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Applied Surface Science (v.253, #14)

Physico-chemical characterization of electrochemical deposit of Ca₁₀(PO₄)₆(OH)₂ on copper surfaces by M.A. El Mhammedi; M. Achak; M. Bakasse; A. Chtaini (pp. 5925-5930).

Surface modification of biomaterials to improve biocompatibility without changing their bulk properties is desired for many clinical applications and has become an emerging technology in biomaterial research and industry. In the present study, a sample electrochemical method of coating the solid surfaces of copper, with a film of apatite, was developed. Thin layer of calcium phosphate crystals formed on the surfaces of copper, was carried out by electrochemical methods, and characterized by XRD, infrared spectroscopy and chemical analysis.

Keywords: PACS; 68.35.Bs; 61.10.Nz; 61.66.BiElectrodeposition; Apatite; X-ray diffraction; Copper; Carbon paste; Square wave voltammetry

Effects of deposition temperature and thickness on the structural properties of thermal evaporated bismuth thin films by Latha Kumari; Shih-Jie Lin; Jin-Han Lin; Yuan-Ron Ma; Ping-Chung Lee; Yung Liou (pp. 5931-5938).

Bismuth (Bi) thin films of different thicknesses were deposited onto Si(100) substrate at various substrate temperatures by thermal evaporation technique. Influences of thickness and deposition temperature on the film morphologies, microstructure, and topographies were investigated. A columnar growth of hexahedron-like grains with bimodal particle size distribution was observed at high deposition temperature. The columnar growth and the presence of large grains induce the Bi films to have large surface roughness as evidenced by atomic force microscopy (AFM). The dependence of the crystalline orientation on the substrate temperature was analyzed by X-ray diffraction (XRD), which shows that the Bi films have completely randomly oriented polycrystalline structure with a rhombohedral phase at high deposition temperature (200°C) and were strongly textured with preferred orientation at low deposition temperatures (30 and 100°C).

Keywords: PACS; 81.05.Bx; 68.03.Fg; 68.37.Hk; 68.37.Ps; 61.10.NzBismuth thin film; Evaporation; Scanning electron microscopy; Atomic force microscopy; X-ray diffraction

Effect of manganese on grain boundary segregation of sulfur in iron by S.B. Gesari; M.E. Pronsato; A. Juan (pp. 5939-5942).

The ASED-MO theory was used to study the electronic effects of S and the S–Mn couple upon the chemical embrittlement of Fe grain boundaries. The results obtained for S alone in a model of grain boundary (GB) are consistent with its observed behavior as a chemical embrittling agent. It was found that the total energy of the cluster decreases when the S atom is located at the GB. When S segregate at the Fe GB containing Mn, the embrittlement process was modified. The crystal orbital overlap population (COOP) curves gives a measure of Fe–Fe bond weakening due to the segregated atoms at the GB. Our calculations show that Mn behaves as a weak embrittler on the Fe GB. The Fe–Mn bonds were strengthened, while Fe–Fe bonds of the capped trigonal prism of the GB (CTP) were weakened. On the other hand, when S segregate at the Mn/Fe cluster, some metallic bonds were resistant to chemical embrittlement.

Keywords: Metals; Surfaces and interfaces; Grain boundary; Electronic states (localized)

Natural variability in the surface roughness of combinatorial libraries of materials by Gregory P. Rockwell; Adam Timmons; Ahmed Touhami; J.R. Dahn (pp. 5943-5946).

Using a conventional method for the fabrication of solid-state combinatorial libraries, we have produced the binary libraries Fe1−_xCr_x and Mo1−_xSn_x (0< x<1) and found that their surface roughness is highly dependent on chemical composition. Roughness enhancements of up to 20-fold have been observed on the nanometer scale and were manifested in the boundaries between structurally dissimilar phases. It is anticipated that this is a common occurrence in thin-film libraries of metals and an obstacle in separating the influence of roughness and composition on the performance of library materials in biomaterial studies.

Keywords: PACS; 68.37.Ps; 68.55.Jk; 81.15.CdCombinatorial materials; Surface roughness; Biomaterials; Thin films; Sputtering; AFM

Stabilization of the pentagonal surface of the icosahedral AlPdMn quasicrystal by controlled Si absorption by J.-N. Longchamp; M. Erbudak; Y. Weisskopf (pp. 5947-5950).

The Debye-temperature of the pentagonal surface of the icosahedral AlPdMn quasicrystal (QC) is measured by means of low-energy electron diffraction after the absorption of different amounts of Si. We observe an increase of the surface Debye-temperature from300±7 K for the freshly prepared surface to330±7 K after the absorption of 60-Å Si. Because the quasicrystalline order persists at the surface in spite of the diffusion of Si into the substrate, we suggest that the diffusion is dominated by a vacancy-mediated process.

Keywords: PACS; 61.14.Hg; 61.44.Br; 63.70.+h; 61.10.; −; iSilicon; Epitaxy; AlPdMn; Quasicrystals; Debye-temperature; LEED

Imaging of aerosols using time of flight secondary ion mass spectrometry by Carolina Font Palma; Greg J. Evans; Rana N.S. Sodhi (pp. 5951-5956).

Interest in environmental aerosol chemistry has grown over the last decade as a result of its role in both climate change and troposheric pollution. In this work, the combination of ToF-SIMS and SEM/EDX was employed to explore the surface chemistry of aerosols. The capabilities and limitations of ToF-SIMS were investigated using particles of known composition and size produced by a vibrating orifice aerosol generator (VOAG). Principal component analysis (PCA) proved to help in the distinction of particles of different types by consolidating the information generated by ToF-SIMS.

Keywords: ToF-SIMS; SEM/EDX; VOAG; PCA; Aerosols; Imaging

Catalysis, by amorphous carbon, of H₂ attack on oxidized U–0.1wt% Cr surfaces by Noah Shamir (pp. 5957-5960).

Amorphous carbon, evaporated on a thin oxide layer covered U–0.1wt% Cr sample, was proven to significantly catalyze H₂ reaction with the metal. A hydride was formed preferentially on the carbon-covered surface, for vacuum pretreatment temperatures of 150 and 190°C and hydrogen reactions of 150 and 90°C, respectively. Dependence of the reaction rate on the thickness of the layer was observed.

Keywords: Catalysis; Uranium; Hydrides; Oxide surfaces; Nucleation and growth: Microscopic aspects; Hot stage microscopy (HSM); Scanning electron microscopy (SEM)

The electrical properties of metal-oxide-semiconductor devices fabricated on the chemically etched n-InP substrate by H. Çetin; E. Ayyildiz (pp. 5961-5966).

The electrical properties of the Cu/n-InP and Al/n-InP Schottky barrier diodes (SBDs) with and without the interfacial oxide layer have been investigated by using current–voltage ( I– V) measurements. The oxide layer on chemically cleaned indium phosphide (InP) surface has been obtained by exposure to water vapor at 1ml/min at 200°C before metal evaporation. The chemical composition of surface oxides grown on the InP is investigated using X-ray photoelectron spectroscopy (XPS). Phosphorus is present as In(PO₃)₃, InPO₄, P₂O₅ and P₄O₁₀. The values of 0.437±0.007 and 0.438±0.003eV for the barrier height of the reference Cu/n-InP and Al/n-InP SBDs were obtained, respectively. Furthermore, the values of 0.700±0.030 and 0.517±0.023eV for the barrier height of the oxidized Cu/n-InP and Al/n-InP SBD were obtained, respectively. The transport properties of the metal-semiconductor contacts have been observed to be significantly affected by the presence of the interfacial oxide layer. Devices built on the oxidized surfaces show improved characteristics compared with those built on chemically cleaned surfaces. The chemical reactivity of the metal with oxide and n-InP is important to the formation of the Schottky barriers. The reactive metal Al gave a low barrier height due to the reduction of oxide and reaction with InP. The transmission coefficients for the oxidized Cu/n-InP and Al/n-InP are equal to 2.23×10⁻⁵ and 4.60×10⁻², respectively.

