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Applied Surface Science (v.254, #13)

Effect of pretreatment methods and chamber pressure on morphology, quality and adhesion of HFCVD diamond coating on cemented carbide inserts by S.K. Sarangi; A. Chattopadhyay; A.K. Chattopadhyay (pp. 3721-3733).

In the present investigation, diamond coating was deposited on cemented carbide substrate by hot filament chemical vapour deposition. The effect of substrate pretreatment methods and chamber pressure on morphology, quality, and adhesion of the diamond film were studied. The carbide inserts were pretreated with acid, Murakami's solution, and Murakami's solution followed by acid, respectively. The chamber pressure was set at 6.6, 13.2, 26.4, 39.6 and 66mbar. Deposition carried out at pressure of 26.4 and 39.6mbar on inserts pretreated with acid exhibited uniform crystal habit and provided coating-substrate adhesion adequate for machining application. Good coating morphology was obtained when deposition was done at 6.6mbar on carbide inserts treated with Murakami's solution. Pretreatment with Murakami's solution followed by acid and deposition at 6.6mbar also resulted in good morphology of diamond film. Indentation (Rockwell C scale) was done on diamond-coated inserts to assess coating-substrate adhesion under three loads of 294, 588 and 980N. The diameter of the indentation crack at the coating-substrate interface was observed under SEM. The results suggested that diamond coating deposited at medium pressure of 26.4mbar on carbide substrate treated with acid not only exhibited best morphology but also highest coating-substrate adhesion and improved machining performance.

Keywords: HFCVD; Pressure; Morphology; Adhesion

Fatigue resistance of plasma-sprayed CrC–NiCr cermet coatings in rolling contact by X.C. Zhang; B.S. Xu; F.Z. Xuan; S.T. Tu; H.D. Wang; Y.X. Wu (pp. 3734-3744).

The aim of this paper was to address the fatigue behavior and failure modes of plasma-sprayed CrC–NiCr cermet coatings in rolling contact under the identical tribological conditions of contact stress at room temperature. For all tests, the thicknesses of the coatings were controlled to be about 100μm. Thirteen rolling contact tests were performed to obtain the statistical result. The Weibull distribution plot of fatigue-life data of the coating specimens was obtained. The failure modes and mechanisms of the coatings were studied on the basis of the worn surface observations of the failed coatings. Experiment results showed that the RCF life data of the coatings exhibited high scattering, since the bimodal distribution of the fatigue-life data of the coatings was observed in the Weibull plot. Different failure modes named as spalling and delamination were observed during this investigation. However, the failure modes might be associated with the microstructure and the bonding strength of the coating, and the distribution of shear stress at the subsurface. The coatings failed in the spalling generally exhibited the relatively high fatigue lives and the coatings failed in the delamination exhibited low lives, resulting in the bimodal distribution of the fatigue-life data in the Weibull plot.

Keywords: Rolling contact fatigue; CrC–NiCr cermet coating; Weibull plot; Bimodal distribution; Failure modes

Effect of flexibility of grafted polymer on the morphology and property of nanosilica/PVC composites by Aiping Zhu; Aiyun Cai; Weidong Zhou; Zhehua Shi (pp. 3745-3752).

In this study, poly(methyl methacrylate)-grafted-nanosilica (PMMA-g-silica) and a copolymer of styrene (St), n-butyl acrylate (BA) and acrylic acid (AA)-grafted-nanosilica (PSBA-g-silica) hybrid nanoparticles were prepared by using a heterophase polymerization technique in an aqueous system. The grafted polymers made up approximately 50wt.% of the resulted hybrid nanoparticles which showed a spherical and well-dispersed morphology. The silica hybrid nanoparticles were subsequently used as fillers in a poly(vinyl chloride) (PVC) matrix to fabricate PVC nanocomposite. Morphology study of PVC nanocomposites revealed that both PMMA- and PSBA-grafted-silica had an adhesive interface between the silica and PVC. The tensile strength and elongation to break were found to be improved significantly in comparison with that of untreated nanosilica/PVC composites. Finally our results clearly demonstrated that the properties (e.g. chain flexibility, composition) of the grafted polymer in the hybrid nanoparticles could significantly affect the dispersion behavior of hybrid nanoparticles in PVC matrix, dynamic mechanical thermal properties and mechanical properties of the resulted PVC composites.

Keywords: Grafting polymerization; Nanosilica; Nanocomposites; Interfacial properties; Mechanical properties

Direct synthesis and characterization of phenyl-functionalized SBA-15 by Xue-mei Wang; Xin-zhen Du; Chun-lan Li; Xu Cao (pp. 3753-3757).

Phenyl-functionalized SBA-15 materials (Ph-SBA-15) were directly synthesized by using tri-block copolymer Pluronic P123 as templating agent under acidic conditions. The samples were characterized by Fourier transform infrared (FT-IR) spectra, X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), thermogravimetry analysis (TGA) and N₂ adsorption–desorption. The results show that the phenyl groups are covalently attached to the pore wall of SBA-15 after modification. The functionalized materials still preserve a desirable two-dimensional P6 mm hexagonal structure and have large specific surface area and pore volume although the molar ratio of phenyltrimethoxysilane in total silica precursors is as high as 23.0%.

Keywords: SBA-15; Mesoporous silica; Mesoporous hybrids; Phenyl functionalization; Direct synthesis

Fabrication of PECVD-grown fluorinated hydrocarbon nanoparticles and circular nanoring arrays using nanosphere lithography by D.K. Sarkar; M. Farzaneh (pp. 3758-3761).

Nanosphere lithography (NSL) masks were created by spin-coating of polystyrene particles onto silicon surfaces. Fluorinated hydrocarbon films were coated on the nanosphere lithography masks using plasma-enhanced chemical vapor deposition (PECVD) to obtain ordered arrays of fluorinated hydrocarbon. Atomic force microscope images show hexagonally ordered nanodots of dimension 225±11nm with a height of 23±4nm. Every hexagon encloses a circular ring of diameter 540±24nm having a height and width of 13.5±0.6nm and 203±16nm, respectively. FTIR analysis shows two distinct zones of atomic bonding of CH_x and CF_x in the plasma coated ordered fluorinated hydrocarbon films.

Keywords: PACS; 81.07.−b; 68.37.Ps; 78.30.JwNanosphere lithography; Plasma-enhanced chemical vapor deposition; Nanodots; Nanorings

One-step solvothermal preparation of TiO₂/C composites and their visible-light photocatalytic activities by Ming Li; Shifeng Zhou; Yuewei Zhang; Guangqin Chen; Zhanglian Hong (pp. 3762-3766).

Preparation of anatase type titania nanoparticles and their carbon modification were synchronously achieved by the solvothermal method with glycerol as the carbon source. The as-prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and diffuse reflectance spectra (DRS). It was found that the glycerol/ethanol ratio affected significantly the morphology and properties of TiO₂/C composites. The TiO₂/C composite which was obtained in the solution with the glycerol/ethanol ratio of 5/75, contained 1.2mass% carbon and exhibited both superior adsorption capability and visible-light photocatalytic activity. Contrary to this, samples prepared in the solution with higher glycerol/ethanol ratio, exhibited lower photocatalytic activity similar to that of the titania without carbon modification. It was suggested that excess addition of glycerol might contribute to large amounts of carbonaceous species and severe aggregation of the as-prepared samples, and thus reduced the surface area. As a result, the adsorption capability and visible-light photocatalytic activity increased at first and then decreased with the increase of glycerol addition. Present study provided a facile one-step method to obtain TiO₂/C composites with a controllable carbon content and photocatalytic performance under mild temperature.

Keywords: TiO; ₂; /C composites; Visible-light; Solvothermal method; Photocatalysis

High surface area thermally stabilized porous iron oxide/silica nanocomposites via a formamide modified sol–gel process by Kamal M.S. Khalil; Salah A. Makhlouf (pp. 3767-3773).

Iron oxide/silica (Fe:Si as 1:10 atomic ratio) composite materials have been prepared by calcination for 3h at different temperatures (400–900°C) of xerogel precursor obtained via a formamide modified sol–gel process. The process involved TEOS and iron(III) nitrate, nitric acid and formamide. Genesis of the composite materials from the xerogel precursor has been investigated by TGA, DSC, FTIR, XRD, SEM and EDX. Results indicated that all the calcined composites are mainly composed of amorphous iron oxide dispersed as finely divided particles in amorphous silica matrixes. Nitrogen adsorption/desorption isotherms revealed a reversible type I of isotherms indicative of microporosity. However, high S_BET surface area and microsporosity were observed for the calcined composite materials (e.g. S_BET=625m²g⁻¹, and S_αs=556m²g⁻¹ for the composite calcined at 400°C). Formation of the porous texture was discussed in terms of the action of formamide, which enhanced strengthening of the silica gel network during evaporation of the more volatile components within the composite body during the drying process.

Keywords: Fe; ₂; O; ₃; /SiO; ₂; Iron oxide/silica; Sol–gel; Nanocomposite; Formamide

Lithium electrochemistry of SiO₂ thin film electrode for lithium-ion batteries by Qian Sun; Bing Zhang; Zheng-Wen Fu (pp. 3774-3779).

The lithium electrochemistry of SiO₂ thin film prepared by reactive radio frequency sputtering has been investigated for the first time. The reversible discharge capacities of SiO₂/Li cells cycled between 0.01 and 3.0V are found in the range from 416 to 510mAh/g during the first 100 cycles. By using ex situ transmission electron microscopy, selected-area electron diffraction and X-ray photo-electron spectroscopy measurements, both Li–Si alloying process and the reversible conversion reaction of SiO₂ into Li₂Si₂O₅ are proposed in the lithium electrochemical reaction of SiO₂. SiO₂ film electrode with high-reversible capacity and good cycle performance exhibits it potential anode material for future lithium-ion batteries.

Keywords: Anode materials; SiO; ₂; Radio frequency sputtering

Fabrication and analysis of ZnO thin film bulk acoustic resonators by Y.C. Lin; C.R. Hong; H.A. Chuang (pp. 3780-3786).

This study employs RF magnetron sputter technique to deposit high C-axis preferred orientation ZnO thin film on silicon substrate, which is then used as the piezoelectric thin film for a thin film bulk acoustic resonator (FBAR). Electrical properties of the FBAR component were investigated by sputtering a ZnO thin film on various bottom electrode materials, as well as varying sputter power, sputter pressure, substrate temperature, argon and oxygen flow rate ratio, so that structural parameters of each layer were changed. The experimental results show that when sputter power is 200W, sputter pressure is 10mTorr, substrate temperature is 300°C, and argon to oxygen ratio is 4:6, the ZnO thin film has high C-axis preferred orientation. The FBAR component made in this experiment show that different bottom electrode materials have great impact on components. In the experiment, the Pt bottom electrode resonant frequency was clearly lower than the Mo bottom electrode resonant frequency, because Pt has higher mass density and lower acoustic wave rate. The component resonant frequency will decrease as ZnO thin film thickness increases; when top electrode thickness is higher, its resonant frequency also drops, due to top electrode mass loading effect and increased acoustic wave path. Therefore, ZnO thin film and top/bottom electrode thickness can be fine-tuned according to the required resonant frequency.

Keywords: RF magnetron sputter; ZnO; Film bulk acoustic resonator

Enhanced field emission characteristics of zinc oxide mixed carbon nano-tubes films by J.Y. Pan; C.C. Zhu; Y.L. Gao (pp. 3787-3792).

A composite material of Zinc oxide and carbon nano-tubes (ZnO–CNTs) paste was synthesized by mixing multi-wall CNTs, ZnO nano-grains and organic vehicles. The microstructures and the morphologies of screen-printed films were characterized by field-emission scanning electron microscope. Results show that ZnO flakes geometrically matched with CNTs by filling into the interspaces of CNTs or directly covering upon CNTs. The field emission characteristics of films are found to be greatly effected by ZnO nano-grains. Especially, the turn-on electric field of ZnO–CNT film (1.17V/μm) which is far lower than that of usual CNT films (1.70V/μm). Furthermore, except that better emission stability is achieved, brightness and emission uniformity are notably enhanced as well. It can be speculated that the special microstructures of ZnO mixed CNT films dominate the enhanced electrical conductivity, thermal conductivity, and effective emitters.

