Applied Surface Science (v.217, #1-4)

Subject Index (IV-XIV).

Author Index (I-III).

Nitrous oxide (N2O) seems to be efficiently destroyed at the room temperature on surfaces of quartz or Pyrex photolysis cells exposed simultaneously to UV radiation (254≤λ≤300 nm) and ozone (O3). Compared to the well-known loss of N2O on various surfaces (including quartz/sand) at high temperatures the new loss process is intriguing. The intriguing aspect is that a combination of UV photons and a gas, rather than the elevated temperature, was instrumental in the surface loss of N2O. Further studies of the loss process might reveal potential useful roles of analogous processes in environmental catalysis and atmospheric chemistry.
Keywords: Surface chemical reaction; Photochemistry; Nitrogen oxides; Ozone; Quartz surface;

Small signal amplification using parametric resonance in NcAFM imaging by Shivprasad Patil; C.V Dharmadhikari (7-15).
The power-spectral analysis of the cantilever signal in large amplitude non-contact atomic force microscopy (NcAFM) is carried out with a view to understanding the dynamics of the system. The analysis shows period doubling bifurcation with respect to mean tip–sample separation. It is observed that period doubling bifurcation can be used for mechanical amplification of small signal using parameter modulation. The possibility of using parametric amplification for the imaging of periodic lattice is proposed. An attempt has been made to image freshly cleaved NaCl single crystal and as received Si(1 1 1) surfaces in ambient conditions.
Keywords: Atomic force microscope; Dynamics of cantilever; Parametric resonance;

Surface modification of TiO2 nanoparticles by polyaniline by Xingwei Li; Wei Chen; Chaoqing Bian; Jinbo He; Ning Xu; Gi Xue (16-22).
A composite of polyaniline (PAn) encapsulating titania (TiO2) with nanometer size was prepared by the oxidating aniline hydrochloride with ammonium peroxodisulfate in the presence of TiO2 nanoparticles. The obtained composite was characterized by Fourier-transform infrared spectra (FTIR), Fourier-transform Raman spectra, thermogravimetric analysis (TGA), wide-angle X-ray diffraction (WXRD) and scanning electron microscope (SEM). The conductivity was also investigated. FTIR and FT-Raman spectra measurements show that PAn and TiO2 nanoparticles are not simply blended or mixed up, and a strong interaction exists at the interface of nano-TiO2 and PAn. It is probably a composite at molecular level. TGA results suggests that PAn/nano-TiO2 composite contains 10% PAn by mass. The conductivity of PAn/nano-TiO2 composite has reached 2.9×10−2  S cm−1 at 20 °C but the morphology and crystallinity of nano-TiO2 were unchanged.
Keywords: Polyaniline; TiO2 nanoparticles; Composite; Interface;

Layered nickel-sulfides (Ni-S) nanocrystals had been successfully prepared by low-temperature hydrothermal approach. Rietveld X-ray diffraction (XRD) analysis revealed that these layered Ni-S materials have two different hexagonal structure phases, NiS1.03 and NiS, both phases are NiAs-type with space group of P63/mmc. X-ray energy dispersive spectra (XEDS) analysis and TEM observations also confirmed these two nanocrystals of NiS1.03 and NiS. High-resolution transmission electron microscopy (HREM) lattice images indicated Moiré fringes with rotational or translational patterns were observed in these layered Ni-S nanophases materials. In particular, it was found that all the simulated HREM images were in good agreement with the observed HREM lattice images. Especially, the simulated selected-area electron diffraction (SAED) patterns obtained from the hexagonal Ni-S crystallographic model showed that the experimental SAED patterns taken along [11.0], [00.1] and [10.0] zone axes presented reflections produced by double diffraction effect.
Keywords: Ni-S nanocrystals; High-resolution transmission electron microscopy; Moiré patterns;

Two kinds of GaN/AlN superlattices (SLs) with different thickness strained layers have been grown on Si(1 1 1) substrate using pulsed laser deposition (PLD) assisted by direct current discharge. The optical and electrical properties of the GaN/AlN SLs were characterized with X-ray diffraction (XRD), Van der Pauw–Hall measurements, micro-Raman spectroscopy, and photoluminescence (PL) spectroscopy. It is observed that the background carrier concentration and electron mobility in the GaN/AlN SL with thicker strained layers is bigger than that with thinner strained layers. From the Raman spectra, the experimental data of thinner strained layers GaN/AlN SL are found to be in agreement with the results of previous reports. For the GaN/AlN SL with the thicker strained layers, the GaN E2 peak is absent and the other peaks are obviously broad and weak. In the PL spectra, the SL with thinner strained layers only has strong band edge emission peak. But the SL with thicker strained layers has weak yellow luminescence peak beside weaker band edge emission peak. These suggest that the thickness of strained layers in the GaN/AlN SLs have significant effect on the optical and electrical properties.
Keywords: Pulsed laser deposition; GaN/AlN; Superlattice; Properties;

