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Applied Surface Science (v.254, #16)

Femtosecond laser ablation of polypropylene for breathable film by Ik-Bu Sohn; Young-Chul Noh; Sung-Chul Choi; Do-Kyeong Ko; Jongmin Lee; Young-Jin Choi (pp. 4919-4924).

A polypropylene (PP) film was ablated using a femtosecond laser with a center wavelength of 785nm, a pulse width of 184fs and a repetition rate of 1kHz. Increments of both the pulse energy and the shot number of pulses lead to co-occurrence of photochemical and thermal effect, demonstrated by the spatial expansion of rim on the surface of PP. The shapes of the laser-ablated PP films were imaged by a scanning electron microscope (SEM) and measured by a 3D optical measurement system (NanoFocus). And, the gas and water vapor transmission rate, mechanical properties of PP film micropatterned by fs laser pulses was characterized. Our results demonstrate that a femtosecond pulsed laser is an efficient tool for breathable packaging films in modifying the flow of air and gas, where the micropatterns are specifically tailored in size, location and number of which is easily controlled by laser processing conditions.

Keywords: Laser materials processing; Femtosecond laser ablation; Polymers; Packaging; Microperforated film

Electrospun ceramic fibers: Composition, structure and the fate of precursors by R.W. Tuttle; A. Chowdury; E.T. Bender; R.D. Ramsier; J.L. Rapp; M.P. Espe (pp. 4925-4929).

Fibers are electrospun from aluminum acetate/polymer mixtures and characterized by an array of techniques before and after annealing at 1200°C. We demonstrate that sodium and boron present in the initial starting materials as adducts and stabilizers remain incorporated into the resulting fibers after annealing and pyrolysis of the host polymer. The influence of these minor constituents on the surfaces of the fibers is suggested by infrared and X-ray photoelectron spectroscopic data. The presence of these species may impact potential chemical applications of small diameter ceramic fibers, such as their use as catalytic supports or for chemical decomposition.

Keywords: Electrospinning; Fibers; Ceramics; NMR; XPS; SEM; FTIR

The improvement of corrosion resistance of Ce conversion films on aluminum alloy by phosphate post-treatment by Haibing Zhang; Yu Zuo (pp. 4930-4935).

A phosphate post-treatment process for Ce conversion film on aluminum was studied. SEM (scanning electronic microscope), XPS (X-ray photoelectron spectroscopy) and electrochemical measurements were used to characterize the properties of the films. After the post-treatment the micro-cracks on the film surface obviously diminished, and corrosion resistance of the conversion film in NaCl solution increased. The conversion film, without post-treatment, was mainly composed of hydrated cerium oxides, and the dehydration of the film may cause cracking of the films. After phosphate treatment, stable cerium phosphate CePO₄ was formed on the surface, and the content of crystal water decreased greatly, leading to improvement of the film performance with less micro-cracks.

Keywords: Ce conversion films; Phosphate post-treatment; Micro-cracks; XPS; Corrosion

An efficient route towards the covalent functionalization of single walled carbon nanotubes by Bhalchandra A. Kakade; Vijayamohanan K. Pillai (pp. 4936-4943).

A simple and efficient method of chemical functionalization of both single and multiwalled carbon nanotubes has been discussed to give enhanced water solubility by rapidly and efficiently generating an appreciable amount of hydrophilic functional groups using microwave radiation. Surface functionalization containing more than 30wt% of oxygen has been achieved, resulting into solubility of 2–5mg/mL. Further covalent functionalization of such soluble SWNTs provides a remarkable degree of aniline functionalization through amidation, where the formation of polyaniline has been avoided. Functionalization of SWNTs is confirmed by techniques like electron microscopy, Fourier transform infrared spectroscopy, thermogravimetry, Raman spectroscopy, cyclic voltammetry and impedance spectroscopy. Electrochemical analysis suggests an enhanced double layer capacitance (∼110F/g) of nanotubes after microwave treatment. Aniline functionalization of SWNTs shows possible variations on the nanotube topography with concomitant formation of a dynamic polymer layer on the nanotube surface.

Keywords: Carbon nanotubes; Microwave; Solubility; Functionalization

Methane activation over Ag-exchanged ZSM-5 zeolites: A theoretical study by Bingjing Ding; Shiping Huang; Wenchuan Wang (pp. 4944-4948).

Methane activation catalyzed over Ag-exchanged ZSM-5 zeolites was investigated by using the density functional theory (DFT) with a cluster model. Two different pathways were taken into account in this work: the “alkyl” and the “carbenium” pathways. The activation barriers obtained are 34.09 and 66.63kcal/mol for the “alkyl” and the “carbenium” pathway, respectively. The calculated results show that the activation barrier of the “alkyl” pathway is smaller than that of “carbenium” pathway. Consequently, the “alkyl” pathway is the preferential reaction pathway. A new mechanism of methane conversion in the presence of ethene was proposed. In the catalytic cycle, the initial step of methane activation proceeds with the “alkyl” pathway and the Ag⁺ cation acts as an acceptor of the methyl group, then ethene reacts with the Ag⁺CH₃⁻ group to form propene. In addition, it is found that the Ag⁺ cations play an important role in the methane activation, compared with the reaction of methane activation over H-ZSM-5.The reaction mechanism of methane activation over Ag-exchanged ZSM-5 zeolites was investigated by using density functional theory (DFT). The calculated results show that the “alkyl” pathway is the preferential reaction pathway. In addition, it is found that the Ag⁺ cations play an important role in the methane activation, compared with the reaction of methane activation over H-ZSM-5.▪

Keywords: Methane activation; Ag-ZSM-5; Density functional theory; Zeolite; Reaction mechanism

Electroless Ni-P/Ni-B duplex coatings for improving the hardness and the corrosion resistance of AZ91D magnesium alloy by W.X. Zhang; Z.H. Jiang; G.Y. Li; Q. Jiang; J.S. Lian (pp. 4949-4955).

The Ni-P/Ni-B duplex coatings were deposited on AZ91D magnesium alloy by electroless plating process and their structure, morphology, microhardness and corrosion resistance were evaluated. The duplex coatings were prepared using dual baths (acidic hypophosphite- and alkaline borohydride-reduced electroless nickel baths) with Ni-P as the inner layer. The coatings were amorphous in as-plated condition and crystallized and produced nickel borides upon heat-treatment. SEM observations showed that the duplex interface on the magnesium alloy was uniform and the compatibility between the layers was good. The Ni-P/Ni-B coatings microhardness and corrosion resistance of having Ni-B coating as the outer layer was higher than Ni-P coatings. The Ni-P/Ni-B duplex coatings on AZ91D magnesium alloy with high hardness and good corrosion resistance properties would expand their scope of applications.

Keywords: Electroless deposition; Duplex nickle coatings; Magnesium alloy; Corrosion resistance; Electrochemical protection

The dopant concentration and annealing temperature dependence of ferromagnetism in Co-doped ZnO thin films by Xiao-Hong Xu; Xiu-Fang Qin; Feng-Xian Jiang; Xiao-Li Li; Ya Chen; G.A. Gehring (pp. 4956-4960).

A series of Zn1−_xCo_xO thin films with the atomic fraction, x, in the range of 0.03–0.10 were deposited on glass substrates at room temperature by magnetron co-sputtering technique and subsequently coupled with the post-annealing treatment for half hour at different temperatures (350°C and 500°C) under vacuum. A systematic study was done on the structural, optical and magnetic properties of Zn1−_xCo_xO thin films as a function of Co concentration and annealing temperature. X-ray diffraction and UV–vis spectroscopy results indicated that there are not any secondary phases and Co²⁺ substituted for Zn²⁺ of ZnO host. Magnetic hysteresis loops were observed at room temperature, indicating that both the as-deposited samples and the annealed ones exhibit the room temperature ferromagnetism. It was also found that the magnetic saturation moment per Co atom decreases with increasing Co concentration, while the post-annealing treatment can enhance the magnetic moment of the films effectively.

Keywords: ZnCoO films; Magnetic measurements; X-ray diffraction; Post-annealing

Cesium ion sputtering with oxygen flooding: Experimental SIMS study of work function change by Y. Kudriatsev; A. Villegas; S. Gallardo; G. Ramirez; R. Asomoza; V. Mishurnuy (pp. 4961-4964).

We investigated the work function (WF) change of a silicon surface being under cesium ion bombardment and simultaneous oxygen flooding with various oxygen pressures at the sample surface. It was found that WF of Cs⁺ ion sputtered Si decreases under oxygen flooding. This decrease provides an essential grow of secondary ion yields of some negative ions, sputtered from Si. At the same time Si⁻ ion yield decreases approximately in two times. In the paper we have discussed possible explanations of our experimental data: we considered a surface composition change, formation of surface dipoles and work function change caused by oxygen adsorption, and their relationships between each other.

Keywords: SIMS; Work function; Ion yield

Electron stimulated desorption of O₂⁺ from gadolinia-doped ceria surfaces by Haiyan Chen; Alex Aleksandrov; Meilin Liu; Thomas Orlando (pp. 4965-4969).