Keywords: Schottky barrier diode; Compound semiconductor; Metal-interfacial-layer-semiconductor; X-ray photoemission electron spectra; Interface states

Effect of heat treatment on the microstructure and microhardness of cold-sprayed tin bronze coating by Wen-Ya Li; Chang-Jiu Li; Hanlin Liao; Christian Coddet (pp. 5967-5971).

Tin bronze (TB) powder was deposited on a stainless steel substrate by cold spraying. Post-deposition heat treatment was conducted in an electrical resistance furnace under nitrogen atmosphere at a temperature of 850°C for 3h. The effect of heat treatment on the microstructure and microhardness of cold-sprayed TB coating was investigated. It was found that the as-sprayed TB coating presented a dense microstructure. Heat treatment significantly influenced the microstructure and microhardness of cold-sprayed TB coating. A distinguishable diffusion layer of about 150μm was formed in the coating near the coating/substrate interface. A compound was precipitated in the diffusion layer. The microhardness in the coating was changed gradually along the coating from the interface to the coating surface after heat treatment. The microhardness in the diffusion layer was high owing to the precipitation of hard phase, while it was much low in other area due to the obvious grain growth during annealing.

Keywords: Cold spraying; Heat treatment; Tin bronze; Coatings; Microhardness

Long term studies on the chemical stability of a superhydrophobic silicone nanofilament coating by Jan Zimmermann; Georg R.J. Artus; Stefan Seeger (pp. 5972-5979).

We have performed extensive studies on the long term chemical stability of a superhydrophobic coating comprised of silicone nanofilaments. Durability was tested by immersion in various liquid media over a period of 6 months. The coating properties were monitored by static contact angle and sliding angle measurements. Changes in surface topography were examined by scanning electron microscopy. The coatings show an exceptional stability in organic solvents, neutral and mildly acidic aqueous solutions and mildly acidic detergent solutions. The superhydrophobic coating properties are stable for several days in mildly basic and strong acidic solutions but deteriorate fast under strong basic conditions.

Keywords: PACS; 81.05.−t; 81.07.−b; 68.08.BcSuperhydrophobic surfaces; Nanofilament; Stability; Durability; Coatings; Wetting

Field emitters with low turn on electric field based on carbon fibers by Qilong Wang; Hui Mu; Xiaobing Zhang; Wei Lei; Jinchan Wang; Hongping Zhao (pp. 5980-5984).

Field emitters of vertical carbon fibers on a silicon substrate are fabricated by catalytic chemical vapor deposition. After an ageing process of 150min, field emission measurement of the fibers is carried out in a vacuum chamber with a base pressure of 5.0×10⁻⁴Pa. The experimental results display that field emission performance of the carbon fibers depends strongly on the vacuum level during the experiments. After the field emission measurement, damage to the carbon fiber field emitters is observed from the scanning electron microscopic images.

Keywords: PACS; 81.05.Uw; 81.15.Gh; 79.70.+qCarbon fibers; Chemical vapor deposition; Field emission

Surface modification study of low energy electron beam irradiated polycarbonate film by Rashi Nathawat; Anil Kumar; Vaibhav Kulshrestha; M. Singh; V Ganesan; D.M. Phase; Y.K. Vijay (pp. 5985-5991).

The effect of low energy electron beam irradiation on polycarbonate (PC) film has been studied here. The PC film of thickness 20μm was exposed by 10keV electron beam with 100nA/cm² current density. The irradiated film was characterized by mean of X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and residual gas analyzer (RGA). Formation of unsaturated bonds and partial graphitization of the surface layer are measured by XPS. Results of the AFM imaging shows electron implantation induce changes in surface morphology of the polymer film. The residual gas analyzer (RGA) spectrum of PC is recorded in situ during irradiation. The results show the change in cross-linking density of the polymer at the top surface.

Keywords: XPS; AFM; Electron beam irradiation; Cross-linking; Polycarbonate

Analysis of the current-transport mechanism across a CVD diamond/silicon interface by A.M. Rodrigues (pp. 5992-5999).

This work presents a study on the mechanism of injection and charge transport through a CVD diamond/n⁺-Si interface. The current–voltage–temperature characteristics of CVD diamond/silicon heterojunctions measured in the temperature range 119–400K have been interpreted according to thermionic theory and thermionic field-emission theory. This junction shows deviations from the ideal thermionic theory current model, suggesting the presence of surface states, thin-layer depletion and/or non-homogeneity in the diamond/silicon interface. The T₀ anomaly has been used to explain the behaviour of the ideality factor with temperature. At very low temperatures tunnelling may occur because the E₀₀ values for these junctions are close to the value expected by thermionic field-emission theory. The usual activation-energy plot deviates from linearity at low temperatures. This deviation has been corrected supposing a ln( J_S/ T²) versus 10³/ nT plot. Under these conditions the Richardson constant is found to be 0.819Acm⁻²K⁻², which is close to the theoretical value of 1.2Acm⁻²K⁻². Field-emission device is a promising application for diamond/silicon structure.

Keywords: Diamond film; Characterization of electrical properties; Schottky diodes; Interface electronic properties; Field emission

Quantitative depth profiling of an alternating Pt/Co multilayer and a Pt–Co alloy multilayer by SIMS using a Buckminsterfullerene (C₆₀) source by Kyung Joong Kim; David Simons; Greg Gillen (pp. 6000-6005).

A Buckminsterfullerene ion beam has been applied to the depth profiling of an alternating pure Pt and pure Co multilayer. Quantitative depth profiling was performed by secondary ion mass spectrometry (SIMS) with C₆₀ ions using Pt–Co alloy films with different compositions. Relative sensitivity factors (RSFs) derived from a Pt₃₉Co₆₁ alloy film were used to convert an original depth profile to a composition depth profile. A severe interface artifact observed in the depth profile of a Pt/Co multilayer was quantitatively correlated with a gradual variation of matrix composition through the Pt/Co and Co/Pt interfaces by comparison with the depth profiling of an alloy multilayer film. Moreover, the interface artifact could be compensated by conversion of the profile to a composition profile using the same RSFs. The depth resolutions of a Pt/Co multilayer derived from the composition depth profile were much larger than the apparent interface widths measured from the original depth profile due to the nonlinear relationship between the Co and Pt ion intensities and their compositions.

Keywords: Buckminsterfullerene ion; SIMS quantification; Depth profiling; Interface artifact

Microstructure and electrical characterization based on AFM of very high-doped polysilicon grains by R. Coq Germanicus; E. Picard; B. Domenges; K. Danilo; R. Rogel (pp. 6006-6012).

In this work, we demonstrate that atomic force microscopy allows topography measurement as well as the local electrical properties of very high-doped polysilicon film prior to any subsequent annealing. AFM and TEM observations showed the columnar microstructure of the polysilicon layer. The electrical effect of this microstructure was characterized using SCM, KFM and C-AFM. Each electric mode gives additional information on the local properties of the polysilicon layer.

