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Applied Surface Science (v.252, #8)

The behaviors of the carrier concentrations and mobilities in indium–tin-oxide thin films by DC and RF-superimposed DC reactive magnetron sputtering at the various process temperatures by Ho-Chul Lee (pp. 2647-2656).

Indium–tin-oxide (ITO) thin films were deposited by DC and RF-superimposed DC (RF-DC) reactive magnetron sputtering at the various process temperatures from 70 to 380°C. And the behaviors of the carrier concentrations and mobilities in ITO thin films by different plasma excitation modes were investigated by means of the Hall technique. The relationship between the carrier concentrations and mobilities in ITO thin films by both DC and RF-DC sputtering had two distinct regions: (i) region I at low process temperatures, where both the carrier concentrations and mobilities increased together; (ii) region II at high process temperatures, where the carrier concentrations further increased but the carrier mobilities decreased.At low process temperatures of region I, the crystallinities were low and the grain boundary scattering was dominant. However, at high process temperatures of region II, ITO thin films were highly crystallized and the ionized impurity scattering from high carrier concentrations was dominant.The overall characterizations, related to the carrier concentrations and mobilities, were also performed using X-ray diffractometer, scanning electron microscopy, UV/vis/NIR spectrometer and atomic force microscope.

Keywords: Indium–tin-oxide; Sputtering; Hall measurement; Carrier concentration; Carrier mobility; Process temperature

Desorption of chemisorbed Carbon on Mo(100) by noble gas ion sputtering: Validation of ground test measurements of ion engine lifetimes by Chih-Sung Ho; Santanu Banerjee; Bruce E. Koel; Olivier B. Duchemin; James E. Polk (pp. 2657-2664).

We report desorption cross section measurements for one monolayer of chemisorbed carbon on a Mo(100) surface induced by sputtering with noble gas ions (Ne⁺, Ar⁺, Xe⁺) at different incident angles, ion energies, and substrate temperatures. Desorption cross sections were determined by using low-energy ion scattering (LEIS) to monitor the increase of the signal from the Mo substrate. A monolayer of p(1×1) carbon adatoms on the Mo(100) surface was created by dosing ethylene (C₂H₄) to the substrate at 800K, and characterized by Auger electron spectroscopy (AES) and low energy electron diffraction (LEED). We find that the carbon desorption cross section increases with increasing mass and energy of the impinging ions, and there is a maximum value for the desorption cross section at an incident angle for the ions of 30° from the surface plane. The desorption cross section also increases up to a substrate temperature of 300°C. Values for the carbon desorption cross section for carbon adatoms on Mo(100) by 400-eV Xe⁺ ion sputtering are about 2×10⁻¹⁵cm², which is one order of magnitude higher than those for bulk carbon samples. This information is particularly important for evaluation of ion-engine lifetimes from ground-test measurements in which contaminant carbon is deposited on Mo accelerator grids, potentially altering the sputtering rate of the Mo. Our measurements show that monolayer amounts of carbon on Mo have desorption cross sections that are two orders of magnitude higher than estimates of what would be required to reduce the Mo erosion rate, and thus ground-test measurements can be used with confidence to predict ion-engine wear in space, from this perspective.

Keywords: PACS; 81.05.Bx; 82.30.-b; 82.65.-i; 82.65.My; 82.65.Jv; 82.80.Pv; 82.80.YcDesorption; Carbon; Mo(1; 0; 0); Sputtering; Ions; Ne; ⁺; Ar; ⁺; Xe; ⁺; Low-energy ion scattering (LEIS); Desorption cross section; Ion-engine lifetimes

Selective metal pattern formation and its EMI shielding efficiency by Ho-Chul Lee; Jin-Young Kim; Chang-Ho Noh; Ki Yong Song; Sung-Heon Cho (pp. 2665-2672).

A novel method for selective metal pattern formation by using an enhanced life-time of photoexcited electron-hole pairs in bilayer thin film of amorphous titanium dioxide and hole-scavenger-containing poly(vinyl alcohol) was proposed. By UV-irradiation through photomask on the bilayer film, the photodefined image of photoelectrons could be easily and simply produced, consequently resulting in selective palladium (Pd) catalyst deposition by reduction. The successive electrolessplating on Pd catalysts and electroplating on electrolessplated pattern were possible. Furthermore, the electromagnetic interference shielding efficiencies of the metal mesh patterns with various characteristic length scales of line width and thickness were investigated.

Keywords: Selective deposition; Amorphous TiO; ₂; Hole-scavenger; Life-time; Photoelectron; Mesh pattern; EMI; Shielding

The orbital interaction of adsorbed CO on NiO (001;111) surface: A periodic density functional theory study by Wenfeng Wang; Junqian Li; Yongfan Zhang (pp. 2673-2683).

The DOS structures of NiO (001;111) surfaces and CO adsorption on these surfaces have been studied with spin-unrestricted and periodic DFT (B3LYP) methods. On the basis of the analysis of orbital interaction on DOSs, the bonding properties of surface atomic orbitals have also been interpreted. It is found that CO adsorption on (001) and (111) surfaces have different mechanisms and adsorption energies. A four-electron σ orbital interaction is produced when CO is adsorbed on NiO (111), CO adsorbption on NiO (111) surface is obviously stronger than that on surface (001). It is easy for the clean NiO (111) surface to reconstruct to (2×2) structure, but the surface covered by CO does not undergo such a reconstruction.

Keywords: Orbital interaction; DOS analysis; Periodic DFT method

Enhanced corrosion resistance of mild steel in molar hydrochloric acid solution by 1,4-bis(2-pyridyl)-5H-pyridazino[4,5-b]indole: Electrochemical, theoretical and XPS studies by F. Bentiss; F. Gassama; D. Barbry; L. Gengembre; H. Vezin; M. Lagren�e; M. Traisnel (pp. 2684-2691).

The inhibition effect of the new pyridazine derivative, namely 1,4-bis(2-pyridyl)-5H-pyridazino[4,5-b]indole (PPI) against mild steel corrosion in 1M HCl solutions was evaluated using weigh loss and electrochemical techniques (potentiodynamic polarisation curves and impedance spectroscopy). The experimental results suggest that PPI is a good corrosion inhibitor and the inhibition efficiency increased with the increase of PPI concentration, while the adsorption followed the Langmuir isotherm. X-ray photoelectron spectroscopy (XPS) and theoretical calculation of electronic density were carried out to establish the mechanism of corrosion inhibition of mild steel with PPI in 1M HCl medium. The inhibition action of this compound was, assumed to occur via adsorption on the steel surface through the active centres contained of the molecule. The corrosion inhibition is due to the formation of a chemisorbed film on the steel surface.

Keywords: Corrosion inhibition; Mild steel; Pyridazine; HCl solution; Adsorption

Density functional study of hypophosphite adsorption on Ni (111) and Cu (111) surfaces by Yue Zeng; Shubin Liu; Lihui Ou; Jianlong Yi; Shanci Yu; Huixian Wang; Xiaoming Xiao (pp. 2692-2701).

Surface structures and electronic properties of hypophosphite, H₂PO₂⁻, molecularly adsorbed on Ni(111) and Cu(111) surfaces are investigated in this work by density functional theory at B3LYP/6-31++g(d, p) level. We employ a four-metal-atom cluster as the simplified model for the surface and have fully optimized the geometry and orientation of H₂PO₂⁻ on the metal cluster. Six stable orientations have been discovered on both Ni (111) and Cu (111) surfaces. The most stable orientation of H₂PO₂⁻ was found to have its two oxygen atoms interact the surface with two PO bonds pointing downward. Results of the Mulliken population analysis showed that the back donation from 3d orbitals of the transition metal substrate to the unfilled 3d orbital of the phosphorus atom in H₂PO₂⁻ and 4s orbital's acceptance of electron donation from one lone pair of the oxygen atom in H₂PO₂⁻ play very important roles in the H₂PO₂⁻ adsorption on the transition metals. The averaged electron configuration of Ni in Ni₄ cluster is 4s^0.634p^0.023d^9.35 and that of Cu in Cu₄ cluster is 4s^1.004p^0.033d^9.97. Because of this subtle difference of electron configuration, the adsorption energy is larger on the Ni surface than on the Cu surface. The amount of charge transfers due to above two donations is larger from H₂PO₂⁻ to the Ni surface than to the Cu surface, leading to a more positively charged P atom in Ni_nH₂PO₂⁻ than in Cu_nH₂PO₂⁻. These results indicate that the phosphorus atom in Ni_nH₂PO₂⁻ complex is easier to be attacked by a nucleophile such as OH⁻ and subsequent oxidation of H₂PO₂⁻ can take place more favorably on Ni substrate than on Cu substrate.

