Applied Surface Science (v.179, #1-4)
11th Conference on Applied Surface Science – AOFA 11 Leipzig, 24–28 September, 2000 by Heinz Böhlig; Peter Streubel; Rüdiger Szargan (xi-xii).
Synthesis and characterization of nanoscaled and nanostructured carbon containing materials produced by thermal plasma technology by H.-D Klotz; R Mach; F Oleszak; H.-E Maneck; H Goering; K.-W Brzezinka (1-7).
Single-walled carbon nanotubes (SWNT) and carbon nitride films are synthesized by a direct current (dc) arc discharge at slightly reduced pressure and by an inductively coupled r.f. plasma (ICP) at atmospheric pressure, respectively. By treatment with nitric acid SWNT are purified from by-products and characterized by scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), and Raman spectroscopy. ICP allows the deposition of carbon nitride films on steel substrate. The deposition of the films creates a relatively strong radial symmetric profile. The structure of the films are rather independent of the distance between substrate and plasma. Raman, Fourier transform infrared (FTIR), and energy dispersive X-ray (EDX) spectroscopy are used for analyzing the carbon nitride materials.
Keywords: Single-walled carbon nanotubes; Carbon nitride films; Arc discharge; Inductively coupled r.f. plasma;
Evaluation of AFM tips using nanometer-sized structures induced by ion sputtering by F. Frost; D. Hirsch; A. Schindler (8-12).
In this study, we report on a process for the fabrication of nanometer-sized surface structures using low-energy Ar+ sputtering of InP surfaces. The dimension of these structures (≤100 nm) and the distance between them can be tuned by the parameters of the sputter process (sputter time, ion energy, ion incidence angle, sputter time, and ion current density or ion flux, respectively). With the help of surfaces prepared by this way, we have evaluated the influence of the actual AFM tip quality on the measured surface topography. Furthermore, we have shown that the tip quality has a strong influence on the surface roughness parameters extracted from the AFM images particularly for surfaces with a low surface roughness (∼1 nm) as generally obtained by means of thin film technologies.
Keywords: Sputtering; Topography; Morphology; Atomic force microscopy; AFM tip; Thin film;
Structural characterisation of hardening of Ti–Al–V alloys after nitridation by plasma immersion ion implantation by F Berberich; W Matz; U Kreissig; E Richter; N Schell; W Möller (13-19).
The surface hardness of the titanium alloy Ti–6Al–4V, widely used as construction material, can be improved by nitrogen implantation. The paper reports on a complex study of the structural mechanisms of hardening and its loss at higher temperatures with different methods (grazing incidence X-ray diffraction (GIXRD), in situ high-temperature diffraction with synchrotron radiation, elastic recoil detection analysis (ERDA), hardness measurements and surface inspection by scanning electron microscopy (SEM)). Plasma immersion ion implantation (PIII) produces a nitrogen profile directly below the surface. The formation of small TiN crystallites is detected, but the hardness increase is only about 40%. Annealing leads to the reduction of the TiN phase and the formation of Ti2N deeper in the material. The in situ X-ray diffraction (XRD) study of the phase formation gives information about the temperature dependence of these changes. The hardness increases after annealing by a factor of 2.5 compared to the unimplanted state. It is explained by precipitation hardening due to the formation of titanium nitrides in different depths of the material.
Keywords: Ti–6Al–4V; Plasma immersion ion implantation; XRD; Hardness; ERDA;
Improved sputter depth resolution in Auger thin film analysis using in situ low angle cross-sections by Uwe Scheithauer (20-24).
A non-conventional approach for depth profiling of thin film systems with enhanced depth resolution has been developed using standard Auger microprobe instruments. For the preparation of an in situ low angle cross-section, the sample is partly covered by an appropriate mask. Utilising the edge of this mask, the sample is sputtered in the Auger microprobe with ions at nearly grazing incidence. In the shadow of the mask, this produces a low angle cross-section through the thin film system. Then, a conventional depth profile is measured at the point of interest where part of the thin film system is covered only by a thin top layer. As demonstrated a considerable improvement of depth resolution Δz/z can be obtained by this method.
Keywords: Auger electron spectroscopy; Sputter depth profiling; Thin film analysis; In situ low angle cross sections; Enhanced depth resolution;
AES depth profiling multilayers of 3d transition metals by S. Baunack; S. Menzel; W. Brückner; D. Elefant (25-29).
Multilayer structures composed of 3d transition metals were investigated by AES in combination with sputter depth profiling. The samples were trilayers Permalloy/Cu/Permalloy, Co/Cu multilayers and a spin-valve structure. Overlapping Auger peaks were separated by a fit-to-spectra of bulk standards. Sample rotation during sputtering improves the depth resolution and made detection of unintentionally deposited Cu possible.For very thin films the depth profiles are influenced by measuring effects. The effects of atomic mixing, surface roughness and information depth onto the depth profiles in the spin-valve structure were simulated using the MRI model.
Keywords: Giant magnetoresistance; Thin film; AES; Sputter induced effects; Transition metals;
Depth profiling of electrically non-conductive layered samples by RF-GDOES and HFM plasma SNMS by Vasile-Dan Hodoroaba; Wolfgang E.S Unger; Holger Jenett; Volker Hoffmann; Birgit Hagenhoff; Sven Kayser; Klaus Wetzig (30-37).
The work is intended to compare the capabilities of two similar depth profiling techniques to analyse electrically non-conductive samples. In order to get a better evaluation of the depth resolution, various multilayer sandwiches, such as SiO2/TiO2 and Si3N4/SiO2 deposited on glass substrates have been investigated. Optimised depth profiles are presented for both methods, glow discharge optical emission spectrometry (GDOES) and radiofrequency mode (known as “HFM” in the SNMS literature) of plasma secondary neutral mass spectrometry (SNMS). The optimisation procedure, necessary to get the best set of plasma parameters, which result in the optimal depth resolution, is also described for one selected sample. Additionally, sputtering crater profilometry was carried out in order to check out the flatness of the sputtered crater. The influence of the thickness of the sample substrate on the sputtering rate is discussed. Finally, advantages and disadvantages of the use of these two depth profiling methods, especially for the non-conductive samples, are concluded from this comparative study. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) analysis of a cross-sectioned sample was carried out in order to get supplementary information.
Keywords: rf-Glow discharge; HFM plasma SNMS; Non-conductive layered samples; Depth resolution; Crater shape; ToF-SIMS;
Kossel and pseudo Kossel CCD pattern in comparison with electron backscattering diffraction diagrams by S Däbritz; E Langer; W Hauffe (38-44).
