requires the development of new methods.
Keywords: Nuclear fuel; UO2; Shielded SIMS;

Study of the carbon distribution in multi-phase steels using the NanoSIMS 50 by N. Valle; J. Drillet; O. Bouaziz; H.-N. Migeon (7051-7053).
An advanced understanding of phase transformation mechanisms and of microstructure/properties relationships in steels requires to investigate the distribution of carbon. The improvement of mechanical properties of these materials led to develop finer microstructures. Thus, the mean size of the constituents (austenite/austenite islands and bainite laths) of the high strength steels is under the micron. The small size combined in some case with low concentration of carbon renders the analysis of these materials difficult.The NanoSIMS 50, which associates high spatial resolution and high sensitivity, seems to be a tool of choice to answer to this new analytical challenge. In this objective, we have explored the potentialities of such an instrument for the qualitative and quantitative study of carbon in multi-phase steels. In particular, a calibration curve was established from reference samples containing martensite and ferrite with a known carbon content.
Keywords: Steels; Carbon quantification; Ionic image; NanoSIMS 50;

The emission of MCs+ secondary ions (M designates the analyte species) from TiO x (0.2 ≤  x  ≤ 2) and GeO x (0.001 ≤  x  ≤ 0.8) films under Cs+ bombardment was examined. The relative calibration factors of OCs+/TiCs+ and OCs+/GeCs+ were determined and were found to depend pronouncedly on the O/Ti and O/Ge atomic concentration ratios. Specifically, with increasing oxygen content OCs+ ions form much more efficiently (as compared to TiCs+ or GeCs+ ions), an enhancement amounting to more than a factor of 10 for the highest oxygen concentrations. Concurrently, the formation of TiOCs+ or GeOCs+ ions increases drastically. For both oxide systems, an empirical relation for the oxygen-concentration dependence of the relative calibration factors could be established.
Keywords: MCs+ secondary ions; Calibration factors; TiO x ; GeO x ;

RuO2/SiO2/Si and SiO2/porous Si/Si interfaces analysed by SIMS by Michał Ćwil; Piotr Konarski; Michał Pająk; Tomasz Bieniek; Andrzej Kosiński; Krzysztof Kaczorek (7058-7061).
Compared are interfaces between thin silicon oxide layers and two substrates bulk silicon and porous silicon. About 2 μm thick porous silicon was prepared by an electrochemical etching of Si in HF solution. Oxide layers were formed by thermal oxidation. Part of SiO2/Si samples were covered with 50 nm RuO2 oxide. SIMS depth profiles of these interfaces were performed using ultra-low energy (880 eV) and low energy (5 keV) argon ion beams at several incidence angles. Positive and negative secondary ions were analysed by quadrupole mass spectrometer QMA 410 Balzers during Ar+ bombardment with the use of 06-350E Physical Electronics ion gun. Charge build-up effects during positive secondary ion detection were observed dependent of the thickness of silicon oxide layer.The SiO2/Si interface regions characterised by SIMS show differences related to the kind of a substrate used. In case of 50 nm SiO2/porous Si interface, characteristic oxygen depletion region (20 nm thick) is present on the porous silicon side. The observed depletion was confirmed also by Auger depth profiling. The depletion formation mechanism is explained on the basis of ion beam induced redeposition of oxygen inside the pores.
Keywords: Porous silicon; Nanopores; Silicon oxide nanostructure; SIMS; Depth profile analysis; Oxygen depletion; Charge build-up effect;

In order to understand the influence of boron on the grain size and microstructure of a series of low carbon steel rods the imaging of elemental distributions of B, N and C has been undertaken using Cameca NanoSIMS 50. This instrument provides the high sensitivity, spatial and mass resolution required for the identification of small precipitates and segregation of light elements that are traditionally difficult to study by other micro-analytical techniques. However, the use of NanoSIMS to investigate metallurgical problems is complicated by matrix effects. This leads to changes in ionization yield and variable sputter rates due to the matrix composition. In order to help overcome this problem, the results from the sequential characterisation of exactly the same area of a sample using first transmission electron microscopy (TEM) and then NanoSIMS will be described. This permits the direct comparison of sensitivity and spatial resolution on precisely the same individual particles, which can help us determine the most efficient characterisation strategy.
Keywords: NanoSIMS; TEM; Boron; Steel;

SIMS analysis of nitrogen in various metals and ZnO by Yupu Li; Shaw Wang; Stephen P. Smith (7066-7069).
In this paper, we report an optimized way to measure nitrogen in ZnO using a Cs+ primary beam while monitoring (O + N). Because of ion yield variations and mass interferences, monitoring molecular ions of the type (matrix + N) may not be useful for metal films such as Cu and Ni. In this work, based on 15N+-implanted samples, we also report N profile measurements in Cu and Ni using a Cs+ primary beam and monitoring Cs-attached cluster ions: e.g. (Cs2N)+ in Cu and (CsN)+ in Ni. For a given profiling energy such as 5.5 keV and using Cs2 + as the “matrix” signal for quantification, it has been found that the ratio of (Cs2N)+ or (CsN)+ ion yield to (Cs2)+ ion yield (i.e. the relative sensitivity factor) is independent of the chosen sputter rate, but depends on the matrix materials. The range data measured by SIMS are compared with the simulated data from SRIM. The agreements are found to be very good in ZnO, and good in Cu and Ni films.
Keywords: SIMS; Nitrogen profile; (Cs2N)+ or (CsN)+; ZnO; Copper; Nickel;

Sodium and hydrogen analysis of room temperature glass corrosion using low energy Cs SIMS by S. Fearn; D.S. McPhail; R.J.H. Morris; M.G. Dowsett (7070-7073).
Corrosion affects commercial float glass production and glasses used to contain high level nuclear waste. In order to prevent the corrosion it is necessary to understand the composition of the corroded glass and the corrosion mechanism taking place. SIMS depth profiling lends itself well to monitoring the compositional changes that occur during the corrosion process. However, most studies have analysed glass that has been corroded using accelerated ageing conditions. In this work a soda–lime glass has been aged at room temperature under known atmospheric humidity for increasing periods of time. The aged glass has then been depth profiled using a low energy (1 keV) Cs beam monitoring both the sodium and hydrogen signals concurrently. The depth profiles show that in the region directly below the glass surface that is severely depleted in sodium, there is an increased level of hydrogen compared to the bulk glass indicating an increase in the water content within this region.
Keywords: Glass; Corrosion; Low energy SIMS; Caesium; Depth profiles;

Zinc oxide and copper/zinc sulphide layers are formed during vulcanisation and moulding of rubber to brass-coated steel tyre reinforcing cords. Previous studies have described how zinc diffuses through the rubber–brass interface to form zinc sulphide, and combines with oxygen to create zinc oxide during dezincification. The zinc is usually assumed to originate in the brass of the tyre cord, however, zinc oxide is also present in the rubber formulation. We reveal how zinc from these sources is distributed within the interfacial bonding layers, before and after heat and humidity ageing.Zinc oxide produced using 64Zn-isotope depleted zinc was mixed in the rubber formulation in place of the natural ZnO and the zinc isotope ratios within the interfacial layers were followed by secondary ion mass spectroscopy (SIMS) depth profiling. Variations in the relative ratios of the zinc isotopes during depth profiling were measured for unaged, heat-aged and humidity-aged wire samples and in each case a relatively large proportion of the zinc incorporated into the interfacial layer as zinc sulphide was shown to have originated from ZnO in the rubber compound.
Keywords: Tyre cord adhesion; Isotope ratio; SIMS depth profiling;

SIMS characterisation of superconductive MgB2 layers prepared by ion implantation and pulsed plasma treatment by P. Konarski; M. Ćwil; J. Piekoszewski; J. Stanislawski (7078-7081).
Thin films of magnesium diboride (MgB2), an intermetallic compound, possessing superconductive properties, were analysed by secondary ion mass spectrometry (SIMS). The samples were prepared using a new two-step technique of ion implantation followed by plasma treatment. Two kinds of structures were obtained when boron and magnesium were used as targets. Eighty kiloelectronvolt magnesium ions were implanted into boron samples and 100 keV boron ions into magnesium strips. Plasma treatment was performed using hydrogen and argon 1 μs plasma pulses of fluence 2–5 J/cm2. Magnetic moment and electrical conductivity measurements confirmed superconducting properties of the obtained layers.SIMS depth profiling was performed using 5 keV Ar+ ion beam (06-350E Physical Electronics) and quadrupole mass spectrometry (QMA 410 Balzers). Sensitivity factors for boron and magnesium were obtained based on SIMS analyses of bulk reference samples MgB2, B and Mg. Obtained results allow modifying technology parameters of thin film MgB2 synthesis.
Keywords: MgB2; Secondary ion mass spectrometry; Superconductivity; Ion implantation; Pulse plasma treatment; Depth profile analysis;

