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Applied Surface Science (v.255, #6)

Synthesis and characterization of nano-sized nickel catalyst supported on SiO₂–Al₂O₃ by Islam Hamdy Abd El Maksod; Eman Z. Hegazy; Sayed H. Kenawy; Tamer S. Saleh (pp. 3471-3479).

SiO₂–Al₂O₃ support material was prepared by sol–gel method, followed by calcination at 500, 1000 and 1500°C. The supported nickel catalyst containing 5wt% was obtained by impregnating a known mass of the calcined support material with nickel sulfate solution followed by drying and reduction with hydrazine hydrate at 80–100°C. The prepared catalysts were fully characterized by XRD and SEM, EDX and ESR. The hydrogenation of p-nitrophenol into p-aminophenol was performed using hydrazine hydrate as hydrogen donor. The product of the reaction was examined using IR, and NMR. The results showed that the degree of crystallinity of the support affects the catalytic activity of nano-sized Ni catalyst. It was observed that as the degree of crystallinity of the support material increases the catalytic activity increases. On the other hand, intermolecular interaction between nano-nickel clusters disappears completely in samples whose support was calcined at 1500°C.

Keywords: SiO; ₂; –Al; ₂; O; ₃; support; Nickel catalyst; Catalytic activity; XRD; SEM; EDX; ESR

Control of a- and c-plane preferential orientations of ZnO thin films by Dae-Hyung Cho; Ji-Hong Kim; Byung-Moo Moon; Yeong-Deuk Jo; Sang-Mo Koo (pp. 3480-3484).

We report orientation-controllable growth of ZnO thin films and their orientation-dependent electrical characteristics. ZnO thin films were deposited on single-crystalline (100) LaAlO₃ and (100) SrTiO₃ substrates using pulsed laser deposition (PLD) at different substrate temperatures (400–800°C). It was found that the orientation of ZnO films could be controlled by using different substrates of single-crystalline (100) LaAlO₃ and (100) SrTiO₃. The a-plane (112¯0) and c-plane (0002) oriented ZnO films are formed on LaAlO₃ and SrTiO₃, respectively. In both cases, the degree orientation increased with increasing deposition temperature T_s. Both the surface free energy and the degree of lattice mismatch are ascribed to play an important role for the orientation-controllable growth. Further characterization show that the grain size of the films with both orientations increases for a substrate temperature increase (i.e. from T_s=400°C to T_s=800°C), whereas the electrical properties of ZnO thin films depend upon their crystalline orientation, showing lower electrical resistivity values for a-plane oriented ZnO films.

Keywords: PACS; 73.61.Ga; 81.10.Aj; 81.15.Fg; 61.05.cp; 84.37.+qZnO thin films; Orientation control; Lattice mismatch; Pulsed laser deposition; X-ray diffraction; TLM

Preparation and characterization of silica-coated Fe₃O₄ nanoparticles used as precursor of ferrofluids by Ruo-Yu Hong; Jian-Hua Li; Shi-Zhong Zhang; Hong-Zhong Li; Ying Zheng; Jian-min Ding; Dong-Guang Wei (pp. 3485-3492).

Fe₃O₄ magnetic nanoparticles (MNPs) were synthesized by the co-precipitation of Fe³⁺ and Fe²⁺ with ammonium hydroxide. The sodium citrate-modified Fe₃O₄ MNPs were prepared under Ar protection and were characterized by Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), X-ray powder diffraction (XRD) and vibrating sample magnetometer (VSM). To improve the oxidation resistance of Fe₃O₄ MNPs, a silica layer was coated onto the modified and unmodified MNPs by the hydrolysis of tetraethoxysilane (TEOS) at 50°C and pH 9. Afterwards, the silica-coated Fe₃O₄ core/shell MNPs were modified by oleic acid (OA) and were tested by IR and VSM. IR results revealed that the OA was successfully grafted onto the silica shell. The Fe₃O₄/SiO₂ core/shell MNPs modified by OA were used to prepare water-based ferrofluids (FFs) using PEG as the second layer of surfactants. The properties of FFs were characterized using a UV–vis spectrophotometer, a Gouy magnetic balance, a laser particle size analyzer and a Brookfield LVDV-III+ rheometer.

Keywords: PACS; 81.07.−b; 74.25.Bt; 74.25.Ha; 75.50.MmMagnetic nanoparticles; Fe; ₃; O; ₄; /SiO; ₂; Surface modification; Ferrofluids; Rheology

Structure and transport mechanisms of Si/porous Si n–p junctions prepared by liquid phase epitaxy by A.A.M. Farag (pp. 3493-3498).

Heterojunction devices of n-Si/p-PSi were fabricated by growing n-Si films onto p-type porous Si substrates by liquid phase epitaxy. The structure of the grown films was checked using scanning electron microscopy and X-ray diffraction spectroscopy. X-ray diffraction measurements showed that the grown films have monocrystalline structure oriented along (111) direction with mainly cubic phase. Current–voltage ( I– V) and capacitance–voltage ( C– V) characteristics were measured over the temperature range from 298 to 398K. The analysis of the dark I– V characteristics of n-Si/p-PSi at several temperatures is done to elucidate the conduction mechanisms and the evaluation of the heterojunction parameters is presented. Two carrier transport mechanisms are believed to be at the origin of the forward current. At low bias voltage ( V≤0.4V) the forward current is dominated by the recombination at the porous silicon side of the space charge region. In the 0.5V≤ V≤1.4V region, the current transport is due to the space charge—limited current mechanism dominated by a single trapping level of energy 0.41eV. The reverse current is considered to be mainly generated in the depletion region of the porous silicon. The capacitance–voltage results confirm an abrupt junction with a homogenous distribution of the impurities inside the space charge region. Information on the depletion region, built-in voltage and net carrier concentration were obtained from the dark C– V characteristics.

Keywords: Conduction mechanism; Heterojunction; Liquid phase epitaxy; Porous silicon

Modification of polystyrene-based activated carbon spheres to improve adsorption of dibenzothiophene by Qin Wang; Xiaoyi Liang; Wenming Qiao; Chaojun Liu; Xiaojun Liu; Rui Zhang; Licheng Ling (pp. 3499-3506).

Polystyrene-based activated carbon spheres (PACS) were modified with either air, HNO₃, (NH₄)₂S₂O₈, H₂O₂ or H₂ to improve their adsorption properties of dibenzothiophene (DBT). The texture and surface chemistry of PACS were characterized by N₂ adsorption, scanning electron microscopy (SEM), temperature-programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), acid–base titration and elemental analysis. The results showed that HNO₃ and (NH₄)₂S₂O₈ treatments introduced large amount of acidic groups such as carboxylic, lactones and anhydride groups, while air and H₂O₂ had relatively mild effects and introduced a small quantity of phenol, carbonyl and ether groups. In the HNO₃ treatment, the acidic groups might be fixed on the internal and external surface of PACS, which may act as active sites of adsorption, resulting in increase of the adsorption amount by 45%. Whereas H₂O₂ and (NH₄)₂S₂O₈ treatments might fix more oxygen-containing groups on the external surface, which may hinder DBT molecule enter into micropores, leading to rather lower adsorption capacity with the extent of oxidation. So, the concentration, distribution and types of the acidic functional groups are responsible for the removal of DBT.

Keywords: Activated carbon spheres; Modification; Dibenzothiophene; Adsorption

A novel method to fabricate superhydrophobic surfaces based on well-defined mulberry-like particles and self-assembly of polydimethylsiloxane by Jinxin Yang; Pihui Pi; Xiufang Wen; Dafeng Zheng; Mengyi Xu; Jiang Cheng; Zhuoru Yang (pp. 3507-3512).

A superhydrophobic surface was obtained by combining application of CaCO₃/SiO₂ mulberry-like composite particles, which originated from violent stirring and surface modification, and self-assembly of polydimethylsiloxane. Water contact angle and sliding angle of the superhydrophobic surface were measured to be about 164±2.5° and 5°, respectively. The excellent hydrophobicity is attributed to the synergistic effect of micro–submicro–nano-meter scale roughness (fabricated by composite particles) and the low surface energy (provided by polydimethylsiloxane). This procedure makes it possible for widespread applications of superhydrophobic film due to its simplicity and practicability.

Keywords: Superhydrophobic surface; Polydimethylsiloxane; CaCO; ₃; /SiO; ₂; composite particle; Self-cleaning

Physical bounds of metallic nanofingers obtained by mechano-chemical atomic force microscope nanolithography by O. Akhavan; M. Abdolahad (pp. 3513-3517).

To obtain metallic nanofingers applicable in surface acoustic wave (SAW) sensors, a mechano-chemical atomic force microscope (AFM) nanolithography on a metallic thin film (50nm in thickness)/piezoelectric substrate covered by a spin-coated polymeric mask layer (50–60nm in thickness) was implemented. The effective shape of cross-section of the before and after etching grooves have been determined by using the AFM tip deconvolution surface analysis, structure factor, and power spectral density analyses. The wet-etching process improved the shape and aspect ratio (height/width) of the grooves and also smoothed the surface within them. We have shown that the relaxed surface tension of the polymeric mask layer resulted in a down limitation in width and length of the lithographed nanofingers. The surface tension of the mask layer can be changed by altering the initial concentration of the polymer in the deposition process. As the surface tension reduced, the down limitation decreased. In fact, an extrapolation of the analyzed statistical data has indicated that by decreasing the surface tension from 39 to 10nN/nm, the minimum obtainable width and length of the metallic nanofingers was changed from about 55nm and 2μm to 15nm and 0.44μm, respectively. Using the extrapolation’s results, we have shown that the future SAW sensors buildable by this nanolithography method possess a practical bound in their synchronous frequency (∼58GHz), mass sensitivity (∼6125MHz-mm²/ng), and the limit of mass resolution (∼4.88×10⁻¹⁰ng/mm²).

Keywords: PACS; 68.37.Ps; 81.16.Nd; 02.50.FzAFM; Nanolithography; Al nanofingers; Resist mask layer; Scratching; Tip deconvolution

Atom beam sputtered Mo₂C films as a diffusion barrier for copper metallization by C.C. Tripathi; Mukesh Kumar; Dinesh Kumar (pp. 3518-3522).

The saddle field fast atom beam sputtered (ABS) 50nm thick molybdenum carbide (Mo₂C) films as a diffusion barrier for copper metallization were investigated. To study the diffusion barrier properties of Mo₂C films, the as-deposited and annealed samples were characterized using four probes, X-ray diffraction, field enhanced scanning electron microscopy, energy dispersive X-ray analysis, atomic force microscopy and Rutherford back scattering techniques. The amorphous structure of the barrier films along with presence of carbon atoms at the molybdenum carbide–silicon interface is understood to reduce effective grain boundaries and responsible for increased thermal stability of Cu/Mo₂C/Si structure. The lowest resistivity of the as-deposited molybdenum carbide barrier films was ∼29μΩcm. The low carbon containing molybdenum carbide was found thermally stable up to 700°C, therefore can potentially be used as a diffusion barrier for copper metallization.

Keywords: Diffusion barrier; Atom beam sputtering; Molybdenum carbide; Copper metallization; Interface interaction

Adsorption-transport modeling of anions through PVD membrane in the presence of the screen phenomenon by S.S. Madaeni; E. Salehi (pp. 3523-3529).