The interactions of gas phase oxygen with gadolinia-doped ceria (GDC) surfaces are investigated by electron stimulated desorption (ESD). The primary desorbed cationic species related to molecular oxygen adsorption is O₂⁺. The threshold energy for ESD of O₂⁺ is 13–14eV, indicating electron impact ionization of molecular oxygen bound at oxygen vacancies. Dependence of O₂⁺ velocities upon incident electron energy and substrate temperature reveals the dominant influence of the effective charge of the adsorption complex. The O₂⁺ velocity distribution is bimodal, and the onset of the faster components at room temperature is related to the balance between fluxes of incident electrons and secondary electron emission, causing effective hole production and neutralization of trapped electrons at surface states.

Keywords: PACS; 79.20.Kz; 81.05.JeOxygen molecule; Gadolinia-doped ceria; Electron stimulated desorption

Pressure and solvent induced low-temperature synthesis of monodisperse superparamagnetic nanocrystals: The case of Fe₃O₄ in alkanols by Guozhu Li; Wenchao Peng; Xianyu Li; Xiaobin Fan; Xiaojun Li; Guoliang Zhang; Fengbao Zhang (pp. 4970-4979).

The synthesis of nanoparticles via the decomposition of organometallic compounds has been studied extensively, but the effect of pressure has received little attention. Here we firstly focus on the pressure effect, and utilize it as well as the solvent and temperature effects to develop a “green” cheap low-temperature (140–200°C) strategy via the decomposition of iron oleate in alcohol (or other alkanols) using oleic acid as the protecting reagent. The obtained monodisperse Fe₃O₄ nanocrystals (NCs) exhibit satisfying superparamagnetism. The mechanism of the process has been investigated and it was shown both high pressure and alkanol as the solvent can facilitate the formation of magnetite NCs. Furthermore, the solvent used in the preparation can control the shape, size and dispersion of NCs. In addition, the effects of reactant concentration, reaction time, temperature, and the mol ratio of oleic acid on the Fe₃O₄ NCs have also been discussed.

Keywords: Pressure; Solvent; Nanocrystals; Magnetite; Synthesis

Surface energy and hybridization studies of amorphous carbon surfaces by A. Zebda; H. Sabbah; S. Ababou-Girard; F. Solal; C. Godet (pp. 4980-4991).

Surface properties of a large number of amorphous carbon (a-C) films have been investigated using contact angle measurements and X-ray photoelectron spectroscopy (XPS). Dense a-C surfaces with variable sp³/(sp²+sp³) average hybridization were grown using sputtering or pulsed laser deposition (PLD) and were further chemically modified by thermal annealing, ion bombardment or covalent grafting of organic monolayers. The average carbon hybridization, impurity level and mass density, were deduced from XPS and photoelectron energy loss spectroscopy (PEELS). The depth sensitivity of the dispersive (Lifshitz–van der Waals) interaction, estimated at 1–2nm from the dependence of γ^LW on the grafted perflorodecene molecule coverage, is much better than XPS which probes a 3–5nm depth. The observation of a non-monotonic behavior in the correlation between surface hybridization and electron donor component of surface energy reveals that the average carbon hybridization alone does not describe the entire surface energy physics. The role of π bond clustering in the polar interactions is thus considered and some implications on surface reactivity and mutual interactions with molecular or biomolecular species are discussed.

Keywords: PACS; 79.60.HT; 68.35.Md; 82.80.PvAmorphous carbon; XPS; Surface energy; Contact angle

Photo-conversion and evolution of one-dimensional Cu nanoparticles under femtosecond laser irradiation by Gang Chang; Yasuhiko Shimotsuma; Masaaki Sakakura; Toshirou Yuasa; Hidekazu Homma; Munetaka Oyama; Kiyotaka Miura; Jiarong Qiu; Peter G. Kazansky; Kazuyuki Hirao (pp. 4992-4998).

Metal nanowires with electric conductive properties can be useful for optical polarization control medium and electro-conductive nanomaterial. We report on metallic Cu nanowires with a length of 1.0μm and a diameter of 85nm which were successfully photo-converted from commercial scale-like Cu particles, dispersed in a methanol solution, by using femtosecond laser irradiation. The growth mechanism of Cu nanowires under laser irradiation was suggested to be a nucleation growth process.

Keywords: PACS; 81.16.−c; 52.38.−r; 68.65.−k; 61.46.Km; 62.23.HjMetal nanowire; Ultrashort pulse laser; Nucleation growth process; Polarization

Electrode contact study for SiGe thin film operated at high temperature by Lionel Fabrice Houlet; Woosuck Shin; Maiko Nishibori; Noriya Izu; Toshio Itoh; Ichiro Matsubara (pp. 4999-5006).

A study on the electrode contact of the sputtered SiGe thin film is reported for application of devices working at high temperature. Surface morphological characterization with optical microscope and AFM (atomic force microscope) together with the electrical characterization by TLM measurements (transmission line method) were performed before and after aging at 500°C for 24h using various sputtered multilayer electrodes, Ti/Au/Ti, Ta/Pt/Ta and Ti/Pt/Ti, on 300-nm B-doped SiGe thin film deposited by magnetron sputtering and furnace crystallisation at high temperature. After aging at 500°C for 24h, the Ti/Au/Ti multilayer electrodes seriously degraded to be non-ohmic contact, showing rough surface morphology. The Ti/Pt/Ti metal layers showed the lowest specific contact, resistivity before and after aging, 1.46×10⁻³Ωcm² and 1.68×10²Ωcm² respectively.

Keywords: PACS; 73.40.NS; 68.55.J−; 68.60.Dv; 84.37.+q; 81.15.CdSiGe; Sputtering; Electrode; Contact; TLM; High temperature; Specific contact resistivity; Adhesion layer

Promoting effect of low concentration of benzotriazole on the corrosion of Cu10Ni alloy in sulfide polluted salt water by Nageh K. Allam; Elsayed A. Ashour (pp. 5007-5011).

The interaction of benzotriazole (BTAH) with the surface of a corroding copper–nickel alloy in a sulfide polluted salt solution reveals a change in its role from an inhibitor to a promoter of localized corrosion as its concentration changes. A concentration of BTAH ≥5×10⁻⁴M inhibits the corrosion reaction in both the polluted and the unpolluted media. On the other hand, a concentration of 10⁻⁴M BTAH promotes the localized corrosion of the alloy in the polluted medium while it acts as an inhibitor in the unpolluted salt solution. This finding is substantiated by measurements of mass loss and current transients and examination of the surface by SEM microscopy.

Keywords: Copper–nickel; Alloy; Seawater; Benzotriazole; Inhibitor; Promoter; Sulfide pollution

The effect of hydrogen on copper nitride thin films deposited by magnetron sputtering by Guangan Zhang; Pengxun Yan; Zhiguo Wu; Jun Wang; Jiangtao Chen (pp. 5012-5015).

Copper nitride thin films were deposited on Si (100) wafers by reactive magnetron sputtering at various H₂/N₂ ratios. X-ray diffraction measurements show that the films are composed of Cu₃N crystallites with anti-ReO₃ structure and exhibit preferred orientation of [100] direction. Although the relative composition of the films has obviously changes with the H₂/N₂ ratios, the orientations of the films keep almost no changes. However, the grain size, lattice parameter and composition of the films are strongly dependent on the H₂/N₂ ratios. The copper nitride films prepared at 10% H₂/N₂ ratios show poor stability and large weight gain compared to the copper nitride films prepared at 0% H₂/N₂ ratios.

Keywords: Copper nitride; Thin films; Hydrogen; Structure; Thermal properties

A novel process for electroless nickel plating on anodized magnesium alloy by Shuo Sun; Jianguo Liu; Chuanwei Yan; Fuhui Wang (pp. 5016-5022).

In this paper, a novel palladium-free activation electroless nickel (EN) plating process, by which a TiB₂ powders contained intermediate film was used as catalyst, was introduced for anodized magnesium alloy AZ91D. The corrosion behavior of AZ91D without and with coating was compared and the bonding strength of the EN plating to the substrate was also measured. The results showed that the EN plating could easily take place on the intermediate catalytic layer, directly on which a smooth and compact Ni–P alloy layer without obvious flaws, about 20μm thickness, was successfully deposited. The catalytic function was principally from TiB₂ powder. The adhesive tensile test indicated a good bonding strength of about 11MPa between the substrate and the catalytic layer. An obvious passivation range and higher E_corr (−0.323V) for the EN plating during anodic polarization in 3.5wt.% NaCl solution, implied a typical character of a compact Ni–P alloy layer, with an effective protection for the substrate.

Keywords: Magnesium alloy; Electroless nickel plating; Palladium-free activation; Catalytic; Corrosion resistance

Effect of carbonitride precipitates on the abrasive wear behaviour of hardfacing alloy by Ke Yang; Shengfu Yu; Yingbin Li; Chenglin Li (pp. 5023-5027).