Characterization of laser-fired contacts in PERC solar cells: SIMS and TEM analysis applying advanced preparation techniques by U. Zastrow; L. Houben; D. Meertens; A. Grohe; T. Brammer; E. Schneiderlöchner (7082-7085).
In this study we apply ion-beam supported preparation techniques for both mesa formation by trench sputtering and FIB ‘lift-out’ lamella cutting for dynamic SIMS and TEM analysis of laser-fired Al point contacts on Si, respectively. Detailed compositional and structural informations about the metallurgical contact formation process are obtained combining both characterization techniques. While TEM micrographs and microdiffraction patterns reveal a mixture of Al- and Si-crystals within the ∼1 μm thick Al rich re-solidified surface layer according to the Al–Si phase diagram, spatially resolved SIMS depth profiling indicates ppm-range Al-diffusion a few hundred nm into the buried, substantially undisturbed Si-lattice.
Keywords: Solar cell; Laser-fired contact; Sample preparation; SIMS; TEM; Microdiffraction analysis;

TOFSIMS analysis of Cu–SiC composites for thermal management applications by R. Treichler; T. Weissgaerber; T. Kiendl (7086-7088).
TOFSIMS elemental mapping was applied to characterize SiC reinforced copper. SiC grain in Cu, compressed by hot isostatic pressing, is an innovative substrate material for improved heat dissipation of high-power semiconductor devices so that traditional substrates like Cu, Al, Al2O3 and metal alloys could be complemented. The TOFSIMS imaging capabilities combined with its excellent detection limits were used to monitor the matrix components as well as the distribution of an alloying additive (Ti) which is necessary to improve the mechanical strength. It turned out that SiC–Ti interface reactions lead to a dissipation of Si into the Cu matrix which deteriorates heat conduction. The TOFSIMS analyses helped to gain a better understanding of the complex Cu/SiC composite system which in turn gives room for further process improvements.
Keywords: TOFSIMS; Cu(Ti)/SiC composite; Thermal heat management;

The geological microprobe: The first 25 years of dating zircons by W. Compston; S.W.J. Clement (7089-7095).
Andersen and Hinthorne reported in situ Pb isotope ages for lunar minerals in the early 1970s. ‘Peak stripping’ was used to subtract isobaric interferences but it worked only for old, U-rich targets. Jim Long entered the race for in situ mineral dating using high resolution to separate isobars. Despite low sensitivity, he achieved 207Pb/206Pb dating of zircons in the late 1970s. In 1980 we finished the large instrument SHRIMP I based on the magnetic analyser design of Matsuda that delivered both high resolution and high sensitivity. A year later we found zircon grains 4200 million years old, far older than any previous terrestrial age.Certain in situ isotope studies remained inaccessible, such as Sr isotopes in Ca-rich minerals. All need 20,000 R with high sensitivity to accumulate enough counts for worthwhile precision. In 1990, Matsuda published new reverse-geometry designs that have still higher resolution, one of which we completed in 1997. We achieved 20,000 R but so far only at reduced sensitivity. Its full potential will be realised after further testing including computer simulations.
Keywords: Magnetic mass-analysers; SIMS dating; Zircon ages; High mass-resolution;

Applications of SIMS to cultural heritage studies by A. Adriaens; M.G. Dowsett (7096-7101).
This paper discusses the use of secondary ion mass spectrometry in cultural heritage studies recently reported in the literature, and includes material on the analysis of pigments, glass and metals. Applications of depth profiling, imaging, speciation and the topic of ultra-low energy SIMS depth profiling are addressed.
Keywords: SIMS; Cultural heritage; Inorganic materials; Imaging; Speciation; Depth profiling;

NanoSIMS: A new tool in cosmochemistry by P. Hoppe (7102-7106).
The Cameca NanoSIMS 50 is a new generation ion microprobe, characterized by high spatial resolution (down to 50 nm), high transmission, and simultaneous detection of up to six isotopes. After 4 years of operation the NanoSIMS has now become a well established tool in cosmochemistry which has significantly contributed to a better understanding of the presence of presolar matter in primitive solar system materials and on the early solar system history. Examples of important breakthroughs are: (i) discovery of silicate stardust in interplanetary dust particles and primitive meteorites; (ii) extension of isotopic studies to submicrometer-sized presolar SiC and spinel grains separated from primitive meteorites by chemical and physical treatments; (iii) identification of isotopic heteorogeneities within micrometer-sized presolar grains; (iv) coordinated NanoSIMS-TEM studies made it possible to obtain simultaneous information on the mineralogy, structure, and isotopic composition of presolar materials; (v) detection of radiogenic 60Ni from the decay of radioactive 60Fe (half life 1.5 Ma) and of radiogenic 53Cr from the decay of radioactive 53Mn (half life 3.7 Ma) in meteoritic minerals.
Keywords: NanoSIMS; Ion imaging; Cosmochemistry; Presolar grains; Extinct radioactivity;

Some applications of SIMS in conservation science, archaeometry and cosmochemistry are described. Ultra-low energy SIMS depth profiling and TOF-SIMS imaging are used to study the corrosion of low-lime glass vessels from the V&A museum. Static SIMS and focused ion beam (FIB) SIMS are used to study the effects of laser cleaning on museum artefacts. Archaeological glass from Raqqa, Syria is studied with FIB-SIMS and micrometeorite impacts on space vessels are studied with FIB and FIB-SIMS. The new analytical challenges provided to the SIMS community by these materials are presented and the ethical issues associated with sampling and destructive analysis discussed.
Keywords: Archaeometry; Conservation; Cosmochemistry; Depth Profiling; FIB; Imaging; SIMS;

In the 15–17th centuries tapestry manufacture was at its peak and was the definitive iconographic symbol of power, wealth and cultural style. However, in the subsequent centuries the condition of the tapestries has generally deteriorated due to poor handling and exhibition lighting conditions. The tapestries are composed of wool, silk and precious metal threads and all undergo physicochemical changes during ageing. In this study the wool component in particular is investigated using ToF-SIMS with a view to understanding the nature of the initial greasy wool, the effect of scouring and dyeing, and the nature of the ageing process.
Keywords: ToF-SIMS; Wool; Tapestry; Scouring; Dyeing; Ageing;

We have constructed a TOFSIMS instrument based upon the BIOTOF design. SIMS mapping of mass resolved secondary ions and molecules with an intrinsic mass resolving power of 3700 has been achieved with an estimated spatial resolution of 250 nm. We have conducted studies of non-resonant laser post-ionization of sputtered neutrals in order to improve the ionization efficiency over SIMS and avoid matrix effects for more precise quantification of element abundances. The laser used is a GAM F2 excimer laser producing up to 4.5 mJ per pulse at 750 Hz at a wavelength of 157 nm. With a photon energy of 7.9 eV, around 60% of the elements of the periodic table may be non-resonantly photo ionized by single photon ionization. SNMS laser post ionization improves detection sensitivity especially for elements with mid-range first ionization potentials up to the single photon energy of 7.9 eV. We are currently quantifying the highest sensitivities obtainable using this technique for a range of elements.
Keywords: SNMS; SIMS; Secondary ionization; Quantification; Laser ionization; Stardust;

Analysis of simulated hypervelocity impacts on a titanium fuel tank from the Salyut 7 space station by V. Jantou; D.S. McPhail; R.J. Chater; A. Kearsley (7120-7123).
The aim of this project was to gain a better understanding of the microstructural effects of hypervelocity impacts (HVI) in titanium alloys. We investigated a titanium fuel tank recovered from the Russian Salyut 7 space station, which was launched on April 19, 1982 before being destroyed during an un-controlled re-entry in 1991, reportedly scattering debris over parts of South America. Several sections were cut out from the tank in order to undergo HVI simulations using a two-stage light gas gun. In addition, a Ti–6Al–4V alloy was studied for further comparison. The crater morphologies produced were successfully characterised using microscope-based white light interferometry (Zygo® Corp, USA), while projectile remnants were identified via secondary ion mass spectrometry (SIMS). Microstructural alterations were investigated using focused ion beam (FIB) milling and depth profiling, as well as transmission electron microscopy (TEM). There was evidence of a very high density of dislocations in the vicinity of the crater. The extent of the deformation was localised in a region of about one to two radii of the impact craters. No notable differences were observed between the titanium alloys used during the hypervelocity impact tests.
Keywords: Simulated hypervelocity impacts; α/β Titanium alloys; Secondary ion mass spectrum; Depth profiles; FIB milling; Microstructural alterations;

Surface analysis of ancient glass artefacts with ToF-SIMS: A novel tool for provenancing? by F.J.M. Rutten; M.J. Roe; J. Henderson; D. Briggs (7124-7127).
Scientific analysis of ancient glass artefacts has the potential to reveal a great deal of information about ancient manufacturing techniques and trade relations between ancient civilisations. In this paper we applied ToF-SIMS to gain unique knowledge about the presence of a range of (trace) elements in the matrix and micron-sized inclusions in opaque glasses dated to the 14th century BC found at sites in the Middle East and Egypt. Establishment of a careful multi-technique analysis protocol allowed the detection of a range of elements not previously found in such inclusions by other techniques. Comparison with data acquired from a glass standard reference sample has, moreover, enabled quantification of major and trace elements in the glass matrix. It is hoped that this may yield important additional identifying information to assist in provenancing ancient glass artefacts as well as provide new information about the ancient technologies used to produce them.
Keywords: ToF-SIMS; Imaging; Archaeometry; Ancient glass; Opacifier;