A mathematical model for transport and adsorption of chloride and sulphate ions through PVD membrane is presented at two pressures; 8 and 15bar and 40°C. The PVD membrane is negatively charged. Saturated brine containing NaCl with the concentration higher than 97% was challenged with the membrane as the feed. Other available ions in the solution were Fe²⁺, Ca²⁺, Mg²⁺ and SO₄²⁻. The screen effect of the cations on the membrane surface charge facilitates the passage of the anions through the membrane without any noticeable electrostatic repulsion. Hermia blocking laws combined with experimental results indicate that the internal pore closure of the membrane by anions and cake deposition on the membrane surface by cations are the separation mechanisms. The transmission of anions through the membrane may be predicted with a simple transport equation (convection and diffusion) combined with an adsorption isotherm. Both Langmuir and Freundlich adsorption isotherms were employed due to the simplicity and validity in liquid systems. The isotherm’s parameters were determined at 10bar during the unsteady state filtration. Under this condition, the permeate flux and concentration varied sharply due to adsorption. Finally, the model was compared with the experimental rejection data. An acceptable agreement around 95% at 8bar and 92% at 15bar was observed between theoretical model and experimental data.

Keywords: Modeling; Membrane; Transport; Adsorption; Screen phenomenon

Green-emission and n-type conductivity of ZnO:Zn films obtained using vapor deposition method by Junying Zhang; Liang Cong; Hui Wan; Tianmin Wang (pp. 3530-3533).

ZnO:Zn films with strong adhesion to the substrate were obtained by evaporating ZnO powders in the mixture of N₂ and H₂. The ZnO:Zn films produced in the reductive gas showed bright green photoluminescence and n-type conductivity. After the ZnO:Zn films were re-fired in the air, the conductivity and luminescent intensity decrease to less than 1% and about 50% of the initial values, respectively. For the two different types of samples obtained in the reductive gas and in the air, respectively, their point defects showed notable difference as indicated by the measurements of electron spin resonance and X-ray photoelectron spectroscopies. The native defects account for the green-emission while the n-type conductivity is perhaps associated with the hydrogen doping.

Keywords: PACS; 72.20.−i; 33.50.−jZnO; Vapor deposition; Photoelectron spectroscopy; Luminescence; Electrical conductivity

Computational analysis of effect of modification on the interfacial characteristics of a carbon nanotube–polyethylene composite system by Qingbin Zheng; Dan Xia; Qingzhong Xue; Keyou Yan; Xili Gao; Qun Li (pp. 3534-3543).

In this study, the non-covalent association of single-walled nanotube (SWNT) with polyethylene (PE) molecule and the influence of sidewall modification on the interfacial bonding between the SWNTs and polymer were investigated using molecular mechanics (MM) and molecular dynamics (MD) simulations. The model of interaction between the initially separated PE and SWNT fragments, which can be either wrapping or filling, was computed. The possible extension of polymers wrapping or filling SWNTs can be used to structurally bridge the SWNTs and polymers to significantly improve the load transfer between them when SWNTs are used to produce nanocomposites. The interfacial bonding characteristics between the single-walled nanotubes, on which –COOH, –CONH₂, –C₆H₁₁, or –C₆H₅ groups have been chemically attached, and the polymer matrix were also investigated by performing pullout simulations. The results show that appropriate functionalization of nanotubes at low densities of functionalized carbon atoms drastically increase their interfacial bonding and shear stress between the nanotubes and the polymer matrix, where chemisorption with –C₆H₅ groups to as little as 5.0% of the nanotube carbon atoms increases the shear stress by about 1700%. Furthermore, this suggests the possibility to use functionalized nanotubes to effectively reinforce other kinds of polymer-based materials as well.

Keywords: PACS; 81.05.TpCarbon nanotube polymer composites; Molecular mechanics; Molecular dynamics; Interfacial characteristics

Structural and optical properties of zinc nitride films prepared by rf magnetron sputtering by Tianlin Yang; Zhisheng Zhang; Yanhui Li; MaoShui Lv; Shumei Song; Zhongchen Wu; Jincheng Yan; Shenghao Han (pp. 3544-3547).

Zinc nitride films were prepared on quartz substrates by rf magnetron sputtering using pure zinc target in N₂–Ar plasma. X-ray diffraction (XRD) analysis indicates that the films just after deposition are polycrystalline with a cubic structure and a preferred orientation of (400). X-ray photoelectron spectroscopy (XPS) analysis also confirms the formation of N–Zn bonds and the substitution incorporation of oxygen for nitrogen on the surface of the films. The optical band gap is calculated from the transmittance spectra of films just after deposition, and a direct band gap of 1.01±0.02eV is obtained. Room temperature PL measurement is also performed to investigate the effect of defect on the band gap and quality of the zinc nitride films.

Keywords: PACS; 68.55.Jk; 73.61.LeZinc nitride; rf magnetron sputtering; Optical band gap

The studies of Ge quantum dots on strained Si_0.7Ge_0.3 layer by photoluminescence and deep level transient spectroscopy by Zhensheng Tao; Ning Zhan; Hongbin Yang; Yan Ling; Zhenyang Zhong; Fang Lu (pp. 3548-3551).

Systematic studies of Ge quantum dots (QDs) grown on strained Si_0.3Ge_0.7 layer have been carried out by photoluminescence (PL) and deep level transient spectroscopy (DLTS). In PL measurements, two peaks around 0.7eV are distinguished, which are assigned to two types of QDs observed by atomic force microscopy (AFM). Large blueshifts of the PL peaks from small QDs with the increase of excitation power are observed and attributed to the band bending effects typical for type-II band alignment. From DLTS measurements, the energy levels of holes in both types of QDs are derived, which shift with the change of the number of holes in QDs due to their charge energy. By comparing results from PL and DLTS measurements, further understanding of band alignment with the increase of the number of excitons in QDs is deduced.

Keywords: GeSi quantum dots; Photoluminescence; DLTS

Annealing effects on the bonding structures, optical and mechanical properties for radio frequency reactive sputtered germanium carbide films by C.Q. Hu; J.Q. Zhu; W.T. Zheng; J.C. Han (pp. 3552-3557).

The effects of thermal annealing in vacuum on the bonding structures, optical and mechanical properties for germanium carbide (Ge1−_xC_x) thin films, deposited by radio frequency (RF) reactive sputtering of pure Ge(111) target in a CH₄/Ar mixture discharge, are investigated. We find that there are no significant changes in the bonding structure of the films annealed below 300°C. The fraction of Ge–H bonds for the film annealed at temperatures ( T_a) above 300°C decreases, whereas that of C–H bonds show a decrease only when T_a exceeds 400°C. The out-diffusion of hydrogen promotes the formation of Ge–C bonds at T_a above 400°C and thus leads to a substantial increase in the compressive stress and hardness for the film. The refractive indices and optical gaps for Ge1−_xC_x films are almost constant against T_a, which can be ascribed to the unchanged ratios of Ge/C and sp²-C/sp³-C concentrations. Furthermore, we also find that the excellent optical transmission for an antireflection Ge1−_xC_x double-layer film on ZnS substrate is still maintained after annealing at 700°C.

Keywords: PACS; 78.20; 62.20Germanium carbide films; Bonding structure; Optical and mechanical properties; Annealing

Formation of sub-micron size carbon structures by plasma jets emitted from a pulsed capillary discharge by H. Bhuyan; M. Favre; E. Valderrama; G. Avaria; E. Wyndham; H. Chuaqui; J. Baier; H. Kelly; D. Grondona; A. Marquez (pp. 3558-3562).

We have performed an experimental investigation of the potential use of intense plasma jets produced in a repetitive pulsed capillary discharge (PCD) operating in methane gas, to irradiate Si (100) substrates. The surface modifications induced by the plasma jet using two different material inserts at the capillary end, graphite and titanium, are characterized using standard surface science diagnostic tools, such as scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) analysis and Raman spectroscopy (RS). It has been found that the application of methane plasma jet results in the formation of sub-micron size carbon structures. It is observed that the resulting plasma irradiated surface morphologies are different, depending on the different material inserts used at the capillary end, at otherwise identical operational conditions. To investigate the species responsible for the observed surface changes in different material inserts to the capillary, optical-emission spectroscopy (OES) was recorded using a 300–1000nm spectrometer. The OES results show the presence of H, CH and C₂ Swan band in the discharge plasma, which play a significant role in the formation of the carbon structures.

Keywords: PACS; 52.80.Tn; 52.77.-jPlasma jets; Carbon coatings; Capillary discharge

Large-area silica nanotubes with controllable geometry on silicon substrates by Mingzhe Hu; Rong Yu; Judith L. MacManus-Driscoll; Adam P. Robinson (pp. 3563-3566).

The synthesis of a highly uniform, large-scale nanoarrays consisting of silica nanotubes above embedded nanohole arrays in silicon substrates is demonstrated. In situ anodized aluminium oxide (AAO) thin film masks on Si substrates were employed, and the nanotubes were fabricated by Ar ion milling through the masks. The geometries of the nanoarrays, including pore diameter, interpore distance and the length of both nanopores and nanotubes could be controlled by the process parameters, which included that the outer pore diameter of silica tube was tuned from ∼80nm to ∼135nm while the inner tube diameter from ∼40nm to ∼65nm, the interpore distance of the nanotube arrays was from 100nm to 180nm and the length of silica tube changed from ∼90nm to ∼250nm. The presented nanostructure fabrication method has strong potential for application in intensity and frequency adjustable high luminescence efficiency optoelectronic devices.

Keywords: PACS; 81.16.Rf; 81.16.−cSilica nanotubes; AAO thin film; Ion beam technology

Stoichiometry, contamination and microstructure of MnSb(0001) surfaces by S.A. Hatfield; J.D. Aldous; G.R. Bell (pp. 3567-3575).

The stoichiometry, microstructure and surface composition of MnSb have been investigated using X-ray photoelectron spectroscopy, electron diffraction and microscopy. Epitaxially grown samples were exposed to ambient air for several weeks and methods for preparing clean, stoichiometric and smooth surfaces were investigated. Air-stored sample surfaces are chemically stratified but dominated by Mn oxides 4–5nm thick. These oxides are difficult to remove by ion bombardment and annealing (IBA), but a brief etch in HCl removes them very efficiently. It leaves the surface Sb-rich, and clean, smooth and stoichiometric surfaces are then readily recovered by IBA. These surfaces exhibit a (2×2) surface reconstruction with atomically flat terraces. This reconstruction can be reversibly changed to a (1×1) by Sb deposition and annealing.

Keywords: MnSb; XPS; Surface contamination; Surface cleaning; Wet etching; MBE; Ferromagnet–semiconductor interface; Half-metal

Radiation-induced decomposition of the metal-organic molecule Bis(4-cyano-2,2,6,6-tetramethyl-3,5-heptanedionato)copper(II) by David Wisbey; Ning Wu; Yaroslav Losovyj; Ihor Ketsman; A.N. Caruso; Danqin Feng; John Belot; Elio Vescovo; Peter A. Dowben (pp. 3576-3580).

The effects of vacuum ultraviolet radiation on the adsorbed copper center molecule bis(4-cyano-2,2,6,6-tetramethyl-3,5-heptanedionato)copper(II) (or Cu(CNdpm)₂), (C₂₄H₃₆N₂O₄Cu, Cu(II)) was studied by photoemission spectroscopy. Changes in the ultraviolet photoemission spectra (UPS) of Cu(CNdpm)₂, adsorbed on Co(111), indicate that the ultraviolet radiation leads to decomposition of Cu(CNdpm)₂ and this decomposition is initially dominated by loss of peripheral hydrogen.

Keywords: PACS; 61.80.−x; 33.80.Eh; 82.30.Lp; 79.60−iMolecular magnets; Decomposition of organic compounds; Ultraviolet photoemission spectroscopy

The sodium diffusion in aluminium-oxide by H. Lovas; V.K. Josepovits; Z. Tóth (pp. 3581-3585).

