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Applied Surface Science (v.252, #20)

Adhesive-free bonding of Zerodur glass to silicon by M. Waris; M. Ahmed (pp. 7327-7330).

This work demonstrates anodic bonding of Zerodur glass having very low co-efficient of thermal expansion (CTE) to Si, Zerodur glass to thermally grown silicon dioxide on silicon and Pyrex glass to Ge. Bonding results, using point cathode contact and plate cathode contact configurations, are discussed. Bonding parameters, i.e. applied dc voltage, temperature and bonding time were determined. Heating and cooling rates for crack-free bonding of Zerodur glass were also determined.

Keywords: PACS; 68.35.Np; 82.45.CcAnodic bonding; Zerodur glass; Pyrex glass; Si; Ge

Energy calculation of (011) twist grain boundary in noble metals by Xiu-Mei Wei; Jian-Min Zhang; Ke-Wei Xu (pp. 7331-7336).

With modified analytical embedded atom method (MAEAM), the energy of (011) twist grain boundary (GB) has been calculated for three noble metals Cu, Ag and Au. The results show that the unrelaxed energy keeps almost constant with twist angle θ except several cusps at low Σ boundaries. The GB energies drop significantly after expansion perpendicular to the boundary. In-boundary translation results in a periodic energy variation and the rectangular period is 1/ Σ of their own CSL smallest unit cell. Three specific positions, the corners or centre of the periodic rectangle, or the midpoints of the sides, are preferable in GB translation.

Keywords: PACS; 61.43.Bn; 61.72.Mm; 98.38.BnGrain boundary energy; MAEAM; Volume expansion; Translation

Spatial and geometrical control of silicification using a patterned poly-l-lysine template by Randall T. Butler; Nicholas J. Ferrell; Derek J. Hansford (pp. 7337-7342).

A simple process to achieve patterned silica films is described. The patterning of the catalyst poly-l-lysine via photolithography and liftoff enables the spatial and geometrical control of silicification. Microscopy and chemical characterization demonstrate that this process enables consistent patterning of silica with 10μm resolution in a variety of geometries. In addition, the spatial and geometrical control of the silica is demonstrated under different reaction conditions and yields various silica morphologies. The ability to simultaneously pattern bio-inspired silica and control its morphology may allow the tailoring of silica and other silicon-based materials for future applications.

Keywords: PACS; 81.15.Lm (liquid phase deposition); 81.16.Be (chemical synthesis)Silica; Biosilicification; Patterning; Poly-; l; -lysine

Direct writing of microtunnels using proton beam micromachining by Laurent Marot; Frans Munnik; Sergueï Mikhaïlov (pp. 7343-7346).

The production of high aspect ratio microstructures is a potential growth area. The combination of deep X-ray lithography with electroforming and micromolding (i.e. LIGA) is one of the main techniques used to produce 3D microstructures. The new technique of proton micromachining employs focused MeV protons in a direct write process which is complementary to LIGA. During ion exposure of positive photoresist like PMMA, scission of molecular chains occurs. These degraded polymer chains are removed by the developer. The aim of this paper is to investigate the capabilities of proton micromachining as a lithographic technique. We show the realization of sub-surface channels, or microtunnels, which have been fabricated in only one exposure and without cutting or resurfacing the material. Using our Van-de-Graaff accelerator, the resist (PMMA) has been exposed with high-energy protons (2.5MeV). The range of charged particles in matter is well-defined and depends on the energy. Therefore, it is possible to obtain a dose which is sufficient to develop the bottom part of the ion paths but not the top part. Thus, by selecting the energy and the exposure time, a big variety of microtunnels can be realized.

Keywords: PMMA; Ion beam lithography; Microtunnels; Micromachining

Growth of single-walled carbon nanotubes on porous silicon by Rui Wang; Huaming Xu; Liqiu Guo; Ji Liang (pp. 7347-7351).

Porous silicon is an important and versatile material in the semiconductor industry, and can be achieved by electrochemically etching silicon wafers. Employing porous silicon as substrates, this article presents a new approach to grow single-walled carbon nanotubes on wafers for device applications. Free from support materials, this method is a clean one. At the same time it is feasible and robust, as porous silicon is remarkably superior to polished surface in facilitating the nucleation of catalyst. The superiority of porous silicon over polished surface is attributed to their different dewetting manners.

Keywords: Single-walled carbon nanotubes; Porous silicon; Synthesis; Silicon wafers; Dewetting

Sub-layer growth of MnHg(SCN)₄(C₂H₆OS)₂ crystal by Y.L. Geng; D. Xu; X.Q. Hou; X.Q. Wang; H.B. Zhang; W.F. Guo; G.H. Zhang (pp. 7352-7355).

Growth steps and 2D nuclei are observed by AFM on the {001} faces of MnHg(SCN)₄(C₂H₆OS)₂ (MMTD) crystals. Measurements of the heights of steps and nuclei show the lowest value is equal to c/4. According to the interplanar distance modification established by Donney and Harker, the lowest height should be c/2. Appearance of the sub-layer growth is correlative with the crystal structure of MMTD.

Keywords: Steps; Atomic force microscopy; 2D nucleation; Crystal structure; Nonlinear optical materials

A novel high-frequency resistance coating by utilizing nano titania particle by Jianhui Fang; Qingdong Zhong; Michael Rohwerder; Liyi Shi; Jianping Zhang (pp. 7356-7360).