Keywords: Density functional calculations; Hypophosphite; Nickel; Copper; Adsorption

Corrosion behavior of sputtered Cr–Si–Ni and Cr–Si–Ni–Al resistive films in 0.1M NaOH by Yuqin Zhang; Xianping Dong; Jiansheng Wu (pp. 2702-2710).

The corrosion behavior of magnetron sputtered Cr–Si–Ni and Cr–Si–Ni–Al resistive films had been investigated by means of the relative resistance change (Δ R/ R), polarization measurements, AES, and SEM in 0.1M NaOH solution at 25°C and 50°C, which simulated an alkaline environment. The results revealed that both the annealed Cr–Si–Ni and Cr–Si–Ni–Al films in Ar ambient exhibited good corrosion resistance and long-term reliability in 0.1M NaOH solution at 25°C, due to the formation of a protective oxide layer on the surface of two types of the films during corrosion. However, the corrosion properties of two types of the films became degraded rapidly with the solution temperature at 50°C. The studies showed that the pro-formation of a protective oxide layer on the surface of two types of the films by annealing in air had an enhancing effect on the corrosion properties of the films in 0.1M NaOH solution at 50°C, and that Cr–Si–Ni–Al films by annealing in air had more improving effect on the corrosion resistance and long-term reliability than Cr–Si–Ni films.

Keywords: Resistive films; Corrosion behavior; Relative resistance change; Alkaline environments

Electrostatic assembly of Cu₂O nanoparticles on DNA templates by Li Wang; Gang Wei; Bin Qi; Hualan Zhou; Zhiguo Liu; Yonghai Song; Xiurong Yang; Zhuang Li (pp. 2711-2716).

In this paper, a method for highly ordered assembly of cuprous oxide (Cu₂O) nanoparticles (NPs) by DNA templates was reported. Cetyltrimethylammonium bromide (CTAB)-capped Cu₂O NPs were adsorbed onto well-aligned λ-DNA chains to form necklace-like one-dimensional (1D) nanostructures. UV–vis, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) were used to characterize the nanostructure. The Cu₂O nanostructures fabricated with the method are both highly ordered and quite straight.

Keywords: PACS; 61.46.; 61.16.C; 82.70.DAssembly; Nanoparticles; DNA templates; Atomic force microscopy; Colloids

Qualitative electroless Ni/Au plating considerations for the solder mask on top of sequential build-up layers by Sam Siau; Alfons Vervaet; Lieven Degrendele; Johan De Baets; Andre Van Calster (pp. 2717-2740).

Advanced printed circuit boards (PCBs) with sequential build-up (SBU) layers require alternating dielectric and copper layers on top of a core substrate. This can be achieved by lamination of resin coated copper (RCC) or by coating of dielectric polymers followed by copper deposition. The plating of electroless Ni/Au used as a solderability preservative on top of sequential build-up layers is investigated. For this application a solder mask polymer has to be applied in order to separate solder pads. Experiments showed that on parts of the underlying build-up layer exposed to the electroless Ni plating solution electroless Ni can grow. This overplating is caused by the remains of colloidal Pd/Sn catalyst on top of the build-up layer from preceding electroless Cu deposition. At very small features skipping of the plating can also take place. The overplating and skipping phenomena are influenced by a number of parameters, such as the temperature, the concentration of the stabilizer and pH. The dimensions of features on the board and the thickness of the solder-mask polymer also influence skipping. Based on qualitative analyses of the skipping and overplating phenomena rules of thumb for the solder mask design based on the plating conditions are proposed.

Keywords: Build-up layer; Solder mask; Electroless Ni plating

Determination of the inelastic mean free paths (IMFPs) in Ti by elastic peak electron spectroscopy (EPES): Effect of impurities and surface excitations by B. Lesiak; J. Zemek; P. Jiricek (pp. 2741-2746).

Surface excitations are important in surface sensitive electron spectroscopes, especially in elastic peak electron spectroscopy (EPES) since they may distort quantitative information. This phenomenon is more pronounced at low electron energy and glancing emission angles and should be appropriately corrected.In the present work we investigate quantitatively the role of contaminations, density and surface excitations on electron inelastic mean free paths (IMFPs) in Ti determined by elastic peak electron spectroscopy (EPES) using Cu standard. In the Monte Carlo algorithm the new NIST 3.1 database of electron elastic scattering cross sections was applied. It has been also shown that accounting for surface excitations, as well as for appropriate input parameters (surface composition, density, hydrogen) in the EPES method, is important for accuracy of evaluated IMFPs. Due to high reactivity of Ti, the IMFPs for contaminated Ti may be of interest. The authors indicate the magnitude of various corrections on the IMFPs derived by EPES.

Keywords: Elastic peak electron spectroscopy; EPES; Inelastic mean free path; IMFP; Electron elastic scattering cross sections; Surface excitations; Ti; Cu

Formation of highly textured (111) Bi₂O₃ films by anodization of electrodeposited bismuth films by T.P. Gujar; V.R. Shinde; C.D. Lokhande; R.S. Mane; Sung-Hwan Han (pp. 2747-2751).

Highly textured bismuth oxide (Bi₂O₃) thin films have been prepared using anodic oxidation of electrodeposited bismuth films onto stainless steel substrates. The Bi₂O₃ films were uniform and adherent to substrate. The Bi₂O₃ films were characterized for their structural and electrical properties by means of X-ray diffraction (XRD), electrical resistivity and dielectric measurement techniques. The X-ray diffraction pattern showed that Bi₂O₃ films are highly textured along (111) plane. The room temperature electrical resistivity of the Bi₂O₃ films was 10⁵Ωcm. Dielectric measurement revealed normal oxide behavior with frequency.

Keywords: Bismuth film; Anodic oxidation; Bi; ₂; O; ₃; XRD studies

Effect of polarization on femtosecond laser pulses structuring silicon surface by Jing-Tao Zhu; Yi-Feng Shen; Wen Li; Xiao Chen; Gang Yin; De-Ying Chen; Li Zhao (pp. 2752-2756).

Arrays of conical-like spikes can be formed on silicon surface after irradiated with femtosecond laser pulses in ambient of SF₆ or N₂. In this article, we report our observations on how the shape of the spikes formed on silicon surface varies with the polarization of laser beam. The experimental results show that, with circular polarized laser irradiation, the shape of the spikes is conical; however, with linearly polarized laser irradiation, the spikes show elliptic conical shape, and the long-axes are perpendicular to the direction of the polarization of laser beam. The asymmetric shape of spikes produced by linearly polarized laser beam can be explained by considering the polarization dependence of Fresnel-refraction.

Keywords: PACS; 81.68.Cf; 81.05.Bx; 42.62.Cf; 52.38.Mf; 61.80.BaFemtosecond laser pulses; Polarization effect; Silicon surface microstructure

Role of pH and calcium ions in the adsorption of an alkyl N-aminodimethylphosphonate on steel: An XPS study by I. Frateur; A. Carnot; S. Zanna; P. Marcus (pp. 2757-2769).