Measurement of sulfur isotope ratios in micrometer-sized samples by NanoSIMS by B. Winterholler; P. Hoppe; M.O. Andreae; S. Foley (7128-7131).
Sulfur isotope ratios of atmospheric aerosol particles can provide detailed information with regard to the origin and the transport of sulfur in the environment. The new Cameca NanoSIMS 50 ion microprobe technique permits analysis of individual aerosol particles with volumes down to 0.5 μm3 and a precision for δ34S of 3–10‰ (2σ). This technique will set new standards in the analysis of isotope ratios in atmospheric aerosol. For the first time it is possible to directly compare chemical and isotopic composition of individual aerosol particles, identify internal and external mixtures and investigate reactions of anthropogenic gases with natural aerosol such as sea salt and mineral dust.
Keywords: Sulfur isotopic composition; Aerosol particles; NanoSIMS;

uleSIMS characterization of silver reference surfaces by V.V. Palitsin; M.G. Dowsett; B. Guzmán de la Mata; I.W. Oloff; R. Gibbons (7132-7135).
Ultra low energy SIMS (uleSIMS) is a high sensitivity analytical technique that is normally used for ultra shallow profiling at a depth resolution of up to1 nm. This work describes the use of uleSIMS as both a spectroscopic and depth-profiling tool for the characterization of the early stages of corrosion formed on reference surfaces of silver. These samples are being developed to help with the characterization of tarnished surfaces in a cultural heritage context, and uleSIMS enables the tarnishing to be studied from its very earliest stages due to its high sensitivity (ppm–ppb) and surface specificity. We show that, uleSIMS can be used effectively to study the surface chemistry and aid the development of reference surfaces themselves. In particular, handling contaminants, surface dust, and residues from polishing are relatively easy to identify allowing them to be separated from the parts of the mass spectrum specific to the early stages of corrosion.
Keywords: Cultural heritage; Archaeometry; Ultra low energy SIMS; Mass spectrometry; Silver tarnish;

TOF-SIMS analysis of corroding museum glass by S. Fearn; D.S. McPhail; B. Hagenhoff; E. Tallarek (7136-7139).
Corrosion salts form on the surface of vulnerable low lime glass as it corrodes and if left to develop, reduce the clarity of the object and ultimately permanently damage and stain the glass surface. The glass artefacts must therefore be cleaned to remove these corrosion products as they appear. The cleaning procedure used must not, of course, speed up the deterioration process. However, the effect of cleaning procedures on glass objects has not been monitored systematically to date. In this work, a replica museum glass was cleaned using a known surfactant (Synperonic N) and then aged at 40%RH and room temperature for 1 week. A sample which had not been cleaned was also aged under the same conditions. The glass was then analysed and imaged using an ION-TOF GmbH SIMS instrument (TOF.SIMS 5) fitted with a Bismuth ion source. The results showed that the corrosion salts were forming heterogeneously across the surface of the glass and analysis of these salts indicated the presence of formates and carbonates.
Keywords: Glass; Corrosion; Museums; TOF-SIMS;

ToF-SIMS applied to historical archaeology in the Alps by R.N.S. Sodhi; W.C. Mahaney; M.W. Milner (7140-7143).
The actual route Hannibal followed during the invasion of Italia in the Second Punic War is one of the major questions of antiquity, one that historians/archaeologists have long studied. There are six possible passes Hannibal could have used and one of the many bits of evidence in the ancient literature that might help answer this question is the location of fired rock, the result of a conflagration Hannibal is reputed to have employed to reduce the size of boulders in a two-tier blocking rockslide on the lee side (e.g. Italian) some distance down from the high col. The only route with fired rock along the roadway leading to the Po River Valley or the Dora Riparia is below the Col du Clapier, one of the possible northern routes. ToF-SIMS investigation of the 100-μm thick burned crust in hornblende schist interlaced with veins of quartz-feldspathic minerals yields various elements C, Mg, Na, Ca, Si, Ti, P, Al, Fe and their associated fragments. Hydrocarbon fragments are thought to be products of combustion whereas Ca and Na along with Mg–Fe silicates are derived from the country rock. Aeolian components along with clay minerals settled onto rock surfaces following firing. While the SIMS data clearly would not provide an age for the burnt rock, compositional evidence of the conflagration may relate to Hannibal's actual route.
Keywords: Historical archaeology; ToF-SIMS; Hannibal; Alps; Fired rock;

Further development on the water diffusion dating of archaeological obsidian tools, based on Fick's law of diffusion, is presented. It involves (a) a reassessment of surface saturation layer location and (b) a novel in-house made MATLAB software with reference to the age sensitivity of the SS layer, and the propagation of errors. So far, 11 dates have been produced for archaeological obsidian tools over the World and the SIMS-SS ages with present software versus archaeological and mean radiocarbon ages were in excellent concordance.
Keywords: SIMS; Diffusion; Dating; Obsidians; Archaeological; Software;

Automated ion imaging with the NanoSIMS ion microprobe by E. Gröner; P. Hoppe (7148-7151).
Automated ion imaging systems developed for Cameca IMS3f and IMS6f ion microprobes are very useful for the analysis of large numbers of presolar dust grains, in particular with respect to the identification of rare types of presolar grains. The application of these systems is restricted to the study of micrometer-sized grains, thereby by-passing the major fraction of presolar grains which are sub-micrometer in size. The new generation Cameca NanoSIMS 50 ion microprobe combines high spatial resolution, high sensitivity, and simultaneous detection of up to 6 isotopes which makes the NanoSIMS an unprecedented tool for the analysis of presolar materials. Here, we report on the development of a fully automated ion imaging system for the NanoSIMS at MPI for Chemistry in order to extend its analytical capabilities further. The ion imaging consists of five steps: (i) Removal of surface contamination on the area of interest. (ii) Secondary ion image acquisition of up to 5 isotopes in multi-detection. (iii) Automated particle recognition in a pre-selected image. (iv) Automated measurement of all recognised particles with appropriate raster sizes and measurement times. (v) Stage movement to new area and repetition of steps (ii)–(iv).
Keywords: NanoSIMS; Ion imaging; Presolar grains; Aerosol particles;

SIMS quantification of very low hydrogen contents by D. Rhede; M. Wiedenbeck (7152-7154).
The absolute quantification of hydrogen at the ppm level has become a key analytical challenge for the earth science for which no fully satisfying solution has yet been found. SIMS offers a direct and simple means of measuring the water content of silicate non-conductors at very low concentration, however at least two analytical problems need to be addressed before SIMS can be seen as a routine and robust solution. Here, we report initial findings from our work on calibrating SIMS analyses for very low H2O contents and also a description of the sources of hydrogen background, which determine the method's ultimate limit of detection.
Keywords: Hydrogen; Background; Adsorption; Vacuum contamination;

Preferential oxidation of chalcopyrite surface facets characterized by ToF-SIMS and SEM by Mohammad Al-Harahsheh; Frank Rutten; David Briggs; Sam Kingman (7155-7158).
The use of hydrometallurgical methods for the production of copper from chalcopyrite has become more attractive due to environmental drivers such as lower energy demand and less gaseous emissions such as SO2. Unfortunately, chalcopyrite is known to be a highly unreactive mineral in hydrometallurgical processes. This work reports that a freshly cleaved chalcopyrite surface exhibits highly selective reactivity depending on the exposed fracture planes. ToF-SIMS was used to qualitatively characterise various fracture planes from freshly cleaved chalcopyrite particles, prior to and after hydrometallurgical treatment (leaching). It was found that prior to treatment certain areas exhibit pronounced contamination from atmospheric hydrocarbons upon fracture, whereas others were highly unreactive and remarkably free from adventitious hydrocarbon contamination. The positive ion spectra recorded from these areas are indeed dominated by peaks from Fe and Cu elements and related compounds. The negative ion spectra for the reactive areas showed a high content of oxidised (sulphur) species. After leaching, the differences between the sites of low and high reactivity were more subtle than prior to this treatment, whereas SEM analysis showed clear evidence for selective attack of ferric sulphate to specific planes after such treatment. Attempts are made to rationalise these observations with regards to selective dissolution based on different exposed chemistries at various cleavage planes within chalcopyrite crystals.
Keywords: ToF-SIMS; Imaging; Chalcopyrite; Mining; Fracture surface; Metal extraction;

High throughput screening of novel oxide conductors using SIMS by S. Fearn; J.C.H. Rossiny; J.A. Kilner; Y. Zhang; L. Chen (7159-7162).
Conventional synthesis of ceramic oxide compositions is time consuming and consequently limits the compositions that can be studied. A way round this is the use of combinatorial methods to explore much wider ranges of compositions. Using an inkjet based robot system; London University Search Instrument (LUSI) combinatorial arrays of ceramic dot samples can be produced. The first part of the study consists of the characterisation of a printed array of La0.8Sr0.2CoO3−δ to ensure the reproducibility and quality of the ceramic dots and suitability for isotopic exchange experiments.
Keywords: Combinatorial methods; Mixed conductors; SOFC cathodes; Isotopic exchange;