Nanoscale oxide structures induced by dynamic electric field on Si with AFM by Xiaodong Hu; Tong Guo; Xing Fu; Xiaotang Hu (34-38).
Nanoscale oxide structures are very important for the study of functional nanodevices. Local oxidation induced by electric field with scanning probe microscopy is a promising method. Some oxide lines and dots on Si surface were fabricated using conductive atomic force microscope in this paper. Nanoscale oxide lines induced by dc voltages exhibit the characteristic of single peak, but the hollow structures with higher aspect ratio are observed under the effect of square wave voltages. We present the hollow structures result from the finite diffuse speed and concentration of oxygen ion, and the higher aspect ratio results from the effect of dynamic electric field in the conductor–nonconductor–semiconductor junction formed in the course of fabrication.
Keywords: AFM; Oxide structure; Nanofabrication; Dynamic electric field;

Nanoscale silicon prepared on different substrates using electron-beam evaporation and their field-emission property by Xinyun Xie; Qing Wan; Weili Liu; Chuanling Men; Qing Lin; Chenglu Lin (39-42).
Silicon nanorods (about 10–35 nm height) on silicon and porous silicon substrates were synthesized using ultra-high vacuum electron-beam evaporation in the present of a Fe catalyst. Atomic force microscopy (AFM) is used to estimate the dimension and check the morphology of the silicon nanoclusters. The electron field emission is used to reveals the property of silicon nanorods grown on different substrates.
Keywords: Silicon nanorods; Electron-beam evaporation;

Characterization of ceramic-metal composite hydrogen separation membranes consisting of barium oxide, cerium oxide, yttrium oxide and palladium by R.V. Siriwardane; J.A. Poston; E.P. Fisher; T.H. Lee; S.E. Dorris; U. Balachandran (43-49).
Cermet (ceramic-metal composite) hydrogen separation membranes consisting of barium oxide, cerium oxide, yttrium oxide and palladium were characterized by utilizing X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS). Characterization was performed at room temperature and 650 °C, and after exposure to hydrogen. Changes in both elemental composition and oxidation states were observed at elevated temperatures and as a function of time. Permeation of hydrogen through the membranes also changed with time and temperature.
Keywords: High temperature membranes; Hydrogen separation membranes; Ceramic membranes; Surface characterization of membranes;

We have studied the annealing behavior of anodically etched porous Zn (p-Zn) as a function of annealing time. It is found that 10 min ambient air annealing of Zn yields efficient UV luminescence with a very weak deep-level defect-related luminescence. The emergence of the green luminescence band is observed with an increase of annealing time. Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) have been performed on annealed p-Zn. STM studies reveal a more smooth surface for p-Zn annealed for a short period. STS analysis shows a good agreement with observed PL spectra, especially concerning the existence or absence of defect-related luminescence.
Keywords: ZnO; Anodic etching; Annealing; Scanning tunneling microscopy; Scanning tunneling spectroscopy;

The electronic effect of carbon and hydrogen in an (1  1 ̄  1) edge dislocation core system in bcc iron by S Simonetti; M.E Pronsato; G Brizuela; A Juan (56-67).
The Fe–C–H interaction in a dislocated bcc structure was studied using qualitative structure calculations in the framework of the atom superposition and electron delocalisation molecular orbital (ASED-MO) theory. Calculations were performed using Fe85 cluster to simulate a dislocated bcc structure. The cluster geometry and atomic parameters were optimised to make a better approximation to the repulsive energy terms. The most stable position for C atom inside the cluster was determined. Therefore, and H atom was approximated to the minimum energy region where the C atom was previously located. The total energy of the cluster decreases with the C atom near the dislocation core. The a/2[1  1 ̄  1] dislocation creates an energetically favourable zone for accumulation of C. The presence of C in the dislocation core make no favourable H accumulation. The C acts such as an expeller of H and could reduce the weakening of Fe–Fe bonds. In addition, a sort of Fe–C–Fe “bridge” could prevent dislocation displacement if a shear stress would be applied.
Keywords: Dislocation; Iron; Carbon; Hydrogen; Embrittlement;

Alkali halide coatings have been reported to act as effective dipole layers to lower the surface work function and induce a negative electron affinity of diamond surfaces. Here, the results of the analysis of films grown on silicon and quartz substrates by 193 nm pulsed laser ablation from a commercially available sintered disk of LiF are reported. The morphology, composition and crystallinity of films grown are examined and suitable deposition parameters for optimising the growth are suggested. The ablation was shown to be very efficient at removing a large amount of material from the target, even at relatively low fluence. The morphology of the films produced was poor, however, with a high density of asperities categorised as either particulates produced by exfoliation, or as droplets produced by hydrodynamic sputtering. An improved morphology with smaller droplets and fewer particulates could be produced by mounting the substrate at an angle of 65° to the axis of the ablation plume and using a fluence close to the measured ablation threshold of 1.2±0.1 J/cm2. The elemental composition of the films was shown to be indistinguishable from that of bulk LiF, despite evidence for significant recondensation of Li back onto the target. Films containing crystal grains oriented with the 〈1 0 0〉 direction normal to the substrate surface were observed at substrate temperatures in excess of 300  °C. An improved extent of orientation was observed on the quartz substrates.
Keywords: Lithium fluoride; Pulsed laser ablation;

