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Applied Surface Science (v.253, #17)

Stability of polymer thin-film transistors based on poly(2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene) by Y.R. Liu; J.B. Peng; P.T. Lai (pp. 6987-6991).

Polymer thin-film transistors (PTFTs) based on poly(2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene) (MEH-PPV) semiconductor are fabricated by spin-coating process and characterized. In the experiments, solution preparation, deposition and device measurements are all performed in air for large-area applications. Hysteresis effect and gate-bias stress effect are observed for the devices at room temperature. The saturation current decreases and the threshold voltage shifts toward the negative direction upon gate-bias stress, but carrier mobility hardly changes. By using quasi-static C– V analysis for MOS capacitor structure, it can be deduced that the origin of threshold-voltage shift upon negative gate-bias stress is predominantly associated with hole trapping within the SiO₂ gate dielectric near the SiO₂/MEH-PPV interface due to hot-carrier emission.

Keywords: PACS; 85.30.Tv; 85.30.De; 72.80.LeSemiconducting polymer; Thin-film transistor; Field-effect mobility; Stability

Growth of thin Fe(001) films for terahertz emission experiments by C.A. Meserole; G.L. Fisher; D.J. Hilton; R.D. Averitt; D.J. Funk; A.J. Taylor (pp. 6992-7003).

The electrical and magnetic properties of thin iron (Fe) films have sparked significant scientific interest. Our interest, however, is in the fundamental interactions between light and matter. We have discovered a novel application for thin Fe films. These films are sources of terahertz (THz) radiation when stimulated by an incident laser pulse. After intense femtosecond pulse excitation by a Ti:sapphire laser, these films emit picosecond, broadband THz frequencies. The terahertz emission provides a direct measure of the induced ultrafast change in magnetization within the Fe film. The THz generation experiments and the growth of appropriate thin Fe films for these experiments are discussed. Several criteria are used to select the substrate and film growth conditions, including that the substrate must permit the epitaxial growth of a continuous, monocrystalline or single crystal film, yet must also be transparent to the emitted THz radiation. An Fe(001) film grown on the (001) surface of a magnesium oxide (MgO) substrate makes an ideal sample. The Fe films are grown by physical vapor deposition (PVD) in an ultrahigh vacuum (UHV) system. Low energy electron diffraction (LEED) and Auger electron spectroscopy (AES) are used to characterize the Fe(001) films. Two substrate surface preparation methods are investigated. Fe(001) films grown on MgO(001) substrates that are used as-received and films grown on MgO(001) substrates that have been UV/ozone-cleaned ex vacuo and annealed in vacuo produce the same results in the THz generation experiments. Either substrate preparation method permits the growth of samples suitable for the THz emission experiments.

Keywords: PACS; 42.65.Ky; 68.43.−h; 81.15.−zMolecular beam epitaxy; Thin films; Iron; Magnesium oxide; Terahertz

Opto-electrical properties of amorphous carbon thin film deposited from natural precursor camphor by Debabrata Pradhan; Maheshwar Sharon (pp. 7004-7010).

A simple thermal chemical vapor deposition technique is employed for the pyrolysis of a natural precursor “camphor” and deposition of carbon films on alumina substrate at higher temperatures (600–900°C). X-ray diffraction measurement reveals the amorphous structure of these films. The carbon films properties are found to significantly vary with the deposition temperatures. At higher deposition temperature, films have shown predominately sp²-bonded carbon and therefore, higher conductivity and lower optical band gap (Tauc gap). These amorphous carbon (a-C) films are also characterized with Raman and X-ray photoelectron spectroscopy. In addition, electrical and optical properties are measured. The thermoelectric measurement shows these as-grown a-C films are p-type in nature.

Keywords: PACS; 81.05.Gc; 73.61.Jc; 78.30.−j; 73.50.Lw; 78.20.−eCamphor; a-C films; Raman spectroscopy

Electrochemical synthesis and optical properties of ZnO thin film on In₂O₃:Sn (ITO)-coated glass by Changdong Gu; Jun Li; Jianshe Lian; Guoqu Zheng (pp. 7011-7015).

ZnO thin films were electrochemically deposited onto the ITO-coated glass substrate from an electrolyte consisted of 0.1M Zn(NO₃)₂ aqueous solution at 65±1°C. A compact ZnO film with (002) preferred orientation was obtained at the applied potential of −1.3V for 1200s. It was also found that the morphology of the ZnO films grown at the potential of −1.3V was characterized of single or coalescent hexagonal platelets. However, the ZnO crystals grown at the potential of −2.0V was changed to be a bimodal size distribution. The band gap energy of the as deposited ZnO films, about 3.5eV, was independent of both the applied potential and the deposition time, respectively. The minor amount of Zn(OH)₂ might be co-deposited with the formation of ZnO revealed by the FT-IR spectroscopy. Three strategies to improve the ZnO crystal quality based on the photoluminescence properties were proposed in the paper, which were (a) adopting the lower deposition potential, (b) increasing the deposition time at a certain potential, and (c) annealing after as-deposition, respectively.

Keywords: PACS; 61.46.Hk; 61.82.Fk; 67.70.+n; 78.20.−eZnO; Photoluminescence; Nanostructures; Electrodeposition

Epitaxially grown ZnO thin films on 6H-SiC(0001) substrates prepared by spin coating-pyrolysis by Young-Sun Jeon; Doo-Man Kim; Kyu-Seog Hwang (pp. 7016-7018).

Epitaxially grown ZnO thin film on 6H-SiC(0001) substrate was prepared by using a spin coating-pyrolysis with a zinc naphthenate precursor. As-deposited film was pyrolyzed at 500°C for 10min in air and finally annealed at 800°C for 30min in air. In-plane alignment of the film was investigated by X-ray pole-figure analysis. Field emission-scanning electron microscope, scanning probe microscope, and He–Cd laser (325nm) was used to analyze the surface morphology, the surface roughness and photoluminescence of the films. In the photoluminescence spectra, near-band-edge emission with a broad deep-level emission was observed. The position of the near-band-edge peak was around 3.27eV.

Keywords: PACS; 68.55.−a; 81.20.Fw; 78.55.−mZnO thin film; 6H-SiC(0; 0; 0; 1); Photoluminescence

Growth of TiN films at low temperature by L.I. Wei; Chen Jun-Fang (pp. 7019-7023).

Thermodynamic analysis on growth of TiN films was given. The driving force for deposition of TiN is dependent on original Ti(g)/N(g) ratio and original partial pressure of N(g). TiN films were deposited by ion beam assisted electron beam evaporation system under suitable nitrogen gas flow rate at 523K while the density of plasma varied with diverse discharge pressure had been investigated by the Langmuir probe. TiN films were characterized by means of Fourier transform infrared absorption spectrum (FTIR), X-ray diffraction (XRD) and observed by means of atom force microscopy (AFM). The results of these measurements indicated preferential TiN(111) films were deposited on substrate of Si(100) and glass by ion beam assisted electron beam evaporation system at low temperature, and it was possible for the deposition of TiN films with a preferential orientation or more orientations if the nitrogen gas flow rate increased enough. Sand Box was used to characterize the fractal dimension of surface of TiN films. The results showed the fractal dimension was a little more than 1.7, which accorded with the model of diffusion limited aggregation (DLA), and the fractal dimension of TiN films increased with increase of the temperature of deposition.

Keywords: PACS; 47.54.Jk; 68.65.−kTitanium nitride (TiN); Driving force; Fractal dimension; Temperature of deposition

Visible-light photocatalysis of nitrogen-doped TiO₂ nanoparticulate films prepared by low-energy ion implantation by Hong Shen; Lan Mi; Peng Xu; Weidian Shen; Pei-Nan Wang (pp. 7024-7028).

Nitrogen-doped TiO₂ (N–TiO₂) films were prepared by low-energy implantation of nitrogen ions into pulsed laser deposited anatase TiO₂ films. The anatase phase of the films was not changed by the implantation with very low energy of 200eV. XPS measurements revealed that the implanted nitrogen species were mainly interstitial ones. The nitrogen concentration was increased with increasing ion flux which could be controlled by adjusting the gas flow rate of the ion source. All the produced N–TiO₂ films exhibited visible-light photocatalytic activities in degradation of methylene blue in aqueous solutions, indicating that interstitial nitrogen could also be responsible for the photocatalysis in visible region. Higher visible-light photocatalytic efficiency was achieved with higher implanted nitrogen concentration.

Keywords: PACS; 81.16.Hc; 61.72.Vv; 78.67.BfNitrogen-doped titanium oxide; Visible light photocatalyst; Ion implantation

Pt/N-codoped TiO₂ nanotubes and its photocatalytic activity under visible light by L.H. Huang; C. Sun; Y.L. Liu (pp. 7029-7035).