Resonant laser-SNMS of boron for analysis of paleoceanographic samples by G. Vering; C. Crone; P. Kathers; J. Bijma; H.F. Arlinghaus (7163-7166).
Calcite shells of foraminifera, which are accumulated in the ocean sediment, are an important object of paleoceanographic studies to reconstruct environmental parameters of the past. Foraminifera are unicellular organisms living in almost all parts of the ocean during the entire paleoceanographic time scale. The isotope ratio of boron incorporated in the calcite shell delivers information about the pH-value of the ocean at the time the shell was formed. Since the boron fraction of such a shell is about 5 ppm, an extremely sensitive technique is necessary for an exact boron isotope ratio determination. Resonant laser secondary neutral mass spectrometry (r-laser-SNMS) was used to measure boron isotope ratios in calcite shells.Analysis was carried out with a time-of-flight mass spectrometer equipped with an electron impact gun for sputtering and a Ga+ primary ion source. Resonant ionization of sputtered boron neutrals was performed via a three-step ionization scheme accomplished with two tunable dye lasers and the fundamental wavelength of a Nd:YAG laser. After optimizing the boron ionization and detection process, boron isotope ratios were directly measured on single foraminiferal shells after removing contaminants by Ar+ ion beam sputtering.
Keywords: Resonant laser-SNMS; Boron; Isotope ratio; Climate research; Foraminifera; Trace elements;

Characterizing high-k and low-k dielectric materials for semiconductors: Progress and challenges by J. Bennett; M. Quevedo-Lopez; S. Satyanarayana (7167-7171).
SIMS has been applied to the characterization of high-k and low-k materials used in the semiconductor manufacturing process. Profiles of thin high-k films, particularly HfO2 and HfSiO, exhibit preferential sputtering that affects ion yields and sputter rates in the films as well as in the Si substrate. These artifacts make it difficult to quantify major constituents and dopants in the films and substrate. The ion yields of B were observed to vary by as much as 3× as a function of Si content in HfSiO films, while As ion yield variations are not as great. Evidence for B penetration from a highly-doped Si substrate into the high-k films was also observed and quantified. First generation low-k films are not as susceptible to charging as the newer, porous materials. Backside SIMS was used to show Ti migration into the open pores of a low-k film during the metal deposition step.
Keywords: Depth profiling; High-k; Low-k; Preferential sputtering; Dopant quantification;

Characterization of HfO2 dielectric films with low energy SIMS by Z.X. Jiang; K. Kim; J. Lerma; D. Sieloff; H. Tseng; R.I. Hegde; T.Y. Luo; J.Y. Yang; D.H. Triyoso; P.J. Tobin (7172-7175).
This work investigated optimal conditions for SIMS analyses of HfO2/Si and TiN/HfO2 interfaces as well as nitrogen distributions in HfO2 films. It was demonstrated that SIMS profiling from the back side of wafers was desirable to eliminate artificial tails of Hf+ and Ti+ as often observed during profiling from the front side. The data suggested good thermal stability of the interfaces in this study. Meanwhile, accurate characterization of shallow nitrogen in HfO2 was achieved by using a low energy O2 + beam at oblique incidence and detecting 30NO secondary ions. It was revealed that nitrogen was mainly incorporated into the top part of the HfO2 films through plasma nitridation and could be released rapidly during post nitridation anneal at a high temperature.
Keywords: HfO2; TiN; Interface; Nitrogen; Diffusion; SIMS;

SIMS analysis of HfSiO(N) thin films by Shiro Miwa; Susumu Kusanagi; Hajime Kobayashi (7176-7178).
We have measured the N profile in HfSiON film using Cs primary ions under various conditions and observed an enhancement of the N ion signal at the surface and interface between HfSiON/Si. We have found that the enhancement is alleviated by glancing angle Cs primary ions and O2 flooding. Our backside SIMS measurements show that Hf is diffused into the Si substrate from HfSiON film during the thermal processes.
Keywords: HfSiO; N profile; Backside-SIMS;

Back side SIMS analysis of hafnium silicate by C. Gu; F.A. Stevie; J. Bennett; R. Garcia; D.P. Griffis (7179-7181).
High-k dielectrics are under study as part of the effort to continually reduce semiconductor device dimensions and hafnium silicate (HfSi x O y ) is one of the most promising high-k materials. A requirement of the dielectric is that the constituent elements cannot diffuse into adjacent device regions during thermal processing. Analysis for inter-diffusion using front side SIMS of high-k dielectrics has been complicated by matrix and sputtering effects.Use of a back side analysis sample preparation procedure that was successful for copper diffusion and site specific studies produced a HfSiO specimen that has less than 250 nm silicon remaining and minimal slope over the analysis region. Magnetic Sector (CAMECA IMS-6F) SIMS analysis of this specimen with low energy O2 + bombardment does not show the matrix and sputtering effects noted in the front side data. Sufficient depth resolution was obtained to define the interface between the silicon substrate and the HfSiO layer and indicate what appears to be an interfacial layer. There is no indication of hafnium diffusion into the silicon substrate.
Keywords: SIMS; High-k dielectrics; Back side analysis; Hafnium silicate;

A study of dynamic SIMS analysis of low-k dielectric materials by Ian A. Mowat; Xue-Feng Lin; Thomas Fister; Marius Kendall; Gordon Chao; Ming Hong Yang (7182-7185).
Dynamic SIMS is an established tool for the characterization of dielectric layers in semiconductors, both for contaminant levels and for composition. As the silicon-based semiconductor industry moves towards the use of copper rather than aluminum, there is also a need to use lower k-dielectric materials to reduce RC delays and to reduce cross-talk between closely spaced metal lines. New dielectric materials pose serious challenges for implementation into semiconductor processes and also for the analytical scientist doing measurements on them.The move from inorganic materials such as SiO2 to organic or carbon-rich low-k materials is a large change for the SIMS analyst. Low-k dielectric films from different sources can be very different materials with different analytical issues. A SIMS challenge for these materials is dealing with their insulating nature and their also fragility, particularly for porous films. These materials can be extremely sensitive to electron beam damage during charge neutralization, leading to difficulties in determining depth scales and introducing unknown errors to secondary ion counts and their subsequent conversion to concentrations.This paper presents details regarding an investigation of the effects of electron beam exposure on a low-k material. These effects and their potential impact on SIMS data will be investigated using FT-IR, TOF-SIMS, AFM and stylus profilometry.
Keywords: Low-k dielectric; Charge compensation; Electron beam effects; Polymers;

ToF-SIMS and AFM studies of low-k dielectric etching in fluorocarbon plasmas by P. Lazzeri; X. Hua; G. Oehrlein; E. Iacob; M. Barozzi; M. Bersani; M. Anderle (7186-7189).
Surface modifications and etching mechanisms of several nanoporous low-k dielectrics (spin-on and PECVD) using fluorocarbon plasmas have been investigated by ToF-SIMS and AFM and compared with those of SiO2. The results show a fluoropolymer film growing on the materials using highly polymerizing discharges (C4F8). The fluoropolymers are converted into fluoroether-like compounds upon etching low-porosity dielectrics in ion-rich C4F8/90% Ar plasmas. These layers mitigate the influx of plasma species and inhibit the etching rate. No surface roughness develops for these conditions, keeping the plasma/material interaction regime stationary. On the other hand, the surface coverage by fluoroethers is reduced when the porosity exceeds a given threshold. Consequently, direct plasma/dielectric interactions including ion bombardment take place, causing an increase of the etching rate, surface roughening and severe modifications of the pristine dielectric.
Keywords: Low-k; Dielectric; Etching; Porosity; ToF-SIMS; AFM;

The reduction of the change of secondary ions yield in the thin SiON/Si system by J. Sameshima; H. Yamamoto; T. Hasegawa; T. Nishina; T. Nishitani; K. Yoshikawa; A. Karen (7190-7193).
For the analyses of gate insulating materials of thin silicon oxy-nitride (SiON) and dielectric films, SIMS is one of the available tool along with TEM and ESCA, etc. Especially, to investigate the distribution of dopant in the thin films, SIMS is appreciably effective in these techniques because of its depth profiling capability and high sensitivity. One of the problem occurring in this SIMS measurement is the change of secondary ion yield at the interface as well as in the layers with different chemical composition. To solve this problem, some groups have researched the phenomenon for SiO2/Si interface [W. Vandervorst, T. Janssens, R. Loo, M. Caymax, I. Peytier, R. Lindsay, J. Fruhauf, A. Bergmaier, G. Dollinger, Appl. Surf. Sci. 203–204 (2003) 371–376; S. Hayashi, K.Yanagihara, Appl. Surf. Sci. 203–204 (2003) 339–342; M. Barozzi, D. Giubertoni, M.Anderle, M. Bersani, Appl. Surf. Sci. 231–232 (2004) 632–635; T.H. Buyuklimanli, J.W. Marino, S.W. Novak, Appl. Surf. Sci. 231–232 (2004) 636–639]. In the present study, profiles of boron and matrix elements in the Si/SiON layers on Si substrate have been investigated. The sensitivity change of Si and B profiles in SiON layer become smaller by using oxygen flood than those without oxygen flood for both O2 + and Cs+ beam. At the range of 0–25 at.% of N composition, 11B dosimetry in SiON layer implanted through amorphous Si depends on N composition. This trend could be caused by the sensitivity change of 11B, or it indicates real 11B concentration change in SiON lyaer. N areal density determined by Cs+ SIMS with oxygen flooding also shows linear relationship with N composition estimated by XPS.
Keywords: SIMS; SiON; Sensitivity change;