Keywords: ISD polysilicon; LPCVD; AFM; TEM; SCM; Surface potential; C-AFM

Effects of anodizing conditions on bond strength of anodically oxidized film to titanium substrate by Yeong-Joon Park; Kyung-Ha Shin; Ho-Jun Song (pp. 6013-6018).

The bond strength of the oxide film to the titanium substrate and its inherent structural characteristics are very important preconditions for the success of titanium implants. The purpose of this study was to evaluate the micro-morphologies, crystalline structures, and bond strengths of the anodically oxidized films formed on titanium with the variation of electrolytes and applied current densities. In contrast to the specimens produced using sulfuric acid as the electrolyte, those produced using phosphoric acid showed quite different shapes and densities of the pores as the applied current densities were varied. The oxide films anodized in sulfuric acid consisted of anatase and rutile TiO₂, whileTiP₂O₇ was predominantly formed on the Ti surfaces anodized using phosphoric acid as the electrolyte. The oxide films, which did not experience spark deposition showed amorphous shape and their bond strengths were significantly lower than those of the other groups ( p<0.05). Those specimens which experienced initial spark deposition with a low current condition showed the highest bond strengths (34.2MPa) within each electrolyte sub-set. The growing rates of the oxide film thicknesses in relation to the electric current changes varied according to the type of electrolyte, and the oxide film thickness influenced the bond strength.

Keywords: PACS; 87.68.+z; 81.65.MqTitanium; Anodic oxidation; Bond strength; Electrolyte

Textural changes during CO₂ activation of chars: A fractal approach by Manuel María Mahamud (pp. 6019-6031).

In this paper two series of active carbons obtained at different flow rates of the activating agent, CO₂, are characterized in order to establish the different mechanisms of pore development during the activation step. This study complements previous works on textural development during the different steps in the process of obtaining active carbons: coal oxidation, coal pyrolysis and char gasification. As the characteristics of the original and intermediate materials are of capital importance in the pore development of active carbons, the properties of the active carbons, precursor chars and coals were considered and analyzed together. Mercury porosimetry and helium picnometry were used to determine classical textural parameters as well as to perform a more detailed study of the pore volume generation during the different conditions of the activation step. Data obtained from the mercury porosimetry determinations was also employed for fractal determinations according to the methodologies proposed by Friesen and Mikula, Zhang and Li and the procedure of Neimark. Average surface fractal dimensions as well as fractal profiles and local surface fractal dimensions were calculated. The use of different flow rates during the activation step produces changes not only in the ordinary textural parameters but also in the fractal characteristics of the active carbons. Activation at higher flow rates leads to smoother fractal profiles and also to lower values of the average surface fractal dimensions of the active carbons.

Keywords: PACS; 81.05Uw; 91.60.NpMercury porosimetry; Fractal analysis; Active carbon texture; Carbon dioxide activation; Flow rate; Burn-off

Hydrophobic and physical properties of the ambient pressure dried silica aerogels with sodium silicate precursor using various surface modification agents by A. Parvathy Rao; A. Venkateswara Rao; G.M. Pajonk (pp. 6032-6040).

The experimental results on the synthesis and physical properties of the ambient pressure dried hydrophobic silica aerogels in the presence of various surface modification (silylating) agents are presented. The silica aerogels were prepared with 1.12 specific gravity ion exchanged sodium silicate solution, 1N ammonium hydroxide, solvent exchanged with ethanol and hexane, and surface modification with 20% silylating agent in hexane followed by drying the modified gel up to 200°C. The molar ratio of sodium silicate, water, ammonium hydroxide and silylating agent was kept at 1:45:4.3×10⁻²:5, respectively. The physical properties of the aerogels such as density, % of porosity, pore volume, thermal conductivity and contact angle measurements were studied by using various mono, di and tri alkyl or aryl silylating agents (SAs). The tri alkyl silylating agents produced low % of volume shrinkage (2%), low density (0.06g/cm³), low refractive index (1.011), more pore volume (16.15cm³/g), high percentage of porosity (96.9%) and hydrophobic (contact angle >150°) silica aerogels. It was found from the Fourier transform infrared spectroscopic (FTIR) studies of the aerogels that the intensity of the bands related to the SiC and CH are more and the SiOH andOH are less with the tri than mono and di alkyl SAs. It was found from the TGA-DTA studies of the aerogels with increase in temperature above 325°C, the % of weight decrease in TGA and exothermic peak in DTA are more with tri than the mono and di alkyl SAs. The SEM studies of the aerogels showed the large pore and particle sizes in the silica network with the tri alkyl SAs. The % of optical transmission of the aerogels is less with the tri alkyl SAs than the mono and di alkyl SAs. It was found from the contact angle and water adsorption studies that the hydrophobicity of the silica aerogel is more with tri alkyl than the di and mono alkyl silylating agents.

Keywords: Silylation; Optical transmission; Hydrophobicity; Contact angle; Surface modification

Atmospheric pressure chemical vapour deposition of vanadium diselenide thin films by Nicolas D. Boscher; Christopher S. Blackman; Claire J. Carmalt; Ivan P. Parkin; A. Garcia Prieto (pp. 6041-6046).

Atmospheric pressure chemical vapour deposition (APCVD) of vanadium diselenide thin films on glass substrates was achieved by reaction of [V(NMe₂)₄] and^tBu₂Se. X-ray diffraction showed that the VSe₂ films were crystalline with preferential growth either along the (101) or the (110) direction. Energy-dispersive analysis by X-rays (EDAX) gave a V:Se ratio close to 1:2 for all films. The films were matt black in appearance, were adhesive, passed the Scotch tape test but could be scratched with a steel scalpel. SEM showed that the films were composed of plate-like crystallites orientated parallel to the substrate which become longer and thicker with increasing deposition temperature. Attempts to produce vanadium selenide films were also performed using^tBu₂Se and two different vanadium precursors: VCl₄ and VOCl₃. Both were found to be unsuitable for producing VSe₂ from the APCVD reaction with^tBu₂Se. The VSe₂ showed charge density wave transition at 110–115K.

Keywords: Chemical vapour deposition; Vanadium diselenide; Thin films

Morphology and fluorescence spectra of rubrene single crystals grown by physical vapor transport by Xionghui Zeng; Deqiang Zhang; Lian Duan; Liduo Wang; Guifang Dong; Yong Qiu (pp. 6047-6051).

Rubrene single crystals with pentagon, hexagon, lath-like, and needle-like shape were grown by physical vapor transport. The morphology of surface and transect of rubrene crystals was characterized by optical microscope, atomic force microscope and scanning electron microscope. Monolayers and layer-like structures were observed on the rubrene crystal surface and in the interior of single crystals, respectively. Size and quality of rubrene crystals could be controlled by tuning growth parameters including source temperature, deposition temperature, and growth time. Compared with the emission peak at 555nm of rubrene solution with the concentration of 10⁻⁵M, the emission peak of rubrene single crystals is at 649nm with a shift of 94nm. Hexagon etching pits with typical ladder-like structure were also observed on the (100) crystal plane and the density of dislocation lines is about 10³cm⁻².

Keywords: Rubrene; Single crystal; Morphology; Physical vapor transport; Fluorescence spectrum

Corona-induced graft polymerization for surface modification of porous polyethersulfone membranes by Li-Ping Zhu; Bao-Ku Zhu; Li Xu; Yong-Xiang Feng; Fu Liu; You-Yi Xu (pp. 6052-6059).