Kossel and pseudo Kossel interferences, i.e. lattice source interferences (LSI) and divergent beam X-ray interferences (DBI), as well as electron backscattering diffraction (EBSD) are complementary physical methods of investigation, by means of which material-physical parameters can be obtained from microscopic small specimen areas in a non-destructive way. The interferences are taken with a high-resolution and time-integrating CCD camera [in Proceedings of the 15th International Congress on X-Ray Optics and Microanalysis (ICXOM), August 1998, Antwerp, Belgium; J. Anal. At. Spectrom. (The Royal Society of Chemistry) 14 (1999) 409] and at once transmitted to the computer for evaluation. Thus, these techniques can be used in situ. For the methods LSI and DBI, the reflections are indexed and evaluated with the own developed simulation program KOPSKO [Cryst. Res. Technol. 34 (7) (1999) 801].In the present case, these three methods, besides other detectors, were additionally installed by us in the CamScan CS44 scanning electron microscope for the analysis of micro regions in solids. Because of the different excitation or diffraction ranges of the techniques, information comes from different specimen depths of some nanometers to about 100 μm. On this way, the range of application for the determination of the parameters was considerably increased. By the examples of a single-crystalline ceramic specimen of BaTiO3 as well as a Fe monocrystal one the range of application is demonstrated by the determination of the crystallographic direction with respect to the specimen surface all three methods are compared.
Keywords: Lattice source interferences; Kossel technique; Divergent beam X-ray interferences; Pseudo Kossel technique; Electron backscattering diffraction (EBSD); CCD camera;
Lattice constant determination from Kossel patterns observed by CCD camera by E Langer; S Däbritz; C Schurig; W Hauffe (45-48).
The Kossel technique is known due to its precision for lattice constant determination in micro ranges by use of X-ray films. Recently we observed the Kossel interferences also by a CCD camera in a good quality. Thus, the diffraction interferences could be immediately processed and evaluated by computer permitting considerable time saving. In order to obtain the similar accuracy as for measurements with X-ray films further technical and experimental improvements were necessary, especially for a better contrast to observe intersection points of several weak reflections, for evaluating digital patterns, for optimizing of the shortest focus-screen distance and for considering the image field curvature of the objective. As a result, a precision in lattice constant determination could be achieved at a Fe-crystal coming relatively close to the one of comparable X-ray film patterns, which is still about one order of magnitude better for the time being.
Keywords: Fe; Kossel technique; Lattice source interferences; Lattice constant; CCD camera;
Carbon-induced reconstructions on Si(111) investigated by RHEED and molecular dynamics by C. Koitzsch; D. Conrad; K. Scheerschmidt; F. Scharmann; P. Maslarski; J. Pezoldt (49-54).
The adsorption of carbon trimers on Si(1 1 1) 1×1 is investigated by means of empirical molecular dynamics based on a Tersoff potential. A priori unknown carbon terminated Si(1 1 1) surfaces are modeled. The energetics of different adsorption sites, specifically the S5, T4 and H3 sites are investigated. The obtained structural models are used to simulate their response to a RHEED experiment. This enables us to further elucidate on the feasibility of the models by comparing theoretical data to in situ RHEED observations during the MBE experiments. Implications of the models to growth of 3C SiC by carbonization are discussed.
Keywords: SiC; Carbonization; RHEED; Molecular dynamics; Silicon reconstruction;
Deposition and characterization of Ge–Sb–Te layers for applications in optical data storage by S Kyrsta; R Cremer; D Neuschütz; M Laurenzis; P Haring Bolivar; H Kurz (55-60).
Ge–Sb–Te films for optical data storage applications were deposited by magnetron sputtering of separate Ge, Sb, and Te targets on Si(1 1 1) wafers in a dc argon plasma. To investigate the influence of the chemical composition of the phase change material on its optical properties, films with lateral compositional gradients of up to 30 at.% were deposited. The composition and structure of the films were investigated by X-ray photoelectron spectroscopy (XPS), electron probe microanalysis (EPMA) and X-ray diffraction (XRD) on plain Si wafers, whereas the phase change velocity of Ge–Sb–Te as a re-writable optical data storage medium was determined on Si/Al/SiO2/Ge–Sb–Te multilayers near to technical conditions.The phase change of Ge–Sb–Te films was induced and characterized with a static tester consisting of an optical microscope with an integrated high power laser diode. The change in reflectivity induced by the laser pulses was measured by a high sensitivity photodetector. Depending on the composition, the crystallization time was determined between 220 and 500 ns, while the amorphization time was between 20 and 120 ns.
Keywords: Magnetron sputtering; Ge–Sb–Te; Phase change; Optical data storage;
Analysis of nanoscale multilayers by EDXS and EELS in the STEM by Jürgen Thomas; Timon Fliervoet; Klaus Wetzig (61-67).
After a short description of a model for calculation of element specific linescan intensity profiles measured in an analytical transmission electron microscope on cross-sections of nanoscale multilayers by EDXS and EELS in the STEM mode the essential influences to the results are discussed. Particularly, the signal-to-noise ratio is considered. To confirm the model measured and calculated profiles are compared. Investigations on nanoscale multilayers require a field emission gun and a specimen stage with high stability. Specimen drift can lead to completely confused intensity profiles and has to be avoided or corrected during the measurement.
Keywords: Analytical TEM; STEM; EDXS; EELS; Nanoscale multilayers;
Optical studies on thin copper films on Si(111) by A Masten; P Wissmann (68-72).
Thin copper films of about 15 nm thickness were deposited on Si(111) substrates at room temperature and subsequently annealed at higher temperatures. The ellipsometric analysis was performed in situ under UHV conditions in the wavelength range 400–800 nm. The as-deposited films can be described by a two-layer model taking into account the excitation of surface plasmon polaritons (SPP) at the rough copper–silicon interface. During annealing, two steep rises in the ellipsometrical angles Δ and ψ are observed at 125 and 300°C which are attributed to the coagulation of copper and the silicide formation, respectively.
Keywords: Ellipsometry; Copper; Silicon; Two-layer model; Island films; Surface plasmon polaritons;
Composition and morphology studies of ultrathin CaF2 epitaxial films on silicon by W Bohne; J Röhrich; M Schmidt; A Schöpke; B Selle; R Würz (73-78).