Keywords: Carbon nano-tube (CNT); Zinc oxide (ZnO); Field emission characteristics; Uniformity

Nanostructure of photocatalytic TiO₂ films sputtered at temperatures below 200°C by J. Šícha; J. Musil; M. Meissner; R. Čerstvý (pp. 3793-3800).

The article reports on correlations between the process parameters of reactive pulsed dc magnetron sputtering, physical properties and the photocatalytic activity (PCA) of TiO₂ films sputtered at substrate surface temperature T_surf≤180°C. Films were deposited using a dual magnetron system equipped with Ti (Ø50mm) targets in Ar+O₂ atmosphere in oxide mode of sputtering. The TiO₂ films with highly photoactive anatase phase were prepared without a post-deposition thermal annealing. The decomposition rate of the acid orange 7 (AO7) solution during the photoactivation of the TiO₂ film with UV light was used for characterization of the film PCA. It was found that (i) the partial pressure of oxygenpO2 and the total sputtering gas pressure p_T are the key deposition parameters influencing the TiO₂ film phase composition that directly affects its PCA, (ii) the structure of sputtered TiO₂ films varies along the growth direction from the film/substrate interface to the film surface, (iii) ∼500nm thick anatase TiO₂ films with high PCA were prepared and (iv) the structure of sputtered TiO₂ films is not affected by the substrate surface temperature T_surf when T_surf<180°C. The interruption of the sputtering process and deposition in long (tens of minutes) pulses alternating with cooling pauses has no effect on the structure and the PCA of TiO₂ films and results in a decrease of maximum value of T_surf necessary for the creation of nanocrystalline nc-TiO₂ film. It was demonstrated that crystalline TiO₂ films with high PCA can be sputtered at T_surf≤130°C. Based on obtained results a phase zone model of TiO₂ films was developed.

Keywords: TiO; ₂; film; Structure; Anatase; UV induced photocatalysis; Low-temperature sputtering; Dual magnetron

Ionization probability of sputtered particles as a function of their energy by Y. Kudriavtsev; S. Gallardo; A. Villegas; G. Ramirez; R. Asomoza (pp. 3801-3807).

In this paper we represent the experimental ionization probability of sputtered silicon atoms as a function of their energy, which has been obtained for positive Si⁺ ions sputtered from silicon by O₂⁺ ion beam. To explain the experimental data, we have considered ionization of an outgoing atom at a critical distance from the surface, which occurs due to the electron transition between this atom and the surface, and suggested the formation of a local surface charge with the polarity opposite to that of the outgoing ion that has just been formed. Then we have considered the interaction between those two charges, outgoing ion, and surface charge as a process of the particle passage through a spherical potential barrier; as a result, we have obtained the theoretical energy distribution of secondary ions. Together with the well-known Sigmund–Thompson energy distribution of sputtered atoms, the obtained ion energy distribution allowed us to derive the equation for the secondary ion yield versus the sputtered particle energy. Both equations derived have exhibited a quite good correlation with our experimental results and also with a large number of published experimental data.

Keywords: Secondary ion emission; Ion sputtering; Energy distribution; SIMS

Structure control of Pt–Sn bimetallic catalysts supported on highly oriented pyrolytic graphite (HOPG) by Yunxi Yao; Qiang Fu; Zhen Zhang; Hui Zhang; Teng Ma; Dali Tan; Xinhe Bao (pp. 3808-3812).

PtSn bimetallic catalyst nanoparticles were grown on highly oriented pyrolytic graphite (HOPG) surfaces using the sequential deposition and co-deposition of Pt and Sn. The surface morphology and composition of the prepared PtSn catalysts were investigated by scanning tunneling microscopy and CO adsorption experiment. It is found that the structure of the PtSn catalysts can be controlled by the deposition process. The deposition sequence of 1st Pt and 2nd Sn and co-deposition of Pt and Sn produce Sn-shell and Pt-core structure, while the deposition sequence of 1st Sn and 2nd Pt leads to the growth of individual Pt and Sn particles. The formation of various PtSn bimetallic structures was attributed to the different surface energy of Pt and Sn, and the interaction of the metals with the HOPG surfaces.

Keywords: Bimetallic catalyst; Electrocatalyst; HOPG; PtSn; CO adsorption; STM

Formation of CdO films from chemically deposited Cd(OH)₂ films as a precursor by T.P. Gujar; V.R. Shinde; Woo-Young Kim; Kwang-Deog Jung; C.D. Lokhande; Oh-Shim Joo (pp. 3813-3818).

Formation of cadmium hydroxide at room temperature onto glass substrates from an aqueous alkaline cadmium nitrate solution using a simple soft chemical method and its conversion to cadmium oxide (CdO) by thermal annealing treatment has been studied in this paper. The as-deposited film was given thermal annealing treatment in oxygen atmosphere at 450°C for 2h for conversion into cadmium oxide. The structural, surface morphological and optical studies were performed for as-deposited and the annealed films. The structural analyses revealed that as-deposited films consists of mixture of Cd(OH)₂ and CdO, while annealed films exhibited crystalline CdO. From surface morphological studies, conversion of clusters to grains after annealing was observed. The band gap energy was changed from 3.21 to 2.58eV after annealing treatment. The determination of elementals on surface composition of the core–shell nanoparticles of annealed films was carried out using X-ray photoelectron spectroscopy (XPS).

Keywords: Cd(OH); ₂; CdO; Thin film; M-CBD; Surface morphology and optical properties

Electronic and atomic structure computation of disordered low index surfaces ofγ-alumina by Anthony Dyan; Christophe Azevedo; Pierre Cenedese; Pierre Dubot (pp. 3819-3828).

Electronic and atomic structure of low index polar (001, 011, 111) spinelγ-alumina surfaces have been investigated using a modified large-scale quantum semi-empirical simulations. Atomic structure optimization and electronic structure calculation were done in the direct space on periodic large unit cells in which random distribution of cationic vacancies close to the surface were included. Predicted electronic structures match more accurate ab initio Density Functional Theory (DFT) results on aluminum oxides. We found that the restructured surfaces behave as amorphous-like shapeless planes provided unit cell dimensions are much greater than primitive translations as periodicity constraints are weakened. Aluminum ions vacancies in the surface region are shown to induce a surface atomic disordering even at 0K, correlated with the appearance of low coordinated ions, as proven experimentally and theoretically with classical Molecular Dynamics (MD) calculation on some aluminum oxide systems. The lowering of the surface charge density is obtained from two distinct mechanisms involving large ion movements. On the oxygen rich plane termination, this results from the formation of O₂ δ⁻entities. On the aluminum rich plane termination, the same effect is related to a loss of co-ordination number together with a reduction of cationic charge. Furthermore, large-scale simulations allow to statistically quantify specific relaxed surface ion densities for which the Local Density of States (LDOS) is evaluated. Their inferred electronic properties are then compared to available probe molecule adsorption experiments investigated by infrared spectroscopy. We show that surface electronic states are not a simple function of ion coordination. Our large-scale quantum semi-empirical calculation fills the gap between atomic structures predicted by classical MD approach with electronic structure results obtained by DFT on small systems.

Keywords: PACS; 68.35.; −; p; 68.43.; −; h; 73.20.Hb; 73.20.AtAlumina; Surface defects; Electronic structure; Atomic structure; Large-scale quantum simulation

Adsorption and deposition of anthraquinone-2-carboxylic acid on alumina studied by inelastic electron tunneling spectroscopy, infrared reflection absorption spectroscopy, X-ray photoelectron spectroscopy, and atomic force microscopy by Morihide Higo; Takeshi Miake; Masaru Mitsushio; Toshifumi Yoshidome; Yoshihisa Ozono (pp. 3829-3838).

The adsorption state of anthraquinone-2-carboxylic acid (AQ-2-COOH) deposited from acetone solutions (0.01–1.00mg/ml) on native oxide surfaces of Al films was characterized by inelastic electron tunneling spectroscopy, infrared reflection absorption spectroscopy, and X-ray photoelectron spectroscopy. The oxide was prepared on evaporated Al films at room temperature in an oxygen-dc glow discharge. The morphology of the deposited AQ-2-COOH on the oxide surfaces was observed and analyzed by atomic force microscopy. These surface analyses showed that AQ-2-COOH is adsorbed predominantly as a uniform nanometer-scale film of carboxylate anions on the oxide surfaces deposited from solutions with concentrations lower than or equal to 0.02mg/ml. It was found that AQ-2-COOH is adsorbed as both a uniform film of anions and as micron-sized particles of neutral molecules with heights of a few tens of nanometers when AQ-2-COOH is deposited from solutions with concentrations higher than 0.02mg/ml. A comparison of the results obtained by these surface analytical techniques clearly shows the features and advantages of these analytical techniques.

Keywords: PACS; 68. 37. Ps; 68. 43. −h; 68. 47. Gh; 73. 40. Rw; 73. 43. Jn; 78. 30. −j; 79. 60. −iAnthraquinone-2-carboxylic acid; Adsorption; Deposition; Alumina; Inelastic electron tunneling spectroscopy; Infrared reflection absorption spectroscopy; X-ray photoelectron spectroscopy; Atomic force microscopy

Growth and characterization of ZnO-SDS hybrid thin films prepared by electrochemical self-assembly method by Xiaoyan Gan; Xiangdong Gao; Jijun Qiu; Xiaomin Li (pp. 3839-3844).

ZnO-SDS hybrid thin films were grown on ITO glass using the potentiostatic electrodeposition route from aqueous zinc nitrate solution containing surfactant sodium dodecyle sulfanate (SDS). The electrochemical process of the hybrid films was analyzed by comparing the cyclic voltammetric curve and current–time curve with those of pure ZnO film. Results showed that the addition of a small amount of SDS could decrease the deposition current density, and inhibit the growth of ZnO crystals significantly. The hybrid films electrodeposited at −0.9V for 30min exhibited smooth and platelet-like morphology, with the film thickness of about 110nm. The well-defined ZnO-SDS lamellar structures could be clearly observed, with two interlayer spaces of 35.1 and 30.9Å, respectively. Optical analysis showed that the hybrid films had good optical quality, and exhibited the fundamental absorption edge of ZnO at 380nm.

Keywords: ZnO; Hybrid thin film; Electrodeposition; SDS; Self-assembly

Manipulation of optical properties of Ag/Cu alloy nanowire arrays embedded in anodic alumina membranes by Xiaoye Hu; Zhenyang Wang; Tianci Zhang; Xiaoyan Zeng; Wei Xu; Junxi Zhang; Jian Yan; Jinping Zhang; Lide Zhang (pp. 3845-3848).

Arrays of Ag/Cu alloy nanowires embedded in anodic alumina membranes (AAMs) were synthesized by directly electrodepositing from a mixing electrolyte solution containing Ag⁺ and Cu²⁺ ions. Manipulations of optical properties of the resulting samples were successfully achieved by tuning the molar ratio of Ag⁺ and Cu²⁺ ions in the starting materials. When the ratio is less than 2:20, two surface plasma resonance (SPR) peaks corresponding to Ag and Cu appear, respectively. After annealing treatment, the SPR peak corresponding to Cu disappears, and that of Ag presents a red shift. Furthermore, this red shift can be up to 85nm when the molar ratio of Ag⁺ and Cu²⁺ reduce to 1:20, which is attributed to the transferable electrons from Cu atoms.

Keywords: Ag/Cu nanowires; Surface plasma resonance; Redshift; Electrodeposition

Microstructure and properties of TiB₂-containing coatings prepared by arc spraying by Jian-Jun Fang; Zhu-Xin Li; Yao-Wu Shi (pp. 3849-3858).

