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Applied Surface Science (v.255, #22)

Characterization of self-assembled monolayers (SAMs) on silicon substrate comparative with polymer substrate for Escherichia coli O157:H7 detection by Carmen Moldovan; Carmen Mihailescu; Dana Stan; Lavinia Ruta; Rodica Iosub; Raluca Gavrila; Munizer Purica; Schiopu Vasilica (pp. 8953-8959).

This article presents the characterization of two substrates, silicon and polymer coated with gold, that are functionalized by mixed self-assembled monolayers (SAMs) in order to efficiently immobilize the anti- Escherichia coli O157:H7 polyclonal purified antibody.A biosurface functionalized by SAMs (self-assembled monolayers) technique has been developed. Immobilization of goat anti- E. coli O157:H7 antibody was performed by covalently bonding of thiolate mixed self-assembled monolayers (SAMs) realized on two substrates: polymer coated with gold and silicon coated with gold. The F(ab′)₂ fragments of the antibodies have been used for eliminating nonspecific bindings between the Fc portions of antibodies and the Fc receptor on cells. The properties of the monolayers and the biofilm formatted with attached antibody molecules were analyzed at each step using infrared spectroscopy (FTIR-ATR), atomic force microscopy (AFM), scanning electron microscopy (SEM) and cyclic voltammetry (CV). In our study the gold-coated silicon substrates approach yielded the best results.These experimental results revealed the necessity to investigate each stage of the immobilization process taking into account in the same time the factors that influence the chemistry of the surface and the further interactions as well and also provide a solid basis for further studies aiming at elaborating sensitive and specific immunosensor or a microarray for the detection of E. coli O157:H7.

Keywords: Mixed self-assembled monolayers; Escherichia coli; O157:H7 gold; Immunosensor; FTIR-ATR

Plasma sterilization using the RF glow discharge by Liqing Yang; Jierong Chen; Junling Gao; Yafei Guo (pp. 8960-8964).

In the present work, glow discharge oxygen plasma was used to sterilize the Pseudomonas aeruginosa on the polyethylene terephthalate (PET) sheets. In a self-designed plasma reaction equipment, active species (electron, ion, radical, UV light, etc.) were separated effectively, and the discharge area, afterglow area and remote area were plotted out in the plasma field. Before and after plasma treatment the cell morphology was studied by scanning electron microscopy (SEM). The results showed that after treatment of 30s the germicidal effect is 4.26, 3. 84, 2.61, respectively in the three areas on the following conditions: discharge power was 40W and gas flux was 20cm³/min. SEM results revealed the cell morphology before and after plasma treatment. The walls or cell membrane cracking was testified by determining the content of protein using coomassie light blue technique. The results from electron spin resonance spectroscopy (ESR) and double Langmuir electron probe showed that electron, ion and oxygen free radical played important roles in sterilization in the discharge area, but only oxygen radicals acted to sterilize the bacteria in the afterglow area and the remote area.

Keywords: Glow discharge plasma; Pseudomonas aeruginosa; Germicidal effect; Mechanism

Study of tribochemical decomposition of ionic liquids on a nascent steel surface by Renguo Lu; Shigeyuki Mori; Kimihiro Kobayashi; Hidetaka Nanao (pp. 8965-8971).

Tribological properties and the decomposition process of ionic liquids (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide and 1-dodecyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide) on a nascent surface of bearing steel 52100 were investigated by a ball-on-disk friction tester in a vacuum chamber equipped with a quadrupole mass spectrometer (Q-MS). Ionic liquids exhibited better tribological properties than synthetic hydrocarbon oil (multialkylated cyclopentane (MAC)) in high vacuum conditions. The induction period for decomposition of MAC was about 10km, while no obvious gaseous products were observed for ionic liquids even after a sliding distance of 22km under the same mechanical conditions. The mass spectra indicated that both the anionic and cationic moieties of ionic liquids decomposed on the nascent steel surface during friction processes. The cationic moiety with a longer alkyl chain was more difficult to decompose on the nascent steel surface than that with a shorter alkyl chain. XPS analysis revealed that the tribofilm formed by ionic liquid was mainly composed of FeF₂ and FeS, which deactivated the nascent surface. As a result, desorption rate of gaseous products decreased appreciably comparing with MAC. The critical load for the mechanical activation of the decomposition correspondingly increased from 1.1N of MAC to 8N of ionic liquids.

Keywords: Ionic liquid; Steel; Nascent surface; Boundary lubrication; Tribochemistry; Mass spectrometry; Lubricant decomposition

Stress relaxation induced faceted Cu and W particles on the surfaces of Cu–Zr and W thin films by H.L. Sun; Z.X. Song; F. Ma; K.W. Xu (pp. 8972-8977).

Faceted copper and tungsten particles in submicron-scale were obtained by annealing copper–zirconium thin films on polyimide (PI) substrates as well as in the deposited tungsten films on Si substrates. It was interesting to find that the Cu particles are faceted and seem to be single crystal from their extraordinarily regular appearance. However, it is another case for W particles which are polycrystalline and irregular. Different mechanisms are put forward to elucidate the formation of Cu and W particles according to the morphological characterization, residual stress analysis and their distinct atomic diffusivity.

Keywords: Copper–zirconium film; Tungsten film; Surface morphology; Stress relaxation; Regular particles

Following the evolution of morphology, composition and crystallography of alumina based catalysts after laser ablation: Implications for analysis by LA-ICP-AES by G. Alloncle; N. Gilon; C. Legens; C.-P. Lienemann; B. Rebours; L. Sorbier; S. Morin; R. Revel (pp. 8978-8985).

Fundamental understanding of aerosol formation during laser ablation is important for the development of LA-ICP analysis of complex samples. Using a Lina Spark Atomizer™, the application of this technique to the field of heterogeneous catalysis gave an accuracy of 5–15% while extreme values of +100% could be obtained in some cases. To improve understanding of laser ablation processes, particles generated during ablation of alumina based catalysts were collected and analysed using different microscopy and surface analysis techniques. Morphological study by scanning electron microscopy showed that most of the particles leaving the ablation cell were nanoparticle aggregates generated from vapor condensation. An XRD study of these aerosols revealed that the condensation converge on the formation of a spinel structure with large coherence domains. Elemental composition of the aerosol was also followed and exhibited differences between a catalyst containing large Mo concentration or low Pt concentration.

Keywords: PACS; 52.38.Mf (laser ablation); 81.70.−q (methods of materials testing and analysis)Laser ablation-ICP; Aerosol; Fractionation; Alumina; Catalysts

Role of the MOCVD deposition conditions on physico-chemical properties of tetragonal ZrO₂ thin films by K. Galicka-Fau; C. Legros; M. Andrieux; M. Brunet; J. Szade; G. Garry (pp. 8986-8994).

High-k ZrO₂ thin films suitable for microelectronics applications were deposited by DLI-MOCVD method on planar Si (100) and pores etched in Si (100). The effects of various experimental parameters such as temperature of substrates, injection frequency, concentration of the precursor and oxygen partial pressure in the reactive chamber, were investigated in order to produce a single tetragonal ZrO₂ phase which exhibits, according to the literature, the best permittivity.Taking into account the crystal structure, microstructure and chemistry of the films, the expected phase was successfully deposited for high temperature of substrates, relatively high feeding rate and low oxygen partial pressure. Although the 3D coverage is actually not perfect in high aspect ratio pores, the electric properties of this sample are very promising with permittivity up to 27.

Keywords: DLI-MOCVD; ZrO; ₂; Tetragonal and monoclinic phases; 3D; High aspect ratio pores

Stress distribution and hillock formation in Au/Pd thin films as a function of aging treatment in capacitor applications by S. Nazarpour; O. Jambois; C. Zamani; F. Afshar; A. Cirera (pp. 8995-8999).

Effect of quenching in different media on hillock formation and electrical resistivity has been studied in the Au–Pd layers. Oxygen was released from substrate due to substrate relaxation process. It was suggested that hillocks appear on the triple junction grain boundaries. However, lower electrical resistivity has been seen in the sample which quenched in the air. It was concluded that grain boundary scattering decreases the conductivity of the quenched films due to higher density of dislocations.

Keywords: Hillock formation; Au/Pd thin film; Grain boundary scattering

Modification of polycarbonate surface properties by nano-, micro-, and hierarchical micro–nanostructuring by Inka Saarikoski; Mika Suvanto; Tapani A. Pakkanen (pp. 9000-9005).