Thin CaF2 films with thicknesses between 1 and 100 nm were grown on Si(1 1 1) at UHV conditions by evaporation from a CaF2 source. The correlation of film composition and growth morphology with the deposition parameters was studied by various techniques such as heavy-ion elastic recoil detection analysis (ERDA), RBS/channeling, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and auger electron spectroscopy (AES). The composition and morphology of the CaF2 films strongly depend on the substrate temperature during deposition. Epitaxial growth is observed at deposition temperatures higher than 450°C. The F/Ca ratio of the films in the monolayer range is found to deviate appreciably from the stoichiometric composition (F/Ca=2) suggesting that the interface composition does not obey the rules of bulk equilibrium chemistry. AES results show the formation of different bonding configurations (in particular of silicide-like bonds) at the CaF2/Si interface.
Keywords: Ion scattering; Electron spectroscopy; AFM; Epitaxial growth; Calcium fluoride (CaF2);
Chemical structure and morphology of ultrathin combustion CVD layers on zinc coated steel by B Schinkinger; R Petzold; H.-J Tiller; G Grundmeier (79-87).
Combustion chemical vapor deposition (CCVD) as an atmospheric process offers an environmental friendly alternative to conventional surface treatments for reactive metals. Ultrathin nanoscaled silica like layers can be deposited on various metallic substrates. The here presented results focus on the deposition of thin SiO2-layers on zinc coated steel as an interface layer between an organic coating and the metal substrate.Infrared reflection absorption spectroscopy (FT-IRRAS) and X-ray photoelectron spectroscopy were used to reveal the chemical structure of the films. While no residual carbon was detectable the SiO2-film contains free surface hydroxyl groups. The characteristic sub-microscopic features and the initial growth of the layer are characterized by means of field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM).The increasing coverage of the surface on a technical galvanized steel surface was followed by means of AFM as well as by cyclic voltammetry. The latter surface electrochemical technique allowed to quantify the residual free surface area. It could be shown that 99% coverage can be achieved in less than 1 s deposition time.
Keywords: Combustion CVD; FE-SEM; AFM; FT-IRRAS; XPS; Surface electrochemistry;
Characterization of sputter deposited cBN-films by low energy electron loss spectroscopy LEELS by H Oechsner; S Westermeyr; Jian Ye (88-94).
The characteristic energy losses of inelastically backscattered electrons of 0.2−2 keV measured by low energy electron loss spectroscopy (LEELS) are shown to enable a destruction free determination of the sp2- and the sp3-coordinated fractions in BN-films. The specific loss structures from plasmon excitation in hBN and cBN, and from the π→π ∗ -transition in hBN are evaluated accordingly. In contrast to the commonly employed Fourier transform infrared spectroscopy (FTIR) the LEELS-method as surface sensitive technique is not influenced by contributions from the substrate or the commonly present hBN-baselayer for cBN-nucleation. Thus, the near surface region of properly deposited films could be shown to consist of pure cBN. When controlling the mean penetration depth of the primary electrons by changing their energy, phase sensitive depth profiling becomes possible. This is applied to determine the destruction depth of the cubic phase of BN under bombardment with Ar+-ions of 0.5−3 keV.
Keywords: Fourier transform infrared spectroscopy (FTIR); Auger electron spectroscopy (AES); Low energy electron loss spectroscopy (LEELS);
Evolution of surface topography of fused silica by ion beam sputtering by D. Flamm; F. Frost; D. Hirsch (95-101).
The evolution of the surface topography of fused silica during low-energy Ar ion beam sputtering was studied by atomic force microscopy. Depending on the incidence angle of the ion beam and the ion energy the topography was dominated by regular ripple structures with an orientation perpendicular or parallel to the ion beam direction and a characteristic wavelength λ between 30 and 300 nm. The time evolution of the ripple wavelength follows the power law λ∼t γ , while γ depends on the ion beam parameters.In addition, we found a distinct energy dependence of the ripple wavelength as well as the resulting scaling behaviour of the surface roughness. These results will be discussed within the limits of existing continuum models for surface erosion by ion sputtering.
Keywords: Sputtering; Topography; Ripple; Scaling; Atomic force microscopy; Fused silica;
Angle-resolved XPS measurements on copper phthalocyanine thin films by Barbara Adolphi; Olena Berger; Wolf-Joachim Fischer (102-108).
Copper phthalocyanine films about 100 nm in thickness were produced by vacuum sublimation. Different heat treatments transformed the layer from the starting α- to the β-structure. The chemical states of the layer were characterized by XPS during this transformation. The measurements from core level peaks and the valence band spectra showed systematic changes. At temperatures above 300°C the Cu detached itself from the chemical bonds in the molecule, the aromatic share of the carbon decreased and new CN bonds were formed.
Keywords: XPS; Organic layer; Valence band spectra; Chemical states;
Standard operating procedure (SOP) for the quantitative determination of organic silicon compounds at the surface of elastomeric sealants by Th Gross; D Treu; W Unger (109-112).
Elastomeric sealants may contain organic silicon compounds. The use of these sealants for housings for electronic components is harmful for the reliability of electric contacts inside. In order to prevent electronic components from malfunction, quality control of elastomeric sealants is required. An analytical procedure developed to fulfil this requirement was developed. It is based on electron spectroscopy for chemical analysis (ESCA). Information on the silicon compounds existing at the surface of elastomeric sealants is provided by this method. Silicon in organic and inorganic compounds can be differentiated with the help of Si 2p photoelectron spectra. Quantitative results can be obtained too. The uncertainty budget of the quantitative procedure is estimated.
Keywords: ESCA; Silicone; Standard operation procedure;
Raman spectroscopy: a powerful tool for characterisation of Ag/3,4,9,10-perylene-tetracarboxylic-dianhydride/GaAs heterostructures by G Salvan; D.A Tenne; T.U Kampen; R Scholz; G Jungnickel; Th Frauenheim; D.R.T Zahn (113-117).
The present contribution emphasises the capabilities of Raman spectroscopy for the characterisation of chemical and structural properties of thin organic films. As an example, a perylene derivative is presented, namely 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA). The focus will be directed to the Raman monitoring of dynamic processes. First, the PTCDA film formation on GaAs substrates by organic molecular beam deposition will be followed. The changes in the GaAs bands and PTCDA internal and external vibrational modes will be investigated as indicators for the interface formation. Secondly, the PTCDA internal modes will be monitored upon the deposition of silver onto the PTCDA/GaAs heterostructure.
Keywords: PTCDA; GaAs; Ag; Raman spectroscopy; SERS;
Application of temperature-programmed oxidation, multinuclear MAS NMR and DRIFT spectroscopy to the surface characterization of modified silica nanoparticles by F Bauer; A Freyer; H Ernst; H.-J Gläsel; R Mehnert (118-121).