Low cost arc spraying and cored wires were used to deposit composite coatings consisting of TiB₂ and TiB₂/Al₂O₃ hard particles in a Ni(Cr) and stainless steel 304L matrix. Four coatings were prepared namely Ni(Cr)–TiB₂, Ni(Cr)–TiB₂/Al₂O₃, 304L–TiB₂ and 304L–TiB₂/Al₂O₃. The microstructural characteristics of powders and coatings were observed by scanning electron microscopy (SEM). Phase compositions of powders were analyzed by X-ray diffraction (XRD). Although all the analyzed coatings exhibited similar lamella structure, remarkable differences not only in the morphology of hard phase and matrix but also in the size and distribution of hard phases were observed from one coating to another. Tribological behavior of the coatings was analyzed in room temperature dry sliding wear tests (block-on-ring configuration), under 75N at low velocity (0.5m/s). The coatings showed far high wear resistance than low carbon steel substrate under same conditions examined. Wear loss of 304L–TiB₂ and Ni(Cr)–TiB₂ coatings were lower nearly 15 times than that of steel substrate. TiB₂ hard phases in coatings bonded well with metal matrix contributed to high wear resistance.

Keywords: TiB; ₂; Reinforcement phase; Composite coatings; Arc spraying; Wear resistance

Influence of sulfidation treatment on the structure and tribological properties of nitrogen-doped diamond-like carbon films by Qun-feng Zeng; Guang-neng Dong; You-bai Xie (pp. 3859-3866).

The nitrogen-doped diamond-like carbon (DLC) films were deposited on high speed steel (HSS) substrates in the direct current unbalanced magnetron sputtering system. Sulphurized layer was formed on the surface of DLC films by means of liquid sulfidation in the intermixture of urea and thiourea solution in order to improve the tribological properties of DLC films. The influence of sulfidation treatment on the structure and tribological properties of DLC films was investigated in this work. The structure and wear surface morphology of DLC films were analyzed by Raman spectroscopy, XPS and SEM, respectively. It reveals that the treated films are smooth and uniform; and sulfur atoms are bonded chemically. The treated films have broader distribution of Raman spectra in the range of 1000–1800cm⁻¹ and higher I_D/ I_G ratio than the untreated films as a result of the appearance of the crystalline graphite structure after the sulfidation treatment. It is showed that the sp² relative content increase in the treated films from the XPS measurement. The Raman results are consistent with the XPS results. The tribological properties of DLC films were investigated using a ball-on-disk rotating friction and wear tester under dry friction conditions. It is found that the sulfidation concentration plays an important part in the tribological properties of the treated DLC films. The results showed the treated films with low sulfidation concentration have a lower friction coefficient (0.1) than the treated films with high sulfidation concentration (0.26) and the untreated films (0.27) under the same friction testing conditions, which can be attributed to both the presence of sulfur-containing materials and the forming of the mechanical alloyed layer on the wear surface. Adding the dry nitrogen to the sliding surface in the testing system helps the friction coefficient of the treated films with low sulfidation concentration to decrease to 0.04 further in this work. On the basis of the experimental results, it is indicated that the liquid sulfidation technique, which is low-cost, non-polluting and convenience, would be an appropriate method for the surface treatment of DLC films.

Keywords: Diamond-like carbon films; Unbalanced magnetron sputtering; Sulfidation treatment; Structure analysis; Tribological properties

Substrate and orientation influence on electrical properties of sputtered La-doped PZT thin films by G. Leclerc; G. Poullain; C. Yaicle; R. Bouregba; A. Pautrat (pp. 3867-3872).

Pb1−2 y_/3La_yZr_xTi1−_xO₃ (PLZT) thin films have been prepared “in situ” by multi-target sputtering on Silicon, LaAlO₃ (LAO) and MgO substrates covered with a Pt bottom electrode. The purpose was to grow tetragonal PLZT films (Zr/Ti=28/72 with different La contents) on these various substrates and to compare their electrical properties. To this aim, Pt was first deposited on the three different substrates to get (111)Pt/Si, (111)Pt/LAO and (200)Pt/MgO. Then PLZT was deposited in a same run on these three kinds of substrates and the influence of La contents and film orientation on electrical properties was investigated. The La content was varied from y=0 to y=32 in order to explore the phase transition between ferroelectric and paraelectric phases as a function of the substrate. For large amount of Lanthanum, relaxor behavior has been observed and studied.

Keywords: PACS; 68.55.Jk; 77.84.s; 81.15.CdPLZT thin films; Crystallographic orientation; Multi-target sputtering; Dielectric properties; Ferroelectricity

The morphology and optical properties of Cr-doped ZnO films grown using the magnetron co-sputtering method by Y.M. Hu; Y.T. Chen; Z.X. Zhong; C.C. Yu; G.J. Chen; P.Z. Huang; W.Y. Chou; J. Chang; C.R. Wang (pp. 3873-3878).

Undoped ZnO and Zn_0.9Cr_0.1O films were prepared on Al₂O₃ (0001) substrates using the magnetron co-sputtering technique. X-ray diffraction scans show that all films exhibit nearly single-phase wurtzite structure with c-axis orientation. Both chromium doping and growth ambient have a significant impact on the lattice constants and nucleation processes in ZnO film. A large quantity of subgrains (10nm in size) has been observed on Zn_0.9Cr_0.1O film grown under Ar+O₂, while irregular plateau-like grains 40–50nm in size were observed on Zn_0.9Cr_0.1O film grown under Ar+N₂. The ultraviolet–visible transmittance and optical bandgap of all films were also examined. The photoluminescence spectra of all films exhibit a broad emission located around 400nm, which is composed of one weak ultraviolet luminescence and another rather intense near-violet one, as determined by Gaussian peak fitting. The near-violet emission centered on 400nm might originate from the electron transition between the band tail state levels of surface defects and/or lattice imperfection in the ZnO film.

Keywords: PACS; 68.55.Jk; 78.55.EtZinc oxide; Chromium; Nitrogen; Sputtering; Scanning electron microscopy; Surface morphology; Photoluminescence; Violet

Porosity, mechanical properties, residual stresses of supersonic plasma-sprayed Ni-based alloy coatings prepared at different powder feed rates by X.C. Zhang; B.S. Xu; Y.X. Wu; F.Z. Xuan; S.T. Tu (pp. 3879-3889).

The aim of this paper was to investigate the effect of powder feed rate (PFR) on the microstructure and mechanical properties of the supersonic plasma-sprayed Ni–Cr–B–Si–C coatings. The microstructure, porosity and mechanical properties of the coatings and the residual stresses at the coating surfaces were experimentally determined. Results showed that the variations of porosity, elastic moduli and micro-hardness of the coatings followed Weibull distribution. From the statistical trend, the porosity of the coating increased with increasing PFR. However, the elastic modulus and the micro-hardness of the coating decreased and reached local minima and then increased with increasing PFR. Elastic modulus could be generally considered to be an increasing function of micro-hardness. The mean value of the elastic modulus of the coating calculated from Weibull plot was almost proportional to the square root of the mean value of the micro-hardness of the coating. Moreover, with increasing PFR, the residual stress at the coating surface, which was mainly governed by the elastic modulus of the coating, decreased to a local minimum and then increased.

Keywords: Ni-based alloy coating; Powder feed rate; Porosity; Mechanical properties; Residual stress

Synthesis of carbon nanotubes directly over TEM grids aiming the study of nucleation and growth mechanisms by Carla Verissimo; Angelo L. Gobbi; Stanislav A. Moshkalev (pp. 3890-3895).

A novel approach to produce electron-transparent multi-layer membranes over TEM grids for transmission electron microscopy analysis is presented. The membranes have been used to grow and analyze carbon nanostructured materials in a thermal–chemical vapor deposition process using Ni and Cu as catalysts and silicon oxide thin films as support layers, at temperatures as high as 900°C. It is important that conditions of the synthesis using the electron-transparent multi-layer membrane system are similar to those for a conventional chemical vapor deposition process, where oxidized silicon wafers are employed. In particular, the thickness of the silicon oxide and the catalyst layers are the same, and similar carbon tubular structures were grown using both substrates. The use of membranes was crucial especially for the study of the nucleation mechanism for carbon nanotubes. These electron-transparent multi-layer membranes are relatively easy to obtain and they can be used for transmission electron microscopy studies of high-temperature synthesis of different nanostructured materials.

Keywords: Carbon nanotubes; Chemical vapor deposition; Methane decomposition; Nickel and copper catalysts; Scanning and transmission electron microscopy; Electron-transparent multi-layer membranes

Synthesis and tribological behaviors of diamond-like carbon films by electrodeposition from solution of acetonitrile and water by Jisheng Zhang; Lina Huang; Laigui Yu; Pingyu Zhang (pp. 3896-3901).

Diamond-like carbon (DLC) films were prepared on silicon substrates by liquid phase electrodeposition from a mixture of acetonitrile and deionized water. The deposition voltage was clearly reduced owing to the presence of deionized water in the electrolyte by changing the basic properties (dielectric constant and dipole moment) of the electrolyte. Raman spectra reveal that the ratio of sp³/sp² in the DLC films is related to the concentration of acetonitrile. The surface roughness and grain morphology determined by atomic force microscopy are also influenced by the concentration of the acetonitrile. The UMT-2 universal micro-tribometer was used to test the friction properties of the DLC films obtained from electrolytes with different concentration. The results convey that the DLC film prepared from the electrolyte containing 10vol.% acetonitrile has the better surface morphology and friction behavior comparing with the other. In addition the growth mechanism of the film was also discussed.

Keywords: PACS; 61.43.−j; 81.15.Pq; 68.55.−a; 62.20.QpDiamond-like carbon; Electrochemistry deposition; Solution of acetonitrile and water; Tribological behavior

Fluorocarbon nano-coating of polyester fabrics by atmospheric air plasma with aerosol by F. Leroux; C. Campagne; A. Perwuelz; L. Gengembre (pp. 3902-3908).

A fluorocarbon coating was deposited on polyester (PET) woven fabric using pulse discharge plasma treatment by injecting a fluoropolymer directly into the plasma dielectric barrier discharge. The objective of the treatment was to improve the hydrophobic properties as well as the repellent behaviour of the polyester fabric. Plasma treatment conditions were optimised to obtain optimal hydrophobic properties which were evaluated using water contact angle measurement as well as spray-test method at the polyester fabric surface. The study showed that adhesion of the fluoropolymer to the woven PET was greatly enhanced by the air plasma treatment. X-ray photoemission spectroscopy (XPS) analyses revealed chemical surface modifications occurring after the plasma treatments.

Keywords: Atmospheric plasma; Fluoropolymer; Wetting; Repellency; XPS; Textile; Liquid aerosol

Characterization of Ti–Zr–N films deposited by cathodic vacuum arc with different substrate bias by E.W. Niu; L. Li; G.H. Lv; H. Chen; X.Z. Li; X.Z. Yang; S.Z. Yang (pp. 3909-3914).

Ti–Zr–N (multi-phase) films were prepared by cathodic vacuum arc technique with different substrate bias (0 to −500V), using Ti and Zr plasma flows in residual N₂ atmosphere. It was found that the microstructure and mechanical properties of the composite films are strongly dependent on the deposition parameters. All the films studied in this paper are composed of ZrN, TiN, and TiZrN ternary phases. The grains change from equiaxial to columnar and exhibit preferred orientation as a function of substrate bias. With the increase of substrate bias the atomic ratio of Ti to Zr elements keeps almost constant, while the N to (Ti+Zr) ratio increases to about 1.1. The composite films present an enhanced nanohardness compared with the binary TiN and ZrN films deposited under the same condition. The film deposited with bias of −300V possesses the maximum scratch critical load ( L_c).

