Applied Surface Science (v.252, #14)

Molecular dynamics simulations incorporating an analytic embedded atom potential have been used to investigate the atomic structure and surface order of the Al vicinal surfaces for the temperature up to 900 K. The relaxation, mean square vibrational amplitude, and structure factor as a function of temperature, and of the terrace width for the p(1 0 0) × (1 1 1) surfaces (2 ≤  p  ≤ 10) are discussed. The obtained structure factor indicates that the anharmonic effect reduces with increasing terrace widths. The decrease of surface energy with increasing terrace width also supports this conclusion.
Keywords: Vicinal surfaces; Molecular dynamics; Anharmonic effect;

Comparative XPS study of surface reduction for nanocrystalline and microcrystalline ceria powder by Limei Qiu; Fen Liu; Liangzhong Zhao; Ying Ma; Jiannian Yao (4931-4935).
Nanoscale materials have attracted great interest because of their distinct properties. By means of XPS, the present work investigated the difference of reduction behavior between nanocrystalline and microcrystalline ceria on condition of Ar+ bombardment or X-ray irradiation. For the first time, the results indicate that the reduction level of Ce4+ to Ce3+ is lower for nanocrystalline ceria than for microcrystalline ceria although the experimental conditions are identical. These differences have been attributed to the differences in the concentration of oxygen vacancies in the bulk and the diffusion ability of oxygen atoms between them. Besides, the key factor for the reduction of ceria produced by X-ray exposure is discussed.
Keywords: Nanocrystalline ceria; Microcrystalline ceria; XPS; Surface reduction; Oxygen vacancy; Oxygen diffusion;

Energy calculation for symmetrical tilt grain boundaries in iron by Jian-Min Zhang; Yu-Hong Huang; Xi-Jun Wu; Ke-Wei Xu (4936-4942).
An atomic study of [0 0 1] symmetrical tilt grain boundary (STGB) in iron has been made with modified analytical embedded atom method (MAEAM). The energies of two rigid-body crystals joined together directly are unrealistically high due to very short distance between atoms near grain boundary (GB) plane in either crystal. For each of 27 (hk  0) GB planes, a relative slide between grains could result in a decrease in GB energy and a minimum value could be obtained at specific translation distance L min/L (hk  0). Three lowest minimum-energies are corresponding to (3 1 0), (5 3 0) and (5 1 0) boundary successively, from minimization of GB energy, these boundaries should be preferable in (hk  0) boundaries. In addition, the minimum energy increases with increasing ∑, but decreases with increasing interplanar spacing.
Keywords: Fe; STGB; GB energy; MAEAM;

Ab initio comparative study of C54 and C49 TiSi2 surfaces by Tao Wang; Soon-Young Oh; Won-Jae Lee; Yong-Jin Kim; Hi-Deok Lee (4943-4950).
A theoretical comparison of C54 and C49 TiSi2 surfaces is presented, using ab initio plane-wave ultrasoft pseudopotential method based on generalized gradient approximation (GGA). The different surface energies of TiSi2 have not only been calculated out, but the preferential formation of C49 phase in solid-state reaction could be explained by smaller surface energies and Poisson's ratio of C49 TiSi2 as well. As for polar C54 TiSi2(1 0 0) and C49 TiSi2(0 1 0) surfaces, the Si termination surfaces are more stable.
Keywords: Ab initio; Silicide; TiSi2; Surface energy;

Adsorption behavior of binary mixed alkanethiol molecules on Au: Scanning tunneling microscope and linear-scan voltammetry investigation by Yong-Kwan Kim; Jae Pil Koo; Chul-Joon Huh; Jeong Sook Ha; Ung Hwan Pi; Sung-Yool Choi; JunHo Kim (4951-4956).
Adsorption behavior of binary mixed alkanethiol molecules of octanethiol (OT) and dodecanethiol (DDT) on Au substrate has been investigated with a variation of molar fraction in solution at room temperature. Linear-scan voltammograms (LSV) taken from the binary mixed self-assembled monolayer (SAM) on Au/Si showed a single reductive desorption peak, continuously shifting with a variation of mixing ratio in solution. Molecule-resolved scanning tunneling microscope (STM) images obtained from the binary SAM on Au/mica showed the phase separation with a few nanometer sized domains. The difference in the chain length between OT and DDT was not large enough to induce the phase separation with much larger domains, which could be well detected by LSV. There was no preferential adsorption of DDT to OT.
Keywords: Binary self-assembled monolayer; Scanning tunneling microscope; Linear-scan voltammetry; Adsorption behavior; Phase separation;

Annealing time effect on Bi-2223 phase development in LFZ and EALFZ grown superconducting fibres by M.F. Carrasco; V.S. Amaral; R.F. Silva; J.M. Vieira; F.M. Costa (4957-4963).
The application of an electrical current during solidification by laser floating zone (LFZ) technique of superconducting fibres of the Bi-Sr-Ca-Cu-O system was recently proposed as a very suitable method to improve crystal alignment. This novel electrical assisted laser floating zone (EALFZ) technique also leads to a strong modification on the phase nature. In the present study, the effect of the annealing time at 860 °C on superconducting properties of Bi2Sr2Ca2Cu4O11 nominal composition fibres was investigated. Two sets of samples, grown by LFZ and EALFZ using an electric current of 150 mA, were annealed at three different times (24, 96 and 192 h). The critical current density values revealed to be strongly dependent on the 2223 phase amount and on crystal orientation. Current application during the solidification process favours the early development of the 2223 phase, while long annealing times are required in the conventional LFZ processed fibre. The highest critical current density was achieved for the EALFZ fibres annealed during 192 h due to the 2223 stoichiometry optimization and decreasing of second phases.
Keywords: BSCCO superconductors; Laser processing; LFZ; EALFZ;