Hardfacing alloy of martensitic stainless steel expect higher abradability to be achieved through the addition of nitrogen being provided by the fine scale precipitation of complex carbonitride particles. Niobium and titanium as the most effective carbonitride alloying elements were added in the Fe–Cr13–Mn–N hardfacing alloy to get carbonitride precipitates. Carbonitride was systematically studied by optical microscopy, scanning electronic microscopy and energy spectrum analysis. Abrasive wear resistance of hardfacing alloy in as-welded and heat-treated conditions was tested by using the belt abrasion test apparatus where the samples slide against the abrasive belt. It is found that carbonitride particles in the hardfacing alloy are complex of Cr, Ti and Nb distributing on the grain boundary or matrix of the hardfacing alloy with different number and size in as-welded and heat-treated conditions. A large number of carbonitrides can be precipitated with very fine size (nanoscale) after heat treatment. As a result, the homogeneous distribution of very fine carbonitride particles can significantly improve the grain-abrasion wear-resisting property of the hardfacing alloy, and the mass loss is plastic deformation with minimum depth of grooving by abrasive particles and fine delamination.

Keywords: Carbonitride; Precipitate; Abrasive wear; Hardfacing alloy

CdS/ZnS core–shell nanoparticles in arachidic acid LB films by P. Mandal; R.S. Srinivasa; S.S. Talwar; S.S. Major (pp. 5028-5033).

Core–shell CdS/ZnS nanoparticles in arachidic acid film were prepared through a novel Langmuir–Blodgett (LB) approach. Post-deposition treatment of the precursor LB multilayers of cadmium arachidate with H₂S gas followed by intercalation of Zn²⁺ ions and further sulfidation result in the formation of CdS/ZnS nanoparticles in the LB film. The formation of these nanoparticles and resulting changes in layered structures were studied by FTIR and X-ray reflection measurements. The optical properties were studied using UV–vis absorption and photoluminescence spectroscopy. A red-shift in the absorption spectrum and enhancement of CdS excitonic emission together with reduction of surface states emission suggest that after the intercalation step, a thin layer of ZnS surrounds the CdS nanoparticles, thus forming a core–shell structure. Subsequent to the second sulfidation, a further red-shift in absorption suggests the formation of a thicker ZnS coating on CdS. Electron diffraction of CdS nanoparticles coated with thicker ZnS showed the diffraction patterns of only ZnS, as expected for core–shell structures.

Keywords: PACS; 81.07.−b; 78.67.Bf; 68.37.LpCdS/ZnS; Core–shell; Nanoparticles; LB multilayers; Photoluminescence

A spectroscopic ellipsometric investigation of new critical points of Zn1−_xMn_xS epilayers by D.-J. Kim; J.-W. Lee; Y.-M. Yu; Y.D. Choi (pp. 5034-5038).

Zn1−_xMn_xS epilayers were grown on GaAs (100) substrates by hot-wall epitaxy. X-ray diffraction (XRD) patterns revealed that all the epilayers have a zincblende structure. The optical properties were investigated using spectroscopic ellipsometry at 300K from 3.0 to 8.5eV. The obtained data were analyzed for determining the critical points of pseudodielectric function spectra, 〈 ɛ( E)〉=〈 ɛ₁( E)〉+ i〈 ɛ₂( E)〉, such as E₀, E₀+ Δ₀, and E₁, and three E₂ (Σ, Δ, Γ) structures at a lower Mn composition range. These critical points were determined by analytical line-shapes fitted to numerically calculated derivatives of their pseudodielectric functions. The observation of new peaks, as well as the shifting and broadening of the critical points of Zn1−_xMn_xS epilayers, were investigated as a function of Mn composition by ellipsometric measurements for the first time. The characteristics of the peaks changed with increasing Mn composition. In particular, four new peaks were observed between 4.0 and 8.0eV for Zn1−_xMn_xS epilayers, and their characteristics were investigated in this study.

Keywords: PACS; 78.20.−e; 78.40.FyZn; 1−; _x; Mn; _x; S epilayer; Spectroscopic ellipsometry; Critical points

Physical properties of ZnS thin films prepared by chemical bath deposition by T. Ben Nasr; N. Kamoun; C. Guasch (pp. 5039-5043).

Zinc sulphide thin films are deposited on SnO₂/glass using the chemical bath deposition technique. X-ray diffraction and atomic force microscopy are used to characterize the structure of the films; the surface composition of the films is studied by Auger electrons spectroscopy, the work function and the photovoltage are investigated by the Kelvin method. Using these techniques, we specify the effect of pH solution and heat treatment in vacuum at 500°C. The cubic structure corresponding to the (111) planes of β-ZnS is obtained for pH equal to 10. The work function ( Φ_material− Φ_probe) for ZnS deposited at pH 10 is equal to −152meV. Annealing at 500°C increases Φ_m (by about 43meV) and induces the formation of a negative surface barrier. In all cases, Auger spectra indicate that the surface composition of zinc sulphide thin films exhibits the presence of the constituent elements Zn and S as well as C and O as impurity elements.

Keywords: Zinc sulphide; Chemical bath deposition; Physical properties

Bias-tunable electron transport in a magnetic double-barrier nanostructure by Jian-Duo Lu (pp. 5044-5047).

In this paper, the bias-dependent electron transport is investigated in detail in a magnetic double-barrier nanostructure in the presence of two bias voltages. It is shown that the large spin-polarization can be achieved in such a nanostructure, and the degree of the spin-polarization is strongly dependent on the applied bias. These interesting properties can provide an alternative scheme to spin-polarize electrons into semiconductors, and this device may be used as a bias-tunable spin filter.

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

Investigation of the role of oxygen in NO reduction by C₂H₄ on the surface of stepped Pt(332) by Yuhai Hu; Keith Griffiths (pp. 5048-5054).

The influence of pre-dosed oxygen on NO–C₂H₄ interactions on the surface of stepped Pt(332) has been investigated using Fourier transform infrared reflection–absorption spectroscopy (FTIR-RAS) and thermal desorption spectroscopy (TDS). The presence of oxygen significantly suppresses the adsorption of NO on the steps of Pt(332), leading to a very specific adsorption state for NO molecules when oxygen–NO co-adlayers are annealed to 350K (assigned as atop NO on step edges). An oxygen-exchange reaction also takes place between these two kinds of adsorbed molecules, but there appears to be no other chemical reaction, which can result in the formation of higher-valence NOx.C₂H₄ molecules which are post-dosed at 250K to adlayers consisting of¹⁸O and NO do not have strong interactions with either the NO or the¹⁸O atoms. In particular, interactions which may result in the formation of new surface species that are intermediates for N₂ production appear to be absent. However, C₂H₄ is oxidized to C¹⁸O₂ by¹⁸O atoms at higher annealing temperature. This reaction scavenges surface¹⁸O atoms quickly, and the adsorption of NO molecules on step sites is therefore quickly restored. As a consequence, NO dissociation on steps proceeds very effectively, giving rise to N₂ desorption which closely resembles that following only NO exposure on a clean Pt(332), both in peak intensity and desorption temperature. It is concluded that the presence of¹⁸O₂ in the selective catalytic reduction (SCR) of NO with C₂H₄ on the surface of Pt(332) does not play a role of activating reactants.

Keywords: NO; Platinum; C; ₂; H; ₄; deNOx; Hydrocarbon; Selective catalytic reduction; Oxygen

Surface modification of indium tin oxide anode with self-assembled monolayer modified Ag film for improved OLED device characteristics by L.Y. Yang; X.Z. Chen; H. Xu; D.Q. Ye; H. Tian; S.G. Yin (pp. 5055-5060).

Modification of electrodes has attracted much attention in the study of organic semiconductor devices. A self-assembled monolayer (SAM) of 4-fluorothiophenol is employed to modify the Ag film on the surface of indium tin oxide (ITO) to improve the hole injection and the surface morphology. The modified anode was characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscope (AFM), and UV–vis transmittance spectra. To investigate the effect of the modification on the device characteristics, typical double layer devices with the structure of anode/α-naphthylphenylbiphenyl diamine (NPB, 60nm)/tris-(8-hydroxyquinoline) aluminum (Alq₃, 60nm)/LiF(0.7nm)/Al(100nm) were fabricated using the modified anode and the bare ITO. The effect of Ag layer thickness on the device performance is also investigated. The results revealed that SAM modified ultra-thin Ag film is an effective buffer layer for organic light emitting diode. The device using the ITO/Ag (5nm)/SAM as anode show improved device characteristics than that of using bare ITO as anode. The enhancements in luminance and efficiency are attributed to enhanced hole injection and smooth surface between anode and the organic material. The Ag thickness of 5nm is chosen as an acceptable compromise between substrate transparency and the device performance.

Keywords: Self-assembled monolayer; Organic light emitting diodes; Anode; Silver; Modification

Surfactant-assisted synthesis of defective zirconia mesophases and Pd/ZrO₂: Crystalline structure and catalytic properties by J.A. Wang; L.F. Chen; M.A. Valenzuela; J. Salmones; D.R. Acosta; X. Bokhimi; O. Novaro (pp. 5061-5072).