The role of pH and calcium ions in the adsorption of an alkyl N-aminodimethylphosphonate on mild steel (E24) surfaces was investigated by XPS. Fe 2p_3/2 and O 1s spectra show that the oxide/hydroxide layer developed on the steel surface, immersed in the diphosphonate solution (7≤pH≤13, without Ca²⁺) or in a filtered cement solution (pH 13, 15.38mmoll⁻¹ of Ca²⁺), consists of Fe₂O₃, covered by a very thin layer of FeOOH (goethite). The total thickness of the oxide/hydroxide layer is ∼3nm and is independent of the pH and the presence/absence of Ca²⁺. In the absence of Ca²⁺ ions, the N 1s and P 2p spectra reveal that the adsorption of the diphosphonate on the outer layer of FeOOH takes place only for pH lower than the zero charge pH of goethite (7.55). At pH 7, the adsorbed diphosphonate layer is continuous and its equivalent thickness is ∼24Å (monolayer). In the presence of Ca²⁺ ions, the C 1s and Ca 2p signals indicate that calcium is present on the steel surface as calcium phosphonate (and Ca(OH)₂, in very small amount). The adsorption of the diphosphonate molecules on the steel surface is promoted in alkaline solution (pH>7.55) by the doubly charged Ca²⁺ ions that bridge the O⁻ of goethite and the P–O⁻ groups of the diphosphonate molecules. The measured values for the Ca/P intensity ratio are in the range 0.75–1, which suggests that the diphosphonate molecules are adsorbed on steel forming a polymer cross-linked by calcium ions through their phosphono groups. In the presence of Ca²⁺ ions in alkaline solution, the adsorbed diphosphonate layer is discontinuous and the surface coverage is found to be ∼34%.

Keywords: PACS; 82.65.−i; 82.80.PvSteel; Phosphonate; Adsorption; pH; Calcium; XPS

Band-edge photoluminescence in nanocrystalline ZnO:In films prepared by electrostatic spray deposition by Dam Hieu Chi; Le Thi Thanh Binh; Nguyen Thanh Binh; Le Duy Khanh; Nguyen Ngoc Long (pp. 2770-2775).

ZnO:In films are successfully prepared by using the electrostatic spray deposition technique. X-ray diffraction indicates that the ZnO:In films have a polycrystalline hexagonal wurtzite structure with lattice parametersa=3.267 Å andc=5.209 Å. Photoluminescence properties of the films are investigated in the temperature range of 11.6–300 K, showing strong luminescence in the whole range of temperature. The temperature dependence of the photoluminescence are carried out with full profile fitting of spectra, which clearly shows that the ultraviolet (UV) emission in In-doped ZnO films at low temperature are attributed to emission of a neutral donor-bound exciton (D^∘X) and recombination of donor–acceptor pairs (DAP), while the UV emission at room temperature originates from radiative transition of an electron bound on a donor to the valence band.

Keywords: PACS; 78.55.Et; 81.05.Dz; 81.15.RsSemiconductors; Chemical synthesis; Luminescence

Energy levels in doped SiGe quantum well studied by admittance spectroscopy by X.S. Cai; J. Qin; H.B. Yang; F.Y. Yuan; Y.L. Fan; F. Lu; Z.M. Jiang (pp. 2776-2781).

SiGe/Si quantum wells (QWs) with different Boron doping concentrations were grown by molecular beam epitaxy (MBE) on p-type Si(100) substrate. The activation energies of the heavily holes in ground states of QWs, which correspond to the energy differences between the heavy hole ground states and Si valence band, were measured by admittance spectroscopy. It is found that the activation energy in a heavily doped QW increases with doping concentration, which can be understood by the band alignment changes due to the doping in the QWs. Also, it is found that the activation energy in a QW with a doping concentration of 2×10²⁰cm⁻³ becomes larger after annealing at a temperature of 685°C, which is attributed to more Boron atoms activation in the QW by annealing.

Keywords: Molecular beam epitaxy; Heavy doping; SiGe; Quantum well; Admittance spectroscopy; Activation energy

Comparative study between IR and UV laser radiation applied to the removal of graffitis on urban buildings by C. G�mez; A. Costela; I. Garc�a-Moreno; R. Sastre (pp. 2782-2793).

The present article focuses on a comparison between cleaning process of graffitis on urban buildings by using laser radiation at 308nm (XeCl excimer laser) and 1064nm (Nd:YAG laser). Laser-induced breakdown spectroscopy (LIBS) elemental analysis was applied as real-time diagnostic technique, safeguarding against possible damage of the substrate during ablation rate studies. The morphological analysis of the etched surfaces by optical microscopy and environmental scanning electron microscopy reveals remarkable features of interest to understand the wavelength dependence of the ablation efficiency. The ablation threshold fluences of different paints sprayed on several substrates were determined applying a photoacoustic technique. To remove graffitis from urban buildings the laser radiation at 1064nm was observed to be the most efficient wavelength, supporting the best result.

Keywords: PACS; 42.62.−b; 61.80.Ba; 8i.65.Cf; 43.60.+dLaser cleaning; Excimer; Nd:YAG; Laser-induced breakdown spectroscopy; Photoacoustic technique; Graffitis

Effect of La surface treatments on corrosion resistance of A3 xx. x/SiC_p composites in salt fog by A. Pardo; M.C. Merino; R. Arrabal; S. Merino; F. Viejo; A.E. Coy (pp. 2794-2805).

The influence of the SiC_p proportion and the matrix concentration of four aluminium metal matrix composites (A360/SiC/10p, A360/SiC/20p, A380/SiC/10p, A380/SiC/20p) modified by lanthanum-based conversion or electrolysis coating was evaluated in neutral salt fog according to ASTM B 117. Lanthanum-based conversion coatings were obtained by immersion in 50�C solution of La(III) salt and lanthanum electrolysis treatments were performed in ethylene glycol mono-butyl ether solution. These treatments preferentially covered cathodic areas such as intermetallic compounds, Si eutectic and SiC_p. The kinetic of the corrosion process was studied on the basis of gravimetric tests. Both coating microstructure and nature of corrosion products were analyzed by scanning electron microscopy (SEM), atomic force microscopy (AFM), energy dispersive X-ray analysis (EDS) and low angle X-ray diffraction (XRD) before and after accelerated testing to determine the influence of microstructural changes on corrosion behaviour during exposure to the corrosive environment. The corrosion process was more influenced by the concentration of alloy elements in the matrix than by the proportion of SiC_p reinforcement. Both conversion and electrolysis surface treatments improved the behaviour to salt fog corrosion in comparison with original composites without treatment. Additionally, electrolysis provided a higher degree of protection than the conversion treatment because the coating was more extensive.

Keywords: PACS; 81.65.Kn (corrosion protection)Aluminium; Silicon carbide; Composites; Lanthanum; Chemical conversion; Salt spray

Effect of deposition parameters on morphology and size of FeCo nanoparticles synthesized by pulsed laser ablation deposition by Happy; S.R. Mohanty; P. Lee; T.L. Tan; S.V. Springham; A. Patran; R.V. Ramanujan; R.S. Rawat (pp. 2806-2816).

The experimental parameters that control the surface morphology and size of iron cobalt nanoparticles synthesized at room temperature by pulsed laser ablation deposition (PLAD) technique have been systematically investigated. The nanoparticle synthesis has been achieved at higher operating gas pressures of argon. It was found that nanoparticles upon deposition formed small clusters, the size of which increases with decreasing pressure, increasing laser-energy density, and decreasing target-to-substrate distance. This trend could be attributed to change in the kinetic energy of deposited nanoparticles with varying argon pressure, laser-energy, and target-to-substrate distance. The nanoparticles size and size distribution showed strong dependence on argon pressure and weak dependence on laser-energy density and target-to-substrate distance.

Keywords: PACS; 81.05.Ys; 81.15.FgNanoparticles; FeCo; Pulsed laser ablation deposition

Enhancement of the photocatalytic activity of TiO₂ nanoparticles by surface-capping DBS groups by Wang Baiqi; Jing Liqiang; Qu Yichun; Li Shudan; Jiang Baojiang; Yang Libin; Xin Baifu; Fu Honggang (pp. 2817-2825).