Grafting of organosilane-functionalized substances onto the surface of nano-sized silica particles was studied by temperature-programmed oxidation (TPO), solid-state 13 C and 29 Si MAS NMR and DRIFT spectroscopy. By using 29 Si MAS NMR quantitative data on the proportions of the various grafted structures, grafting yields and the reactivity of the geminal and free silanols towards the coupling agent were obtained. For 3-(trimethoxysilyl)propylmethacrylate as coupling agent and maleic acid as catalyst, the TPO weight loss of about 24 wt.% revealed a hypothetical coverage of about 5.5 graft/nm2. Compared to the surface concentration of 2-3-OH groups per nm2, this value can be only explained by grafting precondensed silane molecules onto nano-sized silica, assuming a core shell principle.
Keywords: Nanoparticle; Silica; Surface modification; Silane; Scratch resistance;
Investigation of the structure and properties of a-C:H coatings with metal and silicon containing interlayers by M Nöthe; U Breuer; F Koch; H.J Penkalla; W.P Rehbach; H Bolt (122-128).
The structure of the interface of a-C:H coatings deposited with metal and Si-containing interlayers has been studied. Carbide forming metals (Al, Ti, Cr) can improve the chemical bonding compared with a substrate material which does not form carbides extensively by itself. In addition, a graded transition zone enlarges the interface between the carbon layer and the interlayer metal. In the present work the metal atoms were evaporated and ionized into a dense Ar plasma and deposited onto Si (100) substrates. A graded interface between the metal interlayer and the a-C:H coating was produced by introducing C2H2 with increasing amount into the Ar/He plasma during the PAPVD metal deposition process. The PACVD a-C:H deposition process was continued after the termination of metal evaporation to produce the pure a-C:H top layer. Further to Al-, Cr-, Ti- and Cu-interlayers, Si-containing interlayers were investigated. The Si-containing interlayers were deposited by a PACVD process using tetraethoxysilane Si(OC2H5)4 (TEOS) and tetramethylsilane Si(CH3)4 (TMS).The characterization of the deposited layer systems was performed by SIMS, SNMS and XPS analyses as well as SEM and analytical TEM methods.
Keywords: a-C:H; Metal interlayer; Silicon containing interlayer; Graded coating; Adhesion;
Auger spectroscopy study of MgLi melt affected carbon/pyrocarbon fibres by S Kúdela; A John; S Baunack; S Kúdela; K Wetzig (129-132).
Mg–12wt.% Li matrix composite reinforced with T300 carbon fibres coated with pyrolytic carbon (∼100 nm) was manufactured by the infiltration of the carbon fibre bundle with MgLi melt. The fibre/matrix chemistry was studied by means of in situ Auger electron spectroscopy of the fibre jacket and the fibre cross-fracture in ultra-high vacuum broken composite bars. The fibre bulk attack with lithium is concluded wherein C(KVV) lineshape indicates that lithium carbide is the only reaction product, and its distribution in the fibre bulk is quite uniform. Magnesium penetrates also the fibre bulk but its role in the fibre attack is marginal. It is assumed that lithium carbide is formed as a dispersed minor phase in the fibre bulk via decomposition of intermediate lithium intercalation products.
Keywords: Auger electron spectra; Metal matrix composites; Composite interface; Carbon fibre; MgLi alloy; Lithium carbide; Lithium intercalated carbon;
SIMS investigation of chemical solution-deposited SrTiO3/LaNiO3 by C Pollak; K Reichmann; H Hutter (133-137).
A chemical solution-deposited multilayer system of SrTiO3 (STO)/LaNiO3 (LNO)/Pt/TiO2/SiO2/Si was investigated by dynamic secondary ion mass spectroscopy (SIMS). Depth profiles of the main components were obtained, revealing intense diffusion processes which must have occurred during the deposition/crystallisation processes. Ti is found to diffuse into the LNO layer, where it either forms a second phase or is soluble. La diffuses into the above-lying STO phase. Ni penetrates the Pt layer and is found to cause a second maximum of the amu=60 signal within the TiO2 phase. At the surface of the sample as well as at the LNO/Pt and the TiO2/SiO2 interfaces, the Al signal shows a maximum, indicating a diffusion of Al from the substrate during synthesis of the multilayer system.
Keywords: SIMS; Chemical solution deposition; Electroceramic thin films;
Reaction paths in the system Al2O3–hBN–Y by K Reichert; O Oreshina; R Cremer; D Neuschütz (138-142).
As part of the investigations on the suitability of a new concept for a tailored fiber–matrix interface in sapphire fiber reinforced NiAl matrix composites for application as a high-temperature structural material, the interfacial reactions in the system alumina–hexagonal boron nitride–yttrium (Al2O3–hBN–Y) have been examined in the temperature range of 1100–1300°C. For this, alumina substrates were coated with hBN by means of CVD and subsequently with sputter deposited yttrium. Afterwards the samples were annealed for up to 16 h under inert atmosphere. Grazing incidence X-ray diffraction (GIXRD) served to analyze the phases formed by diffusion processes in the reaction zone. The peak intensities in these diffraction patterns were used to evaluate the sequence of phases formed due to diffusion and reaction. After the initial formation of YN and YB2, the phases Y2O3, Al2Y, and YB4 were observed. Even longer annealing times or higher temperatures, respectively, led to the formation of the ternary oxides YAlO3 and Y3Al5O12 as well as metallic aluminum.
Keywords: Alumina; Boron nitride; Yttrium; Interface reactions; X-ray diffraction;
Analytical TEM for the investigation of thin functional layers by Klaus Wetzig; Jürgen Thomas; Hans-Dietrich Bauer (143-149).
At first a survey of the methodic state of the art in analytical transmission electron microscopy is given. This concerns both the lateral and the analytical resolution, contrast phenomena and electron–solid interactions. The efficiency of the analytical techniques electron nanodiffraction, energy dispersive X-ray spectroscopy (EDXS), and electron energy loss spectroscopy (EELS) is discussed.The possibilities and the limitations of analytical TEM are demonstrated at cross-sections of nanometer scaled multilayers of relevant functional materials. Concentration profiles are taken from EDX and EEL spectra of Fe–Cr and Co–Cu multilayers, which are standard systems for the investigation of giant magnetoresistance (GMR). Furthermore, from the course of the electron energy loss near edge structure (ELNES) conclusions concerning the chemical bonding are possible. This will be discussed for the oxygen bonding in interface regions of the system Al2O3–TiN. The results allow to distinguish between different oxide phases in thin functional layers.
