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Applied Surface Science (v.255, #21)

Transformation of medical grade silicone rubber under Nd:YAG and excimer laser irradiation: First step towards a new miniaturized nerve electrode fabrication process by C. Dupas-Bruzek; O. Robbe; A. Addad; S. Turrell; D. Derozier (pp. 8715-8721).

Medical grade silicone rubber, poly-dimethylsiloxane (PDMS) is a widely used biomaterial. Like for many polymers, its surface can be modified in order to change one or several of its properties which further allow this surface to be functionalized. Laser-induced surface modification of PDMS under ambient conditions is an easy and powerful method for the surface modification of PDMS without altering its bulk properties. In particular, we profit from both UV laser inducing surface modification and of UV laser micromachining to develop a first part of a new process aiming at increasing the number of contacts and tracks within the same electrode surface to improve the nerve selectivity of implantable self sizing spiral cuff electrodes. The second and last part of the process is to further immerse the engraved electrode in an autocatalytic Pt bath leading in a selective Pt metallization of the laser irradiated tracks and contacts and thus to a functionalized PDMS surface. In the present work, we describe the different physical and chemical transformations of a medical grade PDMS as a function of the UV laser and of the irradiation conditions used. We show that the ablation depths, chemical composition, structure and morphology vary with (i) the laser wavelength (using an excimer laser at 248nm and a frequency-quadrupled Nd:YAG laser at 266nm), (ii) the conditions of irradiation and (iii) the pulse duration. These different modified properties are expected to have a strong influence on the nucleation and growth rates of platinum which govern the adhesion and the thickness of the Pt layer on the electrodes and thus the DC resistance of tracks.

Keywords: Poly-dimethylsiloxane; Silicone rubber; Irradiation and laser ablation; Physical and chemical transformation

The role of Pb²⁺ ions doping in the mechanism of chromate adsorption by goethite by Syed Mustafa; Sadullah Khan; Muhammad Iqbal Zaman; Samad Yar Husain (pp. 8722-8729).

Pure and 0.384% Pb²⁺ ions doped goethite samples were prepared in the laboratory by the coprecipitation method. The laboratory-prepared goethite samples were characterized for pH of point of zero charge (pH_pzc), surface area, XRD, TG-DTA, TEM, SEM and FTIR analysis, which suggest that the Pb²⁺ ions are incorporated into the crystals of goethite and are also present on the surface in the hydroxylated form. Chromate adsorption studies were carried out in the concentration range 0.25–2.01mmolL⁻¹ at pH 3, 5 and 7, which show that maximum chromate is adsorbed at the lowest pH of 3 by both the samples of goethite. Effect of temperature on the adsorption of chromate, in the range 303–323K, shows that the process of adsorption is endothermic in case of pure goethite and exothermic in case of Pb-doped goethite. The values of isosteric heat of adsorption(ΔH¯) were positive for pure goethite and negative for Pb-doped goethite, which are consistent with the effect of temperature on the process of adsorption. Langmuir isotherm was found applicable to the experimental data. FTIR analysis and equilibrium pH changes reveal that at pH 3 outersphere while at pH 5 and 7 innersphere complexation is the dominant mechanism for chromate adsorption by both the samples of goethite.

Keywords: Pb; ²⁺; ions doping; Goethite; Chromate adsorption; Langmuir isotherm; Isosteric heat

Optical emission spectroscopic studies on laser ablated TiO₂ plasma by Gaurav Shukla; Alika Khare (pp. 8730-8737).

Optical emission spectroscopic investigations of the plasma produced during Nd:YAG laser ablation of sintered TiO₂ targets, in oxygen and argon gas environments are reported. The spatial variations of electron temperature ( T_e) and electron number density ( N_e) are studied. The effect of oxygen/argon pressure on electron temperature ( T_e) and electron number density ( N_e) is presented. The kinematics of the emitted particles and expansion of plume edge are discussed. Spatio-temporal variations of various species in TiO₂ plasma were recorded and corresponding velocities were calculated. The effect of oxygen pressure on intensity of neutral/ion species and their corresponding velocities is also reported.

Keywords: PACS; 32.30.Jc; 32.70.JzOptical emission spectroscopy; Laser produced plasma; Stark broadening; Titanium oxide; Pulsed laser ablation

Towards chemical state resolution in regularized depth profiles derived from ARXPS data taken on plasma-oxidized polystyrene by R.W. Paynter (pp. 8738-8742).

ARXPS data obtained from a plasma-oxidized polystyrene sample were evaluated by means of 3-parameter and 10-parameter depth profile models, with and without regularization. It was found that the partially regularized 3-parameter model gave equivalent results compared to the regularized 10-parameter model, but requiring one fifteenth of the computational effort.

Keywords: Angle-resolved X-ray photoelectron spectroscopy; Polymer surface; Tikhonov regularization

Formation of single-crystalline TiO₂ nanomaterials with controlled phase composition and morphology and the application in dye-sensitized solar cell by Yuanmei Xu; Xiaoming Fang; Zhengguo Zhang (pp. 8743-8749).

Single-crystalline TiO₂ nanomaterials with controlled phase composition and morphology were synthesized by hydrothermal transformation of H-titanate nanotubes under different pH. Rutile rectangle nanorods with two four-side tapered tips were produced at pH of 0, whereas anatase nanoparticles with mainly of rhombic shape were obtained at pH from 2 to 7 and their average particle size increased with pH. The transformation mechanisms at different pH were discussed. The single-crystalline anatase nanoparticles obtained at pH of 2 had ca. 12nm in average particle size, and the powder possessed as large as 112m²/g specific surface areas; the conversion efficiency of the dye-sensitized solar cell based on the nanoparticles was increased by over 40% as compared with that of the cell based on P25.

Keywords: TiO; ₂; Nanomaterials; Single-crystalline; Hydrothermal transformation; Dye-sensitized solar cells

Comparative XPS study between experimentally and naturally weathered pyrites by Yuanfeng Cai; Yuguan Pan; Jiyue Xue; Qingfeng Sun; Guizhen Su; Xiang Li (pp. 8750-8760).