Pt/N-codoped TiO₂ nanotubes were prepared and characterized by various analytical methods, such as transmission electron microscope (TEM), diffuse reflection spectra (DRS), X-ray powder diffraction (XRD), X-ray photoelectron emission spectroscopy (XPS) and fluorescence spectra (FL). The photocatalytic efficiency was evaluated by the photodegradation of Rhodamine B (RB) in an aqueous solution under visible light irradiation. It has been confirmed that Pt/N-codoped TiO₂ nanotubes could be excited by visible light and the recombination rate of electron–hole pairs declined significantly. The higher visible light activity is due to the codoping of nitrogen and platinum.

Keywords: Platinum; Nitrogen; Titanium dioxide; Nanotubes; Codoping

Thermal stability of Ag films in air prepared by thermal evaporation by Jing Lv; Fachun Lai; Limei Lin; Yongzhong Lin; Zhigao Huang; Rong Chen (pp. 7036-7040).

The thermal stability of silver films in air has been studied. Pure Ag films, 250nm in thickness, were prepared on glass substrates by thermal evaporation process, and subsequently annealed in air for 1h at temperatures between 200 and 400°C. The structure and morphology of the samples were investigated by X-ray diffraction, Raman spectra and atomic force microscopy. It is found that the crystallization enhances for the annealed films, and film surface becomes oxidized when annealing temperature is higher than 350°C. The electrical and optical properties of the films were studied by van der Pauw method and spectrophotometer, respectively. Reflectance drops sharply as Ag films are annealed at temperatures above 250°C. Film annealed at 250°C has the maximum surface roughness and the minimum reflectance at 600nm optical wavelength. Film annealed at 200°C has the minimum resistivity, and resistivity increases with the increasing of the annealing temperature when temperature is above 200°C. The results show that both oxidization on film surface and agglomeration of silver film result in infinite of electrical resistivity as the annealing temperature is above 350°C.

Keywords: PACS; 68.60.Dv; 68.55.−a; 73.61.At; 81.40.TvSilver; Thermal stability; Electrical properties; Optical properties

Ag nanoparticle mediated growth of CdS nanobelts by K. Sreejith; J. Nuwad; C. Thinaharan; G.K. Dey; C.G.S. Pillai (pp. 7041-7045).

Catalytic growth of CdS have been carried out on large scale by evaporation of bulk CdS on Ag deposited Si (111) at atmospheric pressure. The as prepared CdS had wurtzite structure as evidenced by X-ray diffraction. The nanostructures were beltlike with several tens of micrometers length, several micrometers width and few nanometers to tens of nanometers thick as seen by scanning electron microscope and confirmed by TEM studies. The nanobelts were single crystalline in nature and showed reflection corresponding to (112) and (002) planes in SAED. The PL studies revealed the green band due to band gap emission and red band due to emission from the surface states. The higher intensity of the defect emission indicated the presence of considerable concentration of surface defects in the as prepared sample. The deposition of CdS could be explained on the basis of catalyst assisted vapor–liquid–solid and vapor–solid mechanism.

Keywords: PACS; 81.15.Kk; 71.55.Gs; 68.37.Lp; 78.55.EtVapor phase deposition; II–VI semiconductors; Photoluminescence; Transmission electron microscopy

Field emission properties of carbon nanotubes film grown on NiCr alloy films by T. Chen; L.L. Wang; Y.W. Chen; W.X. Que; Z. Sun (pp. 7046-7049).

Carbon nanotubes (CNTs) are prepared on NiCr alloy films by low pressure thermal chemical vapor deposition at 600°C. NiCr alloy films are deposited by magnetic co-sputtering method, and the various thickness and Ni/NiCr ratios are controlled by sputtering power. The diameter and length of CNTs, as well as the roughness of the CNTs films, mainly depend on the Ni/NiCr ratio. The field emission current density of the CNTs film increases with the increasing Ni/NiCr ratio from 65wt% to 83wt%, and decreases when the Ni/NiCr ratio is more than 87wt% in the alloy film.

Keywords: Carbon nanotube; Field emission; NiCr alloy

Amorphous to crystalline phase transition in pulsed laser deposited silicon carbide by M. Tabbal; A. Said; E. Hannoun; T. Christidis (pp. 7050-7059).

SiC thin films were grown on Si (100) substrates by excimer laser ablation of a SiC target in vacuum. The effect of deposition temperature (up to 950°C), post-deposition annealing and laser energy on the nanostructure, bonding and crystalline properties of the films was studied, in order to elucidate their transition from an amorphous to a crystalline phase. Infra-red spectroscopy shows that growth at temperatures greater than 600°C produces layers with increasingly uniform environment of the Si–C bonds, while the appearance of large crystallites is detected, by X-ray diffraction, at 800°C. Electron paramagnetic resonance confirms the presence of clustered paramagnetic centers within the sp² carbon domains. Increasing deposition temperature leads to a decrease of the spin density and to a temperature-dependent component of the EPR linewidth induced by spin hopping. For films grown below 650°C, post-deposition annealing at 1100°C reduces the spin density as a result of a more uniform Si–C nanostructure, though large scale crystallization is not observed. For greater deposition temperatures, annealing leads to little changes in the bonding properties, but suppresses the temperature dependent component of the EPR linewidth. These findings are explained by a relaxation of the stress in the layers, through the annealing of the bond angle disorder that inhibits spin hopping processes.

Keywords: PACS; 81.15.Fg; 76.30.−v; 81.40.EfLaser ablation; Silicon carbide; Atomic force microscopy; X-ray diffraction; Infra-red spectroscopy; Electron paramagnetic resonance

Synthesis of Fe-based amorphous composite coatings with low purity materials by laser cladding by Zhu Qingjun; Qu Shiyao; Wang Xinhong; Zou Zengda (pp. 7060-7064).

Amorphous composite coatings Fe₃₈Ni30−_XSi₁₆B₁₄V₂M_X ( X=0, 1, 2) (M contains Al, Ti, Mo, and C) were prepared with low purity of raw materials by laser cladding. X-ray diffraction and transmission electron microscopy results show that the coating have an amorphous structure with a few crystalline phase on it. The amorphous phase is the primary phase. The glass forming ability as well as the microhardness of the Fe-based alloy made from low purity raw materials can be much enhanced by adding small amount of multi-components. However, the elements addition has its optimal quantity. When X is equal to 1, the microstructure of the coating contains 97.93% amorphous phase and 2.07% crystalline phase on it. As a result, the microhardness of the coating reaches maximum. With further increasing of the additions, the amorphous phase in the coating lessens instead of augment and the crystalline phase begins to accumulate, which result in the decrease of the microhardness.

Keywords: Amorphous; Composite coating; Elements addition; Laser cladding

An investigation of natural oxidation process on stain-etched nanoporous silicon by micro-Raman spectroscopy by P.G. Abramof; C.R.B. Miranda; A.F. Beloto; A.Y. Ueta; N.G. Ferreira (pp. 7065-7068).

Micro-Raman spectra of porous silicon (PS) samples as-formed, from stain etching process using heavily doped silicon wafers, and after 750 days storage in air were analyzed around Si peak (300–600cm⁻¹) and at photoluminescence (PL) range (300–8000cm⁻¹). The first-order Raman spectra in the vicinity of Si peak were fitted from phonon confinement model including a term taking into account the amorphous phase. This analysis allowed the determination of the correlation length, which corresponds to the crystallite size, also considering the PS natural oxidation process. The photoluminescence band, generated by Si crystallites located on the outermost part of the PS layer, was also fitted with a Gaussian distribution. In order to investigate the porous silicon nanostructure, the micro-Raman spectra were measured for different sets of porous silicon samples. These spectra showed good reproducibility and the effects of the natural oxidation at different periods. A slight decrease in the crystallite size was observed for all samples sets studied, while the spectral part related to the amorphous phase did not describe significant changes. The central position of PL band, analyzed after the oxidation process, exhibited consistently a shift to higher energies. In addition, top view high resolution scanning electron microscopy (HRSEM) images also confirmed a reasonable reproducibility and homogeneity. The results showed that after storing in air, natural oxidation can modify the Si crystallites size at the surface but not increase the amorphous phase.

Keywords: Porous silicon; Phonon confinement model; Raman spectrocospy; Oxidation

Effect of film thickness on interface and electric properties of BiFeO₃ thin films by Chia-Ching Lee; Jenn-Ming Wu (pp. 7069-7073).

Bismuth ferrite (BFO) thin films were fabricated by RF-magnetron sputtering deposition method on Pt/Ti/SiO₂/Si(100) substrate. The effect of the thickness of BFO films varying from 85 to 280nm on electrical properties was investigated. Saturated coercive fields were found to increase with the BFO film thickness. The dielectric constant of BFO thin films measured at 1kHz decreased with decreasing thickness from 98 to 86, while tangent losses increased from 0.013 to 0.021. The presence of bismuth oxide at the interface between BFO films and Pt bottom electrodes was responsible for the high leakage currents in thin BFO thin films as was demonstrated by X-ray diffraction, grazing-incident X-ray diffraction, and secondary ion mass spectroscopy analysis.