Keywords: Analytical TEM; Nanoanalysis; Nanostructure; Functional materials; Nanoscale multilayers;
Influence of BN fiber coatings on the interfacial structure of sapphire fiber reinforced NiAl composites by K Reichert; K Wen; R Cremer; W Hu; D Neuschütz; G Gottstein (150-155).
A new concept for a tailored fiber-matrix interface for sapphire fiber reinforced NiAl matrix composites is proposed, consisting of an initial hexagonal boron nitride (hBN) fiber coating. For this, single crystal Al2O3 fibers were coated with hBN by chemical vapor deposition (CVD). Following a comprehensive characterization of the CVD coating as to composition and structure by means of X-ray photoelectron spectroscopy (XPS) and grazing incidence X-ray diffraction (GIXRD), the fiber reinforced NiAl matrix composites were fabricated by diffusion bonding at 1400°C. The interfaces NiAl/BN and BN/Al2O3 were analyzed by scanning electron microscopy (SEM), analytical transmission electron microscopy (TEM), and selected area diffraction (SAD). An interfacial reaction between NiAl and hBN to form AlN was revealed using these analytical techniques.
Keywords: Intermetallic matrix composites; Boron nitride; Fiber coating; Interface structure;
Macroscopic and microstructural properties of CSi x N y thin films deposited by RF nitrogen-plasma-assisted pulsed laser deposition by T Thärigen; M Lorenz (156-160).
Carbon silicon nitride (CSi x N y ) thin films have been grown by pulsed laser deposition (PLD) of various [C(1−z)(Si3N4) z ]-targets using an additional nitrogen RF plasma source on [1 0 0] oriented silicon substrates without additional heating. At the beginning of the deposition the resulting microstructure is amorphous with some embedded microcrystals of ≈30 nm diameter, which induce increasing internal stress. After less than 200 nm thickness the growth of the films is changing, resulting in an amorphous microstructure with textured nanocrystallites. In this growth-mode the internal stress is decreasing. Due to the resulting low internal stress, CSi x N y films can be grown to a thickness above 3 μm, in contrast to DLC films. The microstructure of the films is found as textured graphitic planes of small size connected to each other by fullerene-like three-dimensional CN x -structures. This three-dimensional bonding network leads to high nanohardness of up to 20 GPa. Most of the silicon is bonded to carbon, which results in anisotropic hardness properties.
Keywords: Carbon silicon nitride; Laser ablation; Local bonding; TEM; Microstructure; Hardness;
Visualization of 3D-SIMS measurements by H. Hutter; K. Nowikow; K. Gammer (161-166).
Secondary ion mass spectroscopy (SIMS) provides a method to examine the 3D distribution of chemical elements in solids. We created a software program (Visualizer) for the visualization of SIMS 3D data using the visualization toolkit (VTK), a free C++ class library for 3D graphics. Furthermore, we used fusion in order to obtain one single image from several 3D images, each showing the 3D distribution of one chemical element within the sample.
Keywords: Visualization toolkit; 3D-SIMS; Channel plate correction;
Applied surface analysis in magnetic storage technology by Johannes Windeln; Christian Bram; Heinz-Ludwig Eckes; Dirk Hammel; Johanna Huth; Jan Marien; Holger Röhl; Christoph Schug; Michael Wahl; Andreas Wienss (167-180).
This paper gives a synopsis of today’s challenges and requirements for a surface analysis and materials science laboratory with a special focus on magnetic recording technology. The critical magnetic recording components, i.e. the protective carbon overcoat (COC), the disk layer structure, the read/write head including the giant-magnetoresistive (GMR) sensor, are described and options for their characterization with specific surface and structure analysis techniques are given.For COC investigations, applications of Raman spectroscopy to the structural analysis and determination of thickness, hydrogen and nitrogen content are discussed. Hardness measurements by atomic force microscopy (AFM) scratching techniques are presented. Surface adsorption phenomena on disk substrates or finished disks are characterized by contact angle analysis or so-called piezo-electric mass adsorption systems (PEMAS), also known as quartz crystal microbalance (QCM).A quickly growing field of applications is listed for various X-ray analysis techniques, such as disk magnetic layer texture analysis for X-ray diffraction, compositional characterization via X-ray fluorescence, compositional analysis with high lateral resolution via electron microprobe analysis. X-ray reflectometry (XRR) has become a standard method for the absolute measurement of individual layer thicknesses contained in multi-layer stacks and thus, is the successor of ellipsometry for this application.Due to the ongoing reduction of critical feature sizes, the analytical challenges in terms of lateral resolution, sensitivity limits and dedicated nano-preparation have been consistently growing and can only be met by state-of-the-art Auger electron spectrometers (AES), transmission electron microscopy (TEM) analysis, time-of-flight–secondary ion mass spectroscopy (ToF–SIMS) characterization, focused ion beam (FIB) sectioning and TEM lamella preparation via FIB. The depth profiling of GMR sensor full stacks was significantly improved by the ToF–SIMS Cs method.
Keywords: Magnetic recording; Carbon overcoat hardness; X-ray analysis; Electron beam; Electron spectroscopy; ToF–SIMS; Focused ion beam; Magnetic force microscopy; Raman spectroscopy;
Characterization of ITO- and TiO x N y films by spectroscopic ellipsometry, spectraphotometry and XPS by J Bartella; J Schroeder; K Witting (181-190).
Within the last years, several new application for optical coatings were found. To assist R&D activities in the development of new films and coating sources, combination of different analytical techniques is required: spectraphotometry measures reflectance, transmittance and absorbance. Spectroscopic ellipsometry is applied to determine optical constants n(λ) and k(λ). For high absorbing TiN and TiON films for CRT display applications, these constants were evaluated by combination of photometry and ellipsometry.Spectroscopic ellipsometry is introduced in quality control of ITO films for flat panel displays. Differences of the optical constants indicate enhanced failure rate of the complete display systems. With X-ray photon spectrometry (XPS) depth profiling and electron microprobe (EMP) analysis, Na-diffusion from the glass substrates into the films is found to be a source of the failures. Additionally, AFM is applied to monitor film structures and measure surface roughness.
Keywords: Optical constants; Spectroscopic ellipsometry; Thin films;
Structure and luminescence of GaN layers by T Barfels; H.-J Fitting; J Jansons; I Tale; A Veispals; A von Czarnowski; H Wulff (191-195).
GaN films grown on 〈1 1 1〉 Si substrate by means of low pressure MOCVD technique in a horizontal flow quartz reactor are characterized by different thin layer analysis methods. The polycrystalline hexagonal structure of the GaN layers has been checked by means of grazing incidence X-ray diffractometry and IR spectroscopy. Cathodoluminescence (CL) spectra and their time kinetics are studied. The mean decay time of the 3.44 eV UV bound exciton transition is below 1 ns, whereas the 3.26 eV violet band shows a slow hyperbolical decay over about 1 μs. A third yellow band appears at 2.12 eV due to transitions via localized states.