Mesoporous zirconia nanophases with structural defects were synthesized by using a surfactant-templated method. Physicochemical properties and crystalline structures of the zirconia nanophases were studied by means of thermogravimetric analysis (TGA), N₂ physosorption isotherm and in situ Fourier transform infrared (FT-IR) spectroscopy, transmission electron microscopy (TEM) and X-ray diffraction (XRD) techniques. The resultant materials show typical mesoporous features which vary with calcination temperature. The cationic surfactant in the network of the solids induces structural deformation and defect creation. The zirconia consists of monoclinic and tetragonal nanophases which contains many structural defects, and its crystalline structure shows microstrain. Both, concentration of lattice defects and degree of the crystal microstrain, decrease as the calcination temperature is increased. When CO is adsorbed on the surface of Pd/ZrO₂, linear bonds of CO–Pd⁰, CO–Pd^δ+ and CO–Zr⁴⁺ are formed, accompanying with CO₂ production. Catalytic evaluation shows that the Pd/ZrO₂ catalyst is very active for CO oxidation and NO reduction. In the case of oxygen absence from reaction mixture, high selectivity to N₂ is achieved without any NO₂ formation. In the oxygen rich condition, CO conversion is enhanced but less than 19% NO₂ is produced. N₂O is formed only in the reducing condition and its selectivity is sensitive to reaction temperature. The possible mechanisms of NO+CO and NO+CO+O₂ reactions over Pd/ZrO₂ catalyst related to reactant dissociation on the Pd metals and to defective structure of the nanozirconia support are discussed.

Keywords: Zirconia nanophase; Rietveld refinement; Structural defect; Surfactant-templated synthesis; NO reduction; Catalyst

The growth of carbon nanotubes on montmorillonite and zeolite (clinoptilolite) by M. Kadlečíková; J. Breza; K. Jesenák; K. Pastorková; V. Luptáková; M. Kolmačka; A. Vojačková; M. Michalka; I. Vávra; Z. Križanová (pp. 5073-5079).

Synthesis of carbon nanotubes described in the present work is based on activation of methane in a hot filament CVD reactor and subsequent creation of nanostructures on a catalyst pre-treated polished surface of silicon. An essential step of the synthesis is the use of natural minerals as catalysts. We have studied the catalyst parameters, the way of its application and the amount of Fe³⁺ cations on the surface of aluminosilicates on the quality of the grown nanotube layers. The growth of carbon nanotubes catalyzed by montmorillonite and zeolite (clinoptilolite) was confirmed by scanning electron microscopy and Raman spectroscopy.

Keywords: PACS; 81.07.De; 81.16.HcCarbon nanotubes; Chemical vapour deposition; Montmorillonite; Clinoptilolite

Characteristics and electrochemical performance of Ni-coated ZnO prepared by an electroless plating process by Y.F. Yuan; J.P. Tu; S.Y. Guo; J.B. Wu; M. Ma; J.L. Yang; X.L. Wang (pp. 5080-5084).

ZnO was coated homogeneously with amorphous Ni film by an electroless plating process. After electroless Ni plating, transmission electron microscope (TEM) images and energy dispersive spectrometry spectra (EDS) of ZnO clearly indicated that Ni was coated on the surface of ZnO, the coatings and ZnO contacted enough. X-ray diffraction and high-resolution TEM showed that the Ni film on ZnO was amorphous. Electrochemical performance of Ni-coated ZnO was investigated by the galvanostatic charge/discharge cycling test. Compared to that of uncoated ZnO, the charging–discharging performance of Ni-coated ZnO was obviously improved, e.g. the average discharge capacity of the Ni-coated ZnO increased 71.5% at the stage of stable cycling test.

Keywords: Electroless plating; Ni; ZnO; Electrochemical performance

Superhard nanocomposite nc-TiC/a-C:H film fabricated by filtered cathodic vacuum arc technique by Yaohui Wang; Xu Zhang; Xianying Wu; Huixing Zhang; Xiaoji Zhang (pp. 5085-5088).

Superhard nanocomposite nc-TiC/a-C:H films, with an excellent combination of high elastic recovery, low friction coefficient and good H/ E ratio, were prepared by filtered cathodic vacuum arc technique using the C₂H₂ gas as the precursor. The effect of C₂H₂ flow rate on the microstructure, phase composition, mechanical and tribological properties of nanocomposite nc-TiC/a-C:H films have been investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy disperse spectroscopy (EDS), microindentation and tribotester measurements. It was observed that the C₂H₂ flow rate significantly affected the Ti content and hardness of films. Furthermore, by selecting the proper value for C₂H₂ flow rate, 20sccm, one can deposit the nanocomposite film nc-TiC/a-C:H with excellent properties such as superhardness (66.4GPa), high elastic recovery (83.3%) and high H/ E ratio (0.13).

Keywords: Nanocomposite nc-TiC/a-C:H film; Superhardness; Microstructure

Influence of embedded particles on microstructure, corrosion resistance and thermal conductivity of CuO/SiO₂ and NiO/SiO₂ nanocomposite coatings by Qingjie Yu; Xuehu Ma; Mingzhe Wang; Chunjian Yu; Tao Bai (pp. 5089-5094).

Homogeneous CuO/SiO₂ and NiO/SiO₂ nanocomposite coatings containing CuO and NiO nanoparticles in silica matrix were successfully synthesized by sol–gel process on an aluminum alloy substrate, respectively. The evolution of phase and morphology of both nanocomposites was characterized by XRD, SEM, TEM and FTIR. The effect of incorporating various nanoparticles on the corrosion behavior and the thermal conductivity of nanocomposite coatings was investigated by potentiodynamic polarization curve and comparative exponential method. The thermal conductivity as well as the corrosion resistance of nanocomposite coatings was significantly improved by the introduction of metal oxide particles. In comparison with NiO/SiO₂ nanocomposite coatings, CuO/SiO₂ composite coatings displayed lower protective behavior as well as higher thermal conductivity. Experimental results revealed that those improvements can directly be related to the nanocomposite effect and the nature of added nanoparticles.

Keywords: PACS; 81.05.Pj; 61.46.+wNanocomposite; Corrosion resistance; Thermal conductivity

Characterization of optical waveguides in β-BaB₂O₄ crystals formed by 3.0MeV Ni²⁺ ions implantation by Chuan-Lei Jia; Xue-Lin Wang; Lei Wang; Ke-Ming Wang; Hong-Ji Ma; Rui Nie (pp. 5095-5099).

We report on the optical planar waveguides formation and modal characterization in β-BaB₂O₄ crystals by Ni²⁺ ion implantation at energy of 3.0MeV and doses of ∼10¹⁴ions/cm². The prism coupling method was used to investigate the dark-mode property at wavelengths of 633nm and 1539nm, respectively. The refractive index profiles of the waveguides with different doses were reconstructed by an effective refractive index method based on the reflectivity calculation method (RCM). The modal analysis indicates that the fields of TM modes can be well restricted in the guiding region, which means the formation of non-leaky waveguide in the crystal.

Keywords: PACS; 61.80.Jh; 42.70.Mp; 42.65.WiIon irradiation effects; Nonlinear optical materials; Nonlinear waveguides

Influence of excitation light wavelength on the photoluminescence properties for ZnO films prepared by magnetron sputtering by Q.P. Wang; X.J. Zhang; G.Q. Wang; S.H. Chen; X.H. Wu; H.L. Ma (pp. 5100-5104).

Highly orientated polycrystalline ZnO films were deposited on sapphire, silicon and quartz substrates at room temperature by r.f. magnetron sputtering. Different photoluminescence (PL) spectra were observed when excited with different wavelength light. A UV emission peak (356nm) and a blue peak (446nm) were generated for the films on sapphire, silicon and quartz substrates, and only the 446nm blue emission appeared for the films on glass substrates when the wavelength of the excitation light was 270nm. With increasing the wavelength of the excitation light up to 300 and 320nm, the UV emission disappeared for films on various substrates and the wavelength of the PL peaks increased up to 488 and 516nm, respectively. When the wavelength of the excitation light increased to 398nm, the PL spectrum becomes a wide band that is consistent with three emission peaks.

Keywords: PACS; 78.66.hf; 78.55.Et; 81.15.CodZnO films; Photoluminescence; RF sputtering; Excitation light

Laser micro-machining using near-field optics by Haseung Chung; Katsuo Kurabayashi; Suman Das (pp. 5105-5110).

Solid immersion lenses (SIL) facilitate high numerical aperture (NA) and consequent sub-wavelength diffraction limited focusing in near-field optics based systems. Such systems are in commercial and research use for various applications including near-field scanning optical microscopy, ultra-high-density magneto-optic data storage and near-field nanolithography. Here, we present a novel manufacturing method using SIL-based near-field optics for laser-induced patterning on silicon wafers. The near-field effect of SILs was investigated by using hemispherical lenses made of three different materials (BK7, Sapphire, LaSFN9) to superfocus an incident Q-switched, 532nm Nd:YAG laser beam transmitted through a focusing objective. This optical arrangement achieved a laser-processed feature resolution near the diffraction limit in air. Results of experiments that were conducted at various processing conditions to investigate the effects of varying incident laser power (with peak pulse power less than 1W), pulse width, number of pulses and size of SIL on processed feature size and resolution are presented. Experimental results are compared with numerical simulations using the simplified model.