Graft polymerization of acrylic acid (AA) onto porous polyethersulfone (PES) membrane surfaces was developed using corona discharge in atmospheric ambience as an activation process followed by polymerization of AA in aqueous solution. The effects of the corona parameters and graft polymerization conditions on grafting yield (GY) of AA were investigated. The grafting of AA on the PES membranes was confirmed by ATR-FTIR and X-ray photoelectron spectroscopy (XPS) analysis. Porosimetry measurements indicate the average pore diameters and porosities of the modified membranes decrease with the increase of the GY. The hydrophilicity and surface wetting properties of the original and modified membranes were evaluated by observing the dynamic changes of water contact angles. It is found that the grafting of AA occurs not only on the membrane surfaces, but also on the pore walls of the cells inside the membrane. The permeability experiments of protein solution reveal that the grafting of PAA endows the modified membranes with enhanced fluxes and anti-fouling properties. The optimized GY of AA is in the range of 150–200μg/cm². In addition, the tensile experiments show the corona discharge treatment with the power lower than 150W yields little damage to the mechanical strength of the membranes.

Keywords: Corona discharge; Graft polymerization; Surface modification; Porous membrane

Fabrication of p-type ZnMgO films via pulsed laser deposition method by using Li as dopant source by Xinhua Pan; Zhizhen Ye; Jiesheng Li; Yujia Zeng; Xiuquan Gu; Liping Zhu; Binghui Zhao; Yong Che (pp. 6060-6062).

p-Type Zn_0.9Mg_0.1O thin films have been realized via monodoping of Li acceptor by using pulsed laser deposition. The Li-doped Zn_0.9Mg_0.1O thin films possessed a good crystallinity with a (0002) preferential orientation and a high transmittance in the visible region. Secondary ion mass spectroscopy revealed that Li has been successfully incorporated into the Zn_0.9Mg_0.1O films. The obtained films with the best electrical properties show a hole concentration in the order of 10¹⁷cm⁻³ and a room-temperature resistivity in the range of 58–72Ωcm.

Keywords: PACS; 61.72.V; 72.80.E; 73.61.G; 78.66.HZnMgO; Li-doped; Pulsed laser deposition; p-Type conduction

Preparation and optical properties of Cu₂O hollow microsphere film and hollow nanosphere powder via a simple liquid reduction approach by Weixin Zhang; Chunyan Luan; Zeheng Yang; Xueting Liu; Dapeng Zhang; Shihe Yang (pp. 6063-6067).

In this work, we report a simple liquid reduction approach to prepare Cu₂O hollow microsphere film and hollow nanosphere powder with Cu(OH)₂ nanorods as precursor and ascorbic acid as the reductant at 60°C. When Cu(OH)₂ nanorod array film grown on a copper foil is used as the precursor, Cu₂O thin film made up of hollow microspheres with average diameter of 1.2μm is successfully prepared. When the Cu(OH)₂ nanorods are scraped from the copper foil and then used as the precursor, Cu₂O hollow nanosphere powder with the average diameter of 270nm is obtained. The samples are characterized by X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and ultraviolet–vis light (UV–vis) absorption spectra. A possible formation mechanism of Cu₂O hollow spheres is discussed.

Keywords: PACS; 78.67.−nNanostructures; Chemical synthesis; Transmission electron microscopy; X-ray diffraction

The role of oxygen and hydrogen partial pressures on structural and optical properties of ITO films deposited by reactive rf-magnetron sputtering by Rajesh Das; Koel Adhikary; Swati Ray (pp. 6068-6073).

Sn doped In₂O₃ films are deposited by rf-magnetron sputtering at 300°C under Ar, Ar+O₂ and Ar+H₂ gas ambients. For the film prepared under argon ambient, electrical resistivity 6.5×10⁻⁴Ωcm and 95% optical transmission in the visible region have been achieved optimizing the power and chamber pressure during the film deposition. X-ray diffraction spectra of the ITO film reveal (222) and (400) crystallographic planes of In₂O₃. With the introduction of 1.33% oxygen in argon, (222) peak of In₂O₃ decreases and resistivity increases for the deposited film. With further increase of oxygen in the sputtering gas mixture crystallinity in the film deteriorates and both the peaks disappeared. On the other hand, when 1.33% hydrogen is mixed with argon, the resistivity of the deposited film decreases to 5.5×10⁻⁴Ωcm and the crystallinity remains almost unchanged. In case of reactive sputtering, the deposition rate is lower compared to that in case of non-reactive sputtering. HRTEM and first Fourier patterns show the highly crystalline structure of the samples deposited under Ar and Ar+H₂ ambients. Crystallinity of the film becomes lower with the introduction of oxygen in argon but refractive index increases from 1.86 to 1.9. The surface morphology of the ITO films have been studied by high resolution scanning electron microscopy.

Keywords: ITO film; rf-Magnetron sputtering; Reactive sputtering; Crystallographic planes; X-ray diffraction spectra; First Fourier pattern

The Rh influence on the surface distribution of the ternary alloy Pt–Pd–Rh by Yu Chen; Shuzhi Liao; Huiqiu Deng (pp. 6074-6079).

Using the modified analytical embedded atom method (MAEAM) and combining with Monte Carlo computer simulations, the surface segregations of Pd–Rh and Pt–Pd–Rh have been simulated. The simulation results indicate that Pd enriched at both Pd–Rh and Pt–Pd–Rh (111) surface, but in the ternary ones, the surface Pd concentrations are influenced by bulk Rh compositions. Differences and similarities of the surface segregations between Pt–Pd, Pd–Rh and Pt–Pd–Rh have been discussed. Because of the lack of the experimental data, we finally compared present simulation results with available experiment data and theory calculation results of Au–Cu–Ni and Cu–Ag–Au. It is shown that the present results of simulations are in qualitative agreement with the experimentally observed trends, and it will be helpful for a better understanding of the segregation behaviors in Pt–Pd–Rh.

Keywords: Surface segregation; Pd–Pt–Rh ternary alloy; MAEAM method

Thickness-dependent surface morphology of La_0.9Sr_0.1MnO₃ ultrathin films by Meng He; Jie Qiu; X. Liang; Hui-Bin Lu; Kui-Juan Jin (pp. 6080-6084).

La_0.9Sr_0.1MnO₃ (LSMO) ultrathin films with various thickness (in the range of 5–50unit cells) are grown on (001) substrates of the single-crystal SrTi_0.99Nb_0.01O₃ by laser molecular-beam epitaxy (laser-MBE), and the surface morphology of these films were measured by scanning tunneling microscopy (STM). STM images of LSMO ultrathin film surface reveal that surface morphology becomes more flat with increasing film thickness. This study highlights the important effect of strain caused by the lattice mismatch between substrates and ultrathin films. And the results should be useful to the investigations on growing manganite perovskite materials.

Keywords: PACS; 68.37.Ef; 68.55.Jk; 73.20−rScanning tunneling microscopy; Ultrathin films; Oxide

Effect of Ce₂(SO₄)₃ on structure and properties of Ni–Co/Al₂O₃ composite coating deposited by pulse reverse current method by L.M. Chang; H.F. Guo; M.Z. An (pp. 6085-6089).

Composite coating of Ni–Co/Al₂O₃ was deposited in Ce₂(SO₄)₃ containing electrolyte by pulse reverse current (PRC) method. The effect of Ce₂(SO₄)₃ in electrolyte on morphology, microstructure, composition, micro-hardness and residual macrostress of composite coating was investigated. The results indicates that with addition of Ce₂(SO₄)₃ in electrolyte, the composite coating becomes uniform, compact and possesses finer grains, the composite content of Al₂O₃ is enhanced, the micro-hardness of composite coating is improved, while the residual macrostress is decreased.