Keywords: Thin film; Ferroelectric; Film thickness; Bismuth ferrite

Study on spatial dispersion theory of excess conduction loss in normal metals surface below terahertz frequencies by Xiaoxia Zhang; Wei Pan (pp. 7074-7077).

We have developed a rigorous model for analyzing excess conduction loss in normal metals surface by using the spatial dispersion theory. We have used the model to account excess conduction loss and dissect the discrepancies between excess conduction loss measurements and classical theoretical predictions in normal metals surface below terahertz frequencies. Our analysis shows that the conductivity is not only frequency but also wave vector dependent. We demonstrate good quantitative agreement with the published experimental data for the room temperature excess conduction loss of normal metals surface below terahertz frequencies.

Keywords: PACS; 77.22.Gm; 78.20.Ci; 78.20.Bh; 78.30.ErSpatial dispersion; Excess conduction loss; Normal metals surface; Terahertz frequencies

Theoretical study on structure of boron nitride fullerenes by Won Ha Moon; Myung Sik Son; Ho Jung Hwang (pp. 7078-7081).

We propose the parameters of the Stillinger–Weber potential for hexagonal boron nitride (BN) structures. For the reliability of these parameters, the structural property of BN fullerenes is investigated. The stability of BN fullerenes increases with increasing the number of atoms, due to the reduction of the curvature effect of BN fullerenes. The structures of the relative stable fullerenes are B₁₆N₁₆, B₁₈N₁₈, B₂₂N₂₂, B₂₅N₂₅, and B₂₈N₂₈.

Keywords: PACS; 61.48.+c; 81.05.Tp; 61.43.Bn; 82.20.WtHexagonal boron nitride; Fullerene; Stillinger–Weber potential

Fabrication and structural characterization of metal films coated on cenosphere particles by magnetron sputtering deposition by Xiaozheng Yu; Zhigang Shen; Zheng Xu; Sen Wang (pp. 7082-7088).

Metal films were successfully coated on cenosphere particles using a magnetron sputtering deposition system in which a newly designed sample stage equipped with an ultrasonic vibration generator was used for the tumbling of cenosphere particles. It was found by FE-SEM and AFM results that the films were well compacted and highly uniform in thickness. Due to the difference in sputtering rate, the film thicknesses estimated from FE-SEM characterizations in backscattered mode were <10, 39, 50 and 134nm for Co, Ni, Cu and Ag films, respectively, under the same sputtering deposition conditions. The RMS values derived from the AFM measurements were 1.94, 4.31, 10.92 and 18.33nm for Co, Ni, Cu and Ag films, respectively, which can ascribe to the different crystallization behaviors for the four metals. The experiment results indicate that the coating method can be applicable for the fabrication of many other films on cenosphere particles which can be sputter deposited.

Keywords: Cenosphere; Magnetron sputtering; Metal films

The study of dielectric relaxation and glass forming tendency in Cd–Se–Te glassy system by S.M. El-Sayed (pp. 7089-7093).

The dielectric relaxation spectroscopes of Cd_xSe70−_xTe₃₀ (where x=0, 5, 7, 10) alloy have been investigated in the temperature range 298–373K and in the frequency range 100Hz to 100kHz near the percolation threshold. The frequency and temperature dependence on the dielectric constant showed a Debye dielectric relaxation process. Using Debye relation, the dielectric constant ( ɛ′), the most probable relaxation time ( τ) and the barrier height ( W) were estimated for binary ternary chalcogenide systems.In addition, the analysis of the results suggests that the effect of Cd content on electronic conduction of the system. The experimental results support to some extent the above criterion in the case of Cd–Se–Te ternary alloy.

Keywords: Semiconductors; Amorphous; AC conductivity; Dielectric properties

Crystallization and electrical properties of V₂O₅ thin films prepared by RF sputtering by Alaa A. Akl (pp. 7094-7099).

V₂O₅ thin films were prepared under various conditions by using reactive RF sputtering technique. The microstructure and electrical properties of the films are have been investigated. X-ray diffraction data revealed the films deposited at low O₂/Ar ratio are amorphous. The orthorhombic structure of film improved after post annealing at 873K. The microstructure parameters (crystallite/domain size and macrostrain) have been evaluated by using a single order Voigt profile method. Using the two-point probe technique, the dark conductivity as a function of the condition parameters such as film thickness, oxygen content and temperature are discussed. It was also found that, the behaviour of ρd versus d was found to fit properly with the Fuchs–Sondheimer relation with the parameters: ρ_o=2.14×10⁷Ωcm and ℓ_o=112±2nm. At high temperature, the electrical conductivity is dominated by grain boundaries, the values of activation energy and potential barrier height were 0.90±0.02eV and 0.92±0.02V, respectively.

Keywords: Vanadium pentoxide; Thin films; RF sputtering; Electrical properties

Influence of remaining C on hardness and emissivity of SiC/SiO₂ nanocomposite coating by J. Yi; X.D. He; Y. Sun; Y. Li; M.W. Li (pp. 7100-7103).

SiC/SiO₂ nanocomposite coating was deposited by electron beam-physical vapor deposition (EB-PVD) through depositing SiC target on pre-oxidized 316 stainless steel (SS) substrate. High melting point component C remained and covered on the surface of ingot after evaporation. When SiC ingot was reused, remaining C had an effect on the composition, hardness and emissivity of SiC/SiO₂ nanocomposite coating. The composition of ingot and coating was studied by X-ray photoelectron spectroscopy (XPS). The influence of remaining C on hardness and spectral normal emissivity of SiC/SiO₂ nanocomposite coating was investigated by nanoindentation and Fourier transform infrared spectrum (FTIR), respectively. The results show that remaining C has a large effect on hardness and a minor effect on spectral normal emissivity of SiC/SiO₂ nanocomposite coating.

Keywords: Vapor deposition; Composition fluctuations; Optical spectroscopy

Surface characterization of a corroded bronze-leaded alloy in a salt spray cabinet by João Cura D’Ars de Figueiredo Junior; Vanessa de Freitas Cunha Lins; Vito Modesto De Bellis (pp. 7104-7107).

The corrosion products of a TM 23 bronze-leaded alloy (Cu 72%, Pb 15%, Zn 8% and Sn 5%) were obtained in a salt spray cabinet after exposition during 120h and 1000h. The products obtained were studied using scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction. The major products of bronze-leaded corrosion were oxides and basic salts of Cu, CuCl₂·3Cu(OH)₂, and Pb, Pb(OH)Cl. The results can be attributed to a kinetic control of the corrosion reactions.

Keywords: PACS; 82.45.BbBronze; Lead; Basic salts; Kinetic control

CO₂ adsorption on Cr(110) and Cr₂O₃(0001)/Cr(110) by S. Funk; T. Nurkic; B. Hokkanen; U. Burghaus (pp. 7108-7114).

We attempt to correlate qualitatively the surface structure with the chemical activity for a metal surface, Cr(110), and one of its surface oxides, Cr₂O₃(0001)/Cr(110). The kinetics and dynamics of CO₂ adsorption have been studied by low energy electron diffraction (LEED), Aug

Keywords: er electron spectroscopy (AES), and thermal desorption spectroscopy (TDS), as well as adsorption probability measurements conducted for impact energies of E_i=0.1–1.1eV and adsorption temperatures of T_s=92–135K. The Cr(110) surface is characterized by a square shaped LEED pattern, contamination free Cr AES, and a single dominant TDS peak (binding energy E_d=33.3kJ/mol, first order pre-exponential 1×10¹³s⁻¹). The oxide exhibits a hexagonal shaped LEED pattern, Cr AES with an additional O-line, and two TDS peaks ( E_d=39.5 and 30.5kJ/mol). The initial adsorption probability, S₀, is independent of T_s for both systems and decreases exponentially from 0.69 to 0.22 for Cr(110) with increasing E_i, with S₀ smaller by ∼0.15 for the surface oxide. The coverage dependence of the adsorption probability, S( Θ), at low E_i is approx. independent of coverage (Kisliuk-shape) and increases initially at large E_i with coverage (adsorbate-assisted adsorption). CO₂ physisorbs on both systems and the adsorption is non-activated and precursor mediated. Monte Carlo simulations (MCS) have been used to parameterize the beam scattering data. The coverage dependence of E_d has been obtained by means of a Redhead analysis of the TDS curves.

Effect of the preparation conditions of Ni-supported shock-wave synthesized nanodiamond catalysts by V. Mavrodinova; M. Popova; I. Kolev; S. Stavrev; Ch. Minchev (pp. 7115-7123).

