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Applied Surface Science (v.255, #16)

Surface-defect-states photoluminescence in CdS nanocrystals prepared by one-step aqueous synthesis method by Qi Xiao; Chong Xiao (pp. 7111-7114).

CdS nanocrystals were prepared by a simple one-step aqueous synthesis method using thioglycolic acid (TGA) as the capping molecule, and characterized by X-ray powder diffraction (XRD), UV–vis absorption spectra and photoluminescence (PL) emission spectroscopy. The effects of both TGA/Cd and Cd/S molar ratio on the surface-defect-state PL intensity of CdS nanocrystals have been investigated. It was found that all of the as-prepared CdS nanocrystals showed a strong broad emission in the range of 450–700nm centered at 560nm, which was attributed to the recombination of an electron trapped in a sulfur vacancy with a hole in the valance band of CdS. The surface-defect-states emission intensity of CdS nanocrystals significantly increased with the increase of Cd/S molar ratio, and showed a maximum when Cd/S molar ratio was 2.0. If Cd/S molar ratio continued to increase, namely more than 2.0, the surface-defect-states emission intensity would decrease. It was found that the surface-defect-states emission intensity increased with the increase the TGA/Cd molar ratio, and showed a maximum when the TGA/Cd molar ratio was equal to 1.8, and a further increase of the TGA/Cd molar ratio would lead to the decrease of the surface-defect-states emission intensity.

Keywords: CdS nanocrystals; Surface-defect-state emission; Photoluminescence

Influence of C₃H₈O₃ in the electrolyte on characteristics and corrosion resistance of the microarc oxidation coatings formed on AZ91D magnesium alloy surface by Di Wu; Xiangdong Liu; Kai Lu; Yaping Zhang; Huan Wang (pp. 7115-7120).

Ceramic coatings were fabricated on AZ91D Mg-alloy substrate by microarc oxidation in Na₂SiO₃–NaOH–Na₂EDTA electrolytes with and without C₃H₈O₃ addition. The effects of different concentrations of C₃H₈O₃ contained in the electrolyte on coatings thickness were investigated. The surface morphologies, RMS roughness, phase compositions and corrosion resistance property of the ceramic coatings were analyzed by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), and electrochemical corrosion test respectively. It is found that the addition of C₃H₈O₃ into silicate electrolyte leads to increase of the unit-area adsorptive capacity of the negative ions at anode–electrolyte interface and thus improves the compactness and corrosion resistance of the MAO coating. The coating thickness decreases gradually with the increase of concentrations of C₃H₈O₃ in the electrolyte. The oxide coating formed in base electrolyte containing 4mL/L C₃H₈O₃ exhibits the best surface appearance, the lowest surface RMS roughness (174nm) and highest corrosion resistance. In addition, both ceramic coatings treated in base electrolyte with and without C₃H₈O₃ are mainly composed of periclase MgO and forsterite Mg₂SiO₄ phase, but no diffraction peak of Mg phase is found in the patterns.

Keywords: PACS; 52.80−Mg; 52.80−Wq; 81.15−z; 85.40−SzMagnesium alloy; Microarc oxidation; Coatings; Corrosion test

Passivation of GaSb and InAs by pH-activated thioacetamide by R. Stine; E.H. Aifer; L.J. Whitman; D.Y. Petrovykh (pp. 7121-7125).

We describe the passivation by thioacetamide (TAM) of GaSb and InAs—two III–V semiconductor materials important for fabricating IR devices from Type-II superlattices (T2SLs). We use X-ray photoelectron spectroscopy (XPS) to characterize GaSb and InAs (001) surfaces treated by TAM under both acidic and basic conditions and to analyze the reoxidation of passivated surfaces over time. Both acid- and base-activated TAM treatments produce sulfide layers on GaSb and InAs. The layers produced by base-TAM appear to be of self-limited thickness <1nm, whereas acid-TAM creates considerably thicker (1–2nm) sulfide layers. Passivation by both acid- and base-activated TAM offers significant short-term (<1 day) protection against reoxidation, but does not prevent oxide formation after exposure to ambient air for 1–3 days. Based on this comparative study and previous literature reports, the chemical effects of TAM treatments on Ga, Sb, In, and As depend not only on the individual element and reaction conditions, but also on the compound. In other words, our results suggest that passivation chemistry for a common element in two different III–V materials should not, in general, be assumed to be the same.

Keywords: PACS; 81.05.Ea; 81.65.Rv; 81.65.Mq; 79.60.Dp; 82.80.PvX-ray photoelectron spectroscopy; Gallium antimonide; Indium arsenide; Thioacetamide; Passivation; Oxidation

Microstructural, optical and spectroscopic studies of laser ablated nanostructured tantalum oxide thin films by Renju R. Krishnan; K.G. Gopchandran; V.P. MahadevanPillai; V. Ganesan; Vasant Sathe (pp. 7126-7135).

Thin films of tantalum oxide (Ta₂O₅) have been prepared by pulsed laser deposition technique at different substrate temperatures (300–973K) under vacuum and under oxygen background (pO₂=2×10⁻³mbar) conditions. The films are annealed at a temperature of 1173K. The as-deposited films are amorphous irrespective of the substrate temperature. XRD patterns show that on annealing, the films get crystallized in orthorhombic phase of tantalum pentoxide (β-Ta₂O₅). The annealed films deposited at substrate temperatures 300K and 673K have a preferred orientation along (001) plane, whereas the films deposited at substrate temperatures above 673K show a preferred orientation along (200) crystal plane. The deposited films are characterized using techniques such as grazing incidence X-ray diffraction (GIXRD), atomic force microscopy (AFM), micro-Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy and UV–visible spectroscopy. FTIR and micro-Raman measurements confirm the presence of Ta–O, Ta–O–Ta and O–Ta–O bands in the films. Grain size calculations from X-ray diffraction and AFM show a decrease with increase in substrate temperature. The variation of transmittance and band gap with film growth parameters are also discussed.

Keywords: Tantalum oxide thin films; Nanostructures; Atomic force microscopy; Raman spectra; Pulsed laser ablation; X-ray diffraction; FTIR studies; UV–visible spectra

Surface reaction mechanism of Y₂O₃ atomic layer deposition on the hydroxylated Si(100)-2×1: A density functional theory study by Jie Ren; Guangfen Zhou; Yongqi Hu; David Wei Zhang (pp. 7136-7141).

The surface reaction mechanism of Y₂O₃ atomic layer deposition (ALD) on the hydroxylated silicon surface is investigated by using density functional theory. The ALD process is designed into two half-reactions, i.e., Cp₃Y (Cp=cyclopentadienyl) and H₂O half-reactions. For the Cp₃Y half-reaction, the chemisorbed complex is formed along with the change of metal–Cp bonding from Y–C(π) to Y–C₁(σ). For the H₂O half-reactions, the chemisorbed energies are increased with the relief of steric congestion around yttrium metal center. In addition, Gibbs free energy calculations show that it is thermodynamically favorable for the Cp₃Y half-reactions. By comparing with the reaction of H₂O with {Si}–(O₂)YCp, it is thermodynamically more favorable and kinetically less favorable for the reactions of H₂O with {Si}–OYCp₂ as well as with {Si}–OYCp(OH).

Keywords: PACS; 31.15.E; 77.55.+fDensity functional theory; Dielectrics; Yttria; Atomic layer deposition

Preparation of ZrC nano-particles reinforced amorphous carbon composite coating by atmospheric pressure chemical vapor deposition by W. Sun; X. Xiong; B.Y. Huang; G.D. Li; H.B. Zhang; P. Xiao; Z.K. Chen; X.L. Zheng (pp. 7142-7146).

To eliminate cracks caused by thermal expansion mismatch between ZrC coating and carbon–carbon composites, a kind of ZrC/C composite coating was designed as an interlayer. The atmospheric pressure chemical vapor deposition was used as a method to achieve co-deposition of ZrC and C from ZrCl₄–C₃H₆–H₂–Ar source. Zirconium tetrachloride (ZrCl₄) powder carrier was especially made to control accurately the flow rate. The microstructure of ZrC/C composite coating was studied using analytical techniques. ZrC/C coating shows same morphology as pyrolytic carbon. Transmission electron microscopy (TEM) shows ZrC grains with size of 10–50nm embed in turbostratic carbon. The formation mechanism is that the growth of ZrC crystals was inhibited by surrounding pyrolytic carbon and kept as nano-particles. Fracture morphologies imply good combination between coating and substrate. The ZrC crystals have stoichiometric proportion near 1, with good crystalline but no clear preferred orientation while pyrolytic carbon is amorphous. The heating-up oxidation of ZrC/C coating shows 11.58wt.% loss. It can be calculated that the coating consists of 74.04wt.% ZrC and 25.96wt.% pyrolytic carbon. The average density of the composite coating is 5.892g/cm³ by Archimedes’ principle.

Keywords: ZrC; Amorphous carbon; Composite coating; Chemical vapor deposition

Fabrication of silicon pyramid/nanowire binary structure with superhydrophobicity by Xiaocheng Li; Beng Kang Tay; Philippe Miele; Arnaud Brioude; David Cornu (pp. 7147-7152).

