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Applied Surface Science (v.253, #20)

Friction and wear properties of the co-deposited Ni–SiC nanocomposite coating by Y. Zhou; H. Zhang; B. Qian (pp. 8335-8339).

Ni–SiC nanocomposite coatings were produced by electrodeposition from a nickel sulfate bath containing SiC nanoparticles with an average particle size of 30nm. The characteristics of the coatings were assessed by scanning electron microscopy and microhardness test. The friction and wear performance of Ni–SiC nanocomposite coatings and Ni film were comparatively investigated sliding against Si₃N₄ ceramic balls under non-lubricated conditions. The results indicated that compared to Ni film, Ni–SiC nanocomposite coating exhibited enhanced microhardness and wear resistance. The effect of SiC nanoparticles on the friction and wear resistance is discussed in detail.

Keywords: Electrodeposited; Composite coating; Microhardness; Wear

Influence of heat treatment temperature on the morphological and structural aspects of reticulated vitreous carbon used in polyaniline electrosynthesis by E.S. Gonçalves; C. Dalmolin; S.R. Biaggio; P.A.P. Nascente; M.C. Rezende; N.G. Ferreira (pp. 8340-8344).

Reticulated vitreous carbon (RVC) was obtained from different heat treatment temperature (HTT), in the range from 700 up to 2000°C, and used as a substrate for polyaniline growth from electrosynthesis. The influence of HTT on RVC chemical surface was studied by X-ray photoelectron spectroscopy (XPS) and correlated to electrochemical parameters used in the electrosynthesis. XPS analyses have shown that RVC heteroatoms decrease as HTT increases. The results reveal the migration of chemical bonds from oxidized carbon forms towards carbon atoms as the unique final product. Cyclic voltammetry, electrochemical impedance spectroscopy, and stability test of polyaniline films were performed from oxidized and non-oxidized RVC substrates. Cyclic voltammetry in 0.5molL⁻¹ H₂SO₄ revealed higher capacitance for the RVC treated at 1000°C and oxidized in a hot H₂SO₄ solution. The charge accumulation after RVC chemical treatment has increased around ten times. The lowest electric resistivities and impedances were obtained for the RVC treated at 2000°C, which also showed the highest polyaniline stability.

Keywords: RVC; Polyaniline; Electrosynthesis; Heat treatment temperature

First principle study of SrTiO₃ (001) surface and adsorption of NO on SrTiO₃ (001) by H.J. Zhang; G. Chen; Z.H. Li (pp. 8345-8351).

The results of first-principles calculations about the two possible terminations of (001) surface of SrTiO₃ perovskite and adsorption of NO on SrTiO₃ (001) surface were presented. Both surface parameters (atomic structures and electronic configurations) and adsorption parameters (bond, energy and charge) of NO on SrTiO₃ (001) surface, which have never been investigated before as far as we know were investigated using density functional theory calculations with the local-density approximation (DFT-LDA). It was found that the two possible terminations of SrTiO₃ (001) surface have large surface relaxation, which leads to surface polarization and exhibits different reactivity toward the dissociative adsorption of NO. The electronic states of TiO₂-terminated surface have larger difference than that of bulk, so it is more favorable for adsorption of NO than SrO-terminated surface.

Keywords: PACS; 71.15; 71.20; 73.20Perovskite; Surface relaxation; Adsorption; DFT

A new film analysis method using polycapillary X-ray lens by Jun Yang; Xunliang Ding; Changlin Liang (pp. 8352-8355).

Grazing emission X-ray fluorescence (GE-XRF) is a development of XRF related to total reflection XRF. This paper proposed a GE-MXRF setup involved a polycapillary X-ray lens. Polycapillary lens is an effective optics to obtain μm-size primary X-ray beam. Using this proposed setup, we applied it to the analysis of film samples, and the information of film thickness, composition and density can be acquired, which is very useful in semiconductor industry.

Keywords: PACS; 07.85.-m; 07.85. NcGrazing exit micro X-ray fluorescence; Polycapillary X-ray lens; Film

Preparation of Sn films deposited on carbon nanotubes by W.L. Liu; S.H. Hsieh; W.J. Chen (pp. 8356-8359).

In this work carbon nanotubes were first grown on copper substrate by chemical vapor deposition method. The Sn deposits were then deposited on the surface of as-grown carbon nanotubes by three different methods: electroplating, electroless plating and displacing methods. The Sn deposits on CNTs surface were characterized by both scanning electron microscope and field emission scanning electron microscope. The compositions of Sn deposits were analyzed by energy dispersive X-ray spectroscope. The results showed that both electroless plating and displacing deposits can but the electroplating deposits cannot cover on the surface of CNTs. Besides C, Sn, Ni and Pd, the electroless deposits also contain element of oxygen and the displacing deposits also contain elements of copper and oxygen.

Keywords: Carbon nanotubes (CNTs); Sn film; Electroplating; Electroless plating; Displacement

Modification of surface properties of electrospun polyamide nanofibers by means of a perfluorinated acridine by Andrea Bianco; Giacomo Iardino; Chiara Bertarelli; Luciano Miozzo; Antonio Papagni; Giuseppe Zerbi (pp. 8360-8364).

Polyamide 6 (PA6) nanofibers were prepared from formic acid solutions by using electrospinning technique. The fibers were smooth, defects free and with diameters smaller than 200nm. Small amounts of a perfluorinated acridine were added as dopant to the feed solution to modify the wettability of the fibers. The effect of doping on the contact angle values is well apparent. The contact angle values go from 50° of pure PA6 to 120° when 6% of acridine is added. A comparison between fibers and films of pure and doped polyamide 6 was carried out in order to determine the effect of morphology on wettability. Thermal annealing near the T_g of the polymer promoted the segregation of the molecules to the surface, reaching contact angles of 131° with smaller amounts (4%) of acridine. The surface segregation was also promoted by time aging.