A comparative study has been carried out between experimentally and naturally weathered pyrites. Both were found to share similar species of weathering products and a similar weathering mechanism. The weathering products could be divided into sulphur-bearing or iron-bearing groups. The sulphur-bearing group was comprised of sulphate, sulphite, thiosulphate, elemental sulphur, polysulphide, and mono-sulphide. The iron-bearing group was comprised of goethite, hematite or magnetite, and iron sulphate. The weathering structural profile was also similar for both types of weathering, being composed of a surficial layer and a transitional layer. The surficial layer was made up of both the sulphur-bearing and the iron-bearing products, while the transitional layer was comprised of goethite, and hematite or magnetite. The inward migration of the weathering interface was stimulated by the diffusion of oxygen and moisture. The oxygen was considered to preferably squeeze the iron to form goethite, and the ferric ions of goethite to have acted as a bridge for electron transfer between the oxygen and bulk S₂²⁻ and Fe²⁺ of pyrite.

Keywords: Keyword; Weathered pyrite; XPS; Surficial layer

Effect of deposition temperature on boron-doped carbon coatings deposited from a BCl₃–C₃H₆–H₂ mixture using low pressure chemical vapor deposition by Yongsheng Liu; Litong Zhang; Laifei Cheng; Wenbin Yang; Yongdong Xu (pp. 8761-8768).

A mixture of propylene, hydrogen and boron trichloride was used to fabricate boron-doped carbon coatings by using low pressure chemical vapor deposition ( LPCVD) technique. Effect of deposition temperature on deposition rate, morphologies, compositions and bonding states of boron-doped carbon coatings was investigated. Below 1273K, the deposition rate is controlled by reaction dynamics. The deposition rate increases with increasing deposition temperature. The activation energy is 208.74kJ/mol. Above 1273K, the deposition rate decreases due to smaller critical radius r_c and higher nuclei formation rate J with increasing temperature. Scanning electron microscopy shows that the structure changes from glass-like to nano-laminates with increasing deposition temperature. The boron concentration decreases with increasing deposition temperature, corresponding with increasing carbon concentration. The five types of bonding states are B–C, B-sub-C, BC₂O, BCO₂ and B–O. B-sub-C and BC₂O are the main bonding states. The reactions are dominant at all temperatures, in which the B-sub-C and PyC are formed.

Keywords: Deposition temperature; Boron-doped carbon; LPCVD; Morphologies; Bonding states

Self-assembled monolayers of radical molecules physisorbed on HOPG(0001) substrate studied by scanning tunnelling microscopy and electron paramagnetic resonance techniques by P. Krukowski; Z. Klusek; W. Olejniczak; R. Klepaczko; M. Puchalski; P. Dabrowski; P.J. Kowalczyk; K. Gwozdzinski (pp. 8769-8773).

In this paper, we present a combined STM and EPR study on the adsorption and self-organization of monolayers formed from 2-(14-Carboxytetradecyl)-2-ethyl-4,4-dimethyl-3-oxazolidinyloxy (16DS) and 4′,4′-Dimethylspiro(5α-cholestane-3,2′-oxazolidin)-3′-yloxy (CSL) adsorbed on a highly oriented pyrolitic graphite HOPG(0001) substrate. Both 16DS and CSL molecules are persistent free radicals containing a paramagnetic doxyl group. The STM measurements of 16DS on HOPG(0001) were performed at the liquid–solid interface while the studies of CSL on HOPG(0001) were carried out under ultrahigh vacuum conditions. It was found that the 16DS molecules on the HOPG(0001) surface form a highly-ordered monolayer with a domain structure. The high-resolution STM images show structural details of 16DS molecules on HOPG(0001) revealing the paramagnetic doxyl group. In contrast, CSL molecules on HOPG(0001) form a well-ordered monolayer without domain structure. The EPR results indicate that both compounds deposited on HOPG(0001) substrate are not reduced and retain their paramagnetic character. We believe that the molecular systems described can be used in single spin detection experiments using an electron spin noise-scanning tunnelling microscopy (ESN-STM) technique. In particular, the possibility of obtaining contrast spin signals from the paramagnetic and diamagnetic parts of molecules increases the significance of our results.

Keywords: PACS; 76.30.−v; 75.75.+a; 07.79.CzSTM; HOPG; Radicals; Self-assembled monolayer

Water-dispersible hydroxyapatite nanorods synthesized by a facile method by Junjun Tan; Minfang Chen; Jiaoyang Xia (pp. 8774-8779).

A simple and effective method, using calcium nitrate and triammonium phosphate as starting materials, for the preparation of water-dispersible hydroxyapatite nanorods (HAp) was reported. The process primarily involves the preparation of HAp with the addition of sodium citrate (NaC) and the exchange of absorbed ions (NaC) with sodium hexame taphosphate (NaP). The end products were investigated using various means in order to confirm the particles’ crystal phase and morphology and to understand how to improve their stability. The results demonstrate that the resulting HAp at 90°C is rod-like with length of 300–400nm and width of 40–60nm. The zeta potential values of pure HAp, HAp–NaC, HAp–NaC/NaP are from −15.20, −30.89 to −44.84mV. The settling time test shows the HAp–NaC/NaP could keep stable above 7 months without any creaming or visible sedimentation. The amount of NaC and the reaction temperature play significant roles in the whole process due to the formation of Ca containing precipitates.

Keywords: Hydroxyapatite nanorods; Aqueous colloid; Colloid stability; The zeta potential

Introduction of amino groups on the surface of thin photo definable epoxy resin layers via chemical modification by David Schaubroeck; Johan De Baets; Tim Desmet; Sandra Van Vlierberghe; Etienne Schacht; André Van Calster (pp. 8780-8787).

The introduction of amine groups on the surface of dielectric resins improves the adhesion with electrochemically deposited metals. In this work, etched epoxy resin surfaces are modified with aliphatic amines via a two step wet chemical reaction approach. First, cyanuric chloride is introduced on the surface. Next, the remaining reactive sites of cyanuric chloride are used to couple an aliphatic polyamine. Both reaction steps are optimized by variation of reaction parameters such as concentration, chemicals, temperature and time. A detailed surface characterization after each reaction step is provided using following techniques: ATR-IR, SEM–EDS, XPS and AFM.