Keywords: GaN layers; MOCVD; Crystal structure; Cathodoluminescence; Luminescence decay time;
In situ characterization of the nitridation of AIII–BV semiconductor surfaces by means of X-ray photoelectron spectroscopy by J.-D Hecht; F Frost; T Chassé; D Hirsch; H Neumann; A Schindler; F Bigl (196-202).
The effect of low-energy N2 + ion beam bombardment on InAs, InP, and InSb surfaces has been studied using in situ X-ray photoelectron spectroscopy. The formation of a nitrided surface layer has been observed for all investigated AIII–BV semiconductors. Beside the emerging InN bonds also PN bonds were detected for InP, whereas for InAs and InSb, there is no evidence for the formation of AsN and SbN bonds, respectively. An analysis of the N 1s core level peak also reveals the build-in of interstitial nitrogen. A change of the ion beam incidence angle has great influence on the composition of the surface layer as demonstrated for InP. The amount of nitrogen in PN bonds and of interstitial nitrogen decreases for changing the ion incidence to grazing angles. A detailed XPS analysis provides information on the temporal evolution of the process of nitridation and the thickness of the nitrided surface layer.
Keywords: Ion beam sputtering; Nitridation; InAs; InP; InSb; X-ray photoelectron spectroscopy;
Conductivity type conversion of p-type CuInSe2 due to hydrogenation by K Otte; G Lippold; D Hirsch; R.K Gebhardt; T Chassé (203-208).
The surface of p-type CuInSe2 single crystals prior to and after low energy hydrogen ion implantation at increased substrate temperature has been investigated by X-ray photoelectron spectroscopy (XPS) and Raman measurements. A shift of the Fermi-level by 500 meV closer to the conduction band after the hydrogen exposure has been observed for CuInSe2, oxidized by storage in air. The same behavior was observed for a clean surface prepared in ultra-high vacuum (UHV) by cleavage of CuInSe2. This observation supports the previously suggested type conversion from p- to n-type of the surface of CuInSe2. The conversion is explained by the passivation of Cu vacancies and hydrogen on and interstitial site. For the oxidized sample, the re-activation of oxygen passivated Se vacancies might influence the type conversion additionally.Raman spectroscopy did not reveal any lattice damage after implantation at 300°C sample temperature.
Keywords: Hydrogen; Implantation; XPS; CuInSe2; Defects;
Time-resolved photoluminescence characterisation of thin PTCDA films on Si(100) by A.Yu Kobitski; G Salvan; H.P Wagner; D.R.T Zahn (209-212).
3,4,9,10-Perylenetetracarboxylic dianhydride (PTCDA) thin films on Si(100) substrate are investigated by time-resolved photoluminescence (PL). A sub-band structure together with a bi-exponential decay of the PL spectra have been observed which are attributed to excimer and monomer recombination processes. A comparison with single PTCDA crystals shows that the excimer transition is related to the crystallinity of the PTCDA films. The dependence of the photoluminescence intensity and decay times on the film thickness and on the substrate temperature give further information about the crystallinity of PTCDA films.
Keywords: PTCDA; Time-resolved photoluminescence; Excimer; Monomer;
Auger depth profile analysis and EFTEM analysis of annealed Ti/Al-contacts on Si-doped GaN by Markus Pidun; Peter Karduck; Joachim Mayer; Klaus Heime; Bernd Schineller; Thomas Walther (213-221).
Ti/Al (10 nm/100 nm) bilayer contacts on Si-doped GaN were heat treated for 30 s at 600 and 650°C. The microstructure of the contacts was analysed by Auger depth profiling, SEM and EDX analysis and energy filtering TEM using electron spectroscopic imaging (ESI).The experiments show a strong interdiffusion of Al and Ti leading to the formation of an intermetallic compound. A complex, spatially inhomogeneous structure consisting of an Al-rich phase, a Ti–Al intermetallic compound and regions containing Al-oxide is formed, while the GaN is still covered by a thin, homogeneous Ti-rich layer. A thickness of 2.5 nm was obtained for the Ti-rich layer in the contact heat treated at 650°C.The combination of complementary results from Auger depth profiling, SEM analysis with EDX and ESI provides a comprehensive characterisation of the complex contact structure. The results will be discussed in terms of the contributions and specific advantages of the individual techniques.
Keywords: GaN; Ohmic contacts; Auger; EFTEM; Metallization layer;
Surface states and reactivity of pyrite and marcasite by I Uhlig; R Szargan; H.W Nesbitt; K Laajalehto (222-229).
The sulphur surface sites of pristine marcasite surfaces and their reactivity during initial air oxidation were investigated for the first time using synchrotron radiation excited photoelectron spectroscopy (SRXPS). Both S 2p and Fe 2p spectra were collected and compared to those of the polymorph pyrite. A new sulphur surface component is found additionally to the two known pyrite surface signals. Due to the non-isotropic character of the orthorhombic marcasite structure, its peak intensity depends strongly on the surface orientation. Its binding energy is close to the region of short-chained polysulphides. The signal is assigned to sulphur trimers produced by electron transfer between surface near sulphur dimers and S− formed after ruptures of SS bonds which results in S2− and S3 2−. In the cubic crystal arrangement of pyrite the stabilisation of S− to S2− is realised by an electron transfer from iron to sulphur only. A confirmation of this assumption is found in the Fe 2p spectra. The contribution of Fe3+ species — a result of the electron transfer process — is considerably less pronounced for marcasite.The mechanism of initial oxidation is different for marcasite and pyrite. The sulphur species responsible for the new spectroscopic component are the most reactive sites at the marcasite surface, while S2− is oxidised first in case of pyrite. The signals indicating the products of marcasite oxidation in the S 2p spectrum are less intense as expected from the intensity decreasing of the trimer peak. Therefore, an oxidation of sulphur trimers to elemental sulphur is assumed which could not be detected because of its volatility in the vacuum of the air lock system.
Keywords: Photoemission; Synchrotron radiation; Pyrite; Marcasite; Surface states;
Raman spectroscopy on Psaronius sp.: a contribution to the understanding of the permineralization process by Dagmar Dietrich; Klaus Witke; Ronny Rößler; Günter Marx (230-233).