Keywords: Polyamide 6; Acridine; Wettability; Electrospinning; Contact angle

Enhanced ferroelectric properties of (Pb_0.90La_0.10)Ti_0.975O₃ multilayered thin films prepared by RF magnetron sputtering by Jiagang Wu; Dingquan Xiao; Jiliang Zhu; Jianguo Zhu; Junzhe Tan (pp. 8365-8370).

The (Pb_0.90La_0.10)Ti_0.975O₃/PbTiO₃ (PLT/PT), PbTiO₃/(Pb_0.90La_0.10)Ti_0.975O₃/PbTiO₃ (PT/PLT/PT) multilayered thin films with a PbO_x buffer layer were in situ deposited by RF magnetron sputtering at the substrate temperature of 600°C. With this method, highly (100)-oriented PLT/PT and PT/PLT/PT multilayered thin films were obtained. The PbO_x buffer layer leads to the (100) orientation of the films. The dielectric, ferroelectric and pyroelectric properties of the PLT multilayered thin films were investigated. It is found that highly (100)-oriented PT/PLT/PT multilayered thin films possess higher remnant polarization 2 P_r (44.1μC/cm²) and better pyroelectric coefficient at room temperature p ( p=2.425×10⁻⁸C/cm²K) than these of PLT and PLT/PT thin films. These results indicate that the design of the PT/PLT/PT multilayered thin films with a PbO_x buffer layer should be an effective way to enhance the dielectric, ferroelectric and pyroelectric properties. The mechanism of the enhanced ferroelectric properties was also discussed.

Keywords: PACS; 77.84.−s; 77.80.−e; 77.22.Ej(Pb; _0.90; La; _0.10; )Ti; _0.975; O; ₃; Ferroelectric multilayered thin films; RF magnetron sputtering; Orientation; Electrical properties

Characteristics of CO₂ corrosion scale formed on N80 steel in stratum water with saturated CO₂ by D.G. Li; Y.R. Feng; Z.Q. Bai; M.S. Zheng (pp. 8371-8376).

The component and structure of CO₂ corrosion scale formed on N80 tubing steel were studied by using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and scanning electron microscopy (SEM); the electrochemical property of N80 steel covered by corrosion scale was investigated by electrochemical impedance spectroscopy (EIS). The results shows a double-layer structure of the corrosion scale, in which the principal component of the outer layer is FeCO₃ with a limited amount of ∂-FeOOH; while for the inner scale, FeCO₃ is still the major component, but some Fe positions in FeCO₃ lattice are substituted by Ca, and form a composite compound of (Fe,Ca)CO₃ in the inner scale. EIS study shows that the anodic impedance spectrum has three time constants, i.e., the capacitance at high frequency, Warburg impedance at middle frequency and capacitance at low frequency.

Keywords: Corrosion scale; Double-layer structure; XPS; XRD; EIS

Effect of PMMA on crystallization behavior and hydrophilicity of poly(vinylidene fluoride)/poly(methyl methacrylate) blend prepared in semi-dilute solutions by Wenzhong Ma; Jun Zhang; Xiaolin Wang; Shengmin Wang (pp. 8377-8388).

Films of poly(vinylidene fluoride) (PVDF)/poly(methyl methacrylate) (PMMA) blend were derived from a special procedure of casting semi-dilute solutions. Hydrophilic character and crystallization of PVDF were optimized by variation of PMMA concentration in PVDF/PMMA blends. It was found that a PVDF/PMMA blend containing 70wt% PMMA has a good performance for the potential application of hydrophilic membranes via thermally induced phase separation. The films presented β crystalline phase regardless of PMMA content existed in the blends. Thermal analysis of the blends showed a promotion of crystallization of PVDF with small addition of PMMA which induced larger lamellar thickness of PVDF, leading to the largest spherulitic crystal of PVDF (10wt% PMMA) is about 8μm. SEM micrographs illustrated no phase separation occurred in blends, due to the high compatibility between PVDF and PMMA.

Keywords: Poly(vinylidene fluoride) (PVDF); Hydrophilicity; Crystallinity; Blends

The role of atomic hydrogen in pre-epitaxial silicon substrate cleaning by A. Aßmuth; T. Stimpel-Lindner; O. Senftleben; A. Bayerstadler; T. Sulima; H. Baumgärtner; I. Eisele (pp. 8389-8393).

The cleaning of silicon (Si) surfaces is a very important issue for the fabrication of novel semiconductor devices on the nanoscale. Established methods for the removal of organic impurities and the native or chemical oxide are often combined with high temperature desorption steps. However, devices with small feature sizes will be unfunctional if, for example, out-diffusion of dopants is not prevented. In this paper we present two possible processes for low-temperature cleaning: an atomic hydrogen source, based on dissociative adsorption of hydrogen at a heated tantalum (Ta) surface and a hydrogen DC plasma source as a part of an UHV cluster tool. The influence of atomic hydrogen on carbon and oxide removal is surveyed and the existing model for native oxide etching with an argon/hydrogen DC plasma is adapted.

Keywords: PACS; 68.47.Fg; 81.65.Cf; 82.30.Cf; 82.80.PvAtomic hydrogen; DC plasma; Silicon; Cleaning

Electrochemically decorated carbon nanotubes for hydrogen sensing by Ulrich Schlecht; Kannan Balasubramanian; Marko Burghard; Klaus Kern (pp. 8394-8397).

Low-density networks of single-wall carbon nanotubes have been modified by palladium nanoparticles using an electrochemical method. A major advantage of this approach is that it allows for selective metal deposition on the electrically contacted nanotubes, whereas the remaining substrate surface and the non-contacted tubes remain essentially unaffected. The Pd-decorated networks function as effective hydrogen sensors enabling the detection of hydrogen concentrations as low as 10ppm at room temperature. The electrochemical metal deposition scheme is promising for the development of sensor arrays suitable for analysing gas mixtures.

Keywords: PACS; 61.46+w; 73.90+f; 82.80.FkCarbon nanotubes; Hydrogen sensor; Electrochemical modification; Nanoparticles

Structure and mechanical properties of ceramic coatings fabricated by plasma electrolytic oxidation on aluminized steel by Zhenqiang Wu; Yuan Xia; Guang Li; Fangtao Xu (pp. 8398-8403).