Observed transition from linear to non-linear friction–load behavior using a lateral force microscope by Mark G. Reitsma; Robert G. Cain; Simon Biggs; David W. Smith (4964-4968).
The most commonly observed friction behavior for sliding systems is that described by Amontons laws of friction. In this case, sliding friction is independent of the gross or apparent area of contact between the materials and a linear function of the applied normal load, where the constant of proportionality is called the friction coefficient. However, for dry sliding solids in contact via a single-asperity junction, Amontons (linear) friction–load behavior is not strictly relevant. In experiments measuring sliding friction between a silicon tip and a quartz surface using an atomic force microscope (AFM), a transition from linear to non-linear friction–load behavior has been observed. This is proposed to result from a nanoscale ‘conditioning’ of a multiple-contact tip–surface interface to form a single-asperity contact.
Keywords: Atomic Force Microscope; Contact mechanics; Adhesion; Friction; Wear;

Fabrication of silver nanoparticles ring templated by plasmid DNA by Lanlan Sun; Gang Wei; Yonghai Song; Zhiguo Liu; Li Wang; Zhuang Li (4969-4974).
Silver nanoparticles ring was successfully fabricated by electrostatic assembling 4-aminothiophenol (4-ATP) capped silver nanoparticles on predefined extended circular plasmid pBR322 DNA. The silver nanoparticles ring which was about 1.5 μm in length, and about 2.2 nm in height can be obtained by adjusting the reaction time. The normal Raman scattering spectra reveal that the 4-ATP has contacted with the silver nanoparticles by forming a strong Ag–S bond. The AFM data show that the assembly of 4-ATP capped silver nanoparticles on DNA is ordered.
Keywords: DNA; Electrostatic; Nanoparticle; Ring;

Three kinds of novel corrosion inhibitors, bis-(1,1′-benzotriazoly)-α,ω-succinyldiamide (BSU), bis-(1,1′-benzotriazoly)-α,ω-adipoyldiamide (BAD), and bis-(1,1′-benzotriazoly)-α,ω-azelayldiamide (BAZ) were synthesized and certified by IR and 1H NMR. Their corrosion inhibition effects for copper in 0.5 M H2SO4 were evaluated by weight-loss method. It shows that among the three compounds, only BSU behaves better compared with BTA. The inhibition efficiency (IE) increased with increasing BSU concentration to 85.2% at the 5 × 10−4  M level. Polarization studies showed that BSU suppressed both anodic and cathodic corrosion reactions. The minimum energy conformation of these compounds was obtained by MM2 force field program. The two benzotriazoly moieties in BSU molecule are more parallel than in other compounds. This is benefit to increase the inhibition effects of BSU.
Keywords: Corrosion inhibitors; Copper; Electrochemical impedance spectroscopy; Benzotriazoley dimmers; Polarization curves;

Surface excitation correction of the inelastic mean free path in selected conducting polymers by G. Gergely; M. Menyhard; G.T. Orosz; B. Lesiak; A. Kosinski; A. Jablonski; R. Nowakowski; J. Tóth; D. Varga (4982-4989).
In earlier works, the inelastic mean free path (IMFP) of electrons was determined by elastic peak electron spectroscopy (EPES) using Ni and Ag reference standard samples, but fully neglecting surface excitation. Surface excitation that is characterized by the surface excitation parameter (SEP), and may affect considerably the elastic peak for the sample and the reference material. The SEP parameters of selected conducting polymers (polythiophenes, polyaniline and polyethylene) were determined by EPES using Si and Ge reference samples. Experiments were made with a hemispherical analyzer of energy resolution 100–200 meV in the E  = 0.2–2.0 keV energy range. The composition of the sample surfaces was determined by in situ XPS, their surface roughness by AFM. The experimental SEP parameter data of eight polymer samples were determined by our new procedure, using the formulae of Chen and Werner et al. in the E  = 0.2–2.0 keV energy range. The trial and error procedure is based on the best approach between the experimental and calculated IMFPs, corrected on surface excitation. The improvement in the SEP correction appears in the difference between the corrected and Monte Carlo calculated IMFPs, assuming Gries and Tanuma et al. IMFPs for polymers and standard, respectively. The term describing the improvement by SEP resulted in 50–72% (good correction for five polymers) 24% (poor correction for one polymer), 1–6% (no correction for two polymers). The 100% correction was not achieved, indicating that the difference between experimental and calculated IMFP cannot be entirely explained by surface excitation. Using the SEP data of Si and Ge reference samples based on Chen's and Werner's material parameter values resulted in similar SEP corrections for the polymer samples.
Keywords: Polymers; IMFP; Elastic peak; Surface excitation;