The transport of Na through the polycrystalline ceramic arc tube of high intensity discharge lamps has been investigated. This complex process consists of several steps: solution in the ceramics, diffusion through the ceramics, leaving the bulk phase, evaporation from the surface. Among the listed processes the kinetics of the diffusion was examined in the temperature range 400–1200°C, separately from other disturbing effects. X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS) were used to determine the concentration depth profiles. The obtained results confirmed that the grain boundary diffusion plays an important role in the transport process of sodium through the ceramic wall. The bulk and the grain boundary diffusion coefficients and the temperature dependencies of these transport processes have been determined. The activation energy of Na bulk diffusion is 56.5±6.7kJ/mol at 900–1200°C, respectively the activation energies of Na grain boundary diffusion amount to 97.5±21.6kJ/mol in the temperature range 700–1100°C and 7.7±4.0×10⁻²kJ/mol at 400–700°C. The preexponential factor of the bulk diffusion was found to be D_o=5.1×10⁻¹⁵±9.5×10⁻¹⁷cm²/s in the temperature range 900–1200°C, whereas the preexponential factors of grain boundary diffusion are D_o=1.1×10⁻¹⁰±1.1×10⁻¹¹cm²/s at 700–1100°C and D_o=7.5×10^-15±1.5×10⁻¹⁷cm²/s at 400–700°C.

Keywords: Sodium diffusion; Single-crystal and polycrystalline alumina; Grain boundary diffusion coefficient; Bulk diffusion coefficient; XPS; SIMS

The influence of oxidation with nitric acid on the preparation and properties of active carbon enriched in nitrogen by Robert Pietrzak; Piotr Nowicki; Helena Wachowska (pp. 3586-3593).

The effect of oxidation by 20% nitric acid on the properties and performance of active carbons enriched with nitrogen by means of the reaction with urea in the presence of air has been studied. The study has been made on demineralised orthocoking coal and the carbonisates obtained from it at 600 or 700°C, subjected to the processes of nitrogenation, oxidation and activation with KOH in different sequences. The amount of nitrogen introduced into the carbon with the aid of urea has been found to depend on the stage at which the process of nitrogenation was performed. The process of oxidation of the demineralised coal and the active carbon obtained from the former has been found to favour nitrogen introduction into the carbon structure. In the process of nitrogenation of the carbonisates the amount of nitrogen introduced has inversely depended on the temperature of carbonisation. The modifications of the processes permitted obtaining materials of different textural parameters, different acid–base character of the surface and different iodine sorption capacity.

Keywords: PACS; 81.05.Uw; 81.65.MqActive carbon; Oxidation; Nitrogenation; Adsorption

Determination of interfacial energies in the aminomethylpropanediol-neopentylglycol organic alloy by S. Akbulut; Y. Ocak; K. Keşlioğlu; N. Maraşlı (pp. 3594-3599).

The grain boundary groove shapes for solid aminomethylpropanediol in equilibrium with eutectic aminomethylpropanediol-neopentylglycol liquid were directly observed by using a horizontal temperature gradient stage. From the observed grain boundary groove shapes, the Gibbs–Thomson coefficient, solid–liquid interfacial energy and grain boundary energy of solid aminomethylpropanediol in equilibrium with eutectic aminomethylpropanediol-neopentylglycol liquid have been determined to be (5.3±0.5)×10⁻⁸Km, (8.5±1.3)×10⁻³Jm⁻² and (16.8±2.9)×10⁻³Jm⁻², respectively.

Keywords: Organic materials; Crystal growth; Interfacial energy; Grain boundary energy; Thermal conductivity ratio

TMOS based water repellent silica thin films by co-precursor method using TMES as a hydrophobic agent by Sanjay S. Latthe; Digambar Y. Nadargi; A. Venkateswara Rao (pp. 3600-3604).

The present paper describes the room temperature synthesis of dip coated water repellent silica coatings on glass substrates using trimethylethoxysilane (TMES) as a co-precursor. Silica sol was prepared by keeping the molar ratio of tetramethoxysilane (TMOS) precursor, methanol (MeOH) solvent, water (H₂O) constant at 1:29.27:2.09 respectively, with 0.5M NH₄OH throughout the experiments and the TMES/TMOS molar ratio ( M) was varied from 0 to 3.8. It was found that with an increase in M value, the roughness and hydrophobicity of the films increased, however the optical transmission decreased from 93% to 57% in the visible range. The hydrophobic silica films retained their hydrophobicity up to a temperature of 250°C and above this temperature the films became hydrophilic. The hydrophobic silica thin films were characterized by taking into consideration the surface roughness studies, Fourier transform infrared (FT-IR) spectroscopy, percentage of optical transmission, scanning electron microscopy (SEM) and contact angle measurements.

Keywords: Hydrophobic; Roughness; Contact angle; Optical transmission; Silica thin films

Comparative examination of the microstructure and high temperature oxidation performance of NiCrBSi flame sprayed and pack cementation coatings by D. Chaliampalias; G. Vourlias; E. Pavlidou; S. Skolianos; K. Chrissafis; G. Stergioudis (pp. 3605-3612).

Coatings formed from NiCrBSi powder were deposited by thermal spray and pack cementation processes on low carbon steel. The microstructure and morphology of the coatings were studied by scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD). Flame sprayed coatings exhibited high porosity and were mechanically bonded to the substrate while pack cementation coatings were more compact and chemically bonded to the substrate. The microhardness and the high temperature oxidation resistance of the coated samples were evaluated by a Vickers microhardness tester and by thermogravimetric measurements (TG), respectively. Pack cementation coatings showed higher hardness and were more protective to high temperature environments than the flame sprayed coatings.

Keywords: PACS; 61.05.cp; 68.37.Hk; 81.15.Rs; 81.65.Mq; 81.65.Kn; 81.70.Pg; 81.15.GhNiCrBSi; CVD; Pack cementation; High temperature oxidation

Structure and mechanical properties of Ni–P electrodeposited coatings by Xuetao Yuan; Dongbai Sun; Hongying Yu; Huimin Meng (pp. 3613-3617).

The coatings with different phosphorus contents were obtained by varying the concentration of H₃PO₃ in the electroplating bath. With the increase of phosphorus content, the structure of the Ni–P electrodeposited coatings transformed from microcrystalline to a mixture of nanocrystalline and amorphous phases, then to amorphous phase. A high hardness value of 710HV_0.1 of as-deposited Ni–P coating was obtained at 8.3at.% phosphorus content, and high wear resistance was accordingly achieved. The refined nanocrystalline grains with average size of about 7nm were found to be responsible for the high hardness and improved wear resistance of the as-deposited Ni–P electrodeposited coating.

Keywords: Ni–P electroplating; Microhardness; Wear resistance; TEM

Electrical conductivity dependence of thin metallic films of Au and Pd as a top electrode in capacitor applications by S. Nazarpour; E. Langenberg; O. Jambois; C. Ferrater; M.V. García-Cuenca; M.C. Polo; M. Varela (pp. 3618-3622).

Electrical conductivity dependence of thin metallic films of Au and Pd over the different perovskites was investigated. It is found from electrical properties that crystallographic growth orientation of Au and Pd thin layers attained from X-ray diffraction results indicate the slop of current ( I)–voltage ( V) plots. Besides, surface morphology and topography was considered using Field Emission Scanning Electron Microscopy and Atomic Force Microscopy, respectively. Obtained results showed the Stranski–Krastanov growth of the Pd and Au. Indeed, diminishing of the root-mean-square roughness of Pd/BiMnO₃/SrTiO₃ following by Au deposition should be concerned due to growth of Au onto the crack-like parts of the substrate. These crack-like parts appeared due to parasitic phases of the Bi–Mn–O system mainly Mn₃O₄ (l0l) and Mn₃O₄ (004l).The different response in the electrical properties of heterostructures suggests that electrical conductance of the Au and Pd thin metallic films have the crystallographic orientation dependence. Furthermore, polycrystallinity of the thin metallic films are desired in electrode applications due to increase the conductivity of the metallic layers.

Keywords: Heterostructure; Electrical conductivity; Growth direction; Metallic thin films

The role of adsorption of dodecylethyldimethylammonium bromide and benzyldimethyldodecylammonium bromide surfactants in wetting of polytetrafluoroethylene and poly(methyl methacrylate) surfaces by Joanna Harkot; Bronisław Jańczuk (pp. 3623-3628).

The role of adsorption of dodecylethyldimethylammonium bromide (C₁₂(EDMAB)) and benzyldimethyldodecylammonium bromide (BDDAB) at water–air and polytetrafluoroethylene (PTFE)–water and poly(methyl methacrylate) (PMMA)–water interface, in wetting of PTFE and PMMA surface, was established from the measured values of the contact angle ( θ) of aqueous C₁₂(EDMAB) and BDDAB solutions in PTFE (PMMA)-solution drop–air system, and from the measured values of the surface tension of aqueous C₁₂(EDMAB) and BDDAB solutions. Adsorption of C₁₂(EDMAB) and BDDAB at water–air interface was determined earlier from the Gibbs equation. Adsorption at solid–water interface was deduced from the Lucassen-Reynders equation based on the relationship between adhesion tension ( γ_LVcos θ) and surface tension ( γ_LV). The slope of the γ_LVcos θ– γ_LV curve was found to be constant and equal to −1, and about −0.3 for PTFE and PMMA surface, respectively (in the case of both surfactant studied: C₁₂(EDMAB) and BDDAB, and in the whole range of surfactants concentration in solution). It means that the amount of the surfactant adsorbed at the PTFE–water interface, Γ_SL, was essentially equal to its amount adsorbed at water–air interface, Γ_LV. However, Γ_SL at the PMMA–water interface was about three times smaller as compared to that at water–air interface. By extrapolating the linear dependence between γ_LVcos θ– γ_LV and dependence between cos θ– γ_LV and cos θ=1 we determined the value of the critical surface tension of PTFE and PMMA surface wetting, γ_c. The obtained values of γ_c for PTFE surface were equal 23.4 and 23.8mN/m, 23.1 and 23.2mN/m for C₁₂(EDMAB) and BDDAB, respectively and they were higher than the surface tension of PTFE (20.24mN/m). On the other hand, the obtained values of γ_c for PMMA surface were equal 31.4 and 30.9mN/m, 31.7 and 31.3mN/m for C₁₂(EDMAB) and BDDAB, respectively and they were smaller than the surface tension of PMMA (39.21mN/m). Using the values of PTFE and PMMA surface tension and the measured values of the surface tension of aqueous C₁₂(EDMAB) and BDDAB solutions in the Young equation, the PTFE (PMMA)-solution interfacial tension, γ_SL, was also determined. Next, the work of adhesion ( W_A) was deduced, and it occurred that the dependence between the W_A and the surface tension ( γ_LV) for both studied solids was linear. However, the values of the W_A for PMMA change as a function of log C ( C—surfactant concentration) changed from 91.7 to 68.5mJ/m² and from 91.8 to 65.1mJ/m² for C₁₂(EDMAB) and BDDAB, respectively. On the other hand, the work of adhesion of both studied surfactants solutions to the PTFE surface was practically constant (an average value was equal 45.8 and 45.4mJ/m², respectively). These values were close to the value of the work of water adhesion to PTFE surface (45.5mJ/m²).

Keywords: PACS; 68.35 NpSurface tension; Adhesion tension; Adsorption; Work of adhesion; Wettability; Critical surface tension of wetting; Polytetrafluoroethylene; Poly(methyl methacrylate); Dodecylethyldimethylammonium bromide; Benzyldimethyldodecylammonium bromide

Effect of Cr and V dopants on the chemical stability of AZO thin film by Y.C. Lin; J.H. Jiang; W.T. Yen (pp. 3629-3634).