A pyramid/nanowire binary structure is fabricated on the silicon surface via a NaOH anisotropic etching technique followed by a silver-catalyzed chemical etching process. The silicon surface shows a stable superhydrophobicity with high contact angle of 162° and small sliding angle less than 2° after being modified with octadecyltrichlorosilane (ODTS). The binary roughness of pyramid/nanowire structure presents a stable composite interface of silicon–air–water and responsible for the superhydrophobicity of silicon surface.

Keywords: Silicon; Pyramid/nanowire binary structure; Superhydrophobicity; Contact angle hysteresis; Binary roughness

Electroless deposition of silver on synthesized calcite via surface modification by Chamarthi K. Srikanth; P. Jeevanandam (pp. 7153-7157).

Metallic silver was deposited on the surface of synthesized calcite via a simple electroless deposition method. Calcite with cubic morphology was prepared first by homogeneous precipitation and it was subsequently surface modified using ammonium oxalate. The electroless deposition was carried out using formaldehyde as the reducing agent and silver nitrate as the silver source. Both calcite and the silver deposited calcite were characterized by different techniques. Surface modification of calcite with ammonium oxalate is necessary for the deposition of silver and the size of the deposited silver particles could be controlled by changing the deposition parameters such as concentration of the reagents and the deposition time. Lower concentration of silver ions (e.g. 0.01M AgNO₃) and shorter deposition times (e.g. 30min) lead to the formation of silver nanoparticles on calcite.

Keywords: Calcite; Surface modification; Electroless deposition; Silver coating; Silver nanoparticles

Preparation and optical properties of ZnO@PPEGMA nanoparticles by Xiaoming Peng; Yiwang Chen; Fan Li; Weihua Zhou; Yuehui Hu (pp. 7158-7163).

The poly(poly(ethylene glycol) methyl ether monomethacrylate) (PPEGMA) grafted zinc oxide (ZnO) nanoparticles were successfully prepared via the surface-initiated atom transfer radical polymerizations (ATRP) from the surfaces functionalized ZnO nanoparticles. The 2-bromoisobutyrate (BIB) was immobilized onto the surface of the ZnO nanoparticles through the reaction between 2-bromoisobutyryl bromide (BIBB) and the hydroxyl groups on nanoparticles, serving as the initiator to induce the ATRP of poly(ethylene glycol) monomethacrylate (PEGMA). Well-defined polymer chains were grown from the surfaces to yield hybrid nanoparticles comprised of ZnO cores and PPEGMA polymer shells having multifunctional end groups. The structure and morphology of the nanoparticles were characterized using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The optical properties of the nanoparticles were investigated by UV–vis absorption spectroscopy and photoluminescence spectroscopy (PL). The results showed that the dispersion and near-band edge (NBE) emission of ZnO nanoparticles could be improved by the grafted PPEGMA polymer segments.

Keywords: ZnO; Nanoparticles; Surface modification; PEGMA; ATRP

Codeposition of SiC particles with electrolytic cobalt in the presence of Cs⁺ ions by Ewa Rudnik; Lidia Burzyńska; Jacek Jędruch; Ludwik Błaż (pp. 7164-7171).

Electrodeposition of SiC particles with cobalt matrix in the presence of cesium ions was studied. The influence of Cs⁺ concentration (0–37.6mM) on the cathodic polarization curves was determined in galvanostatic and potentiodynamic measurements. It was found that the presence of Cs⁺ in the solution enhanced adsorption of Co²⁺ ions on SiC, but preferential cesium adsorption occurred simultaneously. The last phenomena resulted in cesium incorporation in the composite coating. Surface charge of SiC powder and amounts of functional groups on SiC surface were determined. The particles incorporation into deposits was only little dependent on cesium concentration in the bath. Structure of the composite coatings was studied by microscopic observations. Microhardness of the deposits was also determined.

Keywords: PACS; 82.45.QrElectrodeposition; Composite; Silicon carbide; Cobalt; Cesium; Adsorption

Influence of transparent coating thickness on thermoelastic force source and laser-generated ultrasound waves by Jijun Wang; Baiqiang Xu; Zhonghua Shen; Xiaowu Ni; Jian Lu (pp. 7172-7178).

A numerical model is established to investigate the influence of transparent coating thickness on the laser-generated thermoelastic force source and ultrasound waves in the coating–substrate system by using the finite element method (FEM). Taking into account the effects of thermal diffusion, the finite width and duration of the laser source, as well as the temperature dependence of material properties, the transient temperature distributions are obtained firstly. Applying this temperature field to structure analyses as thermal loading, the thermoelastic stress field and laser-generated ultrasound wave in the specimen are obtained. The generation and propagation of the laser thermoelastically induced stress field and ultrasonic waves in coating–substrate system are presented in detail. The influence of transparent coating thickness on the transient temperature distribution, thermoelastic force source and the laser-generated ultrasound waveforms is investigated. The numerical results indicate that the thermoelastic force source and laser-generated ultrasound waveform are strongly affected by the coating thickness due to the constraint of coating. This method can provide insight into the generation and propagation of the laser-generated stress field in coating–substrate system consisting of a transparent coating and an opaque metallic substrate. It provides theoretical basics to optimize ultrasonic signal generation in particular applications and invert the physical and geometrical parameter of the coating–substrate system more accurately in the experiment.

Keywords: PACS; 42.62−b; 43.35+d; 02.70.DhLaser-generated ultrasound; Thermoelastic force source; Coating–substrate system; Finite element method

Effect of modification of S-terminated Ge(100) surface on ALD HfO₂ gate stack by Younghwan Lee; Kibyung Park; Kyung Taek Im; June Young Lee; Seongil Im; Jung Han Lee; Yeonjin Yi; Sangwoo Lim (pp. 7179-7182).

When S-termination on a Ge(100) surface was desorbed at an elevated temperature and an atomic layer deposition (ALD) HfO₂ film was deposited, interfacial thickness was less than 1nm. As a result, the equivalent oxide thickness (EOT) of the stack on the initially S-terminated surface was thinner than that deposited on the O₃-oxidized surface, while HfO₂ film thickness was almost identical on both surfaces. Nevertheless, the HfO₂ stack on the initially S-terminated surface exhibited improved leakage current characteristics due to an increase in barrier height. Its thinner but robust interface will contribute to the scaling down of gate oxide integrity.

Keywords: PACS; 61.72.uf; 82.80.GkGermanium; Sulfur-termination; Atomic layer deposition (ALD)

Enhanced photoelectrochemical properties of F-containing TiO₂ sphere thin film induced by its novel hierarchical structure by Xiang Dong; Jie Tao; Yingying Li; Hong Zhu (pp. 7183-7187).

The novel nanostructured F-containing TiO₂ (F-TiO₂) sphere was directly synthesized on the surface of Ti foil in the solution of NH₄F and HCl by one-step hydrothermal approach under low-temperature condition. The samples were characterized respectively by means of field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The results showed that the F-TiO₂ sphere was hierarchical structure, which composed of porous octahedron crystals with one truncated cone, leading to a football-like morphology. XPS results indicated that F⁻ anions were just physically adsorbed on the surface of TiO₂ microspheres. The studies on the optical properties of the F-TiO₂ were carried out by UV–vis light absorption spectrum. The surface fluorination of the spheres, the unique nanostructure induced accessible macropores or mesopores, and the increased light-harvesting abilities were crucial for the high photoelectrochemical activity of the synthesized F-TiO₂ sphere for water-splitting. The photocurrent density of the F-TiO₂ sphere thin film was more than two times than that of the P25 thin film. Meanwhile, a formation mechanism was briefly proposed. This approach could provide a facile method to synthesize F-TiO₂ microsphere with a special morphology and hierarchical structure in large scale.

Keywords: TiO; ₂; Microsphere; One-step synthesis; Hierarchical structure

Carbon nanotubes supported Cu–Ni bimetallic catalysts and their properties for the direct synthesis of dimethyl carbonate from methanol and carbon dioxide by Jun Bian; Min Xiao; Shuan-Jin Wang; Yi-Xin Lu; Yue-Zhong Meng (pp. 7188-7196).

Multi-walled carbon nanotubes (MWCNTs) supported Cu–Ni bimetallic catalysts for the direct synthesis of dimethyl carbonate (DMC) from CH₃OH and CO₂ were synthesized and investigated. The supporting materials and the synthesized catalysts were fully characterized using FTIR, scanning electron microscopy (SEM), transmission electron microscopy (TEM), temperature-programmed reduction (TPR), X-ray diffraction (XRD) and X-ray photoelectron spectrum (XPS) techniques. The catalytic activities were investigated by performing micro-reactions. The experimental results showed that the metal phase and Cu–Ni alloy phase in the catalyst were partially formed during the calcination and activation step. Active metal particles were dispersed homogeneously on the surface of the MWCNTs. Cu–Ni/MWCNTs catalysts were efficient for the direct synthesis of DMC. The highest conversion of CH₃OH was higher than 4.3% and the selectivity of DMC was higher than 85.0% under the optimal catalytic conditions of 120°C and around 1.2MPa. The high catalytic activity of Cu–Ni/MWCNTs in DMC synthesis can be attributed to the synergetic effects of metal Cu, Ni and Cu–Ni alloy in the activation of CH₃OH and CO₂, the unique structure of MWCNTs and the interaction between the metal particles and the supports.