In this paper, a liquid-phase hydrolization method to synthesize nanometer rutile titania directly without transformation from anatase is proposed. By utilizing this method, the particle size of the rutile titania nanoparticles can be controlled by adjusting the reaction conditions, e.g. the concentration of sodium hydroxide solution, reaction temperature, and calcining temperature of the powder. These titania nanoparticles have been used for the preparation of a novel composite insulation coating for magnet wires. First results showed that the lifetime of the modified nanomagnet wire in the inverter-fed motor could be prolonged to eight times compared with the non-modified wire.

Keywords: Titania nanoparticle; Composite insulation coating; Magnet wire

Corrosion resistance and lubricated sliding wear behaviour of novel Ni–P graded alloys as an alternative to hard Cr deposits by Liping Wang; Yan Gao; Tao Xu; Qunji Xue (pp. 7361-7372).

Alternative process to hexavalent chromium, substitute materials and new designs are urgently needed owing to the requirement of “clean�? manufacture. This comparative study was conducted to systematically investigate the corrosion resistance and lubricated sliding wear behavior of graded Ni–P alloy deposits produced from a single plating bath by electrodeposition and hard Cr deposits, using potentiodynamic polarization and reciprocating ball-on-disc tribometer. Results showed that Ni–P deposits heat-treated at 400°C with maximum hardness exhibited more than two orders of magnitude higher corrosion resistance than hard Cr deposits in 10wt.% HCl solution. The Stribeck curves for the heat-treated Ni–P gradient deposits and hard Cr under lubrication conditions were obtained with accurate control of normal load and sliding speed during the wear process, three main different regimes corresponding to different lubrication mechanism were identified. Heat-treated Ni–P gradient deposits showed relatively poor wear resistance than hard Cr deposits under the lubrication conditions, which may be attributed to superior oil-retaining surface structure and the unique “nodular�? effect of hard Cr in wear process.

Keywords: Corrosion resistance; Graded Ni–P deposits; Electrodeposition; Lubrication; Hard chromium

Sputter depth profiling by secondary ion mass spectrometry coupled with sample current measurements by U. Bardi; S.P. Chenakin; A. Lavacchi; C. Pagura; A. Tolstogouzov (pp. 7373-7382).

Ion-induced secondary electron emission determined via sample current measurements (SCM) was employed as a useful adjunct to conventional secondary ion mass spectrometry (SIMS). This paper reports on the results of 3–6keV O₂⁺ SIMS–SCM sputter depth profiling through CrN/AlN multilayer coatings on nickel alloy, titanium dioxide films deposited on stainless steel, and corrosion layers formed onto surface of magnesium alloy after long-term interaction with an ionic liquid. For Au/AlNO/Ta films on silicon, in addition to SIMS–SCM profiles, the signal of mass–energy separated backscattered Ne⁺ ions was monitored as a function of the depth sputtered as well. The results presented here indicate that secondary electron yields are less affected by “matrix effect�? than secondary ion yields, and at the same time, more sensitive to work function variations and surface charging effects. SCM depth profiling, with suppression of “the crater effect�? by electronic gating of the registration system is capable of monitoring interfaces in the multilayer structure, particularly, metal–dielectric boundaries. In contrast to SIMS, SCM data are not influenced by the angle and energy windows of an analyser. However, the sample current measurements provide lower dynamic range of the signal registration than SIMS, and SCM is applicable only to the structures with different secondary electron emission properties and/or different conductivity of the layers. To increase the efficiency, SCM should be accompanied by SIMS measurements or predetermined by proper calibration using other elemental-sensitive techniques.

Keywords: PACS; 68.55.Nq; 82.80.MsDepth profiling; Ion-beam sputtering; Ion-induced secondary electron emission; Ionic liquids; Multilayer structures; Secondary ion mass spectrometry (SIMS)

X-ray topography of polydiacetylene single crystals prepared by using physical vapor growth technique by Sadaharu Jo; Hitoshi Yoshikawa; Akane Fujii; Mitsuru Takenaga (pp. 7383-7388).

The lattice defects in polydiacetylene (PDA) single crystals prepared using physical vapor growth were investigated by white beam X-ray topography. Line patterns along the [001] and [102] directions were clearly observed. Appearance of the line patterns along the [001] direction proves the polymerization direction predicted by Hädicke et al. The topographic results are in good agreement with the surface morphologies investigated by atomic force microscopy (AFM).

Keywords: PACS; 61.72FfPolydiacetylene; Physical vapor growth; Single crystal; X-ray topography; Atomic force microscopy

Study on the properties and charge generation in dye-sensitized n-TiO₂|dye|p-CuI solid state photovoltaic solar cells by M. Rusop; T. Shirata; P.M. Sirimanne; T. Soga; T. Jimbo; M. Umeno (pp. 7389-7396).

Transparent semiconducting copper iodide (CuI) films were prepared by XeCl Excimer laser and their characteristics are investigated. These films exhibited optical transmittance over 80% in the wavelength range from 400 to 900nm and minimum resistivity of about 2kΩcm⁻¹. The optical absorption of the these films shows a remarkable blue shift compared to that of polycrystalline of CuI, which can be explained from the viewpoint formation of ultra fine of CuI grains. The titanium dioxide (TiO₂) films have been prepared by sol–gel method. The properties of pulsed laser deposited CuI and TiO₂ films in power output of n-TiO₂|dye|p-CuI cells is studied. An efficient charge generation is observed through the illumination of TiO₂ layer of the fabricated n-TiO₂|dye|p-CuI solid state photovoltaic solar cells. From the current–voltage characteristics, the fill factor and power conversion efficiency were about of 45 and 3%, respectively. The maximum photo-current of about 12.5mA/cm² and photo-voltage of 475mV under AM 1.5 conditions were obtained for the n-TiO₂|dye|p-CuI solid states photovoltaic solar cells with good reproducibility. Adsorbed dye molecules to the TiO₂ surface act as a relay, especially under illumination through TiO₂ layer in the wave range region of 300–400nm.