The effect of the dopants of Cr and V on the optoelectronic properties of AZO thin film by pulsed DC magnetron sputtering has been investigated. We also use HCl and KOH solutions to conduct the chemical stability of AZO:Cr:V thin film. The experimental results show that the optimum AZO optoelectronic properties without Cr and V doping obtain the resistivity of 9.87×10⁻⁴Ωcm, optical transmittance of 84% and surface roughness rms value of 2.6nm. The chemical stability of AZO will increase after Cr and V doping. Under the added V=0.19wt.%, Cr=0.56wt.%, AZO:Cr:V thin film showed 52% increased chemical stability and 128% decrease in surface roughness after etching (the resistivity was 3.62×10⁻³Ωcm and optical transmittance 81%). From the experimental results, the higher resistivity obtained after KOH etching compared with after HCl etching. The reason is that the Zn/Al ratio will reduce after etching and cause the AZO film carrier density to reduce as well. However, the optical transmittance obtained after KOH etching will be higher than that after HCl etching. This is because that a better surface roughness after KOH etching obtained than after HCl etching.

Keywords: Pulsed DC magnetron sputtering; AZO; Chemical stability; Doping; Transparent conducting oxide

Influence of oxygen plasma treatment on boron carbon nitride film composition by Hidemitsu Aoki; Takuro Masuzumi; Daisuke Watanabe; M.K. Mazumder; Hiroshi Sota; Chiharu Kimura; Takashi Sugino (pp. 3635-3638).

Variations in the composition and bonds of boron carbon nitride (BCN) film caused due to an oxygen (O₂) plasma ashing process are investigated for a low dielectric constant (low-k) insulating film for next generation LSI devices. The O₂ plasma treatment is preformed for BCN samples with various C compositions. The etching rate of BCN films with an O₂ plasma decreases with increasing C composition. The reaction of O atoms is suppressed in the BCN film with a high C composition. B–N and B–C bonds with lower bond energies are easily broken by the O₂ plasma and replaced by the generation of B–O, N–O, and C–O bonds. The B-atom concentration for all samples is decreased significantly by the O₂ plasma treatment. Ion bombardment may play a more dominant role than the O-atom reaction in the etching of the BCN film. The existence of C–N bonds with a high bonding energy may suppress etching and incorporation of O atoms.

Keywords: Ashing; Interconnection; Low-k; BCN; Low dielectric constant; O; ₂; plasma; XPS

Cu⁺-codoping inducing the room-temperature magnetism and p-type conductivity of ZnCoO diluted magnetic semiconductor by P. Cao; D.X. Zhao; D.Z. Shen; J.Y. Zhang; Z.Z. Zhang; Y. Bai (pp. 3639-3641).

Successful synthesis of room-temperature ferromagnetic semiconductors, Cu-codoped ZnCoO films are obtained by sol–gel method. It is found that the essential ingredient in achieving room-temperature ferromagnetism is Cu-codoping. By Hall-effect measurement a p-type conductivity was observed for the Cu-codoped films, the hole concentration increases with the increase in Cu concentration. XPS result confirmed Cu ions are univalent in the films, which induced the room-temperature ferromagnetism.

Keywords: p; -Type conductivity; Room-temperature magnetism

Surface-modification of indium tin oxide nanoparticles with titanium dioxide by a nonaqueous process and its photocatalytic properties by Rongjun Pan; Shenghui Pan; Juying Zhou; Yucheng Wu (pp. 3642-3647).

Indium tin oxide nanoparticles prepared by co-precipitation were re-dispersed in benzyl alcohol and modified successfully with titanium dioxide using titanium tetrachloride as precursor. The morphologies and the re-dispersing processes of both the initial and modified indium tin oxide nanoparticles were investigated, respectively. The photocatalytic properties of the modified nanoparticles were compared with commercial P25 photocatalyst. It was found that (i) the average diameter of the initial indium tin oxide nanoparticles was 10.7nm and that of the surface-modified nanoparticles was 14.5nm; (ii) the optimal ultrasonication time was 10.0min and 8.0min for the initial and surface-modified ITO nanoparticles, respectively; (iii) the modified particles possessed a higher photocatalytic activity than commercial P25 photocatalyst in the photodegradation of rhodamine B in aqueous medium at pH 5.00; (iv) the pH of the medium markedly influences the photodegradation efficiency.

Keywords: PACS; 82.65.+r; 73.40.−c; 79.60.Jv; 81.05.HdTitanium dioxide; Indium tin oxide; Surface-modification; Nonaqueous process; Photocatalytic properties

Vacuum ultraviolet-induced surface modification of cyclo-olefin polymer substrates for photochemical activation bonding by Young-Jong Kim; Yoshinao Taniguchi; Kuniaki Murase; Yoshihiro Taguchi; Hiroyuki Sugimura (pp. 3648-3654).

The surface of cyclo-olefin polymer (COP) was treated with vacuum ultraviolet (VUV) light at 172nm wavelength to improve the wettability and adhesion properties. Through VUV treatment in air, the terminal groups of the COP surface were oxidized into oxygen functional groups, containing CO, CO, and COO components, making the COP surface hydrophilic. The extent of oxygenation was evaluated by XPS and FTIR-ATR spectra, and it was shown that the surface properties, hydrophilicity, and functionalization were dependent on both VUV irradiation distance and irradiation time, which have an effect on the concentration of oxygen functional groups. VUV-light treatment with a short irradiation distance was more effective in introducing oxygen functional groups.

Keywords: Surface modification; Vacuum ultraviolet (VUV); Oxygen functional groups

High temperature ferromagnetism of the vacuum-annealed (In1−_xFe_x)₂O₃ powders by Feng-Xian Jiang; Xiao-Hong Xu; Jun Zhang; Hai-Shun Wu; G.A. Gehring (pp. 3655-3658).

(In1−_xFe_x)₂O₃ ( x=0.02, 0.05, 0.2) powders were prepared by a solid state reaction method and a vacuum annealing process. A systematic study was done on the structural and magnetic properties of (In1−_xFe_x)₂O₃ powders as a function of Fe concentration and annealing temperature. The X-ray diffraction and high-resolution transmission electron microscopy results confirmed that there were not any Fe or Fe oxide secondary phases in vacuum-annealed (In1−_xFe_x)₂O₃ samples and the Fe element was incorporated into the indium oxide lattice by substituting the position of indium atoms. The X-ray photoelectron spectroscopy revealed that both Fe²⁺ and Fe³⁺ ions existed in the samples. Magnetic measurements indicated that all samples were ferromagnetic with the magnetic moment of 0.49–1.73μ_B/Fe and the Curie temperature around 783K. The appearance of ferromagnetism was attributed to the ferromagnetic coupling of Fe²⁺ and Fe³⁺ ions via an electron trapped in a bridging oxygen vacancy.

Keywords: Diluted magnetic semiconductor; High Curie temperature; Fe-doped In; ₂; O; ₃; Vacuum annealing

Anatase type titania nanotube arrays direct fabricated by anodization without annealing by Xiufeng Xiao; Keguan Ouyang; Rongfang Liu; Jianhe Liang (pp. 3659-3663).

In this paper, anatase type titania nanotube arrays were direct fabricated by anodization in dimethyl sulfoxide electrolyte containing 1wt% HF solution at above 50°C without subsequently annealing. The length of the nanotubes decreases with increasing anodization temperature from about approximately 15μm at 40°C to approximately 4.5μm at 60°C. High resolution transmission electron microscope images and selected area electron diffraction pattern confirm the polycrystalline anatase specimen consisting of many nanocrystals with a random orientation.

Keywords: PACS; 61.46.Fg; 81.07.DeAnodization; Nanotube array; Titania; Anatase

Growth of nonpolar a-plane GaN on nano-patterned r-plane sapphire substrates by Haiyong Gao; Fawang Yan; Yang Zhang; Jinmin Li; Yiping Zeng; Junxi Wang (pp. 3664-3668).

Sapphire substrates were nano-patterned by inductive coupled plasma etching process. Nonpolar a-plane GaN films were grown on planar and nano-patterned r-plane sapphire substrates by metal organic chemical vapor deposition. The anisotropic characteristic and the crystalline quality of the a-plane GaN films were studied through XRD rocking curves. The cross section and surface morphologies of the a-plane GaN films were studied using SEM and AFM measurements, respectively. The crystal quality and surface flatness of the nonpolar a-plane GaN were greatly improved through the usage of the nano-patterned r-plane sapphire substrates.

Keywords: PACS; 81.05.Ea; 81.15.Gh; 81.65.Cf; 68.55.−aGaN; Nonpolar; MOCVD; Nano-patterned

Ni/Ni₃Al interface: A density functional theory study by Cong Wang; Chong-Yu Wang (pp. 3669-3675).

The optimal geometries, mechanical and thermal properties, and electronic structures of the three low index (001), (110), (111) Ni/Ni₃Al thin film were studied using first principle calculations. Simulated results indicated that Ni and Al atoms inγ′ phase preferred to place in the hollow site of Ni atoms inγ phase. In hollow site models, electronic states affected by interface localize within 2 atomic layers. While the top site model, electronic states localize within 3 atomic layers. It is also found that hollow site (110) interface has the best mechanical properties. Hollow site (001) interface is the most easily formed interface, which has the best thermodynamic properties.

Keywords: PACS; 05.70.Np; 68.35.bd; 31.15.A−First-principle; Interface; Electronic structure

Catalyst-free, low-temperature growth of high-surface area carbon nanoflakes on carbon cloth by Tsung-Chi Hung; Chia-Fu Chen; Chien-Chung Chen; Wha-Tzong Whang (pp. 3676-3681).

We have used a microwave plasma-enhanced chemical vapor deposition system to synthesize two-dimensional (2D) and three-dimensional (3D) structures of carbon nanoflakes (CNFs). This catalyst-free, low-temperature synthesis involved introducing CO₂ and CH₄ as reactants at a specified ratio of 2:3. We obtained uniform 2D arrays of CNFs at lower microwave powers (200 or 300W) and substrate temperatures (up to 420°C); their thickness was close to 1μm. At a microwave power of 400W, we obtained a 3D architecture comprising the smallest nanoflakes reported to date. The specific surface area of the 3D structure was double that of the corresponding 2D arrays. We suspect that such structured carbon materials might have great potential for energy storage applications.

Keywords: Nanostructures; Chemical vapor deposition; Electrodes

Morphological characterization of ITO thin films surfaces by Davood Raoufi (pp. 3682-3686).

In this study, indium tin oxide (ITO) thin films were deposited by electron beam evaporation method on glass substrates at room temperature, followed by postannealing at 200 and 300°C for annealing time up to 1h. Fractal image processing has been applied to describe the surface morphology of ITO thin films from their atomic force microscopy (AFM) images. These topographical images of the ITO thin films indicate changes in morphological behavior of the film. Also, the results suggest that the fractal dimension D can be used to explain the change of the entire grain morphology along the growth direction.

Keywords: ITO; Thin film; Fractal image processing; Surface morphology

Enhanced photoresponse towards visible light in Ru doped titania nanotube by M. Alam Khan; Do Hung Han; O.-Bong Yang (pp. 3687-3690).

Doping of ruthenium by the ion exchange method to the hydrothermally synthesized titania nanotube (TiNT) was found to be an effective photocatalyst active under visible light for methylene blue dye decoloration. The well dispersed and well embedded ionized ruthenium particles of about ∼2–4nm significantly reduced the band gap energy of synthesized TiNTs from 3.1eV to 2.56eV in (Ru(IE)/TiNT). The loading method, size of ruthenium particles and metal dispersion pattern at the nanotube textures have great influence on its photocatalytic performances exhibiting higher photocatalytic activity (>80%) of methylene blue dye. However, large aggregated ruthenium particles (sizes ∼12–60nm) on Ru(IM)/TiNT prepared by impregnation method failed to respond in visible light. The prepared catalysts were analysed by TEM, FESEM, FE-SEMEDX, XRD, UV–vis DRS spectra, XPS and BET surface area techniques.

Keywords: Titania nanotube; Photocatalysis; Ru ionized; Visible light; Methylene blue

Stress analysis at the interface between Ni–P coating and SiC_p/Al substrate of space mirror by Shaowen Guo; Libo Li; Guangyu Zhang; Wuyi Wang; Xuezeng Zhao (pp. 3691-3695).