Keywords: Dimethyl carbonate; Carbon dioxide; Bimetallic catalyst; Catalysis

Computer simulations of the adsorption and diffusion processes of 1-butene in MCM-22 zeolite by Guo Zhang; Qing-Chuan Zheng; Hong-Xing Zhang; Tao Liu; Yu-Jun Zhu; Hong-Gang Fu (pp. 7197-7202).

The adsorption and diffusion of 1-butene in purely siliceous MCM-22 zeolite have been studied by the grand canonical Monte Carlo and molecular dynamic simulation. The adsorption behavior of 1-butene was explored in detail from adsorption sites, interaction energies. The mass clouds show that 1-butene can be adsorbed freely in MCM-22 zeolite, and adsorbed preferentially in 10-MR (member rings) channel system with high interaction energy. The diffusion characteristic for 1-butene in two independent channel systems was investigated by using molecular dynamic simulation. The results were obtained by analysis the trajectories of diffusion and the diffusion coefficients, which shows that a large diffusion for 1-butene in both channel systems, especially in the supercage system. The adsorption and the diffusion of the hydrocarbon molecules were affected by the different sizes and structures of 10-MR and 12-MR in MCM-22 zeolite. Moreover, the positions where the molecules are expected to react were revealed.

Keywords: MCM-22; 1-Butene; Molecular dynamics; Monte Carlo; Adsorption and diffusion

Ellipsometry investigation of the effects of annealing temperature on the optical properties of indium tin oxide thin films studied by Drude–Lorentz model by Stefano D’Elia; Nicola Scaramuzza; Federica Ciuchi; Carlo Versace; Giuseppe Strangi; Roberto Bartolino. (pp. 7203-7211).

Float glass substrates covered by high quality ITO thin films (Balzers) were subjected for an hour to single thermal treatments at different temperature between 100°C and 600°C. In order to study the electric and optical properties of both annealed and not annealed ITO-covered float glasses, ellipsometry, spectrophotometry, impedance analysis, and X-ray measurements were performed. Moreover, variable angle spectroscopic ellipsometry provides relevant information on the electronic and optical properties of the samples. ITO film is modeled as a dense lower layer and a surface roughness layer. The estimated optical density for ITO and the optical density of the surface roughness ITO layer increases with the annealing temperature. In the near-IR range, the extinction coefficient decreases while the maximum of the absorption in the near UV range shift towards low photon energy as the annealing temperature increases. Spectrophotometry was used to estimate the optical band-gap energy of the samples. The thermal annealing changes strongly the structural and optical properties of ITO thin films, because during the thermal processes, the ITO thin film absorbs oxygen from air. This oxygen absorption decreases the oxygen vacancies therefore the defect densities in the crystalline structure of the ITO thin films also decrease, as confirmed both by ellipsometry and X-ray measurements.

Keywords: Indium tin oxide thin films; Ellipsometry investigation; Optical properties; Thermal annealing

Highly oriented (100) ZnO thin films by spray pyrolysis by T. Prasada Rao; M.C. Santhoshkumar (pp. 7212-7215).

Undoped ZnO thin films have been deposited onto glass substrates by spray pyrolysis. The structural, electrical and optical properties were studied on thin films, prepared from precursor solutions with varying the ethanol concentrations. X-ray diffraction studies have shown polycrystalline nature of the films with a hexagonal wurtzite-type structure. The preferential orientation plane (100) of the ZnO thin film is found to be sensitive to ethanol concentration. The texture coefficient (TC) and grain size value have been calculated. Also ethanol concentration was found to have significant effect on sheet resistivity of the films.

Keywords: PACS; 78.66.Hf; 61.05.cp; 68.55.ag; 68.55.jd; 68.55.jm; 81.15.Rs; 82.30.LpZnO; Spray pyrolysis; Texture coefficient; Sheet resistivity; Ethanol concentration

Effects of CPII implantation on the characteristics of diamond-like carbon films by Ya-Chi Chen; Ko-Wei Weng; Ching-Hsun Chao; Shui-Yang Lien; Sheng Han; Tien-Lai Chen; Ying-Chieh Lee; Han-Chang Shih; Da-Yung Wang (pp. 7216-7220).

A diamond-like carbon film (DLC) was successfully synthesized using a hybrid PVD process, involving a filter arc deposition source (FAD) and a carbon plasma ion implanter (CPII). A quarter-torus plasma duct filter markedly reduced the density of the macro-particles. Graphite targets were used in FAD. Large electron and ion energies generated from the plasma duct facilitate the activation of carbon plasma and the deposition of high-quality DLC films. M2 tool steel was pre-implanted with 45kV carbon ions before the DLC was deposited to enhance the adhesive and surface properties of the film. The ion mixing effect, the induction of residual stress and the phase transformation at the interface were significantly improved. The hardness of the DLC increased to 47.7GPa and 56.5GPa, and the wear life was prolonged to over 70km with implantation fluences of 1×10¹⁷ions/cm² and 2×10¹⁷ions/cm², respectively.

Keywords: Keyword; Diamond-like carbon (DLC), Filter arc deposition (FAD), Surface properties

Temperature-controlled growth and photoluminescence of AlN nanowires by Hyoun Woo Kim; Mesfin Abayneh Kebede; Hyo Sung Kim (pp. 7221-7225).

By varying the substrate temperature in the range of 800–1000°C, the conditions for the synthesis of AlN nanowires were optimized. Al powders were heated under flowing ammonia gas. The samples were characterized by scanning electron microscopy, X-ray diffraction, transmission electron microscopy, and photoluminescence (PL) spectroscopy. Based on the absence of tip particles, the growth mechanism of AlN nanowires was considered to follow a vapor–solid process. The overall intensity of the PL spectra was increased by increasing the synthesis temperature, whereas their shapes were changed by varying the synthesis temperature. The associated emission mechanisms are discussed.

Keywords: Nanowires; AlN; Temperature

The simulation of nanoscale sputter depth profiles using molecular dynamics by M.A. Karolewski (pp. 7226-7233).

The feasibility of using molecular dynamics (MD) for simulation of a nanoscale sputter depth profile experiment is examined for the idealised case of depth profiles of individual atomic layers in a Cu(100) target. Issues relating to the extraction of depth profile information from MD simulations are discussed in detail. The simulations examine the sputter erosion of static and azimuthally-rotated Cu(100) targets produced by 3keV Ar projectiles incident at 25° from the surface. The simulated projectile fluence extends to 5×10¹⁵cm⁻², and the mean value of the sputter depth, z, amounts to 8 Cu(100) monolayers (ML) or 15Å. The simulations directly supply progressive layer erosion profiles (curves that depict the extent of sputter erosion of each atomic layer vs. total sputter depth). A fitting method is then used to extract smooth depth profiles for each atomic layer from these predicted erosion profiles. The depth profile characteristics (height, width, shift) for the first 10 layers of the target show a pronounced dependence on layer depth.

Keywords: PACS; 79.20.Ap; 79.20.Rf; 81.70.JbSputtering; Depth profile; Molecular dynamics

Characterization of ceria–yttria stabilized zirconia plasma-sprayed coatings by Bin Ma; Yao Li; Ke Su (pp. 7234-7237).

Ceria–yttria stabilized zirconia (CYSZ) coatings were prepared by air plasma-sprayed on the nickel alloy. The as-sprayed CYSZ coatings and heat-treated CYSZ coatings were characterized by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The XPS data indicated the coexistence of Ce³⁺, Ce⁴⁺, Y³⁺ and Zr⁴⁺ ions near the surface of the as-sprayed CYSZ coatings and the disappearance of Ce³⁺ ions in the CYSZ coatings after thermal treatment at 1000°C for 15h. From the XRD patterns, the solid solution of CeO₂–Y₂O₃–ZrO₂ formed in the CYSZ coatings because of the lack of any features from Y₂O₃ and ZrO₂ single phases. After thermal treatment, the main phases of all the samples were consistent with the characteristic peaks of cubic ZrO₂.

Keywords: Ceria–yttria stabilized zirconia coatings; XPS; XRD

The effect of growth ambient on the structural and optical properties of Mg_xZn1−_xO thin films by R. Ghosh; D. Basak (pp. 7238-7242).

Mg_xZn1−_xO ( x=0.0–0.20) thin films have been deposited by sol–gel technique on glass substrates and the effect of growth ambient (air and oxygen) on the structural, and optical properties have been investigated. The films synthesized in both ambient have hexagonal wurtzite structure. The c-axis lattice constant decreases linearly with the Mg content ( x) up to x=0.05, and 0.10 respectively for air- and oxygen-treated films, above which up to x=0.20, the values vary irregularly with x. The change in the optical band gap values and the ultraviolet (UV) peak positions of Mg_xZn1−_xO films show the similar change with x. These results suggest that the formation of solid solution and thus the structural and optical properties of Mg_xZn1−_xO thin films are affected by the growth ambient.

Keywords: PACS; 78.66.H; 81.20.F; 84.40.A; 81.40.CWide band gap; Sol–gel; Transparency; Solid solution

Detailed profiling of CNTs arrays along the growth window in a floating catalyst reactor by Morteza Maghrebi; Abbas Ali Khodadadi; Yadollah Mortazavi; Subodh Mhaisalkar (pp. 7243-7250).