Ceramic coatings were formed by plasma electrolytic oxidation (PEO) on aluminized steel. Characteristics of the average anodic voltages versus treatment time were observed during the PEO process. The micrographs, compositions and mechanical properties of ceramic coatings were investigated. The results show that the anodic voltage profile for processing of aluminized steel is similar to that for processing bulk Al alloy during early PEO stages and that the thickness of ceramic coating increases approximately linearly with the Al layer consumption. Once the Al layer is completely transformed, the FeAl intermetallic layer begins to participate in the PEO process. At this point, the anodic voltage of aluminized steel descends, and the thickness of ceramic coating grows more slowly. At the same time, some micro-cracks are observed at the Al₂O₃/FeAl interface. The final ceramic coating mainly consists of γ-Al₂O₃, mullite, and α-Al₂O₃ phases. PEO ceramic coatings have excellent elastic recovery and high load supporting performance. Nanohardness of ceramic coating reaches about 19.6GPa.

Keywords: Hot-dip aluminum; Plasma electrolytic oxidation; Ceramic coatings; Steel substrate

Effect of surface preparation on the properties of Au/p-Cd1−_xZn_xTe by Xi Cheng; Shifu Zhu; Beijun Zhao; Zhiyu He; Deyou Gao; Jun Fang (pp. 8404-8407).

The effect of bromine methanol (BM) etching and NH₄F/H₂O₂ passivation on the Schottky barrier height between Au contact and semi-insulated (SI) p-Cd1−_xZn_xTe ( x≈0.09–0.18) was studied through current–voltage ( I– V) and capacitance–voltage ( C– V) measurements. Near-infrared (NIR) spectroscopy technique was utilized to determine the Zn concentration. X-ray photoelectron spectroscopy (XPS) for surface composition analysis showed that BM etched sample surface left a Te⁰-rich layer, however, which was oxidized to TeO₂ and the surface [Te]/([Cd]+[Zn]) ratio restored near-stoichiometry after NH₄F/H₂O₂ passivation. According to I– V measurement, barrier height was 0.80±0.02–0.85±0.02eV for Au/p-Cd1−_xZn_xTe with BM etching, however, it increased to 0.89±0.02–0.93±0.02eV with NH₄F/H₂O₂ passivation. Correspondingly, it was about 1.34±0.02–1.43±0.02eV and 1.41±0.02–1.51±0.02eV by C– V method.

Keywords: PACS; 71.55.Gs; 73.20.−r; 73.40.Sx; 73.40.QvCd; 1−; _x; Zn; _x; Te; Barrier height; Zn concentration dependence; Native oxide layer

Pulsed laser induced synthesis of scheelite-type colloidal nanoparticles in liquid and the size distribution by nanoparticle tracking analysis by Jeong Ho Ryu; Sin Young Bang; Jong-Won Yoon; Chang Sung Lim; Kwang Bo Shim (pp. 8408-8414).

Pulsed laser ablation (PLA) of ceramic target in liquid phase was successfully employed to prepare calcium tungstate (CaWO₄) and calcium molybdate (CaMoO₄) colloidal nanoparticles. The crystalline phase, particle morphology and optical property of the colloidal nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and Raman spectroscopy. The produced stable colloidal suspensions consisted of the well-dispersed nanoparticles showing a spherical shape. The mechanism for the laser ablation and nanoparticle forming was discussed under consideration of photo-ablation process. Nanoparticle tracking analysis using optical microscope combined with image analysis was proposed to determine the size distribution function of the prepared colloidal nanoparticles. The mean size of the CaWO₄ and CaMoO₄ colloidal nanoparticles were 16 and 29nm, with a standard deviations of 2.1 and 5.2nm, respectively.

Keywords: PACS; 42.62.−b; 78.55.HXPulsed laser ablation; Colloidal nanoparticles; CaWO; ₄; and CaMoO; ₄; Size distribution; Nanoparticle tracking analysis

Effect of deformation on the electrochemical behavior of hot-dip galvanized steel sheets by S.T. Vagge; V.S. Raja; R. Ganesh Narayanan (pp. 8415-8421).

The main purpose of employing pre-coated steel sheets is to minimize corrosion of steel. However, coatings can be severely affected by forming processes. In the forming processes, due to the different modes of deformation, the strain levels are different and so can affect the properties of the coatings to a varying degree. Special attention has to be paid to the influence of deformation conditions on the performance of the coating, as regards protection against corrosion. The adhesion of the coating must remain good, and the surface should not be damaged during forming. Therefore, it is necessary to study the behavior of its corrosion resistance against the deformation.In this work, effect of strain path on the corrosion behavior of hot-dip galvanized steel sheets has been studied. Corrosion behavior of hot-dip galvanized steel sheets at various strain levels has been evaluated under four different strain paths namely, biaxial, plane strain, uniaxial (drawing) and tensile modes. The sheets were deformed by a limiting dome height test (LDH) set-up. A correlation between the degree of deformation and the loss in extent of corrosion protection offered by the coating has been established by carrying out electrochemical studies such as potentiodynamic polarization and impedance spectroscopy (EIS) in 3.5% NaCl solution. The present study shows that increase in deformation increases the extent of delamination of the coating for all the modes of deformation. The severity of deformation on delamination, however, has been found to vary in the order of, tensile

Keywords: Hot-dip galvanized; Deformation; Corrosion; Potentiodynamic polarization; Electrochemical impedance spectroscopy

A sensor for adenosine triphosphate fabricated by laser-induced forward transfer of luciferase onto a poly(dimethylsiloxane) microchip by Yasuyuki Tsuboi; Yosuke Furuhata; Noboru Kitamura (pp. 8422-8427).