Keywords: Surface modification; Cyanuric chloride; Epoxy cresol novolac resin

Microstructure and tribological properties of TiN, TiC and Ti(C, N) thin films prepared by closed-field unbalanced magnetron sputtering ion plating by Guojun Zhang; Bin Li; Bailing Jiang; Fuxue Yan; Dichun Chen (pp. 8788-8793).

TiN, TiC and Ti(C, N) films have been respectively prepared using closed-field unbalanced magnetron sputtering ion plating technology, with graphite target serving as the C supplier in an Ar–N₂ mixture gas. Bonding states and microstructure of the films are characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) in combination with transmission electron microscopy (TEM). The friction coefficients are measured by pin-on-disc test and the wear traces of deposited films are observed by optical microscope. Results show that the TiN film and Ti(C, N) film exhibit dense columnar structure while the TiC film exhibits a mixed microstructure of main nanocrystallite and little amorphous phases. The Ti(C, N) film has the highest microhardness value and the TiC film has the lowest. Because of small amount of pure carbon with sp² bonds existing in the film, the friction coefficients of Ti(C, N) and TiC multilayer films are lower than that of TiN film. In addition, the multilayer structure of films also contributes visually to decrease of friction coefficients. The TiC film has extremely low friction coefficient while the wear ratio is the highest in all of the films. The results also show that the Ti(C, N) film has excellent anti-abrasion property.

Keywords: Microstructure; Tribological property; Ti(C, N); Magnetron sputtering

Structural, optical, and electronic properties of colloidal CuO nanoparticles formed by using a colloid-thermal synthesis process by Dong Ick Son; Chan Ho You; Tae Whan Kim (pp. 8794-8797).

Colloidal cupric oxide (CuO) nanoparticles were formed by using a colloid-thermal synthesis process. X-ray diffraction patterns, transmission electron microscopy (TEM) images, high-resolution TEM images, and X-ray energy dispersive spectrometry profiles showed that the colloidal CuO nanoparticles were formed. The optical band-gap energy of CuO nanoparticles at 300K, as determined from the absorbance spectrum, was 3.63eV. A photoluminescence spectrum at 300K showed that a dominant emission peak appeared at the blue region. X-ray photoelectron spectroscopy profiles showed that the O 1s and the Cu 2p peaks corresponding to the CuO nanoparticles were observed.

Keywords: PACS; 78.55.Et; 78.66.Sq; 78.67.BfColloidal CuO nanoparticles; Structural properties; Optical properties; Electronic properties

Chemical modification of silica gel with synthesized new Schiff base derivatives and sorption studies of cobalt (II) and nickel (II) by Ahmed Nuri Kursunlu; Ersin Guler; Hakan Dumrul; Ozcan Kocyigit; Ilkay Hilal Gubbuk (pp. 8798-8803).

In this study, three Schiff base ligands and their complexes were synthesized and characterized by infrared spectroscopy (IR), thermogravimetric analyses (TGA), nuclear magnetic resonance (NMR), elemental analysis and magnetic susceptibility apparatuses. Silica gel was respectively modified with Schiff base derivatives, (E)-2-[(2-chloroethylimino)methyl]phenol, (E)-4-[(2-chloroethylimino)methyl]phenol and N, N′-[1,4-phenilendi(E)methylidene]bis(2-chloroethanamine), after silanization of silica gel by (3-aminopropyl)trimethoxysilane (APTS) by using a suitable method. Characterization of the surface modification was also performed with IR, TGA and elemental analysis. The immobilized surfaces were used for Co(II) and Ni(II) sorption from aqueous solutions and values of sorption were detected by atomic absorption spectrometer (AAS).

Keywords: Schiff base; Synthesis; Sorption isotherm; Modification

Crystalline structure of the Au(111) surface revealed by stereographic intensity DEPES maps by M. Jurczyszyn; A. Miszczuk; Ł. Poczęsny; I. Morawski; M. Nowicki (pp. 8804-8808).

The intensity of elastically backscattered electrons at the primary electron beam energy 1.9keV was used to obtain a stereographic map of Au(111) by means of the directional elastic peak electron spectroscopy (DEPES). An experimental result is compared with the theoretical data obtained by using multiple scattering calculations (MS) performed for both not-reconstructed and model-reconstructed clusters. The lateral lattice misfit of the first layer leads to quantitative changes of theoretical intensities showing a sensitivity of DEPES to the short atomic chain axial order. This comparison proves that a main contribution of the experimental contrast originates from a higher background level. Moreover an anisotropy of the inelastic mean free path is discussed in the paper.

Keywords: Electron scattering; Multiple scattering (MS) approximation; Inelastic mean free path (IMFP); Directional elastic peak electron spectroscopy (DEPES); GoldPACS; 91.60Ed, 91.55.Nc, 61.05.jd

Atomistic simulation of the vacancy diffusion in (001) surface of MoTa alloy by Fang Wang; Jian-Min Zhang; Ke-Wei Xu; Vincent Ji (pp. 8809-8815).

The formation and diffusion of a single Mo or Ta vacancy in the (001) surface of the B₂-type MoTa alloy have been investigated by using modified analytical embedded-atom method (MAEAM). The results show that the effect of the surface on the vacancy is only down to the sixth layer. It is easier for the vacancy to form in the first layer. Comparing the migration energy of the vacancy migrating in the intra-layer, to the upper layer and to the nether layer via 2NN jump, we find that the vacancy in the first or second layer is preferred to migrate in intra-layer, and that in the third or fourth layer is favorable to migrate to the upper layer. Although 1NN jump will result in an anti-site so that a disorder in the order alloy, it may also occur due to the much lower migration energy especially for the vacancy in the second and third layer to migrate to the first and second layer, respectively.