Keywords: Solid immersion lenses; Numerical aperture; Optics; Laser

Effect of oxygen partial pressure on PLD cobalt oxide films by S. Laureti; E. Agostinelli; G. Scavia; G. Varvaro; V. Rossi Albertini; A. Generosi; B. Paci; A. Mezzi; S. Kaciulis (pp. 5111-5115).

Thin CoO oxide layers with superior properties in terms of crystallographic ordering, surface roughness and constant and controlled chemical compositions have been prepared by pulsed laser deposition in reactive O₂ atmosphere at 400°C. Such systems are particularly suitable both for applications and for basic studies, any time high quality and controlled surfaces are required, for example in multilayered systems whose behaviour critically depends on interface properties, such as magnetically exchange-coupled systems. A structural and microstructural study of such films is presented, together with the compositional analysis for different process conditions. The best control on film stoichiometry was obtained by protecting the surface with a thin Pt cap-layer, before air exposure.

Keywords: PACS; 81.15.Fg; 61.10.−i; 79.60.−iPulsed laser deposition; Cobalt oxide; Thin film growth

AFM and electronic transport studies of swift heavy ion irradiated Mn/ p-Si bilayer structure by P.C. Srivastava; M.K. Srivastava; P.S. Pandey (pp. 5116-5119).

Mn/ p-Si structures have been realised by electron beam evaporation of manganese on etched and cleaned p-Si wafers. Bilayer structures have been irradiated by swift heavy ions (of 100MeV Fe⁷⁺ having a fluence of 1×10¹³ions/cm²). The electronic transport features across the bilayer of the structure (i.e. I– V characteristics across the Mn/ p-Si interface) show a significant increase of current (by two orders of magnitude) for the irradiated ones as compared to un-irradiated ones. I– V characteristics across the interface has also been recorded in presence of in-plane (i.e., along the plane of the interface) magnetic field which show a significant magnetic field sensitivity for the irradiated ones. The surface morphological studies from AFM show a granular structure with open face having micro-particles in it, prior to the irradiation and round shaped embedded granular structure after the irradiation. XRD data show the formation of manganese silicide (Mn₅Si₂). The results are understood in the realm of interfacial intermixing which is tailored by the swift heavy ion irradiation.

Keywords: PACS; 64.75.Ef; 67.30.hp; 68.37.PsMixing; Interfaces; Atomic force microscopy (AFM)

Crystal orientation dependence of the in-plane dielectric properties for Ba(Sn_0.15Ti_0.85)O₃ thin films by Sannian Song; Lina Gao; Jiwei Zhai; Xi Yao; Zhiqun Cheng (pp. 5120-5123).

Barium tin titanate Ba(Sn_0.15Ti_0.85)O₃ (BTS) thin films with (100), (110) and (111) orientation were grown on (100), (110) and (111) LaAlO₃ (LAO) single-crystal substrates through sol–gel process, respectively. The in-plane dielectric properties of the films were measured on interdigital capacitor (IDC). Films with the (111) orientation had larger relative dielectric constant and larger tunability against the dc bias electric field than (100)- and (110)-oriented films. This difference in dielectric properties in these three kinds of oriented BTS films may be attributed due to change in the direction and magnitude of electric polarization in orientation engineered BTS films. This work clearly reveals the dielectric properties of BTS films exhibited a strong sensitivity to crystal orientation.

Keywords: PACS; 77.80.−e; 77.84.Dy; 81.20.Fw; 85.50.−nThin films; Sol–gel; Dielectric properties; Orientation; Stress

Self-assembly of β-Ga₂O₃ nanobelts by Ying Guo; Jing Zhang; Feng Zhu; Zhong Xue Yang; Jinzhou Xu; Jianyong Yu (pp. 5124-5128).

Self-assembly of β-Ga₂O₃ (beta-gallium oxide) nanobelts with diameters of 50–100nm and lengths of tens to hundreds of microns have been studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM). Under appropriate conditions such as nanobelts concentration, controlled solvent evaporation, β-Ga₂O₃ nanobelts assemble into a fan-like structure on the substrate. A tendency of these nanobelts to align parallel to each other was also observed. The mechanism behind the formation of self-assembly of β-Ga₂O₃ nanobelts has been proposed on the basis of lateral capillary forces.

Keywords: PACS; 81.16.Dn; 68.03.Kn; 81.07BkSelf-assembly; β-Ga; ₂; O; ₃; nanobelts; Capillary forces

Thermal stability of the structural features in the superhydrophobic boehmite films on austenitic stainless steels by Xiaoxue Zhang; Mari Honkanen; Mikael Järn; Jouko Peltonen; Viljami Pore; Erkki Levänen; Tapio Mäntylä (pp. 5129-5133).

Boehmite thin film with 50–100nm surface flake structure has been synthesized on AISI 316 type austenitic stainless steel by immersing boehmite gel film into boiling water. When further coated with hydrolyzed (heptadecafluoro-1,1,2,2-tetrahydrodecyl) trimethoxysilane (FAS), the boehmite film becomes superhydrophobic with a contact angle for water of 152°. The superhydrophobic property results from both the nanoscale surface flake structure and the low surface energy of the FAS top layer. The topography of such film was revealed by atomic force microscope (AFM) and a set of roughness parameters of such film was discussed. The degradation of superhydrophobicity of the surface was studied as a function of the heat-treatment temperatures. Below 600°C, the surface remained to be superhydrophobic with the FAS top layer. Above 700°C, the surface was not superhydrophobic anymore due to a gradual loss in surface roughness which was revealed by field emission scanning electron microscope (FESEM). A phase change from boehmite to γ-Al₂O₃ occurred during the heat-treatments from 700 to 900°C which was studied by the selected area electron diffraction (SAED) patterns from the transmission electron microscope (TEM) measurement.

Keywords: Superhydrophobic; Sol–gel technique; Roughness parameters; Transmission electron microscope; Selected area electron diffraction

Two-dimensional nanopatterning by PDMS relief structures of polymeric colloidal crystals by Hye Jin Nam; Ju-Hee Kim; Duk-Young Jung; Jong Bae Park; Hae Seong Lee (pp. 5134-5140).

A new constructive method of fabricating a nanoparticle self-assembly on the patterned surface of a poly(dimethylsiloxane) (PDMS) relief nanostructure was demonstrated. Patterned PDMS templates with close-packed microwells were fabricated by molding against a self-assembled monolayer of polystyrene spheres. Alkanethiol-functionalized gold nanoparticles with an average particle size of 2.5nm were selectively deposited onto a hydrophobic self-assembled monolayer printed on the substrate by the micro-contact printing (μCP) of the prepared PDMS microwell, in which the patterned gold nanoparticles consisted of close-packed hexagons with an average diameter of 370nm. In addition, two-dimensional colloidal crystals derived from PMMA microspheres with a diameter of 380nm and a negative surface charge were successfully formed on the hemispherical microwells by electrostatic force using positively charged PAH-coated PDMS as a template to produce multidimensional nanostructures.

Keywords: PACS; 81.16.Rf; 81.16.Dn; 81.65.CfPDMS; Microwells; Self-assembly; Micro-contact printing; Gold nanopattern; Colloidal crystal

Comparison of intrinsic zero-energy loss and Shirley-type background corrected profiles of XPS spectra for quantitative surface analysis: Study of Cr, Mn and Fe oxides by Masaoki Oku; Shigeru Suzuki; Naofumi Ohtsu; Toetsu Shishido; Kazuaki Wagatsuma (pp. 5141-5148).

The intrinsic zero-energy loss profiles of transition metal 2p and 3p XPS spectra for Cr, Mn, and Fe oxides are obtained by spectral deconvolution and compared with Shirley-type background corrected profiles. The metal core level spectra are deconvoluted by O 1s spectra as the response function of each oxide. As the O 1s spectra include intrinsic and extrinsic energy loss parts, the background corrected core level spectra are zero-energy loss spectra. The good agreement of the deconvoluted spectra with the reported spectra obtained by the many body effect theory indicates that the background subtraction method is accurate. A comparison of the deconvoluted with the background corrected spectra of the Shirely-type subtraction reveals that almost all the spectra coincide with each other except for Fe 3p with α-Fe₂O₃. The good coincidence of the Shirley-type corrected spectra with the deconvoluted and calculated spectra indicates that Shirley-type background correction can be used for daily quantitative surface analysis.

Keywords: XPS; Core levels; Intrinsic zero-energy loss profiles; Background correction; Shirley-type; Cr; Mn; Fe; Oxides

Atomic layer deposition of Cr₂O₃ thin films: Effect of crystallization on growth and properties by Aivar Tarre; Jaan Aarik; Hugo Mändar; Ahti Niilisk; Rainer Pärna; Raul Rammula; Teet Uustare; Arnold Rosental; Väino Sammelselg (pp. 5149-5156).