Laser-induced forward transfer (LIFT) of the enzyme luciferase was explored as a potential technique to be used in the fabrication of a microchip adenosine triphosphate (ATP) sensor. Poly(dimethylsiloxane) (PDMS) was selected as the substrate for deposition of the luciferase. In comparison with other solid substrates, such as glass and polystyrene, it was found that the flexibility of PDMS made it a superior substrate for the immobilization of micro-spots of luciferase. LIFT of luciferase onto a PDMS substrate using a 355nm laser was successfully carried out, while the bioactivity of the enzyme was maintained. Yellow luminescence ascribed to luciferase was observed from a transferred spot on the PDMS chip from the enzymatic reaction between luciferin and ATP. A microchip ATP sensor was also fabricated by attaching a small photodiode to the PDMS chip. On the basis of the fabricated microchip, the Michaelis–Menten relation between the luminescence intensity from the spot, and the ATP concentration was confirmed. The potential for fabricating biosensors using a combination of the LIFT technique with a PDMS substrate was shown to be very good.

Keywords: PACS; 81.15.Fg; 81.16.Mk; 87.15.Mi; 87.66.SqEnzyme; Luciferase; Luciferin; LIFT; Luminescence

Synthesis of silicon carbide films by combined implantation with sputtering techniques by Gaobao Li; Jizhong Zhang; Qingli Meng; Wenzhi Li (pp. 8428-8434).

Silicon carbide (SiC) films were synthesized by combined metal vapor vacuum arc (MEVVA) ion implantation with ion beam assisted deposition (IBAD) techniques. Carbon ions with 40keV energy were implanted into Si(100) substrates at ion fluence of 5×10¹⁶ions/cm². Then silicon and carbon atoms were co-sputtered on the Si(100) substrate surface, at the same time the samples underwent assistant Ar-ion irradiation at 20keV energy. A group of samples with substrate temperatures ranging from 400 to 600°C were used to analyze the effect of temperature on formation of the SiC film. Influence of the assistant Ar-ion irradiation was also investigated. The structure, morphology and mechanical properties of the deposited films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and nanoindentation, respectively. The bond configurations were obtained from IR absorption and Raman spectroscopy. The experimental results indicate that microcrystalline SiC films were synthesized at 600°C. The substrate temperature and assistant Ar-ion irradiation played a key role in the process. The assistant Ar-ion irradiation also helps increasing the nanohardness and bulk modulus of the SiC films. The best values of nanohardness and bulk modulus were 24.1 and 282.6GPa, respectively.

Keywords: PACS; 61.80.Jh; 68.55.Nq; 68.60.Bs; 81.15.CdSilicon carbide; MEVVA; IBAD; Ion implantation

Magnesium silicates – adsorbents of organic compounds by Filip Ciesielczyk; Andrzej Krysztafkiewicz; Teofil Jesionowski (pp. 8435-8442).

Studies were presented on production of highly dispersed magnesium silicate at a pilote scale. The process of silicate adsorbent production involved precipitation reaction using water glass (sodium metasilicate) solution and appropriate magnesium salt, preceded by an appropriate optimization stage. Samples of best physicochemical parameters were in addition modified (in order to introduce to silica surface of several functional groups) using the dry technique and various amounts of 3-isocyanatepropyltrimethoxysilane, 3-thiocyanatepropyltrimethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane. The so prepared samples were subjected to a comprehensive physicochemical analysis. At the terminal stage of studies attempts were made to adsorb phenol from its aqueous solutions on the surface of unmodified and modified magnesium silicates. Particle size distributions were determined using the ZetaSizer Nano ZS apparatus. In order to define adsorptive properties of studied magnesium silicates isotherms of nitrogen adsorption/desorption on their surfaces were established. Efficiency of phenol adsorption was tested employing analysis of post-adsorption solution.

Keywords: Magnesium silicate; Silane coupling agents; Surface modification; Phenol adsorption

X-ray interface analysis of aperiodic Mo/Si multilayers by K. Le Guen; H. Maury; J.-M. André; H. Wang; J. Zhu; Z. Wang; P. Jonnard (pp. 8443-8446).

We present the non-destructive analysis of aperiodic Mo/Si multilayers by X-ray emission spectroscopy induced by electrons. The Si 3p occupied valence states of the silicon atoms present within these structures are analysed. Because of the great sensitivity of these states to the physico-chemical environment of the Si atoms, it is possible to distinguish the emission from the center of the Si layer (amorphous silicon) to that of the interfacial zones between the Mo and Si layers. Thus, the presence of molybdenum silicides is evidenced in the interfacial zones. It is also shown that the relative proportion of interfacial silicides depends on the deposition conditions.

Keywords: PACS; 68.35.p; 78.70.En; 68.65.AcAperiodic multilayer; Interface; Silicide; X-ray emission

The effect of inactive impurities on a surface in NO–CO reaction: A Monte Carlo simulation by Waqar Ahmad; Musa Kaleem Baloch (pp. 8447-8452).

The interaction among the reacting species in the NO–CO reaction on a metal catalytic surface that proceeds according to the Langmuir–Hinshelwood thermal mechanism is studied by means of Monte Carlo simulations. The study of this system is essential for the understanding of the influence of impurities on the catalytic oxidation of NO by CO. It is found that this complex system exhibits irreversible phase transitions between active states with sustained reaction and poisoned states without reaction. The same system has also been investigated by non-thermal (Eley-Rideal) mechanism. Both the phase diagrams of the surface coverage and the steady state production of CO₂ and N₂ are evaluated as a function of the partial pressures of the reactants in the gas phase. From this study, it is observed that with the increase of impurities, the production rate reduces and the reaction stops at a certain point. Moreover, the first order transition in the phase diagram converts into second order phase transition that is in accordance with the experimental findings. Therefore, the first order phase transition, which is a characteristic of such catalytic reactions, is eliminated.

Keywords: PACS; 64.60.Ht; 82.65.+r; 83.10.Rs; 87.15.AaCatalytic reactions; NOCO; Monte Carlo simulation; Phase diagrams

Thin aluminum film improving the cycle performance of positive electrode of lithium ion battery by Youlong Xu; Xifei Li; Lipeng Ge; Xiuwen Qu (pp. 8453-8457).