Multilayer films of CdS particles and meso-tetra-(4-trimethylaminophenyl)porphyrin cobalt iodide (CoTAPPI) were fabricated via layer-by-layer self-assembly technique. UV–vis absorption spectra, fluorescence spectra and SEM images were used to compare the differences between the films prepared from freshly synthesized nanoparticles and from aged particles. SEM images show the aged CdS particles and CoTAPPI in the multilayer film, assembling in a linear structure. The mechanism of dipole–dipole interaction was presented to explain linear formation.
Keywords: Aged CdS particles; Meso-tetra-(4-trimethylaminophenyl)porphyrin cobalt iodide; Multilayer films; Linear assemblies; Dipole–dipole interaction;

Fe–N thin films were prepared by dc magnetron sputtering at elevated temperature of 80 °C. The residual stress of the thin film was characterized by means of grazing incidence X-ray diffraction method. The effect of magnetron sputtering parameter on residual stress was investigated. The results indicate that the nitrogen content in working gas has great effects on the residual stress in the Fe–N thin film, and the residual stress increases firstly and then decreases with the increasing of nitrogen content in working gas. Curie temperature measurement shows that tensile residual stress enhances the ferromagnetic–paramagnetic transition temperature of Fe–N thin films under the condition of same phase composition.
Keywords: Residual stress; Curie temperature; Fe–N thin films;

Synthesis of PS colloidal crystal templates and ordered ZnO porous thin films by dip-drawing method by Zhifeng Liu; Zhengguo Jin; Wei Li; Jijun Qiu; Juan Zhao; Xiaoxin Liu (5002-5009).
Polystyrene spheres (PS) were synthesized by an emulsifier-free emulsion polymerization technique and the PS colloidal crystal templates were assembled orderly on clean glass substrates by dip-drawing method from emulsion of PS. Porous ZnO thin films were prepared by filling the ZnO sol into the spaces among the close-packed PS templates and then annealing to remove the PS templates. The effects of ZnO precursor sol concentration and dipping time in sol on the porous structure of the thin films were studied. The results showed an ordered ZnO porous thin film with designed pore size that depended on the sol concentration and PS size could be obtained. And the shrinkage of pore diameter was about 30–43%. X-ray diffraction (XRD) spectra indicated the thin film was wurtzite structure. The transmittance spectrum showed that optical transmittance decreased with the decrease of wavelength, but kept above 80% optical transmittances beyond the wavelength of 550 nm. Optical band gap of the porous ZnO thin film (fired at 500 °C) was 3.22 eV.
Keywords: Porous ZnO thin film; Colloidal crystal template; Polystyrene spheres; Dip-drawing method; Optical transmittance;

In the present work, the formation of compounds associated to the diffusion of reducing elements (Mg, Al and W) to the Ni cap surface of oxide cathode has been studied by a new method. This method used two cathodes, one of them is coated and the other is uncoated, to be in an attach-contact mounted in a dummy tube. Different analytical techniques were used for this study: scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX) and I/V electrical measurements. After oxide cathode plus decomposited and activated, Al and Mg doping elements take place during heating to 810 °C (Ni–Br) under a rich controlled Ba/SrO atmosphere through an acceleration life test.It is shown that the chemical transport occurs mainly by a grain boundary mechanism with significant pile-up of Mg compounds. Al and W show a superficial concentrations and distribution.The dc electrical characteristic shows very strong rectifying behaviour through the M–S junction due to the I/V curves, particularly after 144 h acceleration life time. The characteristics are found to be reversible and reproducible, and viewed a rectification ratio (r) of 100. The calculated ideality factor shows a value of n  = 9.6, which is evidenced to the tunnelling conduction.The theoretical calculation shows that the interface thickness grows to (∼6 μm) after accelerated the cathode to 1896 h.
Keywords: Oxide cathode; Ba and Sr oxides; Electron emission; Electrical properties;

We prepared high quality Au(1 1 1) film on Si wafer through the spin coating and thermal decomposition of a gold ink, spin-coated-and-fired (SCAF) Au film. The X-ray measurements, XRD and pole-figure analysis, showed that the SCAF Au film has a (1 1 1) out-of-plane orientation with a random in-plane orientation. In order to confirm the chemical activity of the SCAF Au film, we demonstrate the formation of patterned structures with the film by using soft lithography technique. The chemical activities of this physically stable SCAF Au film to the alkanethiols were at least equivalent those of physically deposited the Au films. The possibility of the mass production of micro patterned structure with the SCAF Au film was also demonstrated over the wide region on Si wafer by the microcontact lithography. These suggest that the Au film will help the easy fabrication of various nanosized devices on Si wafer and other substrates.
Keywords: Au(1 1 1); SAM; Microcontact printing; Pole figure; Spin coating; Contact angle;

Nd-YAG laser surface treatment was conducted on 7075-T651 aluminum alloy with the aim of improving the stress corrosion cracking resistance of the alloy. Laser surface treatment was performed under two different gas environments, air and nitrogen. After the laser treatment, coarse constituent particles were removed and fine cellular/dendritic structures had formed. In addition, for the N2-treated specimen, an AlN phase was detected. The results of the stress corrosion test showed that after 30 days of immersion, the untreated specimen had been severely attacked by corrosion, with intergranular cracks having formed along the planar grain boundaries of the specimen. For the air-treated specimen, some relatively long stress corrosion cracks and a small number of relatively large corrosion pits were found. The cracks mainly followed the interdendritic boundaries; the fusion boundary was found to be acting as an arrestor to corrosion attacks. In contrast, only few short stress corrosion cracks appeared in the N2-treated specimen, indicating an improvement in corrosion initiation resistance. The superior corrosion resistance was attributed to the formation of the AlN phase in the surface of the laser-melted layer, which is an electrical insulator. The electrochemical impedance measurements taken during the stress corrosion test showed that the film resistance of the laser-treated specimens was always higher than that of the untreated specimen, with the N2-treated specimen showing the highest resistance.
Keywords: Laser surface melting; Aluminum alloy; Stress corrosion;