Keywords: Composite coating; Deposition; Pulse; Micro-hardness; Residual macrostress

The effect of solvent upon molecularly thin rotaxane film formation by Alan A. Farrell; Euan R. Kay; Giovanni Bottari; David A. Leigh; Suzanne P. Jarvis (pp. 6090-6095).

We have investigated variations in molecularly thin rotaxane films deposited by solvent evaporation, using atomic force microscopy (AFM). Small changes in rotaxane structure result in significant differences in film morphology. The addition of exo-pyridyl moietes to the rotaxane macrocycle results in uniform domains having orientations corresponding to the underlying substrate lattice, while a larger, less symmetric molecule results in a greater lattice mismatch and smaller domain sizes. We have measured differences in film heights both as a function of the solvent of deposition and as a function of surface coverage of rotaxanes. Based on these observations we describe how the use of solvents with higher hydrogen-bond basicity results in films which are more likely to favour sub-molecular motion.

Keywords: PACS; 81.10.Dn; 68.55.−a; 81.16.Dn; 68.37.PsThin-films; Rotaxane; Atomic force microscopy; Conformation; Solvent; Hydrogen bond

Diffusion and desorption of submonolayer platinum deposited on the multi-faceted surface of a tungsten micro-crystal by Robert Bryl; Ryszard Błaszczyszyn (pp. 6096-6102).

Diffusion and desorption of platinum on the tungsten micro-crystal in the form of the W(111) oriented emitter tip has been studied using the field electron microscopy (FEM) technique. Diffusion of small dose of platinum (average thickness about 0.18 geometrical ML after spreading) on the thermally clean W emitter tip was studied at temperatures 648–742K. Average activation energy for diffusion E_diff was found to lie between 1.16±0.08eVand 1.30±0.16eV. During annealing at the diffusion temperatures Pt-induced faceting of the emitter surface was visible in the neighbourhood of the {111} pole. The layer equilibrated in the diffusion process was stable at temperatures up to 1100K where reduction of the high voltage at a fixed emission current, characteristic of alloying of Pt with W, was detected. Submonolayer of platinum ( Θ_Pt=0.18ML) started to desorb at tip temperature ≥1780K. The measurements of average activation energy for desorption of ‘zero coverage’ Pt (0.03ML≤ Θ_Pt≤0.06ML) from the entire W emitter surface were carried out at temperatures 1990–2170K and yield the value of E_des=5.19±0.22eV to 5.33±0.19eV. The results are compared with data for diffusion of individual Pt atoms and small clusters and with data for adsorption of Pt atoms on a planar W(110) surface. In discussion the atomic surface structure of the substrate, modified by the strong interaction of Pt with the W micro-crystal, is also taken into account.

Keywords: PACS; 68.37.Vj; 68.43.Jk; 68.43.VxTungsten; Platinum; Surface diffusion; Thermal desorption; Faceting; Field emission microscopy

Interaction between α-actinin and negatively charged lipids membrane investigated by surface plasmon resonance and electrochemical methods by Aixue Li; Ying Ma; Fan Yang; Xiurong Yang (pp. 6103-6108).

α-Actinin has been shown to be capable of interacting with some special membrane phospholipids directly, which is important for its function. In this study, hybrid bilayer membranes composed of negatively charged lipids are constructed on the surface plasmon resonance gold substrate and on the gold electrode, respectively, and the interaction between α-actinin and negatively charged lipids membrane is investigated by surface plasmon resonance, cyclic voltammetry and electrochemical impedance spectroscopy methods. α-Actinin is proved to be able to interact with the negatively charged lipids membrane directly. It can also insert at least partly into the membrane or lead to some defect or lesion in the membrane, which increase the permeability of the membrane. This study would bring some insight on the interaction between the α-actinin and the cell membranes in vivo.

Keywords: α-Actinin; Negatively charged lipids; Surface plasmon resonance; Electrochemical methods

An electrostatic force microscope study of Si nanostructures on Si(100) as a function of post-annealing temperature and time by Hai-Tong Sun; Zheng-Hao Li; Jing Zhou; You-Yuan Zhao; Ming Lu (pp. 6109-6112).

The evolution of Si nanostructures induced by Ar⁺ ion sputtering on Si(100) was studied with electrostatic force microscopy (EFM) as a function of post-annealing temperature ( T=room temperature–800°C) and time ( t=0–160min). The post-annealing of the nanostructure was conducted in vacuum. It was found that with T increasing, the EFM contrast degraded steadily and became nearly undetectable at T=800°C; with t increasing at T=800°C, the EFM contrast fell down steadily as well. However, the surface morphology and roughness were much less affected after annealing. The results suggest that the as-formed Si nanostructures may not be epitaxially grown on Si(100) substrate as claimed before. A plane capacitance model supported this conclusion.

Keywords: PACS; 68.49.Sf; 68.37.Ps; 68.35.BsSilicon; Surface structure; Morphology; Atomic force microscopy; Electrostatic force microscopy

Influence of substrate temperature on properties of MgF₂ coatings by Hua Yu; Hongji Qi; Yun Cui; Yanming Shen; JianDa Shao; ZhengXiu Fan (pp. 6113-6117).

Thermal boat evaporation was employed to prepare MgF₂ single-layer coatings upon both JGS1 and UBK7 substrates at different substrate temperatures. Microstructure, transmittance and residual stress of these coatings were measured by X-ray diffraction, spectrophotometer, and optical interferometer, respectively. Measurement of laser induced damage threshold (LIDT) of the samples was performed at 355nm, 8ns pulses. The results showed that high substrate temperature was beneficial to crystallization of the film. Above 244°C, the refractive index increased gradually with the substrate temperature rising. Whereas, it was exceptional at 210°C that the refractive index was higher than those deposited at 244 and 277°C. The tensile residual stresses were exhibited in all MgF₂ films, but not well correlated with the substrate temperature. In addition, the stresses were comparatively smaller upon JGS1 substrates. A tendency could be seen that the LIDTs reached the highest values at about 244°C, and the films upon JGS1 had higher LIDTs than those upon UBK7 substrates at the same temperature. Meanwhile, the damage morphologies showed that the laser damage of the coating resulted from an absorbing center at the film–substrate interface. The features of the damages were displayed by an absorbing center dominated model. Furthermore, the reason of the difference in LIDT values was discussed in detail.

Keywords: PACS; 81.15.Ef; 68.37.Yz; 81.70.Fy; 68.55.Jk; 79.20.DsThermal boat evaporation; MgF; ₂; single-layer coating; Substrate temperature; LIDT

Preparation of anti-corrosion films by microarc oxidation on an Al–Si alloy by Wenbin Xue; Xiuling Shi; Ming Hua; Yongliang Li (pp. 6118-6124).

Thick ceramic films over 140μm were prepared on Al–7% Si alloy by ac microarc oxidation in a silicate electrolyte. The film growth kinetics was determined by an eddy current technique and film growth features in different stages were discussed. The microstructure and composition profiles for different thick films were analyzed by scanning electron microscopy and energy dispersive X-ray spectroscopy. Their phase components were determined by X-ray diffraction. The electrochemical corrosion behaviors of bare and coated alloys were evaluated using potentiodynamic polarization curves, and their corrosion morphologies were observed. In the initial stage of oxidation, the growth rate is slow with 0.48μm/min due to the effect of Si element though the current density is rather high up to 33A/dm². After the current density has decreased to a stable value of 11A/dm², the film mainly grows towards the interior of alloy. The film with a three-layer structure consists of mullite, γ-Al₂O₃, α-Al₂O₃ and amorphous phases. By microarc discharge treatment, the corrosion current of the Al–Si alloy in NaCl solution was significantly reduced. However, a thicker film has to be fabricated in order to obtain high corrosion-resistant film of the Al–Si alloy. Microarc oxidation is an effective method to form an anti-corrosion protective film on Si-containing aluminum alloys.