On the basis of the results from the FT-IR, XRD and catalytic studies, a suggestion about the mechanism of surface transformations of Ni-supported detonation-synthesized ultradispersed diamond and the influence of these transformations on the state of the loaded metal have been made. It was proposed that in dependence on the inert or oxidative atmosphere applied for the elimination of the Ni salt precursor, different interactions of the support with the NiO species have taken place that determined the way of their coordination and stability as well as the dispersion of the metal nickel phase formed upon their reduction. The catalytic activity of the latter has been tested in the reaction of toluene hydrogenation.

Keywords: Detonation-synthesized ultradispersed diamond; Ni-supported; FT-IR spectroscopy; Toluene hydrogenation

Deposition characteristics of Al–12Si alloy coating fabricated by cold spraying with relatively large powder particles by W.-Y. Li; C. Zhang; X.P. Guo; G. Zhang; H.L. Liao; C. Coddet (pp. 7124-7130).

In this paper, the microstructure, microhardness and adhesive strength of Al–12Si coating produced by cold spraying were investigated. It is found that a thick, dense and well bonded Al–12Si coating could be produced by cold spraying with a relatively large powder through the control of spray conditions. The critical velocity for large Al–12Si particles was lower than that of small Al–12Si particles. The as-deposited Al–12Si coating had the same crystal structure as Al–12Si powder. The localized interface melting occurred resulting from both the adiabatic shearing upon impact and the thermal effect of hot gas. Some fine Si particles precipitated in α-Al matrix because of the thermal effect of hot gas during coating deposition. The dispersed Si particles in Al–12Si coating improved the coating microhardness.

Keywords: Cold spraying; Al–12Si alloy coating; Microstructrure; Microhardness; Adhesive strength

Evolution with temperature of a single sol–gel TIO₂ layer on sapphire (α-Al₂O₃) (0001) by S. Vives; C. Meunier; N. Boubekeur; Y. Kersale; V. Giordano (pp. 7131-7135).

TiO₂ sol–gel layer has been deposited on single crystal sapphire (0001) substrate. Evolution of the layer microstructure with the thermal treatment in the range 100–1100°C has been studied using X-ray diffraction and X-ray reflectometry. TiO₂ layer density first increases with temperature up to 800°C and then decreases with the appearance of a high roughness finally leading to anatase islands formation. The single crystal nature of the substrate seems to contribute to hinder the transformation of the anatase phase into the rutile phase and to induce a preferred orientation of the TiO₂ islands.

Keywords: PACS; 61.10i; 68.55aThin films; Sol–gel; Microstructure

Effect of gun current on the microstructure and crystallinity of plasma sprayed hydroxyapatite coatings by M.F. Morks; A. Kobayashi (pp. 7136-7142).

Hydroxyapatite (HA) is a bioactive material because its chemical structure is close to the natural bone. Its bioactive properties make it attractive material in biomedical applications. Gas tunnel type plasma spraying (GTPS) technique was employed in the present study to deposit HA coatings on SUS 304 stainless steel substrate. GTPS is composed of two plasma sources: gun which produces internal low power plasma (1.3–8kW) and vortex which produces the main plasma with high power level (10–40kW). Controlling the spraying parameters is the key role for spraying high crystalline HA coatings on the metallic implants. In this study, the arc gun current was changed while the vortex arc current was kept constant at 450A during the spraying process of HA coatings. The objective of this study is to investigate the influence of gun current on the microstructure, phase crystallinity and hardness properties of HA coatings. The surface morphology and microstructure of as-sprayed coatings were examined by scanning electron microscope. The phase structure of HA coatings was investigated by X-ray diffraction analysis. HA coatings sprayed at high gun current (100A) are dense, and have high hardness. The crystallinity of HA coatings was decreased with the increasing in the gun current. On the other hand, the hardness was slightly decreased and the coatings suffer from some porosity at gun currents 0, 30 and 50A.

Keywords: Hydroxyapatite; Plasma spraying; Gun current; Microstructure; Crystallinity; Hardness

Polydimethylsiloxane at the interfaces of fumed silica and zirconia/fumed silica by V.M. Gun’ko; M.V. Borysenko; P. Pissis; A. Spanoudaki; N. Shinyashiki; I.Y. Sulim; T.V. Kulik; B.B. Palyanytsya (pp. 7143-7156).

Polydimethylsiloxane (PDMS)/fumed silica A-300 and PDMS/ZrO₂/A-300 were studied using adsorption, thermogravimetry, temperature-programmed desorption (TPD) mass-spectrometry, infrared spectroscopy, XRD, and broadband dielectric relaxation spectroscopy. ZrO₂ was synthesized on fumed silica with zirconium acetylacetonate in CCl₄ at 350K for 1h and calcinated at 773K for 1h (1–4 reaction cycles). PDMS (5–40wt.%) was adsorbed onto silica and zirconia/silica from hexane solution and then dried. Grafted zirconia changes the chemistry of the surface (because of its catalytic capability) and the topology of secondary particles (because of occupation of voids in aggregates of primary silica particles by zirconia nanoparticles) responsible for the textural porosity of the powders. Therefore, many properties (such as structural characteristics of the composites, reactions on heating in air and vacuum, interfacial relaxation phenomena, hydrophobicity as a function of treatment temperature, etc.) of PDMS/zirconia/silica strongly differ from those of PDMS/A-300. Broadening of the α-relaxation of PDMS at the interfaces of disperse oxides suggests both weakening of the PDMS–PDMS interaction and strengthening of the PDMS–oxide interaction.

Keywords: Zirconia/fumed silica; PDMS/fumed silica; PDMS/zirconia/fumed silica; Structural characteristics; Adsorption properties; Infrared spectra; Thermogravimetry; TPD MS; Interfacial relaxation phenomena; DRS

Stabilization in electrical characteristics of hydrogen-annealed ZnO:Al films by Byeong-Yun Oh; Min-Chang Jeong; Jae-Min Myoung (pp. 7157-7161).

Al-doped ZnO (ZnO:Al) films prepared by RF magnetron co-sputtering at room temperature were thermally treated in hydrogen ambient at 300°C to enhance the films’ characteristics for transparent conductive oxide applications. The electrical properties of the hydrogen-annealed films were improved and preserved in air ambient, even though the crystal structures of the films were not changed by the thermal treatment. The optical and oxygen bonding characteristics of ZnO:Al films manifested that absorbed oxygen species on the films were removed by the hydrogen-annealing process. These results supported that the development of the electrically reliable ZnO:Al films could be realized using the hydrogen-annealing process.

Keywords: PACS; 73.61.Ga; 73.61.−r; 81.65.−b; 68.43.−h; 79.60.−iAl-doped ZnO (ZnO:Al); Transparent conductive oxide (TCO); Hydrogen treatment

Growth and Auger electron spectroscopy characterization of donut-shaped ZnO nanostructures by Liang-Chiun Chao; Shih-Hsuan Yang (pp. 7162-7165).

Zinc oxide (ZnO) nanodonuts have been obtained by vapor phase transport process utilizing a mixture of ZnO, graphite and erbium oxide powder as the evaporation source. ZnO nanodonuts prepared under various thermal processes indicate that ZnO nanodonuts start forming during the initial thermal ramp up stage. A subsequent holding of the growth temperature at 1000°C causes the nanodonut to evolve into perfectly donut-shaped nanostructure. Additional deposition of ZnO on top of the nanodonut during the holding of the furnace temperature at 1000°C result in partially filled nanodonuts or hemispherical nanostructures, or donuts that are completely buried beneath ZnO film. Auger electron spectroscopy depth profile analysis indicates that the deposited ZnO film is stoichiometric, whereas the nanodonuts and the completely filled hemispherical nanostructures are porous and are oxygen deficient. The volume density of the nanodonut is estimated to be 20% that of the background ZnO film.

Keywords: PACS; 68.65.+g; 78.66.Hf; 81.05.DzZnO nanostructures; Thermal evaporation; Auger electron spectroscopy

Adsorption of sodium bis(2-ethylhexyl) sulfosuccinate and wettability in polytetrafluoroethylene–solution–air system by Joanna Harkot; Bronisław Jańczuk (pp. 7166-7171).

The role of sodium bis(2-ethylhexyl) sulfosuccinate (AOT) adsorption at water–air and polytetrafluoroethylene–water (PTFE) interfaces in wetting of low energy PTFE was established from measurements of the contact angle of aqueous AOT solutions in PTFE–solution drop–air systems and the aqueous AOT solution surface tension measurements. For calculations of the adsorption at these interfaces the relationship between adhesion tension ( γ_LVcos θ) and surface tension ( γ_LV), and the Gibbs and Young equations were taken into account. On the basis of the measurements and calculations the slope of the γ_LVcos θ– γ_LV curve was found to be constant and equal −1 over the whole range of surfactant concentration in solution. It means that the amount of surfactant adsorbed at the PTFE–water interface, Γ_SL, is essentially equal to its amount adsorbed at water–air interface, Γ_LV. By extrapolating the linear dependence between γ_LVcos θ and γ_LV to cos θ=1 the determined value of critical surface tension of PTFE surface wetting, γ_C, was obtained (23.6mN/m), and it was higher than the surface tension of PTFE (20.24mN/m). Using the value of PTFE surface tension and the measured surface tension of aqueous AOT solution in Young equation, the PTFE–solution interface tension, γ_SL, was also determined. The shape of the γ_SL–log C curve occurred to be similar to the isotherm of AOT adsorption at water–air interface, and a linear dependence existed between the PTFE–solution interfacial tension and polar component of aqueous AOT solution. The dependence was found to be established by the fact that the work of adhesion of AOT solution to the PTFE surface was practically constant amounting 46.31mJ/m² which was close to the work of water adhesion to PTFE surface.