TiO₂ nanoparticles capped with sodium dodecylbenzenesulfonate (DBS) are synthesized by a sol–hydrothermal process using tetrabutyl titanate and DBS as raw materials. The effects of surface-capping DBS on the surface photovoltage spectroscopy (SPS), photoluminescence (PL) and photocatalytic performance of TiO₂ nanoparticles are principally investigated together with their relationships. The results show that the surface of TiO₂ nanoparticles can be well capped by DBS groups while the pH value and added DBS amount are controlled at 5.0 and 2% of TiO₂ mass weight, respectively, and the linkage between DBS groups and TiO₂ surfaces is mainly by means of quasi-sulphonate bond. The intensities of SPS and PL spectra of TiO₂ obviously decrease after DBS-capping, while the activity can greatly increase during the photocatalytic degradation of Rhodamine B (RhB) solution, which are mainly attributed to the electron-withdrawing character of the DBS groups. Moreover, the enhancement of photocatalytic activity of DBS-capped TiO₂ is also related to the increase in the capability for adsorbing RhB.

Keywords: TiO; ₂; Sol–hydrothermal method; DBS; Surface-capping; Photocatalysis

Photoluminescence of thermal-annealed nanocolumnar ZnO thin films grown by electrodeposition by B. Mar�; F.J. Manj�n; M. Mollar; J. Cembrero; R. G�mez (pp. 2826-2831).

Nanostructured zinc oxide thin films formed by partially oriented hexagonal columns with dimensions of about 100nm×300nm have been prepared by cathodic electrodeposition on conducting glass substrates. After subsequent thermal annealing in air at different temperatures (100–500°C), structural information on the films was obtained by means of non-resonant Raman spectroscopy. Increasing the annealing temperature leads to a higher degree of crystallinity. The photoluminescence activity of the samples (at low temperature) also improves for increasing annealing temperatures in two ways: increasing the intensity of the near-band edge emission and decreasing the width of the excitonic peak. No emission band in the visible is detected, which attests the high quality of the ZnO nanocolumnar films.

Keywords: ZnO; Photoluminescence; Nanostructures; Electrodeposition; Transparent conducting oxide

Fabrication of Cu nano particles by direct electrochemical reduction from CuO nano particles by Won-Kyu Han; Jae-Woong Choi; Gil-Ho Hwang; Seok-Jun Hong; Jai-Sung Lee; Sung-Goon Kang (pp. 2832-2838).

In this report, Cu nano particles have been prepared by direct electrochemical reduction from CuO nano particles and the reduction mechanism was investigated. To investigate the reduction mechanism, CuO has been deposited on the AISI 430 by magnetron sputtering in various Ar/O₂ ratio and the cyclic voltammetry (CV) was performed in 0.5M NaCl solution at 300K. This result indicated that the oxygen from the CuO was ionized at −0.874V (versus SCE) and reduced to Cu. To fabricate Cu nano particles, we employed CuO nano particles, which were prepared by a conventional mechanical milling, with a dc rectifier and the specific electrochemical cell. The structure of the films and nano particles were analyzed by XRD, SEM/EDS and XPS.

Keywords: Cu nano particles; Direct electrochemical reduction; Cyclic voltammetry; XPS

Studies of the porosity in electroless nickel deposits on magnesium alloy by Jianzhong Li; Yanwen Tian; Zhenqi Huang; Xin Zhang (pp. 2839-2846).

In the present paper, the porosity of the plating coating was evaluated by the combination of corrodkote and filter paper, the effects of the plating solution on the porosity were investigated, and the properties of the porous coatings were studied through scanning electron microscopy (SEM) and electrochemical potentiodynamic polarization. The results show that the eriothrome black T indicator used as an indicator of the coating porosity for coatings on magnesium alloy is more effective than magneson indicator and sodium alizarinesulfonate indicator. The porosity in electroless nickel deposits on magnesium alloy was well evaluated by the combination of corrodkote and filter paper. It is revealed that the pores exist on both grain surface and grain boundaries. An affecting trend of the plating bath parameters on the coating porosity was obtained.

Keywords: Magnesium alloy; Electroless nickel plating; Porosity; Corrosion resistance

Effect of deposition condition on residual stress of iron nitride thin films prepared by magnetron sputtering and ion implantation by W.L. Li; W.D. Fei; T. Hanabusa (pp. 2847-2852).

The surface roughness and residual stress development in Fe–N thin films prepared by compound technology—combining magnetron sputtering with plasma based ion implantation were investigated by means of atomic force microscope and synchrotron radiation. The results indicate that the grain size of the thin film increases with the increasing of nitrogen ion implantation time, and the state of residual stress is related closely to the formation mechanism of thin films. With the nitrogen ion implantation time increasing, the residual stress of the thin film changes into tensile stress from initial compressive stress, and the tensile stress decreases with the further increasing of ion implantation time.

Keywords: Residual stress; Synchrotron radiation; Sputtering; Ion implantation

Synthesis of bamboo-leaf-shaped ZnO nanostructures by oxidation of Zn/SiO₂ composite films deposited with radio frequency magnetron co-sputtering by Liwei Shi; Yuguo Li; Chengshan Xue; Huizhao Zhuang; Jianting He; Dengheng Tian (pp. 2853-2857).

Bamboo-leaf-shaped ZnO nanostructures were synthesized by oxidation of metal Zn/SiO₂ matrix composite thin films deposited on Si(111) substrates with radio frequency magnetron co-sputtering. The synthesized bamboo-leaf-shaped ZnO are single crystalline in nature with widths ranging from 30 to 60nm and lengths of up to 5–10μm, room temperature photoluminescence spectrum of the nanostructures shows a strong and sharp UV emission band at 372nm and a weak and broad green emission band at about 520nm which indicates relatively excellent crystallization and optical quality of the ZnO nanostructures synthesized by this novel method.

Keywords: PACS; 71.55.Gs; 81.15.−z; 68.65.−kMagnetron co-sputtering; Oxidation; ZnO nanostructures; Optical property

Preparation of palladium film by coating photolysis process using KrF or ArF excimer laser by Yoji Imai; Tatsuo Tsunoda; Kiyoshi Kobayashi; Akio Watanabe (pp. 2858-2866).

The preparation of palladium (Pd) films has been investigated using KrF or ArF laser irradiation on a Pd acetate (PdAc) coated substrate. A crystalline Pd film could be obtained by KrF laser irradiation (fluence=15–40mJ/cm²) but PdAc was found to remain in the film. An increase in the substrate temperature to 423K decreased the inclusion of the unreacted precursor and produced a better crystallinity. An amorphous and uniform Pd film composed of very fine particles was found to be formed by this process under reduced pressure, which is probably due to the preferential ablation of the crystalline nuclei. ArF laser irradiation is more effective for decomposing the PdAc and for producing a Pd film with a better crystallinity and no (or smaller) organic inclusion.

Keywords: PACS; 81.15.Lm (deposition from liquid phases); 81.15.Fg (laser deposition)KrF laser; ArF laser; Pd; Pd acetate; Coating photolysis process

GaAs nanocrystals: Structure and vibrational properties by J. Nayak; S.N. Sahu; S. Nozaki (pp. 2867-2874).

GaAs nanocrystals were grown on indium tin oxide substrate by an electrodeposition technique. Atomic force microscopic measurement indicates an increase in the size of the nanocrystal with decrease in the electrolysis current density accompanied by the change in the shape of the crystallite. Transmission electron microscopic measurements identify the crystallite sizes to be in the range of 10–15nm and the crystal structure to be orthorhombic. On account of the quantum size effect, the first optical transition was blue shifted with respect to the band gap of the bulk GaAs and the excitonic peak appeared prominent. A localized phonon mode ascribed to certain point defect occurred in the room temperature micro-Raman spectrum.