Keywords: Ti–Zr–N films; Cathodic vacuum arc; Nano-scratch

Surface modification of the nanoparticles by an atmospheric room-temperature plasma fluidized bed by Guangliang Chen; Shihua Chen; Wenran Feng; Wenxing Chen; Si-ze Yang (pp. 3915-3920).

Using hexamethyldisiloxane (HMDSO) monomer, the magnetic nanoparticles (NPs) of nickel oxide (NiO) were modified by using an atmospheric room-temperature plasma fluidized bed (ARPFB). The plasma gas temperature of the ARPFB was not higher than 325K, which was favorable for organic polymerization. The plasma optical emission spectrum (OES) of the gas mixture consisting of argon (Ar) and HMDSO was recorded by a UV–visible monochromator. The as-treated NPs were characterized by means of scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The results show that the assembling NPs were isolated greatly after modified by the organosilicon polymer. Moreover, this treatment process changed the wettability of the NPs from super-hydrophilicity to super-hydrophobicity, and the contact angle (CA) of water on the modified NPs surface exceeded 150°. Therefore, the ARPFB is a prospective technology for the NPs surface modification according to the different requirements.

Keywords: PACS; 52.50.Dg; 52.70.Kz; 81.15.−z; 81.07.WxSurface modification; NPs; ARPFB; Organosilicon polymer

Effect of annealing on thermal stability and morphology of pulsed laser deposited Ir thin films by Yansheng Gong; Chuanbin Wang; Qiang Shen; Lianmeng Zhang (pp. 3921-3924).

Iridium (Ir) thin films, deposited on Si (100) substrate by pulsed laser deposition (PLD) technique using Ir target in a vacuum atmosphere, were annealed in air ambient and the thermal stability was investigated. The crystal structure and surface morphology of Ir thin films before and after being annealed were studied by X-ray diffraction, Raman scattering, scanning electron microscope, and atomic force microscopy. The results showed that single-phase Ir thin films with (111) preferred orientation could be deposited on Si (100) substrate at 300°C and it remained stable below 600°C, which showed a promising bottom electrode of integrated ferroelectric capacitors. Ir thin films got oxidized to IrO₂ at temperatures from 650 to 800°C.

Keywords: Iridium thin films; Annealing; Stability; Morphology; Pulsed laser deposition

Weathering properties of treated southern yellow pine wood examined by X-ray photoelectron spectroscopy, scanning electron microscopy and physical characterization by Ghaleb N. Salaita; Frank M.S. Ma; Trudy C. Parker; Gar B. Hoflund (pp. 3925-3934).

In this study the weathering behavior of southern yellow pine (SYP) wood samples pretreated in different solutions has been examined using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and various types of physical characterization regarding material loss and discoloration. The treatment solutions include water as a control, a commercially available water repellent (WR) wood treating additive and polyethylene glycol (PEG) products including PEG PLUS™, PEG 8000 solutions and Compound 20M in varying concentrations. All contained the wood preservative chromated copper arsenate (CCA). One sample was treated with a CCA solution only. The treatments were carried out at 20°C and 150psig for 1/2h after exposure to vacuum (28mmHg) for 15min. Simulated weathering was achieved in an Atlas 65-W Weather-Ometer for 2000h with both light and dark periods and rain. The temperature ranged from 23°C during the dark cycle to 35°C during the light cycle. With weathering the XPS O/C ratios increase due to oxidation of the surface. Exposure to UV light results in bond breakage and reaction with oxygen in the presence of air to form organic functional groups such as ▪, ▪, CO and/or O–C–O. These oxidized products can protect the underlying wood from deterioration if they are insoluble in water and remain on the surface as a protective coating. If soluble, rain washes the compounds away and assists in the degradation. Correlated changes are observed in the XPS O/C ratios, the high-resolution XPS C 1s spectra, the SEM micrographs and physical measurements including thickness alteration, weight loss, and discoloration by yellowing or whitening of the weathered wood. The PEG treatments are effective in protecting wood with the 2% PEG PLUS treatment providing the best weathering behavior similar to that of the CCA treatment. The WR and water treatments yield the poorest weathering properties.

Keywords: PACS; 82.30.−b; 82.50.HpSouthern yellow pine wood; Polyethylene glycol solutions; PEG PLUS; CCA; 20M Compound; XPS; SEM; Physical characterization

Electrochemical deposition of Co nanowire arrays into self-organized titania nanotubes by Yingru Kang; Jianling Zhao; Jinliang Tao; Xixin Wang; Yangxian Li (pp. 3935-3938).

Arrays of Co magnetic nanowires with hexagonal symmetry have been prepared by electrodeposition into self-aligned titania nanotubes membranes. The nanowires have been investigated by X-ray diffraction, SEM, and VSM magnetometry. Magnetization curves of arrays of Co wires indicate that the easy direction of magnetization is a direction perpendicular to the axis of the wire.

Keywords: Co nanowire arrays; Electrochemical deposition; Titania nanotubes

The magnetoresistance effect in a nanostructure with the periodic magnetic barriers by Jian-Duo Lu (pp. 3939-3942).

The magnetoresistance (MR) effect is theoretically investigated in a periodic magnetically modulated nanostructure, which can be realized experimentally by depositing periodic parallel ferromagnetic strips on the top of a heterostructure. We find that there exists a significant conductance difference for electrons through the parallel (P) and antiparallel (AP) magnetization configurations, which results in a considerable magnetoresistance effect. We also find that the magnetoresistance effect depends not only on the temperature but also on the number of the periodic magnetic barriers.

Keywords: PACS; 73.23.; −; b; 73.40.; −; c; 75.75.+a; 85.70.; −; dMagnetic nanostructure; Magnetoresistance effect; MR ratio

Properties of high- k Ti1−_xSi_xO₂ gate dielectric layers prepared at room temperature by Sungyeon Kim; Moon-Ho Ham; Jae-Woong Lee; Woong Lee; Jae-Min Myoung (pp. 3943-3948).

High- k Ti1−_xSi_xO₂ gate dielectric layers were prepared at room temperature by RF magnetron sputtering using SiO₂ and TiO₂ targets to investigate their applicability to transparent thin-film transistors as well as metal–oxide–semiconductor field-effect transistors. Based on XRD and XPS analyses, it was found that, regardless of the deposition time, the Ti1−_xSi_xO₂ gate dielectric layers had more stable Si-based phases with stronger Si–O bonds with increasing SiO₂ RF power. As SiO₂ RF power increased, the capacitance of the dielectric layers decreased due to the higher fraction of the Si-based phases, and the leakage current decreased, dominantly because of the decrease in oxygen vacancies due to the formation of stoichiometric SiO₂. The Ti1−_xSi_xO₂ gate dielectric layers exhibited high transparency above 80% and moderate bandgap of 4.1–4.2eV, which can be applied to transparent thin-film transistors.

Keywords: PACS; 68.37.Hk; 71.55.−i; 72.20.−i; 77.55.+f; 77.84.Bw; 81.15.Cd; 82.80.Pv; 84.37.+q; 85.30.TvTiO; ₂; SiO; ₂; Co-sputtering; High-; k; dielectric

Effect of post-annealing on the properties of copper oxide thin films obtained from the oxidation of evaporated metallic copper by V. Figueiredo; E. Elangovan; G. Gonçalves; P. Barquinha; L. Pereira; N. Franco; E. Alves; R. Martins; E. Fortunato (pp. 3949-3954).

Thin films of copper oxide were obtained through thermal oxidation (100–450°C) of evaporated metallic copper (Cu) films on glass substrates. The X-ray diffraction (XRD) studies confirmed the cubic Cu phase of the as-deposited films. The films annealed at 100°C showed mixed Cu–Cu₂O phase, whereas those annealed between 200 and 300°C showed a single cubic Cu₂O phase. A single monoclinic CuO phase was obtained from the films annealed between 350 and 450°C. The positive sign of the Hall coefficient confirmed the p-type conductivity in the films with Cu₂O phase. However, a relatively poor crystallinity of these films limited the p-type characteristics. The films with Cu and CuO phases show n-type conductivity. The surface of the as-deposited is smooth (RMS roughness of 1.47nm) and comprised of uniformly distributed grains (AFM and SEM analysis). The post-annealing is found to be effective on the distribution of grains and their sizes. The poor transmittance of the as-deposited films (<1%) is increased to a maximum of ∼80% (800nm) on annealing at 200°C. The direct allowed band gap is varied between 2.03 and 3.02eV.

Keywords: PACS; X-ray diffraction-crystal structure 61.10.N; Scanning electron-microscopy 61.16.B; Atomic force-microscopy-surface structure 61.16.C; Optical properties 78.66; Electron beam deposition 81.15.EX-ray diffraction; Physical vapor deposition processes; Copper oxide thin films; Oxides; Semiconducting materials

Growth of lithium silicate crystals inside porous silicon film and their exploitation for ozone detection by K. Ben Saad; H. Hamzaoui; A. Labidi; B. Bessaïs (pp. 3955-3958).

Silicon dioxide was formed by oxidizing porous silicon film and annealed, in a next step, at 920°C with lithium nitrate embedded in its structure. These operations have produced the two lithium silicates, Li₂Si₂O₅ and Li₂SiO₃, as it has been confirmed by the X-ray diffraction measurements. At relative high temperature (230°C), the experimental ionic conductivity of this achieved sample has doubled in presence of ozone flow. A comparison with other samples, prepared with varieties of metallic nitrates and by following the same experimental procedures as for the former one, has proved that the sample prepared with zirconium was also good for ozone detection.

Keywords: Lithium; Zirconium; Silicate; Porous silicon; Ozone; Sensor

Thermochromic VO₂ thin films synthesized by rf-inverted cylindrical magnetron sputtering by J.B. Kana Kana; J.M. Ndjaka; P. Owono Ateba; B.D. Ngom; N. Manyala; O. Nemraoui; A.C. Beye; M. Maaza (pp. 3959-3963).

The novel physical vapor deposition called inverted cylindrical magnetron sputtering (also known as hollow cathode sputtering) is commonly used to coat wires, fibers, ribbons as well as all sides of three-dimensional substrates. It is a reproducible method for the production of nano-structured systems onto complex shapes substrates. This paper reports the first synthesis and feasibility of reliably reproduced stoichiometric pure textured VO₂ nano-structures by the rf-inverted cylindrical magnetron sputtering. Morphological, structural, elemental analysis and optical properties of synthesized VO₂ under optimized conditions are reported.

Keywords: PACS; 81.15.cd; 68.55.jk; 71.30.+h; 61.14.qpVanadium dioxide; Thermochromic; Phase transition; Transition temperature; Cylindrical magnetron sputtering

Study of nanoclusters growth at initial stages of ultrathin film deposition by kinetic modeling by Arvaidas Galdikas (pp. 3964-3970).

Comparative analysis of Au, Cu, Pt, Ni and Fe nanoclusters growth on amorphous carbon substrate by proposed kinetic model based on rate equations is present. Partial sticking coefficients introduced into the model let to discriminate elementary processes such as adatom adsorption and diffusion on bare substrate and on top of islands, nucleation and mobility of islands and its coalescence, 2-d and 3-d island growth modes. The quantitative fittings of experimental time dependencies of surface coverage, clusters density, cluster size are performed by solving model equations. From the best fittings the values of phenomenological coefficients defining elementary processes are found for different materials. Comparative analysis of those coefficients let to discover mechanisms of nanoclusters formation and growth of different materials. It is shown that clusterization for Cu and Au is more favorable than for Pt and Ni. Diffusivity for Pt and Ni on amorphous carbon (a-C) substrate is significantly less than for Au and Cu. In opposite, diffusivity on the top of islands for Ni and Pt is significantly higher than for Au and Cu. The mobility of islands for Au and Cu is much higher than for Ni and Pt. The fitting of experimental curves of Fe deposition on a-C at different temperatures showed that temperature mainly influences sticking process but not diffusion.