Keywords: PACS; 68.35 NpAdsorption; Surface tension; Polytetrafluoroethylene; Surfactant; Sodium bis(2-ethylhexyl) sulfosuccinate

Effect of CeO₂ buffer layer thickness on the structures and properties of YBCO coated conductors by Meiya Li; Xingzhong Zhao; B. Ma; S.E. Dorris; U. Balachandran; V.A. Maroni (pp. 7172-7177).

Biaxially textured YBa₂Cu₃O7−_x (YBCO) films were grown on inclined-substrate-deposited (ISD) MgO-textured metal substrates by pulsed laser deposition. CeO₂ was deposited as a buffer layer prior to YBCO growth. CeO₂ layers of different thickness were prepared to evaluate the thickness dependence of the YBCO films. The biaxial alignment features of the films were examined by X-ray diffraction 2 θ-scans, pole-figure, ϕ-scans and rocking curves of Ω angles. The significant influence of the CeO₂ thickness on the structure and properties of the YBCO films were demonstrated and the optimal thickness was found to be about 10nm. High values of T_c=91K and J_c=5.5×10⁵A/cm² were obtained on YBCO films with optimal CeO₂ thickness at 77K in zero field. The possible mechanisms responsible for the dependence of the structure and the properties of the YBCO films on the thickness of the CeO₂ buffer layers are discussed.

Keywords: PACS; 68.55.Jk; 74.76.Bz; 81.15.zCerium oxide; Thickness effect; Biaxial textures; YBCO coated conductors; Laser ablation

Chemical optimisation of a sol–gel procedure for the development of fluorescence Cu(II) nanosensors by Maria Arduini; Lidia Armelao; Silvia Gross; Fabrizio Mancin; Silvia Marcuz; Mariachiara Montolli; Cinzia Sada (pp. 7178-7187).

A template-assisted sol–gel procedure was developed and optimised for the preparation of silica thin films embedding the fluorescent dye 3-(dansylamido)-propyl-triethoxysilane (DNS-APTES) for Cu(II) sensing purposes. The different parameters involved (solution composition, nature of the template, deposition and annealing conditions, post-synthesis deposition of additional coatings, etc.) were independently changed in order to evaluate their effect on the final microstructure, composition and sensor performances of the films. The optimisation procedure encompassed also the choice of the suitable parameters to ensure stability of the sensing films and to avoid the leaching of the fluorescent dye.Films prepared by using the non-ionic surfactant F127, without an additional coating and with a post-deposition annealing at 100°C for 2h, were proven to be the best performing ones, characterised by the largest and fastest fluorescence quenching. In particular, the presence of a template was demonstrated to play a major role in determining the efficiency of the sensing device. The surface and in-depth composition of thin films was analysed by X-Ray Photoelectron Spectroscopy (XPS) and Secondary Ion Mass Spectrometry (SIMS). The sensing performances of the films were tested by titration experiments with Cu²⁺.

Keywords: Sol–gel; Thin films; Nanostructured fluorescence sensor; Copper(II) sensor; XPS; SIMS

Correlation between Vickers microhardness, porous layer thickness and porosity in p-type nanostructured silicon by M. Morales-Masís; L. Segura; A. Ramírez-Porras (pp. 7188-7191).

Mechanical characteristics via Vickers microindentation technique of nanostructured silicon films have been studied. The samples were grown by the usual electrochemical etching process in presence of hydrofluoric acid in two distinct proportions and for several exposure times. The current density was kept constant for all runs. Porosity and porous layer thickness were measured by gravimetric and optical means, respectively. A linear relation between layer thickness and exposure time shows up, in accordance with previous studies. Correspondingly, a slight decrement in the Vickers hardness is observed. On the contrary, the porosity remains independent of exposure time. A possible explanation is therefore proposed and discussed.

Keywords: PACS; 68.35.Gy; 68.60.BsVickers indentation; Microhardness; Porous silicon

Effect of substrate bias voltage on corrosion of TiN/Ti multilayers deposited by magnetron sputtering by M. Flores; L. Huerta; R. Escamilla; E. Andrade; S. Muhl (pp. 7192-7196).

Austenitic stainless steel can be attack by localized corrosion in saline environments, such as seawater. TiN/Ti multilayers can improve the corrosion resistance of the stainless steel better than TiN monolayers, because the titanium layers improve the impermeability of TiN/Ti multilayers. In this work, 1.75–4.55μm thick layers were deposited on to grounded or −100V biased substrates of 304 stainless steel substrates by reactive magnetron sputtering. The corrosion resistance of the layers was studied by means of potentiodynamic polarization in 0.5M NaCl solutions. It was found that the pitting corrosion resistance was dependent on the bias and period number of the multilayers.

Keywords: PACS; 47.55 dr; 47.54 JkTiN/Ti; Corrosion; Bias; Magnetron sputtering

Hydrothermal growth of ZnO on annealed electrodeposited titanate film: Influence of zinc nitrate and methenamine by Gil-Sung Kim; S.G. Ansari; Hyung-Kee Seo; Young-Soon Kim; O-Bong Yang; Hyung-Shik Shin (pp. 7197-7202).

Hydrothermal growth of hexagonal ZnO nanorods on the annealed titanate nanotube films is reported as a function of molar ratio of Zn(NO₃)₂ and methenamine (1:1–1:4). The molar ratio of 1:4 results in a dense and thinner rod in comparison with other molar ratios. Corn-like structures of the rods are believed to be due to the higher amine concentration. Raman peaks at 437 and 331cm⁻¹ are assigned to E₂ and E_2H–E_2L modes. Near band gap edge and green photoluminescence emission indicates the structural and oxygen vacancy. O 1s peak is found built-up of sub-peaks at 530.62, 531.8 and 532.84eV corresponding to O²⁻ on normal wurtzite structure and OH and oxygen vacancies of ZnO, respectively.

Keywords: PACS; 45.20.dh; 77.84.Dy; 73.40.Sx; 81.07.−bDSSC; Titanate seed; ZnO; Hexagonal nanorods

Fabrication and magnetic property of binary Co–Ni nanowire array by alternating current electrodeposition by Jinxia Xu; Yi Xu (pp. 7203-7206).

Ordered binary Co–Ni nanowire arrays with different components have successfully been fabricated by ac electrodeposition. The as-obtained nanowires exhibit a diameter of about 49.2nm and aspect ratio of more than 30. A highly preferential orientation of the Co–Ni nanowires has been obtained by XRD. The magnetic properties of Co–Ni nanowire arrays determined by VSM are as the function of the Co–Ni components. The maximum value of coercivities perpendicular to the array is 2073Oe. However, the magnetic properties of such nanowire arrays exhibited a bad thermal stability at the medium temperature of 200°C.

Keywords: Perpendicular magnetic recording; Co–Ni; Nanowire array; Alloy component; Annealing temperature

Cone-shaped structures of GeO₂ fabricated by a thermal evaporation process by Hyoun Woo Kim; Seung Hyun Shim; Jong Woo Lee (pp. 7207-7210).

We have synthesized cone-like GeO₂ structures via thermal heating of Ge powders. We have investigated the effects of substrate temperature on the sample morphology, revealing that cone-shaped structures are preferentially obtained at higher temperature. The cone-shaped structures, which gradually become thinner to form a sharp tip, appear to be a single-crystalline, hexagonal structure of GeO₂. Room-temperature photoluminescence measurement revealed two emission peaks, at about 2.78 and 3.04eV.

Keywords: PACS; 81.05.Zx; 61.10.Nz; 78.55.−mGeO; ₂; Cone-shaped structures; Thermal evaporation

Silicon carbonitride by remote microwave plasma CVD from organosilicon precursor: Growth mechanism and structure of resulting Si:C:N films by I. Blaszczyk-Lezak; A.M. Wrobel; M.P.M. Kivitorma; I.J. Vayrynen; A. Tracz (pp. 7211-7218).