Hypervelocity impact resistance of reinforced carbon–carbon/carbon–foam thermal protection systems by M. Grujicic; B. Pandurangan; C.L. Zhao; S.B. Biggers; D.R. Morgan (5035-5050).
Common aero vehicles (CAVs) are aerodynamically designed, (from orbit) re-entry, un-powered military vehicles planned to be used for deployment of the desired munitions with increased accuracy and range. In one of the currently considered designs of the CAVs, their outer skin is planned to be constructed from two-ply panels. The outer play is made of a carbon–carbon composite while the inner ply is constructed from a carbon-based foam. In the present work a transient non-linear-dynamics-based analysis is carried out in order to predict the extent of damage and the probability for failure of the carbon–carbon/carbon–foam CAV panels during potential hypervelocity impact of space debris with the outer surface of the CAVs. The results obtained show that the extent of damage scales with the normal component of the momentum associated with the debris particles just before the impact. In addition, it is found that despite its relatively low strength, the carbon–foam can provide a major increase in the resistance of the CAV panels towards penetration of the hypervelocity debris particles. This finding has been linked with an attendant consolidation of the foam, the process that is capable of absorbing a substantial amount of kinetic energy carried by the debris particles.
Keywords: AUTODYN-3D; Hypervelocity impact; Space debris; CAV; TPS; CFOAM®;

Highly (0 0 2)-oriented Zn0.8Cd0.2O crystal films were prepared on different substrates, namely, glass, Si(1 1 1) and α-Al2O3(0 0 1) wafers by the dc reactive magnetron sputtering technique. The Zn0.8Cd0.2O/α-Al2O3 film has the best crystal quality with a FWHM of (0 0 2) peak of 0.3700°, an average grain size of about 200 nm and a root-mean-square surface roughness of about 70 nm; yet the Zn0.8Cd0.2O/glass holds the worst crystal quality with a much larger FWHM of 0.6281°. SIMS depth profile shows that the Zn and O compositions change little along the film depth direction; the Cd incorporation also almost holds the line towards the top surface other than an accumulation at the interface between the film and the substrate. The Cd content in the film is nearly consistent with that in target.
Keywords: Zn1−x Cd x O films; Substrate; dc sputtering;

A series of Zr–Si–N composite films with different Si contents were synthesized in an Ar and N2 mixture atmosphere by the bi-target reactive magnetron sputtering method. These films’ composition, microstructure and mechanical properties were characterized by energy dispersive spectroscopy, X-ray diffraction, scanning electron microscopy, atomic force microscopy and nanoindentation. Experimental results revealed that after the addition of silicon, Si3N4 interfacial phase formed on the surface of ZrN grains and prevented them from growing up. Zr–Si–N composite films were strengthened at low Si content with the hardness and elastic modulus reaching their maximum values of 29.8 and 352 GPa at 6.2 at% Si, respectively. With a further increase of Si content, the crystalline Zr–Si–N films gradually transformed into amorphous, accompanied with a remarkable fall of films’ mechanical properties. This limited enhancement of mechanical properties in the Zr–Si–N films may be due to the low wettability of Si3N4 on the surface of ZrN grains.
Keywords: Zr–Si–N composite film; Reactive magnetron sputtering; Microstructure; Mechanical properties;

Calcia-doped ceria is of potential interest as an ultraviolet (UV) radiation blocking material in personal care products because of the excellent UV light absorption property and low catalytic ability for the oxidation of organic materials superior to undoped ceria. In order to reduce the oxidation catalytic activity further, calcia-doped ceria was coated with amorphous silica by means of seeded polymerization technique. Generally, nanoparticles of inorganic materials do not provide a good coverage for human skin because of the agglomeration of the particles. The platy particles are required to enhance the covering ability of inorganic materials. This can be accomplished by synthesis of calcia-doped ceria/mica nanocomposite with subsequent silica coating to control catalytic activity of calcia-doped ceria. Calcia-doped ceria/mica nanocomposite was prepared by soft solution chemical method followed by silica coating via seeded polymerization technique. Silica coated calcia-doped ceria/mica nanocomposite was characterized by X-ray diffraction, SEM, TEM, XPS and FT-IR.
Keywords: Ceria; Calcia doping; Silica coating; UV shielding; Platy particle;

Reduction of sidewall roughness in silicon-on-insulator rib waveguides by F. Gao; Y. Wang; G. Cao; X. Jia; F. Zhang (5071-5075).
Silicon-on-insulator (SOI) rib waveguides with residual sidewall roughness were achieved through inductive coupled plasma reactive ion etching (ICPRIE) process. Sidewall roughness is the dominant scattering loss source. Conventional ICPRIE could result in the sidewall ripples derived from the etch/deposition cycle steps. Mixed ICPRIE process and hydrogen annealing were used to improve the sidewall roughness of SOI rib waveguides and eliminate the sidewall ripples. Scan electron microscope and atomic force microscope were used to demonstrate the surface profiles of the sidewall. The results indicated that the sidewall roughness could be low down to 0.3 nm level by optimization and combination of these two techniques and the ripples disappeared. According to the scattering theory developed by Payne and Lacey, the scattering loss could be reduced to below 0.01 dB/cm.
Keywords: Silicon-on-insulator (SOI); Sidewall roughness; Inductive coupled plasma reactive ion etching (ICPRIE); Scattering loss;