A novel method was investigated to improve the cycle performance of the spinel LiMn₂O₄. It is widely different from the traditional way of modifying LiMn₂O₄ particle with compounds or metals. In our study, instead of coating LiMn₂O₄ particle itself with compounds or metals, first we covered the current collector with the mixture of LiMn₂O₄ particle, conductive agents and binders, and then deposited an aluminum film onto it by vacuum evaporation technique. Both of the pristine electrode and the modified one were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), and charge–discharge tests. The results of SEM and XRD demonstrate that the aluminum film was formed successfully onto the positive electrode. And the charge–discharge tests show that the capacity retention of pristine electrode and modified one are 63.7% and 93.5% at C/2 rate in the voltage range of 3.5–4.3V after 200 cycles, respectively. The modified electrode also shows better rate capability in comparison with the pristine one. The improved cycling stability is attributed to the minimizing of Mn dissolution into electrolyte solution and the good electronic conductivity of deposited aluminum film.

Keywords: A novel method; The traditional way; Aluminum film; Capacity retention; Rate capability

Effect of Ni, Pd and Ni–Pd nano-islands on morphology and structure of multi-wall carbon nanotubes by A. Reyhani; S.Z. Mortazavi; O. Akhavan; A.Z. Moshfegh; Sh. Lahooti (pp. 8458-8462).

In this research, the effect of Ni, Pd and Ni–Pd catalysts have studied on morphology and structure of synthesized multi-wall carbon nanotubes (MWCNTs). Initially, thin films of Ni (with two thicknesses of 10 and 20nm), Pd/Ni (5/10nm) and Pd (10nm) were deposited as catalysts on SiO₂ (60nm)/Si(100) substrates, using dc magnetron sputtering technique. The deposited films were annealed at 900°C in ammonia environment for 45min, in order to obtain nano-structured catalyst on the surface. Using scanning electron microscopy (SEM), the average size of Ni nano-islands (synthesized by the 10 and 20nm Ni films), Pd and Ni–Pd nano-islands were measured about 55, 110, 45 and 50nm, respectively. According to X-ray photoelectron spectroscopy analysis (XPS), the ratio of Ni/Pd on the surface was about 3 for the bilayer sample. The CNTs were synthesized on the nano-island catalysts at 940°C in CH₄ ambient using a thermal chemical vapor deposition method. The results revealed that average diameter of the CNTs were about 70, 110, 120nm for Ni, Ni–Pd and Pd catalysts, respectively. Raman spectra of the MWCNTs showed that intensity ratio of two main peaks located in the range of 1550–1600 and 1250–1450cm⁻¹ (as a quality factor for the CNTs) for Ni, Pd and Ni–Pd catalysts were 1.42, 0.91 and 0.85, respectively. Therefore, based on our data analysis, although addition of Pd to Ni catalyst caused a considerable reduction in the quality of the grown MWCNTs as compared to the pure Ni catalyst, but it resulted in an enhancement in the methane decomposition rate. For the pure Pd catalyst samples, both a slow methane decomposition rate as compared with Ni–Pd catalyst samples and a poor quality of CNTs were observed as compared with the Ni catalyst, under similar experimental conditions.

Keywords: Carbon nanotubes; Thermal chemical vapor deposition; Ni–Pd catalyst; Methane decomposition

X-ray photoelectron spectroscopy studies on core-shell structured nanocomposites by M. Mukherjee; S. Basu; B. Ghosh; D. Chakravorty (pp. 8463-8469).

Core-shell nanostructures were grown in silica-based glasses. Copper–copper oxide and iron–iron oxide structures had diameters in the range 3–6nm, with shell thicknesses ∼1–2nm. Silver–lithium niobate core-shell nanostructures had diameters in the range 4.2–46nm and thicknesses varying from 2.2 to 22nm. X-ray photoelectron spectroscopy studies were carried out on all these specimens. The analyses of these results show the presence of Cu⁺/Cu²⁺, Fe²⁺/Fe³⁺ and Nb⁴⁺/Nb⁵⁺ valence states in the above three systems. Electrical resistivity data were fitted satisfactorily to the small polaron hopping model in the case of copper and iron-containing specimens. The presence of ions in the lithium niobate shell provides direct evidence of the formation of localized states between which variable range hopping conduction can be effected.

Keywords: Core-shell structured; X-ray photoelectron spectroscopy

Dependence of the microstructural properties on the substrate temperature in strained CdTe (100)/GaAs (100) heterostructures by K.H. Lee; J.H. Jung; T.W. Kim; H.S. Lee; H.L. Park (pp. 8470-8473).

CdTe thin films were grown on GaAs (100) substrates by using molecular beam epitaxy at various temperatures. The bright-field transmission electron microscopy (TEM) images and the high-resolution TEM (HRTEM) images showed that the crystallinity of CdTe epilayers grown on GaAs substrates was improved by increasing the substrate temperature. The result of selected-area electron diffraction pattern (SADP) showed that the orientation of the grown CdTe thin films was the (100) orientation. The lattice constant the strain, and the stress of the CdTe thin film grown on the GaAs substrate were determined from the SADP result. Based on the SADP and HRTEM results, a possible atomic arrangement for the CdTe/GaAs heterostructure is presented.

Keywords: PACS; 68. 37. Lp; 68. 55. JkCdTe/GaAs heterostructure; Microstructural properties; Atomic arrangement

Optical and mechanical properties of vacuum evaporated vapour chopped polyaniline thin film by J.B. Yadav; R.K. Puri; V. Puri (pp. 8474-8477).

The paper reports the effect of chopping the vapour flow on properties of vacuum evaporated polyaniline thin films synthesized by aqueous polymerization pathway. The chopper was a metallic vane of V-shaped cut out placed between the substrate and boat in the path of evaporated vapour. It interrupted the flow of vapour at a constant rate. Fourier Transform Infra-red (FTIR) studies indicated that the vacuum evaporated films are more in reduced form and contain short chain oligomers. Improved adhesion and reduced intrinsic stress of polyaniline thin film due to chopping are obtained. Higher transmittance and lower refractive index films resulted due to the process of chopping as compared to the deposited films. Chopping also produces smoother surface morphology.