Keywords: Transparent; CuI; TiO; ₂; Dye-sensitized; Charge generation; PLD; Photovoltaic

Poly(3-methylthiophene)-based porous silicon substrates as a urea-sensitive electrode by Joon-Hyung Jin; Nam Ki Min; Suk-In Hong (pp. 7397-7406).

Poly(3-methylthiophene) (P3MT)-based porous silicon (PS) substrates were fabricated and characterized by cyclic voltammetry, scanning electron microscopy, and auger electron spectroscopy. After doping urease (Urs) into the polymeric matrix, sensitivity and physicochemical properties of the P3MT-based PS substrate was investigated compared to planar silicon (PLS) and bulk Pt substrates. PS substrate was formed by electrochemical anodization in an etching solution composed of HF, H₂O, and ethanol. Subsequently, Ti and Pt thin-films were sputtered on the PS substrate. Effective working electrode area ( A_eff) of the Pt-deposited PS substrate was determined from a redox reaction of Fe(CN)₆³⁻/Fe(CN)₆⁴⁻ redox couple in which nearly reversible cyclic voltammograms were obtained. The i_p versus v^1/2 plots showed that A_eff of the PS-based Pt thin-film electrode was 1.62 times larger than that of the PLS-based electrode.Electropolymerization of P3MT on both types of electrodes were carried out by the anodic potential scanning under the given potential range. And then, urease molecules were doped to the P3MT film by the chronoamperometry. Direct electrochemistry of a Urs/P3MT/Pt/Ti/PS electrode in an acetonitrile solution containing 0.1mol/L NaClO₄ was introduced compared to a P3MT/Pt/Ti/PS electrode at scan rates of 10mVs⁻¹, 50mVs⁻¹, and 100mVs⁻¹.Amperometric sensitivity of the Urs/P3MT/Pt/Ti/PS electrode was ca. 1.67μAmM⁻¹ per projected unit square centimeter, and that of the Urs/P3MT/Pt/Ti/PLS electrode was ca. 1.02μAmM⁻¹ per projected unit square centimeter in a linear range of 1–100mM urea concentrations. 1.6 times of sensitivity increase was coincident with the results from cyclic voltammetrc analysis.Surface morphology from scanning electron microscopy (SEM) images of Pt-deposited PS electrodes before and after the coating of Urs-doped P3MT films showed that pore diameter and depth were 2μm and 10μm, respectively. Multilayered-film structures composed of metals and organics for both electrodes were also confirmed by auger electron spectroscopy (AES) depth profiles.

Keywords: Electrochemical devices; Conducting polymers; Porous silicon

The interfacial structures of (Ba, Sr)TiO₃ films deposited by radio frequency magnetron sputtering by J.X. Liao; C.R. Yang; J.H. Zhang; C.L. Fu; H.W. Chen; W.J. Leng (pp. 7407-7414).

Ba_0.6Sr_0.4TiO₃ (BST) films were deposited on Pt/SiO₂/Si substrates by radio frequency magnetron sputtering. The deposited films were crystallized by conventional thermal annealing (CTA) and rapid thermal annealing (RTA). The interfacial structures of BST/Pt were studied. High-resolution transmission electron microscopy (HRTEM) observation shows that there is a transition layer at BST/Pt interface, and the layer is 4–5nm thick for CTA and 2–3nm for RTA. X-ray photoelectron spectroscopy (XPS) investigations show that the layer is composed of perovskited BST phase and non-perovskited BST phase. The content of the non-perovskited BST phase is most for CTA, whereas that of the perovskited BST phase is most for RTA. It is found that the transition layer thickens with the increase of annealing temperature, and CTA corresponds to faster thickening rate. XPS shows that the non-perovskited BST phase does not come from the absorbed CO₂ or CO contaminations, but from other interfacial elements. Also, it is indicated that the RTA-annealed BST film capacitor shows much better dielectric properties, with an average value of 150 higher dielectric constant and almost two orders of magnitude lower leakage current density than the CTA-annealed film capacitor. Grazing X-ray diffraction (GXRD) patterns exhibit that the RTA-annealed BST films present more compact structure. It is such a compact structure that can effectively prevent the absorbed elements further diffusing toward two sides, and cause thinner transition layer, thus result in higher dielectric constant and lower leakage current density.

Keywords: BST; Interfacial structures; Transition layer; Perovskite; Dielectric properties

Deposition of Au/TiO₂ film by pulsed laser by Chongjun Zhao; Quanzhong Zhao; Qitao Zhao; Jianrong Qiu; Congshan Zhu (pp. 7415-7421).

Au nanoparticles, which were photoreduced by a Nd:YAG laser in HAuCl₄ solution containing TiO₂ colloid and accompanied by the TiO₂ particles, were deposited on the substrate surface. The film consisting of Au/TiO₂ particles was characterized by the absorption spectra, scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. The adhesion between the film and substrate was evaluated by using adhesive tape test. It was found that the presence of TiO₂ dramatically enhanced the adhesion strength between the film and the substrate, as well as the deposition rate of film. The mechanism for the deposition of Au/TiO₂ film was also discussed.

Keywords: Au/TiO; ₂; film; Adhesion; Laser; TiO; ₂; colloid

Characterization of ceramic PVD thin films on AZ31 magnesium alloys by Guosong Wu; Xiaoqin Zeng; Wenbin Ding; Xingwu Guo; Shoushan Yao (pp. 7422-7429).