The paper studies surface modification of medical poly(vinyl chloride) (PVC) by remote argon plasma and characterized surface structure, performance of treated PVC by the water contact angle measurement, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Results show that the remote argon plasma makes the surface of the PVC film higher hydrophilic than the direct argon plasma and does not give remarkable degradation on the PVC film surface. The hydrophilicity depends on sample position as well as the RF power and the plasma exposure time. The remote argon plasma contributes more effectively to the dechlorination (Cl/C = 0.01) from the PVC film than the direct argon plasmas (Cl/C = 0.03) and more effectively to the formation oxygen functionalities on the PVC film surface. These experimental results show the possibility that remote argon plasma treatment can enhance interaction reactions with argon radicals relative to those with electron and argon ions.
Keywords: Remote argon plasma; PVC; Surface modification; XPS; SEM;

Surface morphology of metal films deposited on mica at various temperatures observed by atomic force microscopy by Morihide Higo; Katsuya Fujita; Yuya Tanaka; Masaru Mitsushio; Toshifumi Yoshidome (5083-5099).
Thin films of eight metals with a thickness of 150 nm were deposited on mica substrates by thermal evaporation at various temperatures in a high vacuum. The surface morphology of the metal films was observed by atomic force microscopy (AFM) and the images were characterized quantitatively by a roughness analysis and a bearing analysis (surface height analysis). The films of Au, Ag, Cu, and Al with the high melting points were prepared at homologous temperatures T/T m  = 0.22–0.32, 0.40, and 0.56. The films of In, Sn, Bi, and Pb with the low melting points were prepared at T/T m  = 0.55–0.70, where T and T m are the absolute temperatures of the mica substrate and the melting point of the metal, respectively. The surface morphology of these metal films was studied based on a structure zone model. The film surfaces of Au, Ag, and Cu prepared at the low temperatures (T/T m  = 0.22–0.24) consist of small round grains with diameters of 30–60 nm and heights of 2–7 nm. The surface heights of these metal films distribute randomly around the surface height at 0 nm and the morphology is caused by self-shadowing during the deposition. The grain size becomes large due to surface diffusion of adatoms and the film surfaces have individual characteristic morphology and roughnesses as T increases. The surface of the Al film becomes very smooth as T increases and the atomically smooth surface is obtained at T/T m  = 0.56–0.67 (250–350 °C). On the other hand, the atomically smooth surface of the Au film is obtained at T/T m  = 0.56 (473 ± 3 °C). The films of In, Sn, Bi, and Pb prepared at T/T m  = 0.55–0.70 also show the individual characteristic surface morphology.
Keywords: Thermal evaporation; Metal films; Surface morphology; Atomic force microscopy; Structure zone model;

Chemical dissolution of the barrier layer of porous oxide films formed on aluminum foil (99.5% purity) in the 4% phosphoric acid after immersion in 2 mol dm−3 sulphuric acid at 50 °C has been studied. The barrier layer thickness before and after dissolution was determined using a re-anodizing technique. A digital voltmeter with a computer system was used to record the change in the anode potential with re-anodizing time. It has been found that the barrier layer material may consist of two or three regions according to the dissolution rate. The barrier oxide contains two layers at 35 V: the outer layer with the highest dissolution rate and the inner layer with low dissolution rate. The barrier oxide contains three layers at 40 V and above it: the outer layer with high dissolution rate, the middle layer with the highest dissolution rate and the inner layer with low dissolution rate. It has been shown that there is a dependence of the dissolution rate on the surface charge of anodic oxide film. Annealing of porous alumina films for 1 h at 200 °C leads to disappearance of layers with different dissolution rates in the barrier oxide. We explained this phenomenon by the absence of the space charge in the barrier oxide of such films.
Keywords: Porous alumina; Barrier oxide layer; Immobile space charge; Annealing; Dissolution rate; Re-anodizing;

Femtosecond laser-induced damage in reflector by Haiyi Sun; Tianqing Jia; Xiaoxi Li; Chengbin Li; Donghai Feng; Shizhen Xu; Xiaochun Ge; Zhizhan Xu (5109-5115).
We have investigated the damage for ZrO2/SiO2 800 nm 45° high-reflection mirror with femtosecond pulses. The damage morphologies and the evolution of ablation crater depths with laser fluences are dramatically different from that with pulse longer than a few tens of picoseconds. The ablation in multilayers occurs layer by layer, and not continuously as in the case of bulk single crystalline or amorphous materials. The weak point in damage is the interface between two layers. We also report its single-short damage thresholds for pulse durations ranging from 50 to 900 fs, which departs from the diffusion-dominated τ P 1 / 2 scaling. A developed avalanche model, including the production of conduction band electrons (CBE) and laser energy deposition, is applied to study the damage mechanisms. The theoretical results agree well with our measurements.
Keywords: 45° high-reflection mirror; Femtosecond laser; Damage threshold; Ablation depth;