Growth of GaN nanowires through nitridation Ga2O3 films deposited by electrophoresis by Chengshan Xue; Li Yang; Cuimei Wang; Huizhao Zhuang (78-81).
Synthesizing hexagonal wurtzite GaN nanowires involves nitriding Ga2O3 films, which deposited on GaAs(1 1 0) substrates with electrophoresis. The cylindrical structures of GaN nanowires with the diameters ranging from 40 to 200 nm and lengths up to over 100 μm have been obtained. Scanning electron microscopy (SEM) images showed the morphologies of the one-dimensional single crystal materials containing straight and curved nanowires. GaN spherical crystals attached to the fibers with diameters about 600 nm were detected for the first time. The synthesis of one-dimensional GaN nanowires can be achieved without assistance of a template of a catalyst.
Keywords: Nitridation; GaN nanowires; Electrophoresis; Ga2O3 films;

X-ray photoelectron spectroscopy of polycrystalline AlN surface exposed to the reactive environment of XeF2 by Morimichi Watanabe; Yukimasa Mori; Takahiro Ishikawa; Takashi Iida; Keijiro Akiyama; Kyoichi Sawabe; Kosuke Shobatake (82-87).
X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and scanning electron microscopy (SEM) measurements of polycrystalline AlN surfaces exposed to XeF2 vapor at 1.8×10−4  Torr at sample temperatures ranging from T s=300 to 920 K are reported. No change in the chemical composition and morphology of the AlN surface exposed at T s=300 K was observed from a virgin AlN surface. The AlN surface exposed at T s=700 K is partially fluorinated, forming an AlF3 layer, whereas those exposed at T s=750 and 800 K are found to be completely covered with an AlF3 layer although no change was observed in morphology. Above T s=850 K, however, partially fluorinated AlF x (x=1, 2) species and exposed AlN surface area were observed but no AlF3-passivated layer was detected, probably because the AlF3 formed is desorbed as soon as it forms. Therefore, it is concluded that, above T s=850 K, the fast corrosion reaction of AlN by XeF2 proceeds and thus the AlN surface is strongly etched.
Keywords: XPS; SEM; Corrosion; AlN; Plasma reaction; AlF3;

Substrate temperature dependence of the properties of ZAO thin films deposited by magnetron sputtering by En-Gang Fu; Da-Ming Zhuang; Gong Zhang; Wei-Fang Yang; Ming Zhao (88-94).
ZAO (ZnO:Al) transparent conductive thin films have been prepared by middle-frequency alternative magnetron sputtering with ZAO (98 wt.% ZnO+2 wt.% Al2O3) ceramic target. The influences of substrate temperature on the microstructure, optical, and electrical performances of ZAO films have been studied. UV-Vis and Van der Pauw investigated the visible transmittance, carrier concentration, and Hall mobility, respectively, while microstructure has been characterized by X-ray diffraction (XRD). The results show substrate temperature is a dominant factor for microstructure, optical, and electrical performances of ZAO thin films. The lowest resistivity obtained in this study was 4.6×10−4  Ω cm for the film with sheet resistance of 32 Ω, which was deposited at the substrate temperature of 250 °C and operation gas pressure of 0.8 Pa.
Keywords: Magnetron sputtering; ZAO thin films; Substrate temperature; Resistivity; Transmittance;

The thickness dependence of the resistivity for Cu films deposited by ion beam deposition (IBD) was evaluated using Fuchs–Sondheimer (F–S) model for electron surface scattering and Mayadas–Shatzkes (M–S) model for electron grain boundary scattering. For fitting the F–S and M–S models to the experimental data, the approximate equations proposed in both models were discussed and it was confirmed that the experimental resistivity of the Cu films could be described well by a simple form combined of the approximate equations for both models. By means of the simple form in this work, the most reasonable fit to the experimental data could be obtained under the conditions of the surface scattering coefficient p=0 and the reflection coefficient at grain boundary R=0.40.
Keywords: Copper; Thin films; Thickness; Resistivity; Ion beam;

Capacitance characteristics in PbSrSe thin films by K Wang; W.Z Shen; H.F Yang (100-107).
We report bias- and frequency-dependent capacitance characteristics in Pb1−x Sr x Se thin films with Sr composition from 0.066 to 0.276 grown by molecular beam epitaxy on BaF2 substrates. A grain boundary barrier model has been presented, which can well explain the experimental observation of the capacitance in relation with the bias, frequency, as well as the Sr composition. Negative capacitance phenomenon has been observed for samples with different Sr compositions under different bias and frequency conditions. The origin of this negative capacitance effect is believed to be due to the accumulation of minority carriers at the grain boundaries, which produces an additional dynamic capacitance with an opposite sign. In addition, the success in explaining the Sr composition dependent dark current characteristics gives further evidence for the model.
Keywords: Capacitance; PbSrSe; The grain boundary barrier model;