Keywords: Microarc oxidation; Al–Si alloy; Growth kinetics; Corrosion resistance

Effects of Ge doping on the properties of Sb₂Te₃ phase-change thin films by Jialin Yu; Bo Liu; Ting Zhang; Zhitang Song; Songlin Feng; Bomy Chen (pp. 6125-6129).

Ge-doped Sb₂Te₃ films were prepared by magnetron sputtering of Ge and Sb₂Te₃ targets on SiO₂/Si (100) substrates. The effect of Ge doping on the structure was studied in details by X-ray diffraction, differential scanning calorimetry, and X-ray photoelectron spectroscopy measurements. It is indicated that Ge atoms substitute for Sb/Te in lattice sites and form Ge-Te bonds, moreover, a metastable phase was observed in Ge-doped specimens. Both crystallization temperature and resistivity of amorphous Sb₂Te₃ increase after Ge doping, which are beneficial for improving room temperature stability of the amorphous state and reducing the SET current of chalcogenide random access memory.

Keywords: PACS; 68.55.Ln; 61.50.Ks; 68.55.Jk; 84.37.+qGe doping; Sb; ₂; Te; ₃; Structure; X-ray photoelectron spectroscopy; Resistivity

Electrochemical, theoretical and XPS studies of 2-mercapto-1-methylimidazole adsorption on carbon steel in 1M HClO₄ by O. Benali; L. Larabi; M. Traisnel; L. Gengembre; Y. Harek (pp. 6130-6139).

The inhibition of the corrosion of carbon steel in 1M HClO₄ by 2-mercapto-1-methylimidazole (MMI) has been investigated in relation to the concentration of the inhibitor as well as the temperature using weight loss and electrochemical measurements. The effect of the temperature on the corrosion behaviour with addition of different concentrations of MMI was studied in the temperature range 30–60°C. Polarization curves reveal that MMI is a mixed type inhibitor. The inhibition efficiency of MMI is temperature independent but increases with the inhibitor concentration. Changes in impedance parameters (charge transfer resistance, R_t, and double-layer capacitance, C_dl) were indicative of adsorption of MMI on the metal surface, leading to the formation of a protective film. Adsorption of MMI on the carbon steel surface is found to obey the Langmuir adsorption isotherm. Some thermodynamic functions of dissolution and adsorption processes were also determined. The X-ray photoelectron spectroscopy (XPS) of the carbon steel indicated that MMI is chemically adsorbed on the steel surface. Moreover, the electronic properties such as highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO) energy levels and molecular orbital densities were calculated.

Keywords: Carbon steel; 2-Mercapto-1-methylimidazole; Perchloric acid; Adsorption; Theoretical calculations; XPS

SIMS as a subnanometer probe: A new tool for chemical profile analysis of grafted molecules by Frédéric Chérioux; Bernard Gauthier-Manuel; John Eccles; Thierry Grenut; Marc Briant (pp. 6140-6143).

The complexity of modern engineered surfaces requires the development of very powerful methods to analyze and characterize them. We demonstrate that it is possible to obtain chemical information about the skeleton of organic molecules constituting SAMs grafted on a silicon surface by using a new type of SIMS method. A profile can be achieved by the investigation of the temporal variation of secondary ion intensities that correspond to the fractional parts of the molecule constituting the SAMs. The equivalent ablation rate is less than 0.5nm/min.

Keywords: SIMS; Depth profiling; SAMs; Sputtering; Submolecular

Thermal model for nanosecond laser sputtering at high fluences by Duanming Zhang; Dan Liu; Zhihua Li; Li Guan; Xinyu Tan; Li Li; Ranran Fang; Dezhi Hu; Gaobin Liu (pp. 6144-6148).

The vaporization effect and the following plasma shielding generated by high-power nanosecond pulsed laser ablation are studied in detail based on the heat flux equation. As an example of Si target, we obtain the time evolution of the calculated surface temperature, ablation rate and ablation depth by solving the heat flow equations using a finite difference method. It can be seen that plasma shielding plays a more important role in the ablation process with time. At the same time, the variation of ablation depth per pulse with laser fluence is performed. Our numerical results are more agreed with the experiment datum than other simulated results. The result shows that the plasma shielding is very important.

Keywords: PACS; 52.50.Jm; 79.20.DsLaser ablation; Vaporization; Plasma shielding

Comparative study of microstructural characteristics of electrospark and Nd:YAG laser epitaxially growing coatings by Yu-jiang Xie; Mao-cai Wang; Da-wei Huang (pp. 6149-6156).

As low-heat input welding processes, electrospark deposition and pulsed Nd:YAG laser cladding can be commonly used to prepare epitaxially growing coatings. However, these two processes have quite different characteristics in the energy input, the amount of materials involved, and the temperature gradient, and hence might result in dissimilar microstructural characteristics. In this paper, a comparative study has been made between microstructural characteristics in epitaxial growth coatings prepared by electrospark deposition and pulsed Nd:YAG laser cladding. Some interesting results have been achieved. Firstly, epitaxial growth coatings can be commonly achieved by these two techniques. Secondly, microstructural morphologies of these two epitaxial growth coatings are obviously different, cellular columnar structure prevails in the electrospark coating while columnar dendritic structure occupies most of the laser coating thickness, more importantly, electrospark coating remains fully columnar in the whole layer whereas laser coating tends to change from columnar to equiaxed at the top of the layer. Thirdly, electrospark coating possesses finer and more homogeneous microstructure than laser coating.

Keywords: PACS; 81.15.Fg; 52.77.Fv; 61.82.Bg; 81.65.-bElectrospark deposition; Laser cladding; Epitaxial growth; Microstructural characteristics; Coating

Rare-earth chloride seeded growth of GaN nano- and micro-crystals by M.A. Mastro; J.A. Freitas Jr.; R.T. Holm; C.R. Eddy Jr.; J. Caldwell; K. Liu; O. Glembocki; R.L. Henry; J. Kim (pp. 6157-6161).

A novel rare-earth chloride seed was employed as a catalyst for growth of GaN nano- and micro-crystals on c-, a- and r-plane sapphire. The ErCl₃ seed on the substrate surface enhanced the growth rate and density of the GaN crystals. Distinctive green photoluminescence was measured, confirming that Er³⁺ ions were active in the GaN matrix. This technique can be adapted to selectively grow GaN crystals with emission tailored to the particular optical transitions of the rare-earth seed.

Keywords: PACS; 72.80.Ey; 78.55.CrGallium nitride; Rare-earth metal

Investigation into defects occurring on the polymer surface during the photolithography process by D. Bosc; A. Maalouf; S. Haesaert; F. Henrio (pp. 6162-6164).

With a view to improving the realisation of polymer optical waveguide some features relevant to the photolithography process are analysed. This paper focuses on defects that occur on the surface of polymer layers involved in the process. For example, depending on the heat treatment or the deposited material, some worm-like defects appear on the polymer surface. When they occur, the waveguide surface roughness becomes too high (about one hundred nm and more). This means that the optical performance of the waveguides is too poor. In this document, we show the changes in temperature on polymer film surfaces which are coated with a thin inorganic layer and the occurrence of these defects is observed. This work confirms that the defect occurrence is clearly linked to the glass transition temperature. The paper reports that, in some cases, the adjustment of thermal properties by annealing can advantageously shift the glass transition, without changing the target optical properties.