Atomic layer deposition of Cr₂O₃ thin films from CrO₂Cl₂ and CH₃OH on amorphous SiO₂ and crystalline Si(100) and α-Al₂O₃(11¯02) substrates was investigated, and properties of the films were ascertained. Self-limited growth with a rate of 0.05–0.1nm/cycle was obtained at substrate temperatures of 330–420°C. In this temperature range epitaxial eskolaite was formed on the α-Al₂O₃(11¯02) substrates. The predominant crystallographic orientation in the epitaxial films depended, however, on the growth temperature and film thickness. Sufficiently thick films grown on the SiO₂ and Si(100) substrates contained also the eskolaite phase, but thinner films deposited at 330–375°C on these substrates were amorphous. The growth rate data of films with different phase composition allowed a conclusion that the crystalline phase grew markedly faster than the amorphous phase did. The amorphous, polycrystalline and epitaxial films had densities of 4.9, 5.1 and 5.1–5.3g/cm³, respectively.

Keywords: PACS; 81.15.Gh; 81.05.Je; 68.55−aChromium(III) oxide; Thin films; Atomic layer deposition; Epitaxy; Surface phenomena

Adsorption and thermodynamic studies of Cu(II) and Zn(II) on organofunctionalized-kaolinite by Denis Lima Guerra; Claudio Airoldi; Kaline S. de Sousa (pp. 5157-5163).

Kaolinite-bearing clay samples from Perus, São Paulo state, Brazil, were used for chemical modification process with dimethyl sulfoxide and organofunctionalized with the silyating agent (RO)₃Si(CH₂)₃NH(CH₂)₂NH₂ in the present study. The resulting material and natural kaolinite were subjected adsorpion process with Cu(II) and Zn(II) from aqueous solution at pH 6.0 and controlated temperature of 298K. The Langmuir adsorption isotherm model has been applied to fit the experimental data. The results showed that the chemical modification process increases the basal spacing of the natural kaolinite from 0.711 to 0.955nm. The energetic effects caused by Cu(II) and Zn(II) interactions were determined through calorimetric titration at the solid–liquid interface and gave a net thermal effect that enabled the calculation of the exothermic values and the equilibrium constant.

Keywords: Kaolinite; Adsorption isotherms; Calorimetry; Thermodynamic

Amorphous and crystalline IrO₂ thin films as potential stimulation electrode coatings by Sachin S. Thanawala; Ronald J. Baird; Daniel G. Georgiev; Gregory W. Auner (pp. 5164-5169).

Amorphous and crystalline iridium oxide thin films with potential use as coating materials for stimulation electrodes were studied. Characterization of these films by cyclic voltammetry and impedance spectroscopy has revealed a considerable decrease in impedance and an increase in charge capacity of iridium oxide thin films after an electrochemical activation process in 0.9% NaCl solution. The surface morphology of these films was studied by scanning electron microscopy. The two types of IrO₂ films were also compared under conditions relevant to applications as stimulation electrodes. The results indicate that amorphous IrO₂ films have significantly higher charge storage capacity and lower impedance than crystalline IrO₂ films. This makes the amorphous films a preferable coating material for stimulation applications.

Keywords: Iridium oxide; Stimulation electrodes; Coatings; Impedance spectroscopy; Scanning electron microscopy

One-step copolymerization modified magnetic nanoparticles via surface chain transfer free radical polymerization by Shixing Wang; Yang Zhou; Wen Guan; Bingjun Ding (pp. 5170-5174).

Copolymer brushes growing onto magnetic nanoparticles were prepared by surface chain transfer free radical polymerization. Block copolymer brushes (P(PEGMA)- co-PNIPAAm) consist of poly(ethylene glycol) monomethacrylate (PEGMA) and N-isopropylacrylamide monomer. X-ray photoelectron spectroscopy (XPS) characterized the chemical composition of copolymer. Thermogravimetric analysis (TGA) suggested that the amount of copolymer on magnetic nanoparticles decreased with increasing azodiisobutyronitrile (AIBN). The saturation magnetization decreased significantly with increasing P(PEGMA)- co-PNIPAAm. The thermosensitive point is about 43°C for magnetic nanoparticles with 33.8% P(PEGMA)- co-PNIPAAm.

Keywords: Magnetic nanoparticles; Surface free radical polymerization; Thermosensitive

DNA-based organic-on-inorganic semiconductor Schottky structures by Ö. Güllü; M. Çankaya; Ö. Barış; M. Biber; H. Özdemir; M. Güllüce; A. Türüt (pp. 5175-5180).

A sandwich device has been fabricated from DNA molecular film by solution processing located between Al and p-type silicon inorganic semiconductor. We have performed the electrical characteristics of the device such as current–voltage ( I– V), capacitance–voltage ( C– V) and capacitance–frequency ( C– f) at room temperature and in dark. The DNA-based structure has showed the rectifying behavior. From its optical absorbance spectrum, it has been seen that DNA has been a semiconductor-like material with wide optical band energy gap of 4.12eV and resistivity of 1.6×10¹⁰Ωcm representing a p-type conductivity.

Keywords: Schottky barrier; Organic–inorganic contact; DNA; Organic semiconductor

Synthesis and physico-chemical characteristics of nanosized particles produced by laser ablation of a nickel target in water by R. Mahfouz; F.J. Cadete Santos Aires; A. Brenier; B. Jacquier; J.C. Bertolini (pp. 5181-5190).

Ablation of Ni targets in water by laser impact (532nm, 40mJ/pulse, 10Hz and 8ns duration) focused on massive samples (∼2mm diameter) generates colloids with fine nanoparticles. The amount of metal released in the solution (measured by mass loss of the target or ICP) was found to increase first linearly with time, but slower after 8min of impact. The size distribution of the nanoparticles thus produced was measured (by TEM) to be in the range 3–5.3nm in diameter, with a tendency for the size to be smaller for larger number of laser shots. Actually, nickel oxide nanoparticles were produced, rather than nickel nanoparticles as it was shown by HRTEM. XPS photoemission measurements evidenced the presence of nickel oxide species on the crater of the nickel sample surface after laser ablation.

Keywords: Ni; NiO; Nanoparticles; Laser ablation in liquid phase; HRTEM; XPS photoemission

Role of phosphorus in synthesis of phosphated mesoporous TiO₂ photocatalytic materials by EISA method by Xiaoxing Fan; Tao Yu; Ying Wang; Jing Zheng; Ling Gao; Zhaosheng Li; Jinhua Ye; Zhigang Zou (pp. 5191-5198).

The phosphated mesoporous TiO₂ (PMT) were synthesized by using evaporation-induced self-assembly approach (EISA) with phosphorus content from 1 to 15mol%. The X-ray diffraction and N₂ adsorption–desorption isothermal results reveal that the incorporating of phosphorus is of benefit to improving the thermal stability and enhancing the surface area of mesoporous TiO₂ by constraining the growth of anatase crystallite. XPS confirms the phosphorus in the calcined PMT exists as amorphous titanium phosphate in a pentavalent-oxidation state (P⁵⁺) and embedded into the nanocrystalline anatase TiO₂. In photodegradation gas phase acetaldehyde, the photocatalytic activity of PMT samples is higher than that of pure mesoporous TiO₂ and P25. It is believed that the enhancing photocatalytic activity of phosphated mesoporous TiO₂ is mainly caused by two factors relative with the incorporating of phosphorus in framework.

Keywords: Phosphated mesoporous TiO; ₂; Amorphous titanium phosphate; Photocatalysis; Acetaldehyde

Localized dissolution electrochemistry at surface irregularities of pipeline steel by X. Tang; Y.F. Cheng (pp. 5199-5205).

The localized electrochemical dissolution behavior at surface irregularities, including scratch, mechanically induced hole and corrosion pit, on pipeline steel was investigated in both near-neutral pH and high pH solutions by scanning vibrating micro-electrode and localized electrochemical impedance spectroscopy measurements. In near-neutral pH solution, the localized dissolution behavior at surface irregularities is dependent of their geometrical depth, which is critical to development of a local electrochemical condition to support the further localized dissolution. Therefore, surface irregularities exceeding a certain depth provide potential sites to initiate stress corrosion cracks in near-neutral pH solution. The strong passivating capability of high pH solution would result in the formation of oxide film over the whole electrode surface to “equalize” the electrochemical activity at irregularities to the intact area. Therefore, the irregularities would not result in localized dissolution electrochemistry. Consequently, localized corrosion and crack initiation are not anticipated to initiate from the geometrical irregularities in high pH solution. However, corrosion pits generating due to passive film breakdown could support the high local dissolution kinetics in high pH solution, providing potential sites for crack initiation. The effects of hydrogen-charging on anodic dissolution at regularities depend on the defect geometry and the solution pH.

Keywords: Anodic dissolution; Surface irregularities; Pipeline steel; Scanning vibrating micro-electrode; Localized electrochemical impedance spectroscopy

Structural and optical properties of pulsed laser deposited SrBi₂Nb₂O₉ thin films by Kansong Chen; Haoshuang Gu (pp. 5206-5210).