Polycarbonate surfaces were patterned with nanopillars, microbumps, or nanopillars superimposed on microbumps. Patterning was achieved by applying nanoporous anodized aluminum oxide (AAO) membranes, microstructured aluminum foil, or anodic alumina on microstructured aluminum as mold inserts in injection molding. The effect of the different-sized structures on properties of the polycarbonate surface was investigated in contact angle measurements with water and oleic acid. The water contact angle increased from 82° on the smooth surface to 139° on the hierarchical micro–nanostructure. The transmittance of the polycarbonate increased with nanopatterning, while the reflection properties of the polycarbonate surface decreased. Reflection was lowest for the nanostructure with 53nm pillar diameter and 77nm interpillar distance. Values ranged from 0.6 to 1.1% over the whole wavelength range of visible light, which was 4–5% units lower than the corresponding values for the smooth polycarbonate.

Keywords: Polycarbonate (PC); Nano- and microstructures; Wettability; Reflection; Transmittance

ZnO:CeO₂-based nanopowders with low catalytic activity as UV absorbers by Juliana Fonseca de Lima; Renata Figueredo Martins; Cláudio Roberto Neri; Osvaldo Antonio Serra (pp. 9006-9009).

Ultrafine systems of zinc oxide and cerium oxide for use as ultraviolet filter were synthesized by a non-alkoxide sol–gel process at different temperatures, to obtain solid materials (40 and 70°C), that were characterized by X-ray diffraction, scanning electron microscopy, UV–vis reflectance. Their catalytic and photocatalytic activities were also evaluated. ZnO:CeO₂ systems present higher UV absorption and transparency in the visible region. The photocatalytic activity of ZnO:CeO₂ systems for the oxidation of organic materials is much smaller than that of titania, ceria and zinc oxide, suggesting that ZnO:CeO₂ systems are promising candidates for use as optical materials in UV-filters.

Keywords: Cerium oxide; Ceria; Zinc oxide; Rare earth; Sunscreen; UV protection

Effect of hydrogen doping in ZnO thin films by pulsed DC magnetron sputtering by Young Ran Park; Juho Kim; Young Sung Kim (pp. 9010-9014).

This study examined the role of hydrogen impurities in highly oriented ZnO thin films. Hydrogen intentionally incorporated was found to play an important role as a donor in n-type conduction, improving the free carrier concentration. The increase in the conductivity of ZnO thin films was attributed to the two centers assigned to isolated hydrogen atoms in the anti-bonding sites as well as bond-centered interstitial hydrogen located between the Zn–O bonds and Zn vacancy passivated by one or two hydrogen atoms. Micro Raman spectroscopy showed two additional modes at approximately 501 and 573cm⁻¹. These two peaks were attributed to damage to the crystal lattice, which could be explained by the optical-phonon branch at the zone boundary and host lattice defects, such as vacancy clusters, respectively.

Keywords: Zinc oxide (ZnO); Hydrogen effect; Film; Shallow donors; FT-IR; Micro Raman

Ordered ultra thin ZnO films on metal substrate by Donghui Guo; Mingshan Xue; Qinlin Guo; Kehui Wu; Jiandong Guo; E.G. Wang (pp. 9015-9019).

Ultra thin ZnO films were prepared on metal Mo(110) substrate under ultrahigh vacuum conditions either by depositing Zn in ∼10⁻⁵Pa oxygen or by oxidizing pre-deposited Zn films. The films were characterized in situ by various surface analytical techniques, including Auger electron spectroscopy, X-ray and ultraviolet photoelectron spectroscopies, low energy electron diffraction and high resolution electron energy loss spectroscopy. The results indicate that a long-range ordered and stoichiometric ZnO films are formed along its [0001] direction. The annealing experiments show that as-prepared ZnO films are thermal stable until 800K. This study provides constructive information to further understand the growth mechanism of ZnO films on different substrates.

Keywords: ZnO thin films; ZnO growth on metal; Surface analysis; Electronic structure

Low resistance dye-sensitized solar cells based on all-titanium substrates using wires and sheets by Hai Wang; Yong Liu; Hong Huang; Minyi Zhong; Hui Shen; Yuanhao Wang; Hongxing Yang (pp. 9020-9025).

Low resistance dye-sensitized solar cells (DSSCs) based on all-titanium substrates were proposed in this paper. To minimize the internal resistance of DSSCs, the titanium wires and titanium sheets were used as the substrates of the photoanode and the counter electrode, respectively. Compared with the FTO substrate, titanium wires could absorb much diffused light by back reflection since the reflectivity in the titanium sheet was highly increased up to 53.12%. Furthermore, the transmittance of the front cover was increased by 13.2% using the super white glass instead of FTO substrate. The thickness of TiO₂ thin film coated on titanium wire was optimized to achieve a high cell performance. The efficiency of 5.6% for the cell was obtained with a J_sc of 15.41mAcm⁻², V_oc of 0.59V, and FF of 0.62. The results showed that the titanium-based DSSCs had superiority for producing the large-scale DSSCs without metal grid line.

Keywords: Dye-sensitized solar cell; All-titanium substrate; TiO; ₂; thin films; Sheet resistance; Counter electrode

Synthesis and photocatalytic oxidation of different organic dyes by using Mn₂O₃/TiO₂ solid solution and visible light by Tanmay K. Ghorai; Susmita Pramanik; Panchanan Pramanik (pp. 9026-9031).

Mn₂O₃/TiO₂ solid solution was prepared from two different oxides, manganese oxide (from KMnO₄ and ethanol) and TiO₂, these samples were characterized by BET, XRD, EDAX, SEM, FT-IR, ESR, XPS and UV–vis absorption spectroscopy. Photocatalytic activities of Mn₂O₃/TiO₂ powder was investigated by photooxidation of different dyes like Rhodamine B, thymol blue, methyl orange and Bromocresol green under visible light (300-W Xe lamp; λ>420nm). The results show that the alloy of TiO₂ with 1mol% of Mn₂O₃ (MNT1) exhibit photocatalytic activity 3–5 times higher than that of P25 TiO₂ for oxidation of various dyes (RB, TB, MO and BG). The average particle size and crystallite size of MNT1 were found to be 100nm and 12nm measured from SEM and XRD, respectively. The EPR spectra of the Mn₂O₃/TiO₂ samples is a sharp five-line Mn(III) component centered on g_eff=1 .99.

Keywords: Mn; ₂; O; ₃; /TiO; ₂; alloys; Nanostructures; Semiconductors; Photocatalysts

First-principles study of the relaxation and energy of bcc-Fe, fcc-Fe and AISI-304 stainless steel surfaces by Jun Yu; Xin Lin; Junjie Wang; Jing Chen; Weidong Huang (pp. 9032-9039).

Relaxations and surface energies of bcc-Fe, fcc-Fe and AISI-304 stainless steel surfaces are investigated by using first-principles total energy calculations. The low-index surfaces (100), (110), and (111) are optimized with respect to the atomic coordinates. The calculations are performed within the density functional framework using the projector augmented plane wave (PAW) method. The structural property, surface relaxations and surface energies of bcc-Fe agree well with experimental data from previous computational studies. For bcc-Fe, the order of surface relaxations and surface energies is (110)<(100)<(111). The orders of surface relaxations and energies for fcc-Fe and AISI-304 stainless steel are (111)<(100)<(110) and (100)<(111)<(110), respectively. The surface energies of AISI-304 stainless steel achieved in this study provide a good basis for future experimental application.

Keywords: First-principles calculations; Surface relaxation; Surface energy; Iron; AISI-304 stainless steel

Diffractive multi-beam surface micro-processing using 10ps laser pulses by Zheng Kuang; Walter Perrie; Dun Liu; Stuart Edwardson; Jian Cheng; Geoff Dearden; Ken Watkins (pp. 9040-9044).

A high repetition rate picosecond laser system is combined with a spatial light modulator (SLM) for diffractive multiple beam processing. The effect of the zero order beam is eliminated by adding a Fresnel zone lens (FZL) to defocus the un-diffracted beam at the processing plane. Chromatic dispersion, which is evident with a large bandwidth femtosecond pulses leading to the problem of distorted hole shape is eliminated due to the much narrower spectral bandwidth, ∼0.1nm at 10ps pulselength, resulting in highly uniform intensity spots, independent of diffraction angle. In addition, high-throughput processing is demonstrated by combining the high power laser output, 2.5W at λ≈1064nm and fast repetition rate, f≈20kHz with P>1.2W diffracted into 25 parallel beams. This has the effect of creating an “effective” repetition rate of 500kHz without restrictive scan speeds.

Keywords: PACS; 42.40.Jv; 42.62.Cf; 81.20.WkPicosecond laser; Spatial light modulator (SLM); Computer generated holograms (CGH)

Effect of annealing temperature on microstructure, optical and electrical properties of sputtered Ba_0.9Sr_0.1TiO₃ thin films by Zuci Quan; Hao Hu; Shishang Guo; Wei Liu; Sheng Xu; Huiming Huang; Bobby Sebo; Guojia Fang; Meiya Li; Xingzhong Zhao (pp. 9045-9053).