SrBi2Nb2O9 (SBN) thin films deposited by laser ablation on epitaxial (1 0 0)Pt and (1 1 0)Pt have been studied using an atomic force microscope (AFM) in the so-called “piezoresponse” mode. Previous X-ray studies have shown that in the first case two different orientations coexist in the film: a predominant (0 0 1) orientation with a (1 1 5) orientation. AFM topographical images reveal the presence of two different kinds of grains of different shape corresponding to each orientation and AFM piezoresponse images are in agreement with the crystallographic orientation of the grains: only the expected (1 1 5) oriented grains show a piezoelectric contrast. Moreover, hysteresis loops are obtained over (1 1 5) grains and not over (0 0 1) regions. Although (1 1 5) grains can be in a monodomain state, they also show intragranular ferroelectric domains with nanometric sizes, which orientation can be reversed by applying a dc field between the AFM tip and the grounded conductive bottom electrode of the sample. In the second case, the use of a (1 1 0)Pt electrode instead of a (1 0 0)Pt electrode leads to preferentially (1 1 6) SBN oriented films, inducing far better ferroelectrics properties. In spite of a weak remnant polarization, the surface shows an homogeneous polarization when a 1  μm×1  μm area is probed after the reversal of the polarization by the AFM tip.
Keywords: SBN; Atomic force microscope; Hysteresis loops; Ferroelectric domains; Thin films;

Laser assisted surface microstructuring of Me/ZrO2 bilayered thin film system by K. Starbova; E. Krumov; M. Radoeva; N. Starbov; D. Popov; G. Schlaghecken; E.W. Kreutz (118-124).
A novel method for microstructuring of metal/zirconia (ZrO2) bilayered thin film system based on a combination of pulsed laser irradiation and electroless metal plating is presented. Electron beam and conventional thermal evaporation techniques are applied for consecutive deposition of ZrO2 and Bi, Sb or Ag on clean glass substrates. The samples are subjected to excimer or Nd:YAG laser radiation through suitable metal masks in order to evaporate or ablate the top metal film and the remaining non-irradiated areas are further processed in copper electroless chemical bath. All processing stages are studied by secondary electron imaging and various analytical techniques. Possibilities for microstructuring of Me/ZrO2 system and selective deposition of bright electroconductive Cu coating in non-irradiated areas are shown.
Keywords: Metal/zirconia bilayered thin films; Laser modification; Electroless metal plating; Microstructuring;

Effect of ruthenium cluster on the photoluminescence of chemically derivatized porous silicon by Rabah Boukherroub; Davit Zargarian; Christian Reber; David J. Lockwood; Arthur J. Carty; Danial D.M. Wayner (125-133).
A green photoluminescent triruthenium cluster (I) has been chemisorbed on highly luminescent porous silicon (PSi) layers, either freshly prepared or chemically modified with 1-decene, ethyl undecylenate, or undecylenic acid, in order to study the influence of the cluster on the photoluminescence (PL) arising from the PSi. Immersing the hydrogen-terminated PSi in a hexane solution of (I) for several days at room temperature led to the quenching of PL arising from PSi; the only PL detected was due to the Ru cluster (I). A complete quenching of the PL due to PSi was also observed when derivatized PSi surfaces were exposed to the same solution of (I); in these cases, the PL of (I) also shifted to lower energies. Both the quenching of the PL arising from the PSi layers and the shift in the PL of the cluster (I) are likely due to the difference in the chemical interaction of the PO moiety and the CO groups of the Ru cluster with the terminal functional group of the organic monolayer.
Keywords: Porous silicon; Chemical modifications; Organic monolayer; Photoluminescence; Ruthenium cluster;

Decomposition of N2O in a microwave-absorbent assisted discharge of N2 at atmospheric pressure by Masaharu Tsuji; Jun Kumagae; Kousuke Nakano; Toshinori Matsuzaki; Takeshi Tsuji (134-148).
The decomposition of N2O has been studied in a microwave-absorbent assisted discharge of N2 at atmospheric pressure. Although discharge could not be maintained without using microwave absorbents, stable discharge could be maintained by using two rods type of Zr or W absorbents. The maximum conversion of N2O was ≥97% at a microwave power of 150–200 W and a distance of 10 mm between the rods. The decomposition mechanisms of N2O in the gas phase and on the hot surfaces of absorbents were discussed on the basis of mass spectroscopic data of products and optical spectroscopic analysis of discharge spectra. The best conversion of O atom in N2O into O2 was obtained by using Zr rods at the longest distance of 10 mm between the rods and the highest high N2 flow rate of 1000 sccm.
Keywords: N2O removal; Microwave discharge; Microwave absorbent; Optical emission spectroscopy;

In this work, the influence of the ambient gas (He, Ne, N2, air, Ar and Kr) on the mechanisms of particle formation and deposition in laser micromachining of Al2O3–TiC ceramics using pulsed 193 and 248 nm radiation was investigated. Two kinds of particles redeposited around the processed area could be identified: ultrafine particles, of a few tens of nanometers (debris), which aggregate upon redeposition to form a continuous film; and larger particles, with a diameter of 0.5–8 μm (particulates), which remained individualised. The behaviour of debris follows blast wave theory predictions, indicating that this type of particles results from collisions behind the ablation plume front. The particulates are formed above a threshold laser fluence, which decreases with increasing ambient gas atomic/molecular weight and pressure. This threshold is lower for 193 than for 248 nm radiation, but shows the same dependence on the atmosphere for both wavelengths. Experimental evidence and theoretical analysis suggest that the particulates result from ejection of droplets from growing protuberances on the irradiated surface, due to the recoil pressure produced by the plume.
Keywords: Laser ablation; Al2O3–TiC; Debris; Particulates;