Keywords: PACS; 68.35.Ct; 68.37.Ps; 68.47.Mn; 68.60.DvPolymers; Surfaces; Thermal properties; Atomic force microscopy

Intrinsic mechanical properties of ultra-thin amorphous carbon layers by P. Lemoine; J.P. Quinn; P.D. Maguire; J.F. Zhao; J.A. McLaughlin (pp. 6165-6175).

In this work, we extracted the film's hardness ( H_F) of ultra-thin diamond-like carbon layers by simultaneously taking into account the tip blunting and the substrate effect. As compared to previous approaches, which did not consider tip blunting, this resulted in marked differences (30–100%) for the H_F value of the thinner carbon coatings. We find that the nature of the substrate influences this intrinsic film parameter and hence the growth mechanisms. Moreover, the H_F values generally increase with film thickness. The 10nm and 50nm thick hydrogenated amorphous carbon (a-C:H) films deposited onto Si have H_F values of, respectively, ∼26GPa and ∼31GPa whereas the 10nm and 50nm thick tetrahedral amorphous carbon (t-aC) films deposited onto Si have H_F values of, respectively, ∼29GPa and ∼38GPa. Both the a-C:H and t-aC materials also show higher density and refractive index values for the thicker coatings, as measured, respectively by X-ray reflectometry and optical profilometry analysis. However, the Raman analysis of the a-C:H samples show bonding characteristics which are independent of the film thickness. This indicates that in these ultra-thin hydrogenated carbon films, the arrangement of sp² clusters does not relate directly to the hardness of the film.

Keywords: Amorphous hydrogenated amorphous carbon; Tetrahedral amorphous carbon; Hardness

Interfacial reactions during sputter deposition of Ta and TaN films on organosilicate glass: XPS and TEM results by J.A. Wilks; N.P. Magtoto; J.A. Kelber; V. Arunachalam (pp. 6176-6184).

The evolution of the interface between organosilicate glass (OSG) and sputter deposited Ta or TaN films has been characterized by X-ray phototelectron spectroscopy (XPS). Cross-sectional TEM (XTEM) was also used to analyze Ta/OSG and TaN/OSG/interfaces for samples formed under different deposition conditions. XPS data show that Ta deposition onto OSG results in formation of an interphase between 1 and 2nm thick composed of oxidized Ta and C. Metallic Ta is then formed on top of the interfacial region. In contrast, Ta-rich TaN formation occurs with some nitridation of the substrate, but with no significant interphase formation. The XPS data are consistent with the XTEM data. The XTEM results for Ta/OSG indicate a spatially irregular interface over a length scale of ∼2nm, while results for TaN/OSG indicate a spatially abrupt region.

Keywords: Diffusion barrier; Dielectrics; Physical vapor deposition (PVD); Tantalum; Tantalum nitride; Transmission electron microscopy; X-ray photoelectron spectroscopy (XPS)

Surface cleaning and preparation in AlGaN/GaN-based HEMT processing as assessed by X-ray photoelectron spectroscopy by Fernando González-Posada; Jennifer A. Bardwell; Simona Moisa; Soufien Haffouz; Haipeng Tang; Alejandro F. Braña; Elías Muñoz (pp. 6185-6190).

The chemical composition of the AlGaN/GaN surface during typical process steps in transistor fabrication was studied using X-ray photoelectron spectroscopy (XPS). The steps studied included organic solvent cleaning, 1:1 HCl:H₂O dip, buffered oxide etch dip, oxygen plasma descum and rapid thermal annealing (RTA). The surface composition was calculated after correction for the interference of the Ga Auger lines in the N 1s portion of the spectra. The buffered oxide etched (BOE) surface showed a greater tendency for Al (compared to Ga) to be oxidized in the surface, under a layer of adventitious carbon. Three different treatments were found to yield a combination of low C and O levels in the surface. Both plasma cleaning and RTA were highly effective at reducing the carbon contamination of the surface, but did increase the oxygen levels. The RTA treated surface was found to have low levels of oxygen incorporation to a depth of 2–6nm.

Keywords: PACS; 81.05.Ea (III–V semiconductors); 81.65.−b (surface treatments); 81.65.Cf (surface cleaning, etching, patterning); 82.80.Pv (electron spectroscopy: X-ray photoelectron spectroscopy (XPS), auger electron spectroscopy (AES), etc.); 85.30.Tv (field effect devices)AlGaN; XPS; Surface treatments; Surface cleanings; HEMTs

Mechanical properties of Mo–Ru thin films with Ni interlayer of different thickness by Chi-Yun Kang; Yung-I Chen; Chih-Hsiung Lin; Jenq-Gong Duh (pp. 6191-6195).

Noble metal coatings are usually introduced to increase lifetime of glass molding die. In this study, Mo–Ru coatings with Ni interlayer were deposited on tungsten carbide by DC sputtering processes at an elevated temperature of 550°C to modify the properties in molding die materials. Phase identification was investigated by X-ray diffractometry (XRD). The surface morphology and composition of coatings were evaluated by atomic force microscopy (AFM) and field-emission electron probe microanalyzer (FE-EPMA), respectively. Hardness of the Mo–Ru films was measured by nanoindentation testing. In the aspects of adhesion, the influence on interlayer of different thickness was probed by the scratch test, and the different composition of Mo–Ru resulted in various kinds of fracture configurations. The scratch test exhibited spalling and chipping failure between substrate and layer.

Keywords: Mo–Ru; Ni interlayer; DC sputter; Scratch

Surface morphology characterization of pentacene thin film and its substrate with under-layers by power spectral density using fast Fourier transform algorithms by Taketsugu Itoh; Noriyoshi Yamauchi (pp. 6196-6202).

Surface morphology of pentacene thin films and their substrates with under-layers is characterized by using atomic force microscopy (AFM). The power values of power spectral density (PSD) for the AFM digital data were determined by the fast Fourier transform (FFT) algorithms instead of the root-mean-square (rms) and peak-to-valley value. The PSD plots of pentacene films on glass substrate are successfully approximated by the k-correlation model. The pentacene film growth is interpreted the intermediation of the bulk and surface diffusion by parameter C of k-correlation model. The PSD plots of pentacene film on Au under-layer is approximated by using the linear continuum model (LCM) instead of the combination model of the k-correlation model and Gaussian function. The PSD plots of SiO₂ layer on Au under-layer as a gate insulator on a gate electrode of organic thin film transistors (OTFTs) have three power values of PSD. It is interpreted that the specific three PSD power values are caused by the planarization of the smooth SiO₂ layer to rough Au under-layer.

Keywords: PACS; 87.80.Pa Morphometry and streology; 81.15.Aa Theory and models of film growthPentacene; Atomic force microscopy; Fast Fourier transform; Power spectral density

Electrostatic forces in micromanipulations: Review of analytical models and simulations including roughness by M. Sausse Lhernould; A. Delchambre; S. Régnier; P. Lambert (pp. 6203-6210).

Manipulations by contact of objects between 1μm and 1 mm are often disturbed by adhesion between the manipulated object and the gripper. Electrostatic forces are among the phenomena responsible for this adhesive effect. Analytical models have been developed in the literature to predict the electrostatic forces. Most models are developed within the framework of scanning probe microscopy, i.e. for a contact between a conducting tip and a metallic surface. Models are reviewed in this work and compared with our own simulations using finite elements modeling. The results show a good correlation. The main advantage of our simulations lies in the fact that they can integrate roughness parameters. For this purpose, a fractal representation of the surface topography was chosen through the use of the Weierstrass-Mandelbrot function. Comparisons with experimental benchmarks from the literature show very good correlation between experimental results and simulations. It demonstrates the importance of surface topography on electrostatic forces at very close separation distances.