The remote microwave hydrogen plasma chemical vapor deposition (RP-CVD) from bis(dimethylamino)methylsilane precursor was used for the synthesis of silicon carbonitride (Si:C:N) films. The effect of thermal activation on the RP-CVD process was examined by determining the mass- and the thickness-based film growth rate and film growth yield, at different substrate temperature ( T_S). It was found that the mechanism of the process depends on T_S and for low substrate temperature regime, 30°C≤ T_S≤100°C, RP-CVD is limited by desorption of film-forming precursors, whereas for high substrate temperature regime, 100°C< T_S≤400°C, RP-CVD is a non-thermally activated and mass-transport limited process. The Si:C:N films were characterized by X-ray photoelectron and Fourier transform infrared spectroscopies, as well as by atomic force microscopy. The increase of T_S enhances crosslinking in the film via the formation of nitridic Si–N and carbidic Si–C bonds. On the basis of the structural data a hypothetical crsosslinking reactions contributing to silicon carbonitride network formation have been proposed.

Keywords: Remote hydrogen plasma CVD; Bis(dimethylamino)methylsilane precursor; Silicon carbonitride film; Film chemical structure; Film surface morphology

Preparation of PMMA grafted aluminum powder by surface-initiated in situ polymerization by Hui Liu; Hongqi Ye; Yingchao Zhang (pp. 7219-7224).

Poly(methyl methacrylate) (PMMA) grafted aluminum powder was successfully prepared by surface-initiated in situ polymerization. The process was divided into two steps: adsorption of initiator and polymerization of monomer. It was found that the driving force of adsorption between initiator and aluminum was due to electrostatic force, not chemical bonding, and the percentage of adsorption (PA) and adsorption efficiency (AE) would reach as high as 31.2% and 52.0%, respectively. As for the process of in situ polymerization, the conversion of monomer ( C), percentage of grafting (PG) and grafting efficiency (GE) were investigated by evolved hydrogen detection. It was shown that the PG and GE obtained were consistent with those calculated through TGA analysis.

Keywords: PACS; APoly(methyl methacrylate); Aluminum powder; Graft; Surface-initiated in situ polymerization

Formation of Co ultrathin films on Si(111): Growth mechanisms, electronic structure and transport by N.I. Plusnin; V.M. Il’yashenko; S.A. Kitan; S.V. Krylov (pp. 7225-7229).

The AES, EELS, AFM and resistance measurement investigations have been performed to determine the growth mechanism, electronic structure and resistance-thickness dependence of Co layers on silicon at the thickness range from submonolayer up to several monolayer coverage. These layers were obtained under UHV high-rate deposition with using re-evaporation of Co from a Ta foil. The layer-by-layer growth of Co on Si(111) with some light segregation of Si has been found on the AES data. An enlarged and reduced concentration of valence electrons in the interface Si layer at the thickness ranges 0–1Å and in the Co film at d=1–2Å has been observed. Resistance measurement of the Co film showed a fast decrease of the resistance down to some value limited by quantum-size effect in accordance with the formation of a two-dimensional Co phase at d=1–2Å.

Keywords: Auger electron spectroscopy; Electron energy loss spectroscopy; Growth; Electron structure; Electrical conductivity; Co; Si(1; 1; 1)

Investigations on the oxidation of zirconium nitride films in air by nuclear reaction analysis and backscattering spectrometry by G.L.N. Reddy; J.V. Ramana; Sanjiv Kumar; S. Vikram Kumar; V.S. Raju (pp. 7230-7237).

The thermal oxidation of dc magnetron sputter deposited thin ZrN films in air in the temperature range of 100–475°C has been studied by depth profiling N using nuclear reaction analysis (NRA) involving¹⁵N(¹H,αγ)¹²C resonance reaction and O using 3.05MeV¹⁶O(α,α)¹⁶O resonant scattering. The structural and morphological changes accompanying the process have also been investigated. NRA/backscattering spectrometry measurements show that oxidation results in the formation of ZrO_1.8±0.1 at the surface. An interface consisting of Zr, O and N is also formed underneath the surface oxide. For an isothermal annealing, oxide layer as well as interface exhibits parabolic growth with the duration of annealing. The diffusion of oxygen through the already grown oxide layer ( D=5.6×10⁻¹⁴cm²s⁻¹ at 475°C) forms the rate-controlling step of oxidation. The diffusion may be facilitated by the high concentration of oxygen vacancies in the oxide layer. Glancing incidence X-ray diffraction (GIXRD) measurements indicate that zirconia films formed are phase-singular (monoclinic) and are textured in (200) and (311) orientations. Examination by scanning electron microscopy (SEM) reveals the formation of blisters on sample surfaces on prolonged oxidation. The blistering can be attributed to intrinsic growth stress arising due to the larger molar volume of zirconium oxide in comparison to zirconium nitride, a fact demonstrated by the depth profile measurements as well.

Keywords: Rutherford backscattering spectrometry; Nuclear resonance reaction analysis; Oxidation; ZrN

The effects of Si₃N₄ interlayer on the thermal stability and hardness of Ti/TiN_x ( x=0.5–1) nanolayered coatings by Xiaoming Bai; Weitao Zheng; Fei Xiong; Qing Jiang (pp. 7238-7241).

The polycrystalline Ti/TiN_x multilayer films were deposited by magnetron sputtering, and the as-deposited multilayer coatings were annealed at 500–800°C for 2–4h in vacuum. We investigated the effects of annealing temperature and annealing time on the microstructural, interfacial, and mechanical properties of the polycrystalline Ti/TiN_x multilayer films. It was found that the hardness increased with annealing temperature. This hardness enhancement was probably caused by the preferred crystalline orientation TiN(111). The X-ray reflectivity measurements showed that the layer structure of the coatings could be maintained after annealing at 500°C and the addition of the Si₃N₄ interlayer to Ti/TiN_x multilayer could improve the thermal stability to 800°C.

Keywords: PACS; 68.35Ti/TiN; _x; nano-multilayer; Annealing; Hardness; Thermal stability

Novel preparation methods of electrical contacts in Ge–Sb–Te thin films by Saleh T. Mahmoud; H. Ghamlouche; N. Qamhieh; Hessa Al-Shamisi (pp. 7242-7245).

New preparation methods of electrical contacts have been developed to minimize their effect on Ge–Sb–Te thin films. Impedance spectroscopy technique has been used to extract the contributions of both electrical contacts and the material under investigation. Three different configurations of electrical contacts were investigated. The results show that the effect of the contacts disappears when silver paste is placed on the gold electrode only without touching and interacting with the Ge–Sb–Te film.

Keywords: PACS; 73.61.−r; 73.61.Jc; 73.50.−hImpedance spectroscopy; Thin films; Electrical contacts; Ge–Sb–Te

Electrical characteristics of the hydrogen pre-annealed Au/n-GaAs Schottky barrier diodes as a function of temperature by Ö. Güllü; M. Biber; S. Duman; A. Türüt (pp. 7246-7253).

We investigated the passivation effects of hydrogen gas on the Au/n-GaAs Schottky barrier diodes in a wide temperature range. Reference diodes were prepared by evaporating barrier metal on semiconductor wafers un-annealed in N₂ gas atmosphere. The other diodes were made by evaporating barrier metal on n-GaAs semiconductor substrates annealed in H₂ atmosphere. Then, electrical measurements of all diodes were carried out by using closed-cycle Helium cryostat by steps of 20K in the temperature range of 80–300K in dark. The basic diode parameters such as ideality factor and barrier height were consequently extracted from electrical measurements. It was seen that ideality factors increased and barrier heights decreased with the decreasing temperature. The case was attributed to barrier inhomogeneity at the metal/semiconductor interface. Barrier heights of the diodes made from samples annealed in H₂ gas atmosphere were smaller than those of reference diodes at low temperatures. Here, it was ascribed to the fact that hydrogen atoms passivated dangling bonds on semiconductor surface in accordance with former studies.

Keywords: Schottky contact; Hydrogen passivation; GaAs; Barrier inhomogeneity

Evaluation of bacterial adhesion on Si-doped diamond-like carbon films by Q. Zhao; Y. Liu; C. Wang; S. Wang (pp. 7254-7259).

Diamond-like carbon (DLC) films as biomaterial for medical devices have been attracting great interest due to their excellent properties such as hardness, low friction and chemical inertness. It has been demonstrated that the properties of DLC films can be further improved by the addition of silicon into DLC films, such as thermal stability, compressive stress, etc. However no research work on anti-bacterial properties of silicon-doped diamond-like carbon films has been reported. In this paper the surface physical and chemical properties of Si-doped diamond-like carbon films with various Si contents on 316 stainless steel substrate prepared by a magnetron sputtering technique were investigated, including surface topography, surface chemistry, the sp³/sp² ratio, contact angle, surface free energy, etc. Bacterial adhesion to Si-doped DLC films was evaluated with Pseudomonas aeruginosa, Staphylococcus epidermidis and Staphylococcus aureus which frequently cause medical device-associated infections. The experimental results showed that bacterial adhesion decreased with increasing the silicon content in the films. All the Si-doped DLC films performed much better than stainless steel 316L on reducing bacterial attachment.