Determination of correct composition in nickel–phosphorus films by XPS angle resolved technique by V Sirtori; L Lombardi; P.L Cavallotti; L Magagnin (163-169).
Surface sputtering is a commonly used technique for surface analysis. The standard method of Ar+ sputtering was found to produce surface changes or damages. In this work, nickel–phosphorus films are characterized by X-ray photoelectron spectroscopy (XPS) angle resolved technique before and after sputtering. A method is presented to determine the correct atomic ratio between Ni and P in the surface layers, taking into account that nickel atoms are mainly displaced toward inner layers, as a consequence of 4–5 at.% argon ion implantation within top 1.5–3.7 nm from the surface. The experimental argon implantation and nickel displacement ranges match with Lindhard–Scharff model. Metallic nickel formation in the first layer is detected after sputtering by X-ray diffractometry at low glancing angle. No detectable difference was found between the binding energy of nickel in the metallic state and in the Ni–P coating, showing a similar chemical state for nickel in both conditions.
Keywords: Nickel; Phosphorus; X-ray photoelectron spectroscopy; Sputtering; Ion implantation;

Laser ablation of pure copper was performed using a pulsed Nd:YAG laser operating at 355 nm in air. Oxide nanoparticles redeposited near the edge of the crater results in the formation of the halo. Chemical states in both crater and halo were measured by X-ray photoelectron spectroscopy (XPS). After UV laser ablation, there are an obvious shoulder around 934.4 eV and a shake up satellite around 942.5 eV for the Cu 2p3/2 spectra in both crater and halo. Deconvoluting the Cu 2p3/2 spectra, a component was detected at 933.7 eV corresponding to CuO in both crater and halo as expected. Also, another component at 935.1 eV can be assigned to Cu(OH)2. The formation of CuO and Cu(OH)2 is probably due to the reactions of copper with O2 and water vapor in air. This suggest that the ablation atmosphere plays an important role for the formation of chemical species in both crater and halo. Moreover, an enhanced oxidation in the halo was found at higher fluence: the FWHM of the Cu 2p3/2 spectra and the peak areas of CuO and Cu(OH)2 were significantly higher than those in the crater. This is probably due to the formation of the laser-induced plasma. In addition, peak areas of CuO and Cu(OH)2 in the halo markedly increase with increasing the laser fluence.
Keywords: UV laser ablation; Copper; Chemical state; X-ray photoelectron spectroscopy (XPS);

Electrical conductivity of conductive carbon blacks: influence of surface chemistry and topology by Dana Pantea; Hans Darmstadt; Serge Kaliaguine; Christian Roy (181-193).
Conductive carbon blacks from different manufacturers were studied in order to obtain some insight into the relation between their electrical conductivity and their surface properties. The surface chemistry was studied by X-ray photoelectron spectroscopy (XPS) and static secondary ion mass spectroscopy (SIMS), whereas the topology of the carbon black surface was investigated using low-pressure nitrogen adsorption. All these techniques yield information on the graphitic character of the surface. In general, the electrical conductivity of the conductive blacks increases with the graphitic character of the surface. For low surface area conductive blacks, the electrical conductivity correlates well with the surface chemistry. In the case of the XPS and SIMS data, this correlation is also valid when other types of carbon blacks such as thermal and furnace blacks are included, confirming the determining influence of the carbon black surface chemistry on the electrical conductivity.
Keywords: Carbon black; Electrical conductivity; XPS; SIMS; Gas adsorption;

Sintering: the role of interface energies by Douglas Gouvêa; Ricardo H.R Castro (194-201).
Sintering has been recognized as a complex evolution of microstructure during thermal treatments. The densification in such process is usually attributed to diffusion parameters, i.e. certain mass transport mechanisms would promote densification and others would not. In this work, a new model demonstrating that the interface energies are determinant factors in the densification is drawn. Considering that the mass transport mechanism of grain growth is the same as that of pore elimination, and supposing some reasonable hypothesis about the geometric evolution during sintering, densification is related to the dihedral angle of the system. Since the dihedral angle is directly proportional to interface energies, the ratio between grain surface and grain boundary energies determines densification. Good agreement of the numerical predictions with the experimental data was obtained.
Keywords: Sintering; Model; Interface; Energy; Dihedral angle;

Laser ablation of CsI analyzed by delayed extraction by F Fernández-Lima; V.M Collado; C.R Ponciano; L.S Farenzena; E Pedrero; E.F da Silveira (202-209).
Secondary ion emission from polycrystalline CsI irradiated by pulsed-UV laser (337 nm) is analyzed by time-of-flight (TOF) mass spectrometry. Measurements were performed for different laser intensities and for several delayed extraction times (0–200 ns). The TOF peak shape is characterized by a Gaussian-like structure (fast component), followed by a tail (slow component) that is more pronounced when the extraction field is delayed. A thermal-sputtering uni-dimensional model is employed to describe the solid surface and plasma temperatures as a function of time. Heat diffusion, vapor photo-ionization, radiative emission and plume expansion are considered. Within the approximations used, the model predicts reasonable drift velocities of the plume (≈1.4 km s−1) but very high plasma temperatures (≈105  K). The width of the TOF peak fast component allows determination of the plume temperature during its expansion.
Keywords: Laser ablation; Plasma diagnostic; Plasma temperature; TOF; Delayed extraction;