Ceramic thin films have been widely used to protect the metal substrate as coatings in the past years. In order to improve the poor corrosion resistance of AZ31 magnesium alloy, the study in this paper used the electron beam evaporation method to prepare ceramic PVD films on its surface with TiO₂ and Al₂O₃ as donors, respectively. Atomic force microscopy (AFM), scanning electron microscope (SEM), energy dispersive X-ray spectrometer (EDS), Auger electron spectroscopy (AES) and X-ray diffraction (XRD) were used to investigate the surface morphology, composition and microstructure of the thin films. Both films deposited on AZ31 took on compact top surface morphologies and grew as amorphous structures on substrate. AES test not only showed that films compositions deviated the standard stoichiometric ratios, but also found that element Mg diffused into films and existed as magnesium oxide in the TiO_x film as well as the AlO_x film. In the electrochemical corrosion test, the AlO_x coating on AZ31 exhibited the largest electrochemical impedance in a 3.5% NaCl solution. But it did not show better corrosion resistance than others for the poorer adhesion. Even if its thickness was small, the TiO_x coating on AZ31 exhibited the best corrosion resistance in this study. According to the observation and analysis, the damage of these films on AZ31 in aggressive solutions was mainly due to the existence of pores, microcracks, vacancies and poor adhesion between coating and substrate.

Keywords: Ceramic thin films; Magnesium alloys; Corrosion resistance; PVD

Surface energetics of poly( N-vinyl-2-pyrrolidone)/chitosan blend films by Tuncer Çaykara; Ali Alaslan; Mehmet S. Eroğlu; Olgun Güven (pp. 7430-7435).

Poly( N-vinyl-2-pyrrolidone) (PVP) and chitosan (CTS) with three different molecular weights (MW: 150,000, 400,000 and 600,000g/mol) blends were prepared as films having 13, 20, 33, 43 and 50% (w/w) CTS by solution casting method. Surface properties of the films were analyzed by contact-angle measurements and scanning electron microscopy (SEM). The contact angles of water, glycerol, ethylene glycol, formamide and paraffin oil drop were measured on these films. The contact-angle results were evaluated in terms of surface free energy components by using Van Oss–Good methodology. It was found that all PVP/CTS blend surfaces are enriched in low surface free energy component, i.e. CTS. This conclusion was further confirmed by the cross-sectional SEM images observation of these blends.

Keywords: Surface energy; Contact angle; Blends; Chitosan

Characterization and structure study of the anodic oxide film on Zircaloy-4 synthesized using NaOH electrolytes at room temperature by Juan Li; Xinde Bai; Dailan Zhang; Hongyi Li (pp. 7436-7441).

Thick crystalline zirconium oxide films were synthesized on Zircaloy-4 substrates by anodic oxidation at room temperature in NaOH solution with a stable applied voltage (300V). The film is approximately 4.7μm in thickness. The XPS and SEM analysis shows that the film is a three-layer structure in water, hydroxide and oxide parts. The thickness of that order is ∼0.01μm, ∼1μm, ∼3.7μm, respectively. The oxide layer is composed of tetragonal and monoclinic phases with the volume ratio about 0.2. Furthermore, the thick anodic film acts as a barrier to oxygen and zirconium migrations. It effectively protects zirconium alloys against the worse corrosion. An extremely low passive current density of ∼0.018μA/cm² and a low oxidation weight gain of ∼0.411mg/cm² were also observed in the films.

Keywords: PACS; 68.55.-a; 81.15.-z; 81.65.Kn; 81.65.MqZircaloy-4; Anodization; XRD; XPS; SEM; Polarization curve

Growth of ZnO thin films on c-plane Al₂O₃ by molecular beam epitaxy using ozone as an oxygen source by Y.W. Heo; K. Ip; S.J. Pearton; D.P. Norton; J.D. Budai (pp. 7442-7448).

The growth of c-axis oriented ZnO thin films on c-plane Al₂O₃ via molecular beam epitaxy (MBE) using dilute ozone (O₃) as an oxygen source was investigated. Four-circle X-ray diffraction (XRD) indicates that films grown at 350°C are epitaxial with respect to the substrate, but with a broad in-plane and out-of-plane mosaic. The films were highly conductive and n-type. Epitaxial film growth required relatively high Zn flux and O₃/O₂ pressure. The growth rate decreased rapidly as growth temperature was increased above 350°C. The drop in growth rate with temperature reflects the low sticking coefficient of Zn at moderately high temperatures and limited ozone flux for the oxidation of the Zn metal. Characterization of the films included atomic force microscopy (AFM), X-ray diffraction, photoluminescence, and Hall measurements. These results show that molecular beam epitaxy of ZnO using ozone is rate limited by the ozone flux for growth temperatures above 350°C.

Keywords: Zinc oxide; Semiconductors; Oxides; Molecular beam epitaxy

Silicon surface morphology study after exposure to tailored femtosecond pulses by V. Hommes; M. Miclea; R. Hergenröder (pp. 7449-7460).

Temporal pulse shaping of ultrashort laser pulses has been used for laser ablation of semiconductors. Even the simplest double pulse sequence with a delay of several picoseconds shows remarkable differences in the interaction process, compared to a single pulse of the same total energy. We discuss the interaction of double pulses with single crystal silicon sample in the context of crater morphology for multiple pulses on the same spot. The growth of the typical columnar structures in helium at atmospheric pressure is suppressed and the crater bottom is flat despite the Gaussian beam profile. The influence of the temporal pulse shape has to be treated in conjunction with the influence of the other ablation parameters.

Keywords: PACS; 52.38.Mf; 79.20.Ds; 81.05.CyFemtosecond laser ablation; Silicon; Pulse shaping; Crater morphology

Preparation and conducting performance of LaNiO₃/Ag film and its interface reaction by Wenqing Yao; Haipeng Yang; Yu Chang; Yongfa Zhu (pp. 7461-7468).