Thermal effects on 1H and 2H distributions determined by SIMS in atomic layer deposition of HfO2 and Al2O3 using heavy water by P. Holliger; C. Hobbs; D. Jalabert; F. Martin; F. Pierre; G. Reimbold; P. Rivallin (7194-7197).
Incorporation of deuterium using D2O as the oxidant during the atomic layer deposition of high-k gate dielectric on silicon should lead, after post metal annealing, to a better passivation of defects and interface states than this obtained with hydrogen species. However, an optimised high-k/D2O anneal is required for manufacturing high performance CMOS devices. This paper reports new investigations by SIMS on the deuterium incorporation inside thin HfO2 and Al2O3 layers deposited by atomic layer deposition using HfCl4 and trimethylaluminium (TMA), respectively and heavy water. A wide range of thermal treatments are investigated. The results highlight the hydrogen/deuterium isotope effect at different annealing temperatures. The deuterium profile shows a concentration peak at the high-k/substrate interface; however, the D dose is low and the interface peak becomes sharper at high temperature. This preferential incorporation of deuterium at high temperature could improve the interface quality and enhance the high-k device stability and reliability.
Keywords: SIMS; Depth profiling; Interface; High-k material; Hydrogen; Deuterium;

Ultra low energy SIMS depth profiling of sub-1.5 nm silicon oxynitride films by C.P.A. Mulcahy; B. Böck; P.A. Ebblewhite; H.P. Hebert; S. Biswas (7198-7200).
Silicon oxynitride is one of the most researched silicon-based dielectric currently used in IC fabrication. Properties of the oxynitride films can be modified to achieve desirable functions by specific engineering of thickness and stoichiometry. In the case of gate stacks, considerable progress has been made in optimising the properties of oxynitride dielectrics in order to reduce boron penetration and dielectric leakage with respect to pure SiO2, allowing sub-2 nm dielectrics.In this study ultra low energy (ULE) secondary ion mass spectrometry (SIMS) has been used to assess a range of ultra thin (<1.5 nm) silicon oxynitride films containing varied amounts of nitrogen (up to 18 at.%) and the results have been compared with shallow angle surface X-ray photoelectron spectroscopy (XPS). Despite the limited number of atomic layers available for probing, this investigation indicates that both techniques are capable of extracting useful and reliable chemical and physical information from these oxynitride films. Critical parameters such as stoichiometry and film thickness have been evaluated, whilst consistency between the two techniques is also addressed.
Keywords: SIMS; XPS; SiON; Oxynitride; Stoichiometry; Thickness;

Dimensional scaling of classical CMOS silicon devices, used to improve device performance, has neared the end of its usefulness due to unacceptable increases in device standby current. This requires changes in device structure and materials to continue to provide improvements in circuit speed and operation. Emerging materials for device development include metal gates, fully silicided gate electrodes or FUSI, and high permitivity-constant gate dielectric materials. The effect these materials changes will have on SIMS depth profiling for device development and characterization is investigated with measurements in alternative materials to illustrate the future for depth profiling for semiconductor development.
Keywords: Depth profiling; SIMS; Semiconductor materials;

The Cation Mass Spectrometer (CMS) is a SIMS prototype developed in our laboratory in order to perform quantitative analysis with optimal sensitivity and high depth and lateral resolution in the MCs x + and M modes. For this aim, a patented neutral Cs evaporator for varying the Cs surface concentration over the whole range has been developed. The sputtering and the Cs introduction have been decoupled successfully by applying simultaneously X y+ bombardment and neutral Cs deposition. X stands for any element except Cs. Currently the CMS is equipped with a Cs+ and a Ga+ gun. These guns are used for studying the useful yield variations of negative secondary ions (Si, Al, Ni, In, P) with respect to the Cs surface concentration. Furthermore, the observed variations of the useful yield were linked to work function shifts. Qualitative agreement with the predictions of the electron tunnelling model are obtained. Several applications give further evidence of successful optimization of the useful yield for elements with high electron affinity.
Keywords: SIMS; Neutral Cs deposition; Cs concentration; Work function; Useful yield;

SIMS quantitative depth profiling of matrix elements in semiconductor layers by G. Guryanov; T.P. St. Clair; R. Bhat; C. Caneau; S. Nikishin; B. Borisov; A. Budrevich (7208-7210).
A new SIMS approach is proposed for quantified depth profiling of III–V semiconductor alloys. We show that the ratio of MCs+ ion intensities to the sum of all element intensities (M1Cs+  + M2Cs+…) from semiconductor alloys gives accurate elemental mole fraction when elements from the same periodic group are considered. Results obtained using SIMS show good agreement with data acquired using XPS and RBS.
Keywords: SIMS; XPS; RBS; Semiconductor compound; Quantification;

SIMS depth profiling of boron ultra shallow junctions using oblique O2 + beams down to 150 eV by M. Juhel; F. Laugier; D. Delille; C. Wyon; L.F.Tz. Kwakman; M. Hopstaken (7211-7213).
An epitaxial Si grown multi-layer stack consisting of boron delta-doped layers separated by 6.4 nm thick undoped films has been profiled using a Cameca IMS Wf magnetic SIMS. Using low energy oblique O2 + beam, the boron depth resolution is improved from 1.66 nm/decade at 500 eV down to 0.83 nm/decade at 150 eV. At very low impact energy O2 + bombardment induces a near full oxidation of silicon and oxygen flooding is then no more needed in the analytical chamber to get a smooth sputtering of silicon at 45° incidence angle.
Keywords: SIMS; Low energy; Boron; Depth resolution; Oxygen;

Comparison between the SIMS and MEIS techniques for the characterization of ultra shallow arsenic implants by D. Giubertoni; M. Bersani; M. Barozzi; S. Pederzoli; E. Iacob; J.A. van den Berg; M. Werner (7214-7217).
SIMS and medium energy ion scattering (MEIS) have been applied to the characterization of ultra shallow distribution of arsenic in silicon obtained by ion implantation at 1 and 3 keV and successive annealing at low temperature (lower than 700 °C). In case of heavy elements in light matrices, the MEIS ultimate depth resolution and its ability to obtain quantitative results from first principles result in a good reference for SIMS depth profiling. The comparison of the results obtained by the two techniques allows to discriminate among different SIMS quantification processes in order to individuate the best in terms of accuracy in the initial transient width and at the SiO2–silicon interface: the simple normalization of 28Si75As curve to the average of 28Si2 results in the best agreement between SIMS and MEIS in the surface region. Moreover SIMS profile of the 3 keV as implanted sample resulted 1.9 nm shallower than correspondent MEIS profiles whereas samples annealed at either 650 °C or 700 °C for 10 s show a good alignment of the As segregation peak at the SiO2/Si interface. The sample annealed at 550 °C for 200 s shows a reduced shift between SIMS and MEIS measured As peak: a possible effect of the residual amorphous layer on the sputtering rate is pointed out as responsible of these different shifts.
Keywords: SIMS; MEIS; Arsenic; Ultra shallow junctions;

RF-plasma source qualification and compositional characterisation of GaNAs superlattices using SIMS by C.P.A. Mulcahy; S.J. Barker; R.S. Williams; M. Hopkinson; M.J. Ashwin; P.N. Stavrinou; G. Parry; S. Biswas; T.S. Jones (7218-7220).
The potential of GaAs-based dilute nitride alloys, such as GaNAs and GaInNAs, for use in long-wavelength telecommunication applications has led to intensive research into their growth and physical properties. In order to produce high quality GaNAs-based devices it is essential that the material and growth source is fully characterised. In this paper, we present a study of MBE grown dilute GaN x As1−x (x  ≈ 0.01) structures grown using two different nitrogen RF-plasma sources. The samples have been characterised using low energy secondary ion mass spectrometry (SIMS), whilst the attributes of the RF-plasma sources have also been fully assessed with this analytical technique. The study shows that low energy SIMS is essential in order to fully characterise the structure and purity of the GaNAs superlattices grown and can also assist in qualification of the RF-plasma source used for growth.
Keywords: SIMS; Dilute nitrides; GaNAs; MBE;

This work shows how the surface potential instabilities observed during uleSIMS profiling of various semiconductor and semi-insulating materials can be overcome by using coincident bombardment with laser light to excite electron–hole pairs. We show that the causes of the problem differ according to the material system, and may sometimes be due to the material alone, or to the interaction between the material and the primary ion beam. In some cases (e.g. Si1−x Ge x , phosphorus implanted silicon) it is sufficient to irradiate the SIMS crater with a photon flux density above some threshold determined by the primary ion current. In others, the laser irradiation pattern must be tailored so as to create a conducting path from the crater to the sample holder.
Keywords: Ultra low energy SIMS; Charge compensation; Semi-insulators; Semiconductors;

SIMS depth profiling of deuterium labeled polymers in polymer multilayers by Shane E. Harton; Fred A. Stevie; Dieter P. Griffis; Harald Ade (7224-7227).
Thin planar polymer films are model systems for probing physical phenomena related to molecular confinement at polymer surfaces and polymer/polymer interfaces. Existing experimental techniques such as forward recoil spectrometry (FRES) and neutron reflectometry (NR) have been used extensively for analysis of these systems, although they suffer from relatively low depth resolution (FRES) or difficulties associated with inversion to real space (NR). In contrast, secondary ion mass spectrometry (SIMS) can provide real-space depth profiles of tracer labeled polymers directly with sufficient depth resolution for optimal analyses of these systems. Deuterated polystyrene (dPS) has been employed as the tracer polymer and has been embedded in a matrix of either unlabeled polystyrene (PS) or poly(cyclohexyl methacrylate) (PCHMA). These doped films have been placed on either poly(methyl methacrylate) (PMMA) or poly(2-vinyl pyridine) (P2VP) and thermally annealed. Varied analysis conditions for a magnetic sector SIMS instrument (CAMECA IMS-6f) were used to optimize the depth resolution and detection sensitivity while minimizing matrix effects and sample charging. Both Cs+ and O2 + primary ions have been used along with detection of negative and positive secondary ions, respectively. Impact energy and primary ion species have been shown to affect matrix secondary ion count rate for the various films studied.
Keywords: Depth profiling; Polymers; SIMS; Thin films;