Surface modification of a biomedical poly(ether)urethane by a remote air plasma by J.E. Gray; P.R. Norton; K. Griffiths (210-222).
Plasma modification of polymer surfaces is widely used, but the plasma/polymer interaction is very complex and still not fully understood. In this paper, the interaction of a biomedical poly(ether)urethane with a remote air plasma treatment has been studied. Atomic force microscopy studies show the domain structure of the polymer as well as the absence of any surface roughening due to plasma treatment. Contact angle goniometry shows an improved wettability of the surface after plasma treatment. X-ray photoelectron spectroscopy indicates an increase in CO and CC at the surface, as well as the presence of new functional groups such as alcohols, ketones, aldehydes and imines. There is also evidence that the energy imparted to the polymer during plasma treatment causes surface segregation of polyol segments.
Keywords: Poly(ether)urethane; Plasma; Surface modification; Microdomain; X-ray photoelectron spectroscopy;

In situ spectroscopic and corrosion studies of ultra-thin gradient plasma polymer layers on zinc by Guido Grundmeier; Matthias Brettmann; Petra Thiemann (223-232).
By means of an audio frequency plasma polymerisation ultra-thin gradient plasma polymer layers were deposited on zinc and zinc-coated iron. The aim was to generate an interfacial polymeric layer which bonds to an oxidised metal as well as to a subsequently applied organic coating and acts as an interfacial barrier layer for ions and water. Surface modifications were done in an in situ plasma cell with infrared reflection absorption spectroscopy (IRRAS). The zinc surface was first activated by an oxygen plasma to provide a freshly oxidised and contamination free oxide surface. The intermediate stages of the surface reactions could be revealed. Carbon dioxide molecules as oxidation products adsorbed on the growing zinc oxide and were desorbed at a later stage. An organosilicon plasma polymer was deposited directly on top of the oxide layer from a hexamethyldisilane (HMDS) plasma. Afterwards a cyclohexene (CHEX)/hexamethyldisilane co-plasma polymer was deposited. The top plasma polymer layer was deposited from a pure cyclohexene plasma. The resulting polyethylene-like surface film was subsequently plasma oxidised. This led to a surface with incorporated oxygen containing polar groups. Complementary X-ray photoelectron spectroscopy (XPS) measurements confirmed the vertical gradient in the chemical composition of the layer. The overall thickness of the ultra-thin gradient layers was less than 10 nm.The stability of the gradient layer in corrosive environments was studied by means of the Scanning Kelvin Probe (SKP). A model organic polymer was deposited onto the plasma modified zinc surface and the delamination kinetics were measured as a function of time. The ultra-thin plasma polymer layer led to a significant increase of the corrosion resistance.
Keywords: Plasma oxidation; Plasma polymer; Zinc; Gradient; In situ; Infrared spectroscopy;

Bulk versus surface effects in magnetic thin films obtained by pulsed laser deposition by Monica Sorescu; A Grabias; D Tarabasanu-Mihaila; L Diamandescu (233-238).
In this paper we present a direct comparison between the properties of bulk magnetic systems and those of corresponding thin films obtained by pulsed laser deposition. These are Fe50Co50, Fe3O4, Fe3O4:Co and Fe2O3:Cr. Using X-ray diffraction, transmission and conversion electron Mössbauer spectroscopy, we present results on the bulk and surface hyperfine magnetic fields, site populations and magnetic texture. Our results support an increase in the hyperfine field values at surfaces, a more pronounced out-of-plane magnetic texture in the films, as well as a perfect transfer of stoichiometry and substitution level from target to substrate materials.
Keywords: Mössbauer spectroscopy; Iron oxides; Polycrystalline surfaces; Polycrystalline thin films;

X-ray photoelectron spectroscopy (XPS) results referring to the interface formed upon vapor deposition of Ni atoms on NiO(0 0 1) indicate, that upon annealing the deposited Ni is oxidized forming a NiO overlayer. The oxidation process is activated and becomes very fast above 900 K, resulting in a surface that exhibits identical photoelectron spectrum with the clean substrate. In addition, it was found that during the oxidation process two extra components in the O 1s XPS peak spectra appear, with binding energies above and below the main lattice oxygen peak, manifesting the existence of oxygen atoms carrying charges that deviate from their formal ionic value. Moreover, by molecular dynamics simulations it was found that upon deposition of Ni ions, neighboring O surface atoms become adatoms and combine with the Ni ions forming a series of Ni x O y oxides, most of which eventually coalesce into small NiO islands. Consequently, the lower binding energy component of the O 1s XPS peak may be attributed to intermediate oxides with x>y, while the higher binding energy component to intermediate oxides with x<y.
Keywords: Ionic value; Gas sensors; Transition metal;