SrBi₂Nb₂O₉ (SBN) thin films were prepared on fused quartz substrates at room temperature by pulsed laser deposition. The influence of deposition parameters such as target-to-substrate distance, oxygen pressure and annealing temperature on film crystallization behavior was investigated by X-ray diffraction. Results indicated that the films grown at the optimum processing conditions have polycrystalline structure with a single layered perovskite phase. The optical transmittance of the films prepared at various oxygen pressures was measured in the wavelength range 200–900nm using UV–vis spectrophotometer. The results showed that there is a red shift in the optical absorption edge with a rise in the oxygen pressure. Refractive index as a function of wavelength and optical band gap of the films were determined from the optical transmittance spectra. The results indicated that the refractive index increases with increasing oxygen pressure at the same incident light wavelength, while the band gap reduces from 4.13 to 3.88eV. It may be attributed to an increase in packing density and grain size, and decrease in oxygen defects.

Keywords: PACS; 77.84.Dy; 78.20.Ci; 81.15.FgSrBi; ₂; Nb; ₂; O; ₉; thin films; Pulsed laser deposition; Optical transmittance; Optical band gap

RF-sputtered CrB₂ diffusion barrier for Ni/Au Ohmic contacts on p-CuCrO₂ by W.T. Lim; P.W. Sadik; D.P. Norton; B.P. Gila; S.J. Pearton; I.I. Kravchenko; F. Ren (pp. 5211-5215).

Ohmic contacts to p-type CuCrO₂ using Ni/Au/CrB₂/Ti/Au contact metallurgy are reported. The samples were annealed in the 200–700°C range for 60s in flowing oxygen ambient. A minimum specific contact resistance of ∼2×10⁻⁵Ωcm² was obtained after annealing at 400°C. Further increase in the annealing temperature (>400°C) resulted in the degradation of contact resistance. Auger Electron Spectroscopy (AES) depth profiling showed that out-diffusion of Ti to the surface of the contact stacks was evident by 400°C, followed by Cr at higher temperature. The CrB₂ diffusion barrier decreases the specific contact resistance by almost two orders of magnitude relative to Ni/Au alone.

Keywords: CuCrO; ₂; Ohmic contacts

Preparation and characterization of a novel Si-incorporated ceramic film on pure titanium by plasma electrolytic oxidation by Wei Zhang; Keqin Du; Chuanwei Yan; Fuhui Wang (pp. 5216-5223).

A Si-incorporated bioactive ceramic film was prepared on pure titanium by plasma electrolytic oxidation (PEO) in a new bath containing Ca²⁺, H₂PO₄⁻ and SiO₃²⁻. The film was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscope (XPS). The apatite-induced ability of PEO film was evaluated by soaking in a simulated body fluid (SBF) for various periods. The results showed that Si-incorporated PEO film present a porous microstructure, the pore size is around 1–5μm. The film mainly consists of anatase and rutile and a small amount of CaHPO₄ and CaO, besides, bioactive compounds such as CaSiO₃ and SiO₂, also exist in the Si-incorporated PEO film. After immersion in SBF for 28 days, not only the surface layer but also the pores inside the Si-incorporated PEO film were completely filled by apatite crystals, whereas on the surface of a benchmark PEO film free of Si just present small piles of apatite crystals. Silicon incorporated into the PEO film provided more heterogeneous nucleation sites for apatite deposition and hence increased remarkably bioactivity of the PEO film.

Keywords: Titanium; Plasma electrolytic oxidation; Ceramic film; Bioactivity; Apatite

Preparation of silver nanoparticles by laser ablation in polyvinylpyrrolidone solutions by Takeshi Tsuji; D.-H. Thang; Yuuki Okazaki; Masataka Nakanishi; Yasuyuki Tsuboi; Masaharu Tsuji (pp. 5224-5230).

We performed laser ablation of a silver plate in polyvinylpyrrolidone (PVP) aqueous solutions to prepare silver nanoparticles. Secondary laser irradiation onto the prepared colloidal solutions was also carried out. It was revealed that the formation efficiency was increased by addition of PVP as well as the stability of nanoparticles. The result of shadowgraph measurements suggested that the increased ablation efficiency by PVP is attributable to increased secondary etching efficiency by the solvent-confined plasma toward the silver plate. On the other hand, the size decrease of the nanoparticles by addition of PVP was more remarkable during the secondary irradiation process than in the laser ablation (nanoparticle preparation) process. This result indicates that emitted materials interact less sufficiently with PVP molecules in the laser ablation process than in the secondary laser irradiation process.

Keywords: PACS; 42.62.−b; 79.20.Ds; 82.70.DdLaser ablation; Silver; Nanoparticles; Silver; Polyvinylpyrrolidone

Investigations on the optical, thermal and surface modifications of electron irradiatedl-threonine single crystals by G. Ramesh Kumar; S. Gokul Raj; K.A. Bogle; S.D. Dhole; V.N. Bhoraskar; R. Mohan (pp. 5231-5235).

l-Threonine single crystals have been irradiated by 6MeV electrons. Irradiated crystals at various electron fluences were subjected to various techniques such as UV–vis–NIR, atomic force microscopy (AFM) and thermomechanical analyses. Thermal strength of the irradiated crystals has also been studied through differential scanning calorimetry (DSC) measurements. The results have been discussed in detail.

Keywords: NLO crystal; Electron irradiation; UV–vis–NIR spectra; AFM; TMA analysis

A facile strategy for covalent binding of nanoparticles onto carbon nanotubes by Ping Xu; Daxiang Cui; Bifeng Pan; Feng Gao; Rong He; Qing Li; Tuo Huang; Chenchen Bao; Hao Yang (pp. 5236-5240).

This paper describes a simple strategy for covalently attaching nanoparticles onto the carbon nanotubes (CNTs) to fabricate hybrid nanostructure. Densely distributed magnetite nanoparticles (MNPs) with a size of ∼8nm have been deposited on the surface of carbon nanotubes by covalent interaction. Transmission electron microscopy (TEM), FT-IR spectroscopy, and X-ray diffraction (XRD) analysis have been used to study the formation of MNP/CNT nanostructure. The strategy employed herein is quite generic and applicable to a variety of nanoparticles, including metal, quantum dot and oxide. These composite nanostructures should open up new possibilities in areas such as nanoelectronics, chemical sensing, field-emission displays, nanotribology, and cell adhesion/biorecognition investigations.

Keywords: Carbon nanotubes; Magnetite nanoparticles; Covalent binding; Nanohybrids

Strain relaxation and surface morphology of high indium content InAlAs metamorphic buffers with reverse step by Zhongwei Jiang; Wenxin Wang; Hanchao Gao; Linshen Liu; Hong Chen; Junming Zhou (pp. 5241-5246).

Low-temperature step-graded high indium content InAlAs (In%=0.75) metamorphic buffer layers with reverse step layer grown on GaAs substrate by molecular beam epitaxy are investigated in this paper. The composition and the strain relaxation of the top InAlAs layer are determined by high-resolution triple-axis X-ray diffraction measurements, which show that the top InAlAs layer is nearly fully relaxed and the growth parameters for these samples have little influence on the strain relaxation ratio. Surface morphology is observed by reflection high-energy electron diffraction pattern and atomic force microscopy. The surface morphology is found to depend strongly on both the growth temperature and the As flux. Compared with other samples, the sample growth under the optimized conditions has the smallest value of root mean square surface roughness. Furthermore, the ω−2 θ and ω scans of the triple-axis X-ray diffraction and transmission electron microscopy result also show the sample grown under the optimized conditions has good crystalline quality.

Keywords: PACS; 81.15; 72.80.e; 68.55Molecular beam epitaxy; Metamorphic buffer layer; X-ray diffraction; Atomic force microscopy

Effect of heat-pretreatment of the graphite rod on the quality of SWCNTs by arc discharge by Zijiong Li; Liangming Wei; Yafei Zhang (pp. 5247-5251).

Single-walled carbon nanotubes (SWCNTs) have been synthesized in high yield by the dc arc discharge technique under heat-pretreatment of the graphite rod conditions. Before executing arc discharge, the graphite rods containing the catalysts were heat treated at 600, 700, 800 and 900°C for 1–3h, respectively. Effects of heat-pretreatment of the graphite rod on the quality of SWCNTs by arc discharge were investigated. The heat-treatment temperature and time were found to be crucial for a high yield of high-purity SWCNTs. Optimum parameter was found to be at the heat-treatment temperature of 800°C for 2h. The SWCNTs synthesized under the optimum condition have better field-emission characteristics. The turn-on field needed to produce a current density of 10μA/cm² is found to be 1.9V/μm and the threshold field where current density reaches 10mA/cm² is 3.9V/μm.

Keywords: Single-walled carbon nanotubes; Arc discharge; Heat-pretreatment; Raman spectroscopy; Field emission

Electrical and piezoresistive properties of ion beam deposited DLC films by Š. Meškinis; R. Gudaitis; V. Kopustinskas; S. Tamulevičius (pp. 5252-5256).