Ba_0.9Sr_0.1TiO₃ (BST) thin films were deposited on fused quartz and Pt/TiN/Si₃N₄/Si substrates by radio frequency magnetron sputtering technique. Microstructure and chemical bonding states of the BST films annealed at 700°C were characterized by field emission scanning electron microscopy, X-ray photoelectron spectroscopy, glancing angle X-ray diffraction and Raman spectrum. Optical constants including refractive indices, extinction coefficients and bandgap energies of the as-deposited BST film and the BST films annealed at 650, 700 and 750°C, respectively, were determined from transmittance spectra by envelope method and Tauc relation. Dielectric constant and remnant polarization for the BST films increase with increasing annealing temperature. Leakage current density-applied voltage ( J– V) data indicate that the dominant conduction mechanism for all the BST capacitors is the interface-controlled Schottky emission under the conditions of 14V< V<30V and −30V< V<−14V. Furthermore, the inequipotential J– V characteristics for the BST films annealed at various temperatures are mainly attributed to the combined effects of the different thermal histories, relaxed stresses and strains, and varied Schottky barrier heights in the BST/Pt and Pt/BST interfaces.

Keywords: Ba; _0.9; Sr; _0.1; TiO; ₃; thin films; Annealing temperature; Optical properties; Electrical properties

Effects of deposition temperature on the surface roughness and the nonlinear optical susceptibility of sprayed deposited ZnO:Zr thin films by K. Bahedi; M. Addou; M. El Jouad; S. Bayoud; Z. Sofiani (pp. 9054-9057).

Zirconium doped zinc oxide thin films were deposited by reactive chemical pulverization spray pyrolysis technique on heated glass substrates at 400°C, 450°C and 500°C using zinc and zirconium chlorides as precursors. The effect of zirconium dopant and surface roughness on the nonlinear optical properties was investigated using atomic force microscopy (AFM) and third harmonic generation (THG). The best value of susceptibility χ⁽³⁾ was obtained from the doped films with less roughness. A strong third order nonlinear optical susceptibility χ⁽³⁾=20.49×10⁻¹² (esu) of the studied films was found for the 5% doped sample at 450°C.

Keywords: Spray pyrolysis; ZnO; Zirconium; THG; AFM; Nonlinear optics

Effects of flow ratios on surface morphology and structure of hydrogenated amorphous carbon films prepared by microwave plasma chemical vapor deposition by S.B. Yang; F.M. Pan; Y.E. Yang; W.C. Zhang (pp. 9058-9061).

A series of hydrogenated amorphous carbon (a-C:H) films were deposited on silicon substrates by microwave plasma chemical vapor deposition technique with a mixture of hydrogen and acetylene. The effects of flow ratio of hydrogen to acetylene on surface morphology and structure of a-C:H films were investigated using surface-enhanced Raman spectroscopy and scanning probe microscope (SPM) in the tapping AFM mode. Raman data imply a transition from graphite-like phase to diamond-like bonding configurations when the flow ratio increases. AFM measurements show that the increase in hydrogen content, to some extent, can smoothen the surface morphology and decrease the RMS roughness. Excessive hydrogen is found to cause the formation of polymeric hydrocarbon clusters in the films and reduce deposition rate.

Keywords: Hydrogenated amorphous carbon films; Microwave plasma chemical vapor deposition; Atomic force microscopy; Raman spectroscopy

In situ low-angle cross sectioning: Bevel slope flattening due to self-alignment effects by Uwe Scheithauer (pp. 9062-9065).

Low-angle cross sections are produced inside an Auger microprobe using the equipped depth profile ion sputter gun. Simply the sample is partly covered by a mask. Utilizing the edge of this mask the sample is sputtered with ions. Due to the shading of the mask a cross section is produced in the sample. The slope of this cross section is considerably shallower than given by the geometrical setup. This is attributed to self-alignment effects, which are due to missing sputter cascades in the transition area between sputtered and shaded sample regions and a chamfering of the mask edge.These self-alignment effects are studied here using a 104.6nm thick SiO₂ layer thermally grown on a Si substrate. In this study on one hand for a fixed ion impact angle of 15.8° as function of the sputter time several in situ low-angle cross sections were produced. This way slope angles between an ultimate low slope angle of 0.014° and 0.085° were achieved. On the other hand for a fixed sputter time the ion impact angle was varied between 14.8° and 70.8°. For these samples cross section slope angles between 0.031° and 0.32° are observed. These results demonstrate the distinct slope flatting of in situ cross sectioning.

Keywords: In situ low-angle cross section; Beveling; Ultra-low-angle lapping; Self-alignment effects; SiO; ₂; Auger; AES

The effect of relative plasma plume delay on the properties of complex oxide films grown by multi-laser, multi-target combinatorial pulsed laser deposition by Katherine A. Sloyan; Timothy C. May-Smith; Robert W. Eason; James G. Lunney (pp. 9066-9070).

We report the effects of relative time delay of plasma plumes on thin garnet crystal films fabricated by dual-beam, combinatorial pulsed laser deposition. Relative plume delay was found to affect both the lattice constant and elemental composition of mixed Gd₃Ga₅O₁₂ (GGG) and Gd₃Sc₂Ga₃O₁₂ (GSGG) films. Further analysis of the plasmas was undertaken using a Langmuir probe, which revealed that for relative plume delays shorter than ∼200μs, the second plume travels through a partial vacuum created by the first plume, leading to higher energy ion bombardment of the growing film. The resulting in-plane stresses are consistent with the transition to a higher value of lattice constant normal to the film plane that was observed around this delay value. At delays shorter than ∼10μs, plume propagation was found to overlap, leading to scattering of lighter ions from the plume and a change in stoichiometry of the resultant films.

Keywords: Pulsed laser deposition; Thin film; Garnet crystal; Langmuir probe; Laser plasma; Combinatorial

Effect of In-content on the optical properties of a-Se films by M.F. Kotkata; F.A. Abdel-Wahab; M.S. Al-Kotb (pp. 9071-9077).

The optical transmission spectra of amorphous (a-) Se1−_xIn_x films, with x=0.0, 0.05, 0.18 and 0.35, that prepared by thermal evaporation from their corresponding bulk ingots, are recorded over the spectral region of 500–2500nm. A simple straight forward procedure proposed by Swanepeol has been applied to determine the two components of the complex refractive index (n˜). The dispersion ofn˜ is examined in terms of the Wemple and DiDomenico model and is discussed in terms of In-content. An estimation of various optical parameters such as, the optical energy gap ( E_g=1.96–1.33eV), single oscillator energy ( E_o=3.95–3.16eV), oscillator dispersion energy ( E_d=22.6–31.6eV), lattice oscillator strength ( E_l=0.38–0.61eV) and wavelength at zero material dispersion ( λ_c=2.0569–2.0879μm) have been given and discussed in relation to the coordination number, hydrostatic density and formed chemical bonds that are introduced in the network of a-Se with the introduction of up to 35at.% In.

Keywords: PACS; 42.65.−k; 78.66.Li; 78.66.Jg; 78.20.CiAmorphous semiconductors; Chalcogenides; Optical properties; Thin films; Se–In

Molecular dynamics simulation of wetting on modified amorphous silica surface by Jingchun Chai; Shuyan Liu; Xiaoning Yang (pp. 9078-9084).

The microscopic wetting of water on amorphous silica surfaces has been investigated by molecular dynamics simulation. Different degrees of surface hydroxylation/silanization were considered. It was observed that the hydrophobicity becomes enhanced with an increase in the degree of surface silanization. A continuous transformation from hydrophilicity to hydrophobicity can be attained for the amorphous silica surfaces through surface modification. From the simulation result, the contact angle can exceed 90° when surface silanization percentage is above 50%, showing a hydrophobic character. It is also found that when the percentage of surface silanization is above 70% on the amorphous silica surface, the water contact angle almost remains unchanged (110–120°). This phenomenon is a little different from the wetting behavior on smooth quartz plates in previous experimental report. This change in the wettability on modified amorphous silica surfaces can be interpreted in terms of the interaction between water molecules and the silica surfaces.

Keywords: PACS; 82.65.+r; 68.35.bj; 83.10.RsAmorphous silica; Surfaces; Wetting; Molecular simulation; Hydrophilic; Hydrophobic

Structural characteristics and morphology of Sm_xCe1−_xO2− x_/2 thin films by M. Hartmanová; M. Jergel; C. Mansilla; J.P. Holgado; J. Zemek; K. Jurek; F. Kundracik (pp. 9085-9091).