We report a detailed longitudinal and depth profiles of multi-wall carbon nanotubes (CNTs) arrays synthesized using xylene and ferrocene in a floating catalyst reactor. Point to point analyses of the CNTs grown in a “growth window” with CNTs arrays longer than 0.5mm were performed using optical microscopy, Raman spectroscopy, FESEM, high-resolution TGA/DTA, and TEM techniques. The heights of the CNTs arrays show a maximum at a mid point of the growth window, while a reverse trend of minimum is observed for iron-to-CNTs atomic ratios. The ratio of amorphous carbon to CNTs sharply increases along the growth window and from the bottom to top of CNTs arrays. The CNTs diameter also increases along the growth window, due to deposition of the amorphous carbon, which can be almost removed by temperature programmed oxidation up to around 500°C. A base growth mechanism, the variations of catalyst content, residence time and temperature profile along the growth window, the adsorption and decomposition of polycyclic aromatic hydrocarbons to amorphous carbon, and a limited diffusion of hydrocarbon species through the arrays covered by excessive amorphous carbon may explain the results.

Keywords: PACS; 61.46.Fg; 61.48.De; 81.10.BkCarbon nanotube array; Longitudinal analysis; Growth window; Amorphous carbon; Raman spectroscopy; Catalyst–carbon ratio

Effects of substrate temperature and Zn addition on the properties of Al-doped ZnO films prepared by magnetron sputtering by Y.H. Kim; K.S. Lee; T.S. Lee; B. Cheong; T.-Y. Seong; W.M. Kim (pp. 7251-7256).

Al-doped ZnO (AZO) films prepared at different substrate temperature and AZO films with intentional Zn addition (ZAZO) during deposition at elevated substrate temperature were fabricated by radio frequency magnetron sputtering on glass substrate, and the resulting structural, electrical, optical properties together with the etching characteristics and annealing behavior were comparatively examined. AZO films deposited at 150°C showed the optimum electrical properties and the largest grain size. XPS analysis revealed that AZO films deposited at elevated temperature of 450°C contained large amount of Al content due to Zn deficiency, and that intentional Zn addition during deposition could compensate the deficiency of Zn to some extent. It was shown that the electrical, optical and structural properties of ZAZO films were almost comparable to those of AZO film deposited at 150°C, and that ZAZO films had much smaller etching rate together with better stability in severe annealing conditions than AZO films due possibly to formation of dense structure.

Keywords: PACS; 73.61.−r: 78.20−eAl-doped ZnO; Magnetron sputtering; Deposition temperature; Zn addition; Transparent conducting oxide

Biological response of stainless steel surface modified by N₂O/O₂ glow discharge plasma by Meng Chen; Shigemasa (Gem) Osaki; Paul O. Zamora (pp. 7257-7262).

Stainless steel wafers were treated with the glow discharge plasma of mixed N₂O and O₂ at different molar ratios at a certain discharge condition to create desirable biological characteristics to the surfaces. It was found that the molar ratio of N₂O to O₂ in the mixture at 1:1 used for plasma surface modification caused high apoptotic percentage. Contact angle measurement showed that the surface of stainless steel samples became very hydrophilic after the plasma modification with a value of 15°–30°. The control stainless steel chips without plasma treatment had a contact angle of 40±2°. The data of Electron Spectroscopy for Chemical Analysis (ESCA) indicated that there was a certain amount of oxynitrites formed on the plasma treated surfaces, which was considered to play an important role to cell apoptosis and anti-clot formation in cell culture tests. The ESCA depth profile of up to 250Å from the top surface showed the change of elemental compositions within 40–50Å of the surface by the plasma treatment. The decreased platelet attachment, combined with increased apoptosis in fibroblasts is a distinct combination of biological responses arising from the mixed gas plasma treatment. These initial results suggest it may be of particular use relative to stainless steel stents where decreased platelet attachments are advantageous and induction of apoptosis could limit in-stent restenosis.

Keywords: PACS; 52.40.Hf; 33.60 Fy; 87.14.−gSurface modification; ESCA; Nitrous oxide; Cell culture; Apoptosis; Glow discharge plasma

Superhydrophobicity of polyvinylidene fluoride membrane fabricated by chemical vapor deposition from solution by Zhenrong Zheng; Zhenya Gu; Ruiting Huo; Yonghong Ye (pp. 7263-7267).

Due to the chemical stability and flexibility, polyvinylidene fluoride (PVDF) membranes are widely used as the topcoat of architectural membrane structures, roof materials of vehicle, tent fabrics, and so on. Further modified PVDF membrane with superhydrophobic property may be even superior as the coating layer surface. The lotus flower is always considered to be a sacred plant, which can protect itself against water, dirt, and dust. The superhydrophobic surface of lotus leaf is rough, showing the micro- and nanometer scale morphology. In this work, the microreliefs of lotus leaf were mimicked using PVDF membrane and the nanometer scale peaks on the top of the microreliefs were obtained by the method of chemical vapor deposition from solution. The surface morphology of PVDF membrane was investigated by scanning electronic microscopy (SEM) and atomic force microscope (AFM). Elemental composition analysis by X-ray photoelectron spectroscopy (XPS) revealed that the material of the nanostructure of PVDF membrane was polymethylsiloxane. On the lotus-leaf-like PVDF membrane, the water contact angle and sliding angle were 155° and 4°, respectively, exhibiting superhydrophobic property.

Keywords: Polyvinylidene fluoride; Methyltrichlorosilane; Chemical vapor deposition; Superhydrophobic

Comparable study on the effect of diluted NH₄Cl solution on the postdeposition surface texture of as-deposited aluminum-doped zinc oxide films by direct current pulse and direct current reactive magnetron sputtering by Xiaoyong Gao; Qinggeng Lin; Hongliang Feng; Yongsheng Chen; Shie Yang; Jinhua Gu; Weiqiang Li; Jingxiao Lu (pp. 7268-7272).

Effect of 5.0% diluted NH₄Cl aqueous solution was comparably investigated on the postdeposition surface texture of the as-deposited smooth aluminum-doped zinc oxide (AZO) films by direct current pulse reactive magnetron sputtering (DCP-sputtering) and direct current reactive magnetron sputtering (DC-sputtering). The as-deposited AZO films by DCP-sputtering showed an effective surface texture for light trapping upon the etching of 5.0% diluted NH₄Cl solution, while the as-deposited AZO films by DC-sputtering demonstrated an obscure surface texture upon the same etching treatment. The different result might be attributable to a big difference in film strain and film compactness. The formation of interstitial Zn, interstitial Al and grain boundary is the key to realize effective surface texture for the as-deposited AZO films.

Keywords: PACS; 68.55.jm; 61.72.uj; 68.37.HKAZO film; NH; ₄; Cl aqueous solution; Surface texture; Magnetron sputtering

Hydrophilic modification of polyethersulfone porous membranes via a thermal-induced surface crosslinking approach by Li-Jun Mu; Wen-Zhen Zhao (pp. 7273-7278).

A thermal-induced surface crosslinking process was employed to perform a hydrophilic surface modification of PES porous membranes. Difunctional poly(ethylene glycol) diacrylate (PEGDA) was used as the main crosslinking modifier. The addition of trifunctional trimethylolpropane trimethylacrylate (TMPTMA) into the reaction solutions accelerated the crosslinking progress of PEGDA on PES membranes. The membrane surface morphology and chemical composition were characterized by scanning electron microscopy (SEM) and FTIR-ATR spectroscopy. The mass gains (MG) of the modified membranes could be conveniently modulated by varying the PEGDA concentration and crosslinking time. The measurements of water contact angle showed that the hydrophilicity of PES membranes was remarkably enhanced by the coating of crosslinked PEGDA layer. When a moderate mass gain of about 150μg/cm² was reached, both the permeability and anti-fouling ability of PES membranes could be significantly improved. Excessive mass gain not only contributed little to the anti-fouling ability, but also brought a deteriorated permeability to PES membranes.

Keywords: Polyethersulfone membranes; Hydrophilic modification; Surface crosslinking; Anti-fouling ability

Polytetrafluoroethylene surface modification by filamentary and homogeneous dielectric barrier discharges in air by Zhi Fang; Lili Hao; Hao Yang; Xiangqian Xie; Yuchang Qiu; Kuffel Edmund (pp. 7279-7285).

In this paper, polytetrafluoroethylene (PTFE) films are modified using non-equilibrium plasma generated by homogeneous DBD in air at medium pressure, and the results are compared to those treated by using filamentary DBD in air at atmospheric pressure. The surface properties of PTFE films before and after the treatments are studied using contact angle and surface energy measurement, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). It is found that the plasma treatments modify the PTFE surface in both morphology and composition. The PTFE films modified in both treatments show a remarkable decrease in water contact and a remarkable increase in surface energy. XPS analysis reveals that oxygen-containing polar groups are introduced onto the PTFE surface, and SEM analysis shows that the surfaces of the films are etched after both the treatments. It is found that homogeneous DBD is more effective in PTFE surface modification than filamentary DBD as it can make the contact angle decline to a lower level by introducing more oxygen-containing groups, and the possible reason for this effect is discussed.