Keywords: Vacancy; Diffusion; Surface; MAEAM

Influence of the electrical parameters on the fabrication of copper nanowires into anodic alumina templates by Rosalinda Inguanta; Salvatore Piazza; Carmelo Sunseri (pp. 8816-8823).

Metallic copper nanowires have been grown into the pores of alumina membranes by electrodeposition from an aqueous solution containing CuSO₄^.and H₃BO₃ at pH 3. In order to study the influence of the electrical parameters on growth and structure of nanowires, different deposition potentials (both in the region where hydrogen evolution reaction is allowed or not) and voltage perturbation modes (constant potential or unipolar pulsed depositions) were applied. In all cases, pure polycrystalline Cu nanowires were fabricated into template pores, having lengths increasing with the total deposition time. These nanowires were self-standing, because they retain their vertical orientation and parallel geometry even after total template dissolution.However, the electrical parameters influence the growth rate, length uniformity and crystal size of the nanowires. Continuous electrodeposition resulted in higher growth rates but less uniform lengths of nanowires grown inside different membrane pores, whilst a square pulse deposition produced a slower growth but quite uniform lengths. Also the grain size, of the order of 50nm, was slightly influenced by the potential perturbation mode.

Keywords: Copper nanowires; Anodic alumina membranes; Electrodeposition; Self-standing structures

Self-assembled monolayer and multilayer formation using redox-active Ru complex with phosphonic acids on silicon oxide surface by Takao Ishida; Kei-ichi Terada; Kiichi Hasegawa; Hironao Kuwahata; Kazunori Kusama; Ryo Sato; Miki Nakano; Yasuhisa Naitoh; Masa-aki Haga (pp. 8824-8830).

The formation of self-assembled monolayer and multilayer using redox-active Ru complex molecules with phosphonic acids on SiO₂ surface has been examined using X-ray photoelectron spectroscopy (XPS), ellipsometry, and time of flight secondary mass-ion spectroscopy (TOF-SIMS). We found that an introduction of a Zr adlayer leads to higher surface molecular density of Ru complex SAMs on the SiO₂ surface, compared to that of obtained from the direct adsorption of Ru complex monolayer on the SiO₂ surface. We further tried to fabricate a multilayer film using this molecule with Zr(IV) ion acting as a chemical glue by a successive immersion process. The XPS data revealed that the molecular densities of the multilayers were also higher for the immobilization with Zr adlayer between Ru complex and SiO₂ surface than those without the Zr adlayer, suggesting that Zr adlayer is effective in forming highly packed molecular layer of phosphonic acids on SiO₂ surface. We found the film growth reached a saturation point after 6 layers on the SiO₂ surface. The film growth saturation can be explained by a molecular domain boundary effect encountered due to the large tilt angle of the molecular layer.

Keywords: Self-assembly; Silicon oxide; XPS; Molecular architecture

CO–H₂–O₂ reaction on a catalytic surface: A computer simulation study by Waqar Ahamd (pp. 8831-8835).

The oxidation of carbon monoxide to form carbon dioxide and the oxidation of hydrogen to form water are the reactions of environmental and industrial importance. These two reactions have been studied independently by Monte Carlo computer simulation using Langmuir–Hinshelwood mechanism but no effort has been made to study the combined CO–H₂–O₂ reaction on these lines. Keeping in view the importance of this 3-component system, the surface coverages and production rates are studied as a function of CO partial pressure for different ratios of H₂ and O₂. The diffusion of reacting species on the surface as well as their desorption from the surface is also introduced to include temperature effects. The phase diagrams of the system are drawn to observe the behavior of these atoms/molecules on the surface and the production of CO₂ and H₂O are determined at different concentrations of H₂. The results are compared with 2-component systems.

Keywords: PACS; 82.65.+ r; 82.20. Wt; 83.10. Rs; 02.70. UuCatalytic surfaces; Reaction rates; Computer simulation; Phase diagrams; Desorption

Influence of treating frequency on microstructure and properties of Al₂O₃ coating on 304 stainless steel by cathodic plasma electrolytic deposition by Yunlong Wang; Zhaohua Jiang; Xinrong Liu; Zhongping Yao (pp. 8836-8840).

Alumina ceramic coatings were fabricated on 304 stainless steel by cathodic plasma electrolytic deposition (CPED). Influence of treating frequency of the power supply on the microstructure and properties of the coatings were studied. The results indicated that coatings obtained at various frequencies on 304 stainless steels were all composed of α-Al₂O₃ and γ-Al₂O₃, and α-Al₂O₃ was the dominant phase. The contents of α-Al₂O₃ decreased gradually in a very small rate with increasing the frequency and γ-Al₂O₃ gradually increased. The surface of alumina ceramic coating was porous. With increasing the frequency, the coating surface gradually became less rough and more compact, resulting in low surface roughness. The bonding strength of Al₂O₃ coating was higher than 22MPa and was not strongly affected by treating frequency. With increasing the frequency, the alumina coated steels showed better and gradually increasing corrosion resistance than the uncoated one in 3.5% NaCl solution. The coating steel with desirable corrosion resistance was obtained at 800Hz whose corrosion current potential and corrosion density were −0.237V and 7.367×10⁻⁸A/cm², respectively.

Keywords: Cathodic plasma electrolytic deposition; Alumina ceramic coating; Stainless steel; Corrosion

Optical emission analysis of solid samples by decoupled sputtering/excitation using a low fluence laser synchronized with a pulsed glow discharge by K.A. Tereszchuk; J.M. Vadillo; J.J. Laserna (pp. 8841-8845).

The use of a microsecond-pulsed glow discharge, synchronized with an ablation laser operating under breakdown fluence, assists in the excitation of the ablated material generated during the analysis. With the glow discharge operating in pulsed mode, it is possible to synchronize accurately both sources to maximize the signal. Additionally, both sources can be independently adjusted to optimize the sample removal and its excitation. By means of the decoupling approach, typical laser energies required for detectable emission signals can effectively be lowered below the excitation and ionization thresholds of the analyte to those required solely for ablation of the sample surface. Under these conditions, the laser represents an advantageous mode to transform solid samples into gas phase that will be efficiently excited by the glow discharge. The advantage of the combination of the techniques has been demonstrated in alloyed samples (Cr/Fe and brass) where a net enhancement in the analytes signals even under sub-threshold and sub-sputtering conditions occur.