Effect of the deposition temperature (200 and 500°C) and composition of Sm_xCe1−_xO2− x_/2 ( x=0, 10.9–15.9mol%) thin films prepared by electron beam physical vapor deposition (EB-PVD) and Ar⁺ ion beam assisted deposition (IBAD) combined with EB-PVD on structural characteristics and morphology/microstructure was investigated. The X-ray photoelectron spectroscopy (XPS) of the surface and electron probe microanalysis (EPMA) of the bulk of the film revealed the dominant occurrence of Ce⁴⁺ oxidation state, suggesting the presence of CeO₂ phase, which was confirmed by X-ray diffraction (XRD). The Ce³⁺ oxidation states corresponding to Ce₂O₃ phase were in minority. The XRD and scanning electron microscopy (SEM) showed the polycrystalline columnar structure and a rooftop morphology of the surface. Effects of the preparation conditions (temperature, composition, IBAD) on the lattice parameter, grain size, perfection of the columnar growth and its impact on the surface morphology are analyzed and discussed.

Keywords: Structure; Morphology; Thin film; CeO; ₂; Sm; ₂; O; ₃

FAS grafted superhydrophobic ceramic membrane by Jun Lu; Yun Yu; Jianer Zhou; Lixin Song; Xingfang Hu; Andre Larbot (pp. 9092-9099).

The hydrophobic properties of γ-Al₂O₃ membrane have been obtained by grafting fluoroalkylsilane (FAS) on the surface of the membrane. The following grafting parameters were studied: the eroding time of the original membrane, the grafting time, the concentration of FAS solution and the multiplicity of grafting. Hydrophobicity of the membranes was characterized by contact angle (CA) measurement. The thermogravimetric analysis (TGA) was used to investigate the weight loss process (25–800°C) of the fluoroalkylsilane grafted on Al₂O₃ powders under different grafting conditions. The morphologies of the membranes modified under different parameters were examined by field emission scanning electron microscopy (FE-SEM) and the surface roughness (Ra) was measured using white light interferometers. A needle-like structure was observed on the membrane surface after modification, which causes the change of Ra. On the results above, we speculated a model to describe the reaction between FAS and γ-Al₂O₃ membrane surface as well as the formed surface morphology.

Keywords: PACS; MP; 82.70. UvSurfaces; Superhydrophobic; FAS; Al; ₂; O; ₃; membrane; Contact angle

Particles detection and analysis of hard disk substrate after cleaning of post chemical mechanical polishing by Yating Huang; Xinchun Lu; Guoshun Pan; Bill Lee; Jianbin Luo (pp. 9100-9104).

Scrub, ultrasonic and megasonic are widely used in industry as post-CMP (chemical mechanical polishing/planarization) cleaning procedure. In this paper experiments and results are described to analyze the particle contaminations of hard disk substrate after each process of post-CMP cleaning. A scatter spot method has been exploited to detect the location and characteristics of the particles. SEM with EDX is used to observe and analyze the particles’ shape and size as well as the elements. The results indicate that brush scrub process can remove 99% contaminations after CMP but not that efficient for submicron particle. Megasonic is a refined method for cleaning nano-particles. However, contaminations like metallic particles and bacteria from the equipment may cause pollution. The abrasive particles embedded in the plating pits cannot be removed by mechanical force. Pollution in the dryer is also discussed.

Keywords: Hard disk; Post-CMP cleaning; Particle contamination

Influence of slight microstructural gradients on the surface properties of Ti6Al4V irradiated by UV by A.M. Gallardo-Moreno; M. Multigner; M.A. Pacha-Olivenza; M. Lieblich; J.A. Jiménez; J.L. González-Carrasco; M.L. González-Martín (pp. 9105-9111).

Ti6Al4V alloy is one of the most widely used materials for biomedical implants. Among its properties, it is remarkable the photoactivity displayed by its passive layer, which is mainly composed by titanium dioxide. However, variations in the processing conditions may yield to differences in the microstructure which can be reflected on the surface properties of the machined product. From contact angle measurements taken on different zones of samples removed from a commercial bar of Ti6Al4V, it has been shown that the modifications of the surface Gibbs energy suffered by the alloy under UV irradiation have a radial dependence. This behaviour is related to slight microstructural changes of the alloy, particularly with an increase in the volume fraction of the β-phase when moving to the interior of the sample, which alters the composition and/or microstructure of the passive layer along its radius. This study shows that gradients in the microstructure and physical properties are sample size dependent and are likely related to thermal gradients during processing.

Keywords: Ti6Al4V alloy; Biomaterials; Microstructural gradients; UV irradiation; Surface Gibbs energy; Wettability

Enhanced luminescence from spontaneously ordered Gd₂O₃:Eu³⁺ based nanostructures by Geo Rajan; K.G. Gopchandran (pp. 9112-9123).

Nanostructured Gd₂O₃:Eu³⁺ and Li⁺ doped Gd₂O₃:Eu³⁺ thin films were prepared by pulsed laser ablation technique. The effects of annealing and Li⁺ doping on the structural, morphological, optical and luminescent properties are discussed. X-ray diffraction and Micro-Raman investigations indicate a phase transformation from amorphous to nanocrystalline phase and an early crystallization was observed in Li⁺ doped Gd₂O₃:Eu³⁺ thin films on annealing. AFM images of Li⁺ doped Gd₂O₃:Eu³⁺ films annealed at different temperatures especially at 973K show a spontaneous ordering of the nanocrystals distributed uniformly all over the surface, with a hillocks (or tips) like self-assembly of nanoparticles driven by thermodynamic and kinetic considerations. Enhanced photoemission from locations corresponding to the tips suggest their use in high resolution display devices. An investigation on the photoluminescence of Gd2−_xEu_xO₃ (x=0.10) and Gd2− x−_yEu_xLi_yO₃ (x=0.10,y=0.08) thin films annealed at 973K reveals that the enhancement in luminescence intensity of about 3.04 times on Li⁺ doping is solely due to the increase in oxygen vacancies and the flux effect of Li⁺ ions. The observed decrease in the values of asymmetric ratio from the luminescence spectra of Li⁺ doped Gd₂O₃:Eu³⁺ films at high temperature region is discussed in terms of increased EuO bond length as a result of Li⁺ doping.

Keywords: Thin films; Optical properties; Surface properties; Photoluminescence spectroscopy

Microstructure and corrosion behavior of coated AZ91 alloy by microarc oxidation for biomedical application by Y.M. Wang; F.H. Wang; M.J. Xu; B. Zhao; L.X. Guo; J.H. Ouyang (pp. 9124-9131).

Magnesium and its alloy currently are considered as the potential biodegradable implant materials, while the accelerated corrosion rate in intro environment leads to implant failure by losing the mechanical integrity before complete restoration. Dense oxide coatings formed in alkaline silicate electrolyte with and without titania sol addition were fabricated on magnesium alloy using microarc oxidation process. The microstructure, composition and degradation behavior in simulated body fluid (SBF) of the coated specimens were evaluated. It reveals that a small amount of TiO₂ is introduced into the as-deposited coating mainly composed of MgO and Mg₂SiO₄ by the addition of titania sol into based alkaline silicate electrolytic bath. With increasing concentration of titania sol from 0 to 10vol.%, the coating thickness decreases from 22 to 18μm. Electrochemical tests show that the E_corr of Mg substrate positively shifted about 300∼500mV and i_corr lowers more than 100 times after microarc oxidation. However, the TiO₂ modified coatings formed in electrolyte containing 5 and 10vol.% titania sol indicate an increasing worse corrosion resistance compared with that of the unmodified coating, which is possibly attributed to the increasing amorphous components caused by TiO₂ involvement. The long term immersing test in SBF is consistent with the electrochemical test, with the coated Mg alloy obviously slowing down the biodegradation rate, meanwhile accompanied by the increasing damage trends in the coatings modified by 5 and 10vol.% titania sol.

Keywords: Magnesium alloy; Microarc oxidation; Coating; Biodegradable property

Effect of annealing upon the structure and adhesion properties of sputtered bio-glass/titanium coatings by G.E. Stan; C.O. Morosanu; D.A. Marcov; I. Pasuk; F. Miculescu; G. Reumont (pp. 9132-9138).