In present study diamond like carbon (DLC) films were deposited by closed drift ion source from the acetylene gas. The electrical and piezoresistive properties of ion beam synthesized DLC films were investigated. Diode-like current–voltage characteristics were observed both for DLC/nSi and DLC/pSi heterostructures. This fact was explained by high density of the irradiation-induced defects at the DLC/Si interface. Ohmic conductivity was observed for DLC/nSi heterostructure and metal/DLC/metal structure at low electric fields. At higher electric fields forward current transport was explained by Schottky emission and Poole–Frenkel emission for the DLC/nSi heterostructures and by Schottky emission and/or space charge limited currents for the DLC/pSi heterostructures. Strong dependence of the diamond like carbon film resistivity on temperature has been observed. Variable range hopping current transport mechanism at low electric field was revealed. Diamond like carbon piezoresistive elements with a gauge factor in 12–19 range were fabricated.

Keywords: Diamond like carbon; Ion beam deposition; Electrical properties; Piezoresistive effect

Synthesis and optical characterization of c-axis oriented GaN thin films on amorphous quartz glass via sol–gel process by Godhuli Sinha; Kalyan Adhikary; Subhadra Chaudhuri (pp. 5257-5260).

c-Axis oriented GaN nanocrystalline thin films were fabricated by nitridation of three different thin films of α-GaO(OH), α-Ga₂O₃ or β-Ga₂O₃ obtained by sol–gel technique on amorphous quartz glass substrates. All these GaN thin films showed near band edge emission at 390nm and yellow luminescence at 570nm. The crystalline nature and c-axis orientation as well as luminescence properties of the GaN thin films increased by several times by using a buffer layer of GaN on the substrate.

Keywords: PACS; 61.82.Fk; 61.82.Rx; 71.55.Eq; 78.55.−mGaN; Gallium oxide; Nanocrystals; Thin films; c; -Axis orientation; Photoluminescence

Growth mechanism and characterisation of chemically grown Sb doped Bi₂Se₃ thin films by N.S. Patil; A.M. Sargar; S.R. Mane; P.N. Bhosale (pp. 5261-5265).

The synthesis of combinatorial Bi2−_xSb_xSe₃ thin films by arrested precipitation technique (APT) using triethanolamine-bismuth, triethanolamine-antimony and sodium selenosulphite as sources of Bi³⁺, Sb³⁺ and Se²⁻, respectively is investigated on commercial glass substrates. The growth mechanism of film formation, composition and surface morphology of the as deposited films were studied as a function of preparative parameters and bath composition. The films were monophasic, polycrystalline and covered the surface of the substrate completely. Energy dispersive X-ray analysis gave coherent elemental composition indicating single phase BiSbSe₃ was made. The good results obtained for Bi2−_xSb_xSe₃ thin films revealed that arrested precipitation technique is best suited for the deposition of large area thin films on conducting/nonconducting substrates to produce materials for device applications.

Keywords: Thin Films; Bi; 2−; _x; Sb; _x; Se; ₃; XRD; SEM

Influence of un-cured PDMS chains in stamp using PDMS-based lithography by Jinook Kim; Mikyung Park; Gee Sung Chae; In-Jae Chung (pp. 5266-5270).

We present the compatibility of elastomeric stamp, poly(dimethylsiloxane) (PDMS), with inks for non-photolithography. This ink limitation is important in considering the lamination of hydrophilic solution on the patterned ink surface using an elastomeric stamp. We focus on an increase of the hydrophobicity of the patterned surface due to diffusion of low molecular weight (LMW) silicone polymer chains. This hydrophobicity increases inversely with the PDMS–ink interaction parameter ( χ), which is correlated with the solubility parameter ( δ). This study's results translate into proposed design factors for ink used in the patterned functional layer for PDMS-based lithography. Both the XPS and the contact angle measurement show that the hydrophobicity can be increased by LMW PDMS chains transfer from stamps, and this increase can cause the expansion of the free volume in PDMS pores through a swelling effect.

Keywords: PDMS stamp; Non-conventional lithography; Ink; Solubility parameter

Adsorption kinetics and dynamics of small organic molecules on a silica wafer: Butane, pentane, nonane, thiophene, and methanol adsorption on SiO₂/Si(111) by S. Funk; J. Goering; U. Burghaus (pp. 5271-5275).

The adsorption kinetics (by thermal desorption spectroscopy) and adsorption dynamics (by molecular beam scattering) have been determined for a number of alkanes, methanol, thiophene, and water on a silica wafer—SiO₂/Si(111). No indications for bond activation were present, i.e., all probe molecules adsorb molecularly obeying 1st order kinetics. The coverage-dependent heat of adsorption has been determined accordingly. The adsorption dynamics are precursor-mediated with Kisliuk-like shapes of the adsorption probabilities at low impact energies and adsorbate-assisted adsorption at large impact energies.

Keywords: Kinetics; Dynamics; Alkanes; Thiophene; Methanol; Water; TDS; Molecular beam scattering

Preparation of S-TiO₂ photocatalyst and photodegradation of L-acid under visible light by Yuping Wang; Jie Li; Panying Peng; Tianhong Lu; Lianjun Wang (pp. 5276-5280).

S-doped TiO₂ (S-TiO₂) photocatalyst was synthesized by sol–gel method with tetrabutyl titanate and thiourea as precursor. S-TiO₂ was characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV–vis absorption spectroscopy, transmission electron microscopy (TEM) and the photocatalytic activity was evaluated by 1-naphthol-5-sulfonic acid (L-acid) under UV, visible light and solar light radiation. The results showed that doped S could improve photoabsorption property of TiO₂ in the visible region, leading the increase in the photocatalytical activity of TiO₂.The average particle size of the S-TiO₂ photocatalyst is about 10nm. The S-TiO₂-4 photocatalyst contains 100% anatase crystalline phase of TiO₂. In the S-TiO₂-4 photocatalyst, S does not exist independently, but is incorporated into the crystal lattice of TiO₂. In the inner crystal lattice of the S-TiO₂-4 photocatalyst, S as S²⁻ replaces O in TiO₂, while on the surface of crystal lattice, S exists as S⁴⁺ and S⁶⁺.The photocatalytical activity of S-TiO₂-4 photocatalyst for the photodegradation of L-acid is better than that of pure TiO₂. Under the same conditions, the photodegradation efficiency of L-acid for the S-TiO₂-4 photocatalyst and the solar light irradiation is 85.1%, while it is only 26.4% for pure TiO₂. In addition, the final products of the photocatalysis of L-acid using the S-TiO₂-4 photocatalyst are not organic compounds with low molecular weight, but the inorganic compounds.

Keywords: PACS; 81.15Lm.; 61.72.Vv; 78.67.BfTiO; ₂; S-doped TiO; ₂; 1-Naphthol-5-sulfonic acid; Photocatalyst; Photodegradation

Gradient formation of boride layers by borocarburizing by M. Kulka; A. Pertek (pp. 5281-5290).

In this study borocarburizing was used for the formation of gradient boride layers. The microstructure, microhardness profiles and the low-cycle fatigue strength during radial compression of carburized, borided and borocarburized layer have been compared. The gradient borocarburized layers, formed by boriding of previously carburized substrate, are characterized by two zones in diffusion layer: iron borides zone and carburized zone. After borocarburizing the iron borides show a tendency towards a loss of the needle-like nature. The hardness gradient between iron borides and low-carbon substrate is reduced. The microhardness beneath the iron borides decreases to 900HV in carburized zone and next gradually decreases to 400–450HV in the core of steel. The highest resistance to low-cycle fatigue during radial compression has been observed in case of carburized and through hardened layer. The fatigue strength of gradient boride layer (borocarburized and through hardened) is a little lower. The typical borided and through hardened layer is characterized by the lowest resistance to low-cycle fatigue during radial compression. The profiles of stresses after boriding and borocarburizing have been compared. The obtained profile of stresses and the lower values of tensile stresses at the surface can be the reason for higher frictional wear resistance of borocarburized layers and for higher fatigue strength of these layers, too.

Keywords: Carburizing; Boriding; Borocarburizing; Microstructure; Microhardness; Low-cycle fatigue; Internal stresses

Synthesis and physical behaviour of In₂S₃ films by N. Revathi; P. Prathap; K.T. Ramakrishna Reddy (pp. 5291-5298).

In₂S₃ layers have been grown by close-spaced evaporation of pre-synthesized In₂S₃ powder from its constituent elements. The layers were deposited on glass substrates at temperatures in the range, 200–350°C. The effect of substrate temperature on composition, structure, morphology, electrical and optical properties of the as-grown indium sulfide films has been studied. The synthesized powder exhibited cubic structure with a grain size of 63.92nm and S/In ratio of 1.01. The films grown at 200°C were amorphous in nature while its crystallinity increased with the increase of substrate temperature to 300°C. The films exhibited pure tetragonal β-In₂S₃ phase at the substrate temperature of 350°C. The surface morphological analysis revealed that the films grown at 300°C had an average roughness of 1.43nm. These films showed a S/In ratio of 0.98 and a lower electrical resistivity of 1.28×10³Ωcm. The optical band gap was found to be direct and the layers grown at 300°C showed a higher optical transmittance of 78% and an energy band gap of 2.49eV.

Keywords: In; ₂; S; ₃; thin films; CSE technique; Structural and morphological properties; Optical properties

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Applied Surface Science (v.254, #16)

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Applied Surface Science (v.254, #16)