The current–voltage (IV) characteristics of Sn/hydrogen-terminated p-type Si Schottky contacts have been measured in the temperature range of 150–400 K. It is shown that the occurrence of a Gaussian distribution of then BHs is responsible for the decrease of the apparent BH Φ b0, increase of the ideality factor n and non-linearity in the activation energy plot at low temperatures. A Φ b0 versus 1/T plot was drawn to obtain evidence of a Gaussian distribution of the BHs, and values of Φ ̄ b0 =1.049  eV and σ 0=0.114 V for the mean BH and zero-bias standard deviation have been obtained from this plot, respectively. Then, a modified ln(I 0/T 2)−q 2 σ 0 2/2k 2 T 2 versus 1/T plot gives Φ ̄ b0 and A as 1.026 eV and 14.60 A cm−2  K−2, respectively. It has been concluded that the temperature dependent IV characteristics of the device can be successfully explained on the basis of a thermionic emission mechanism with Gaussian distribution of the BHs. Furthermore, an average value of −0.247 meV K−1 for the temperature coefficient has been obtained; the value of −0.247 meV K−1 for hydrogen-terminated p-type Si differs from those in the literature due to the termination with hydrogen of the p-Si surface.
Keywords: Schottky contacts; Gaussian distribution; Activation energy;

Control of surface roughness of silicon carbide (SiC) is to maintain or improve the electrical stability of high-power devices. The bias power plays an important role in determining the surface roughness. The surface roughness of SiC films etched in a C2F6 inductively coupled plasma is investigated in two ways: a variation in the bias power at fixed plasma conditions; and a shift in process parameters including radio frequency (rf) source power, pressure, O2 fraction, and gap between the wafer and plasma source. The surface roughness was measured by an atomic force microscopy (AFM). Parameter-induced DC bias was also correlated to the surface roughness. Under high pressure, the surface roughness was strongly correlated to the bias power-induced DC bias for the variation in the source power or the gap. Depending on the pressure, a significant discrepancy in the roughness behavior was observed at fixed or varying plasma conditions. Parameter interactions of practical importance were observed near the plasma source or in the presence of O2 fraction at low pressure. For variations in only the source power, the DC bias was strongly correlated to the surface roughness without regard to the pressure.
Keywords: Plasma etching; Silicon carbide; Surface roughness; DC bias; Atomic force microscopy;

In0.25Ga0.75As films growth on the thin GaAs/AlAs buffer layer on the GaAs(0 0 1) substrate by Z.C Zhang; S.Y Yang; F.Q Zhang; B Xu; Y.P Zeng; Y.H Chen; Z.G Wang (268-274).
Thin GaAs/AlAs and GaAs/GaAs buffer layer structure have been fabricated on the GaAs(0 0 1) substrate. The top GaAs buffer layer is decoupled from the host substrate by introduction of a low temperature thin interlayer (AlAs or GaAs), which was mechanically behaved like the compliant substrate. Four hundred nanometer In0.25Ga0.75As films were grown on these substrates and the traditional substrate directly. Photoluminescence (PL), double-crystal X-ray diffraction (DCXRD) and atomic force microscopy (AFM) measurements were used to estimate the quality of the In0.25Ga0.75As layer and the compliant effects of the low temperature buffer layer. All the measurements shown that the qualities of epilayer have been improved and the substrate have been deteriorated severely. The growth technique of the thin GaAs/AlAs structure was found to be simple but very powerful for heteroepitaxy.
Keywords: Strain; Dislocation; Interfaces; Molecular beam epitaxy; Semiconductor III–V materials;

Simulation of the loading effect by R Knizikevičius (275-280).
The loading effect during plasmochemical etching (PCE) of silicon in a CF4+O2 plasma is considered. The loading effect is considered including homogeneous reactions of generation and recombination of chemically active species. The model of chemical composition of CF4+O2 plasma is related to the model of plasmochemical etching of silicon in CF4+O2 plasma to achieve the goal. Using the proposed model the influence of etchable surface area on concentration of F atoms in the plasma and etching rate was determined. It was found that the loading effect is more pronounced at low O2 content in the feed. At low values of the etchable surface area, conversion of F atoms to the reaction products decreases with the increase of O2 content in the feed.
Keywords: CF4+O2 plasma; Silicon; Loading effect;

Simplified sedimentation process for 3D photonic thick layers/bulk crystals with a stop-band in the visible range by François Bresson; Chii-Chang Chen; Gou-Chung Chi; Yu-Wen Chen (281-288).
Self-organization of nano-size spherical particles in opal-like structures has been demonstrated to be a powerful mean to build three-dimensional (3D) photonic crystal. We here present a simplified sedimentation process leading to photonic crystal layer with a non-absolute bandgap in the visible range. The stacking organization is cross checked directly by classical optical microscopy (COM), atomic force microscopy (AFM) and scanning electron microscopy (SEM), giving a detailed scheme of the short range and long range organization, and indirectly by reflection/transmission spectroscopy for different incidence angles. The results show a very good resonance associated with a low cost deposition technique. The implementation of our method for further application like photonic waveguides is also discussed.
Keywords: Photonic crystals; Self-assembly; Opal; Spectroscopy; Defects;

Creating sub-surface channels in PMMA with ion beam lithography in only one step by Yvan Gonin; Frans Munnik; Frédéric Benninger; Sergueı̈ Mikhaı̈lov (289-293).
Ion beam lithography is a very powerful technique for 3D direct and maskless writing of resist materials. Light high-energy ions, like protons, can be used to structure these materials. For positive photoresist, like PMMA, this is possible because the protons cause chain scissions in the molecules. Afterwards the irradiated area can be developed in a chemical bath. In this paper, we show the realization of sub-surface channels, or microtunnels, which have been fabricated in only one exposure and without cutting or resurfacing the material. Using our Van-de-Graaff accelerator, the resist (PMMA) has been exposed with high-energy protons (2.7 MeV). The range of charged particles in matter is well-defined and depends on the energy. In addition the linear energy transfer is highest at the end of the ion path. Therefore, it is possible to obtain a dose which is sufficient to develop the bottom part of the ion paths but not the top part. Thus, by selecting the energy and the exposure time, a big variety of microtunnels can be realized.
Keywords: PMMA; Ion beam lithography; Microstructure; Micromachining; Sub-surface channel;