Photoemission studies of oxygen adsorbed on a LiAl(1 1 0) alloy surface: Role of Li segregation by D. Lee; H.G. Lee; C. Hwang; J.Y. Maeng; S. Kim; K.-J. Kim; B. Kim (5116-5123).
We investigated that the effect of the number of segregated Li atoms on the rate of oxidation on a LiAl alloy surface. Oxygen molecules adsorbed on the LiAl alloy react with the surface atoms to form stable oxides. The segregated Li atoms at reconstructed surfaces ( c ( 2 × 2 ) and ( 2 × 1 )) enhance the oxidation rate and form stable LiAlO x and Li 2 O . The degree of enhancement of oxidation by segregated Li atoms varies as a function of O 2 exposure and annealing temperature, where the latter is directly related to the mode of surface reconstruction by Li segregation.
Keywords: Li segregation; Synchrotron; Photoemission spectroscopy;

The hydrogen content in a-Si1−x Ge x :H thin films is an important factor deciding the density and the optical band gap. We measured the elemental depth profiles of hydrogen together with Si and Ge by elastic recoil detection analysis (ERDA) combined with Rutherford backscattering (RBS) using MeV He2+ ions. In order to determine the hydrogen depth profiles precisely, the energy- and angle-dependent recoil cross-sections were measured in advance for the standard sample of a CH3 +-implanted Si substrate. The cross-sections obtained here are reproduced well by a simple expression based on the partial wave analysis assuming a square well potential (width: r 0  = 2.67 × 10−13  cm, depth: V 0  = −36.9 MeV) within 1%. For the a-Si1−x Ge x :H films whose elemental compositions were determined by ERDA/RBS, we measured the secondary ions yields of HCs2 +, SiCs2 +, H, Si and Ge as a function of Ge concentration x. As a result, it is found that the useful yield ratios of HCs2 +/SiCs2 +, H/Si and Ge/Si are almost constant and thus the elemental depth profiles of the a-Si1−x Ge x :H films can be also determined by secondary ion mass spectrometry (SIMS) within 10% free from a matrix effect.
Keywords: SiGe; ERDA; RBS; SIMS; Hydrogen;

Variations in the structural, optical and electrochemical properties of CeO2–TiO2 films as a function of TiO2 content by Amita Verma; Amish G. Joshi; A.K. Bakhshi; S.M. Shivaprasad; S.A. Agnihotry (5131-5142).
Alcohol based sols of cerium chloride (CeCl3·7H2O) and titanium propoxide (Ti(OPr)4) in ethanol mixed in different mole ratios have yielded mixed oxide films on densification at 500 °C. The reversibility of the intercalation/deintercalation reactions has shown electrochemical stability of the films. Addition of TiO2 in an equivalent mole ratio manifests in producing highly transparent films with appreciable ion storage capacity. The electrochemical studies have revealed the significant role of TiO2 in controlling the ion storage capacity of the films, as it tends to induce the disorder. In addition, the films prepared from an aged sol are observed to exhibit a much higher ion storage capacity than the films deposited using the as-prepared sol. The X-ray photoelectron spectroscopic studies have provided information on the variation of Ce4+/Ce3+ ratio as a function of increased TiO2 content in the films. This study has led to a better understanding of the increased ion storage capacity with the increased TiO2 proportion. The transmission electron microscopic study has demonstrated the presence of CeO2 nanograins even in films, which are amorphous to X-rays. Elucidation of the structural, optical and electrochemical features of the films has yielded information on aspects relevant to their usage in transmissive electrochromic devices. The films have been found to exhibit properties that can find application as counter electrode in electrochromic smart windows in which they are able to retain their transparency under charge insertion, high enough for practical uses. Also, the fastest coloration–bleaching kinetics for the primary electrochromic electrode (WO3) working in combination with Ce/Ti (1:1) electrode stimulates the use of latter in electrochromic windows (ECWs).
Keywords: Sol–gel; Spin coating; CeO2–TiO2; Passive counter electrode; Electrochromism;

Large-scale synthesis and characterization of SiC nanowires by high-frequency induction heating by Wei Min Zhou; Bin Yang; Zhong Xue Yang; Feng Zhu; Li Jun Yan; Ya Fei Zhang (5143-5148).
SiC nanowires were synthesized in large quantity by heating SiO and activated carbon fibers without metal catalysts. The morphologies of product were studied by SEM and TEM and it indicated that the SiC nanowires obtained at the bottom of the activated carbon fibers surfaces were coated by an amorphous silicon oxide layer and the core of SiC nanowires were measured, typically as about 8–20 nm in diameter, while in situ formed nanotree-bud network, Y-junction and the “S” shape nanostructure were observed in those SiC nanowires obtained at the up of the activated carbon fibers surfaces. These SiC/SiO2 heterostructure, particularly novel 2-D heterostructure, would be expected as important blocks in building nanodevices and as reinforcement in advanced composites.
Keywords: High-frequency induction heating; Silicon carbide; Heterostructure; Morphology;