Bio-glass films were deposited by radio-frequency magnetron sputtering technique onto medical grade Ti6Al7Nb alloy substrates from prepared silica based bio-glass target. A low deposition temperature was used (150°C) and three different working pressures, followed by annealing in air at 550 and 750°C. A quasi-stoichiometric target to substrate atomic transfer was found for Si, Ca and P, along with strong enrichment in Na and depletion in K and Mg, as evidenced by the energy dispersive microanalysis. The best results, taking into account stoichiometry and surface roughness, were obtained for the BG layers deposited at 0.3Pa argon working pressure. The infrared spectroscopy of the as-sputtered and of the annealed films evidenced the characteristic molecular vibrations of silicate, phosphate and carbonate functional groups. The as-deposited films are amorphous and became partly crystalline after annealing at 750°C, as evidenced by X-ray diffraction. The pull-out measurements, performed with a certified pull-test machine, gave very strong film–substrate adhesion strength values. For the non-crystalline layers, the pull-out strength is higher than 85MPa, and decreases after annealing at 750°C to 72.9±7.1MPa. The main objective of this work was to establish the influence of the working pressure upon the composition and morphology of the as-deposited films, and of the annealing temperature upon structure and film–substrate adhesion.

Keywords: Bio-glass coatings; Magnetron sputtering; Adherence; Pull-out test; Annealing; Composition; Structure

Photochemical surface modification of PP for abrasion resistance by Thomas Bahners; Rüdiger Häßler; Shang-Lin Gao; Edith Mäder; Andreas Wego; Eckhard Schollmeyer (pp. 9139-9145).

The potential of a photo-chemical approach to increase the surface hardness of polypropylene (PP) has been studied. Using a 222nm excimer lamp, fibers and film were irradiated in the presence of multi-functional substances diallylphthalate (DAP), tetraallyloxyethane (TAE), and pentaerithritoltriacylate (PETA) and characterized with regard to the resulting effect on abrasion resistance. AFM-based methods were employed to analyze thermo-mechanical surface properties. Nanoindentation and microthermal analyses of the outermost surface layers of UV treated fibers gave clear indications of an effective cross-linking of reactive substances present during irradiation. One may assume that the reactive media polymerize on top of the surface of the PP substrate and form a thin-layer. The abrasion resistance of the PP fibers was tested by applying stress through a rotating and axially oscillating roller of defined roughness and measuring the mass loss as a function of time. The abrasion resistance was found to be remarkably improved compared to the untreated fiber. Best effects were achieved using PETA as reactive substance. The experiments clearly showed the influence of processing conditions, namely with regard to homogeneous coverage of the substrate surface with the reactive medium.

Keywords: Photo-chemical cross-linking; Abrasion resistance; Surface hardness

Structural and optical properties of nearly stress-free m-plane ZnO film on (100) γ-LiAlO₂ with a GaN buffer layer by metal-organic chemical vapor deposition by Hui Lin; Shengming Zhou; Hao Teng; Xiaorui Hou; Tingting Jia; Shulin Gu; Shunming Zhu; Zili Xie; Ping Han; Rong Zhang; Ke Xu (pp. 9146-9148).

(101¯0) m-plane ZnO film was epitaxially deposited on (100) γ-LiAlO₂ by metal-organic chemical vapor deposition at 600°C with a GaN buffer layer. The epitaxial relationships between ZnO and GaN, GaN and (100) γ-LiAlO₂ were determined by X-ray diffraction Φ-scans. There exhibits very small decrease for the E₂ mode shift (0.3cm⁻¹) of ZnO in the Raman spectrum, which indicates the epitaxial ZnO film was under a slight tensile stress (5.77×10⁷Pa). Unlike the highly strained a-plane ZnO, temperature dependent photoluminescence spectra show that the free A exiton emission was observed with the temperature ≤138K.

Keywords: m; -Plane ZnO thin film; Semiconductor compounds; Chemical vapor deposition; Residual stress; Photoluminescence spectra

Characteristics of N-doped TiO₂ thin films grown on unheated glass substrate by inductively coupled plasma assisted dc reactive magnetron sputtering by Z.G. Li; S. Miyake (pp. 9149-9153).

N-doped TiO₂ thin films have been deposited on unheated glass substrates by an inductively coupled plasma (ICP) assisted direct current (dc) reactive magnetron sputtering. All films were produced in the metallic mode of sputtering in order to achieve a high deposition rate. The structures and properties of the N-doped TiO₂ films were studied by X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, field emission scanning electron microscopy and UV–Vis spectrophotometer. Experimental results show that we can obtain well crystallized N-doped anatase phase TiO₂ thin films at low deposition temperature and at high deposition rate by using the ICP assisted dc reactive magnetron sputtering process. The doping of nitrogen into TiO₂ lattices leads to a smooth shift of the absorption band toward visible light regions.

Keywords: Metallic sputtering; N-doped TiO; ₂; Crystallinity; Transmission spectra; Binding energy

Nano peel-off fabrication pattern with polymer overcoat layer on glassy carbon electrodes for Pt electrodeposition by Akira Kishi; Minoru Umeda (pp. 9154-9158).

This article describes a new technique for fabricating an electrocatalyst model in which the particle size and interparticle distance are controlled independently. We designed a uniform insulating polymer layer as a mask on an electroconductive glassy carbon substrate and then peeled off a part of the layer in nano-sized dots by scratching the overcoat layer using an atomic force microscope (AFM) cantilever. Pt particles electrodeposited only on the peeled off area of the glassy carbon. To peel-off a small area on the glassy carbon, a 29±2nm thick insulating polymer overcoat layer and a cantilever operating area of 10nm×10nm were used, and the smallest peel-off area obtained was 30nm×30nm. Thereafter, we performed the peel-off procedure on the polymer overcoat layer of the glassy carbon substrate having a cantilever operating area of 80nm×80nm. Pt deposition of 100–150nm in diameter was successfully achieved by adjusting the interparticle distance.

Keywords: PACS; 81.07.−bNano peel-off pattern fabrication; Pt electrodeposition; Glassy carbon electrode; Polymer overcoat layer and atomic force microscopy

Surface properties of ionomers based on styrene-b-acrylic acid copolymers obtained by copolymerization in emulsion by Jolanta Kowalonek; Kazimiera Suchocka-Gałaś (pp. 9159-9165).

Surface properties of styrene-b-acrylic acid copolymers obtained in emulsion and suitable ionomers before and after UV-irradiation were studied by measurements of contact angles and FTIR-ATR spectroscopy.The research focused on the influence of different content of carboxylic acid groups in copolymers, of various types and contents of alkali metal salts in ionomers and of cesium acrylate or methacrylate in ionomers on hydrophilicity of the surfaces of these samples and the course of photodegradation in them.Hydrophilicity of initial copolymer surfaces was higher than this of polystyrene as a result of presence of carboxylic acid groups, which also made the surfaces of these copolymers more sensitive to UV-irradiation.Hydrophilicity of the surfaces of ionomers containing cesium acrylates depended on the content of cesium salt in the samples. The course of ionomer photooxidation was also dependent on the content of this salt.The surface of ionomer containing cesium methacrylate was more polar than this of ionomer containing cesium acrylate.Styrene-based ionomers containing 3.7mol% of various alkali metal acrylates had less polar surfaces than initial copolymer and they were also more resistant to UV-irradiation in comparison to the initial copolymer.Copolymers obtained in emulsion and suitable ionomers had more polar surfaces and they were more sensitive to UV-light compared to copolymers obtained in bulk and their ionomers.

Keywords: Styrene ionomers; Emulsion copolymerization; Contact angle; Surface free energy; FTIR-ATR spectroscopy; Photochemistry

Development of high performance nano-porous polyethersulfone ultrafiltration membranes with hydrophilic surface and superior antifouling properties by Ahmad Rahimpour; Sayed Siavash Madaeni; Mohsen Jahanshahi; Yaghoub Mansourpanah; Narmin Mortazavian (pp. 9166-9173).

Hydrophilic nano-porous polyethersulfone ultrafiltration membranes were developed for milk concentration. The membranes were prepared from new dope solution containing polyethersulfone (PES)/polyvinylpirrolidone (PVP)/polyethyleneglycole (PEG)/cellulose acetate phthalate (CAP)/acrylic acid/Triton X-100 using phase inversion induced by immersion precipitation technique. This casting solution leads to formation of new hydrophilic membranes. The morphological studies were investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). In addition, the hydrophilicity and performance of membranes were examined by contact angel measurements and cross-flow filtration (pure water flux, milk water permeation, protein rejection and antifouling measurements). The contact angle measurements indicate that a surface with superior hydrophilicity was obtained for PES membranes. Two concentrations of PES (16 and 14.4wt.%) and two different non-solvents (pure water and mixtures of water and IPA) were used for preparation of membranes. The morphological studies showed that the higher concentration of PES and the presence of IPA in the gelation media results in formation of a membrane with a dense top and sub-layer with small pores on the surface. The pure water flux of membranes was decreased when higher polymer concentration and mixtures of water and IPA were employed for membrane formation. On the other hand, the milk water permeation and protein rejection were increased using mixtures of water and IPA as non-solvent. Furthermore, the fouling analysis of the membranes demonstrated that the membrane surface with fewer tendencies for fouling was obtained.