LaNiO₃ thin film with perovskite structure was successfully prepared on Ag substrate via an amorphous heteronuclear complex LaNi(DTPA)·6H₂O as a precursor. The influences of precursor concentration and PEG additive with different molecular weight on the texture of the film were carefully studied. The interface states of LaNiO₃/Ag film were revealed by using AES analysis. The effect of annealing time on the interface diffusion of the LaNiO₃/Ag film was shown by using AES depth profile spectrum. The relationship between the electric resistivity of the film and the environmental temperature was measured by using four-probe method. The results showed the film had good metallic conductivity from 300 down to 77K.

Keywords: LaNiO; ₃; /Ag film; Interface; Morphology; AES; Electric resistivity

Morphological and electronic properties of the thin film phase of pentacene investigated by AFM and STM/STS by P. Parisse; M. Passacantando; L. Ottaviano (pp. 7469-7472).

We investigated the morphological, structural and electronic properties of Pentacene thin films grown by vacuum thermal evaporation on different inert substrates at room temperature. The results of our AFM and STM analysis give an interplanar spacing of 1.54 nm corresponding to the (0 0 1) distance of the so-called “thin film phase�?. The STS measurements show an HOMO-LUMO gap of 2.2 eV.

Keywords: PACS; 61.66.Hq; 72.80.Le; 68.55.Jk; 68.37.Ef; 68.37.PsPentacene; Organic semiconductors; AFM; STM; STS

The influence of catalytic activity on the phase transition governed binary switch point of MISiC-FET lambda sensors by Helena Wingbrant; Anita Lloyd Spetz (pp. 7473-7486).

A metal insulator silicon carbide field effect transistor (MISiC-FET) sensor with a catalytic metal gate is currently under development for detecting the lambda value, or air-to-fuel ratio, of gasoline exhausts. It has been noticed that a change from a low to a high signal level of the sensor occurs at a lambda value above 1.00, which is an oxidizing atmosphere. The exact location of the switch point depends both on the kind of gas and gas concentrations chosen to obtain a specific lambda value. The switch point would rather have been expected at 1.00, which is at stoichiometry, irrespective of the composition of the gas mixture. The origin of this phenomenon is studied here by exposing the sensor to lambda stairs while changing different operating parameters. An increase in catalytic activity has been observed to move the switch point of the device towards a lambda value of 1.00. A similar effect is achieved when decreasing the flow or increasing the temperature of operation of the device. The behavior is explained through the introduction of mass transport limitations in the measurement cell, and the difference in diffusion constants and sticking coefficients among the gases when reaction limitation prevails.

Keywords: MISiC-FET; Catalytic activity; Binary switch point; Phase transition; Lambda

Supercapacitive cobalt oxide (Co₃O₄) thin films by spray pyrolysis by V.R. Shinde; S.B. Mahadik; T.P. Gujar; C.D. Lokhande (pp. 7487-7492).

Uniform and adherent cobalt oxide thin films have been deposited on glass substrates from aqueous cobalt chloride solution, using the solution spray pyrolysis technique. Their structural, optical and electrical properties were investigated by means of X-ray diffraction (XRD), scanning electron micrograph (SEM), optical absorption and electrical resistivity measurements. Along with this, to propose Co₃O₄ for possible application in energy storage devices, its electrochemical supercapacitor properties have been studied in aqueous KOH electrolyte. The structural analysis from XRD pattern showed the oriented growth of Co₃O₄ of cubic structure. The surface morphological studies from scanning electron micrographs revealed the nanocrystalline grains alongwith some overgrown clusters of cobalt oxide. The optical studies showed direct and indirect band gaps of 2.10 and 1.60eV, respectively. The electrical resistivity measurement of cobalt oxide films depicted a semiconducting behavior with the room temperature electrical resistivity of the order of 1.5×10³Ωcm. The supercapacitor properties depicted that spray-deposited Co₃O₄ film is capable of exhibiting specific capacitance of 74F/g.

Keywords: PACS; 73.61.W; 78.66.T; 81.15; 61.16.B; 84.37Cobalt oxide; Spray deposition; SEM; Optical and electrical properties; Supercapacitor

Synthesis and characterization of electro-crystallized Cd–Sn–Se semiconductor films for application in non-aqueous photoelectrochemical solar cells by J. Datta; C. Bhattacharya; S. Bandyopadhyay (pp. 7493-7502).

In the present investigation, thin films of CdSnSe have been developed on transparent conducting oxide (TCO) coated glasses by electrolytic deposition. The controlled incorporation of Sn in the semiconducting layer have been achieved by varying the concentration of Sn²⁺ from 5 to 22g/l of SnCl₂ in the deposition bath. The semiconductor film grown on the glass substrate consisted of n-type CdSnSe semiconductor compounds (alloyed and/or mixed type) in the form of highly dispersed, spherically shaped polycrystallites as detected from X-ray diffraction (XRD) studies, atomic force microscopy (AFM) and scanning electron microscopy (SEM). Their optoelectronic properties were determined by spectroscopic analysis and electrochemical measurements. The performance characteristics of a photoelectrochemical (PEC) cell fabricated with the prepared photo-electrode and ferrocene–ferricenium redox couple in dimethyl formamide were observed under dark and illuminated conditions. The prepared semiconductor films were electrochemically characterized through capacitance–voltage measurements. The film that was obtained from 10g/l of Sn²⁺ in the bath, showed an optimum spectral sensitivity and corresponded to a film thickness of 0.65μm and stoichiometry of Cd:Sn:Se as 1:1:1. The pronounced PEC activity of this film compared to the others was attributed to the combined effect of space charge properties, electron–hole recombination processes and transfer of charges through the Helmholtz layer at the semiconductor–solution interface.