Keywords: Anti-adhesion; Anti-bacterial; Bacterial adhesion; Si-doped DLC; Surface energy; Surface treatment

Protective hybrid sol–gel coatings containing bioactive particles on surgical grade stainless steel: Surface characterization by Josefina Ballarre; Damián A. López; Wido H. Schreiner; Alicia Durán; Silvia M. Ceré (pp. 7260-7264).

Metallic materials are the most used materials as orthopaedic or dental implants for their excellent mechanical properties. However, they are not able to create a natural bonding with the mineralized bone and they could release metallic particles that could finally end in the removal of the implant. One way to avoid these effects is to protect the metallic implant with a biocompatible coating. In this work there are analyzed two kinds of protective organic–inorganic sol–gel made coatings with the adding of glass-ceramic particles with the aim of generating bioactivity. The samples are surface characterized by SEM, XRD and XPS. Amorphous hydroxyapatite (aHAp) deposited on the samples after 30 days of immersion in simulated body fluid (SBF) is detected on the samples and its presence is considered as a first signal of bioactivity.

Keywords: Stainless steel; Coatings; Surface characterization; Bioactivity

Surface characterization of porous silicon after pore opening processes inducing chemical modifications by N. Errien; L. Vellutini; G. Louarn; G. Froyer (pp. 7265-7271).

In this paper, we present a study on the porous silicon surface with the aim of filling porous silicon layers with organics. We discuss on two processes used to remove the outer parasitic layer created during the porous silicon formation. We demonstrate that these etching processes influences the surface properties, in particular wetting ability. By XPS and infrared absorption spectroscopy studies, we show that a SF₆ plasma treatment does not modify irreversibly the chemistry of porous silicon surface, nor the surface morphology. We also point out that NaOH etching does bring significant morphological modifications and influences the hydrophilicity of the porous silicon surface. This last treatment increases the polar groups (SiO) concentration on the pore surface and therefore allows a better filling of a porous silicon layer with organics, like dibromo-EDOT which can be thermally converted into PEDOT.

Keywords: Porous silicon; Plasma treatment; NaOH etching; MEB; IRTF and XPS spectroscopy

Femtosecond laser structuring of titanium implants by A.Y. Vorobyev; Chunlei Guo (pp. 7272-7280).

In this study we perform the first femtosecond laser surface treatment of titanium in order to determine the potential of this technology for surface structuring of titanium implants. We find that the femtosecond laser produces a large variety of nanostructures (nanopores, nanoprotrusions) with a size down to 20nm, multiple parallel grooved surface patterns with a period on the sub-micron level, microroughness in the range of 1–15μm with various configurations, smooth surface with smooth micro-inhomogeneities, and smooth surface with sphere-like nanostructures down to 10nm. Also, we have determined the optimal conditions for producing these surface structural modifications. Femtosecond laser treatment can produce a richer variety of surface structures on titanium for implants and other biomedical applications than long-pulse laser treatments.

Keywords: PACS; 42.62.−b; 42.62.Be; 61.80.Ba; 87.80.Mj; 87.83.+aTitanium implants; Surface topography; Femtosecond laser; Microstructures; Nanostructures; Periodic structures

Dissimilar autogenous full penetration welding of superalloy K418 and 42CrMo steel by a high power CW Nd:YAG laser by Xiu-Bo Liu; Gang Yu; Ming Pang; Ji-Wei Fan; Heng-Hai Wang; Cai-Yun Zheng (pp. 7281-7289).

Experiments of autogenous laser full penetration welding between dissimilar cast Ni-based superalloy K418 and alloy steel 42CrMo flat plates with 3.5mm thickness were conducted using a 3kW continuous wave (CW) Nd:YAG laser. The influences of laser welding velocity, flow rate of side-blow shielding gas, defocusing distance were investigated. Microstructure of the welded seam was characterized by optical microscopy (OM), scanning electron microscopy (SEM) and X-ray diffraction (XRD) and energy dispersive spectrometer (EDS). Mechanical properties of the welded seam were evaluated by microhardness and tensile strength testing. Results show that high quality full penetration laser-welded joint can be obtained by optimizing the welding velocity, flow rate of shielding gas and defocusing distance. The laser-welded seam have non-equilibrium solidified microstructures consisting of γ-FeCr_0.29Ni_0.16C_0.06 austenite solid solution dendrites as the dominant and very small amount of super-fine dispersed Ni₃Al γ′ phase and Laves particles as well as MC needle-like carbides distributed in the interdendritic regions. Although the microhardness of the laser-welded seam was lower than that of the base metal, the strength of the joint was equal to that of the base metal and the fracture mechanism showed fine ductility.

Keywords: Laser processing; Metals and alloys; Full penetration welding; Microstructure; Mechanical properties

Direct observation of the temperature field during ablation of materials by multiple femtosecond laser pulses by D.V. Tran; Y.C. Lam; H.Y. Zheng; B.S. Wong; D.E. Hardt (pp. 7290-7294).

We report a direct observation of the temperature field on a steel specimen during ablation by multiple femtosecond laser pulses using an infrared thermography technique. From the experimental results and simulation study of the temperature field, we quantified the deposited thermal power into the specimen during the ablation process. We found that more than two thirds of the incident laser power was deposited in the steel specimen when ablated by multiple femtosecond laser pulses. This result provides further understanding of the heating effect in materials processing by ultrashort laser pulses.

Keywords: PACS; 79.20.Ds; 81.05Femtosecond laser; Ablation; Thermal effect; Temperature field; Steel

Study of surface interactions of ionic liquids with aluminium alloys in corrosion and erosion–corrosion processes by María-Dolores Bermúdez; Ana-Eva Jiménez; Ginés Martínez-Nicolás (pp. 7295-7302).

Surface interactions of alkylimidazolium ionic liquids (ILs) with aluminium alloy Al 2011 have been studied by immersion tests in seven neat ILs [1- n-alkyl-3-methylimidazolium X⁻ (X=BF₄; n=2 (IL1), 6 (IL2), 8 (IL3). X=CF₃SO₃; n=2 (IL4). X=(4-CH₃C₆H₄SO₃); n=2 (IL5). X=PF₆; n=6 (IL6)] and 1-butyl-3-methylpyridinium bis(trifluoromethylsulfonyl)imide (IL7)]. Immersion tests for Al 2011 have also been carried out in 1wt.% and 5wt.% solutions of 1-ethyl,3-methylimidazolium tetrafluoroborate (IL1) in water. No corrosion of Al 2011 by neat ILs is observed. The highest corrosion rate for Al 2011 in water is observed in the presence of a 5wt.% IL1 due to hydrolysis of the anion with hydrogen evolution and formation of aluminium fluoride. Erosion–corrosion processes have been studied for three aluminium alloys (Al 2011, Al 6061 and Al 7075) in a 90wt.% IL1 solution in water in the presence of α-alumina particles. The erosion–corrosion rates are around 0.2mm/year or lower, and increase with increasing copper content to give a corrosion resistance order of Al 6061>Al 7075>Al 2011. Results are discussed on the basis of scanning electron microscopy (SEM) observations, energy dispersive spectroscopy (EDS) analysis, X-ray diffraction (XRD) patterns and X-ray photoelectron spectroscopy (XPS) determinations.

Keywords: Ionic liquids; Aluminium; Corrosion; Erosion–corrosion; Surface chemistry

Effect of plasticizer on surface of free films prepared from aqueous solutions of salts of cationic polymers with different plasticizers by János Bajdik; Máté Fehér; Klára Pintye-Hódi (pp. 7303-7308).

Acquisition of a more detailed understanding of all technological processes is currently a relevant tendency in pharmaceutical technology and hence in industry. A knowledge of film formation from dispersion of polymers is very important during the coating of solid dosage forms. This process and the structure of the film can be influenced by different additives. In the present study, taste-masking films were prepared from aqueous citric acid solutions of a cationic polymer (Eudragit^® E PO) with various hydrophilic plasticizers (glycerol, propylene glycol and different poly(ethylene glycols)). The mechanical properties, film thickness, wetting properties and surface free energy of the free films were studied. The aim was to evaluate the properties of surface of free films to predict the arrangement of macromolecules in films formed from aqueous solutions of salts of cationic polymers. A high molecular weight of the plasticizer decreased the work of deformation. The surface free energy and the polarity were highest for the film without plasticizer; the hydrophilic additives decreased these parameters. The direction of the change in polarity (a hydrophilic component caused a decrease in the polarity) was unexpected. It can be explained by the change in orientation of the macromolecules, a hydrophobic surface being formed. Examination of the mechanical properties and film thickness can furnish additional results towards a knowledge of film formation by this not frequently applied type of polymer from aqueous solution.