Keywords: Polyaniline; Vacuum evaporation: Thin film; Mechanical properties; Chopping; Optical properties

Field electron emission improvement of ZnO nanorod arrays after Ar plasma treatment by Chun Li; Guojia Fang; Longyan Yuan; Nishuang Liu; Jun Li; Dejie Li; Xingzhong Zhao (pp. 8478-8482).

Vertically well-aligned single crystal ZnO nanorod arrays were synthesized and enhanced field electron emission was achieved after radio-frequency (rf) Ar plasma treatment. With Ar plasma treatment for 30min, flat tops of the as-grown ZnO nanorods have been etched into sharp tips without damaging ZnO nanorod geometrical morphologies and crystallinity. After the Ar ion bombardment, the emission current density increases from 2 to 20μAcm⁻² at 9.0Vμm⁻¹ with a decrease in turn-on voltage from 7.1 to 4.8Vμm⁻¹ at a current density of 1μAcm⁻², which demonstrates that the field emission of the as-grown ZnO nanorods has been efficiently enhanced. The scanning electron microscopy (SEM) results, in conjunction with the results of transmission electron microscopy (TEM), Raman spectroscopy and photoluminescence observation, are used to investigate the mechanisms of the field emission enhancement. It is believed that the enhancements can be mainly attributed to the sharpening of rod tops, and the decrease of electrostatic screening effect.

Keywords: PACS; 79.70+q; 81.05.Dz; 81.65.CfField emission; ZnO nanorod arrays; Ar plasma treatment

Structural and optical properties of nitrogen-incorporated HfO₂ gate dielectrics deposited by reactive sputtering by G. He; Q. Fang; G.H. Li; J.P. Zhang; L.D. Zhang (pp. 8483-8488).

High- k HfO_xN_y thin films with different nitrogen-incorporation content have been fabricated on Si (100) substrate by means of radio-frequency reactive sputtering method. Analyses from X-ray diffraction (XRD) and atomic force microscopic have indicated that the increase of the crystallization temperature of HfO₂ thin films and the decrease of the roughness root-mean-square value of HfO₂ thin films due to the incorporation of nitrogen. Based on a parameterized Tauc–Lorentz (TL) dispersion model, the optical properties of the HfO_xN_y thin films related to different nitrogen-incorporation content are systematically investigated by spectroscopic ellipsometer. Increase in the refractive index and the extinction coefficient and reduction in band gap with increase of nitrogen-incorporation content are discussed in detail.

Keywords: High-; k; gate dielectrics; HfO; ₂; thin films; Optical properties; Interfacial layer; Sputtering

A mathematical model for material removal and chemical–mechanical synergy in chemical–mechanical polishing at molecular scale by J. Bai; Y.W. Zhao; Y.G. Wang (pp. 8489-8494).

This paper presents a mathematical material removal model based on the chemical and mechanical synergistic effects in the chemical–mechanical polishing (CMP) process. It seems to explain the transition from a chemically dominant region to a mechanically dominant region. In addition, this model predicts the effects of most variables involved in the CMP process including the processing conditions (velocity, downpressure), pad properties (modulus, hardness and asperity sizes) and slurry characteristics (particle size, concentration and distribution). The results reveal some insights into the micro-contact and wear mechanisms of the CMP process.

Keywords: Chemical–mechanical polishing; Molecular scale; Film generation rate; Modeling

Synthesis and characterization of CdS/PVA nanocomposite films by Hongmei Wang; Pengfei Fang; Zhe Chen; Shaojie Wang (pp. 8495-8499).

A series CdS/PVA nanocomposite films with different amount of Cd salt have been prepared by means of the in situ synthesis method via the reaction of Cd²⁺-dispersed poly vinyl-alcohol (PVA) with H₂S. The as-prepared films were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), ultraviolet-visible (UV–vis) absorption, photoluminescence (PL) spectra, Fourier transform infrared spectroscope (FTIR) and thermogravimetric analysis (TGA). The XRD results indicated the formation of CdS nanoparticles with hexagonal phase in the PVA matrix. The primary FTIR spectra of CdS/PVA nanocomposite in different processing stages have been discussed. The vibrational absorption peak of CdS bond at 405cm⁻¹ was observed, which further testified the generation of CdS nanoparticles. The TGA results showed incorporation of CdS nanoparticles significantly altered the thermal properties of PVA matrix. The photoluminescence and UV–vis spectroscopy revealed that the CdS/PVA films showed quantum confinement effect.

Keywords: CdS nanoparticles; Poly vinyl-alcohol; X-ray diffraction; Optical properties

Enhanced activity of mesoporous Nb₂O₅ for photocatalytic hydrogen production by Xinyi Chen; Tao Yu; Xiaoxing Fan; Haitao Zhang; Zhaosheng Li; Jinhua Ye; Zhigang Zou (pp. 8500-8506).

The mesoporous Nb₂O₅ photocatalysts were synthesized via an evaporation-induced self-assembly (EISA) method. The mesoporous structure of the as-made samples was studied by small-angle X-ray diffraction, N₂ adsorption–desorption isothermal and transmission electron microscopy. The increase of the calcination temperature during the synthesis resulted in enhanced crystallization, but decreased mesoporosity of the samples. The later was found to have a crucial influence on the photocatalytic activity by bringing on decreased BET surface area and especially increscent pore wall thickness. The advantage of the mesoporous Nb₂O₅ was also proved by performing 20 times higher photocatalytic activity than a bulk Nb₂O₅ without any porosity. A model was given to describe the effect of mesoporosity on the transportation and recombination of carriers.