Keywords: PACS; 84.60.Dn; 81.15.Pq; 81.05.E; 73.40.MSemiconductor; Photoelectrochemical cells; Electrochemical deposition; SEM-EDAX; AFM; FIB; Electrochemical impedance spectroscopy

Structural characterization of titanium oxide layers prepared by plasma based ion implantation with oxygen on Ti6Al4V alloy by Jinlong Li; Mingren Sun; Xinxin Ma (pp. 7503-7508).

Ti6Al4V alloy was implanted with oxygen by using plasma based ion implantation (PBII) at pulsed voltage ranging from −10 to −50kV with a frequency of 100Hz. In order to maintain a lower implantation temperature, an oil cooling working table was employed. The structure of the modified layers was characterized by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The results show that the thickness of the titanium oxide layer increases significantly with the increase of implanted voltage. The structure of the modified layer changes along depth. It is found that the surface layer consists of TiO₂, and the subsurface layer is a mixing structure of TiO_2, Ti₂O₃ and TiO. There is crystalline rutile phase existing in the modified layer of sample implanted at high implanted voltage. In addition, in the outmost modified surface, aluminum present as oxidized state, and vanadium could not be detected.

Keywords: Plasma based ion implantation; Ti6Al4V alloy; Structure; X-ray photoelectron spectroscopy; Raman spectroscopy

ZnO/Ag/ZnO multilayer films for the application of a very low resistance transparent electrode by D.R. Sahu; Shin-Yuan Lin; Jow-Lay Huang (pp. 7509-7514).

Transparent conductive ZnO/Ag/ZnO multilayer electrodes having much lower electrical resistance than the widely used transparent electrodes were prepared by simultaneous RF magnetron sputtering of ZnO and DC magnetron sputtering of Ag. An Ag film with different thickness was used as intermediate metallic layers. The optimum thickness of Ag thin films was determined to be 6nm for high optical transmittance and good electrical conductivity. With about 20–25nm thick ZnO films, the multilayer showed high optical transmittance in the visible range of the spectrum and had color neutrality. The electrical and optical properties of the multilayers were changed mainly by Ag film properties. A high quality transparent electrode, having sheet resistance as low as 3ohm/sq and high transmittance of 90% at 580nm, was obtained and could be reproduced by controlling the preparation parameter properly. The above property is suitable as transparent electrode for dye sensitized solar cells (DSSC).

Keywords: ZnO; Transparent electrode; Multilayer

A bonding study of c-C₅H₈ adsorption on Pt(111) by S. Simonetti; P. Jasen; E. Gonzalez; A. Juan; G. Brizuela (pp. 7515-7522).

The chemisorption of cyclopentane (c-C₅H₈) on Pt(111) has been studied using a qualitative band-structure calculations in the framework of tight-binding implementation with the YAeHMOP package. We modeled the metal surface by a two-dimensional slab of finite thickness with an overlayer of c-C₅H₈, in a (3×3) di-σ geometry. The c-C₅H₈ molecule is attached to the surface with its CC atoms bonded mainly with two Pt atoms while the opposite CH₂ bends towards the surface. The PtPt bonds in the underlying surface and the CC bonds of c-C₅H₈ are weakened upon the chemisorption. A noticeable Pt–H and Pt–C interactions has been observed. We found that of Pt5dz2 band plays an important role in the bonding between c-C₅H₈ and the surface, as do the Pt 6s and 6p_z bands. The HOMO-LUMO bands of c-C₅H₈ are very dispersed, indicative of a strong interaction with the metal surface.

Keywords: Platinum; Cyclopentane; Adsorption; Molecular orbital

Molecular dynamics simulation of processing using AFM pin tool by Y.D. Yan; T. Sun; S. Dong; X.C. Luo; Y.C. Liang (pp. 7523-7531).

A three-dimensional molecular dynamics (MD) model is utilized to investigate the effect of tool geometry on the deformation process of the workpiece and the nature of deformation process at the atomic-scale. Results show that different states exist between the atomic force microscope (AFM) pin tool and the workpiece surface, i.e. the non-wear state, the ploughing state, the state in which ploughing is dominant and the state in which cutting plays a key role. A relationship between the deformation process of the workpiece and the potential energy variation is presented. The potential energy variation of atoms in different deformed regions in the workpiece such as plastically deformed region, elastically deformed region and the mixed deformation region is different. The features of variations of potential energy are discussed.

Keywords: PACS; 81.16.NdAFM; MD; Pin tool; Ploughing; Deformation process

Deactivation of TiO₂ photocatalytic films loaded on aluminium: XPS and AFM analyses by Song-Zhe Chen; Peng-Yi Zhang; Wan-Peng Zhu; Le Chen; Sheng-Ming Xu (pp. 7532-7538).

TiO₂ films were loaded on aluminium substrates by dip-coating method. Based on cyclic photocatalytic degradation experiments using benzamide as model molecule, XPS and AFM tests, the deactivating behaviour of the samples was studied. Experiment results show that the samples with less coating times (one to four times) deactivated very quickly, while the samples coated more than five times did not lose activity. Al element was proved to segregate from substrate and diffuse into TiO₂ films during calcination and annealing treatment, existing as mixture of Al₂O₃ and Al(OH)₃ at the boundaries among TiO₂ particles. During photocatalytic reactions in aqueous phase, the transformation of Al from Al₂O₃ to Al(OH)₃ and the leaching of the latter brought out serious alternation of surface morphology to the samples coated one to three times, on whose surface Ti³⁺ and Ti²⁺ centers were also detected after six cycles of photocatalytic reactions, while fresh films and the tested films which did not deactivate possess unique +4 valence Ti. The alteration of surface morphology, together with the change of valence of surface Ti element, resulted in the deactivation encountered in this research.