Keywords: Laser ablation; Glow discharge; Surface analysis; Energy decoupling

The crack control during laser cladding by adding the stainless steel net in the coating by Fujun Wang; Huaidong Mao; Dawei Zhang; Xingyu Zhao (pp. 8846-8854).

The generation of crack is one of the key problems which restrict the development of laser cladding technique. The purpose of this study is to control the cracks during laser cladding by adding a plastic phase—an austenitic stainless steel net in the coatings. With Ni-, Co- and Fe-based alloy powders, laser cladding experiments were carried out. The microstructure of the coatings and the stainless steel net was investigated. Experimental results show that the stainless steel net is partly melted and strongly bonded to the cladding powder materials and the substrate. Thus the crack density is significantly reduced. The amount of the reduction increases as the diameter of the stainless steel net increases. Without preheating the substrate, large area coatings which remain free of cracks can be achieved when adding the stainless steel net with appropriate diameter. The characteristics of the coatings were investigated and the results indicate that the hardness fluctuations of the coatings become larger and the wear resistance decreases when adding 316 stainless steel net.

Keywords: PACS; 42.62.−b; 42.81.Bm; 46.50.+a; 81.15.−zLaser cladding; Crack control; Stainless steel net; Coating

Seebeck and magnetoresistive effects of Ga-doped ZnO thin films prepared by RF magnetron sputtering by F. Wu; L. Fang; Y.J. Pan; K. Zhou; L.P. Peng; Q.L. Huang; C.Y. Kong (pp. 8855-8859).

In this paper, Ga-doped ZnO (GZO) films were deposited on glass substrates at different substrate temperatures by RF magnetron sputtering. The effect of substrate temperature on the structural, surface morphological properties, Seebeck and magnetoresistive effects of GZO films was investigated. It is found that the GZO films are polycrystalline and preferentially in the [002] orientation, and the film deposited at 300°C has an optimal crystal quality. Seebeck and magnetoresistive effects are apparently observed in GZO films. The thermoelectromotive forces are negative. Decreasing substrate temperature and annealing in N₂ flow can decrease carrier concentration. The absolute value of the Seebeck coefficient increases with decreasing carrier concentration. The maximal absolute value of Seebeck coefficient is 101.54μV/K for the annealed samples deposited at the substrate temperature of 200°C. The transverse magnetoresistance of GZO films is related to both the magnetic field intensity and the Hall mobility. The magnetoresistance increases almost linearly with magnetic field intensity, and the films deposited at higher substrate temperature have a stronger magnetoresistance under the same magnetic field, due to the larger Hall mobility.

Keywords: PACS; 73.50.Lw; 73.43.Qt; 68.55.Ln; 81.15.CdGa-doped ZnO thin films; Seebeck effect; Magnetoresistive effect; Magnetron sputtering

Modification of polysulfone membranes via surface-initiated atom transfer radical polymerization by Han-Bang Dong; You-Yi Xu; Zhuan Yi; Jun-Li Shi (pp. 8860-8866).

Hydrophilic poly((poly(ethylene glycol) methyl ether methacrylate) (P(PEGMA)) and poly(glycidylmethacrylate) (PGMA) brushes were grafted from chloromethylated polysulfone (CMPSF) membrane surfaces via surface-initiated atom transfer radical polymerization (ATRP). Prior to ATRP, chloromethylation of PSF was performed beforehand and the obtained CMPSF was prepared into porous membranes by phase inversion process. It was demonstrated that the benzyl chloride groups on the CMPSF membrane surface afforded effective macroinitiators to graft the well-defined polymer brushes.¹H NMR was employed to confirm the structure of CMPSF. The grafting yield of P(PEGMA) and PGMA was determined by weight gain measurement. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) confirmed the grafting of P(PEGMA) and PGMA chains. Water contact angle measurements indicated that the introduction of P(PEGMA) and PGMA graft chains promoted remarkably the surface hydrophilicity of PSF membranes. The effects of P(PEGMA) and PGMA immobilization on membrane morphology, permeability and fouling resistance were investigated. It was found that P(PEGMA) and PGMA grafts brought higher pure water flux, improved hydrophilic surface and better anti-protein absorption ability to PSF membranes after modification. And evidently, macromonomer P(PEGMA) brought much better properties to the PSF membranes than PGMA macromonomer.

Keywords: Polysulfone; Hydrophilicity; Protein absorption resistance; Surface-initiated ATRP

The influence of H₂/(H₂+Ar) ratio on microstructure and optoelectronic properties of microcrystalline silicon films deposited by plasma-enhanced CVD by Zeguo Tang; Wenbin Wang; Bo Zhou; Desheng Wang; Shanglong Peng; Deyan He (pp. 8867-8873).

Hydrogenated microcrystalline silicon films were deposited by glow discharge decomposition of SiH₄ diluted in mixed gas of Ar and H₂. By investigating the dependence of the film crystallinity on the flow rates of Ar and H₂, we showed that the addition of Ar in diluted gas markedly improves the crystallinity due to an enhanced dissociation of SiH₄. The infrared-absorption spectrum reveals that the fraction of SiH bonding increases with increasing the rate ratio of H₂/(H₂+Ar). The surface roughness of the films increases with increasing the flow rate ratio of H₂/(H₂+Ar), which is attributed to the decrease of massive bombardment of Ar ions in the plasma. Refractive index and absorption coefficient of the films were obtained by simulating the optical transmission spectra using a modified envelope method. Electrical measurements of the films show that the dark conductivity increases and the activation energy decreases with the ratio of H₂/(H₂+Ar). A reasonable explanation is presented for the dependence of the microstructure and optoelectronic properties on the flow rate ratio of H₂/(H₂+Ar).