Conductive-tip atomic force microscope (c-AFM) has been extensively used in measuring electrical properties of surface nanostructures, but the electrical conduction in c-AFM tip–sample contacts in nanometer scale is not well understood. In the present work, we experimentally investigated the electrical properties of the nanocontact between a W2C-coated c-AFM tip and granular gold film under small-load (∼5 nN) at ambient air conditions. We found that under a constant bias voltage (10 V), the electrical current passing through the tip–sample junction at fixed location of sample surface dramatically fluctuated and degenerated. By quantitatively estimating the mechanical and electrical aspects of the nanocontact, we explained the observed phenomena as mechanical instabilities, electron tunneling transport and atomic rearrangements at the contact junction. We think that our results are important for the realistic application of c-AFM in nanoelectronic measurement.
Keywords: Atomic force microscope (AFM); Conductive-tip; Nanocontact; Conductance fluctuation and degeneracy;

Synthesis and surface characterization of alkylthioacetyl-capped self-assembled monolayers on gold surface by Abdiaziz A. Farah; Raluca Voicu; Raluca Barjovanu; Farid Bensebaa; Kidus Tufa; Karim Faid (5158-5167).
A novel alkylthioacetyl-capped hydroxyethyl methacrylate monomer and its corresponding homopolymer have been synthesized and characterized. Direct chemisorption of these moieties have been carried out on gold-coated substrate and found to form a strong surface bonding. The surface coverage and the properties of the resultant self-assembled layers have been investigated by multiple surface characterization techniques (i.e. ellipsometry, GA-FTIR, XPS, AFM, and contact angle measurements). These analyses have all confirmed the occurrence of complete chemisorption reactions with typical n-alkanethiol self-assembled characteristics.
Keywords: Acetyl-capped thiol monomer; XPS; Surface functionality; AFM; Self-assembled monolayer; GA-FTIR;

Surface and interfacial properties of PVDF/acrylic copolymer blends before and after UV exposure by X. Gu; C.A. Michaels; D. Nguyen; Y.C. Jean; J.W. Martin; T. Nguyen (5168-5181).
Morphological and chemical properties of both the surface and interface of poly(vinylidene fluoride)/poly(methyl methacrylate)-co-poly(ethyl acrylate) (PVDF/PMMA-co-PEA) blend films have been investigated before and after the samples were exposed to ultraviolet (UV) irradiation using a xenon arc lamp at 50 °C and 9% relative humidity (RH) for 7 months. Surface and interfacial morphologies were studied by atomic force microscopy (AFM). Chemical composition information was obtained by confocal Raman microscopy, attenuated total reflection-FTIR spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), and contact angle measurements. Results show an enrichment of the PVDF material at the air surface, while the acrylic copolymer enriches the interface. Blends having greater than 50% mass fraction of PVDF show little change in the surface morphology after UV exposure for 7 months. However, for a lower PVDF content, blends exhibit significant degradation of PMMA-co-PEA copolymer and a much rougher surface after UV exposure. Microstructural changes in the PVDF spherulites are also observed after UV degradation. It is found that the surface and interfacial morphologies are correlated with the chemical properties.
Keywords: Surface; Interface; PVDF/acrylic copolymer; AFM; UV degradation;

Three quantitative methods, namely profilometry, high speed imaging and recoil momentum measurements using a ballistic pendulum, are used to determine the interplay of vaporization, melt displacement and melt ejection on nanosecond laser induced material removal. At low to moderate fluences (<7 J cm−2) material removal occurs via vaporization and melt displacement in aluminium. At high fluences (>7 J cm−2), material removal occurs predominantly via the explosive ejection of liquid droplets from the melt pool.
Keywords: Nanosecond laser; Laser ablation; Vaporization; Melt displacements; Melt ejection;

The influence of chemical treatment and thermal annealing on Al x Ga1−x N surfaces: An XPS study by B. Boudjelida; M.C. Simmonds; I. Gee; S.A. Clark (5189-5196).
The influences of chemical treatment and thermal annealing of Al x Ga1−x N (x  = 0.20) have been investigated by X-ray photoelectron spectroscopy (XPS). XPS analysis showed that successive chemical treatments and annealing produced changes in the stoichiometry of the Al x Ga1−x N surface, with the surface concentration of N increasing and Al and Ga decreasing with increasing temperature. Band bending occurred at the Al x Ga1−x N surface, in parallel with the observed changes in stoichiometry. These results are discussed in the context of the creation of surface states via the activation of vacancies and induced by defects. These findings point towards the possibility of selecting and/or engineering the band structure at Al x Ga1−x N surfaces through a combination of surface preparation and annealing.
Keywords: AlGaN; Surface; Fermi level pinning; Annealing;

Formation of biaxial texture in metal films by selective ion beam etching by S.J. Park; D.P. Norton; Venkat Selvamanickam (5197-5206).
The formation of in-plane texture via ion bombardment of uniaxially textured metal films was investigated. In particular, selective grain Ar ion beam etching of uniaxially textured (0 0 1) Ni was used to achieve in-plane aligned Ni grains. Unlike conventional ion beam assisted deposition, the ion beam irradiates the uniaxially textured film surface with no impinging deposition flux. The initial uniaxial texture is established via surface energy minimization with no ion irradiation. Within this sequential texturing method, in-plane grain alignment is driven by selective etching and grain overgrowth. Biaxial texture was achieved for ion beam irradiation at elevated temperature.
Keywords: Ion beam etching; Biaxial texture; Crystalline films; Thin film;