Keywords: PACS; 82.65.JTiO; ₂; film; Photocatalysis; Deactivation; Substrate; Dip-coating; Aluminium

Microstructure and dry-sliding wear resistance of PTA clad (Cr, Fe)₇C₃/γ-Fe ceramal composite coating by Yuan-Fu Liu; Jian-Min Han; Rong-Hua Li; Wei-Jing Li; Xiang-Yang Xu; Jin-Hua Wang; Si-Ze Yang (pp. 7539-7544).

A wear resistant (Cr, Fe)₇C₃/γ-Fe ceramal composite coating was fabricated on substrate of a 0.45%C carbon steel by plasma transferred arc (PTA) cladding process using the Fe–Cr–C elemental powder blends. The microstructure, microhardness and dry-sliding wear resistance of the coating were evaluated. Results shown that the plasma transferred arc clad ceramal composite coating has a rapidly solidified microstructure consisting of blocky primary (Cr, Fe)₇C₃ and the inter-blocky (Cr, Fe)₇C₃/γ-Fe eutectics and is metallurgically bonded to the 0.45%C carbon steel substrate. The ceramal composite coating has high hardness and excellent wear resistance under dry sliding wear test condition.

Keywords: PACS; 52. 77. Fv; 68. 55.−a; 62. 20. Qp; 81. 40. PqPlasma transferred arc cladding; (Cr; Fe); ₇; C; ₃; /γ-Fe; Coating; Microhardness; Wear

Electrochemical synthesis of poly-6-amino- m-cresol (poly-AmC) by H. Keleş; İ. Dehri (pp. 7545-7552).

The electropolymerization of 6-amino- m-cresol (AmC) on a platinum electrode was studied in 0.1M Na₂SO₄ solution containing 5×10⁻³M 6-amino- m-cresol at different pHs using cyclic voltammetry technique. Voltammetric results showed that oxidation of 6-amino- m-cresol produced a passivating polymeric film on the platinum surface at all pHs studied. Synthesized polymer has bronze color on platinum. To investigate the structure of poly-6-amino- m-cresol (poly-AmC) films FTIR technique was employed. The spectroscopic results indicate that polymer chain consist of ring opened units rather than phenoxazine structure.

Keywords: 6-Amino-; m; -cresol; Polymer; Electrochemical synthesis; Cyclic voltammetry

Electrical transport properties of thermally evaporated phthalocyanine (H₂Pc) thin films by M.M. El-Nahass; A.M. Farid; A.A. Attia; H.A.M. Ali (pp. 7553-7561).

Thin films of H₂Pc of various thicknesses have been deposited onto glass substrates using thermal evaporation technique at room temperature. The dark electrical resistivity measurements were carried out at different temperatures in the range 298–473K. An estimation of mean free path ( l_o) of charge carriers in H₂Pc thin films was attempted. Measurements of thermoelectric power confirm that H₂Pc thin films behave as a p-type semiconductor. The current density–voltage characteristics of Au/H₂Pc/Au at room temperature showed ohmic conduction mechanism at low voltages. At higher voltages the space-charge-limited conduction (SCLC) accompanied by an exponential trap distribution was dominant. The temperature dependence of current density allows the determination of some essential parameters such as the hole mobility ( μ_h), the total trap concentration ( N_t), the characteristic temperature ( T_t) and the trap density P( E).

Keywords: PACS; 61.10.Nz; 81.15.EfTransport properties; H; ₂; Pc thin films

Variation of microstructure with carbonation in lime and blended pastes by M. Arandigoyen; B. Bicer-Simsir; J.I. Alvarez; D.A. Lange (pp. 7562-7571).

Carbonation, as a reaction of the curing process of both, cement and lime binders, modifies the microstructure. Several microstructure properties, namely porosity, pore size distribution, surface fractal dimension, and specific surface area have been investigated in this study to describe the effect of carbonation on microstructure. Both carbonated and non-carbonated pastes of lime and blended pastes of lime and cement having varying water/binder (W/B) ratios are studied. Results show that carbonation decreases the porosity, but not with the same intensity in all pore size ranges. The highest modification is between 0.03μm and 0.01μm in lime pastes and between 0.2μm and 0.02μm in 50% lime pastes, while in 80% lime pastes the modification is very small. It is also observed that carbonation is a function of the binder composition but not of the W/B ratio. Moreover, surface fractal dimension decreases during the carbonation process, while the specific surface area varies depending of the binder composition.

Keywords: PACS; 81.05.Rm; 68.43.hLime pastes; Blended pastes; Carbonation; Pore size distribution; Surface fractal dimension; W/B ratio

Surface morphology and reaction at Cu/Si interface—Effect of native silicon suboxide by N. Benouattas; A. Mosser; A. Bouabellou (pp. 7572-7577).

Copper thin films are deposited by thermal evaporation on unetched and etched monocrystalline silicon. The study by alpha particles backscattering (RBS) raises a strong diffusion of copper in silicon substrates with and without native suboxide layer. On the other hand, the X-rays diffraction shows the formation and the growth of Cu₃Si and Cu₄Si silicides. Whereas the scanning microscopy underlines large crystallites growth surrounded by black zones of silicon coming from the uncovered substrate, independently to the surface state of the substrate, after annealing at high temperature. The presence of native silicon suboxide at Cu/Si interface, influences in a drastic way the minimal temperature to which the interfacial reaction occurs. The oxygen impurities detected by microanalysis, after heat treatment under vacuum, are closely related to the growth of silicides crystallites.