Keywords: PACS; 78.20.Ci; 78.30.−j; 78.40.Fy; 72.20.−iHydrogenated microcrystalline silicon films; Plasma-enhanced CVD; Ar diluted gas; microstructure; Optoelectronic property

Electrical and optical properties of thin film of amorphous silicon nanoparticles by Zishan H. Khan (pp. 8874-8878).

Electrical and optical properties of thin film of amorphous silicon nanoparticles (a-Si) are studied. Thin film of silicon is synthesized on glass substrate under an ambient gas (Ar) atmosphere using physical vapour condensation system. We have employed Field Emission Scanning Electron Microscopy (FESEM), Transmission Electron Microscopy (TEM) and Atomic Force Microscopy (AFM) to study the morphology and microstructure of this film. It is observed that this silicon film contains almost spherical nanoparticles with size varying between 10 and 40nm. The average surface roughness is about 140nm as evident from the AFM image. X-ray diffraction analysis is also performed. The XRD spectrum does not show any significant peak which indicates the amorphous nature of the film. To understand the electrical transport phenomena, the temperature dependence of dc conductivity for this film is studied over a temperature range of (300–100K). On the basis of temperature dependence of dc conductivity, it is suggested that the conduction takes place via variable range hopping (VRH). Three-dimensional Mott's variable range hopping (3D VRH) is applied to explain the conduction mechanism for the transport of charge carriers in this system. Various Mott's parameters such as density of states, degree of disorder, hopping distance, hopping energy are estimated. In optical properties, we have studied Fourier transform infra-red spectra and the photoluminescence of this amorphous silicon thin film. It is found that these amorphous silicon nanoparticles exhibits strong Si–O–Si stretching mode at 1060cm⁻¹, which suggests that the large amount of oxygen is adsorbed on the surface of these a-Si nanoparticles. The photoluminescence observed from these amorphous silicon nanoparticles has been explained with the help of oxygen related surface state mechanism.

Keywords: Silicon nanoparticles; Physical Vapour Condensation Technique; SEM; TEM; AFM; Electrical properties; Variable range hopping; Mott's parameters; Optical properties; Fourier transform spectrum; Photoluminescence

Formation of zinc sulfide nanoparticles in HMTA matrix by K. Vijai Anand; M. Karl Chinnu; R. Mohan Kumar; R. Mohan; R. Jayavel (pp. 8879-8882).

A hydrothermal method has been optimized for the synthesis of ZnS nanoparticles. The nanoparticles were stabilized using Hexamethylenetetramine (HMTA) as surfactant in aqueous solution. The self-assembling of the surfactant molecules in the water solution forms a unique architecture that can be adopted as the reaction template for the formation of nanomaterials. The average grain size of the nanoparticles calculated from the XRD pattern was of the order of 2nm which exhibits cubic zinc-blende structure. TEM results showed that the synthesized nanoparticles were uniformly dispersed in the HMTA matrix without aggregation. The spectroscopic results revealed that the synthesized ZnS nanoparticles exhibits strong quantum confinement effect as the optical band gap energy increased significantly compared to the bulk ZnS material. Formation of HMTA capped ZnS nanoparticles were confirmed by FTIR studies. The PL spectra exhibit a strong green emission peak around 502nm attributed to some self-activated defect centers related to Zn-vacancies.

Keywords: PACS; 81.05.Dz; 81.16.Be; 78.55.EtHMTA; ZnS nanoparticles; Hydrothermal; Photoluminescence

Self-diffusion dynamic behavior of atomic clusters on Re(0001) surface by Fusheng Liu; Wangyu Hu; Huiqiu Deng; Wenhua Luo; Shifang Xiao; Jianyu Yang (pp. 8883-8889).

Using molecular dynamics simulations and a modified analytic embedded atom potential, the self-diffusion dynamics of rhenium atomic clusters up to seven atoms on Re(0001) surface have been studied in the temperature ranges from 600K to 1900K. The simulation time varies from 20ns to 200ns according to the cluster sizes and the temperature. The heptamer and trimer are more stable comparing to other neighboring non-compact clusters. The diffusion coefficients of clusters are derived from the mean square displacement of cluster's mass-center, and diffusion prefactors D₀ and activation energies E_a are derived from the Arrhenius relation. It is found that the Arrhenius relation of the adatom can be divided into two parts at different temperature range. The activation energy of clusters increases with the increasing of the atom number in clusters. The prefactor of the heptamer is 2–3 orders of magnitude higher than a usual prefactor because of a large number of nonequivalent diffusion processes. The trimer and heptamer are the nuclei at different temperature range according to the nucleation theory.

Keywords: Self-diffusion; Dynamic properties; Re cluster; Molecular dynamics

Preparation and characterization of activated carbon produced from pomegranate seeds by ZnCl₂ activation by Suat Uçar; Murat Erdem; Turgay Tay; Selhan Karagöz (pp. 8890-8896).

In this study, pomegranate seeds, a by-product of fruit juice industry, were used as precursor for the preparation of activated carbon by chemical activation with ZnCl₂. The influence of process variables such as the carbonization temperature and the impregnation ratio on textural and chemical-surface properties of the activated carbons was studied. When using the 2.0 impregnation ratio at the carbonization temperature of 600°C, the specific surface area of the resultant carbon is as high as 978.8m²g⁻¹. The results showed that the surface area and total pore volume of the activated carbons at the lowest impregnation ratio and the carbonization temperature were achieved as high as 709.4m²g⁻¹ and 0.329cm³g⁻¹. The surface area was strongly influenced by the impregnation ratio of activation reagent and the subsequent carbonization temperature.

Keywords: Pomegranate seed; Activated carbon; ZnCl; ₂; activation; Characterization

Effects of synthetic routes of Fe–urea complex on the synthesis of γ-Fe₂O₃ nanopowder by S. Asuha; S. Zhao; X.H. Jin; M.M. Hai; H.P. Bao (pp. 8897-8901).