Keywords: Hydrophilic surface; Membrane; Nano-porous; High performance; Antifouling

Microstructure and wear resistance of Al–SiC composites coatings on ZE41 magnesium alloy by P. Rodrigo; M. Campo; B. Torres; M.D. Escalera; E. Otero; J. Rams (pp. 9174-9181).

Al and Al–SiC composites coatings were prepared by oxyacetylene flame spraying on ZE41 magnesium alloy substrates. Coatings with controlled reinforcement rate of up to 23vol.% were obtained by spraying mixtures containing aluminium powder with up to 50vol.% SiC particles. The coatings were sprayed on the magnesium alloy with minor degradation of its microstructure or mechanical properties. The coatings were compacted to improve their microstructure and protective behaviour. The wear behaviour of these coatings has been tested using the pin-on-disk technique and the reinforced coatings provided 85% more wear resistance than uncoated ZE41 and 400% more than pure Al coatings.

Keywords: Coatings; Thermal spray; Composites; Magnesium alloys; ZE41; Wear

Microrods based on nanocubes of Prussian blue by Shikui Wu; Xiaoping Shen; Zheng Xu; Jili Wu; Cuiling Gao (pp. 9182-9185).

Using a facile dynamic vacuum evaporation method, a novel microrod with diameters of ca. 1–2μm and lengths of up to 80μm has been constructed using uniform Prussian blue (PB) nanocubes as the building blocks. The PB nanocubes are arranged fairly orderly in the rod-like superstructures. The assembled architecture can be transformed from one-dimensional microrods to two-dimensional layers via a fish-bone-like structure by tuning the evaporation rate. The formation of the PB superstructures follows an oriented-attachment mechanism and this provides a simple approach to fabricate hierarchical nanostructures and self-assembled superstructures using nanosized building blocks. Magnetic studies indicate that the PB microrods have a Curie temperature ( T_c) of 4.9K and a coercivity of ca. 26Oe at 1.8K. The photoluminescence (PL) spectra of the PB microrods and the dispersed nanocubes show an UV emission band at 358 and 367nm respectively, suggesting an interesting assembly effect.

Keywords: Nanostructures; Prussian blue; Magnetic properties; Optical properties; Self-assembly

Direct laser interference patterning of poly(3,4-ethylene dioxythiophene)-poly(styrene sulfonate) (PEDOT-PSS) thin films by Andrés F. Lasagni; Jeffrey L. Hendricks; Charles M. Shaw; Dajun Yuan; David C. Martin; Suman Das (pp. 9186-9192).

We have developed a patterning procedure based on selective ablation using interference patterns with ns-laser pulses to fabricate periodic arrays on large areas of poly(3,4-ethylene dioxythiophene)-poly(4-styrene sulfonic acid) (PEDOT-PSS) thin films over a metallic gold–palladium layer. Single pulse laser-ablation experiments were performed to study the ablation characteristics of the thin films as a function of the film thickness. The ablation threshold fluence of the PEDOT-PSS films was found to be dependent on thickness with values ranging from 43mJ/cm² to 252mJ/cm². Additionally, fluences at which the PEDOT-PSS films could be ablated without inducing damage in the underlying metallic films were observed (128mJ/cm² and 402mJ/cm² for film thicknesses of 70nm and 825nm, respectively). Linear periodic arrays with line spacings of 7.82μm and 13.50μm were also fabricated. The surface topography of these arrays was analyzed using scanning electron and atomic force microscopy. For thicker polymeric layers, several peeled sub-layers of the conjugated polymer with average thicknesses of about 165–185nm were observed in the ablation experiments. The size and scale of structures produced by this technique could be suitable for several biomedical applications and devices in which controlling cell adhesion, promoting cell alignment, or improving biocompatibility are important.

Keywords: PACS; 42.25.Hz; 52.38.Mf; 82.35.CdDirect laser interference patterning; DLIP; PEDOT; PSS; Conducting polymers

In situ characterization of localized corrosion of stainless steel by scanning electrochemical microscope by Yuehua Yin; Lin Niu; Min Lu; Weikuan Guo; Shenhao Chen (pp. 9193-9199).

Scanning electrochemical microscopy (SECM) area scan measurements have been performed to investigate the localized corrosion of type 304 stainless steel in neutral chloride solution. Variations in the Faradaic current measured at selected tip potential values can be related to changes in the local concentration and electrochemical activities of electroactive species involved in corrosion reactions occurring at the substrate as a function of immersion times of the substrate and polarized currents or potentials applied on the substrate. To further verify the results acquired from cyclic voltammetric experiments, SECM measurements were employed to in situ study the compositions and electrochemical activity distribution profile of the pitting corrosion products of stainless steel. It has been demonstrated that the combination of feedback current mode with generation-collection (G-C) mode of SECM is suitable to elucidate the possible reaction mechanisms and paths involved in the localize corrosion of stainless steel in neutral chloride solution.

Keywords: Localized corrosion; 304 stainless steel; Characterization; In situ; Scanning electrochemical microscope (SECM)

Structural and mechanical properties of compositionally gradient CrN_x coatings prepared by arc ion plating by Min Zhang; Meng-Ke Li; Kwang Ho Kim; Feng Pan (pp. 9200-9205).

Compositionally gradient CrN_x coatings were fabricated using arc ion plating by gradually increasing N₂ flow rate during the deposition process. The effect of substrate bias, ranging from 0 to −250V, on film microstructure and mechanical properties were systematically investigated with XRD, SEM, HRTEM, nanoindentation, adhesion and wear tests. The results show that substrate bias has an important influence on film microstructure and mechanical properties of gradient CrN_x coatings. The coatings mainly crystallized in the mixture of hexagonal Cr₂N, bcc Cr and fcc rock-salt CrN phases. N₂ flow rate change during deposition results in phase changes in order of Cr, Cr+Cr₂N, Cr₂N, Cr₂N+CrN, and CrN, respectively, along thickness direction. Phase fraction and preferred orientation in CrN_x coatings vary with substrate bias, exerting an effective influence on film hardness. With the increasing of bias, film microstructure evolves from an apparent columnar structure to a highly dense one. The maximum hardness of 39.1GPa was obtained for the coatings deposited at a bias of −50V with a friction coefficient of 0.55. It was also found that adhesion property and wear resistance of gradient CrN_x coatings were better than that of homogeneous CrN coatings.

Keywords: Chromium nitride (CrN); Arc ion plating; Substrate bias; Functionally gradient coatings (FGC); Mechanical property

First stages of surface steel nitriding: X-ray photoelectron spectroscopy and electrical measurements by M. Flori; B. Gruzza; L. Bideux; G. Monier; C. Robert-Goumet; Z. Benamara (pp. 9206-9210).

Quantitative and qualitative analysis techniques were employed to study the first stages of ultra-high vacuum plasma nitriding of the 42CrMo4 steel. At constant treatment temperature, maintained for all samples at about 360°C, we have established the influence of treatment time on the chemical composition, thickness and electrical properties of the nitrided layer.In this purpose it was used a stacking atomic layer model describing the sample surface, which takes into account the attenuation depth of photoelectrons by the atomic monolayers. So, we have found that after 2h of nitriding in laboratory conditions, 70% of the nitrided layer was composed of iron oxide. Also, I– V measurements indicate an influence of the nitride overlayer with increasing treatment time.

Keywords: Plasma nitriding; Glow-discharge source (GDS); 42CrMo4 steel; X-ray photoelectron spectroscopy; Depth profiling; Electrical measurements

Spectroscopic ellipsometry of very thin tantalum pentoxide on Si by I. Karmakov; A. Konova; E. Atanassova; A. Paskaleva (pp. 9211-9216).

Variable angle spectroscopic ellipsometry of very thin T₂O₅ layers on Si and the previously published appropriate algorithm for data interpretation have been successfully applied in terms of accurate characterization of very thin T₂O₅/Si systems. The simulation procedure following a simple three and four layered model was used assuming an existence of inhomogeneous interfacial layers. Quantitative determination of the thicknesses and composition identification were achieved, both for the top T₂O₅ layer and for an interfacial layer. The constituents in the interfacial layer and its depth profiles were recognized.

Keywords: PACS; 68; 68.47.Fg; 68.55.Nq; 68.55.jd; 77.55.+f; 78.67.−n; 78.68.+mSpectroscopic ellipsometry; Algorithm; High-; k; T; ₂; O; ₅; /Si; Constituents; Depth profile

Ablation behaviors of carbon/carbon composites with C-SiC-TaC multi-interlayers by Chen Zhao-ke; Xiong Xiang; Li Guo-dong; Wang Ya-lei (pp. 9217-9223).