Keywords: PACS; 82.45.Vp, 73.23.−b, 78.67.−nMesoporous; Niobium oxide; Photocatalytic activity; Hydrogen production

Surface XPS characterization of NiTi shape memory alloy after advanced oxidation processes in UV/H₂O₂ photocatalytic system by R.M. Wang; C.L. Chu; T. Hu; Y.S. Dong; C. Guo; X.B. Sheng; P.H. Lin; C.Y. Chung; P.K. Chu (pp. 8507-8512).

Surface structure of NiTi shape memory alloy (SMA) was modified by advanced oxidation processes (AOP) in an ultraviolet (UV)/H₂O₂ photocatalytic system, and then systematically characterized with x-ray photoelectron spectroscopy (XPS). It is found that the AOP in UV/H₂O₂ photocatalytic system leads to formation of titanium oxides film on NiTi substrate. Depth profiles of O, Ni and Ti show such a film possesses a graded interface structure to NiTi substrate and there is no intermediate Ni-rich layer like that produced in conventional high temperature oxidation. Except TiO₂ phase, some titanium suboxides (TiO, Ti₂O₃) may also exist in the titanium oxides film. Oxygen mainly presents in metal oxides and some chemisorbed water and OH⁻ are found in titanium oxides film. Ni nearly reaches zero on the upper surface and relatively depleted in the whole titanium oxides film. The work indicates the AOP in UV/H₂O₂ photocatalytic system is a promising way to favor the widespread application of biomedical NiTi SMA by improving its biocompatibility.

Keywords: PACS; 71.20.Lp; 68.47.Gh; 68.55.-a; 79.60.-iNiTi shape memory alloy; Advanced oxidation processes (AOP); Surface structure; X-ray photoelectron spectroscopy (XPS)

Effects of SnO₂ surface coating on the degradation of ZnS thin film phosphor by K.T. Hillie; H.C. Swart (pp. 8513-8516).

Pulsed laser deposited ZnS bare and SnO₂ coated ultra thin films were subjected to prolonged electron beam bombardment with 2keV energy and a steady 44mA/cm² current density, in 1×10⁻⁶Torr O₂ pressure backfilled from a base pressure of 3×10⁻⁹Torr at room temperature. Auger electron spectroscopy (AES) was used to monitor changes of the surface chemical composition of both the bare and coated phosphor films during electron bombardment. Degradation was manifested by the decrease of sulphur and accumulation of oxygen on the surface of the bare phosphor. However, with the SnO₂ coating this phenomenon was delayed until the protective SnO₂ was depleted on the surface through dissociation and reduction.

Keywords: ZnS phosphor; Cathodoluminescence; Degradation; Field emission displays

Hydrocarbon film growth by energetic CH₃ molecule impact on SiC (001) surface by F. Gou; Meng Chuanliang; Z.T. Zhouling; Qiu Qian (pp. 8517-8523).

Classic molecular dynamics (MD) calculations were performed to investigate the deposition of thin hydrocarbon film. SiC (100) surfaces were bombarded with energetic CH₃ molecules at impact energies ranging from 50 to 150eV. The simulated results show that the deposition yield of H atoms decreases with increasing incident energy, which is in good agreement with experiments. During the initial stages, with breaking Si–C bonds in SiC by CH₃ impacting, H atoms preferentially reacts with resulting Si to form Si–H bond. The C/H ratio in the grown films increases with increasing incident energy. In the grown films, CH species are dominant. For 50eV, H–C sp3 bond is dominant. With increasing energy to 200eV, the atomic density of H–C sp2 bond increases.

Keywords: PACS; 52.65.Yy; 81.65.Cf; 52.77.DqMolecular dynamics methods; Hydrocarbon; Plasma-based ion implantation and deposition

Observation of ferromagnetism at room temperature for Cr⁺ ions implanted ZnO thin films by H. Li; J.P. Sang; F. Mei; F. Ren; L. Zhang; C. Liu (pp. 8524-8529).

Single crystalline ZnO films were grown on c-plane GaN/sapphire (0001) substrates by molecular beam epitaxy. Cr⁺ ions were implanted into the ZnO films with three different doses, i.e., 1×10¹⁴, 5×10¹⁵, and 3×10¹⁶cm⁻². The implantation energy was 150keV. Thermal treatment was carried out at 800°C for 30s in a rapid thermal annealing oven in flowing nitrogen. X-ray diffraction (XRD), atomic force microscopy, Raman measurements, transmission electron microscopy and superconducting quantum interference device were used to characterize the ZnO films. The results showed that thermal annealing relaxed the stress in the Cr⁺ ions implanted samples and the implantation-induced damage was partly recovered by means of the proper annealing treatment. Transmission electron microscopy measurements indicated that the first five monolayers of ZnO rotated an angle off the [0001]-axis of the GaN in the interfacial layer. The magnetic-field dependence of magnetization of annealed ZnO:Cr showed ferromagnetic behavior at room temperature.

Keywords: PACS; 61.72.Vv; 75.50.Pp; 78.30.FsZnO; Ion implantation; Thermal annealing; Ferromagnetism

Determination of solid material elastic modulus and surface energy based on JKR contact model by Kuang-Chung Wu; Hsien-I You (pp. 8530-8537).

The JKR contact theory is employed to study the adhesion phenomena between two solid materials in intimate contact. The elastic contact modulus and the work of adhesion of solid materials are obtained during adhesion tests by utilizing a micro force-deflection measuring apparatus. Six of the plastic materials, including polyethylene polyoxymethlene (POM), polyamide (PA), terephthalate (PET), polyvinyl chloride (PVC), polypropylene (PP), and ultra-high molecular weight polyethylene (UHMWPE) are used to evaluate the adhesion effect implied by the JKR theory. Comparison is made between surface energy obtained from the adhesion tests with that by a dynamic contact angle analyser.Results show that the load/deflection data in the loading phase are in good agreement with the predictions of JKR equation, and the experimental data of unloading phase deviate significantly from the JKR theory. The phenomena of adhesion hysteresis in loading tests are responsible for these results due to the effects of molecular reconstruction on solid surfaces in contact. The work of adhesions, and hence surface energies of plastic materials, calculated by the best fitting of JKR equation with the experimental data in the loading phase, agree satisfactorily in a comparable manner with that obtained using the contact angle analyser.