To obtain information about the changes in the topography of sample surfaces during weathering, in situ tapping mode atomic force microscopy (TM-AFM) was used for the investigation of the early stages of corrosion of binary copper/zinc (brass) and copper/tin (bronze) alloys. The emphasis of these investigations is to state the shape and lateral distribution of the corrosion products grown within the first 1300 min of weathering. Investigations were carried out in synthetic air with 80% relative humidity (RH) and 80% RH with 250 ppb SO2. While brass shows a homogeneous growth of features forming a surface film during weathering in 80% RH, the features on the bronze surface reveal a higher growth rate of a few sparsely distributed features.
Keywords: Copper; Zinc; Tin; Alloys; AFM; Atmospheric corrosion;

Anticorrosion coatings were produced by spraying pure simple silane compounds, either tetraethoxysilane (TEOS) or tetraphenoxysilane (TPOS), in a preheated furnace on specimens of carbon steel alloy. These specimens were thermally decomposed over various temperature ranges, covering a total temperature range of 20–1050 °C. This temperature range was divided into four sectors. The specific functions of each of these sectors were described as: hydrolysis (20–50 °C), low pyrolysis (50–250 °C), middle pyrolysis (250–750 °C), and high pyrolysis (750–1050 °C). SEM, ultrasonic vibration (USV), plane-cross polarized microscope, micro-hardness tester, XRD, and cyclic voltammography were utilized for analysis of the produced coatings. A comparison study between the anticorrosion coatings produced using TEOS or TPOS was targeted to evaluate two aspects. The first was the microstructure morphologies and corresponding variations of the chemical constituents and textural surfaces of the TEOS and TPOS coating materials at the selected pyrolysis temperature ranges. The second was the property of the TEOS and TPOS anticorrosion coating materials producing minimal decay for electrochemical protection of carbon steel alloy against corrosion under low and high acidic conditions.
Keywords: TEOS; TPOS; Coatings; Hydrolysis; High pyrolysis; Thermal decomposition; Electrochemical process; SEM; USV; XRD; Cyclic voltammogram; Anticorrosion;

Nanosized β-SiC films prepared by a Cat-CVD with negative bias at low substrate temperature by B Wang; Q Zhao; J.C Li; B.B Wang; X.M Song; X.D Yang; H Yan; M Wang (314-318).
Nanosized β-SiC films were grown on negatively biased Si substrates by using a catalytic chemical vapor deposition (Cat-CVD), at the substrate temperature of 300 °C. The characterization data indicates that the grain size of the films is decreased with the increase of the bias, hence revealing the important role of the bias on the growing process of the films. The bias effect on the film structures is attributed to the ion bombardment, which is considered to be beneficial to the enhancement of both flux and energy of active ions induced by the negative bias. As a result, the ion bombardment leads to the increase of the nucleation sites. Combined with the low substrate temperature, it is suggested that the higher nucleation density induces effectively the growth of nanosized grains of the films.
Keywords: Cat-CVD; Nanosized β-SiC films; Negative bias; Ion bombardment;

Implantation of ions produced by the use of high power iodine laser by L Torrisi; S Gammino; A.M Mezzasalma; J Badziak; P Parys; J Wolowski; E Woryna; J Krása; L Láska; M Pfeifer; K Rohlena; F.P Boody (319-331).
The iodine high power Prague Asterix Laser System (PALS), emitting radiation at 438 nm wavelength (3rd-harmonic of a fundamental radiation wavelength equal to 1315 nm), was employed to irradiate in vacuum different metallic targets (Cu, Ag and Ta). The high energy (up to 230 J) short (400 ps) laser pulses produce non-equilibrium plasma expanding mainly along the normal to the target surface. Plasma contains high charge state ions, with maximum charge states of 27+, 36+ and 49+ for Cu, Ag and Ta, respectively.Time-of-flight (TOF) measurements, performed with the use of an electrostatic ion energy analyser (IEA) placed along the target normal, indicate that the maximum recorded ion kinetic energy is higher than 900 keV for Cu and Ag ions and than 5 MeV for Ta.The laser-produced ions have been implanted into different substrates (polymers, C, Al, Si and Ti) placed at different distances and angles with respect to the target normal. In order to investigate an implantation depth, a density profile of implanted ions and an implanted dose, the samples have been analysed by using the 1.7 MeV helium Rutherford backscattering spectrometry (RBS). The energies of the ions determined with the use of the RBS analysis are in a good agreement with the ion energies measured with the use of the IEA.The results are presented and discussed giving a special attention to the potential of the ion implantation method for modifying the chemical and physical properties of the implanted materials.
Keywords: Laser ablation; Ion implantation; Plasma-laser; Time-of-flight;