Keywords: PACS; 66.30.Ny; 82.80.Yc; 68.37.Hk; 68.55.Jk; 85.40.LsCopper; Copper silicides; Silicon suboxide; Solid-state reaction; Morphology

Analysis of EIS characteristics of CO₂ corrosion of well tube steels with corrosion scales by Z.Q. Bai; C.F. Chen; M.X. Lu; J.B. Li (pp. 7578-7584).

The electrochemical impedance spectroscopy (EIS) was used to study the characteristics of CO₂ corrosion of N80 and 4Cr steels with corrosion scales. The results indicated that CO₂ corrosion scale on tube steel could prevent the rate of mass transfer remarkably, corrosion rate was controlled by ions diffusion in corrosion scale, which led to finite length diffusion impedance occurred in electrochemical impedance spectra. Additionally, pitting of N80 steel could lead to additional capacitive reactance in impedance spectrum. The ion diffusion coefficient in corrosion scale and porosity of corrosion scale could be calculated by Warburg impedance coefficient, the results shown that the value of H⁺ diffusion coefficient in N80 and 4Cr corrosion scale is (3.46 and 1.76)×10⁻¹⁰m²s⁻¹, respectively. The protective ability of 4Cr corrosion scale was better than that of N80 corrosion scale.

Keywords: PACS; 82.45Pitting corrosion; EIS; N80 steel

Metallo-organic decomposition derived (Ca, Sr)ZrO₃ dielectric thin films on Pt coated Si substrate by Changhong Chen; Dexiu Huang; Weiguang Zhu; Xi Yao (pp. 7585-7589).

Metallo-organic decomposition derived dielectric thin films of calcium zirconate doped with various concentrations of strontium ((Ca, Sr)ZrO₃) were prepared on Pt coated silicon substrate. Mainly in this paper, we present the investigations of their structural developments and present their electric and dielectric properties as well. The structural developments show that the CaZrO₃ film has amorphous structure with carbonate existing when annealed at 600°C, while annealed at 650°C and above, the carbonate is decomposed and those films crystallize into perovskite phase without preferred orientation. In addition, the prepared (Ca, Sr)ZrO₃ films with their Zr–O bonds affected by strontium doping are homogenous and stable as solid solutions in any concentration of strontium and all Bragg diffraction characteristics for the films shift downward with the increase in the concentration of strontium. Moreover, the electric properties show that the (Ca, Sr)ZrO₃ films have very low leakage current density and high breakdown strength; typically, the CaZrO₃ film annealed at 650°C has the leakage current density approximately 9.5×10⁻⁸Acm⁻² in the field strength of 2.6MVcm⁻¹. Furthermore, the dielectric properties show that their dielectric constants are higher than 12.8 with very little dispersion in the frequency range from 100Hz to 1MHz and are independent of applied dc bias as well. The dielectric properties, in combination with the electric properties, make the materials promising candidates for high-voltage and high-reliability capacitor applications.

Keywords: PACS; 77.55.+f; 81.20.Fw; 78.30.−jPerovskite-type oxides; Strontium zirconate; Calcium zirconate; Metallo-organic decomposition; Dielectric thin films

Reaction products and oxide thickness formed by Ti out-diffusion and oxidization in poly-Pt/Ti/SiO₂/Si with oxide films deposited by Changhong Chen; Dexiu Huang; Weiguang Zhu; Yi Feng; Xigang Wu (pp. 7590-7593).

In the paper, we present experimental results to enhance the understanding of Ti out-diffusion and oxidization in commercial poly-Pt/Ti/SiO₂/Si wafers with perovskite oxide films deposited when heat-treated in flowing oxygen ambient. It indicates that when heat-treated at 550 and 600°C, PtTi₃+PtTi and PtTi are the reaction products from interfacial interaction, respectively; while heat-treated at 650°C and above, the products become three layers of titanium oxides instead of the alloys. Confirmed to be rutile TiO₂, the first two layers spaced by 65nm encapsulate the Pt surface by the first layer with 60nm thick forming at its surface and by the next layer with 35nm thick inserting its original layer. In addition, the next layer is formed as a barrier to block up continuous diffusion paths of Ti, and thus results in the last layer of TiO2−_x formed by the residual Ti oxidizing.

Keywords: PACS; 05.70.Np; 68.35.MdInterface and surface; Diffusion; Oxidization; Titanium

Thin strain-relaxed SiGe grown by ultrahigh vacuum chemical vapor deposition by Xiangdong Xu; Hockleong Kweh; Zhengcao Zhang; Zhihong Liu; Wei Zhou; Wei Zhang; Peixin Qian (pp. 7594-7598).

Large-scale preparation of thin strain-relaxed SiGe is achieved by combining ion implantation and ultrahigh vacuum chemical vapor deposition. The resulting materials were analyzed by double crystal X-ray diffraction, micro-Raman spectroscopy, and tapping mode atomic force microscope. Results revealed that 100-nm-thick Si_0.7Ge_0.3 layers with the diameter of 125mm and full strain relaxation are successfully prepared by pre-modifying the Si substrates using 50keV Ar⁺ ions. The strain relaxation is also disclosed to change with both ion species and energy. However, post-modification of SiGe by ion implantation will cause serious damage to the crystal structures, and result in the formation of poly-crystal SiGe.

Keywords: PACS; 81.05.Hd; 62.40.+i; 81.15.Gh; 61.72.TtSiGe; Strain relaxation; Ultrahigh vacuum chemical vapor deposition; Ion implantation

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Applied Surface Science (v.252, #20)

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Applied Surface Science (v.252, #20)