Keywords: Dielectric barrier discharge (DBD); Homogeneous DBD; Filamentary DBD; Surface modification; PTFE film

Gas barrier properties of diamond-like carbon films coated on PTFE by K. Ozeki; I. Nagashima; Y. Ohgoe; K.K. Hirakuri; H. Mukaibayashi; T. Masuzawa (pp. 7286-7290).

Diamond-like carbon (DLC) films were deposited on polytetrafluoroethylene (PTFE) using radio frequency (RF) plasma-enhanced chemical vapour deposition (PE-CVD). Before the DLC coating, the PTFE substrate was modified with a N₂ plasma pre-treatment to enhance the adhesive strength of the DLC to the substrate. The influences of the N₂ plasma pre-treatment and process pressure on the gas permeation properties of these DLC-coated PTFE samples were investigated. In the Raman spectra, the G peak position shifted to a lower wave number with increasing process pressure. With scanning electron microscopy (SEM), a network of microcracks was observed on the surface of the DLC film without N₂ plasma pre-treatment. The density of these cracks decreased with increasing process pressure. In the film subjected to a N₂ plasma pre-treatment, no cracks were observed at any process pressure. In the gas barrier test, the gas permeation decreased drastically with increasing film thickness and saturated at a thickness of 0.2μm. The DLC-coated PTFE with the N₂ plasma pre-treatment exhibited a greater reduction in gas permeation than did the samples without pre-treatment. For both sample types, gas permeation decreased with increasing process pressure.

Keywords: Gas barrier; Diamond-like carbon; PTFE; Process pressure; Adhesive strength

Templated growth of smart coatings: Hybrid chemical vapour deposition of vanadyl acetylacetonate with tetraoctyl ammonium bromide by Manfredi Saeli; Russell Binions; Clara Piccirillo; Ivan P. Parkin (pp. 7291-7295).

Hybrid aerosol assisted and atmospheric pressure chemical vapour deposition methodology has been utilised to produce thin films of vanadium dioxide from vanadyl acetylacetonate. Tetraoctyl ammonium bromide (TOAB) was used in the aerosol precursor solution. The films were analysed by X-ray diffraction, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy. Their optical and thermochromic behaviour was also determined. It was found that the use of TOAB had a templating effect that led to a halving in the particle size and that this consequently led to a significant decrease in the thermochromic transition temperature of the films to 34°C.

Keywords: CVD; Vanadium dioxide; Thermochromism; Aerosol

Reversible surface structural changes in Pt-based bimetallic nanoparticles during oxidation and reduction cycles by Rentao Mu; Qiang Fu; Hongyang Liu; Dali Tan; Runsheng Zhai; Xinhe Bao (pp. 7296-7301).

The surface states of supported PtNi nanoparticles treated at alternating O₂ and H₂ atmosphere were studied by X-ray photoelectron spectroscopy. Reversible structural changes at the surfaces of the supported PtNi nanoparticles in response to reaction gases were observed, showing NiO-rich surface in oxidizing gases and Pt-rich surface in reducing gases. The dynamic behaviors can be attributed to two opposite gas-driven mass transport processes at bimetallic particle surfaces, including surface segregation of Pt at the bimetallic particles in H₂ and encapsulation of the particles by NiO in O₂. The similar surface structural changes can be observed in other bimetallic catalyst systems, as exemplified in supported PtCu and PtCo nanoparticles.

Keywords: Bimetallic catalysts; Dynamic surface process; Oxidation; Reduction; XPS

Highly reproducible technique for three-dimensional nanostructure fabrication via anodization scanning probe lithography by SunHyung Lee; Nahiro Saito; Osamu Takai (pp. 7302-7306).

The effects of coated materials for Si probes on the sizes of line structure by using anodization scanning probe lithography (SPL) are investigated by using atomic force microscopy (AFM). Anodization SPL was carried out on the 1-decane monolayer directly attached to hydrogen-terminated silicon. Gold-coated, diamond-coated, and uncoated Si probes were used as the SPL probes in order to fabricate line structures of silicon oxide. In the cases of Au-coated and uncoated Si probes, the widths of line structures are widely influenced by the changes of scanning rate and applied bias voltage. However, the line width fabricated by use of the diamond-coated probe maintained 15nm under any condition of scanning rate and applied bias voltage. One of the most narrow and three-dimensional nanostructures is found to be successfully fabricated on the hydrogen-terminated Si substrates when the diamond-coated probe was used as a probe of anodization SPL. In addition, this result indicated that high reproducibility of oxide nanostructures is attainable by anodization SPL used the diamond-coated probe.

Keywords: Anodization scanning probe lithography; Organic monolayer; Atomic force microscope; Hydrogen-terminated silicon

Effect of welding wires on microstructure and mechanical properties of 2A12 aluminum alloy in CO₂ laser-MIG hybrid welding by Jun Yan; Xiaoyan Zeng; Ming Gao; Jian Lai; Tianxiao Lin (pp. 7307-7313).

This paper represented the effect of welding wires on microstructure and mechanical properties of 2A12 aluminum alloy in CO₂ laser-metal inter gas (MIG) hybrid welding. Plates of 2A12 aluminum alloy were welded by ER4043 and ER2319 welding wires, respectively. Full penetration joints without any defects were produced. The X-ray diffraction was used to analyze the phase composition, while the scanning electron microscopy (SEM) was conducted to study the microstructure, segregation behaviors of major alloying elements and the eutectics formed at dendrite boundaries in the joints. The results showed that silicon and copper were concentrated at the dendrite boundaries and α-Al+Si+Al₂Cu+Mg₂Si eutectic was formed if the ER4043 welding wire was used. However, only copper was concentrated at the dendrite boundaries and α-Al+θ eutectic was formed by ER2319 welding wire. Finally, the tensile tests were performed and the fracture surfaces were analyzed. The results showed that the joint efficiency by ER2319 and ER4043 welding wires reached up to 78% and 69%, respectively. Coarse dimples and voids had been observed in the fractographs. The joints showed a transgranular type failure.

Keywords: Laser welding; Hybrid welding; Aluminum alloy

Structural, morphological and photoluminescence properties of W-doped ZnO nanostructures by B.D. Ngom; O. Sakho; N. Manyala; J.B. Kana; N. Mlungisi; L. Guerbous; A.Y. Fasasi; M. Maaza; A.C. Beye (pp. 7314-7318).

W-doped ZnO nanostructures were synthesized at substrate temperature of 600°C by pulsed laser deposition (PLD), from different wt% of WO₃ and ZnO mixed together. The resulting nanostructures have been characterized by X-ray diffraction, scanning electron microscopy, atomic force microscopy and photoluminescence for structural, surface morphology and optical properties as function of W-doping. XRD results show that the films have preferred orientation along a c-axis (00 L) plane. We have observed nanorods on all samples, except that W-doped samples show perfectly aligned nanorods. The nanorods exhibit near-band-edge (NBE) ultraviolet (UV) and violet emissions with strong deep-level blue emissions and green emissions at room temperature.

Keywords: PACS; 61.10.−I; 68.35.D; 85.40.R; 74.25.Gz; 81.15.ZLaser ablation; Semiconductor; Nanostructures; ZnO nanomaterials

Tunable and reversible surface wettability transition of vertically aligned ZnO nanorod arrays by S.N. Das; J.H. Choi; J.P. Kar; J.M. Myoung (pp. 7319-7322).

Vertically aligned zinc oxide (ZnO) nanorods (NRs) with different surface morphology were grown by metal organic chemical vapor deposition (MOCVD) on sapphire substrate. To study the effect of surface morphology on wettability, the contact angle (CA) of water was measured. It was demonstrated that the CA of the deposited ZnO NRs varied between 104° and 135° depending upon the surface morphology. The ZnO NRs became super-hydrophilic after ultraviolet (UV) illumination. However, the NR arrays were reconverted to their previous hydrophobic state after low temperature annealing (50°C) in open atmosphere. Structural effect and preferential adsorption of water molecules on the defective sites of UV illuminated surface was used to explain the transition mechanism. Under the alternations of heat treatment and UV illumination, a reversible transition between hydrophobicity and super-hydrophilicity were observed.

Keywords: PACS; 82.70.Uv; 81.05.Dz; 61.46.KmHydrophobicity; ZnO; Nanorods

Effect of calcination temperature on the morphology and surface properties of TiO₂ nanotube arrays by Gang Li; Zhong-Qing Liu; Jing Lu; Lei Wang; Zhao Zhang (pp. 7323-7328).

Well-ordered TiO₂ nanotube arrays were prepared by electrochemical anodization of titanium in aqueous electrolyte solution of H₃PO₄+NH₄F at a constant voltage of 20V for 3h, followed by calcined at various temperatures. X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS) and Photoluminescence (PL) were used to characterize the samples. The results showed that the as-prepared nanotube arrays before being calcined were amorphous and could transform to anatase phase at a heat treatment temperature higher than 400°C. As the calcination temperatures increased, crystallization of anatase phase enhanced and rutile phase appeared at 600°C. However, further increasing the calcination temperature would cause the collapse of nanotube arrays. PL intensity of the nanotube arrays annealed at 500°C was the lowest, which was probably ascribed to better crystallization together with fewer surface defects of the nanotube arrays.