This paper investigates the mechanical properties at the interface of the coating–substrate system, which comprises the electroless nickel–phosphorus (Ni–P) coating and the aluminum matrix composite substrate reinforced by the silicon carbide particles (SiC_p/Al), and is used for the space mirror. To estimate the adhesion of Ni–P coating on SiC_p/Al substrate, the scratch adhesion testing has been performed by drawing a spherically tipped diamond indenter with a radius of 200μm over the coated surface. The influence of the coating thickness on the interfacial stress induced by the inertial accelerations, temperature gradients and thermal soaks has been evaluated by simulation analysis based on the finite element method. The results of the scratch testing indicate that the adhesion strength of Ni–P coating to SiC_p/Al composite is more than 3.0GPa. Compared the maximum value of the interfacial stress obtained by simulation analysis with results of the scratch testing, it is can be seen that the mirror has enough safety margin. Furthermore, the most significant conclusion that can be drawn from this work is that the coating thickness should not exceed 45μm in order to ensure the performance and reliability of Ni–P coating and SiC_p/Al substrate system for space applications.

Keywords: PACS; 74.70.Ad; 68.35.Np; 02.70.DhInterfacial stress; Ni–P coating; SiC; _p; /Al composite; Finite element analysis

Characterization of silanization and antibody immobilization on spin-on glass (SOG) surface by Gajanan D. Nagare; S. Mukherji (pp. 3696-3700).

Most embedded optical waveguide biosensors require low dielectric optical material. The prerequisites for such applications include the selection of an appropriate material and effective bio-functionalization. Spin-on glass (SOG) is one of the preferred polymers that can be easily deposited. Further, the chemical properties of the polymer make it amenable for bio-functionalization. This paper reports a detailed study of a protocol for immobilization of antibodies on SOG for possible immunobiosensor applications. The effect of silanization at different pH values on the number of free and usable amine sites was quantified by fluorimetry. Contact angle measurements, ellipsometry, AFM, and fluorescence microscopy was used for assessing the surface properties at various stages of preparation, functionalization and biomolecule immobilization.

Keywords: SOG; Spin-on glass; Silanization; Bio-functionalization; Antibody immobilization

Strain relaxation in SiGe layer during wet oxidation process by Yong Zhang; Kunhuang Cai; Cheng Li; Songyan Chen; Hongkai Lai; Junyong Kang (pp. 3701-3705).

The strain relaxation in SiGe layer on silicon substrate during wet oxidation at 1000°C was investigated. It was proposed that the competition between Ge accumulation and diffusion led to different strain-relaxation behaviors. At the very beginning, Ge atoms at the oxidizing interface were quickly accumulated due to the high oxidation rate resulting in the additional nucleation of misfit dislocations (therefore a lot of threading dislocations) to relieve stress after the thickness of the Ge condensed layer was larger than the critical value. And then, when the Ge accumulation rate was less than the diffusion rate, Ge content started to decrease from a maximum value and the strain in the SiGe layer was mainly relieved through surface roughing and the degree of strain relaxation reached a maximum. When the samples were further oxidized, Ge accumulation could be neglected because of the self-limiting oxidation and the Ge diffusion dominated the consequent processes. As a result, Ge content at the interface was reduced, with the contribution of the strain relaxation in SiO₂ viscously, leading to the decrease of degree of strain relaxation in the SiGe layers slowly.

Keywords: PACS; 81.65.Mq; 68.55.−a; 83.85.StSilicon germanium; Oxidation; Strain relaxation

Ni thin films vacuum-evaporated on polyethylene naphthalate substrates with and without the application of magnetic field by Hideo Kaiju; Akito Ono; Nobuyoshi Kawaguchi; Kenji Kondo; Akira Ishibashi; Jonghan Won; Akihiko Hirata; Manabu Ishimaru; Yoshihiko Hirotsu (pp. 3706-3712).

We study the structural properties of the surface roughness, the surface mound size and the interfacial structure in Ni thin films vacuum-deposited on polyethylene naphthalate (PEN) organic substrates with and without the application of magnetic field and discuss its feasibility of fabricating quantum cross (QC) devices. For Ni/PEN evaporated without the magnetic field, the surface roughness decreases from 1.3nm to 0.69nm and the surface mound size increases from 32nm to 80nm with the thickness increased to 41nm. In contrast, for Ni/PEN evaporated in the magnetic field of 360Oe, the surface roughness tends to slightly decrease from 1.3nm to 1.1nm and the surface mound size shows the almost constant value of 28–30nm with the thickness increased to 35nm. It can be also confirmed for each sample that there is no diffusion of Ni into the PEN layer, resulting in clear Ni/PEN interface and smooth Ni surface. Therefore, these experimental results indicate that Ni/PEN films can be expected as metal/insulator hybrid materials in QC devices, leading to novel high-density memory devices.

Keywords: PACS; 68.35.Ct; 68.37.Ps; 68.37.LpNi thin films; Organic substrates; Surface morphology; Magnetostatic energy; Transmission electron microscopy

Comparative study of electroless copper deposition based on the seed layers of Pd, PtPd and AuPd by Chuanli Ma; Weichun Ye; Xuezhao Shi; Yanlong Chang; Yang Chen; Chunming Wang (pp. 3713-3718).

The article reports on electroless deposition of copper films onto p-silicon (100) using different seed (co-seed) layers of Pd, PtPd and AuPd. The dependence of the compositions and morphologies of different seed layers on resultant Cu films were comparatively studied in detail by atomic force microscopy (AFM), field emission scanning electron microscope (FE-SEM) and X-ray photoelectron spectroscopy (XPS). The activities of electroless copper deposition on the p-silicon (100) with different seed (co-seed) layers were evaluated by polarization curve. It is concluded that the bimetallic AuPd seed displayed the highest catalytic activity for electroless copper deposition, and followed by the order of PtPd>Pd.

Keywords: Electroless copper; Pd seed; PtPd seed; AuPd seed

Influence of Cu electroplating solutions on boron carbon nitride (BCN) film by Hidemitsu Aoki; Makoto Hara; Takuro Masuzumi; Motaharu K. Mazumder; Naoki Ooi; Daisuke Watanabe; Chiharu Kimura; Takashi Sugino (pp. 3719-3722).

Cu electroplating is required for the fabrication of Cu/low-k interconnections. The permeation of a plating solution into low-k films during Cu electroplating is a serious challenge for 45-nm nodes and more complex devices. We investigated the influence of Cu electroplating solutions on boron carbon nitride (BCN) as a low-k film. After dipping it into a Cu electroplating solution that contained additives, the BCN film's hydrophilic surface changed to a hydrophobic surface, and the incorporation of water into the BCN film was suppressed by surfactant adsorption. Sulfuric residue was detected on the BCN sample by thermal desorption spectroscopy after treatment in the Cu electroplating solution with additives; however, it was found through electrical measurements that this solution did not affect the leakage current or the dielectric constant of the BCN film. We successfully fabricated an electroplating Cu layer on a BCN film with good adhesion, and we believe that this BCN film is a sufficiently useful material for Cu/BCN integration in LSI.

Keywords: BCN; Low-k; Cu; Electroplating; Boron carbon nitride

An insight into the KOH activation mechanism through the production of microporous activated carbon for the removal of Pb²⁺ cations by Abdel-Nasser A. El-Hendawy (pp. 3723-3730).

Chemical activation was used through direct mixing of KOH with maize stalks in the smallest amount of water to provide KOH-to-stalk ratios of 33, 50, 66 and 75% by weight. The KOH-treated stalks were carbonized at 700°C to produce a series of four activated carbons, besides a non-activated sample that was prepared and carbonized at 550°C. The porous properties of these carbons were characterized by the Langmuir, BET and Dubinin–Radushkevich linear equations as well as both α_s (alpha- s) and t methods based on nitrogen adsorption isotherms. The chemical reactions involved during the impregnation and the carbonization processes for these hydroxide/lignocellulose mixtures have been proposed. Deep insight has been obtained concerning the possible reactions mechanism. The results showed that the KOH ratio was found to be the basic indicator of micoporosity development. The increase in the concentration of KOH much increased the S^α values of the resulting carbons reaching a maximum limit at 66wt% KOH with S^α of 1684m²/g and micropore ratio of ∼85% displaying an inverse correlation thereafter. The thermal behaviour and the surface microstructure in addition to the surface functional groups of the maize stalks and their prepared carbons were investigated by TGA, SEM and FTIR. The investigated carbons took up significant amounts of Pb²⁺ ions from aqueous solutions, which are ascribed to both the porosity and surface chemical nature of the adsorbents.

Keywords: Activated carbon; Maize stalks; Reaction mechanism; Porosity; Pb; ²⁺; uptake

Rare earth oxide-doped titania nanocomposites with enhanced photocatalytic activity towards the degradation of partially hydrolysis polyacrylamide by Jinhuan Li; Xia Yang; Xiaodan Yu; Leilei Xu; Wanli Kang; Wenhua Yan; Hongfeng Gao; Zhonghe Liu; Yihang Guo (pp. 3731-3738).

Rare-earth oxide-doped titania nanocomposites (RE³⁺/TiO₂, where RE=Eu³⁺, Pr³⁺, Gd³⁺, Nd³⁺, and Y³⁺) were prepared by a one-step sol–gel-solvothermal method. The products exhibited anatase phase structure, mesoporosity, and interesting surface compositions with three oxygen species and two titanium species. The products were used as the photocatalysts to degrade a partially hydrolysis polyacrylamide (HPAM) under UV-light irradiation, a very useful polymer in oil recovery. For comparison, Degussa P25 and as-prepared pure TiO₂ were also tested under the same conditions. The enhanced photocatalytic activity was obtained on as-prepared Eu³⁺ (Gd³⁺, Pr³⁺)/TiO₂ composites, and the reasons were explained. Finally, the degradation pathway of HPAM over the RE³⁺/TiO₂ composite was put forward based on the intermediates produced during the photocatalysis procedure.

Keywords: Photodegradation; Sol–gel; Rare earth; Partially hydrolysis polyacrylamide; Nanocomposite

Surface-initiated atom transfer radical polymerization from TiO₂ nanoparticles by Jung Tae Park; Joo Hwan Koh; Jong Kwan Koh; Jong Hak Kim (pp. 3739-3744).

Two kinds of hydrophilic polymers, poly(oxyethylene methacrylate) (POEM) and poly(styrene sulfonic acid) (PSSA), were grafted from TiO₂ nanoparticles via the surface-initiated atom transfer radical polymerization (ATRP) technique. Chlorine modified TiO₂ nanoparticles (TiO₂-Cl), the ATRP initiators, were synthesized by the reaction of –OH in TiO₂ with 2-chloropropionyl chloride (CPC). FT-IR, UV–vis spectroscopy and X-ray photoelectron spectroscopy (XPS) clearly showed that the polymer chains were successfully grafted from the surface of TiO₂ nanoparticles. The hydrophilically modified TiO₂ nanoparticles have a better dispersion in alcohol than unmodified nanoparticles, as revealed by transmission electron microscopy (TEM). It was also found that the polymer grafting did not significantly alter the crystalline structure of the TiO₂ nanoparticles according to the X-ray diffraction (XRD) patterns. Grafting amounts were 10% of the weight for both TiO₂-POEM and TiO₂-PSSA nanoparticles, as determined by thermogravimetric analysis (TGA).

Keywords: Graft polymerization; TiO; ₂; Surface initiated; Atom transfer radical polymerization (ATRP); Nanoparticles

Structural evolution of electroless Ni–P coating on Al–12wt.% Si alloy during heat treatment at high temperatures by D. Vojtěch; M. Novák; M. Zelinková; P. Novák; A. Michalcová; T. Fabián (pp. 3745-3751).