Keywords: JKR theory; Work of adhesion; Hysteresis

Influence of N₂ flow ratio on the properties of hafnium nitride thin films prepared by DC magnetron sputtering by Longyan Yuan; Guojia Fang; Chun Li; Mingjun Wang; Nishuang Liu; Lei Ai; Yanzhao Cheng; Huimin Gao; Xingzhong Zhao (pp. 8538-8542).

Hafnium nitride (Hf-N) thin films were deposited on fused silica at different N₂ flow ratio (N₂/N₂+Ar) using a reactive DC magnetron sputtering system. A gradual evolution in the composition of the films from Hf₃N₂, HfN, to higher nitrides was found through X-ray diffraction (XRD). Films of Hf₃N₂ and HfN show positive temperature coefficients of resistivity, while higher nitride has a negative one. Highly oriented growth of (001) Hf₃N₂ and NaCl-structure (100) HfN films were fabricated on fused silica substrate at relatively lower temperature of 300°C. The electrical resistivity values of both as-deposited and post-deposition annealed films were measured by a four-point probe method. The obtained minimum resistivity of as-deposited film is 20μΩcm, and this result shows potential application of HfN films as electrode materials in electronic devices.

Keywords: PACS; 73.61.r; 72.80.Ga; 78.66.LiCrystal structure; Reactive magnetron sputtering; Hafnium nitride; Semiconducting materials

Removal of graffiti from the mortar by using Q-switched Nd:YAG laser by Poologanathan Sanjeevan; Agnieszka J. Klemm; Piotr Klemm (pp. 8543-8553).

This paper presents part of the larger study on microstructural features of mortars and it's effects on laser cleaning process. It focuses on the influence of surface roughness, porosity and moisture content of mortars on the removal of graffiti by Nd:YAG laser. The properties of this laser are as follows: wavelength ( λ) 1.06μm, energy: 500mJ per pulse, pulse duration: 10ns. The investigation shows that the variation of laser fluence with the number of pulses required for the laser cleaning can be divided into two zones, namely effective zone and ineffective zone. There is a linear relationship observed between number of pulses required for laser cleaning and the laser fluence in the effective zone, while the number of pulses required for the laser cleaning is almost constant even though the laser fluence increases in the ineffective zone. Moreover, surface roughness, porosity and moisture content of mortar samples have influence on the laser cleaning process. The effect of these parameters become however negligible at the high level of laser fluence. The number of pulses required for the laser cleaning is low for smooth surface or less porous mortar. Furthermore, the wetness of the samples facilitates the cleaning process.

Keywords: Graffiti; Laser cleaning; Moisture content; Porosity; Surface roughness

Influence of activated carbon surface acidity on adsorption of heavy metal ions and aromatics from aqueous solution by Sanae Sato; Kazuya Yoshihara; Koji Moriyama; Motoi Machida; Hideki Tatsumoto (pp. 8554-8559).

Adsorption of toxic heavy metal ions and aromatic compounds onto activated carbons of various amount of surface C–O complexes were examined to study the optimum surface conditions for adsorption in aqueous phase. Cadmium(II) and zinc(II) were used as heavy metal ions, and phenol and nitrobenzene as aromatic compounds, respectively. Activated carbon was de-ashed followed by oxidation with nitric acid, and then it was stepwise out-gassed in helium flow up to 1273K to gradually remove C–O complexes introduced by the oxidation. The oxidized activated carbon exhibited superior adsorption for heavy metal ions but poor performance for aromatic compounds. Both heavy metal ions and aromatics can be removed to much extent by the out-gassed activated carbon at 1273K. Removing C–O complexes, the adsorption mechanisms would be switched from ion exchange to Cπ-cation interaction for the heavy metals adsorption, and from some kind of oxygen-aromatics interaction to π–π dispersion for the aromatics.

Keywords: PACS; 81.05.Uw; 81.65.Mq; 81.65.CfHeavy metal; Aromatics; Carbon; Adsorption; Surface

Synthesis of electrochromic tin oxide thin films with faster response by spray pyrolysis by P.S. Patil; S.B. Sadale; S.H. Mujawar; P.S. Shinde; P.S. Chigare (pp. 8560-8567).

Tin oxide thin films have been synthesized via pyrolysis of tri- n-butyl tin acetate solution at various substrate temperatures. The effect of substrate temperature on electrochromic properties is studied by electrochemical cyclic voltammetry and chronoamperometry. The films deposited at various substrate temperatures (450, 475 and 500°C) were polycrystalline and their preferred orientation changes from (110) to (200). Electrochromic performance indicated faster colour/bleach kinetics with appreciable reversibility in spray deposited SnO₂ films. Maximum colouration efficiency and reversibility was attained for the sample deposited at 500°C. All the spray deposited SnO₂ thin films showed long term electrochemical stability in proton containing electrolyte.

Keywords: Tin oxide; Thin films; Electrochromism; Spray pyrolysis technique

Ultraviolet photoemission spectroscopy of hydrogen complex deactivation on InP:Zn(100) surfaces by M.D. Williams; S.C. Williams; S.A. Yasharahla; N. Jallow (pp. 8568-8570).

Ultraviolet photoemission spectroscopy is used to study the kinetics of the H–Zn complex deactivation in Zn doped InP(100). Hydrogen injected into the material electronically passivates the local carrier concentration. Reverse-biased anneals of the InP under ultra-high vacuum show a dramatic change in the work function of the material with increasing temperature. Spectral features are also shown to be sensitive to sample temperature. To our knowledge, we show the first view of hydrogen retrapping at the surface using photoemission spectroscopy. A simple photoelectron threshold energy analysis shows the state of charge compensation of the material.

Keywords: Photoemission spectroscopy; Hydrogenation; Vacuum

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Applied Surface Science (v.253, #20)