Keywords: PACS; 68.55.−aTiO; ₂; nanotube arrays; Electrochemical anodization; Calcination temperature; Photoluminescence

Styrene-butadiene rubber/halloysite nanotubes nanocomposites modified by sorbic acid by Baochun Guo; Feng Chen; Yanda Lei; Xiaoliang Liu; Jingjing Wan; Demin Jia (pp. 7329-7336).

Sorbic acid (SA) was used to improve the performance of styrene-butadiene rubber (SBR)/halloysite nanotubes (HNTs) nanocomposites by direct blending. The detailed mechanisms for the largely improved performance were studied by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), differential scanning calorimetry (DSC), porosity analysis and crosslink density determination. The strong interfacial bonding between HNTs and rubber matrix is resulted through SA intermediated linkages. SA bonds SBR and HNTs through grafting copolymerization/hydrogen bonding mechanism. Significantly improved dispersion of HNTs in virtue of the interactions between HNTs and SA was achieved. Formation of zinc disorbate (ZDS) was revealed during the vulcanization of the composites. However, in the present systems, the contribution of ZDS to the reinforcement was limited. Effects of SA content on the vulcanization behavior, morphology and mechanical properties of the nanocomposites were investigated. Promising mechanical properties of SA modified SBR/HNTs nanocomposites were obtained. The changes in vulcanization behavior, mechanical properties and morphology were correlated with the interactions between HNTs and SA and the largely improved dispersion of HNTs.

Keywords: Styrene-butadiene rubber; Halloysite nanotubes; Sorbic acid; Interface; Dispersion; Reinforcing mechanism

Adsorption of octylamine on titanium dioxide by Daria Siwińska; Agnieszka Kołodziejczak-Radzimska; Andrzej Krysztafkiewicz; Teofil Jesionowski (pp. 7337-7342).

Processes of adsorption and desorption of a model active substance (octylamine) on the surface of unmodified titanium dioxide (E 171) have been performed. The effects of concentration of octylamine and time of the process on the character of adsorption have been studied and the efficiency of the adsorption/desorption has been determined. The samples obtained have been studied by X-ray diffraction. The nitrogen adsorption/desorption isotherms, particle size distribution and absorption capacities of water, dibutyl phthalate and paraffin oil have been determined. The efficiency of octylamine adsorption on the surface of the titanium dioxide has been found positively correlated with the concentration of octylamine in the initial solution. The desorption of octylamine has decreased with increasing concentration of this compound adsorbed. For octylamine in low concentrations the physical adsorption has been found to dominate, which is desirable when using TiO₂ in the production of pharmaceuticals.

Keywords: Titanium dioxide (E 171); Octylamine; Adsorption and desorption; TiO; ₂; dispersive and adsorptive characteristics

A novel toluene sensor based on ZnO–SnO₂ nanofiber web by Xiaofeng Song; Dejiang Zhang; Meng Fan (pp. 7343-7347).

We proposed in the present work that large-scale synthesis of sensitive ZnO–SnO₂ nanofibres which can be obtained via a simple electrospinning method. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction patterns (XRD) showed the average diameter of ZnO–SnO₂ nanofibres ranging between 100 and 200nm, the mixture of wurtzite (ZnO) and rutile (SnO₂) structure in the composite fibers. The sensitivity of the obtained ZnO–SnO₂ nanofibres to toluene was also investigated. The results showed that under optimal conditions, the calibration curve of response versus toluene concentration was linear in the range of 10–300ppm, the response and recovery time were only several seconds, and sensitivity for toluene was desirable.

Keywords: Electrospinning; ZnO–SnO; ₂; nanofiber; Toluene sensor

Effect of theδ-doping on the electron transport in an antiparallel doubleδ-magnetic-barrier nanostructure by Jian-Duo Lu (pp. 7348-7350).

In this paper, we investigate the effect of the weight and the position of theδ-doping on the electron transport in a nanostructure with an antiparallel doubleδ-magnetic barriers. We find the weight of theδ-doping obviously suppresses the transmission probability and the electron conductance. We also find that there is no spin-polarization when theδ-doping is sited at the middle of the two magnetic fields, while the large degree of the spin-polarization could be achieved by changing the position of theδ-doping. These interesting features will be more helpful for developing new types of devices.

Keywords: PACS; 73.40.Gk; 72.25.−b; 73.23.−bMagnetic nanostructure; δ; -Doping; Spin-polarization

X-ray photoelectron spectroscopic study on surface reaction on titanium by laser irradiation in nitrogen atmosphere by Naofumi Ohtsu; Kenji Kodama; Kuniyuki Kitagawa; Kazuaki Wagatsuma (pp. 7351-7356).

The surface reaction on titanium due to pulsed Nd:YAG laser irradiation in a nitrogen atmosphere was investigated using X-ray photoelectron spectroscopy (XPS). The laser, with a wavelength of 532nm (SHG mode), was irradiated on a titanium substrate in an atmosphere-controlled chamber, and then the substrate was transported to an XPS analysis chamber without exposure to air. This in situ XPS technique makes it possible to clearly observe the intrinsic surface reaction. The characteristics of the surface layer strongly depend on the nitrogen gas pressure. When the pressure is 133kPa, an oxynitride and a stoichiometric titanium nitride form the topmost and lower surface layers on the titanium substrate, respectively. However, only a nonstoichiometric titanium oxide layer containing a small amount of nitrogen is formed when the pressure is lower than 13.3kPa. Repetition of laser shots promotes the formation of the oxide layer, but the formation is completed within a few laser shots. After the initial structure is formed, the chemical state of the surface layer is less influenced by the repetition of laser shots.

Keywords: Laser nitridation; In situ; XPS; Titanium nitride; Repetition of laser shots

Failure behavior of ITO diffusion barrier between electroplating Cu and Si substrate annealed in a low vacuum by S.H. Hsieh; C.M. Chien; W.L. Liu; W.J. Chen (pp. 7357-7360).

A structure of Cu/ITO(10nm)/Si was first formed and then annealed at various temperatures for 5min in a rapid thermal annealing furnace under 10⁻²Torr pressure. In Cu/ITO(10nm)/Si structure, the ITO(10nm) film was coated on Si substrate by sputtering process and the Cu film was deposited on ITO film by electroplating technique. The various Cu/ITO(10nm)/Si samples were characterized by a four-point probe, a scanning electron microscope, an X-ray diffractometer, and a transmission electron microscope. The results showed that when the annealing temperature increases near 600°C the interface between Cu and ITO becomes unstable, and the Cu₃Si particles begin to form; and when the annealing temperature increases to 650°C, a good many of Cu₃Si particles about 1μm in size form and the sheet resistance of Cu/ITO(10nm)/Si structure largely increases.

Keywords: Diffusion barrier; Indium Tin Oxide (ITO); Electroplating Cu; Cu metallization; Si substrate

Solvothermal synthesis and formation mechanism of chain-like triangular silver nanoplate assemblies: Application to metal-enhanced fluorescence (MEF) by Xin He; Xiujian Zhao (pp. 7361-7368).

Novel silver chain-like triangular nanoplate assemblies (CTNAs) were synthesized via a solvothermal approach. The shape of CTNAs was determined by some dominant parameters, including the concentration of poly (vinyl pyrrolidone), reactive time and temperature. Each CTNA is a single crystal with continuous lattice fringes in the inner, and could be considered as the combination of one-dimensional nanobelt and two-dimensional nanoplates. The formation of the CTNAs could be ascribed to the secondary growth of the nanocrystals. The edges of the nanoplates in the assembly were parallel to each other in order to maintain the lower surface energy. Interestingly, this novel nanostructure is a significant improvement for application in metal-enhanced fluorescence. Typical 88- and 13-fold enhancement in the emission intensity of dye Rhodamine B could be respectively achieved on the surface of silver colloids and silver coated-glass. The CTNAs have wide potential applications in the improvement of the sensitivity for medical or biological assays.

Keywords: Silver nanostructure; Chain-like nanoplate assembly; Solvothermal synthesis; Metal-enhanced fluorescence

The wettability of polytetrafluoroethylene and polymethylmethacrylate by aqueous solutions of Triton X-100 and short chain alcohol mixtures by Anna Zdziennicka (pp. 7369-7379).

Measurements of advancing contact angles ( θ) were carried out for aqueous solutions of Triton X-100 (TX-100) and methanol and ethanol mixtures at constant TX-100 concentration equal to 1×10⁻⁷, 1×10⁻⁶, 1×10⁻⁵, 1×10⁻⁴, 6×10⁻⁴ and 1×10⁻³M, respectively, on polytetrafluoroethylene (PTFE) and polymethylmethacrylate (PMMA). Using measured contact angle values the relationships between cos θ, adhesion tension and surface tension of the solutions were determined, and on their basis the critical surface tension of PTFE and PMMA wetting was calculated. The obtained average value of the critical surface tension of PTFE wetting is lying in the range of the PTFE surface tension values which can be found in the literature, while for PMMA it is even lower than the Lifshitz–van der Waals component of its surface tension. From the relationship between the adhesion and surface tension and Lucassen–Reynders equation it results that in the case of PTFE the adsorption at the PTFE–solution and solution–air interfaces is the same, which was confirmed by a linear relationship between the cos θ and 1/ γ_LV and intercept on cos θ axis equal to −1. However, for PMMA the adsorption of the surface active agents at solution–air interface is higher than at PMMA–solution. Using the values of the contact angle the values of the adhesion work of solution to the PTFE and PMMA surface were also determined, which are constant for PTFE, but for PMMA decrease with alcohol concentration increase. Next, using the contact angle values in the Young equation, the PTFE(PMMA)–solution interface tension was also calculated. The obtained values of PTFE–solution interface tension were compared with those evaluated from the Szyszkowski, Connors and Fainerman and Miller equations, and good agreement between these values was observed for all series of TX-100 and alcohol mixtures at a low alcohol concentration.