The work is concerned with the high-temperature heat treatment of an Al–12wt.% Si alloy coated by an electroless Ni–P layer. The electroless deposition took place on a pre-treated substrate in a bath containing nickel hypophosphite, nickel lactate and lactic acid. Resulting Ni–P deposit showed a thickness of about 8μm. The coated samples were heat-treated at 200–550°C/1–24h. LM, SEM, EDS and XRD were used to investigate phase transformations. Adherence to the substrate was estimated from the scratch test and microhardness of the heat-treated layers was also measured. It is found that various phase transformations occur, as both temperature and annealing time increase. These include (1) amorphous Ni–P→Ni+Ni₃P, (2) Al+Ni→Al₃Ni, (3) Ni₃P→Ni₁₂P₅+Ni, (4) Ni₁₂P₅→Ni₂P+Ni, and (5) Al₃Ni+Ni→Al₃Ni₂. The formation of intermetallic phases, particularly Al₃Ni₂, leads to significant surface hardening, however, too thick layers of intermetallics reduce the adherence to the substrate. Based on the growth kinetics of the intermetallic phases, diffusion coefficients of Ni in Al₃Ni and Al₃Ni₂ at 450–550°C are estimated as follows: D(Al₃Ni, 450°C)≈6×10⁻¹²cm²s⁻¹, D(Al₃Ni, 550°C)≈4×10⁻¹¹cm²s⁻¹, D(Al₃Ni₂, 450°C)≈1×10⁻¹²cm²s⁻¹ and D(Al₃Ni₂, 550°C)≈1×10⁻¹¹cm²s⁻¹. Mechanisms of phase transformations are discussed in relation to the elemental diffusion.

Keywords: PACS; 73.61.At; 68.55.Nq; 62.20.QpAl–Si alloy; Electroless coating; Heat treatment; Al–Ni phase; Diffusion; Hardness

Selective formation of silicon nanowires on pre-patterned substrates by LiJuan Wan; WenLi Gong; KeWei Jiang; HuiLin Li; BaiRui Tao; Jian Zhang (pp. 3752-3758).

In this paper, the selective growth of silicon nanowires (SiNWs) was studied. With the aid of photolithography, the vertically aligned silicon nanowires were selectively formed on the patterned substrates via an electroless metal deposition (EMD) method under normal conditions (room temperature, 1atm). Low-pressure chemical vapor deposition (LPCVD) silicon nitride was used as the masking layer for SiNWs preparation. The scanning electron microscope was used to examine the etching results. Both the patterned and the unpatterned silicon substrates were used for study. The results indicated that the growth rates of the SiNWs upon the patterned and the unpatterned substrates are different. For the patterned substrates, the growth rate of SiNWs is dependent upon the pattern shape. The influence of length-to-width ratio for the rectangular-shaped patterns was studied. It is concluded that by designing the proper length-to-width ratio, the nanowires with different lengths can be fabricated simultaneously on the same substrate.

Keywords: Lithography patterning; Silicon nanowires; Electroless metal deposition; Etch rate; Ratio of length-to-width

Nickel doped indium tin oxide anode and effect on dark spot development of organic light-emitting devices by C.M. Hsu; C.S. Kuo; W.C. Hsu; W.T. Wu (pp. 3759-3763).

This article demonstrated that introducing nickel (Ni) atoms into an indium tin oxide (ITO) anode could considerably decrease ITO surface roughness and eliminate the formation of dark spots of an organic light-emitting device (OLED). A dramatic drop in surface roughness from 6.52nm of an conventional ITO to 0.46nm of an 50nm Ni(50W)-doped ITO anode was observed, and this led to an improved lifetime performance of an Alq3 based OLED device attributed to reduced dark spots. Reducing thickness of Ni-doped ITO anode was found to worsen surface roughness. Meanwhile, the existence of Ni atoms showed little effect on deteriorating the light-emitting mechanism of OLED devices.

Keywords: PACS; 85.60.Jb; 68.37.−p; 68.55.JNickel; ITO; OLED; Dark spot

The effect of hydrogen peroxide on polishing removal rate in CMP with various abrasives by R. Manivannan; S. Ramanathan (pp. 3764-3768).

The effect of hydrogen peroxide in chemical mechanical planarization slurries for shallow trench isolation was investigated. The various abrasives used in this study were ceria, silica, alumina, zirconia, titania, silicon carbide, and silicon nitride. Hydrogen peroxide suppresses the polishing of silicon dioxide and silicon nitride surfaces by ceria abrasives. The polishing performances of other abrasives were either unaffected or enhanced slightly with the addition of hydrogen peroxide. The ceria abrasives were treated with hydrogen peroxide, and the polishing of the work surfaces with the treated abrasive shows that the inhibiting action of hydrogen peroxide is reversible. It was found that the effect of hydrogen peroxide as an additive is a strong function of the nature of the abrasive particle.

Keywords: PACS; 81.65.Ps; 85.40.LsChemical mechanical planarization; Shallow trench isolation; Selectivity; Abrasives; Additives

Structural properties of Al₂O₃ dielectrics grown on TiN metal substrates by atomic layer deposition by Chun-I. Hsieh; Tung-Ming Pan; Jian-Chyi Lin; Yan-Bo Peng; Tsai-Yu Huang; Chang-Rong Wu; Steven Shih (pp. 3769-3772).

We investigated on the structural properties of Al₂O₃ dielectrics grown on TiN metal substrates using an atomic layer deposition technique with tri-methyl-aluminum and either O₃ or H₂O as the precursor and oxidant, respectively. The structural and morphological features of these films were examined by atomic force microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy measurements. We find that Al₂O₃ dielectric films with the O₃ oxidant exhibit a rough morphology, a thick TiO₂ film, and a small amount of contaminants such as carbon and hydrogen. The reason for the rapid diffusion of oxygen atoms into the TiN lattice leads to the formation of TiO₂ layer on the TiN substrate. This is due to the higher oxidation potential of the O₃ compared to the H₂O.

Keywords: Al; ₂; O; ₃; dielectrics; TiN metal substrate; O; ₃; H; ₂; O; TiO; ₂

Preparation, characterization of Au (or Pt)-loaded titania nanotubes and their photocatalytic activities for degradation of methyl orange by Qian Zhao; Mei Li; Jinyu Chu; Tingshun Jiang; Hengbo Yin (pp. 3773-3778).

TiO₂ nanotubes were prepared by hydrothermal method and Au (or Pt) was loaded on TiO₂ nanotubes by photodeposition method. The photocatalysts were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), UV–vis diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS) and N₂ adsorption technique, respectively. The photocatalytic properties of the samples were also investigated. The results show that TiO₂ nanotubes with uniform diameter were prepared, and they have specific surface areas over 400m²/g. The specific surface areas of TiO₂ nanotubes decrease with the increasing of calcining temperature, and crystalline phase of TiO₂ in the wall of nanotubes was transformed from anatase into rutile phase in calcination process. The photocatalytic activities of TiO₂ nanotubes are higher than that of nanosized TiO₂, and the photocatalytic activities of TiO₂ nanotubes were enhanced after loading Au (or Pt). After irradiation for 40min under a 300W of middle-pressure mercury lamp (MPML), the degradation rate of methyl orange solution using the Au/TiNT-500 (or Pt/TiNT-500) as a catalyst can reach 96.1% (or 95.1%). On the other hand, Au-loaded sample has evident adsorption peak in visible range, indicating that Au-loaded TiO₂ nanotubes are hopeful to become visible light photocatalyst.

Keywords: Titania nanotubes; Hydrothermal method; Preparation; Photodeposition; Characterization; Photocatalytic activity

Synthesis and characterization of spherical and narrow size distribution indium oxide nanoparticles by E.C.C. Souza; J.F.Q. Rey; E.N.S. Muccillo (pp. 3779-3783).

This work reports the synthesis of indium oxide nanoparticles and their thermal, structural, microstructural and optical characterization. The preparation method is based on a surfactant-free room temperature soft chemistry route. Spherical indium oxide nanoparticles (about 8nm in diameter) were obtained after thermal treatment of gels at 400°C for 2h, as shown by X-ray diffraction experiments and nitrogen adsorption measurements. Transmission electron microscopy observations confirm the single-crystalline nature of the produced nanoparticles. The photoluminescence emission spectrum at room temperature shows a broad peak with onset at approximately 315nm as a result of quantum size effect as revealed by small-angle X-ray scattering.

Keywords: PACS; 81.07.−b; 61.05.cf; 78.55.−mNanostructures; Indium oxide; Photoluminescence; TEM; Small-angle X-ray scattering

The effect of powder preparation method on the corrosion and mechanical properties of TiN-based coatings by reactive plasma spraying by Zhengping Mao; Jing Ma; Jun Wang; Baode Sun (pp. 3784-3788).

TiN-based composite coatings with and without the addition of Cr were deposited by reactive plasma spraying (RPS) in air. Both sintered and mixed powder of Ti and B₄C were used for the RPS process. A thermodynamic model was firstly used to estimate the complicated phase composition of composite coatings prepared by RPS. The phase composition, structures and properties of TiN-based coatings were investigated using XRD, SEM and a Vickers microhardness tester. The results show that the phases in TiN-based coatings do not generate according to priority of Gibbs free energy value due to non-equilibrium reactive course during thermal spraying. The coating deposited using sintered Ti and B₄C powder is composed of two main phases (TiN and TiN_0.3), two minor phases (Ti₂O₃ and TiB₂), and a small fraction of TiC phase. The composition of the coating deposited using the mixed powder with Cr added is predominantly in the TiN and TiB₂ phases, a smaller phase fraction of Ti₂O₃ and TiO₂, and some unreacted Cr. The Vickers microhardness of the coating deposited using sintered powder is higher than that of using mixed powder. The composite coating deposited using mixed powder with the addition of Cr shows superior corrosion resistant to that using sintered powder when tested in 3.5wt.% NaCl electrolytic solution.

Keywords: PACS; 81.05.Je; 81.05.Mh; 81.15.-z; 81.15.RsReactive plasma spraying; In situ formation; Composite coating; Thermodynamic calculation; Polarization curve

In situ functionalized self-assembled monolayer surfaces for selective chemical vapor deposition of copper by Xin Liu; Qi Wang; Liu-Ping Chen (pp. 3789-3794).

Recent studies show that the self-assembled monolayer (SAM) is well suited to control the selectivity of chemical vapor deposition (CVD). Here, we reported the selective CVD for copper on the functionalized SAM surfaces (with –SH, –SS–, and –SO₃H terminal groups). The –SS– and –SO₃H terminal group surfaces were obtained through in situ chemical transformation of –SH terminal group surface of a 3-mercaptopropyltrimethoxysilane-SAM (MPTMS-SAM). As a result, the –SS– terminal group surface reduces copper deposition and the –SO₃H terminal group surface enhances copper deposition comparing to the –SH terminal group surface. In addition, the MPTMS-SAM was irradiated by UV-light through a photo mask to prepare SH-group and OH-group regions. Then, copper films were deposited only on the SH-group region of the substrate in chemical vapor deposition. Finally, patterns of copper films were formed in the way of UV-light irradiation. These results are expected for use of selective deposition of copper metallization patterns in IC manufacturing processes.

Keywords: Copper thin film; Selective chemical vapor deposition; Self-assembled monolayer; In situ; functionalization

Pb(Zr_0.53Ti_0.47)O₃ thin films with different thicknesses obtained at low temperature by microwave irradiation by Ankam Bhaskar; Tsun-Hsu Chang; Horng-Yi Chang; Syh-Yuh Cheng (pp. 3795-3800).