SIMS quantification of matrix and impurity species in Al x Ga1−x N by C.J. Gu; F.A. Stevie; C.J. Hitzman; Y.N. Saripalli; M. Johnson; D.P. Griffis (7228-7231).
The quantification in Al x Ga1−x N with different AlN mole fraction (x) is challenging because of matrix effects and charging effects. For quantitative characterization of both matrix and impurity elements in Al x Ga1−x N, a novel charge neutralization method was employed and calibration curves were created using an O2 + primary beam with positive secondary ion detection and a Cs+ primary beam with negative and MCs+ secondary ion detection. Over the range of 0 <  x  < 0.58, the matrix ion intensity ratios of Al+/Ga+ and AlCs+/GaCs+ appear linear with the mole fraction ratio x/(1 −  x), and the ratio of AlN/GaN is linear with AlN mole fraction (x). The sputter rate decreases as AlN mole fraction increases, while the relative sensitivity factors (RSF's) of impurities have an exponential relationship with AlN mole fraction. These calibration curves allow the quantification of both matrix and impurity species in AlGaN with varying AlN mole fraction. The technique can be employed for impurity control, composition and growth rate determination, as well as structural analysis of the finished optoelectronic and electronic devices.
Keywords: SIMS; Aluminum Gallium Nitride (AlGaN); Quantification; Calibration curve;

Round-robin study of arsenic implant dose measurement in silicon by SIMS by D. Simons; K. Kim; R. Benbalagh; J. Bennett; A. Chew; D. Gehre; T. Hasegawa; C. Hitzman; J. Ko; R. Lindstrom; B. MacDonald; C. Magee; N. Montgomery; P. Peres; P. Ronsheim; S. Yoshikawa; M. Schuhmacher; W. Stockwell; D. Sykes; M. Tomita; F. Toujou; J. Won (7232-7235).
An international round-robin study was undertaken under the auspices of ISO TC201/SC6 to determine the best analytical conditions and the level of interlaboratory agreement for the determination of the implantation dose of arsenic in silicon by secondary ion mass spectrometry (SIMS). Fifteen SIMS laboratories, as well as two laboratories that performed low energy electron-induced X-ray emission spectrometry (LEXES) and one that made measurements by instrumental neutron activation analysis (INAA) were asked to determine the implanted arsenic doses in three unknown samples using as a comparator NIST Standard Reference Material® 2134. The use of a common reference material by all laboratories resulted in better interlaboratory agreement than was seen in a previous round-robin that lacked a common comparator. The relative standard deviation among laboratories was less than 4% for the medium-dose sample, but several percent larger for the low- and high-dose samples. The high-dose sample showed a significant difference between point-by-point and average matrix normalization because the matrix signal decreased in the vicinity of the implant peak, as observed in a previous study. The dose from point-by-point normalization was in close agreement with that determined by INAA. No clear difference in measurement repeatability was seen when comparing Si2 and Si3 as matrix references with AsSi.
Keywords: Arsenic; INAA; LEXES; Matrix normalization; SIMS;

The emission of negative cluster ions in sputtering Si, Ge and their oxides has been investigated by time of flight secondary ion mass spectrometry using Cs+ ions at different energies for sputtering and Ga+ at 25 keV for analysis. In GeO2 the most intense signals come from the O n  ≤ 2 and GeO n  = 2,3 clusters. The mass spectrum of GeO2 is therefore very similar to that of SiO2 where the most intense signals are related to the O n  ≤ 2 and SiO n  = 2,3 clusters. A full spectrum approach has been applied to study the variation of the ionization probability in the different matrices when reducing the Cs+ ion energy, i.e. increasing the cesium concentration at the surface. In all the matrices, the total number of atoms in the ionized fraction of the sputtered flux increases when increasing the cesium content at the surface. Despite these variations in GeO2 (SiO2) the fractions of germanium (silicon) and oxygen in the ionized part of the sputtered flux are independent of the cesium content in the matrix. Moreover, the fractions of silicon and germanium in the two oxides are equivalent.
Keywords: Silicon; Germanium; Oxide; Cesium; Depth profile; ToF-SIMS;

To understand negative ion formation under Cs+ bombardment, we have studied the steady-state Cs depth distribution in Si and Ge with a focus on high-resolution analysis conditions i.e. Cs+ energies between 500 eV and 5 keV and impact angles from 0° to 60°. The in situ internal Cs depth profiles have been measured with a low energy O2 + beam (0.5–1 keV) similar to the work of Yoshikawa [S. Yoshikawa, H. Morita, et al., Appl. Surf. Sci. 203–204 (2003) 252–255]. To minimize the distortions on Cs profiles, a non-oxidizing condition (at impact angle 60°) was chosen instead of an oxidizing condition. The internal Cs profiles in Si have a flat saturation region near the surface, with an intensity independent from the bombardment conditions. Only the profile width scales with impact angles and energies. Whereas in the Ge-case, a Gaussian profile is always obtained. Based on the internal Cs profiles, a possible near surface altered layer formation in Si and Ge under Cs bombardment is suggested.
Keywords: The steady-state Cs depth distribution; The internal Cs profiles;

Ultrashallow junctions in semiconductors and multi-quantum wells (MQW) in lasers demand high depth resolution for accurate depth profiling. SIMS has been widely used in depth profiling and the use of ultralow-energy SIMS has demonstrated a narrower surface transient and an improvement in depth resolution. In this work, we use an ATOMIKA 4500 SIMS depth profiler with O2 + primary ions at an ultralow-energy (E p) of 250 eV and incidence angles (θ) between 0 and 70° without oxygen flooding. A sample with 10 delta layers of Si0.7Ge0.3 nominally grown 11 nm apart is used. We observe that for applications like characterizing ultrashallow junctions, θ  ∼ 0° provides the narrowest surface transient (z tr) of 0.7 nm, which is marginally better than at θ  ∼ 40° with z tr of 1.0 nm. The depth resolution denoted by the full width at half maximum (FWHM) of the 70Ge+ peaks is comparable for both θ  ∼ 0 and 40° at 1.6 and 1.4 nm, respectively. However, in the case of MQW profiling, whereby the quantum wells are normally located deeper, θ  ∼ 40° is preferable. At this angle, the average sputter rate of 47 nm min−1  nA−1  cm−2 is significantly higher, more than double that at θ  ∼ 0° and a better depth resolution with decay length (λ d) of 0.64 nm compared to 0.92 nm at θ  ∼ 0°. Moreover, the dynamic range possible is also better at θ  ∼ 40°. θ  ∼ 60ο is not ideal, even though there is no sign of the onset of roughening. Although the higher sputter rate is an advantage, the depth resolution deteriorates as the profile gets deeper.
Keywords: Ultralow-energy; Depth resolution; Secondary ion mass spectroscopy; Roughening;

High sensitivity analysis of atmospheric gas elements by Shiro Miwa; Ichiro Nomachi; Hideo Kitajima (7247-7251).
We have investigated the detection limit of H, C and O in Si, GaAs and InP using a Cameca IMS-4f instrument equipped with a modified vacuum system to improve the detection limit with a lower sputtering rate We found that the detection limits for H, O and C are improved by employing a primary ion bombardment before the analysis. Background levels of 1 × 1017  atoms/cm3 for H, of 3 × 1016  atoms/cm3 for C and of 2 × 1016  atoms/cm3 for O could be achieved in silicon with a sputtering rate of 2 nm/s after a primary ion bombardment for 160 h. We also found that the use of a 20 K He cryo-panel near the sample holder was effective for obtaining better detection limits in a shorter time, although the final detection limits using the panel are identical to those achieved without it.
Keywords: Atmospheric gas; Detection limit; Vacuum system;

ToF-SIMS depth profiling of (Ga,Mn)As capped with amorphous arsenic: Effects of annealing time by U. Bexell; V. Stanciu; P. Warnicke; M. Östh; P. Svedlindh (7252-7254).
The influence of annealing time on an amorphous As cap layer and the depth distribution of Mn atoms have been investigated. The results show that a ∼1600 Å thick As cap layer is completely desorbed after 3 h of annealing time. The depth distributions of Mn indicate that interstitial Mn atoms have diffused to the outer surface and being passivated. The thickness of the Mn passivation layer was around 90 Å.
Keywords: ToF-SIMS; Depth profiling; (Ga,Mn)As; As cap; Mn diffusion;