Samples of the permineralized tree fern Psaronius sp. from the Lower Permian Rotliegend of Chemnitz were examined to find out their chemical composition and structural behavior. The inhomogenic distribution of elementary constituents of oxides, sulfates and carbonates within the silica-matrix consisting of α-quartz and chalcedony were formerly detected by analytical X-ray microscopy. Most of the compounds could be revealed by Raman spectroscopy. Calcite and barite developed in small fissures. Iron of different oxidation level is the prevailing pigment in the agate preserved adventitious roots. Coalified cellulose whose structure mainly corresponds to anthracite reflects the anatomical detail of the former organic tissues.
Keywords: Raman spectroscopy; Petrified forest; Permineralization;
In situ FT-IR study on the reaction path of skeletal isomerization of n-butene over different zeolites by P Ivanov; H Papp (234-239).
Adsorption and reaction of 1-butene, cis- and trans-2-butene and isobutene on H-ZSM-5 and H-FER were studied by FT-IR spectroscopy between 30–450°C. n-Butenes were monomolecularly adsorbed via π-bonding on H-FER at 30°C. At elevated temperatures butadiene was monitored on H-FER, which was then transformed into dialkyldiphenyl. On H-ZSM-5 all butene isomers were adsorbed via π-bonds, followed by dimerization. From these results and from catalytic measurements a monomolecular pathway is proposed on H-FER and a bimolecular one on H-ZSM-5.
Keywords: Skeletal isomerization; Mechanism; Butene; Zeolite; FT-IR;
Characterization of the 3D-distribution of the components in Al-alloyed high speed steels with SIMS by Katharina Gammer; Sven Musser; Herbert Hutter (240-244).
As prices for steel products have fallen, interest in the research for novel cheaper basic materials for steels is rising. The aim is to achieve more cost-effective production without loss of performance. The outstanding properties of Al and its unlimited availability have brought this element into the center of current research and development. In this study we were investigating high speed steels (HSS) containing 1% aluminum by direct imaging secondary ion mass spectrometry (SIMS). Our aim was to reveal the influence of aluminum on the 3D-distribution of the metallic main and trace components.
Keywords: 3D SIMS; Al-alloyed high speed steels;
AES analysis of failures in Cu based electromigration test samples by S. Baunack; T.G. Kötter; H. Wendrock; K. Wetzig (245-250).
Failures occurring in electromigration test of copper interconnects have been characterized by electron backscatter diffraction (EBSD) and scanning Auger microscopy (SAM). The Cu interconnects were 2 μm wide and 500 nm thick stripes on a Ta/TaN barrier. They are imbedded in trenches in a SiO2 layer on Si. The failure manifests as the appearance of voids with lateral dimension of some micrometers. By EBSD mapping, it could be verified that no sidewall texture in the interconnect exist. Auger analysis clearly showed that the Ta/TaN barrier layer has not been destroyed at the site of electromigration failure. The interaction of the electron beam with small particles (≈0.5 μm) was modelled to understand the contribution of electron scattering in the voids to the lateral resolution.
Keywords: Cu metallization; Electromigration; Scanning Auger microscopy; Electron backscattering diffraction; Monte Carlo simulation;
Activation of nickel-anodes for alkaline fuel cells by M Schulze; E Gülzow; G Steinhilber (251-256).
In alkaline fuel cells (AFC) electrodes containing porous nickel and PTFE can be used as anodes. A low-cost production technique yields passive, polymer covered electrodes, which have to be activated before being used in electrochemical devices. During this activation process the surface structure as well as the chemical composition and the oxidation state of the used materials are changed by a given electrochemical current. The electrodes are investigated in different states during this activation process with X-ray photoelectron spectroscopy, scanning electron microscopy with energy dispersive X-ray spectroscopy and nitrogen adsorption.
Keywords: Alkaline fuel cells; Nickel; Electrodes; X-ray photoelectron spectroscopy; Reduction of nickel oxide;
Black spots on carbon steel after contact to lubricating oil with extreme pressure additives: an XPS study by Th Mayer (257-262).
Unrevealed synergistic effects of certain additive composition of lubricating oil cause the formation of black spots on guiding planes of cast iron. We performed an X-ray photoemission study comparing samples with black spots to samples without. Sputter depth profiles of the elements Fe, O, C, Si, Ca, Mn, S, P and N were recorded. While the shapes of the iron and oxygen spectra do not differ markedly, the thickness of the iron oxide is much larger on black spots. While Si and Mn were found in detectable concentrations in the oxide layer of samples with and without black spots, Ca, S and P were detected on black spot samples only. Since the detected iron oxides are of dark colour and Mn is known to form dark compounds with O, S and P, we conclude that a thick iron oxide layer containing Mn compounds is responsible for the colouring of the black spots.
Keywords: Photoemission; Corrosion; Cast iron; Lubricant; Tribology;
SIMS depth profile analysis of wear resistant coatings on cutting tools and technical components by P Willich; C Steinberg (263-268).
For quantitative depth profile analysis of hard and wear resistant coatings (general composition, metal-C:N:O:H:Ar) by secondary ion mass spectrometry (SIMS) the use of Cs+ primary ions in conjunction with the detection of MCs+ (M: element of interest) molecular ions is proposed. As compared with Rutherford backscatterring spectrometry (RBS)/elastic recoil detection (ERD), the accuracy of MCs+-SIMS is about ±10%, irrespective of oxygen concentrations up to 20 at.%. A depth resolution of Δz∼30 nm at a depth of z=2.5 μm is demonstrated on curved (radius 2 mm) surfaces of polished (R a∼0.005 μm) steel. On rough surfaces (R a>0.1 μm) the depth resolution significantly degrades (Δz=120 nm at z=2.5 μm) due to effects of shadowing and redeposition. This limits detailed and quantitative studies of interlayers and interfaces. Examples are given for local depth profile analysis on technical components under difficult conditions of surface geometry and topography.
Keywords: SIMS; Quantification; Depth resolution; Wear resistant coatings;
SIMS investigation of MoS2 based sputtercoatings by C Heinisch; K Piplits; F Kubel; A Schintlmeister; E Pflüger; H Hutter (269-274).
Several multicomponent lubrication thin films consisting of TiAlN and molybdenum disulfide (MoS2) were manufactured by magnetron cosputtering using different process parameters. The resulting thin films were analyzed by SIMS depth profiling, electron probe micro analysis (EPMA) and X-ray diffraction.EPMA measurements are used to determine the concentration of major elements of the thin film and to calculate relative sensitivity factors (RSFs) for SIMS quantification of the depth profiles. Whereas the concentration of titanium, aluminum and nitrogen nearly conforms the stoichiometric composition of TiAlN2, the concentration of molybdenum and sulfur are almost equal and do not comply the anticipated ratio of stoichiometric MoS2 in all analyzed lubrication films. X-ray diffraction has been used to proof the amorphous nature of the film but also shows a significant difference in the crystalline structure between a pure TiAlN film and layers with cosputtered MoS2. While the TiAlN/MoS2 cosputtered films are completely amorphous the TiAlN layer includes cubic TiN in an otherwise amorphous film. SIMS depth profiling indicates a constant amount of all analyzed elements through the film except sulfur which decreases from the surface to the bottom of the layer.