Analysis of energy and force of Pt adatom on Pt (0 0 1) surface by MAEAM by Jian-Min Zhang; Yu Shu; Ke-Wei Xu (5207-5214).
The energy and perpendicular force of a Pt adatom on Pt (0 0 1) surface have been calculated by MAEAM. With increasing the distance of the adatom from the surface, the energy and force maps can be classified into four regions: repulsive region, transformed region, strongly attractive region and weakly attractive region. In repulsive region, the maximum (minimum) values of the energy and repulsive force appear on the top (hole) of the first layer atoms of Pt (0 0 1) surface due to stronger pair-potential interaction. In other regions, the energy and force maps are more complicated than those in repulsive region due to the effects of the many body interactions and nonspherical distribution of the electrons of the atoms in crystal. The most stable position is 0.1664 nm above the hole of the first layer atoms for a Pt adatom on Pt (0 0 1) surface.
Keywords: Metal surface; Adsorption; Energy; Force; MAEAM;

Superhard Nb–Si–N composite films synthesized by reactive magnetron sputtering by Yunshan Dong; Yan Liu; Jiawei Dai; Geyang Li (5215-5219).
By means of the reactive magnetron sputtering method, a series of Nb–Si–N composite films with different Si contents were deposited in an Ar, N2 and SiH4 mixture atmosphere. These films’ chemical composition, phase formation, microstructure and mechanical properties were characterized by the energy dispersive spectroscopy, X-ray diffraction, transmission electron microcopy, atomic force microscopy and nanoindentation. The experimental results showed that the silicon content in the Nb–Si–N composite films can be conveniently controlled by adjusting the SiH4 partial pressure in mixed gas. The hardness and elastic modulus of the Nb–Si–N films were remarkably increased with a small amount of silicon addition and reached their maximum values of 53 and 521 GPa, respectively, at 3.4 at.% Si. Such an obvious enhancement of mechanical properties is related to the increment of crystal defects in the Nb–Si–N films. With silicon content increasing in the films further, the mechanical properties decreased gradually to somewhat a bit lower than those of the NbN film.
Keywords: Nb–Si–N composite film; Reactive magnetron sputtering; Microstructure; Superhardness;

Nanosized Ti―Ni―O catalysts prepared by a modified sol–gel method have been investigated in the oxidative dehydrogenation of propane (ODP) to propene. At 300 °C the yield to propene of 12.1% was obtained on 9.1 wt.% Ti―Ni―O catalyst with the selectivity of 43%. The continued variety of lattice parameter and variation of chemical value of nickel and titanium ion on the surface indicates that there are strong interactions of TiO2 and NiO. The decreased low temperature oxygen desorption and the weaker reducibility seems to be responsible for the decreased activity and enhanced selectivity of propane oxidative dehydrogenation over Ti―Ni―O catalysts.
Keywords: Nanosized; Sol–gel; Oxidative dehydrogenation of propane; Ti―Ni―O;

Surface modification of zinc oxide nanoparticle by PMAA and its dispersion in aqueous system by Erjun Tang; Guoxiang Cheng; Xiaolu Ma; Xingshou Pang; Qiang Zhao (5227-5232).
Commercial zinc oxide nanoparticles were modified by polymethacrylic acid (PMAA) in aqueous system. The hydroxyl groups of nano-ZnO particle surface can interact with carboxyl groups (COO–) of PMAA and form poly(zinc methacrylate) complex on the surface of nano-ZnO. The formation of poly(zinc methacrylate) complex was testified by Fourier-transform infrared spectra (FT-IR). Thermogravimetric analysis (TGA) indicated that PMAA molecules were absorbed or anchored on the surface of nano-ZnO particle, which facilitated to hinder the aggregation of nano-ZnO particles. Through particle size analysis and transmission electron micrograph (TEM) observation, it was found that PMAA enhanced the dispersibility of nano-ZnO particles in water. The dispersion stabilization of modified ZnO nanoparticles in aqueous system was significantly improved due to the introduction of grafted polymer on the surface of nanoparticles. The modification did not alter the crystalline structure of the ZnO nanoparticles according to the X-ray diffraction patterns.
Keywords: ZnO nanoparticles; Surface modification; Polymethacrylic acid; Dispersion stabilization;

To elucidate the thermionic property of polycrystalline surfaces, a further study is made on the mean work functions (φ , φ e and φ +) effective for negative-ionic, electronic and positive-ionic emissions. Comparison between theoretical analyses and experimental data yields the conclusions as follows. (1) The equation of φ  =  φ e holds always with both mono- and polycrystalline surfaces. (2) The relation of φ  =  φ e  <  φ + applies to polycrystalline surfaces because they bear the thermionic contrast (Δφ *  ≡  φ +  −  φ e  > 0). (3) The value of Δφ * ranges from ∼0.4 to 0.9 eV depending upon the surface species of polycrystalline metals (e.g., W, Re and Pt), whilst Δφ *  = 0 for monocrystalline surfaces. (4) When the degree of monocrystallization (δ m) is less than ∼50%, the theoretical value of Δφ * is virtually independent of δ m and agrees well with experimental data, nearly the same within ±0.1 eV among the so-called “polycrystalline” surfaces of W. (5) As δ m increases beyond ∼80 up to 100%, Δφ * decreases rapidly down to 0 eV, showing again a good agreement between theory and experiment. (6) Our theoretical model is valid in evaluating the effective mean work functions, irrespective of the range of δ m.
Keywords: Effective mean work functions; Negative ion emission; Positive ion emission; Monocrystalline surfaces; Monocrystallization degree; Tungsten;