Quantitative analysis of surface contaminants on silicon wafers by means of TOF-SIMS by P. Rostam-Khani; J. Philipsen; E. Jansen; H. Eberhard; P. Vullings (7255-7257).
Measurement of surface metal contamination on silicon wafers is essential for yield enhancement in IC manufacturing. Vapour phase decomposition coupled with either inductively coupled plasma mass spectrometry (VPD–ICP-MS), or total reflection X-ray fluorescence (VPD–TXRF), TXRF and, more recently, TOF-SIMS are used to monitor surface metal contamination. These techniques complement each other in their respective strengths and weaknesses. For reliable and accurate quantification, so-called relative sensitivity factors (RSF) are required for TOF-SIMS analysis. For quantification purposes in VPD, the collection efficiency (CE) is important to ensure complete collection of contamination. A standard procedure has been developed that combines the determination of these RSFs as well as the collection efficiency using all the analytical techniques mentioned above. Therefore, sample wafers were intentionally contaminated and analysed (by TOF-SIMS) directly after preparation. After VPD–ICP-MS, several scanned surfaces were analysed again by TOF-SIMS. Comparing the intensities of the specific metals before and after the VPD-DC procedure on the scanned surface allows the determination of so-called removing efficiency (RE). In general, very good agreement was obtained comparing the analytical techniques after updating the RSFs for TOF-SIMS. Progress has been achieved concerning the CE evaluation as well as determining the RSFs for 16 elements more precisely for TOF-SIMS.
Keywords: Trace metals; TOF-SIMS; VPD; ICP-MS; Quantification; RSF;

This study deals with the secondary ion yield improvement induced by using C60 + primary ions instead of Ga+ to enhance the detection thresholds of the organic contaminations at the Si wafer surfaces by ToF-SIMS. For that purpose, a piece of Si wafer has been analysed with both ion sources. A large improvement is observed for the detection of hydrocarbon contaminants with C60 + primary ions as compared to Ga+ ions. A similar improvement for organic contaminations, such as phthalates and aliphatic amines, is observed in both secondary ion polarities. The Si atomic ion constitutes a minor peak with C60 + ions while it dominates the spectrum in the case of Ga+ ions. However, with the C60 + source, inorganic combination peaks with the elements Si and O, are observed in the positive spectra (i.e. Si2O2H+), while they are marginal with the Ga+ source. Furthermore, a series of negative silicon oxide clusters, Si n O(2n+1)H, is observed up to n  = 16 (977m/z) in the case of C60 + ions. With Ga+ ions, the largest negative silicon oxide cluster corresponds to n  = 4 (257m/z). The detection of backscattered C60 fragments is evoked to explain the origin of some hydrocarbon peaks with low H content. On average, for a comparable number of primary ions per spectrum, the C60 + ion source gives intensities between two and four orders of magnitude higher than the Ga+ one.
Keywords: C60 +; SiO2 clusters; Si wafer; Hydrocarbon contamination; Static ToF-SIMS;

Quantitative SIMS analysis of SiGe composition with low energy O2 + beams by Z.X. Jiang; K. Kim; J. Lerma; A. Corbett; D. Sieloff; M. Kottke; R. Gregory; S. Schauer (7262-7264).
This work explored quantitative analyses of SiGe films on either Si bulk or SOI wafers with low energy SIMS by assuming a constant ratio between the secondary ion yields of Si+ and Ge+ inside SiGe films. SiGe samples with Ge contents ranging from 15 to 65% have been analyzed with a 1 keV O2 + beam at normal incidence. For comparison, the samples were also analyzed with RBS and/or AES. The Ge content as measured with SIMS, based on a single SiGe/Si or SiGe/SOI standard, exhibited good agreement with the corresponding RBS and AES data. It was concluded that SIMS was capable of providing accurate characterization of the SiGe composition with the Ge content up to 65%.
Keywords: SiGe; SOI; Composition; SIMS; RBS; AES;

SIMS analysis of impurities and nitrogen isotopes in gallium nitride thin films by Hajime Haneda; Takeshi Ohgaki; Isao Sakaguchi; Haruki Ryoken; Naoki Ohashi; Atsuo Yasumori (7265-7268).
Gallium nitride thin films were deposited on sapphire or zinc oxide substrates with a molecular beam epitaxial method. Thin films with a Ga14N/Ga15N/Ga14N isotopic heterostructure were also grown. A CAMECA-type secondary ion mass spectrometry (SIMS) was employed to analyze impurities such as substrate elements. Nitrogen isotopes were also analyzed. Some samples were annealed in a nitrogen atmosphere, and the diffusivities of the elements and isotopes were evaluated. Although the crater surface after using Cs+ ions as the primary ion beam became smoother than after using O2 +, preferential sputtering was observed. It is concluded that this preferential sputtering causes the isotope distribution to be abnormal. Elements of the substrates diffused into the thin films.
Keywords: SIMS; Diffusion; GaN; Nitrogen; Aluminum; Zinc;

“Non-destructive” B, P and As dosimetry using normal incidence oxygen by Hans Maul; H.-Ulrich Ehrke; Norbert Loibl; Christoph Schnürer-Patschan (7269-7271).
Full wafer SIMS provides SIMS metrology without breaking the wafer. SIMS, known as a destructive method in the scientific sense, can be regarded as non-destructive in the practical sense provided it does nothing which would prevent the wafer being returned to production. This can be assumed as long as only oxygen primary ions are used. Depth profiling with oxygen primary ions changes the wafer much less than the oxidation and patterning wafer processing steps. All the oxygen beam bombardment leaves behind is a small, shallow crater with a nanometer layer of SiO2 at the bottom.This work shows that “non-destructive” implant dose monitoring using oxygen primary ions is not limited to B in Si and SiGe. Ultra shallow P and As dose monitoring is also possible using normal incidence oxygen primary ions. Results of high precision dose monitoring and mapping obtained by CAMECA's full wafer quadrupole SIMS 4600 are presented.
Keywords: SIMS; Full wafer; Dose monitoring; Oxygen; Normal incidence; Non-destructive;

In order to minimize the out-diffusion of phosphorous provided during the poly silicon doping procedure, a possible solution is capping the poly Si with a film with a relatively low P diffusivity with respect to the one in the poly. In fact, P diffusion in poly is normally enhanced by inter granular diffusion that in general is higher than the one due to the Si lattice (bulk diffusion). The aim of this work was to analyze, by ToF-SIMS depth profiling, poly Si samples that have been previously P doped by implantation and than subsequently thermally exposed, with and without a Si oxide capping layer, in order to study the effectiveness of this barrier to prevent the P depletion. The work shows the potential of ToF-SIMS depth profiling in being an efficient vehicle for revealing the goodness of this oxide capping approach in microelectronic applications.
Keywords: ToF-SIMS; Poly silicon; Phosphorous; Profile;

We have analyzed a multiple quantum well (MQW) structure in a vertical cavity surface emitting laser (VCSEL) epitaxial wafer using secondary ion mass spectrometry (SIMS). The two energy sputtering method is a very powerful method for providing a depth profile of a GaAs/Al0.2Ga0.8As MQW with a sufficient depth resolution and a large number of data points in a practical measurement time. This method consists of rapid high-energy sputtering for a top mirror layer and subsequent low-energy sputtering for an active layer. The resulting profiles were quantitatively evaluated using the mixing-roughness-information depth (MRI) model. The values of C concentration in modulation-doped Al0.2Ga0.8As barrier layers have been extracted from the original in-depth concentration profile reconstructed by the MRI model. The relationship between depth resolution of the resulting profile and surface morphology measured by atomic force microscopy (AFM) is also discussed.
Keywords: SIMS; VCSEL; MRI model; AFM; Surface roughening;

SIMS and SEM analysis of In1−xy Al x Ga y P LED structure grown on In x Ga1−x P graded buffer by A. Vincze; A. Satka; L. Peternai; J. Kovac; S. Hasenöhrl; M. Vesely (7279-7282).
Composition, grading and doping of In1−xy Al x Ga y P LED structures grown on the GaP substrate by step-wise graded In x Ga1−x P buffer were investigated by employing SIMS and SEM methods. Different amount of Al precursor has been used during MOCVD growth, resulting different Al content and correspondingly different wavelength of the emitted light. The buffer comprised of eight intentionally 300 nm thick In x Ga1−x P layers with step increase of In Δx In  ≈ 3% toward In1−xy Al x Ga y P LED layers were grown to accommodate relatively high lattice mismatch between In1−xy Al x Ga y P and GaP. Vertical structure of the samples has been visualised using backscattered electron method of the SEM. From the cleaved edge of samples the layers of different composition were revealed and the thickness of In1−xy Al x Ga y P and In x Ga1−x P layers has been determined. In contrary p–n junction position was determined from SIMS depth profiling of the dopants and estimated only from secondary electron images. The compositional changes in the structures were examined using SIMS depth profiling, from which all the eight different In content steps in In x Ga1−x P buffer layers were detected. Composition of the LED layers has been determined from EDS measurements and compared with SIMS depth profiles. From SIMS and EDS measurements quaternary composition of the components Al, In, P and Ga were evaluated and optimized for the growth process.
Keywords: LED; InGaP; Buffer; InAlGaP/GaP; SIMS; MOCVD;

Dynamic SIMS has been applied to investigate the influence of impurity profiles on the characteristics of ultra-shallow GaAs sidewall tunnel junctions. SIMS depth profile on test-element-group areas on the device chips have shown that the Be profiles pile-up, with concentrations of up to 1020  cm−3 at the tunnel junction interfaces. This result illustrates one of the dominant causes why very high peak current densities are achieved.
Keywords: Semiconductor; GaAs; Impurity doping; Epitaxial growth; Tunnel junction; Dynamic SIMS;