Keywords: Thin island films; Nanoclusters; Adsorption; Surface diffusion; Coalescence; Kinetic modeling; Rate equations

Direct laser sintered WC-10Co/Cu nanocomposites by Dongdong Gu; Yifu Shen (pp. 3971-3978).

In the present work, the direct metal laser sintering (DMLS) process was used to prepare the WC-Co/Cu nanocomposites in bulk form. The WC reinforcing nanoparticles were added in the form of WC-10wt.% Co composite powder. The microstructural features and mechanical properties of the laser-sintered sample were characterized by X-ray diffraction (XRD), atomic force microscope (AFM), scanning electron microscope (SEM), energy dispersive X-ray spectroscope (EDX), and nanoindentation tester. It showed that the original nanometric nature of the WC reinforcing particulates was well retained without appreciable grain growth after laser processing. A homogeneous distribution of the WC reinforcing nanoparticles with a coherent particulate/matrix interfacial bonding was obtained in the laser-sintered structure. The 94.3% dense nanocomposites have a dynamic nanohardness of 3.47GPa and a reduced elastic modulus of 613.42GPa.

Keywords: PACS; 42.62.Cf; 81.05.Ni; 61.46.DfDirect metal laser sintering (DMLS); Nanocomposites; Metal-matrix composites (MMCs); WC-Co; Nanoindentation

Low temperature deposition and characterization of TiO₂ photocatalytic film through cold spray by Guan-Jun Yang; Chang-Jiu Li; Feng Han; Wen-Ya Li; Akira Ohmori (pp. 3979-3982).

Cold spray was employed as a novel low temperature approach to deposit titanium dioxide (TiO₂) photocatalytic film. The film microstructure was characterized using X-ray diffraction and scanning electron microscopy. The photocatalytic performance was examined through acetaldehyde degradation under ultraviolet illumination. Results showed that TiO₂ film was successfully deposited on substrate surface through cold spray. The film thickness reached up to 15μm. The film presented a rough surface and porous structure. Owing to the low temperature of spray powder, no phase and particle size changes occurred to TiO₂ during deposition. It was found that the cold-sprayed TiO₂ film was active for photodegradation of acetaldehyde.

Keywords: Titanium oxide; Film; Photocatalysis; Cold spray

Cleaning results of new and fouled nanofiltration membrane characterized by contact angle, updated DSPM, flux and salts rejection by Ahmed Al-Amoudi; Paul Williams; A.S. Al-Hobaib; Robert W. Lovitt (pp. 3983-3992).

In membrane process industries, membrane cleaning is one of the most important concerns from both economical and scientific points of view. Though cleaning is important to recover membrane performance, an inappropriate selection of cleaning agents may result into unsatisfactory cleaning or irreparable membrane.In this study the cleaning performance has been studied with measurements of membrane contact angle, Updated Donnan steric partitioning pore model (UDSPM) and salt rejection as well as flux measurement. Thin film nanofiltration (NF) membranes such as DK, HL and DL provided by GE Osmonics are used in this study. Tests were carried out with virgin DK, HL and DL as well as fouled DK membranes. Several cleaning agents were investigated; some of them were analytical grade such as HCl, NaOH and others such as SDS, mix agents were commercial grade agents that are already in use in commercial plants. Contact angle, DSPM and salt rejection as well as flux of virgin and fouled membranes before and after chemical cleaning were measured and compared. The contact angle measurements with and without chemical cleaning of different virgin and fouled membranes revealed very interesting results which may be used to characterise the membrane surface cleanliness. The contact angle results revealed that the cleaning agents are found to modify membrane surface properties (hydrophobicity/hydrophilicity) of the treated and untreated virgin and fouled membranes. The details of these results were also investigated and are reported in the paper. However, UDSPM method did not give any valuable information about pore size of the untreated and treated NF membranes. The salt rejection level of monovalent and divalent ions before and after cleaning by high and low pH cleaning agents is also investigated and is reported in the paper.

Keywords: Cleaning; Contact angle; Fouling; Nanofiltration membranes; Cleaning agents

Preparation of Ni-doped carbon nanospheres with different surface chemistry and controlled pore structure by L. Zubizarreta; A. Arenillas; J.J. Pis (pp. 3993-4000).

In classic carbon supports is very difficult to control pore size, pore size distribution, and surface chemical properties at the same time. In this work microporous carbons derived from furfuryl alcohol are used as support to prepare Ni-doped carbon materials. The N₂ flow rate used during the carbonisation process of the precursor influences on the size of the nanospheres obtained but not in their textural properties. Microporous carbon nanospheres have been synthesised with a narrow pore size distribution centred in 5.5Å. The surface chemistry of these materials can be easily modified by different treatments without detriment of the pore structure of the doped carbon nanospheres.

Keywords: PACS; 81.05.Rm; 81.07.Wx; 82.45.Jn; 82.65.+r; 68.43.−hAdsorption; Catalysis; Nickel; Polymers; Nanostructures

Low temperature preparation of anatase TiO₂-activated carbon composite film by Yanhui Ao; Jingjing Xu; Degang Fu; Xunwei Shen; Chunwei Yuan (pp. 4001-4006).

Anatase titania-activated carbon composite film was prepared by a simple method at low temperature (75°C at most). The film was characterized by XRD, SEM and BET analysis. Results showed that the composite film was porous because it formed a nano-micro structure. The photocatalytic activity of the composite film was determined by degradation of 4-cholophenol (4-CP) under UV irradiation, and was compared to pure titania film and P25 film. It exhibited that the photocatalytic activity of composite film enhanced a lot. The recycle ability of the composite film was also investigated. The degradation ratio which was still higher than 85% after 5 cycles, decreased only 3% compared to the first cycle.

Keywords: Composite film; Nano-micro structure; Photocatalysis; Titania; Activated carbon; Low temperature

Ion and photon emission from laser-generated titanium-plasma by L. Torrisi; D. Margarone; A. Borrielli; F. Caridi (pp. 4007-4012).

Titanium-plasma was obtained by nanosecond pulsed laser ablation technique. A Nd:Yag laser was employed to irradiate titanium in vacuum. The ion emission from plasma was on-line monitored by an electrostatic ion energy analyzer which permitted to measure the ion kinetic energy and charge state. The visible photon emission was monitored by an optical spectrometer. The ion energy, charge state and angular distributions, the temperature and density of the non-equilibrium plasma were investigated. The temperature gradient of the plasma plume was evaluated and discussed.

Keywords: Optical spectroscopy; Laser-generated plasma; Ion energy distribution

Surface modification of a WTi thin film on Si substrate by nanosecond laser pulses by S. Petrović; B. Gaković; D. Peruško; M. Trtica; B. Radak; P. Panjan; Š. Miljanić (pp. 4013-4017).

Interaction of a nanosecond transversely excited atmospheric (TEA) CO₂ laser, operating at 10.6μm, with tungsten–titanium thin film (190nm) deposited on silicon of n-type (100) orientation, was studied. Multi-pulse irradiation was performed in air atmosphere with laser energy densities in the range 24–49J/cm². The energy absorbed from the laser beam was mainly converted to thermal energy, which generated a series of effects. The following morphological changes were observed: (i) partial ablation/exfoliation of the WTi thin film, (ii) partial modification of the silicon substrate with formation of polygonal grains, (iii) appearance of hydrodynamic features including nano-globules. Torch-like plumes started appearing in front of the target after several laser pulses.

Keywords: PACS; 68.55.Jk; 52.38.Mf; 79.20.DsWTi thin films; Laser ablation; Nanosecond laser pulse

Structural, optical and electrical characterization of highly conducting Mo-doped In₂O₃ thin films by R.K. Gupta; K. Ghosh; S.R. Mishra; P.K. Kahol (pp. 4018-4023).

Highly conducting and transparent thin films of molybdenum-doped indium oxide were deposited on quartz by pulsed laser deposition. The effect of growth temperature and oxygen partial pressure on the structural, optical and electrical properties was studied. We find that the film transparency depends on the growth temperature. The average transmittance of the films grown at different temperatures is in range of 48–87%. The X-ray diffraction results show that the films grown at low temperature are amorphous while the films grown at higher temperature are crystalline. Electrical properties are found to be sensitive to both the growth temperature and oxygen pressure. Resistivity of the films decreases from 1.3×10⁻³Ωcm to 8.9×10⁻⁵Ωcm while mobility increases from 9cm²/Vs to 138cm²/Vs as the growth temperature increases from room temperature to 700°C. However, with increase in oxygen pressure, resistivity increases but the mobility decreases after attaining a maximum. The temperature-dependent resistivity measurements show transition form semiconductor to metallic behavior. The film grown at 500°C under an oxygen pressure of 1.0×10⁻³mbar is found to exhibit high mobility (250cm²/Vs), low resistivity (6.7×10⁻⁵Ωcm), and relatively high transmittance (∼90%).

Keywords: PACS; 72.20; 78.66; 73.50J; 61.16CSemiconductor; Electrical properties; Thin films; Indium oxide; Molybdenum; Optical materials and properties

AES, EELS and TRIM investigation of InSb and InP compounds subjected to Ar⁺ ions bombardment by A. Abdellaoui; M. Ghaffour; A. Ouerdane; K. Hamaida; Y. Monteil; N. Berrouachedi; Z. Lounis; M. Bouslama (pp. 4024-4028).

The interaction of ions with matter plays an important role in the treatment of material surfaces. In this paper we study the effect of argon ion bombardment on the InSb surface in comparison with the InP one. The Ar⁺ ions, accelerated at low energy (300eV) lead to compositional and structural changes in InP and InSb compounds. The InP surface is more sensitive to Ar⁺ ions than that of InSb. These results are directly inferred from the qualitative Auger electron spectra (AES) and electron energy loss spectroscopy (EELS) analysis. However, these techniques alone do not allow us to determine with accuracy the disturbed depth in Ar⁺ ions of InP and InSb compounds. For this reason, we combine AES and EELS with the simulation method TRIM (transport and range of ions in matter) to show the mechanism of interaction between the ions and the InP or InSb and hence determine the disturbed depth as a function of Ar⁺ energy.

Keywords: EELS; AES; Simulation method TRIM; Surface; Interaction ions-matter

Low temperature ageing of silicas Gasil-I and TK800 by K.E. Collins; M.C. Gonçalves; R.B. Romero; R.F. Conz; V.R. de Camargo; C.H. Collins (pp. 4029-4035).

Gasil-I (a mesoporous silica) and TK800 (a non-porous pyrogenic silica) were investigated in the early 1970s as standard reference materials. Since then the specific surface areas of both silicas have decreased to ∼85% of their initial values, suggesting that the surface character and the ageing mechanism may be the same for both. Comparisons of the shapes of nitrogen-adsorption isotherms, confirmed by comparisons of the shape ratios for Gasil-I and TK800, indicate that Gasil-I has greater microbore character and a higher absorption at p/ p₀>0.5 than TK800 and that the isotherm shapes have changed little since 1974. The specific volume of Gasil-I has remained nearly constant during the ageing period but the pore size distribution (PSD) has shifted markedly to higher values.Electron micrographs show that low (room) temperature gas–solid ageing results in similar enlargement at the point of contact between attached secondary particles as that which occurs in hydrothermal ageing. In the gas–solid case, this change, which accounts for the decrease in overall surface area, is attributed to the surface transport of silica material in the presence of near monolayer quantities of adsorbed water. Ageing in this manner is geometry-limited so that the rate of ageing is expected to approach zero, resulting in time-stable silicas.

Keywords: Low temperature ageing; Surface area; Shape ratios; Gasil-I; TK800

Investigation on corrosion and wear behaviors of nanoparticles reinforced Ni-based composite alloying layer by Jiang Xu; Jie Tao; Shuyun Jiang; Zhong Xu (pp. 4036-4043).