Keywords: MoS2; TiAlN; SIMS;
Characterisation of Cr intermediate layers in Cu–C-system with SIMS method by Karl E Mayerhofer; Erich Neubauer; Christoph Eisenmenger-Sittner; Herbert Hutter (275-280).
In the design of new high speed chip generations, the greatest problem is to bleed off process heat during their operation. The installation of heat sinks onto such chips is necessary. A copper–carbon (Cu–C) composite is one possible material. It combines high thermal conductivity with low density and tailorable coefficient of thermal expansion (CTE). Because of low wettability of carbon by copper, a thin layer of chromium (Cr) has to be deposited first to contact copper with the carbon fibers.The optimization of processing parameters was done on vitreous carbon substrates (Sigradur G) as a model for carbon fibers. Onto these substrates, 2 nm chromium and 1 μm copper were deposited. In the later serial fabrication of the composite, a hot pressing step will follow the deposition, which is simulated with a heat treatment of the compound.Secondary ion mass spectrometry (SIMS) investigations were done to obtain information on the depth distribution of the main elements copper, chromium and carbon. Two samples, one as deposited and one subjected to a heat treatment after deposition are compared in this investigation.
Keywords: Sputter deposition; Interface; Metal matrix composite; SIMS; Layer structure;
Activation of galvanized steel surfaces before zinc phosphating — XPS and GDOES investigations by M Wolpers; J Angeli (281-291).
The effect of activation in the zinc phosphating has been studied phenomenologically by SEM and AFM. Kinetic investigations show that the activation plays an important role for the phosphating reaction. The activations underlie coagulation and sedimentation due to their colloidal character which again affect the reaction kinetics of phosphating. The adsorption of the titanium phosphate colloids was analyzed by XPS and GDOES. Whereas ESCA is not able to detect the adsorbed titanium phosphate particles using titanium as a central element, it is possible to identify it with GDOES.
Keywords: Zinc phosphating; Activation; Colloids; Galvanized steel; XPS; GDOES;
The influence of surface effects on the hydrogen absorption investigated on the V–H model system by K.-H Müller; H Paulus; G Kiss (292-300).
The system V–O–H has been chosen as a model system to investigate surface effects on hydrogen absorption in metals. By means of XPS, SIMS, and thermal desorption mass spectrometry (TDMS) methods, the influence of oxygen segregated from the bulk as well as adsorbed from the gas phase has been pointed out. Segregated oxygen obstructs the hydrogen absorption, whereas non-stoichiometric and stoichiometric oxides have a preventing effect already with coverages in the range of monolayers. Ion bombardment in connection with sputter-cleaning or SNMS and SIMS analyses produces additional absorption sites in the surface near region for hydrogen. These can be populated by hydrogen from the gas phase during H2 exposure or diffusing from the bulk, if the sample was H2 loaded before.Beside elements like vanadium, there exist alloys (e.g. TiFe, LaNi5, TiMn2), which are particularly suitable for practical storage purposes. It is important for the further development of such alloys but also for a better understanding of absorption kinetics to investigate the influence of surface effects also on these alloys.
Keywords: Hydrogen storage; Metal hydride; Segregation; Oxide formation; Hydrogen absorption;
XPS investigations of surface segregation of doping elements in SnO2 by D. Szczuko; J. Werner; S. Oswald; G. Behr; K. Wetzig (301-306).
Various doped tin oxide (dopants Sb, Nb, In) were prepared. By means of X-ray photoelectron spectroscopy (XPS) the dependence of the surface concentration on doping element, doping concentration and preparation technique was determined. Simultaneously, the electrical and morphological properties are strongly influenced even by low doping concentration. The dopant distribution was studied by XPS and SIMS depth profiling. A model for dopant distribution in the fine powders was proposed. At low concentrations, the doping element is build into the lattice of SnO2 partially and the residue substitutes Sn atoms in the topmost layer. Particles of the second phase are found at higher doping concentrations. Additionally, the analysis of Sb 3d3/2 peak position and shape in Sb doped samples shows a decrease of oxidation state of antimony with increasing doping concentration.
Keywords: Tin oxide; XPS; Segregation; Powders;
Binding state information from XPS depth profiling: capabilities and limits by S Oswald; R Reiche (307-315).
Depth profiling with X-ray photoelectron spectroscopy (XPS) in combination with ion sputtering is a useful tool especially for the investigation of conductive and semiconductive samples. Considering the in general comfortable possibilities for binding state determination by evaluation of peak shift and peak shape changes in XPS, it is in great request to get such information also from sputter depth profiling. The paper critically discusses for a wide spread of examples the possibilities of such a methodology especially in connection with data analysis procedures like factor analysis, but also the limitations occurring due to bombardment-induced damage. It is concluded that despite of that damage useful binding state information can be derived in many cases, however, the amount of distortion has to be checked critically in every case.
Keywords: X-ray photoelectron spectroscopy; Depth profiling; Binding state identification; Sputtering artifacts; Factor analysis;
XPS and factor analysis for investigation of sputter-cleaned surfaces of metal (Re, Ir, Cr)–silicon thin films by R Reiche; S Oswald; K Wetzig (316-323).
XPS and factor analysis were used for investigation of the electronic structure of Me x Si1−x (Me=Re, Ir or Cr) thin films which show a semiconductor-to-metal transition at a critical (metal) concentration x c. Sputter cleaning applied for surface preparation leads to enrichment of Me and, as proved by TEM investigations, to silicide formation. For Re x Si1−x and Ir x Si1−x films, this influences the XPS valence band and the core level spectra, signals of silicide bonding are extracted and their contributions to the XPS data are quantified by factor analysis. On that way, an indirect connection to x c for Re x Si1−x films is found by quantification of metallic Re contributions. For the Cr x Si1−x films, valence band studies are more promising, energy shifts of the valence band edge correlate with the electrical transport properties.
Keywords: X-ray photoelectron spectroscopy; Factor analysis; Metal–silicon thin films; Silicides; Sputtering artifacts;
Author Index (325-328).
Subject Index (329-340).