Keywords: PACS; 61.46.+w; 81.07.−bQuantum size effect; Point defect; Micro-Raman spectroscopy; Orthorhombic phase

Molecular organization of phospholipid monolayers on the water surface by Maxwell displacement current measurement by Khaulah Sulaiman; Wan Haliza Abdul Majid; Muhamad Rasat Muhamad (pp. 2875-2881).

The monolayer of organic molecules at the air–water interface has been studied using the Maxwell displacement current (MDC) technique. The materials used in this study were the biological materials of phosphatidyl ethanolamine (PE) and phosphatidic acids (PA). The configuration of the experimental set-up consists of the metal/air-gap/monolayer/metal coupled with the Langmuir method. This measurement enables the detection of current without destroying the monolayer. The phase transition and molecular orientation of the phospholipid monolayers were investigated using MDC measurement without mechanical contact between electrodes and the materials. Direct evidence of phase transition from gaseous to the polar ordering phase can be obtained across phospholipid monolayers even though at very low surface pressure. Relaxation process of the phospholipid monolayers was investigated by using the step compression on the MDC signals.

Keywords: PACS; 68.35.RhPhospholipids; Langmuir monolayer; Maxwell displacement current (MDC); Phase transitions; Physico-chemical behaviours; Dielectric relaxation phenomena

Effect of nano-Y₂O₃ on microstructure of laser cladding cobalt-based alloy coatings by Li Mingxi; He Yizhu; Yuan Xiaomin (pp. 2882-2887).

Cobalt-based alloy coatings with and without nano-Y₂O₃ particles produced by a 5kW CO₂ laser on Ni-based superalloy were introduced. Solidified microstructure, phase compositions and distribution of nano-particles were investigated by using optical microscope, SEM, TEM and XRD. The results showed that metastable phases, such as γ-Co and Cr₂₃C₆ existed in cobalt-based alloy coatings. Another two phases (Y₂O₃ and ɛ-Co) were found by adding nano-Y₂O₃. Without nano-Y₂O₃, rapid directional solidified microstructure of columnar dendrite appeared. Fine and short dendritic microstructure and columnar to equiaxed transition (CET) occurred by adding nano-Y₂O₃ particles. With the increase in amount of nano-Y₂O₃, fully equiaxed crystallization appeared and the formation mechanism was analyzed. The results also showed that the sub-microstructure of the coatings changed from dislocation to stacking fault by adding nano-Y₂O₃.

Keywords: Laser cladding; Nano-Y; ₂; O; ₃; particles; Co-based alloy; Equiaxed grain

Influence of buffer layer thickness on the structure and optical properties of ZnO thin films by Ruijin Hong; Jianda Shao; Hongbo He; Zhengxiu Fan (pp. 2888-2893).

A series of ZnO thin films were deposited on ZnO buffer layers by DC reactive magnetron sputtering. The buffer layer thickness determination of microstructure and optical properties of ZnO films was investigated by X-ray diffraction (XRD), photoluminescence (PL), optical transmittance and absorption measurements. XRD results revealed that the stress of ZnO thin films varied with the buffer layer thickness. With the increase of buffer layer thickness, the band gap edge shifted toward longer wavelength. The near-band-edge (NBE) emission intensity of ZnO films deposited on ZnO buffer layer also varied with the increase of thickness due to the spatial confinement increasing the Coulomb interaction between electrons and holes. The PL measurement showed that the optimum thickness of the ZnO buffer layer was around 12nm.

Keywords: Zinc Oxide; Sputtering; Structure; Photoluminescence

Electrochemical and XPS studies of decylamides of α-amino acids adsorption on carbon steel in acidic environment by O. Olivares; N.V. Likhanova; B. G�mez; J. Navarrete; M.E. Llanos-Serrano; E. Arce; J.M. Hallen (pp. 2894-2909).

Corrosion inhibition of steel in hydrochloric acid by decylamides of α-amino acids derivatives was studied using gravimetric and electrochemical techniques. Protection efficiencies of 90% were obtained with 100ppm of tyrosine and glycine derivatives, while alanine and valine derivatives reached only 80%. The order of increasing inhibition efficiency was correlated with the modification of the molecular structure of inhibitors. Potentiodynamic polarization curves indicated that both the decylamide of tyrosine and glycine acted primarily as anodic type inhibitors, whereas the decylamide of alanine and valine were of the cathodic type. Thermodynamic parameters and Flory–Huggins adsorption isotherms described the experimental findings. The number of active sites, equilibrium constant, enthalpy and change of free energy were computed for all inhibitors studied. This information suggested that organic molecules were adsorbed and displaced water molecules from the steel surface. X-ray photoelectron spectroscopy confirmed that species of N, C and O interacted with steel to form a continuous protective film.

Keywords: Corrosion inhibitor; Amides of α-amino acids; C-1018 carbon steel; Acidic medium; Gravimetric measurements; Polarization scans; Flory–Huggins adsorption isotherms; X-ray photoelectron spectroscopy

A study of the effect of ZrO₂ on the magnetic properties of FePt/ZrO₂ multilayer by Xiao-Hong Xu; Xiao-Li Li; Fang Wang; Feng-Xian Jiang; Hai-Shun Wu (pp. 2910-2914).

Fe_xPt100−_x(30nm) and [Fe_xPt100−_x(3nm)/ZrO₂]₁₀ ( x=37, 48, 57, 63, 69) films with different ZrO₂ content were prepared by RF magnetron sputtering technique, then were annealed at 550°C for 30min. This work investigates the effect of ZrO₂ doping on the microstructural evolution, magnetic properties, grain size, as well as the ordering kinetics of FePt alloy films. The as-deposited films behaved a disordered state, and the ordered L1₀ structure was obtained by post-annealing. The magnetic properties of the films are changed from soft magnetism to hard magnetism after annealing. The variation of the largest coercivities of [Fe_xPt100−_x/ZrO₂]₁₀ films with the Fe atomic percentage, x and differing amounts of ZrO₂ content reveals that as we increase the ZrO₂ content we must correspondingly increase the amount of Fe. This phenomenon suggests that the Zr or O atoms of ZrO₂ preferentially react with the Fe atoms of FePt alloy to form compounds. In addition, introducing the nonmagnetic ZrO₂ can reduce the intergrain exchange interactions of the FePt/ZrO₂ films, and the interactions are decreased as the ZrO₂ content increases, the dipole interactions are observed in FePt/ZrO₂ films as the ZrO₂ content is more than 15%.

Keywords: pacs; 81.15.C; 75.60.G; 75.70.KFePt/ZrO; ₂; multilayers; Coercivity; Annealing; Exchange interaction

The surface alloying behavior of martensitic stainless steel cut with wire electrical discharge machine by Ching An Huang; Chwen Lin Shih; Kung Cheng Li; Yau-Zen Chang (pp. 2915-2926).

The surface alloying behavior of tempered martensitic stainless steel multi-cut with wire electrical discharge machine (WEDM) is studied in this paper. Before machined with WEDM, the steel specimens were quenched at 1050�C and then tempered at 200�C, 400�C, and 600�C, respectively. The microstructure and surface morphology of the multi-cut surfaces were examined with scanning and transmission electron microscopes integrated with an energy-dispersive X-ray spectrometer for chemical composition analysis. Experimental results show that the cut surfaces of the steel specimens were alloyed with wire-electrode material in various extent. Especially the cut surface was much more alloyed when the steel was cut with the first rough cutting pass by using negatively biased potential and final fine cutting using positively biased potential. Alloying degree of cut surfaces can be distinguished with their anodic polarization curves in 0.5M HClO₄+0.2wt% NaCl at 27�C. Higher passive current density induces deeper alloyed surface. On the severely alloyed surface, a secondary anodic peak in the potential of 120mV (versus Ag/AgCl_sat.) of its anodic polarization curve was observed. The presence of the secondary anodic peak was attributed to dissolution of copper, which was the major element of wire-electrode material from the alloyed surface.