In order to investigate the role of amorphous SiO₂ particles in corrosion and wear resistance of Ni-based metal matrix composite alloying layer, the amorphous nano-SiO₂ particles reinforced Ni-based composite alloying layer has been prepared by double glow plasma alloying on AISI 316L stainless steel surface, where Ni/amorphous nano-SiO₂ was firstly predeposited by brush plating. The composition and microstructure of the nano-SiO₂ particles reinforced Ni-based composite alloying layer were analyzed by using SEM, TEM and XRD. The results indicated that the composite alloying layer consisted of γ-phase and amorphous nano-SiO₂ particles, and under alloying temperature (1000°C) condition, the nano-SiO₂ particles were uniformly distributed in the alloying layer and still kept the amorphous structure. The corrosion resistance of composite alloying layer was investigated by an electrochemical method in 3.5%NaCl solution. Compared with single alloying layer, the amorphous nano-SiO₂ particles slightly decreased the corrosion resistance of the Ni–Cr–Mo–Cu alloying layer. X-ray photoelectron spectroscopy (XPS) revealed that the passive films formed on the composite alloying consisted of Cr₂O₃, MoO₃, SiO₂ and metallic Ni and Mo. The dry wear test results showed that the composite alloying layer had excellent friction-reduced property, and the wear weight loss of composite alloying layer was less than 60% of that of Ni–Cr–Mo–Cu alloying layer.

Keywords: Double glow; Amorphous nano-SiO; ₂; particle; Corrosion and wear resistance; Particle-reinforced composites alloying layer

Excimer laser processing as a tool for photocatalytic design of sol–gel TiO₂ thin films by K. Starbova; V. Yordanova; D. Nihtianova; W. Hintz; J. Tomas; N. Starbov (pp. 4044-4051).

Nanostructured sol–gel TiO₂ thin films spin coated on silicate glass plates are subjected to excimer (KrF^*) pulsed laser irradiation in order to tailor their structure and photocatalytic properties. The surface morphology of virgin and laser-processed films are followed applying electron optical imaging and atomic force microscopy. The evolution of the surface roughness and pore formation are shown to be accompanied by optical absorption edge shift to infrared wavelength range. Conventional X-ray diffraction analysis and high-resolution transmission electron imaging are applied in order to obtain information on the phase composition. Co-existence of amorphous and anatase TiO₂ phases in nonirradiated sol–gel films is found. It is established that after laser processing the most intense XRD anatase peak is shifted to lower 2 θ range. The analysis of high-resolution transmission electron images of film profiles evidences for the laser induced phase transitions. Formation of rutile and brookite TiO₂ accompanied by evolution of oxygen deficient Ti_nO2 n₋₁ phases are identified in the subsurface region. The contribution of laser processing for increasing the photocatalytic efficiency of laser-modified films toward the oxidation of methylene blue water solution is demonstrated. The results obtained reveal a novel-processing route for designing sol–gel titania films with improved photocatalytical activity.

Keywords: Titania; Sol–gel; Thin films; Laser modification; Phase transitions; Photocatalysis

Green chemistry-mediated synthesis of nanostructures of afterglow phosphor by Pooja Sharma; D. Haranath; Harish Chander; Sukhvir Singh (pp. 4052-4055).

Various nanostructures of SrAl₂O₄:Eu²⁺, Dy³⁺ (SAC) afterglow phosphor were prepared in a single-step reaction using a green chemistry-mediated modified combustion process. The evolution of hazardous NxOx gases during the customary combustion reaction was completely eliminated by employing an innovative complex formation route. Another fascinating feature of the process was that, a slight change in the processing conditions ensured the synthesis of either nanoparticles or nanowires. The photoluminescence spectrum of nanophosphor showed a slight blue shift in emission (∼511nm) as compared to the bulk phosphor (∼520nm). The afterglow (decay) profiles of SAC nanoparticles, nanowires and bulk phosphor were compared. The chemistry underlying the nanostructure synthesis and the probable afterglow mechanism were discussed.

Keywords: Phosphor; Afterglow; Nanoparticle; Nanowire; Green chemistry

Electropolymerization of pyrrole on silanized polycrystalline titanium substrates by Z. Mekhalif; D. Cossement; L. Hevesi; J. Delhalle (pp. 4056-4062).

In this work is reported the silanization of titanium substrates and subsequent polymerization of pyrrole on the resulting substrates. First, titanium substrates were modified by n-hexyltrichlorosilane (HTCS) and 6-(1′-pyrrolyl)- n-hexyltrichlorosilane (PyHTCS). The corresponding self-assembled monolayers were characterized by X-ray photoelectron spectroscopy and contact angle measurements. They were found to be densely packed. Second, pyrrole was electrochemically polymerized on silanized titanium substrates. Chronoamperometry was used to study the growth of polypyrrole films. The polymer films were characterized by qualitative peel tests, cyclic voltametry and scanning electron spectroscopy. Polypyrrole grown from PyHTCS was found to adherent as compared to HTCS modified and bare substrates. Cyclic voltametry indicated that polymer films formed from PyHTCS have an oxidation peak potential located at higher values than HTCS-modified and bare substrates. Moreover, the films grown on the three types of substrates were found to be equally uniform. Finally, we improved the electrochemical properties of the polypyrrole films using a two-step process, electroreticulation of the PyHTCS monolayers followed by a pyrrole polymerization.

Keywords: Titanium; Polypyrrole; Organosilane; Electrochemistry

Pulsed electron beam deposition of highly oriented thin films of polytetrafluoroethylene by Vimlesh Chandra; Solomon S. Manoharan (pp. 4063-4066).

Thin films of polytetrafluoroethylene (PTFE) were deposited by pulsed electron deposition (PED) technique. The transmission electron microscopy (TEM) image of the RT fabricated (20Å thick) film on carbon coated copper grid shows crystalline nature. Infrared spectra show one to one correspondence between PED ablated film and the PTFE bulk target. The asymmetrical and symmetrical –CF₂– stretching modes were observed at 1220 and 1156cm⁻¹, respectively. The –CF₂– wagging and bending modes occur at 644 and 512cm⁻¹, respectively. X-ray diffraction patterns of the film deposited at room temperature (RT) show oriented film along (100) plane of hexagonal structure and the crystalline nature is retained up to 300°C on vacuum annealing. The room temperature fabricated film shows smooth and pin hole free surface whereas post-annealing brings discontinuity, roughness and pin holes.

Keywords: PACS; 77.22.Jp; 85.75.−dPolytetrafluoroethylene; Pulse electron deposition; Insulator; Spintronics

Effective biaxial modulus and strain energy density of ideally ( h k l)-fiber-textured cubic polycrystalline films by Huaping Wu; Linzhi Wu; Junfeng Hui; Xin Jin; Shanyi Du (pp. 4067-4074).

The effective biaxial modulus ( M_eff) and strain energy density ( W) of cubic polycrystalline films with ideally ( h k l) fiber textures are estimated using Vook–Witt (VW) grain interaction model and the data are compared with those derived from Voigt, Reuss and Voigt–Reuss–Hill (VRH) models. Numerical results show that the VW average of M_eff for ideally (100)- or (111)-fiber-textured films is identical to the VRH average of M_eff. For (110) and (112) planes, however, the VW average of M_eff for (110)-fiber-textured film is larger than that of (112)-fiber-textured film when the Zener anisotropic factor ( A_R) is not equal to 1. Furthermore, M_eff and W exhibit incremental tendencies with the increase of the orientation factor (Γ h k_l) for the [ h k l] axis when A_R>1, implying that M_eff and W have the minimums on the (100) plane. Reversely, M_eff and W decrease with the increasing Γ h k_l when A_R<1. This means that M_eff and W on (111) plane have the minimums.

Keywords: PACS; 68.35.Gy; 68.55.Jk; 81.40.Jj; 62.20.-xEffective biaxial modulus; Strain energy density; Vook–Witt grain interaction model; Fiber texture

Stabilization of catalytically active gold species in Fe-modified zeolites by N. Bogdanchikova; A. Simakov; E. Smolentseva; A. Pestryakov; M.H. Farias; J.A. Diaz; A. Tompos; M. Avalos (pp. 4075-4083).

The influence of iron additive on redox, electronic and catalytic properties of gold incorporated into zeolite catalysts has been studied by means of TEM, XPS, XRD, TPR, ICP and AES. The interaction of gold with iron modifier was observed in Y-zeolites and mordenites with different cations and method of Fe incorporation (impregnation or ion exchange). This interaction leads to mutual influence on redox properties of Fe and Au ionic species and facilitates their reduction. Limited diffusion of Au precursor after Fe species deposition in narrow mordenite channels does not permit to incorporate Au in adequate concentration, while in large super-cage of Y-zeolites this limitation is absent. The structure of Y-zeolites favors formation of active gold species. Catalytic tests in CO oxidation show that Fe additive stabilizes the gold active species active at low-temperature (partly charged clusters) and makes them insensitive to redox treatments.

Keywords: PACS; 36.40.Cg (electronic and magnetic properties of clusters); −82.80.Gk (analytical methods involving vibrational spectroscopy); −82.65.+r (surface and interface chemistry heterogeneous catalysis at surfaces)Gold; Iron additive; Zeolite; Nanoparticles; Impregnation; Ion exchange

Growth characteristics of plasma electrolytic oxidation ceramic coatings on Ti–6Al–4V alloy by Zhongping Yao; Yanli Jiang; Fangzhou Jia; Zhaohua Jiang; Fuping Wang (pp. 4084-4091).

The aim of this work is to discuss the growth characteristics of the ceramic coatings on Ti alloy by plasma electrolytic oxidation (PEO) technique. Ceramic coatings were prepared on Ti alloy by plasma electrolytic oxidation in different electrolyte solutions under different pulse modes. The composition and the structure of the coatings were investigated by X-ray diffraction and scanning electron microscopy (SEM), respectively. The amount of the dissolved titanium into the electrolytes during PEO process was measured by inductively coupled plasma-atomic emission spectrometer (ICP-AES). The structure and the composition of the coatings were related to the mode of the spark discharge during PEO process. (a) Under the pulsed single-polar mode: In Na₃PO₄ solution, the spark discharge was mainly due to the breakdown of the oxide film, and the coatings prepared were porous and mainly structured by the Ti from the substrate. In K₄ZrF₆–H₃PO₄ and NaAlO₂–Na₃PO₄ solutions, the main mode of the spark discharge was the breakdown of the oxide film at the initial stage, and then changed into the breakdown of the vapor envelope, and the coatings were rough and thick, and mainly structured by the elements from the electrolyte. (b) Under the pulsed bi-polar mode in NaAlO₂–Na₃PO₄ solution, the spark discharge may be mainly due to the breakdown of the oxide film, the coatings prepared were dense in inner layer and loose in outer layer, and structured by the elements from both the substrate and the electrolyte. Besides, the ICP-AES analyses showed that the amount of the dissolved titanium in the electrolyte during PEO process was more under the breakdown of the oxide film than under the breakdown of the vapor envelope, which was consistent with the changes of the structure of the coatings. Cathode pulse in the pulsed bi-polar mode increased the amount of the dissolved titanium in the electrolyte, compared with the pulsed single-polar one.

Keywords: Plasma electrolytic oxidation; Growth characteristics; Ti alloy; Ceramic coatings

Morphological investigation of nanostructured CoMo catalysts by B. Pawelec; P. Castaño; T.A. Zepeda (pp. 4092-4102).