Carbon/carbon composites with C-SiC-TaC multi-interlayers were prepared by isothermal chemical vapor infiltration. The ablation behaviors of the composites were tested with an oxyacetylene flame. The mass loss rate increases markedly in the initial 10s, then reaches a steady state or decreases slightly in 10–40s; while after 40s, the mass loss rate increases remarkably. A similar trend is observed in the linear loss rate, except that it begins to increase only after 60s. After ablation for 5s, the composite surface consists in black carbon fibers and white ceramic oxides. After 20s, three different regions with different ablation behaviors are observed: central, transition and border. After 100s, the composites are severely ablated and the shape is completely destroyed. A cross-section of the composites after ablation for 20s shows three distinct regions: a rugged oxide layer, a smooth oxide layer and the matrix. The tantalum compounds have not been able to protect efficiently the material from constant oxide evolution, possibly because of a too large pore volume fraction.

Keywords: Chemical vapor infiltration; C/C composites; C-SiC-TaC multi-interlayer; Ablation

Fabrication of nitrogen-doped TiO₂ layer on titanium substrate by Guangze Tang; Jinlong Li; Mingren Sun; Xinxin Ma (pp. 9224-9229).

In this paper, macropores TiO₂ layer was fabricated on titanium substrates based on plasma based ion implantation (PBII). In order to increase the photodegradation efficiency of fabricated TiO₂ layer, two approaches are used: (1) preparation of macropores on TiO₂ layer to increase the total photodegradation area and (2) nitrogen doping (N-doping) to increase light absorption efficiency. The fabrication process of the N-doped macropores TiO₂ layer comprises four steps: firstly, helium plasma based ion implantation (He-PBII) is employed to generate He bubbles in substrate; secondly, oxygen plasma based ion implantation (O-PBII) and a followed annealing in air are executed to obtain rutile and anatase mixture TiO₂ phases; thirdly, He bubbles are exposed to the surface via an Ar ion sputter process; lastly, the samples are doped by nitrogen PBII (N-PBII). The photodegradation of Rhodamine B solution under Xe lamp indicates that the TiO₂ layer with surface macropores and N-doping has higher light photocatalysis efficiency.

Keywords: Macropores TiO; ₂; layer; Photocatalysis; Nitrogen doping; Titanium

In-situ TiC particle reinforced Ti–Al matrix composites: Powder preparation by mechanical alloying and Selective Laser Melting behavior by Dongdong Gu; Zhiyang Wang; Yifu Shen; Qin Li; Yufang Li (pp. 9230-9240).

Mechanical alloying of Ti–Al–graphite elemental powder mixture was performed to synthesize nanocomposite powder with Ti(Al) solid solution matrix reinforced by in-situ formed TiC particles. The evolutions in phases, microstructures, and compositions of milled powders with the applied milling times were investigated. It showed that with increasing the milling time, the starting irregularly shaped powder underwent a successive change in its morphology from a flattened shape (10h) to a highly coarsened spherical one (15h) and, eventually, to a fine, equiaxed and uniform one (above 25h). The prepared TiC/Ti(Al) composite powder was nanocrystalline, with the estimated average crystallite size of ∼12nm and of ∼7nm for Ti(Al) and TiC, respectively. Formation mechanisms behind the microstructural development of powders were elucidated. The Ti(Al) solid solution is formed through a gradual and progressive solution of Al into Ti lattice. The formation of TiC is through an abrupt, exothermic, and self-sustaining reaction between Ti and C elements. Selective Laser Melting (SLM) of as-prepared TiC/Ti(Al) composite powder was performed. The TiC particle reinforced TiAl₃ (a major phase) and Ti₃AlC₂ (a minor phase) matrix composite part was obtained after SLM. Although a slight grain growth occurred as relative to as-milled powder, the SLM processed composites still exhibited a refined microstructure.

Keywords: PACS; 42.62.Cf; 71.20.Lp; 72.80.TmMechanical alloying (MA); Nanocomposites; Rapid Manufacturing (RM); Selective Laser Melting (SLM); Titanium aluminides

Effect of pH values on surface modification and solubility of phosphate bioglass-ceramics in the CaO–P₂O₅–Na₂O–SrO–ZnO system by Xudong Li; Shu Cai; Wenjuang Zhang; Guohua Xu; Wei Zhou (pp. 9241-9243).

The bioactive glass-ceramics in the CaO–P₂O₅–Na₂O–SrO–ZnO system were synthesized by the sol–gel technique, and then chemically treated at different pH values to study the solubility and surface modification. Samples sintered at 650°C for 4h consisted of the crystalline phase β-Ca₂P₂O₇ and the glass matrix. After soaking in the solution at pH 1.0, the residual glass matrix on the surface appeared entirely dissolved and no new phase could be detected. Whereas at pH 3.0, web-like layer exhibiting peaks corresponding to CaP₂O₆ was formed and covered the entire surface of the sample. When conducted at pH 10.0, only part of the glass matrix was dissolved and a new phase Ca₄P₆O₁₉ was precipitated, forming the petaline layer. The chemical treatment can easily change the surface morphologies and phase composition of this bioactive glass-ceramics. The higher level of surface roughness resulting from the new-formed layer would improve the interface bonding and benefit for cell adhesion.

Keywords: Solubility; Surface modification; Chemical treatment

Fabrication of stable, transparent and superhydrophobic nanocomposite films with polystyrene functionalized carbon nanotubes by Jin Yang; Zhaozhu Zhang; Xuehu Men; Xianghui Xu (pp. 9244-9247).

Stable, transparent and superhydrophobic carbon nanotube (CNT) nanocomposite films were fabricated by one-step spray casting process using the polystyrene functionalized CNTs, which were prepared by “living” free-radical polymerization and analyzed by means of infrared spectroscopy and thermal gravimetric analysis. The CNT film has a high water contact angle of 160° and a sliding angle of less than 3°. The surface topography of the fabricated film was characterized by field emission scanning electron microscopy. The transparency of the CNT film was investigated by UV–vis spectroscopy. The result shows that the CNT film has light transmittance of about 78% in the visible light region.

Keywords: Carbon nanotubes; Polystyrene; Stable; Superhydrophobic; Transparent

X-ray photoelectron spectroscopy study of Pd oxidation by RF discharge in oxygen by L.S. Kibis; A.I. Titkov; A.I. Stadnichenko; S.V. Koscheev; A.I. Boronin (pp. 9248-9254).

The low-temperature oxidation of polycrystalline palladium by RF oxygen plasma was studied via X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Detailed information about the electronic states of palladium and oxygen was obtained based on the XPS curve fitting analysis of Pd3d and Pd3p+O1s lines. The results showed that Pd oxidation by oxygen plasma was different from Pd oxidation in pure O₂ at high temperature. SEM shows well-structured submicron PdO particles result from oxidation in pure O₂, whereas plasma oxidation results in the predominant formation of two-dimensional PdO structures covering the initial crystallites of the Pd foil. Further oxidation to a three-dimensional PdO phase occurs under prolonged treatment with oxygen plasma. The formation of a PdO_x ( x>1) species, characterized by a E_b(Pd3d_5/2)=338.0–338.2eV value that is close to the Pd⁴⁺ oxidation state, was also observed. This PdO_x species was found to have low thermal stability ( T<400K). It is proposed that the PdO_x species can be localized within the boundaries of crystallites.

Keywords: Palladium surface; XPS; Plasma oxidation; PdO

Impact of organic contamination on the laser-induced damage in vacuum by Xiulan Ling; Yuanan Zhao; Dawei Li; Shuhong Li; Ming zhou; Jianda Shao; Zhengxiu Fan (pp. 9255-9258).

The impact of two organic contaminations on the damage characteristics of anti-reflector (AR) at 1064nm is investigated. Contamination experiments were made with toluene and acetone in liquid phase on the surface of AR coatings. Chemical and morphological characterization methods were used to identify and understand the damage process. The possible damage process is analyzed and discussed. It is found that toluene decreases laser-induced damage threshold and acetone seems to be benign and has little influence on laser-induced damage threshold due to its quickly spreading into the coating. Adsorption and droplet micro-lensing effect mechanism are the main cause of enhanced laser-induced damage of toluene.

Keywords: PACS; 42.79.Wc; 81.70.Fy; 68.37.HkVacuum; Laser-induced damage; Anti-reflection films; Organic contamination

Electronic properties of single-molecule junction: Effect of the molecular distortion by W. Gao; M. Zhao; Q. Jiang (pp. 9259-9263).