Maghemite (γ-Fe₂O₃) nanopowder was prepared by the thermal decomposition of Fe–urea complex ([Fe(CON₂H₄)₆](NO₃)₃) that was synthesized by various routes including wet and dry synthetic methods. Then the effects of synthetic routes of the [Fe(CON₂H₄)₆](NO₃)₃ on resulting iron oxide crystalline phases and their magnetic properties have been studied using X-ray powder diffraction (XRD) and magnetic measurements. The result of XRD shows that the iron oxide crystalline phases are strongly dependent on the synthetic routes of the [Fe(CON₂H₄)₆](NO₃)₃. When [Fe(CON₂H₄)₆](NO₃)₃ is synthesized in ethanol, thermal decomposition of the compound results in pure γ-Fe₂O₃. When [Fe(CON₂H₄)₆](NO₃)₃ is synthesized either by an aqueous synthetic method or by a dry synthetic method, however, thermal decomposition of the compound results in mixed phases of γ-Fe₂O₃ and α-Fe₂O₃. Magnetic measurements show that resulting iron oxide nanopowder exhibits a ferromagnetic characteristic with a maximum saturation magnetization (Ms) of 69.0emu/g for the pure γ-Fe₂O₃ nanopowder.

Keywords: Maghemite; Nanopowder; Magnetic materials; Thermal decomposition

Plasticity and ab initio characterizations on Fe₄N produced on the surface of nanocrystallized 18Ni-maraging steel plasma nitrided at lower temperature by M.F. Yan; Y.Q. Wu; R.L. Liu (pp. 8902-8906).

18Ni-maraging steel has been entirely nanocrystallized by a series of processes including solution treatment, hot-rolling deformation, cold-drawn deformation and direct electric heating. The plasma nitriding of nanocrystallized 18Ni-maraging steel was carried out at 410°C for 3h and 6h in a mixture gas of 20% N₂+80% H₂ with a pressure of 400Pa. The surface phase constructions and nitrogen concentration profile in surface layer were analyzed using an X-ray diffractometer (XRD) and the glow discharge spectrometry (GDS), respectively. The results show that an about 2μm thick compound layer (mono-phase γ′-Fe₄N) can be produced on the top of the surface layer of nanocrystallized 18Ni-maraging steel plasma nitrided at 410°C for 6h. The measured hardness value of the nitrided surface is 11.6GPa. More importantly, the γ′-Fe₄N phase has better plasticity, i.e., its plastic deformation energy calculated from the load-displacement curve obtained by nano-indentation tester is close to that of nanocrystallized 18Ni-maraging steel. Additionally, the mechanical properties of γ′-Fe₄N phase were also characterized by first-principles calculations. The calculated results indicate that the hardness value and the ratio of bulk to shear modulus ( B/ G) of the γ′-Fe₄N phase are 10.15GPa and 3.12 (>1.75), respectively. This demonstrates that the γ′-Fe₄N phase has higher hardness and better ductility.

Keywords: PACS; 61.10.Nz; 61.43.Bn; 61.46.+w; 62.20.Dc; 62.20.Fe; 62.25.+g; 71.20.BeNanocrystallized 18Ni-maraging steel; Plasma nitriding; γ′-Fe; ₄; N; Mechanical properties; First-principles calculations

Optical and electrical characterization of aluminium doped ZnO layers by C. Major; A. Nemeth; G. Radnoczi; Zs. Czigany; M. Fried; Z. Labadi; I. Barsony (pp. 8907-8912).

Al doped ZnO (ZAO) thin films (with Al-doping levels 2 at.%) were deposited at different deposition parameters on silicon substrate by reactive magnetron sputtering for solar cell contacts, and samples were investigated by transmission electron microscopy (TEM), electron energy loss spectroscopy (EELS) and spectroscopic ellipsometry (SE). Specific resistances were measured by the well known 4-pin method. Well visible columnar structure and in most cases voided other regions were observed at the grain boundaries by TEM. EELS measurements were carried out to characterize the grain boundaries, and the results show spacing voids between columnar grains at samples with high specific resistance, while no spacing voids were observed at highly conductive samples. SE measurements were evaluated by using the analytical expression suggested by Yoshikawa and Adachi [H. Yoshikawa, S. Adachi, Japanese Journal of Applied Physics 36 (1997) 6237], and the results show correlation between specific resistance and band gap energy and direct exciton strength parameter.

Keywords: Zinc oxide; Transparent conductive oxides; Spectroscopic ellipsometry; Reactive sputtering; Structure–property relation

Surface chemical states of barium zirconate titanate thin films prepared by chemical solution deposition by L.L. Jiang; X.G. Tang; S.J. Kuang; H.F. Xiong (pp. 8913-8916).

Ba(Zr_0.05Ti_0.95)O₃ (BZT) thin films grown on Pt/Ti/SiO₂/Si(100) substrates were prepared by chemical solution deposition. The structural and surface morphology of BZT thin films has been studied by X-ray diffraction (XRD) and scanning electron microscope (SEM). The results showed that the random oriented BZT thin film grown on Pt/Ti/SiO₂/Si(100) substrate with a perovskite phase. The SEM surface image showed that the BZT thin film was crack-free. And the average grain size and thickness of the BZT film are 35 and 400nm, respectively. Furthermore, the chemical states and chemical composition of the films were determined by X-ray photoelectron spectroscopy (XPS) near the surface. The XPS results show that Ba, Ti, and Zr exist mainly in the forms of BZT perovskite structure.

Keywords: PACS; 68.55.−a; 77.80.−e ;79.60.−I; 81.15.Gh; 81.15.Lm; 81.65.Mq; 81.70.Jb; 82.80.PvBZT thin films; Chemical solution deposition; Surface chemical states; X-ray photoelectron spectroscopy

Impact of an extended source in laser ablation using pulsed digital holographic interferometry and modelling by E. Amer; P. Gren; A.F.H. Kaplan; M. Sjödahl (pp. 8917-8925).