Keywords: Mechanical properties; Plasticizer; Polarity; Salts of cationic polymers; Surface free energy

Annealing studies of Ti/Al multilayer film by slow positron beam by L.Z. Zhang; D.N. Wang; B.Y. Wang; R.S. Yu; L. Wei (pp. 7309-7312).

Single detector and coincidence Doppler broadening (CDB) spectroscopy measurements using slow positron beam were carried out to study as-deposited and annealed Ti/Al multilayer films. The changes of the film structure and defects in each layer by heat treatment have been investigated through the analysis of Doppler broadening lineshape variation. The coincidence Doppler broadening measurements revealed that Ti is the dominant diffusion species during the alloying process of Ti/Al by high temperature annealing. These results highlight the potential of slow positron beam in characterizing the vacancy-type defects evolution and mechanism of interlayer diffusion in Ti/Al multilayer film.

Keywords: Ti/Al multilayer; Slow positron beam; S; -Parameter; Coincidence Doppler broadening

Electrosynthesis and characterization of Fe doped CdSe thin films from ethylene glycol bath by S.M. Pawar; A.V. Moholkar; K.Y. Rajpure; C.H. Bhosale (pp. 7313-7317).

The CdSe and Fe doped CdSe (Fe:CdSe) thin films have been electrodeposited potentiostatically onto the stainless steel and fluorine doped tin oxide (FTO) glass substrates, from ethylene glycol bath containing (CH₃COO)₂·Cd·2H₂O, SeO₂, and FeCl₃ at room temperature. The doping concentration of Fe is optimized by using (photo) electrochemical (PEC) characterization technique. The deposition mechanism and Fe incorporation are studied by cyclic voltammetry. The structural, surface morphological and optical properties of the deposited CdSe and Fe:CdSe thin films have been studied by X-ray diffraction, scanning electron microscopy (SEM) and optical absorption techniques respectively. The PEC study shows that Fe:CdSe thin films are more photosensitive than that of undoped CdSe thin films. The X-ray diffraction analysis shows that the films are polycrystalline with hexagonal crystal structure. SEM studies reveal that the films with uniformly distributed grains over the entire surface of the substrate. The complete surface morphology has been changed after doping. Optical absorption study shows the presence of direct transition and a considerable decrease in bandgap, E_g from 1.95 to 1.65eV.

Keywords: Electrodeposition; CdSe thin films; Fe:CdSe thin films; X-ray diffraction; Optical absorption

Microstructure and nanohardness of the diluted magnetic semiconducting Cd1−_xMn_xS nano-crystalline films by D. Sreekantha Reddy; B.K. Reddy; N. Koteeswara Reddy; K.R. Gunasekhar; P. Sreedhara Reddy (pp. 7318-7322).

Cd1−_xMn_xS nano-crystalline films (0≤ x≤0.5) were formed on glass substrates by thermal evaporation technique at room temperature (300K). AFM studies showed that all the films were in nano-crystalline form with the grain size varying in the range between 36 and 58nm and exhibited hexagonal structure of the host material. The lattice parameters varied linearly with composition, following Vegard's law in the entire composition range. The nanohardness and Young's modulus decreased sharply with ‘Mn’ content upto x=0.3 and increased with high Mn content.

Keywords: PACS; 62.25.+g; 68.47.Fg; 61.72.Vv; 62.20.−x; 68.35.Gy; 68.37.PsDiluted magnetic semiconductors; Cd; 1−; _x; Mn; _x; S nano-crystalline films; Microstructure; Nanohardness and Young's modulus

A study on the antimicrobial efficacy of RF oxygen plasma and neem extract treated cotton fabrics by K. Vaideki; S. Jayakumar; G. Thilagavathi; R. Rajendran (pp. 7323-7329).

The paper deals with a thorough investigation on the antimicrobial activity of RF oxygen plasma and Azadirachtin (neem extract) treated cotton fabric. The hydrophilicity of cotton fabric was found to improve when treated with RF oxygen plasma. The process parameters such as electrode gap, time of exposure and oxygen pressure have been varied to study their effect on improving the hydrophilicity of the cotton fabric. The static immersion test has been carried out to assess the hydrophilicity of the oxygen plasma treated samples and the process parameters were optimized based on these test results. The formation of carbonyl group during surface modification in the plasma treated sample was analysed using FTIR studies. The surface morphology has been studied using SEM micrographs.The antimicrobial activity was imparted to the RF oxygen plasma treated samples using methanolic extract of neem leaves containing Azadirachtin. The antimicrobial activity of these samples has been analysed and compared with the activity of the cotton fabric treated with neem extract alone. The investigation reveals that the surface modification due to RF oxygen plasma was found to increase the hydrophilicity and hence the antimicrobial activity of the cotton fabric when treated with Azadirachtin.

Keywords: Hydrophilicity; Antimicrobial activity; RF oxygen plasma; Neem extract (Azadirachtin); X-ray diffractogram; SEM micrograph; FTIR spectrum

Influence of substrate temperature on the optical and piezoelectric properties of ZnO thin films deposited by rf magnetron sputtering by Seong Jun Kang; Yang Hee Joung (pp. 7330-7335).

In this study, ZnO thin films were fabricated using the rf magnetron sputtering method and their piezoelectrical and optical characteristics were investigated for various substrate temperatures. The ZnO thin film has the largest crystallization orientation for the (002) peak and the smallest FWHM value of 0.56° at a substrate temperature of 200°C. The surface morphology shows a relatively dense surface structure at 200°C compared to the other substrate temperatures. The surface roughness shows the smallest of 1.6nm at a substrate temperature of 200°C. The piezoelectric constant of the ZnO thin film measured using the pneumatic loading method (PLM) has a maximum value of 11.9pC/N at a substrate temperature of 200°C. The transmittance of the ZnO thin film measured using spectrophotometry with various substrate temperatures ranged from 75 to 93% in the visible light region. By fitting the refractive index from the transmittance to the Sellmeir dispersion relation, we can predict the refractive index of the ZnO thin film according to the wavelength. In the visible light range, the refraction index of the ZnO thin film deposited at a substrate temperature of 200°C is the range of 1.88–2.08.

Keywords: PACS; 73.61.Ga; 77.65.−j; 78.66.−wZnO thin film; rf sputtering; Piezoelectric constant; Refractive index

Theoretical investigation of the conduction and valence band offsets of GaAs1_−x N_x/GaAs1−_yN_y heterointerfaces by A. Gueddim; N. Bouarissa (pp. 7336-7341).

Theoretical investigations of the conduction band offset (CBO) and valence band offset (VBO) of the relaxed and pseudo-morphically strained GaAs1−_xN_x/GaAs1−_yN_y heterointerfaces at various nitrogen concentrations ( x and y) within the range 0–0.05 and along the [001] direction are performed by means of the model-solid theory combined with the empirical pseudopotential method under the virtual crystal approximation that takes into account the effects of the compositional disorder. It has been found that for y< x, the CBO and VBO have negative and positive signs, respectively, whereas the reverse is seen when y> x. The band gap of the GaAs1−_xN_x over layer falls completely inside the band gap of the substrate GaAs1−_yN_y and thus the alignment is of type I (straddling) for y< x. When y> x, the alignment remains of type I but in this case it is the band gap of the substrate GaAs1−_yN_y which is fully inside the band gap of the GaAs1−_xN_x over layer. Besides the CBO, the VBO and the relaxed/strained band gap of two particular cases: GaAs1−_xN_x/GaAs and GaAs1−_xN_x/GaAs_0.98N_0.02 heterointerfaces have been determined.

Keywords: PACS; 71.20.Nr; 71.15.−m; 71.15.DxHeterointerface; Strain; Band offsets; Type 1-alignment; Dilute alloys

Nanoscale coatings for control of interfacial bonds and nanotube growth by Rajasekhar V. Pulikollu; Sharmila M. Mukhopadhyay (pp. 7342-7352).

This paper describes the usefulness of nanoscale coatings in improving some engineering materials having porous and uneven surfaces (microcellular foam, nanofibers, nanotubes, etc.). It is shown that 3–5nm coatings deposited in microwave plasma can influence crucial properties for a wide variety of applications. Two coatings resulting in opposite chemistries have been studied, an oxide layer that increases surface reactivity_, and a similar fluorocarbon layer that makes it inert. In-depth atomic level microscopic and spectroscopic investigations of nucleation and growth of these layers on various substrates have been reported earlier. The effectiveness of such coatings in modifying bond strength, wettability and catalytic activity of various porous and uneven carbon surfaces have been shown here. The following influences of nanoscale functional coatings have been elaborated upon: (a) modification of carbon–polymer interfaces (b) controlled metallization of carbon (c) influence of nano-coatings on catalytic activity, for formation of carbon nanotubes on larger structures.

Keywords: Foam; Nanofibers; Carbon nanotube; Nano-coatings; Metallization

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Applied Surface Science (v.253, #17)