This work reports the morphological investigation of nanostructured sulfided CoMo catalysts by means of high-resolution transmission electron microscopy (HRTEM). The catalysts were supported on Ti-modified hexagonal mesoporous silica (HMS-Ti) and P-modified HMS-Ti (P/HMS-Ti) materials. The oxide precursors were characterized by specific surface area (S_BET), temperature-programmed reduction (TPR), diffuse reflectance infrared Fourier transform spectroscopy in the OH region (DRIFTS-OH) and X-ray photoelectron spectroscopy (XPS) in order to elucidate the influence of the impregnation sequence (successive vs. simultaneous) and the effect of P-incorporation into HMS-Ti material on the morphology of calcined CoMo catalysts. Both TPR and XPS measurements indicate that the catalysts prepared by successive impregnation possess well-dispersed MoO₃ and CoO phases, whereas their counterparts prepared by simultaneous impregnation additionally possess the CoMoO₄ phase. For all sulfided catalysts, the presence of MoS₂ phase with particle size in the range 3.3–4.4nm was confirmed by HRTEM. Catalytic activity was evaluated in the reaction of hydrodesulfurization (HDS) of dibenzothiophene (DBT) carried out in a flow reactor at 593K and hydrogen pressure of 5.5MPa. P-incorporation into the HMS-Ti material led to an overall increase in HDS activity and the hydrogenation ability of the sulfided catalysts. All catalysts proved to be stable during 10h time-on-stream (TOS) operation. The activity of sulfide catalysts in the target reaction depends linearly on the surface exposure of Co species in the oxide precursors, as determined by XPS, and on the morphology of the sulfide form of catalysts (surface density of MoS₂ particles and their sizes) as determined by HRTEM.

Keywords: Surface modification; CoMo catalyst; Mesoporous silicas; TEM; Hydrodesulfurization; Dibenzothiophene

Development of phosphate inter layered hydroxyapatite coating for stainless steel implants by S.M.A. Shibli; A.C. Jayalekshmi (pp. 4103-4110).

As zinc phosphate acts as a versatile material for potential biomedical applications, it was modified into a thin layer coating for orthopaedic applications in the present study. A unique layering system consisting of pure substrate (316L SS), thick Fe–Zn alloy layers, thin ZnP layer on which a hydroxyapatite (HA) layer, was developed and studied. The composition, surface morphology and corrosion resistance characteristics of the layering system was evaluated. The stability of the multi-layered coating system consisting of ZnP inter layer, was evaluated by subjecting to different extent of dissolution in aggressive physiological media followed by allowing for re-growth in simulated body fluid (SBF). The coating system revealed good stability.

Keywords: Hot-dip galvanization; Conversion coating; Hydroxyapatite; Bioactivity; Phosphating

Effects of hydrogen and oxygen on the electrochemical corrosion and wear-corrosion behavior of diamond films deposited by hot filament chemical vapor deposition by C.K. Lee (pp. 4111-4117).

A diamond film was deposited on silicon substrate using hot filament chemical vapor deposition (HFCVD), and H₂ and O₂ gases were added to the deposition process for comparison. This work evaluates how adding H₂ and O₂ affects the corrosion and wear-corrosion resistance characteristics of diamond films deposited on silicon substrate. The type of atomic bonding, structure, and surface morphologies of various diamond films were analyzed by Raman spectrometry, X-ray diffraction (XRD) and atomic force microscopy (AFM). Additionally, the mechanical characteristics of diamond films were studied using a precision nano-indentation test instrument. The corrosion and wear-corrosion resistance of diamond films were studied in 1M H₂SO₄+1M NaCl solution by electrochemical polarization. The experimental results show that the diamond film with added H₂ had a denser surface and a more obvious diamond phase with sp³ bonding than the as-deposited HFCVD diamond film, effectively increasing the hardness, improving the surface structure and thereby improving corrosion and wear-corrosion resistance properties. However, the diamond film with added O₂ had more sp² and fewer sp³ bonds than the as-deposited HFCVD diamond film, corresponding to reduced corrosion and wear-corrosion resistance.

Keywords: Diamond film; HFCVD; Wear-corrosion; Electrochemical corrosion

Can surface preparation with CVD diamond tip influence on bonding to dental tissues? by Fernando Aparecido Kawaguchi; Sergio Brossi Botta; Samuel Nilo Vieira; Washington Steagall Júnior; Adriana Bona Matos (pp. 4118-4122).

This study evaluated the influence of chemical vapor deposition (CVD) tips surface treatments of enamel and dentin on bonding resistance of two adhesive systems. Thirty embedded samples were divided in 12 groups ( n=10), according to factors: substrate (enamel and dentin), adhesive system [etch-and-rinse (SB) and self-etch]; and the surface treatments (paper discs, impact CVD tips and tangential CVD tip). When CVD tip was used in the impact mode the tip was applied perpendicular to dental surface, while at tangential mode, the tip worked parallel to dental surface. Specimens were tested in tension after 24h at 0.5mm/min of cross-head speed. ANOVA results, in MPa showed that in enamel, only adhesive system factor was statistically significant ( p=0.015) under tested conditions, with higher bond strength observed for SB groups. However, in dentin the best bonding performance was obtained in SE groups ( p=0.00). In both tested substrates, results did not show statistically significant difference for factors treatment and its interactions.It may be concluded that CVD-tip surface treatment, in both tested modes, did not influence on adhesion to enamel and dentin. But, it is important to choose adhesive system according to the tissue available to bonding.

Keywords: PACS; 80; 81Dentistry; Cavity preparation; Chemical vapor deposition; Enamel; Dentin; Adhesion

Observing the effect of water vapor on post-irradiated surface morphology of SiO₂ and Si₃N₄ insulators by atomic force microscopy by You-Lin Wu; Jing-Jenn Lin; Chiung-Yi Huang; Shi-Tin Lin (pp. 4123-4127).

In this work, we investigated the effect of water-vapor treatment on the surface morphology of SiO₂ and Si₃N₄ insulators before and after Co⁶⁰ gamma-ray irradiation by using the atomic force microscopy (AFM) operated under non-contact mode. Before irradiation, no apparent surface morphology change was found in SiO₂ samples even they were water vapor treated. However, bright spots were found on post-irradiated water-vapor-treated SiO₂ sample surfaces but not on those without water-vapor treatment. We attributed the bright spots to the negative charge accumulation in the oxide due to charge balancing between hydroxyl (OH⁻) ions adsorbed on SiO₂ surface and electron–hole pairs (ehps) generated during irradiation since they can be annealed out after low temperature annealing process. On the contrary, no bright spots were observed on post-irradiated Si₃N₄ samples with and without water-vapor treatment. This result confirms that Si₃N₄ is a better water-resist passivation layer than SiO₂ layer.

Keywords: Passivation layer; Surface morphology; Irradiation; Atomic force microscopy

Calculation of surface energy and simulation of reconstruction for diamond cubic crystals (001) surface by Jian-Min Zhang; Hong-Yan Li; Ke-Wei Xu; Vincent Ji (pp. 4128-4133).

The energies of the ideal (1×1), dimer (2×1) and trimer (3×1) structures on (001) surfaces have been calculated by using MEAM for three diamond cubic crystals C, Si and Ge. From energy minimization, the dimer (2×1) and trimer (3×1) reconstructions can be formed naturally and without any barrier. The dimer corresponding to the lowest energy implies it is the easiest to be formed and the most stable as well. This is consistent with the experimental result and other theoretical prediction. Determined dimer bond length of 2.43Å for Si drops in the experimental range of 2.20–2.47Å, and of 2.5Å for Ge is close to the 2.55Å measured by X-ray diffraction. The trimer, constructed here firstly, has not been observed in the experimental due to its slightly higher energy than dimer. Its bond lengths have been determined to be 1.96, 2.64 and 2.75Å for C, Si and Ge, respectively. Further experimental testing is needed.

Keywords: Semiconductors; Surfaces; Microstructure; Electronic structure

Ir-based diffusion barriers for Ohmic contacts to p-GaN by L.F. Voss; L. Stafford; B.P. Gila; S.J. Pearton; F. Ren (pp. 4134-4138).

Ir-based electrical contacts to p-type GaN have been fabricated and characterized. Both GaN//Ni/Au/Ir/Au and GaN//Ni/Ir/Au contact structures were deposited, however, only the former produced Ohmic current–voltage characteristics. At an anneal temperature of 500°C, the Ni/Au/Ir/Au contact had a specific contact resistance of ∼2×10⁻⁴Ωcm², comparable or superior to conventional Ni/Au contacts that are less thermally stable. Anneal temperatures above 500°C caused the Ir-based contact to fail. Auger electron spectroscopy was used to obtain depth profiles of both types of contacts at a variety of temperatures in order to provide insight into the mechanism of Ohmic formation as well as potential reasons for failure. A comparison to other metallization schemes on p-GaN is also given.

Keywords: GaN; Ohmic contacts

Correlation of excitation-wavelength dependent photoluminescence with the fractal microstructures of porous silicon by Yuan Ming Huang; Bao-gai Zhai; Fu-fang Zhou (pp. 4139-4143).

The correlation of the excitation-wavelength dependent photoluminescence with the fractal microstructures of porous silicon has been investigated. As the excitation wavelength increases from 340 to 650nm, the photoluminescence of porous silicon redshifts from 500 to 780nm. The excitation-wavelength dependent photoluminescence suggests the existence of a size distribution for the large number of silicon nanocrystallites in porous silicon. Using scanning electron microscopy and computer simulation, we have investigated the fractal features of the microstructures of porous silicon. Our results have demonstrated that the fractal features in the microstructures of porous silicon indicate the existence of a size distribution for the silicon nanocrystallites in porous silicon. The recorded excitation-wavelength dependent photoluminescence of porous silicon can be interpreted in terms of the bond-order-length-strength correlation theory.

Keywords: PACS; 78.55.Mb; 78.55.Ap; 68.03.Hj; 68.55.AcPorous silicon; Fractals; Photoluminescence; Microstructure

A TiB₂ metal matrix composite coating enriched with nitrogen: Microstructure and wear properties by M. Darabara; L. Bourithis; S. Diplas; G.D. Papadimitriou (pp. 4144-4149).

Metal matrix composites containing titanium nitrides or titanium borides raise great interest to researchers due to their high wear resistance and enhanced corrosion properties. In the present investigation composite coatings containing both titanium nitrides/carbonitrides and titanium diborides were produced on plain steel substrates using the plasma transferred arc (PTA) technique with argon–nitrogen mixtures in the plasma and shielding gas. The microstructure of the metal matrix composites (MMC) obtained was thoroughly studied and found to consist of primary titanium diboride particles surrounded by a eutectic matrix containing, apart from ferrite, both titanium diboride and titanium carbonitride particles. The wear behavior of the composite coatings was assessed by pin on disk experiments. The wear rate against both a tool steel counterbody and an alumina counterbody is of the order of 10⁻⁴mm³/m. The friction coefficient for both the alloyed layer–tool steel system and the alloyed layer–alumina system increases up to sliding speed of 0.30m/s and then decreases, when the sliding speed increases further. Specifically, the friction coefficients are varied between the values 0.5 and 0.65. The wear mechanism for the tribosystem alloyed layer–tool steel is characterized by plastic deformation and adherence of material coming from the alloyed layer to the surface of the ball, while for the tribosystem alloyed layer–alumina ball, severe plastic deformation and formation of oxide layer are observed.

Keywords: Plasma transferred arc (PTA); Titanium diboride (TiB; ₂; ); Metal matrix composite (MMC); Titanium carbonitride Ti(C,N); Wear

XPS study of the formation of ultrathin GaN film on GaAs(100) by L. Bideux; G. Monier; V. Matolin; C. Robert-Goumet; B. Gruzza (pp. 4150-4153).

The nitridation of GaAs(100) surfaces has been studied using XPS spectroscopy, one of the best surface sensitive techniques. A glow discharge cell was used to produce a continuous plasma with a majority of N atomic species. We used the Ga3d and As3d core levels to monitor the chemical state of the surface and the coverage of the species. A theoretical model based on stacked layers allows to determine the optimal temperature of nitridation. Moreover, this model permits the determination of the thickness of the GaN layer. Varying time of nitridation from 10min to 1h, it is possible to obtain GaN layers with a thickness between 0.5nm and 3nm.