Keywords: Wire electrical discharge machine (WEDM); Martensitic stainless steel; Microstructure; Electrochemical behavior

Deposition of duplex Al₂O₃/aluminum coatings on steel using a combined technique of arc spraying and plasma electrolytic oxidation by Weichao Gu; Dejiu Shen; Yulin Wang; Guangliang Chen; Wenran Feng; Guling Zhang; Songhua Fan; Chizi Liu; Size Yang (pp. 2927-2932).

Plasma electrolytic oxidation (PEO) is a cost-effective technique that can be used to prepare ceramic coatings on metals such as Ti, Al, Mg, Nb, etc., and their alloys, but this promising technique cannot be used to modify the surface properties of steels, which are the most widely used materials in engineering. In order to prepare metallurgically bonded ceramic coatings on steels, a combined technique of arc spraying and plasma electrolytic oxidation (PEO) was adopted. In this work, metallurgically bonded ceramic coatings on steels were obtained using this method. We firstly prepared aluminum coatings on steels by arc spraying, and then obtained the metallurgically bonded ceramic coatings on aluminum coatings by PEO. The characteristics of duplex coatings were analyzed by X-ray diffractometer (XRD) and scanning electron microscopy (SEM). The corrosion and wear resistance of the ceramic coatings were also studied. The results show that, duplex Al₂O₃/aluminum coatings have been deposited on steel substrate after the combined treatment. The ceramic coatings are mainly composed of α-Al₂O₃, γ-Al₂O₃, θ-Al₂O₃ and some amorphous phase. The duplex coatings show favorable corrosion and wear resistance properties. The investigations indicate that the combination of arc spraying and plasma electrolytic oxidation proves a promising technique for surface modification of steels for protective purposes.

Keywords: PACS; 81.15.−z; 82.45.Hk; 52.80.Wq; 68.47.Gh; 77.22.JpPlasma electrolytic oxidation; Ceramic coatings; Properties; Combined technique

Adsorption of nicotine and tar from the mainstream smoke of cigarettes by oxidized carbon nanotubes by Zhigang Chen; Lisha Zhang; Yiwen Tang; Zhijie Jia (pp. 2933-2937).

The adsorption of nicotine and tar from the mainstream smoke (MS) by the filter tips filled respectively with oxidized carbon nanotubes (O-CNTs), activated carbon and zeolite (NaY) has been investigated. O-CNTs show exceptional removal efficiency and their adsorption mechanism is investigated. Capillary condensation of some ingredients from MS in the inner hole of O-CNTs is observed and may be the primary reason for their superior removal efficiency. The effect of O-CNTs mass on the removal efficiencies is also studied and the results show that about 20–30mg O-CNTs per cigarette can effectively remove most of nicotine and tar.

Keywords: PACS; 68.43.−h; 68.35.−pCarbon nanotubes; Cigarette smoke; Adsorption; Tar and nicotine

Field emission properties and synthesis of carbon nanotubes grown by rf plasma-enhanced chemical vapor deposition by J. Jiang; T. Feng; J.H. Zhang; X.H. Cheng; G.B. Chao; B.Y. Jiang; Y.J. Wang; X. Wang; X.H. Liu; S.C. Zou (pp. 2938-2943).

Plasma-enhanced chemical vapor deposition (PECVD) method was employed to grow the Fe-catalyzed carbon nanotubes (CNTs). The grown CNTs with a uniform diameter in the range of about 10–20nm and the typical lengths beyond 1μm resulted in a very high aspect ratio. The Raman and TEM results showed that the grown CNTs contained a large amount of carbonaceous particles and crystal defects, such as pentagon–heptagon pair defects. XPS measurement indicated that the CNTs had CH covalent bonds. Field emission characteristics exhibited the low turn-on threshold field of 2.75V/μm and the maximum emission current density of 7.75mA/cm² at 6.5V/μm. The growth mechanism of CNTs and the effects of hydrogen plasma on their structure were discussed.

Keywords: PACS; 79.70.+q; 72.80.RjCarbon nanotubes; Plasma enhanced chemical vapor deposition; Growth mechanism; Defects

Cutting of multi walled carbon nanotubes by Jinyong Li; Yafei Zhang (pp. 2944-2948).

Multi walled carbon nanotubes (MCNT) synthesized by CVD method have been successfully cut into different lengths by controlling H₂SO₄/HNO₃ (5:3) oxidation time. During the cutting process H₂SO₄ and HNO₃ were added independently and the oxidation processes were carried out at a lower temperature to void excess weight loss and damage to MCNT. The resulting shorted MCNT (s-MCNT) formed stable dispersion state in the polar solvents without the help of surfactants that provided possibility for further functionalization and application. Moreover, NaOH solution was used to determine the total percentage of acidic sites and the total percentage of acidic sites are about 0.2–1%.

Keywords: PACS; 81.07.De; 81.70.Jb; 61.46.TwMulti walled carbon nanotubes (MCNT); Cutting; Titration; Scanning electron microscopy

Inhibition of copper corrosion by self-assembled films of new Schiff bases and their modification with alkanethiols in aqueous medium by M. Ehteshamzade; T. Shahrabi; M.G. Hosseini (pp. 2949-2959).

The inhibitive action of self-assembled films derived from two ligands Schiff bases, including N, N′-ethylen-bis (salicylidenimine) and N, N′- ortho-phenylen-bis (salicylidenimine) on copper surface has been studied by electrochemical techniques in chloride and acidic solutions. It was found that when the concentration of the inhibitors was increased the inhibition efficiency was increased, too. The results of the electrochemical studies have illustrated that the inhibition efficiency of S- o-ph-S is higher than S-E-S. Both the Schiff bases obeyed the Langmuir isotherm and thermodynamics calculations revealed that S- o-ph-S had larger adsorption constant and more negative free energy of adsorption with respect to S-E-S. When the films were modified by propanethiol and 1-dodecanethiol, the corrosion resistance of mixed films was significantly increased.

Keywords: Schiff bases; Corrosion inhibitors; Acidic medium; Chloride medium; Self-assembled films; Copper

Surface characteristics and antistatic mechanism of plasma-treated acrylic fibers by Yan-Chun Liu; Yan Xiong; Da-Nian Lu (pp. 2960-2966).

Acrylic fibers are treated by nitrogen glow-discharge plasma to promote surface antistatic properties. The treated surfaces are characterized by scanning electron microscopy (SEM), specific surface area analysis (BET) and X-ray photoelectron spectroscopy (XPS). Plasma treatment is found to increase the surface roughness, to modify the nature and density of surface functionalities, and to drastically improve the wettability and antistatic ability of acrylic fibers.

Keywords: Acrylic fibers; Plasma; Surface characteristics; Antistatic mechanism

In situ sol–gel composition of multicomponent hybrid precursor to hexagon-like Zn₂SiO₄:Tb³⁺ microcrystalline phosphors with different silicate sources by Honghua Huang; Bing Yan (pp. 2967-2972).

Zn₂SiO₄ doped with Tb³⁺ were in situ synthesized by a modified sol–gel technology with the assembly hybrid precursor employed four different silicate sources, i.e. 3-aminopropyl-trimethoxysilane (APMS), 3-aminopropyl-triethoxysilane (APES), 3-aminopropyl-methyl-diethoxysilane (APMES) and tetraethoxysilane (TEOS), respectively. The SEM result shows that there exist some novel unexpected micromorphological structures of hexagon-like with the dimension of 0.5–1.0μm. The photoluminescent properties of Zn₂SiO₄:Tb³⁺ phosphors have been studied as a function of Tb³⁺ doping concentration. Cross-relaxation process between identical Tb³⁺ ions results in the quenching of the⁵D₃ emission for high concentration sample.

Keywords: 78.20.−e; 78.55.−mHexagon-like; In situ sol–gel; Luminescent properties

Room-temperature electrosynthesized ZnO thin film with strong (002) orientation and its optical properties by Y.F. Mei; G.G. Siu; Ricky K.Y. Fu; Paul K. Chu; Z.M. Li; Z.K. Tang (pp. 2973-2977).