Influence of changes in the resistivity of the sample surface on ultra-shallow SIMS profiles for arsenic by M. Barozzi; D. Giubertoni; S. Pederzoli; M. Anderle; E. Iacob; M. Bersani (7286-7289).
High concentration dopant distributions in silicon like those required to form ultra shallow junctions can affect SIMS analyses introducing matrix effects on secondary ions, otherwise not observed in more dilute regimes. In this work the effect of high arsenic concentration on negative secondary ion yield has been investigated when sputtering with a 0.5 keV Cs+ primary beam in a magnetic sector instrument. Two effects have been distinguished: the first one is a variation of matrix signals observed on as implanted samples in correspondence with the projected range, probably due to the damage induced by the high dose implant; the second is a step observed for several species and related to the arsenic distribution. The latter seems due to the effect of the active dopant on secondary ion energy distributions. A wide and well-centred energy slit can limit this effect allowing a more accurate quantification of the activated high As concentrations.
Keywords: SIMS; Arsenic; Matrix effect; Energy distribution;

Secondary ion measurements for oxygen cluster ion SIMS by Satoshi Ninomiya; Takaaki Aoki; Toshio Seki; Jiro Matsuo (7290-7292).
We have proposed to use oxygen cluster ions, which are much larger than molecular ions, as primary ions for secondary ion mass spectrometry (SIMS). A high intensity gas cluster ion source with a current density of a few μAs/cm2 has been developed. Secondary ions emitted from Si have been investigated under O2 and Ar cluster ion bombardment. A large enhancement of the yield of secondary ions produced by large O2 and Ar cluster ions was found. The SIMS system utilizing large O2 cluster ions must give both excellent depth resolution and high secondary ion yield.
Keywords: Oxygen cluster ion; Secondary ion mass spectrometry; Low energy; Sputtering yield;

Shave-off depth profiling: Depth profiling with an absolute depth scale by M. Nojima; A. Maekawa; T. Yamamoto; B. Tomiyasu; T. Sakamoto; M. Owari; Y. Nihei (7293-7296).
Shave-off depth profiling provides profiling with an absolute depth scale. This method uses a focused ion beam (FIB) micro-machining process to provide the depth profile. We show that the shave-off depth profile of a particle reflected the spherical shape of the sample and signal intensities had no relationship to the depth. Through the introduction of FIB micro-sampling, the shave-off depth profiling of a dynamic random access memory (DRAM) tip was carried out. The shave-off profile agreed with a blue print from the manufacturing process. Finally, shave-off depth profiling is discussed with respect to resolutions and future directions.
Keywords: Shave-off; Depth profiling; FIB; SIMS;

The NRL trace element accelerator mass spectrometer facility has recently added a modified Cameca IMS 6F SIMS instrument as a high-performance ion source, providing the advantages of accelerator mass spectrometry to SIMS analysis. These advantages include removal of molecular interferences, a greatly reduced background, and composition analysis using molecular ions (after breaking them into atomic constituents before detection). This last feature compensates for a requirement to use only negative secondary ions, as it enables measurement of electropositive elements. In addition, the NRL facility provides for parallel mass analysis, thus improving isotope ratio precision and practical sensitivity. Spatial analysis of the sample is still provided by raster of the primary Cs beam. The modified Cameca includes the Cs primary column, sample chamber, and the secondary ion column up to the standard electrostatic analyzer. The NRL accelerator facility supplants the normal mass spectrometer portion of the IMS 6F instrument. Additional recent facility upgrades provide improved mass spectrometry performance, both for a prior radiocarbon ion source and the now installed SIMS. An example measurement, using silver ions, demonstrates the system's capabilities.
Keywords: Accelerator mass spectrometry; Secondary ion mass spectrometry; Trace element; Molecular interference;

Isotope ratio measurement with a multicollector detector on the cameca IMS nf by Jan Lorincik; Richard Hervig; Klaus Franzreb; Georges Slodzian; Peter Williams (7301-7303).
The ASU IMS 3f secondary ion microanalyzer has been converted to a multiple ion detection mass spectrometer with double focusing for three neighbouring masses. We present preliminary experimental tests of the modified instrument. For that purpose we chose sulphur isotope ratio measurements in three pyrite samples using a small triple Faraday cup assembly as a multicollector. We achieved high mass resolution for off-axis masses and an accuracy of 32S/34S isotopic ratio of ∼0.2%.
Keywords: Multicollector SIMS; Isotopic ratio;

The development of a range of C60 ion beam systems by R. Hill; P. Blenkinsopp; A. Barber; C. Everest (7304-7307).
C60 ion beams are being used in a widening variety of analytical applications. The interaction of the C60 molecule with most sample surfaces differs markedly from that of an atomic ion beam, leading to elevated sputter yields and ion yields. A further important consequence of C60 bombardment is very low residual damage after sputtering of surface layers.We have developed a range of C60 ion beam systems for use in static SIMS, dynamic SIMS, SIMS imaging, including intracellular imaging of biological compounds, and in surface cleaning and depth profiling in electron spectroscopy.We describe the design criteria for the C60 range and illustrate the performance of these systems with recent applications data.
Keywords: ToF SIMS; Ion beams; XPS; Fullerene; Imaging;

Development of a ToF version of the desktop MiniSIMS utilising a continuous primary ion beam by A.J. Eccles; P. Vohralik; B. Cliff; C. Jones; N. Long (7308-7311).
The Millbrook MiniSIMS remains a unique concept in SIMS instrumentation. An upgraded version of the MiniSIMS based on a time-of-flight (ToF) mass spectrometer has now been developed. Unlike the vast majority of ToFSIMS instruments, the ToF MiniSIMS uses a continuous primary ion beam and a pulsed secondary ion beam. The instrument has the usual ToF attributes of parallel mass detection, extended mass range and higher mass resolution, but also features a high duty cycle. The result is very fast data acquisition, especially in imaging mode. Moreover, in depth profiling, a continuous beam allows all sputtered material to contribute to the analysis by eliminating the requirement for cycling between etching and analysis modes. The combination of a ToF spectrometer and a continuous primary beam is thus ideally suited to the MiniSIMS concept of a high-throughput instrument able to acquire spectra, images and depth profiles. The higher performance opens up new applications for the MiniSIMS instrument in the identification of organic materials and small area analysis, especially for materials with largely unknown composition or depth distribution.
Keywords: Instrumentation; Desktop; SIMS; Time-of-flight; Secondary ion pulsing;

Performance of a C60 + ion source on a dynamic SIMS instrument by Albert J. Fahey; Greg Gillen; Peter Chi; Christine M. Mahoney (7312-7314).
Keywords: Buckminsterfullerene; Ion source; SIMS ion source; Cluster ion beams;

Boron ultra low energy SIMS depth profiling improved by rotating stage by M. Bersani; D. Giubertoni; E. Iacob; M. Barozzi; S. Pederzoli; L. Vanzetti; M. Anderle (7315-7317).
Optimization of oblique incidence ultra low energy O2 + SIMS analysis of ultra shallow boron distributions has been investigated varying the atmosphere in the analysis chamber (ultra high vacuum or oxygen flooding) and evaluating the effect of a rotating stage allowing a 20 rpm rotation during the analysis. The impact of the different analytical approaches to the ripple formation on the crater bottom has been investigated on a boron delta doped silicon sample by AFM analysis. The combined use of a 0.5 keV O2 + beam at 68° of incidence with oxygen flooding and stage rotation of 20 rpm gave a decay length of 2.0 nm/decade at 60 nm depth without any appreciable detection of variation of sputtering rate.
Keywords: SIMS; O2 + analysis; Roughness; Ripples; Ultra shallow junctions;

SIMS analysis using a new novel sample stage by Shiro Miwa; Ichiro Nomachi; Hideo Kitajima (7318-7320).
We have developed a novel sample stage for Cameca IMS-series instruments that allows us to adjust the tilt of the sample holder and to vary the height of the sample surface from outside the vacuum chamber. A third function of the stage is the capability to cool sample to −150 °C using liquid nitrogen. Using this stage, we can measure line profiles of 10 mm in length without any variation in the secondary ion yields. By moving the sample surface toward the input lens, the primary ion beam is well focused when the energy of the primary ions is reduced. Sample cooling is useful for samples such as organic materials that are easily damaged by primary ions or electrons.
Keywords: Sample stage; Tilt; Sample cooling;

Caesium sputter ion source compatible with commercial SIMS instruments by S.F. Belykh; V.V. Palitsin; I.V. Veryovkin; A.P. Kovarsky; R.J.H. Chang; A. Adriaens; M. Dowsett; F. Adams (7321-7325).
A simple design for a caesium sputter cluster ion source compatible with commercially available secondary ion mass spectrometers is reported. This source has been tested with the Cameca IMS 4f instrument using the cluster Si n and Cu n ions, and will shortly be retrofitted to the floating low energy ion gun (FLIG) of the type used on the Cameca 4500/4550 quadruple instruments. Our experiments with surface characterization and depth profiling conducted to date demonstrate improvements of analytical capabilities of the SIMS instrument due to the non-additive enhancement of secondary ion emission and shorter ion ranges of polyatomic projectiles compared to atomic ions with the same impact energy.
Keywords: Caesium sputter ion source; Non-additive sputtering; Atomic and cluster ion bombardment; Depth profiling; Floating low energy ion gun; Cluster–solid interaction;