Keywords: XPS; Gallium arsenide; Gallium nitride; Semiconductor–semiconductor thin film structure; Heterojunctions

Preparation of TiO₂–carbon surface composites with high photoactivity by supercritical pretreatment and sol–gel processing by Youji Li; Mingyuan Ma; Shuguo Sun; Wenbin Yan; Yuzhu Ouyang (pp. 4154-4158).

TiO₂–carbon surface (TCS) composites were prepared by pretreatment of a sealing substrate in supercritical carbon dioxide using paraffin as a plugging agent, and sol–gel processing using tetrabutyl orthotitanate as a precursor. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectrum (XPS), optical absorption spectroscopy and nitrogen absorption. The photoactivity of TCS was checked by monitoring the decomposition of methylene blue (MB) in aqueous solution under UV irradiation. The results indicated that compared with TC prepared only by the sol–gel method, the small nanosize TiO₂ particles are well dispersed on carbon surface with large amount of micropores and high Eg values, meanwhile TCS have high Ti³⁺ concentration due to supercritical pretreatment providing a amount of carbon on the composite surface with interfacial energy effects, which controls the growth of TiO₂ nanoparticles, baffles the agglomeration of TiO₂ nanoparticles and easily produces Ti³⁺ ions. These are reasons why TCS has a higher efficiency of decomposing MB than TiO₂–carbon (TC) composites and pure TiO₂. Additional, it is also attributed to the fact that TCS produce a high concentration of organic compounds near TiO₂ in comparison with TC and pure TiO₂, because their surface area are greater than that of TC and pure TiO₂.

Keywords: Titanium dioxide; Carbon surface; Catalysts; Supercritical; Sol–gel preparation

Immobilization of quaternary ammonium salts on grafting particle polystyrene/SiO₂ and preliminary study of application performance by Baojiao Gao; Changsheng Qi; Qing Liu (pp. 4159-4165).

Polystyrene (PSt) was grafted on the surface of silica gel particles in the manner of “grafting from” in a solution polymerization system, and grafting particles PSt/SiO₂ was obtained. The chloromethylation reaction of the grafted polystyrene was performed using a novel chloromethylation reagent, 1,4-bis(chloromethyoxy)butane which is un-carcinogenic, and grafting particles CMPS/SiO₂ was gained. Subsequently, grafted CMPS was quaternized (denoted as QPS) using tertiary amine, and finally functional composite-type particles QPS/SiO₂, on which quaternary ammonium groups were immobilized, were prepared. The catalysis activity of the particle QPS/SiO₂ as a triphase catalyst in phase-transfer catalysis systems and its antibacterial activity as a water-insoluble antibacterial material were studied preliminarily. The experimental results show that the particle QPS/SiO₂ exhibits higher catalysis activity as a triphase catalyst for the reaction between benzyl chloride in organic phase and sodium acetate in aqueous phase to form benzyl acetate, and under a mild condition of 60°C for 7h of reaction time a conversion of 66% for benzyl chloride can be obtained. The particle QPS/SiO₂ has high antibacterial activity as a water-insoluble antibacterial material against Escherichia coli ( E. coli).

Keywords: Quaternary ammonium salt; Immobilization; Polystyrene; Grafting; Triphase catalysis; Antibacterial

Fabrication, morphology, and photoluminescence properties of GaN nanowires and nanorods by ammoniating Ga₂O₃/V films on Si(111) by Zhaozhu Yang; Chengshan Xue; Huizhao Zhuang; Lixia Qin; Jinhua Chen; Hong Li; Dongdong Zhang (pp. 4166-4170).

GaN nanowires and nanorods have been successfully synthesized on Si(111) substrates by magnetron sputtering through ammoniating Ga₂O₃/V films at 900°C in a quartz tube. X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) spectrum were carried out to characterize the structure, morphology, and photoluminescence properties of GaN sample. The results show that the GaN nanowires and nanorods with pure hexagonal wurtzite structure have good emission properties. The growth direction of nanostructures is perpendicular to the fringes of (101) plane. The growth mechanism is also briefly discussed.

Keywords: PACS; 68.65.−k; 71.55.Eq; 81.15.CdGaN; Magnetron sputtering; Ammoniating; VLS mechanism

Effects of rf power on surface-morphological, structural and electrical properties of aluminium-doped zinc oxide films by magnetron sputtering by Dengyuan Song (pp. 4171-4178).

Aluminium-doped zinc oxide (ZnO:Al) films were prepared by magnetron sputtering at different radio-frequency powers ( P_rf) of 50, 100, 150 and 200W. The properties of the films were characterised by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), Raman microscopy, and spectrophotometry with the emphasis on the evolution of compositional, surface-morphological, optical, electrical and microstructural properties. XPS spectra showed that within the detection limit the films are chemically identical to near-stoichiometric ZnO. AFM revealed that root-mean-square roughness of the films has almost linear increase with increasing P_rf. Optical band gap E_gopt of the films increases from 3.31 to 3.51eV when P_rf increases from 50 to 200W. A widening E_gopt of the ZnO:Al films compared to the band gap (∼3.29eV) of undoped ZnO films is attributed to a net result of the competition between the Burstein–Moss effect and many-body effects. An electron concentration in the films was calculated in the range of 3.73×10¹⁹ to 2.12×10²⁰cm⁻³. Raman spectroscopy analysis indicated that well-identified peaks appear at around 439cm⁻¹ for all samples, corresponding to the band characteristics of the wurtzite phase. Raman peaks in the range 573–579cm⁻¹ are also observed, corresponding to the A₁ (LO) mode of ZnO.

Keywords: Al-doped zinc oxide; Sputtering; X-ray photoelectron spectroscopy; Raman spectroscopy

Structural and electrical properties of zinc oxides thin films prepared by thermal oxidation by Mihaela Girtan; G.G. Rusu; Sylvie Dabos-Seignon; Mihaela Rusu (pp. 4179-4185).

We report on zinc oxide (ZnO) thin films ( d=55–120nm) prepared by thermal oxidation, at 623K, of metallic zinc films, using a flash-heating method. Zinc films were deposited in vacuum by quasi-closed volume technique onto unheated glass substrates in two arrangements: horizontal and vertical positions relative to incident vapour. Depending on the preparation conditions, both quasi-amorphous and (002) textured polycrystalline ZnO films were obtained. The surface morphologies were characterized by atomic force microscopy and scanning electron microscopy. By in situ electrical measurements during two heating–cooling cycles up to a temperature of 673K, an irreversible decrease of electrical conductivity of as flash-oxidized Zn films was revealed. The influence of deposition arrangement and oxidation conditions on the structural, morphological and electrical properties of the ZnO films is discussed.

Keywords: PACS; 61.10.Nz; 68.37.Ef; 68.37.Ps; 72.80.−rVacuum deposition; ZnO; Thin films; XRD; Electrical conductivity

The influence of oxidation temperature on structural, optical and electrical properties of thermally oxidized bismuth oxide films by T.P. Gujar; V.R. Shinde; C.D. Lokhande (pp. 4186-4190).

Monoclinic bismuth oxide (Bi₂O₃) films have been prepared by thermal oxidation of vacuum evaporated bismuth thin films onto the glass substrates. In order to obtain the single phase Bi₂O₃, the oxidation temperature was varied in the range of 423–573K by an interval of 50K. The as-deposited bismuth and oxidized Bi₂O₃ films were characterized for their structural, surface morphological, optical and electrical properties by means of X-ray diffraction, scanning electron microscopy (SEM), optical absorption and electrical resistivity measurements, respectively. The X-ray analyses revealed the formation of polycrystalline mixed phases of Bi₂O₃ (monoclinic, α-Bi₂O₃ and tetragonal, β-Bi₂O₃) at oxidation temperatures up to 523K, while at an oxidation temperature of 573K, a single-phase monoclinic α-Bi₂O₃ was formed. From SEM images, it was observed that of as-deposited Bi films consisted of the well-defined isolated crystals of different shapes while after thermal oxidation the smaller dispersed grains were found to be merged to form bigger grains. The changes in the optical properties of Bi₂O₃ films obtained by thermal oxidation at various temperatures were studied from optical absorption spectra. The electrical resistivity measurement depicted semiconducting nature of Bi₂O₃ with high electrical resistivity at room temperature.

Keywords: Bi; ₂; O; ₃; thin film; Thermal oxidation; Structural; Surface morphology; Optical and electrical properties

Surface modification of polystyrene with atomic oxygen radical anions-dissolved solution by Lian Wang; Lifeng Yan; Peitao Zhao; Yoshifumi Torimoto; Masayoshi Sadakata; Quanxin Li (pp. 4191-4200).

A novel approach to surface modification of polystyrene (PS) polymer with atomic oxygen radical anions-dissolved solution (named as O⁻ water) has been investigated. The O⁻ water, generated by bubbling of the O⁻ (atomic oxygen radical anion) flux into the deionized water, was characterized by UV-absorption spectroscopy and electron paramagnetic resonance (EPR) spectroscopy. The O⁻ water treatments caused an obvious increase of the surface hydrophilicity, surface energy, surface roughness and also caused an alteration of the surface chemical composition for PS surfaces, which were indicated by the variety of contact angle and material characterization by atomic force microscope (AFM) imaging, field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), and attenuated total-reflection Fourier transform infrared (ATR-FTIR) measurements. Particularly, it was found that some hydrophilic groups such as hydroxyl (OH) and carbonyl (CO) groups were introduced onto the polystyrene surfaces via the O⁻ water treatment, leading to the increases of surface hydrophilicity and surface energy. The active oxygen species would react with the aromatic ring molecules on the PS surfaces and decompose the aromatic compounds to produce hydrophilic hydroxyl and carbonyl compounds. In addition, the O⁻ water is also considered as a “clean solution” without adding any toxic chemicals and it is easy to be handled at room temperature. Present method may suit to the surface modification of polymers and other heat-sensitive materials potentially.

Keywords: Polystyrene; O; ⁻; water; Surface modification; Hydrophilicity

Effects of laser fluence on near-field surface nanostructuring by Xuhui Feng; Xinwei Wang (pp. 4201-4210).

In this work, molecular dynamics simulation is performed to explore the long-time (up to 5ns) behavior of argon crystal in surface nanostructuring with an extremely localized near-field laser beam. The surface nanostructuring region is limited to tens of nanometers in diameter, although the simulated systems are much larger (comprised of more than 770,000 atoms). This study focuses on the long-time solidification and crystallization procedure, which is driven by the heat conduction in the material. The effect of the computational domain on the final nanostructure is studied in detail. Different laser fluences are used in the simulation to explore how and to what extent the energy input affects the dynamic melting behavior and the final dimension and profile of the surface nanostructure. In-depth theoretical investigation gives satisfactory explanation of the effect of the laser fluence on the melting depth. Spot-like structural defects in the sub-surface region are observed and investigated until full solidification.

Keywords: Effect of laser fluence; Surface nanostructuring; Molecular dynamics simulation

Photonic quantum dots based on Bragg reflectors grown by conformal deposition on patterned substrates by San Chen; Bo Qian; Kunji Chen; Xiangao Zhang; Jun Xu; Zhongyuan Ma; Wei Li; Xinfan Huang (pp. 4211-4215).

A new approach, that combines the photolithography and conformal deposition techniques, was proposed to fabricate Si-based three-dimensional optical microcavities on patterned substrates. Different from the lateral optical confinement of 3D microcavities by using total internal reflection, Bragg reflectors are used for all three-dimensional optical confinement. From the room temperature photoluminescence spectra, discrete optical modes with obvious side-dependence were observed. With the lateral size decreased from 4.5μm to 1.5μm, the modes shift to higher energies and the mode splitting increases, which indicates that 3D optical microcavities act like photonic quantum dots. The numerical calculations of quantized photon states in photonic quantum dots show a quantitative agreement with these observed discrete optical eigenmodes.

Keywords: Microcavity; Photonic quantum dot; Conformal coverage

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Applied Surface Science (v.254, #13)

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Applied Surface Science (v.254, #13)