Keywords: Triton X-100; Alcohol; Wetting; Critical surface tension; Adhesion work; Solid–liquid interfacial tension

Formation of Ag₂, Au₂ and AgAu particles on MgO(100): DFT study on the role of support-induced charge transfer in metal–metal interactions by Silvia A. Fuente; Patricia G. Belelli; María M. Branda; Ricardo M. Ferullo; Norberto J. Castellani (pp. 7380-7384).

The formation of Ag₂, Au₂ and AgAu particles oriented perpendicularly to the MgO(100) surface was studied using the density functional theory. While the support induces a slight enhancement of the Ag–Ag bond (by 0.3–0.4eV), the Au–Au bond is strongly enhanced (by 0.8–1.1eV). Concerning the bimetallic particle, the Ag–Au bond stabilization depends on the relative position of each atom. Thus, in general terms, the strength of the metal–metal bond is determined by the nature of the terminal atom; the bond is stronger in Au-terminal particles. The partial electronic charge transfer to the terminal Au atom and its ability to polarize this charge are responsible for this energetic stabilization.

Keywords: Au/MgO; Ag/MgO; Gold–silver clusters; DFT; Cluster model

Fabrication, characterization and photoelectrochemical properties of Fe₂O₃ modified TiO₂ nanotube arrays by Shuyun Kuang; Lixia Yang; Shenlian Luo; Qingyun Cai (pp. 7385-7388).

TiO₂ nanotube (NT) arrays modified by Fe₂O₃ with high sensibility in the visible spectrum were first prepared by annealing anodic titania NTs pre-loaded with Fe(OH)₃ which was uniformly clung to the titania NTs using sequential chemical bath deposition (S-CBD). The photoelectrochemical performances of the as-prepared composite nanotubes were determined by measuring the photo-generated currents and voltages under illumination of UV–vis light. The titania NTs modified by Fe₂O₃ showed higher photopotential and photocurrent values than those of unmodified titania NTs. The enhanced photoelectrochemical behaviors can be attributed to the modified Fe₂O₃ which increases the probability of charge–carrier separation and extends the range of the TiO₂ photoresponse from ultraviolet (UV) to visible region due to the low band gap of 2.2eV of Fe₂O₃.

Keywords: TiO; ₂; nanotube array; Fe; ₂; O; ₃; Visible light; Water splitting; Photocatalyst

Tracking hydroxyl adsorption on TiO₂ (110) through secondary emission changes by H.P. Marques; A.R. Canário; A.M.C. Moutinho; O.M.N.D. Teodoro (pp. 7389-7393).

In surface science, rutile TiO₂ continues to be one of the most studied surfaces and in the catalysis field numerous groups study how adsorbates interact with this surface. All groups face the difficult problem of reproducibility due to surface preparation unknowns like defect concentration and the continuous aging of the crystals. Recent studies, using STM imaging, showed that hydroxyl adsorption takes place even in very good vacuum conditions. Upon adsorption, the surface electric field is reduced and the work function decreases. We found that this change may be readily detected in the onset energy of the secondary electrons. By following the onset region of secondary electron emission it is possible to track hydroxyl adsorption in quantities well below the detection level of XPS and LEIS. With this knowledge, we show that the time elapsed after surface preparation and water partial pressure should be accounted in the study of TiO₂ surfaces.

Keywords: Titanium oxide; Hydroxyl adsorption; Work function measurements; Secondary electron emission measurements

Studies of the electrochemical reduction processes of Bi³⁺, HTeO₂⁺ and their mixtures by Fei-Hui Li; Fa-Long Jia; Wei Wang (pp. 7394-7402).

The reduction process of Bi³⁺, HTeO₂⁺ and their mixtures on Au electrode surface was studied by cyclic voltammetry, linear sweep voltammetry, electrochemical impedance spectroscopy and chronoamperometry. XRD and EDS methods were also used to measure the reductive products prepared under different potentials and provide the evidences of the reactions. The results indicate that the reduction of HTeO₂⁺ occurs at more positive potential than that of Bi³⁺, but its reduction rate is slower and adsorption phenomenon exists during its reduction process. Bi₂Te₃ compound can be obtained potentiostatically at a proper potential in all the mixed solutions with concentration ratioCHTeO2+/CBi3+ in our research range (0.1–10). But pure Bi₂Te₃ compound can only be obtained at 42mV in the solution with concentration ratioCHTeO2+/CBi3+ equaling to 1. And the formation of Bi₂Te₃ compound is an inductive co-depositing process: (1) HTeO₂⁺+4e⁻+3H⁺→Te⁰+2H₂O, (2) 3Te⁰+2Bi³⁺+6e⁻→Bi₂Te₃.

Keywords: HTeO; ₂; ⁺; Bi; ³⁺; Electrochemical reducing process

Deposition of nanostructured crystalline and corrosion resistant alumina film on bell metal at low temperature by rf magnetron sputtering by H. Kakati; A.R. Pal; H. Bailung; Joyanti Chutia (pp. 7403-7407).

Aluminium oxide films deposited by rf magnetron sputtering for protective coatings have been investigated. The alumina films are found to exhibit grainy surface microstructure. The grain size, structure and density depend on different system parameters such as argon and/or oxygen flow rate and applied rf power etc. The effect of transition of the discharge from metallic to reactive mode on the surface characteristics of the alumina film is studied. X-ray diffractometry reveals that in poisoned mode of sputtering and under optimized power and pressure, crystalline alumina film can be grown. Different system conditions are optimized for corrosion resistant aluminium oxide films with good adhesion properties. Nanostructured alumina film is obtained at lower pressure (8×10⁻⁴ to 9×10⁻⁴Torr) by rf reactive magnetron sputtering.

Keywords: Crystalline alumina; Rf magnetron sputtering; Corrosion; Adhesion

Structure, hardness and corrosion behavior of a gradient CrN_x thick coating applied to turbine blades by Zhao-yun Chen; Zhi-qiang Li; Xiang-hong Meng (pp. 7408-7413).

In order to protect turbine blades from solid particle erosion, a gradient CrN_x coating was deposited on 10% Cr heat-resistant steel by ion plating; the thickness of the coating was about 40μm. The chemical composition, microstructure and nano-hardness of gradient CrN_x coating were analyzed. The bonding force was determined using scratch test. The potentiodynamic polarization and high-temperature oxidation tests were respectively conducted to investigate the corrosion behavior. The results indicate that gradient variation of phase structure, chemical composition and nano-hardness in the coating is found, and the bonding force with substrate is excellent. The microstructure obtained can enhance the corrosion performance of the substrate. The corrosion resistance improvement is not only attributed to the increase of coating in thickness, but also to internal microstructure and chemical composition of coating. Based on SEM and TEM observations, the cross-sectional fracture of the coating shows nano-crystalline and fine columnar crystalline structures. There are no penetrable pinholes, which could validly reduce the electrolyte transferring to inner substrate. In addition, the corrosion resistance of coating is further improved by the formation of nitrogen and chromium rich transition layers.

Keywords: Coating; Corrosion; Oxidation; Chromium nitride; Ion plating

Surface roughness and friction coefficient in peened friction stir welded 2195 aluminum alloy by Omar Hatamleh; James Smith; Donald Cohen; Robert Bradley (pp. 7414-7426).

The tribological properties of friction stir welded 2195 aluminum alloy joints were investigated for several laser- and shot-peened specimens. The first portion of this study assessed the surface roughness changes at different regions of the weld resulting from the various peening processes and included an atomic force microscopy (AFM) study to reveal fine structures. The second portion investigated the friction characteristics for various conditions when slid against a 440C ball slider. Shot peening resulted in significant surface roughness when compared to the unpeened and laser-peened samples. The initial friction for all types of specimens was highly variable. However, long-term friction was shown to be lowest for samples with no peening treatment. Laser peening caused the friction to increase slightly. The shot peening process on the other hand resulted in an increase of the long-term friction effects on both sides of the weld.

Keywords: Friction stir welding; Laser peening; Shot peening; Surface roughness; Friction; AA 2195

Evolution mechanism of alumina coating layer on rutile TiO₂ powders and the pigmentary properties by Yumin Liu; Yunsheng Zhang; Chen Ge; Hengbo Yin; Aili Wang; Min Ren; Hui Feng; Jun Chen; Tingshun Jiang; Longbao Yu (pp. 7427-7433).