For a model system consisting of a benzenedithio (BDT) molecule sandwiched between two Au plates, the electronic properties as a function of different BDT geometry are investigated using density functional theory. The distorted BDT structures are got through stretching the electrode distance. The corresponding electronic properties, including the spatial distribution of the frontier orbits, the gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital levels and density of states at the Fermi energy are determined. It reveals that the molecular distortion essentially determines electronic structures. The result should be beneficial to understand the stress-dependent or structure-dependent transport mechanism of electrons of the BDT junction.

Keywords: Density functional theory; Single-molecule junction; Electronic properties

Effect of H₂ dilution on a-CN:H films deposited by hot-wire chemical vapor deposition by Bibhu P. Swain; Bhabani S. Swain; Nong M. Hwang (pp. 9264-9267).

Hydrogenated amorphous carbon nitride (a-CN:H) thin films were deposited by hot-wire chemical vapor deposition (HWCVD) using the gas mixture of CH₄, NH₃ and H₂ precursor gases. The structural and electronic environments studies of H₂ diluted a-CN:H films were carried out by Raman spectroscopy and X-ray photoelectron spectroscopy. The nitrogen content increases while the total carbon contents decreases with increase in H₂ flow rate from 0sccm to 20sccm in the a-CN:H films. Moreover, the detail analysis of the carbon core orbital, valence band and hole states of a-CN:H were discussed with different H₂ flow rate.

Keywords: a-CN:H; Valence band; XPS; HWCVD

New ablation experiment aimed at metal expulsion at the hydrodynamic regime by Ardian B. Gojani; Jack J. Yoh (pp. 9268-9272).

The effects of nanosecond visible laser on metallic materials have been studied experimentally. High laser energies (>10¹³W/cm²) created a hydrodynamic regime, where the ablation pressure and the ensuing shock wave are the main mechanisms for material expulsion. Plasma shielding caused a constant material removal despite the increase of energy, while the increase of number of pulses resulted in an almost linear increase of the crater volume, despite the lower depths reached with every subsequent pulse. Our results show that there is a correlation between ablation efficiency and material properties, namely ablation efficiency decreases with melting temperature and bulk modulus.

Keywords: Metal ablation; Plasma shield; Hydrodynamic regime; Nano-second laser; Crater

Effects of Cr dopant on the microstructure and electromigration performance of Cu interconnects by Xinjian Wang; Xianping Dong; Jiansheng Wu (pp. 9273-9278).

Cu and Cu(Cr) alloy films were deposited on SiO₂ substrates by magnetron sputtering. The microstructure and electromigration performance of films were investigated. A small amount of Cr refines the Cu grains and improves the surface morphology of Cu films. After annealing at 450°C, in contrast to the Cu film with large lateral grown grains, the Cu(Cr) alloy film exhibits fine columnar grains with a 〈111〉 preferred orientation. Most of Cr in the annealed Cu(Cr) film has segregated at the film surface and the film/substrate interface. The grain boundary grooving at the film/substrate interface is completely prohibited for Cu(Cr) films. As a result, the electromigration lifetimes of annealed Cu(Cr) lines are 10–100 times longer than those of annealed Cu lines. The final resistivity of the annealed Cu(Cr) film is 2.55μΩcm which is close to that of the annealed Cu film. With the improved surface morphology and high electromigration resistance, the dilute Cu(Cr) alloy film can be a viable interconnect material or a seed layer in the Cu-damascene technology.

Keywords: Cu(Cr) alloy films; Surface morphology; Columnar grain; Electromigration

Structural, defect and optical properties of ZnO films grown under various O₂/Ar gas ratios by Y. Hu; Y.Q. Chen; Y.C. Wu; M.J. Wang; G.J. Fang; C.Q. He; S.J. Wang (pp. 9279-9284).

Thin wurtzite (002) textured ZnO thin films were deposited on glass substrates by radio frequency magnetron sputtering under O₂/Ar ratios R varying from 0.05 to 1.0 at room temperature. The structure of, and defects in, the films were investigated by XRD, SEM and slow positron beam techniques. The XRD spectra showed that ZnO thin films were polycrystalline with hexagonal structure and a good c-axis orientation perpendicular to the substrate. The thickness, grain size and the crystalline quality of the films strongly depended on R; the larger grain size and thicker ZnO films were grown when R was lower. Positron beam Doppler broadening measurements showed that in low R films additional vacancy-type defects (e.g. Zn-related vacancy complexes or clusters) were formed. Photoluminescence spectra found that the film with R=0.4 had the highest luminescence efficiency, in good agreement with the best c-axis preferential orientation. The transmittance spectra of the films decreased with decreasing R, due to the thickness effect. Correlations between microstructure, defect and optical properties are discussed.

Keywords: ZnO film; Positron annihilation; Defects; Optoelectronics; Oxygen

Effect of C doping on the structural and optical properties of sol–gel TiO₂ thin films by Lixiang Mai; Chunming Huang; Dawei Wang; Zhiguang Zhang; Yinyue Wang (pp. 9285-9289).

Undoped and C-doped TiO₂ thin films have been prepared by sol–gel process. Their structure and optical properties have been investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and UV–vis spectroscopy. It has been observed that C dopants retard the transformation from anatase-to-rutile phase. Namely, C doping effect is attributed to the anatase phase stabilization. The optical analyses show that the optical band gap of anatase C-doped TiO₂ decreases with increasing amount of C. Also, it is founded that C dopants have been shown to make TiO₂ have a visible light photoresponse.

Keywords: PACS; 73.61.L; 78.40.F; 78.66; 61.10.NCrystal structure; Optical properties; Sol–gel process; Thin films; Titanium dioxide

Kinetics of the formation of Fe₂B layers in gray cast iron: Effects of boron concentration and boride incubation time by I. Campos-Silva; M. Ortiz-Domínguez; M. Keddam; N. López-Perrusquia; A. Carmona-Vargas; M. Elías-Espinosa (pp. 9290-9295).

The growth kinetics of Fe₂B layers formed at the surface of gray cast iron were evaluated in this study. The pack-boriding process was applied to produce the Fe₂B phase at the material surface, and the variables included three temperatures (1173, 1223 and 1273K) and four exposure times (2, 4, 6 and 8h). Taking into account the growth fronts obtained at the surface of the material and the mass balance equation at the Fe₂B/substrate interface, the boron diffusion coefficient on the borided phase was estimated for the range of treatment temperatures. Likewise the parabolic growth constant, the instantaneous velocity of the Fe₂B/substrate interface, and the weight gain in the borided samples were established as a function of the parameters τ( t) and α( C), which are related to the boride incubation time ( t₀( T)) and boron concentration at the Fe₂B phase, respectively. Observation of the growth kinetics of the Fe₂B layers in gray cast irons suggest an optimum value of boron concentration that is in good agreement with the set of boriding experimental conditions used in this work.

Keywords: Pack boriding; Boride layers; Growth kinetics; Diffusion model; Boride incubation time; Boron concentration

Nanopatterned surface with adjustable area coverage and feature size fabricated by photocatalysis by Yang Bai; Yan Zhang; Wei Li; Xuefeng Zhou; Changsong Wang; Xin Feng; Luzheng Zhang; Xiaohua Lu (pp. 9296-9300).

We report an effective approach to fabricate nanopatterns of alkylsilane self-assembly monolayers (SAMs) with desirable coverage and feature size by gradient photocatalysis in TiO₂ aqueous suspension. Growth and photocatalytic degradation of octadecyltrichlorosilane (OTS) were combined to fabricate adjustable monolayered nanopatterns on mica sheet in this work. Systematic atomic force microscopy (AFM) analysis showed that OTS-SAMs that have similar area coverage with different feature sizes and similar feature size with different area coverages can be fabricated by this approach. Contact angle measurement was applied to confirm the gradually varied nanopatterns contributed to the gradient of UV light illumination. Since this approach is feasible for various organic SAMs and substrates, a versatile method was presented to prepare tunable nanopatterns with desirable area coverage and feature size in many applications, such as molecular and biomolecular recognition, sensor and electrode modification.

Keywords: Atomic force microscopy (AFM); Self-assembled monolayers (SAMs); Feature size; Area coverage; Photocatalysis

A new texturing technique of monocrystalline silicon surface with sodium hypochlorite by Linfeng Sun; Jiuyao Tang (pp. 9301-9304).

This work proposes a new texturing technique of monocrystalline silicon surface for solar cells with sodium hypochlorite. A mixed solution consisting of 5wt% sodium hypochlorite and 10vl% ethanol has been found that results in a homogeneous pyramidal structure, and an optimal size of pyramids on the silicon surface. The textured silicon surface exhibits a lower average reflectivity (about 10.8%) in the main range of solar spectrum (400–1000nm).

Keywords: Surface structure; Etching; Texturing; Silicon; Pyramidal structures

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Applied Surface Science (v.255, #22)