Pb(Zr_0.53Ti_0.47)O₃ (PZT) thin films with different thicknesses (99–420nm) were prepared on Pt(111)/Ti/SiO₂/Si(100) substrates by sol–gel method and films were annealed at 450°C for 30min using a single-mode cavity of 2.45GHz microwaves. X-ray diffraction analysis indicated that the pyrochlore phase was transformed to the perovskite phase at above 166nm films. The grain sizes were increased, surface roughnesses were decreased, and electrical properties were improved with film thickness. The leakage current density was 9×10⁻⁸A/cm² at an applied electrical field of 100kV/cm. The ohmic and field-enhanced Schottky emission mechanisms were used to explain leakage current behavior of the PZT thin films. These results suggest that microwave annealing is effective for obtaining low temperature crystallization of thin films with better properties.

Keywords: Microwave annealing; Surface roughness; Lead zirconate titanate; Leakage current

The wettability of polytetrafluoroethylene and polymethylmethacrylate by aqueous solutions of Triton X-100 and propanol mixtures by Anna Zdziennicka (pp. 3801-3810).

Measurements of advancing contact angles ( θ) were carried out for aqueous solutions of Triton X-100 (TX-100) and propanol mixtures at constant TX-100 concentration equal to 1×10⁻⁷, 1×10⁻⁶, 1×10⁻⁵, 1×10⁻⁴, 6×10⁻⁴ and 1×10⁻³M, respectively, on polytetrafluoroethylene (PTFE) and polymethyhmethacrylate (PMMA). Using obtained results the changes of cos θ and adhesional tension against surface tension of all series of aqueous solutions of TX-100 and propanol mixtures ( γ_LV) for PTFE and PMMA surfaces were shown. On the basis of these changes it was deduced that adsorption of TX-100 and propanol mixtures at PTFE-solution and solution-air interfaces is the same but the adsorption of TX-100 and propanol mixtures at solution-air interface is considerably higher than at PMMA-solution one. In the case of PTFE this conclusion was confirmed by relationship between cos θ and the reciprocal of the surface tension of solution. Extrapolation of the relationships between cos θ and/or adhesional tension and the surface tension of solutions to the points corresponding to the cos θ=1 and adhsional tension equal to the surface tension of solution, the critical surface tension of PTFE and PMMA wetting was determined. The average values of critical surface tension of wetting determined from these relationships for PTFE are lying in the range of its surface tension values determined from contact angles of different kinds of liquids, which can be find in the literature, but for PMMA are considerably lower than the surface tension. The double value of the critical surface tension of PTFE wetting is equal to adhesion work of the solution to its surface and for PMMA there is not any correlation between these magnitudes.Using the measured values of the contact angles and Young equation the PTFE(PMMA)-aqueous solution interfacial tension was determined. The interfacial tension values of PTFE-aqueous solution were also calculated from the Fainerman and Miller equation in which the correcting parameter of nonideality of the surface monolayer was introduced and compared to those obtained from Young equation. From this comparison it results that the changes of PTFE-solution interface tension as a function of propanol concentration can be described by the Fainerman and Miller equation.

Keywords: PACS; 68.35 NpTriton X-100; Propanol; Wetting; Critical surface tension; Solid-liquid interfacial tension

The effect of nanostructured surface layer on the fatigue behaviors of a carbon steel by D. Li; H.N. Chen; H. Xu (pp. 3811-3816).

A nanostructured surface layer was formed on a carbon steel by means of surface mechanical attrition treatment (SMAT). The microstructure of the surface layer of the SMATed sample was characterized by using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Microhardness and residual stress distribution along the depth from the SMATed surface layer were measured at the same time. Fatigue behaviors of the carbon steel subjected to the SMAT process were investigated. A nanostructured layer with average grains size of ∼12.7nm was formed, of which microhardness is more than twice as high as that in matrix and residual compressive stress can reach about −400MPa with maximum depth of ∼600μm. The fatigue strength of as-received sample is 267MPa and that of SMATed sample is 302MPa based on fatigue life 5×10⁶cycles. The SMAT process has improved the fatigue strength by as much as 13.1% for the carbon steel. It is shown that the SMAT is an effective method to render the material with the features, such as a nanostructured and work-hardened surface layer as well as compressive residual stresses, which can pronouncedly improve the fatigue strength of the carbon steel.

Keywords: Surface mechanical attrition treatment; Carbon steel; Nanostructured surface layer; Fatigue behavior

Field emission properties of DLC and phosphorus-doped DLC films prepared by electrochemical deposition process by Shanhong Wan; Liping Wang; Junyan Zhang; Qunji Xue (pp. 3817-3821).

Field emission behavior of diamond-like carbon (DLC) and phosphorus-doped DLC (p-DLC) films prepared by electrochemical deposition process was comparatively investigated. It was shown phosphorus incorporation in the DLC film could lower the turn on field from 12 to 9.5V/μm and increase the current density from 12.6 to 45.7μA/mm² under high electric field. And better field emission performance of p-DLC films would be mainly attributed to the influence of the surface morphology and the changes of microstructure due to the phosphorus incorporation.

Keywords: Phosphorus-doped DLC film; Electrochemical deposition; Field emission behavior

Investigation of the microstructure and tribological behavior of cold-sprayed tin-bronze-based composite coatings by Xueping Guo; Ga Zhang; Wenya Li; Yang Gao; Hanlin Liao; Christian Coddet (pp. 3822-3828).

In this paper, tin-bronze/TiN and tin-bronze/quasicrystal (AlCuFeB) composite coatings were fabricated by cold spray process. Microstructure and microhardness of the prepared coatings were investigated. Ball-on-disc dry sliding wear tests were conducted in an ambient condition to examine the tribological behavior of the composite coatings. The results show that the microhardness and the density of composite coatings increase significantly compared to the pure tin-bronze coating. The friction coefficient of composite coating decreases when reinforcing particles were introduced. Furthermore, the bronze/quasicrystal composite coating has a lower friction coefficient and wear rate than the bronze/TiN coating. Tribological mechanisms of the composite coatings were discussed.

Keywords: Cold spray; Tin-bronze; Quasicrystal; Composite coating; Dry sliding wear

The bias- and temperature-dependent electron transport in a magnetic nanostructure by Jian-Duo Lu; Yu-Hua Wang; Yang-Lai Hou; Ting-Ping Hou (pp. 3829-3832).

In this paper, we theoretically investigate the effect of the bias and temperature on the electron transport properties in a magnetic nanostructure. It is found that the large spin-polarization can be achieved in such a nanostructure, and the degree of spin-polarization obviously increases with increasing applied bias. It is also found that the conductance curves for the different temperatures obviously intersect at the same Fermi energy for the low Fermi energy, and the degree of spin-polarization decreases with the increase of temperature. Thus, we can control the electron transport through changing the bias and temperature.

Keywords: PACS; 73.23.; −; b; 72.25.; −; b; 73.40.GkMagnetic nanostructure; Spin filtering; Spin-polarization

A combined approach to fabricating Si nanocrystals with high photoluminescence intensity by Zhi-qiang Xie; Jiang Zhu; Miao Zhang; You-yuan Zhao; Ming Lu (pp. 3833-3836).

This work demonstrates that by combining three methods with different mechanisms to enhance the photoluminescence (PL) intensity of Si nanocrystals embedded in SiO₂ (or Si-nc:SiO₂), a promising material for developing Si light sources, a very high PL intensity can be achieved. A 30-layered sample of Si-nc:SiO₂/SiO₂ was prepared by alternatively evaporating SiO and SiO₂ onto a Si(100) substrate followed by thermal annealing at 1100°C. This multilayered sample possessed a fairly high PL efficiency of 14% as measured by Greenham's method, which was 44 times that of a single-layered one for the same amount of excess Si content. Based on this multilayered sample, treatments of CeF₃ doping and hydrogen passivation were subsequently applied, and a high PL intensity which was 167 times that of a single-layered one for the same amount of excess Si content was achieved.

Keywords: PACS; 78.55.−m; 73.63.Bd; 78.68.+mSi nanocrystal; Photoluminescence; Photoluminescence efficiency

Ruthenium adsorption and diffusion on the GaN(0001) surface by César Ortega López; William López Pérez; Jairo Arbey Rodríguez M. (pp. 3837-3842).

We report first principles calculations to analyze the ruthenium adsorption and diffusion on GaN(0001) surface in a2×2geometry. The calculations were performed using the generalized gradient approximation (GGA) with ultrasoft pseudopotential within the density functional theory (DFT). The surface is modeled using the repeated slabs approach. To study the most favorable ruthenium adsorption model we consideredT1,T4 andH3 special sites. We find that the most energetically favorable structure corresponds to the Ru-T4 model or the ruthenium adatom located at theT4 site, while the ruthenium adsorption on top of a gallium atom (T1 position) is totally unfavorable. The ruthenium diffusion on surface shows an energy barrier of 0.612eV. The resultant reconstruction of the ruthenium adsorption on GaN(0001)-2×2 surface presents a lateral relaxation of some hundredth of Å in the most stable site. The comparison of the density of states and band structure of the GaN(0001) surface without ruthenium adatom and with ruthenium adatom is analyzed in detail.

Keywords: PACS; 68.35.Bs; 68.35.Md; 68.43.Bc; 68.43.Fg; 71.15.Mb; 73.20.AtSurface; Adsorption;Diffusion; DFT; GGA; Pseudopotential

Synthesis of N-deficient GaN nanoparticles and its enhanced dielectric response by P.G. Li; M. Lei; Y.X. Du; X. Guo; W.H. Tang (pp. 3843-3847).

In this paper, GaN nanoparticles were firstly synthesized through a facile solid-state reaction using an organic reagent cyanamide (CN₂H₂) and Ga₂O₃ as precursors. The structural properties were investigated in detail. It is found that these nanoparticles having average size of 40nm were N-deficient with the N vacancies reaching as high as 12%. The Raman scattering spectrum of these nanoparticles presented some interesting features. The room-temperature frequency spectrum of the relative dielectric constant ɛ_r was measured and indicated that these nanoparticles exhibited sharp enhancement at low frequency range comparing with GaN nanomaterials and N-deficient microparticles. It is thought both the rotation direction polarization (RDP) and the space charge polarization (SCP) process should be responsible for the enhancement of ɛ_r in these N-deficient GaN nanoparticles.

Keywords: N-deficient GaN; Nanoparticles; Raman scattering spectrum; Dielectric response

Characterization of tungsten–titanium oxide electrode for electrochromic applications by Ko-Wei Weng; Sheng Han; Ya-Chi Chen; Da-Yung Wang (pp. 3848-3853).

Titanium oxide films are of critical importance for the electrochromic device technology. The substrate, a conductive glass being coated with indium tin oxide (ITO) thin films, was deposited tungsten and titanium oxide by pulsed co-sputtering deposition system. The film thickness increased with the ion beam power. However, the slope of the curve of thickness against power at an ion beam power of less than 300W was greater than that at a power of 400 or 500W. A high ion beam power resulted produced a crystalline structure, as revealed by X-ray diffraction (XRD). Moreover, increasing the ion beam power resulted in the high Li-ions transport. The electrochromic behavior was optimal at an ion beam power of 200W.

Keywords: Titanium oxide; Co-sputtering; Eelectrochromic behavior

Antibacterial activities of surface modified electrospun poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) fibrous membranes by Chen Yao; Xinsong Li; K.G. Neoh; Zhilong Shi; E.T. Kang (pp. 3854-3858).

Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) membrane, with its excellent chemical and mechanical properties, has good potential for broad applications. However, due to its hydrophobic nature, microbial colonization is commonly encountered. In this work, electrospun PVDF-HFP fibrous membranes were surface modified by poly(4-vinyl- N-alkylpyridinium bromide) to achieve antibacterial activities. The membranes were first subjected to plasma pretreatment followed by UV-induced surface graft copolymerization of 4-vinylpyridine (4VP) and quaternization of the grafted pyridine groups with hexylbromide. The chemical composition of the surface modified PVDF-HFP electrospun membranes was studied by X-ray photoelectron spectroscopy (XPS). The morphology and mechanical properties of pristine and surface modified PVDF-HFP fibrous membranes were characterized by scanning electron microscopy (SEM) and tensile test, respectively. The antibacterial activities of the modified electrospun PVDF-HFP fibrous membranes were assessed against Gram-positive Staphylococcus aureus ( S. aureus) and Gram-negative Escherichia coli ( E. coli). The results showed that the PVDF-HFP fibrous membranes modified with quaternized pyridinium groups are highly effective against both bacteria with killing efficiency as high as 99.9999%.

Keywords: PACS; 81.65.−b (Surface treatment); 81.05.Lg (Fibers, synthetic and natural)Electrospinning; Antibacterial; Surface modification; Poly(vinylidene fluoride-co-hexafluoropropylene)

Laser shock wave consolidation of nanodiamond powders on aluminum 319 by Pal Molian; Raathai Molian; Rajeev Nair (pp. 3859-3867).

A novel coating approach, based on laser shock wave generation, was employed to induce compressive pressures up to 5GPa and compact nanodiamond (ND) powders (4–8nm) on aluminum 319 substrate. Raman scattering indicated that the coating consisted of amorphous carbon and nanocrystalline graphite with peaks at 1360cm⁻¹ and 1600cm⁻¹ respectively. Scanning electron microscopy revealed a wavy, non-uniform coating with an average thickness of 40μm and absence of thermal effect on the surrounding material. The phase transition from nanodiamond to other phases of carbon is responsible for the increased coating thickness. Vicker's microhardness test showed hardness in excess of 1000kg_f/mm² (10GPa) while nanoindentation test indicated much lower hardness in the range of 20MPa to 2GPa. Optical surface profilometry traces displayed slightly uneven surfaces compared to the bare aluminum with an average surface roughness ( R_a) in the range of 1.5–4μm depending on the shock wave pressure and type of confining medium. Ball-on-disc tribometer tests showed that the coefficient of friction and wear rate were substantially lower than the smoother, bare aluminum sample. Laser shock wave process has thus aided in the generation of a strong, wear resistant, durable carbon composite coating on aluminum 319 substrate.

Keywords: Laser; Shock wave; Nanodiamond; Coating; Aluminum

Post-annealing effect upon optical properties of electron beam evaporated molybdenum oxide thin films by Shih-Yuan Lin; Ying-Chung Chen; Chih-Ming Wang; Po-Tsung Hsieh; Shun-Chou Shih (pp. 3868-3874).

Molybdenum oxide (MoO₃) thin films were deposited by electron beam evaporation. The chemical composition, microstructure, optical and electrical properties of MoO₃ thin films depend on the annealing temperature and ambient atmosphere. X-ray diffraction (XRD) shows that crystalline MoO₃ films can be obtained at various post-annealing temperatures from 200 to 500°C in N₂ and O₂. X-ray photoelectron spectroscopy (XPS) results reveal that the O-1s emission peak was shifted slightly toward lower binding energies as the annealing temperature in N₂ was increased. The oxygen vacancies and conductivity of MoO₃ film increased with the annealing temperature. However, when the MoO₃ films were annealed in an atmosphere of O₂, the optical transmission, the O/Mo ratio and the photon energy increased with the annealing temperature. The results differ from those for films annealed in a N₂ atmosphere.

Keywords: PACS; 61.72.Hh; 78.20.Ci; 81.15.Jj; 81.40.EfMoO; ₃; thin films; Electron beam evaporation; Post-annealing; Optical properties; Oxygen vacancies

Study on low-energy bombardment of Au (111) by noble metal atoms with molecular dynamics simulations by C. Yan; C. Zhang; Q.Y. Zhang; T.W. Liu; H. Huang (pp. 3875-3879).

The low-energy bombardment of Au (111) surface by noble metal atoms is studied with molecular dynamics (MD) simulations. With the incident-energy dependence of adatom yields, sputtering yields, and vacancy yields for different projectiles, we find that the implantation of projectiles in shallow layers below surface can be distinguished by subplantation (in the first and second layers) and implantation (deeper than the third layer). The transition from subplantation to implantation occurs at the incident energy of about 45eV for the low-energy bombardment of noble metal atoms on Au (111). The incident-energy dependence of defect yields is obviously different for the subplantation and implantation of projectiles. Based on our MD simulations, we discuss the influence of low-energy bombardment on film growth and the guide to the search for optimum deposition parameters.

Keywords: PACS; 79.20.Rf; 68.49.Sf; 81.15.JjMolecular dynamics simulation; Low-energy deposition; Adatom; Sputtering; Vacancy

Growth behavior of electroless Ni–Co–P deposits on Fe by W.L. Liu; S.H. Hsieh; W.J. Chen; Y.C. Hsu (pp. 3880-3883).

The electroless Ni–Co–P films were deposited on Fe film in plating baths using sodium hypophosphite as reducing agent and nickel and cobalt sulphates as ion source at pH value of 9 and plating temperature from 60 to 85°C. The effect of the mol ratio of CoSO₄/CoSO₄+NiSO₄ in plating bath on the growth behavior of electroless Ni–Co–P films was studied. The electroless Ni–Co–P films were characterized by transmission electron microscopy for the microstructure and thickness, and energy dispersive spectrometer for the composition. The results showed that the electroless Ni–Co–P films can be deposited on Fe films without the step of sensitization and activization; the surface of electroless Ni–Co–P film on Fe is quite even; the more the Co²⁺ ion in plating bath, the larger the activation energy and the smaller the plating rate of electroless Ni–Co–P films; and the mol ratio of Co/Co+Ni in film is larger than that in plating bath (with the exception of the film deposited in the bath with 0.9mol ratio of CoSO₄/CoSO₄+NiSO₄)

Keywords: Ni–Co–P alloy; Electroless deposition; Growth behavior; Plating rate; Activation energy

Characterization and catalytic performance of pure and Li₂O-doped CuO/CeO₂ catalysts by N.M. Deraz (pp. 3884-3890).

Pure and Li₂O-doped CuO/CeO₂ catalysts calcined at 500°C were prepared by impregnation method. The catalysts are characterized by DTA, TG-DTG, XRD, IR, TEM, nitrogen adsorption at −196°C and the catalytic decomposition of hydrogen peroxide at 30°C.The effects of molar ratio, heat treatment time and the doping on the structural, surface and catalytic properties of nanocrystalline Cu/Ce-mixed oxides system have been studied. It was found that the catalytic activity of ceria-supported copper oxide catalysts increased by increasing both the heat treatment time and dopant content. However, the pure Cu/Ce-mixed oxide solids containing 10wt.% CuO exhibited the best performance. The characterization results indicated that the higher surface area, the formation of solid solution between copper and cerium oxides, and the high dispersion of copper species on the ceria were responsible for the high catalytic activity of the CuO/CeO₂ catalysts.

Keywords: XRD; S; _BET; Catalytic activity; Dispersion; Ceria

Octanethiolated Cu and Cu₂O nanoparticles as ink to form metallic copper film by T.-Y. Dong; H.H. Wu; C. Huang; J.M. Song; I.G. Chen; T.H. Kao (pp. 3891-3896).

The synthesis and spectroscopic characterizations of size-controlled Cu and Cu₂O nanoparticles forming self-assembled 2D superlattices with hexagonal packing are described. The scanning electron microscopy (SEM), nuclear magnetic resonance (NMR), and X-ray photoelectron spectroscopy (XPS) were used to characterize the octanethiol-protected copper nanoparticles. Analysis of XPS confirms the formation of oxidized copper nanoparticles. Conductivity of copper metal film (0.1μm) on the Si wafer can be improved simply by thermal annealing of copper monolayer protected clusters (MPCs) film (4.8±0.5×10²μΩcm) under air at 300°C for 1h, and then for another 5h under a protective atmosphere of 90% N₂–10% H₂.

Keywords: Nanoparticle; Monolayer protected cluster; Conductivity; Film

On the use of a O₂:SF₆ plasma treatment on GaAs processed surfaces for molecular beam epitaxial regrowth by O. Desplats; P. Gallo; J.B. Doucet; G. Monier; L. Bideux; L. Jalabert; A. Arnoult; G. Lacoste; C. Armand; F. Voillot; C. Fontaine (pp. 3897-3901).

Preparation of processed GaAs surface cleaning in view of molecular beam epitaxy regrowth by means of a O₂SF₆ microwave plasma has been investigated. Photoemission, Auger electron spectroscopy, atomic force microscopy and secondary ion mass spectrometry have been used for characterization. The O₂SF₆ plasma treatment was found to be very efficient for decontaminating the GaAs surface and leads to the formation of an oxide layer that can be taken off by a thermal or low-temperature H-plasma-assisted deoxidation. The levels of oxygen and carbon contaminants at the regrowth interface were measured to be in the range of a standard homoepitaxial layer–epiready substrate interface. Fluorine was observed to be eliminated upon deoxidation while sulphur is present, particularly in the case of low temperature grown layers. This plasma treatment was found to be efficient for preparation of processed GaAs surfaces for molecular beam epitaxial regrowth.

Keywords: PACS; 81.65.−b; 81.65.Mq; 81.15.Hi; 68.47.Fg; 68.47.GhPlasma treatment; Oxidation; Gallium arsenide; Molecular beam epitaxy; Regrowth

Comment on “Surface XPS characterization of NiTi shape memory alloy after advanced oxidation processes in UV/H₂O₂ photocatalytic system” (R.M. Wang et al., Appl. Surf. Sci. 253 (2007) 8507) by F. Müller; S. Hüfner (pp. 3902-3903).

Superhydrophobic surfaces based on dandelion-like ZnO microspheres by Qinmin Pan; Yuexiang Cheng (pp. 3904-3907).

This study presents a simple method to fabricate superhydrophobic surface based on ZnO nanoneedles. ZnO nanoneedles had been constructed on zinc layers by immersing in an aqueous NH₄OH solution at 80°C. The ZnO films were characterized by X-ray diffraction, scanning electron microscopy and X-ray photoelectron spectroscopy. The ZnO films exhibited excellent superhydrophilicity (contact angle for water was 0°), while they changed wettability to superhydrophobicity with a water contact angle greater than 150° after further chemical modification with n-dodecanoic acid. The procedure reported here only needs readily available reagents and laboratory equipments, which can be applied to various substrates of any size and shape.

Keywords: ZnO microspheres; Dandelion-like; Nanoneedles; Superhydrophobicity

Speedy photoelectric exchange of CdSe quantum dots/mesoporous titania composite system by Y. Shen; J. Bao; N. Dai; J. Wu; F. Gu; J.C. Tao; J.C. Zhang (pp. 3908-3911).

Two classes of important nano-materials, mesoporous titania (MT) and CdSe quantum dots, are prepared via chemical methods. Rapid immobilization of CdSe quantum dots into mesoporous titania has been achieved and the composite system is characterized by high-resolution transmission electron microscopy and photoluminescence. The band-to-band photoluminescence emission of CdSe quantum dots is blue-shifted for 20nm after the dots are immobilized into mesoporous titania. Loading CdSe quantum dots into mesoporous titania leads to speedy photoelectric exchange process of the system and a significant rise in photoconductivity (for a factor of 8), which would attract great deal of attention in quantum dots solar cell.

Keywords: Mesoporous titania; CdSe quantum dots; Photoelectric exchange; Photon antenna

Corrigendum to “Effect of fluoride-ion implantation on the biocompatibility of titanium for dental applications” [Applied Surface Science 254 (20) (2008) 6305–6312] by H.Y. Liu; X.J. Wang; L.P. Wang; F.Y. Lei; X.F. Wang; H.J. Ai (pp. 3912-3912).

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Applied Surface Science (v.255, #6)

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Applied Surface Science (v.255, #6)