The evolution of alumina coating layers on rutile TiO₂ particle surfaces was investigated starting from aluminum sulfate by a chemical liquid deposition method. The morphology of the alumina coating layers was determined by transmission electron microscopy. The chemical structure and the evolution mechanism of the alumina coating layers on TiO₂ surfaces were investigated by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and powder X-ray diffraction techniques. The dispersibility of the alumina-coated TiO₂ powders was determined by dynamic laser scattering (DLS) mode. The alumina coating layers existed in boehmite phase, AlOOH, and anchored at the surfaces of TiO₂ via Ti–O–Al bond. The formation of alumina coating layers on TiO₂ surfaces depended on the pH value of the deposition solution and the alumina loading. After coated by alumina layer, the dispersibility, whiteness, brightness, and light scattering index of the resultant samples were promoted.

Keywords: Rutile TiO; ₂; Alumina; Coating layer; Coating

Effect of defects on the reflectivity of Cr/C multilayer soft X-ray mirror at 4.48nm by Songwen Deng; Hongji Qi; Kui Yi; Zhengxiu Fan; Jianda Shao (pp. 7434-7438).

Cr/C is a promising material combination for multilayer mirror in the “near water window region” (4.4–6.7nm). In the present paper, the effect of defects on the reflectivity of Cr/C soft X-ray multilayer mirror deposited by magnetron sputtering was studied. Formation of thin interlayer due to the interdiffusion, rough interface due to the non-sharp layer and contamination of O happened during the deposition process were found by a method combined by XPS, soft X-ray reflectivity at 4.48nm and grazing incidence hard X-ray reflectivity at 0.154nm. The XPS results show that both interlayers (Cr-on-C and C-on-Cr) are mixture composed of C sp2, C sp3, CO, CO, CrCr and CrO bondings. No chromium carbide was found at the interlayer probably due to the blocking of oxides’ formation. Through the analysis of X-ray reflectivity, we obtained the multilayer structure parameters (thickness and roughness) and optical constants of each layer at 4.48nm. Based on those results, a further calculation was carried out. The result shows that the formation of the thin interlayer contributes little to the decrease of the reflectivity, the rough interface decreases the reflectivity most and the contaminant (O) not only decreases the reflectivity but also shifts the position of the peak.

Keywords: PACS; 78.20.−e; 81.70.−qMultilayer structure; X-ray reflectivity; XPS; Interlayer; Contamination

Superhydrophobic surfaces via electroless displacement of nanometric Cu layers by Ag⁺ by R. Brenier; S.M.M. Ramos; M. Montchanin (pp. 7439-7445).

This paper explores the possibility of making hydrophobic and superhydrophobic surfaces from electroless displacement of Cu by Ag⁺, in the case where Cu oxidation is limited owing to Cu layers of nanometric thicknesses. The morphology of the Ag layers is studied by scanning electron microscopy for Cu thicknesses between 10 and 80nm. The mapping of the elemental content of the layers by electron dispersive X-ray analysis also has been used to clarify the particle growing by diffusion limited aggregation. It is shown that the average size and the shape complexity of the Ag particles increase with the Cu thickness. The addition of dimethyl sulfoxide in the Ag⁺ aqueous solution improves the surface homogeneity, increases the particle density and decreases their sizes. The wetting behaviour of the surfaces, after grafting with octadecanethiol, has been studied from measurements of the contact angles of a drop of water. According to the thickness of the initial Cu layer and the morphology of the Ag layer, contact angles range between 110° and 154°. Superhydrophobic surfaces are obtained from 80nm thick Cu layers.

Keywords: PACS; 68.08.Bc; 68.35.C.tWetting; Superhydrophobic; Silver; Diffusion; Galvanic; Roughness

Impact of Mo and Ce on growth of single-walled carbon nanotubes by chemical vapour deposition using MgO-supported Fe catalysts by Abdel-Nasser A. El-Hendawy; Robert J. Andrews; Andrew J. Alexander (pp. 7446-7450).

A series of nine catalysts containing Ce/Fe and Mo/Fe at various loadings on MgO supports have been studied as catalysts for chemical vapour deposition (CVD) of single-walled carbon nanotubes (SWCNTs) using a methane carbon source. Our results show that the Ce/Fe system is very suitable as a catalyst that favours SWCNT growth, and we question the special importance that has been attributed to Mo as an additive to Fe-based catalysts for SWCNT growth, as it appears that Ce is equally effective. Our results indicate that dehydroaromatization (DHA) is not a defining step for the growth mechanism, as has been suggested for Mo/Fe systems previously, and show that Ce and Mo do not seriously perturb the well-known Fe/MgO system for growth of high quality SWCNT. Using Raman spectroscopy, we have shown that the Ce/Fe/MgO catalyst system favours growth of SWCNTs with a different distribution of chiralities compared to the analogous Mo/Fe/MgO system.

Keywords: Carbon nanotubes; Chemical vapour deposition

Room-temperature ferromagnetism and in-plane magnetic anisotropy characteristics of nonpolar GaN:Mn films by Lili Sun; Fawang Yan; Huixiao Zhang; Junxi Wang; Guohong Wang; Yiping Zeng; Jinmin Li (pp. 7451-7454).

Diluted magnetic nonpolar GaN:Mn films have been fabricated by implanting Mn ions into nonpolar a-plane (112¯0) p-type GaN films and a subsequent rapid thermal annealing process. The ferromagnetism properties of the films were studied by means of superconducting quantum interference device (SQUID). Clearly in-plane magnetic anisotropy characteristics of the sample at 10K were revealed with the direction of the applied magnetic field rotating along the in-plane [0001]-axis. Moreover, obvious ferromagnetic properties of the sample up to 350K were detected by means of the temperature-dependent SQUID.

Keywords: PACS; 75.50.Pp; 81.05.Ea; 81.15.Gh; 85.40.RyDiluted magnetic semiconductors (DMSs); Nonpolar a-plane GaN:Mn films; Ion implantation; Room-temperature ferromagnetic properties; In-plane magnetic anisotropy

Preparation and characterization of modified nano-porous PVDF membrane with high antifouling property using UV photo-grafting by A. Rahimpour; S.S. Madaeni; S. Zereshki; Y. Mansourpanah (pp. 7455-7461).

In this study, the poly(vinylidene fluoride) (PVDF) membrane was prepared via immersion precipitation technique and modified by UV photo-grafting of hydrophilic monomers on the top membrane surface. Acrylic acid (AA) and 2-hydroxyethylmethacrylate (HEMA) as acrylic monomers and 2,4-phenylenediamine (PDA) and ethylene diamine (EDA) as amino monomers were used at different concentrations to modify the membrane and improve the hydrophilicity with less fouling tendency. Moreover the presence of benzophenon as photo-initiator for grafting the hydrophilic monomers onto PVDF membrane surface was elucidated. The virgin and modified PVDF membranes were characterized by contact angle, ATR–FTIR, SEM and cross-flow filtration. The contact angle measurements demonstrated that the hydrophilicities of the membranes were significantly enhanced by UV photo-grafting of hydrophilic monomers onto the membrane surface. The ATR–FTIR confirmed the occurrence of modification on PVDF membrane by UV photo-grafting. The pure water flux of membranes was declined by UV photo-grafting but the milk water permeation and protein rejection were slightly improved. Moreover the antifouling properties and flux recovery of PVDF membrane were improved by UV photo-grafting of hydrophilic monomers.

Keywords: Membrane; Nano-porous; UV; Grafting; Poly(vinylidene fluoride)

Critical behaviour of magnetic thin film with Heisenberg spin-S model by R. Masrour; M. Hamedoun; K. Bouslykhane; A. Hourmatallah; N. Benzakour; A. Benyoussef (pp. 7462-7467).

The magnetic properties of a ferromagnetic thin film of face centered cubic (FCC) lattice with Heisenberg spin-S are examined using the high-temperature series expansions technique extrapolated with Padé approximations method. The critical reduced temperature of the system τ_c is studied as function of thickness of the film and the exchange interactions in the bulk, and within the surfaces J_b, J_s and J_⊥ respectively. A critical value of surface exchange interaction above which surface magnetism appears is obtained. The dependence of the reduced critical temperature on the film thickness L has been investigated.

Keywords: PACS; 75.70.Ak; 71.70.Gm; 77.80.BhHigh-temperature series expansions; Magnetic thin film exchange interactions; Heisenberg model

Decomposition of gaseous toluene on thermally-excited titanium dioxide and its ESR study under high temperatures by Harumitsu Nishikawa (pp. 7468-7470).

Decomposition of gaseous toluene on thermally-excited activated titanium dioxide (TiO₂) was investigated using a simple flow system. The decomposition of toluene on the TiO₂ bead was 92% at 400°C. The irregular phenomena in the toluene decomposition at around 300°C seemed to be due to the coloration of the TiO₂ bead. Electron spin resonance (ESR) measurement at high temperatures was carried out using the heating unit. Since the g-value of the signal was 1.996, the existence of Ti³⁺ in TiO₂ material was confirmed. That is, oxygen vacancy generated by thermally-excitation of TiO₂, and the reaction activity of the TiO₂ bead for gaseous toluene must be due to spins on the material.

Keywords: Titanium dioxide; Thermally-excitation; Toluene; Decomposition; ESR study

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Applied Surface Science (v.255, #16)