Pulsed digital holographic interferometry has been used to study the effect of the laser spot diameter on the shock wave generated in the ablation process of an Nd:YAG laser pulse on a Zn target under atmospheric pressure. For different laser spot diameters and time delays, the propagation of the expanding vapour and of the shock wave were recorded by intensity maps calculated using the recorded digital holograms. From the latter, the phase maps, the refractive index and the density field can be derived. A model was developed that approaches the density distribution, in particular the ellipsoidal expansion characteristics. The induced shock wave has an ellipsoid shape that approaches a sphere for decreasing spot diameter. The ellipsoidal shock waves have almost the same centre offset towards the laser beam and the same aspect ratio for different time steps. The model facilitates the derivation of the particle velocity field. The method provides valuable quantitative results that are discussed, in particular in comparison with the simpler point source explosion theory.

Keywords: Laser ablation; Shock wave; Particle velocity; Pulsed digital holographic interferometry

Thickness dependence of optoelectrical properties of tungsten-doped indium oxide films by R.K. Gupta; K. Ghosh; P.K. Kahol (pp. 8926-8930).

Pulsed laser deposition technique is used for deposition of tungsten-doped indium oxide films. The effect of film thickness on structural, optical and electrical properties was studied using X-ray diffraction (XRD), atomic force microscopy, UV–visible spectroscopy, and electrical measurements. X-ray diffraction study reveals that all the films are highly crystalline and oriented along (222) direction and the film crystallinity increases with increase in film thickness. Atomic force microscopy analysis shows that these films are very smooth with root mean square surface roughness of ∼1.0nm. Bandgap energy of the films depends on thickness and varies from 3.71eV to 3.94eV. It is observed that resistivity of the films decreases with thickness, while mobility increases.

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

Molecular dynamics of contact behavior of self-assembled monolayers on gold using nanoindentation by Te-Hua Fang; Win-Jin Chang; Yu-Cheng Fan; Cheng-I Weng (pp. 8931-8934).

Molecular dynamics simulation is used to study nanoindentation of the self-assembled monolayers (SAMs) on an Au surface. The interaction of SAM atoms is described by a general universal force field (UFF), the tight-binding second-moment approximation (TB-SMA) is used for Au substrate, and the Lennard-Jones potential function is employed to describe interaction among the indenter, the SAMs, and the Au substrate atoms. The model consists of a planar Au substrate with n-hexadecanethiol SAM chemisorbed to the substrate. The simulation results show that the contact pressure increases as the SAMs temperature increases. In addition, the contact pressure also increases as the depth and velocity of indentation increase.

Keywords: PACS; 62.20.−x; 87.15.apSelf-assembled monolayer; Molecular dynamics simulation; Contact pressure

Formation of nanocrystalline TiO₂ by 100MeV Au⁸⁺ by Madhavi Thakurdesai; T. Mohanty; D. Kanjilal; Pratap Raychaudhuri; Varsha Bhattacharyya (pp. 8935-8940).

Nanocrystalline TiO₂ structures are formed by irradiation of 100MeV Au⁸⁺ ion beam on amorphous thin films of TiO₂. Surface morphology of the nanocrystals is studied by Atomic Force Microscopy (AFM). Amorphous to nanocrystalline phase transformation is identified by Glancing Angle X-ray Diffraction (GAXRD) and Raman spectroscopic studies. Optical characterization is carried out by UV–VIS spectroscopy technique. Blue shift observed in absorption band edge indicates the formation of nanophase TiO₂ after irradiation. The impinging swift heavy ion (100MeV Au⁸⁺) induces nucleation of nanoparticles along the ion trajectory through inelastic collisions of the projectile with electrons of the material. It is observed that the shape and size of nanoparticles formed is dependant on the irradiation fluence.

Keywords: PACS; 61.82.Rx; 61.80.Jh; 68.37.Ps; 78.30.−jTiO; ₂; nanophase; Swift heavy ions; AFM; Raman spectroscopy; UV–VIS absorption spectroscopy

The interfacial properties of MgCl₂ films grown on a flat SiO₂/Si substrate. An XPS and ISS study by S. Karakalos; A. Siokou; S. Ladas (pp. 8941-8946).

The interaction between MgCl₂ and SiO₂ was investigated by X-ray photoelectron spectroscopy (XPS), ion scattering spectroscopy (ISS) and contact potential difference (CPD) measurements. A thin SiO₂ layer was grown for this purpose on a Si(100) wafer and MgCl₂ was applied on this support at room temperature by evaporation under UHV conditions. It was found that magnesium chloride is deposited molecularly on the SiO₂ substrate, growing in layers and covering uniformly the oxide surface. The interaction with the substrate is initially very weak and limited to the interfacial layer. Above 623K, most of the molecular MgCl₂ is re-evaporated and the interfacial interaction becomes stronger, as Mg–Cl bonds in the remaining sub-monolayer chloride break and Cl atoms desorb. This leaves on the surface sub-stoichiometric MgCl_x, which interacts with oxygen atoms from the substrate to form a complex surface species. At 973K all Cl atoms desorb and Mg remains on the surface in the form of an oxide.

Keywords: Photoelectron spectroscopy; Ion scattering spectroscopy; Contact potential difference; Silicon oxide; Magnesium halide; Ziegler–Natta

Shallow surface etching of organic and inorganic compounds by electrospray droplet impact by Kenzo Hiraoka; Yuji Sakai; Yoshitoki Iijima; Daiki Asakawa; Kunihiko Mori (pp. 8947-8952).

The electrospray droplet impact (EDI) was applied to bradykinin, polyethylene terephthalate (PET), SiO₂/Si, and indium phosphide (InP). It was found that bradykinin deposited on the stainless steel substrate was ionized/desorbed without the accumulation of radiation products. The film thickness desorbed by a single collisional event was found to be less than 10 monolayers. In the EDI mass spectra for PET, several fragment ions were observed but the XPS spectra did not change with prolonged cluster irradiation. The etching rate for SiO₂ by EDI was measured to be ∼0.2nm/min. The surface roughness of InP etched by EDI was found to be one order of magnitude smaller than that etched by 3keV Ar⁺ for about the same etching depths. EDI is capable of shallow surface etching with little damage left on the etched surface.

Keywords: Electrospray droplet impact; Cluster ion etching; Shallow surface etching

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Applied Surface Science (v.255, #21)