ZnO thin film with strong orientation (002) and smooth surface morphology was electrosynthesized on ITO-coated glass substrate at room temperature under pulsed voltage. Photoluminescence (PL) shows two obvious peaks: violet band and strong green band. The former is due to the free-excitonic transition and the latter is believed to arise from the single ionized oxygen vacancy ( V_O⁺). Raman scattering reveals that the 580cm⁻¹ mode and the shoulder peak mode at 550cm⁻¹ originate from the N-related local vibration mode (LVM) and E₁ (LO) mode, respectively.

Keywords: PACS; 71.55.Gs; 81.15.Pq; 78.55.−m; 78.30.−jII-VI semiconductors; Electrodeposition; Photoluminescence; Infrared and Raman spectra

Back flux at polyatomic gas expansion for pulsed laser evaporation by A.A. Morozov (pp. 2978-2988).

The back flux value at polyatomic gas expansion under pulsed laser evaporation is determined on the basis of one-dimensional direct Monte Carlo simulation. Calculations are performed for a wide range of evaporated matter amount. Taking into account rotational and vibrational degrees of freedom substantially increases the back flux. Dependence of the back recondensed fraction on the relaxation collision number is shown. The data are generally in good agreement with available analytical predictions. Importance of consideration of energy transfer from the internal degrees of freedom to the translational ones is illustrated by an example of pulsed laser evaporation of polytetrafluoroethylene (PTFE) and polymethylmethacrylate (PMMA).

Keywords: PACS; 52.38.Mf; 79.20.Ds; 81.15.FgPulsed laser ablation; Back flux; Direct simulation Monte Carlo; PTFE; PMMA

Tribological behavior of microarc oxidation coatings formed on titanium alloys against steel in dry and solid lubrication sliding by Y.M. Wang; B.L. Jiang; L.X. Guo; T.Q. Lei (pp. 2989-2998).

The coatings mainly composed of nanostructured TiO₂ were deposited on Ti6Al4V alloy by microarc oxidation (MAO). The duplex coatings of microarc oxidation combined with spraying graphite process were fabricated for the antifriction purpose. The tribological properties of unpolished, polished and duplex coating against steel under dry friction conditions were examined. It is found that antifriction property of the polished microarc oxidation coating is superior to that of the unpolished one. The improvement is attributed to the low surface roughness and the nanocrystalline structure of coatings. The duplex coating exhibits best antifriction property, registering a lower and steady friction coefficient of ≈0.12 than that of the polished microarc oxidation coating sliding in the similar condition. The good tribological property is attributed to the specially designed duplex structure, the coating adhering strongly to the substrate and serving as the load-supporting underlayer and the graphite layer on top of it working as solid lubricant.

Keywords: Titanium alloy; Microarc oxidation; Coating; Microstructure; Tribological property

Current transport mechanism in Al/Si₃N₄/p-Si (MIS) Schottky barrier diodes at low temperatures by S. Zeyrek; Ş. Altındal; H. Yüzer; M.M. Bülbül (pp. 2999-3010).

The current–voltage ( I– V) and capacitance–voltage ( C– V) characteristics of metal–insulator–semiconductor (Al/Si₃N₄/p-Si) Schottky barrier diodes (SBDs) were measured in the temperature range of 80–300K. By using the thermionic emission (TE) theory, the zero-bias barrier height Φ_B0 calculated from I– V characteristics was found to increase with increasing temperature. Such temperature dependence is an obvious disagreement with the negative temperature coefficient of the barrier height calculated from C– V characteristics. Also, the ideality factor decreases with increasing temperature, and especially the activation energy plot is nonlinear at low temperatures. Such behaviour is attributed to Schottky barrier inhomogeneties by assuming a Gaussian distribution of barrier heights (BHs) at interface. We attempted to draw a Φ_B0 versus q/2 kT plot to obtain evidence of a Gaussian distribution of the BHs, and the values of Φ_Bo=0.826eV and α_o=0.091V for the mean barrier height and standard deviation at zero-bias, respectively, have been obtained from this plot. Thus, a modified ln( I_o/ T²)− q² σ_o²/2( kT)² versus q/ kT plot gives Φ_B0 and Richardson constant A^* as 0.820eV and 30.273A/cm²K², respectively, without using the temperature coefficient of the barrier height. This value of the Richardson constant 30.273A/cm²K² is very close to the theoretical value of 32A/cm²K² for p-type Si. Hence, it has been concluded that the temperature dependence of the forward I– V characteristics of the Al/Si₃N₄/p-Si Schottky barrier diodes can be successfully explained on the basis of TE mechanism with a Gaussian distribution of the barrier heights. In addition, the temperature dependence of energy distribution of interface state density ( N_SS) profiles was determined from the forward I– V measurements by taking into account the bias dependence of the effective barrier height and ideality factor.

Keywords: PACS; 73.30.+y: 73.40.Qv: 73.40.NsMIS diode; Temperature dependence; Interface states; Insulator layer; Nitride passivation

Surface assisted electric transport in Ag₂S thin films by D. Karashanova; N. Starbov (pp. 3011-3022).

Electric transport measurements of thickness-dependent electronic and ionic conductivity of epitaxial Ag₂S films are used to split both kinds of conductivity into bulk and surface components. The established considerable electronic and ionic surface conductances demonstrate unambiguously the co-existance of electronic and ionic space charge regions in the vicinity of silver sulfide free surface oriented along the zone axes [1¯01¯]. The parameters of both space charge layers – surface potential, thickness of the space charge region and concentration of the surface compensating charges, are calculated. It is estimated that for intrinsic silver sulfide, the effective surface potential of (1¯01¯) Ag₂S surface is negative, its value being about −610mV at 400K.

Keywords: PACS; 66.10.Ed; 73.25.+i; 81.15.KkAg; ₂; S thin epitaxial films; DC dark ionic and electronic conductivity; Ionic and electronic space charge layers; Surface potential

Defect behaviors in n-channel power VDMOSFETs during HEFS and thermal post-HEFS annealing by Goran S. Ristić; Mom�?ilo M. Pejović; Aleksandar B. Jakšić (pp. 3023-3032).

The results of positive/negative Fowler–Nordheim high electric field stress and thermal post-high electric field stress annealing of commercial n-channel power VDMOSFETs have been presented. They have shown that gate bias sign has an influence on the fixed trap behavior during high electric field stress, but has no influence on any defect type behavior during thermal post-high electrical field stress annealing. In addition, slow switching traps have different behavior, but fast switching traps have the same behavior during thermal post-high electrical field stress annealing and thermal post-irradiation annealing.

Keywords: PACS; 78.40.Fy; 73.40.Qv; 72.20.Ht; 72.20.JvOxide trapped charge; Interface traps; High electric field stress; Fowler–Nordheim injection; Annealing; MOS transistor

Nanomechanical characterizations of InGaN thin films by Sheng-Rui Jian; Te-Hua Fang; Der-San Chuu (pp. 3033-3042).

In_xGa1−_xN thin films with In concentration ranging from 25 to 34at.% were deposited on sapphire substrate by metal-organic chemical vapor deposition (MOCVD). Crystalline structure and surface morphology of the deposited films were studied by using X-ray diffraction (XRD) and atomic force microscopy (AFM). Hardness, Young's modulus and creep resistance were measured using a nanoindenter. Among the deposited films, In_0.25Ga_0.75N film exhibits a larger grain size and a higher surface roughness. Results indicate that hardness decreases slightly with increasing In concentration in the In_xGa1−_xN films ranged from 16.6±1.1 to 16.1±0.7GPa and, Young's modulus for the In_0.25Ga_0.75N, In_0.3Ga_0.7N and In_0.34Ga_0.66N films are 375.8±23.1, 322.4±13.5 and 373.9±28.6GPa, respectively. In addition, the time-dependent nanoindentation creep experiments are presented in this article.

Keywords: InGaN; XRD; AFM; Nanoindentation; Creep

Influence of cracks generation on the structural and optical properties of GaN/Al_0.55Ga_0.45N multiple quantum wells by Q. Sun; J.C. Zhang; Y. Huang; J. Chen; J.F. Wang; H. Wang; D.Y. Li; Y.T. Wang; S.M. Zhang; H. Yang; C.L. Zhou; L.P. Guo; Q.J. Jia (pp. 3043-3050).

Both cracked and crack-free GaN/Al_0.55Ga_0.45N multiple quantum wells (MQWs) grown on GaN template by metalorganic chemical vapor deposition have been studied by triple-axis X-ray diffraction, grazing-incidence X-ray reflectivity, atomic force microscope, photoluminescence spectroscopy and low-energy positron annihilation spectroscopy. The experimental results show that cracks generation not only deteriorates the surface morphology, but also leads to a period dispersion and roughens the interfaces of MQWs. The mean density of dislocations in MQWs, determined from the average full-width at half-maximum of ω-scan of each satellite peak, has been significantly enhanced by the cracks generation. Furthermore, the measurement of annihilation-line Doppler broadening reveals a higher concentration of negatively charged vacancies in the cracked MQWs. The combination of these vacancies and the high density of edge dislocations are assumed to contribute to the highly enhanced yellow luminescence in the cracked sample.

Keywords: Nitrides; Multiple quantum wells; Cracks; Dislocations; Vacancies; X-ray diffraction

Structural properties of CuInSe₂ films prepared by selenization of metallic precursors on MoN_x film substrates by F.D. Jiang; L. Zhang; J.Y. Feng (pp. 3051-3057).

The aim of this work was to study the effect of MoN_x film substrates on the structural properties of CuInSe₂ films prepared by selenization of metallic Cu–In alloy precursors. MoN_x films were prepared by reactive dc-magnetron sputtering. All the CuInSe₂ films exhibit single phase chalcopyrite structure with (112) preferred orientation, which can be explained by the reduction of lattice mismatch between CuInSe₂ and MoN_x. The bulk composition of selenized CuInSe₂ films are near stoichiometric, but the surface composition analysis suggests Cu deficiency on surface area. Furthermore, ordered defect compound, CuIn₂Se_3.5 is found on the surface of CuInSe₂ films. The results will be helpful for fabricating Cd-free ZnO buffer layer CuInSe₂ and Cu(In1−_xGa_x)Se₂ based thin film solar cells.

Keywords: PACS; 68.55.JkMagnetron sputtering; Selenization; Preferred orientation; Ordered defect compound

Improvement of hot-dip zinc coating by enriching the inner layers with iron oxide by S.M.A. Shibli; R. Manu (pp. 3058-3064).

The performance of hot-dip galvanic coating formed on steel not only depends on the alloy composition of the superficial layer but also significantly, on the composition of the inner alloy layers at the coating/substrate interface. Further, the presence of barrier oxide layers, if any can also improve the performance of galvanic coating. In the present work, the effect of inner iron oxide barrier layer formed prior to hot-dip galvanization was investigated. A continuous and adherent iron oxide layer was formed on steel by anodic oxidation of the steel substrate. Although the wettability of oxide surface by liquid zinc was initially poor, the increase in dipping time and the transition of the oxide layer to unstable form due to the presence of Cl⁻ ion in the flux facilitated localized growth of Fe–Zn alloy phases. The inhibitive nature of the oxide layer was temporary, since the presence of Cl⁻ induces micro cracks on the oxide surface thereby facilitating better zinc diffusion. The modification of the substrate structure during galvanization was found to influence the galvanizing process significantly. The present study predicts scope for application of this process for protection of rusted steel specimens too.

Keywords: Corrosion; Iron oxide; Zinc coating; Anodic dissolution; Galvanizing

Synthesis and characterization of superhard Ti–Si–N films obtained in an inductively coupled plasma enhanced chemical vapor deposition (ICP-CVD) with magnetic confinement by Hong-yu Zhao; Qiu-lin Fan; Li-xin Song; Tao Zhang; Er-wei Shi; Xing-fang Hu (pp. 3065-3072).

Using a novel inductively coupled plasma enhanced chemical vapor deposition (ICP-CVD) with magnetic confinement system, Ti–Si–N films were prepared on single-crystal silicon wafer substrates by sputtering Ti and Si (5at.%:1at.%) alloyed target in argon/nitrogen plasma. High-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), X-ray diffractometer (XRD), field emission scanning electron microscope (FESEM), atomic force microscopy (AFM) and Nano Indenter XP tester were employed to characterize nanostructure and performances of the films. These films were essentially composed of TiN nanocrystallites embedded in an amorphous Si₃N₄ matrix with maximum hardness value of 44GPa. Experimental results showed that the film hardness was mainly dependent on the TiN crystallite size and preferred orientation, which could be tailored by the adjustment of the N₂/Ar ratio. When the N₂/Ar ratio was 3, the film possessed the minimum TiN size of 10.5nm and the maximum hardness of 44GPa.

Keywords: Ti–Si–N films; Hardness; Inductively coupled plasma CVD; Titanium nitride; Silicon nitride

Surface studies of radiation grafted sulfonic acid membranes: XPS and SEM analysis by Mohamed Mahmoud Nasef; Hamdani Saidi (pp. 3073-3084).

PTFE-g-polystyrene sulfonic acid membranes prepared by radiation-induced graft copolymerization of styrene onto poly(tetrafluoroethylene) (PTFE) films followed by sulfonation reactions were investigated with respect to their morphology and surface chemical properties. The chemical composition of the membranes surfaces was monitored at various degrees of grafting using X-ray photoelectron spectroscopy (XPS). Considerable differences in the concentration of the chemical components of the surfaces were observed despite the predominance of all membranes surfaces by a hydrocarbon fraction originated from the incorporated sulfonated polystyrene grafts. The distribution of the sulfonated polystyrene grafts in membranes having various degrees of grafting was investigated by scanning electron microscopy (SEM). The membranes achieved a homogenous distribution at degrees of grafting of 24% and above. The results of this work suggest that the membranes have a chemically sensitive surfaces and this is most likely to have an impact on their interfacial properties and chemical stability.

Keywords: XPS; Surface elemental analysis; SEM; Radiation grafted sulfonic acid membranes

Strongly oriented BST films on La_0.9Sr_1.1NiO₄ electrodes deposited on various substrates for integration of high capacitances on silicon by L. Goux; M. Gervais; F. Gervais; C. Champeaux; A. Catherinot (pp. 3085-3091).

In this study, we demonstrate the successful oriented growth of Ba_0.6Sr_0.4TiO₃( h00)/La_0.9Sr_1.1NiO₄(00l) stacks by pulsed laser deposition on SiO₂/Si for application in integrated capacitances. We show that for specific deposition conditions the La_0.9Sr_1.1NiO₄ layer spontaneously grows along its c-axis both on SiO₂/Si and on Pt/Ti/SiO₂/Si substrates, serving as a template for the subsequent oriented growth of Ba_0.6Sr_0.4TiO₃ (BST). Moreover, as the resistivity of the La_0.9Sr_1.1NiO₄ layer is ∼1mΩcm, it also fulfills the function of bottom electrode for integration of perovskite-based capacitors on silicon. This holds the promise of integrating epitaxial BST with very high dielectric constant compared to polycrystalline BST films. Still, preliminary capacitance measurements on Al/BST/La_0.9Sr_1.1NiO₄/SiO₂/Si capacitors indicate that the stack deposition needs further optimization.

Keywords: PACS; 68.55; 81.15.FgPLD; BST; La; 2−; _x; Sr; _x; NiO; ₄; Epitaxial growth; Conductive oxide; High-; k; capacitor

Erratum to “The corrosion performance of polyaniline on nickel plated mild steel�? [Appl. Surf. Sci. 242 (1–2) (2005) 97–106] by A.T. Özyılmaz; G. Kardaş; M. Erbil; B. Yazıcı (pp. 3092-3092).

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Applied Surface Science (v.252, #8)

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Applied Surface Science (v.252, #8)