Keywords: PACS; 41.20.Cv; 68.35.Np; 68.35.CtMicromanipulations; Adhesion; Electrostatic forces; Roughness; Fractals

Study micromechanism of surface planarization in the polishing technology using numerical simulation method by Xuesong Han (pp. 6211-6216).

With the development of semiconductor industry, the chemical mechanical polishing technology has already became the main stream method of realize the surface global flatness. In order to understanding physical essence underlying this technology, the author carried out nanometer polishing experiment of silicon wafer using molecular dynamics (MD) simulation method. The simulation result shows that larger slurry grain generate much more vacancy, dislocation, larger residual stress and intensive plastic deformation than that of small one although the larger grain acquire better surface quality.

Keywords: Chemical mechanical polishing; Molecular dynamics; Silicon wafer; Vacancy; Dislocation

An XPS study of Al₂Au and AlAu₄ intermetallic oxidation by C. Xu; T. Sritharan; S.G. Mhaisalkar; M. Srinivasan; S. Zhang (pp. 6217-6221).

Samples of Al₂Au and AlAu₄ were examined using XPS after controlled oxidation in air. AlAu₄ showed a strong tendency to oxidize compared to Al₂Au. The binding energies (b.e.) of Au 4f and Al 2p XPS emissions were determined for both intermetallics. Heavy oxidation of AlAu₄ resulted in a unique Au 4f emission near the surface which was attributed to Au dissolved in aluminum oxide.

Keywords: X-ray photoelectron spectroscopy; Binding energy; Intermetallic compounds; Oxidation; Gold

Enhanced ferroelectric property of (Pb_0.95Ca_0.05)(Nb_0.02Zr_0.80Ti_0.20)O₃ thin films prepared by RF magnetron sputtering by Jiagang Wu; Jiliang Zhu; Dingquan Xiao; Jianguo Zhu; Junzhe Tan; Qinglei Zhang; Yuanyu Wang (pp. 6222-6225).

(Pb_0.95Ca_0.05)(Nb_0.02Zr_0.80Ti_0.20)O₃ [PCNZT] thin films were deposited on the Pt(111)/Ti/SiO₂/Si(100) substrates by RF magnetron sputtering with and without a LaNiO₃ [LNO] buffer layer. Ca and Nb elements in PZT films enhance the ferroelectric property, LaNiO₃ buffer layer improves the crystal quality of the PCNZT thin films. PCNZT thin films possess better ferroelectric property than that of PZT films for Ca and Nb ion substitution, moreover, PCNZT thin films with a LNO buffer layer possess (100) orientation and good ferroelectric properties with high remnant polarization ( P_r=38.1μC/cm²), and low coercive field ( E_c=65kV/cm), which is also better than that of PCNZT thin films without a LNO buffer layer ( P_r=27.9μC/cm², E_c=74kV/cm). The result shows that enhanced ferroelectric property of PZT films can be obtained by ion substitution and buffer layer.

Keywords: PACS; 77.84.−s; 77.80.−e; 77.22.Ej; 85.50PCNZT ferroelectric thin films; RF magnetron sputtering; LaNiO; ₃; buffer layer; Ferroelectric property; Ferroelectric random access memories

Growth kinetics of borided layers: Artificial neural network and least square approaches by I. Campos; M. Islas; G. Ramírez; C. VillaVelázquez; C. Mota (pp. 6226-6231).

The present study evaluates the growth kinetics of the boride layer Fe₂B in AISI 1045 steel, by means of neural networks and the least square techniques. The Fe₂B phase was formed at the material surface using the paste boriding process. The surface boron potential was modified considering different boron paste thicknesses, with exposure times of 2, 4 and 6h, and treatment temperatures of 1193, 1223 and 1273K. The neural network and the least square models were set by the layer thickness of Fe₂B phase, and assuming that the growth of the boride layer follows a parabolic law. The reliability of the techniques used is compared with a set of experiments at a temperature of 1223K with 5h of treatment time and boron potentials of 2, 3, 4 and 5mm. The results of the Fe₂B layer thicknesses show a mean error of 5.31% for the neural network and 3.42% for the least square method.

Keywords: Boriding process; Growth kinetics; Neural networks; Least square method; Boron paste; Boride layers

GaAs surface passivation by ultra-thin epitaxial GaP layer and surface As–P exchange by A. Aierken; J. Riikonen; M. Mattila; T. Hakkarainen; M. Sopanen; H. Lipsanen (pp. 6232-6235).

The GaAs surface passivation effects of epitaxially grown ultra-thin GaP layers and surface As–P exchange have been investigated. Optical properties of passivated and unpassivated InGaAs/GaAs near-surface quantum wells (QWs) grown by metal organic vapor phase epitaxy (MOVPE) are studied by low-temperature continuous-wave and time-resolved photoluminescence (PL). By optimizing the growth conditions, smooth surface morphologies and significant improvement of optical properties were observed for both passivation methods. Passivation improved the PL intensity more than two orders of magnitude and notably increased the PL decay time.

Keywords: PACS; 68.65.Fg; 81.65.Rv; 78.67.De; 81.07.St; 81.15.GhSurface passivation; Quantum wells; MOVPE; GaAs

Laser cladding of copper with molybdenum for wear resistance enhancement in electrical contacts by K.W. Ng; H.C. Man; F.T. Cheng; T.M. Yue (pp. 6236-6241).

Laser cladding of Mo on Cu has been attempted with the aim of enhancing the wear resistance and hence increasing the service life of electrical contacts made of Cu. In order to overcome the difficulties arising from the large difference in thermal properties and the low mutual solubility between Cu and Mo, Ni was introduced as an intermediate layer between Mo and Cu. The Ni and Mo layers were laser clad one after the other to form a sandwich layer of Mo/Ni/Cu. Excellent bonding between the clad layer and the Cu substrate was ensured by strong metallurgical bonding. The hardness of the surface of the clad layer is seven times higher than that of the Cu substrate. Pin-on-disc wear tests consistently showed that the abrasive wear resistance of the clad layer was also improved by a factor of seven as compared with untreated Cu substrate. The specific electrical contact resistance of the clad surface was about 5.6×10⁻⁷Ωcm².

Keywords: Cu electrical contact; Laser cladding; Molybdenum; Wear; Electrical contact resistance

Investigation of evolution hydrocarbon species on a Si surface during methane plasma with and without substrate bias, using infrared spectroscopy in multiple internal reflection geometry by Masanori Shinohara; Hiromichi Shibata; Ken Cho; Tatsuyuki Nakatani; Keishi Okamoto; Yoshinobu Matsuda; Hiroshi Fujiyama (pp. 6242-6247).

We investigated evolution of hydrocarbon species on a Si surface during methane plasma both with and without substrate bias, using infrared spectroscopy in multiple internal reflection geometry (MIR-IRAS). We found that the relative density of the sp³-CH or sp³-CH₂ species to the sp³-CH₃ species was low in the low exposure regions, but that the relative density of the sp³-CH or sp³-CH₂ species increased as the exposure was higher. Substrate temperatures rose as the plasma exposure was higher. The changes of ratios would be ascribed to the substrate heating effect by plasma exposure, which would enhance the etching and/or hydrogen abstraction effects. We also found the change of CH_1–2/CH₃ ratios was enhanced when the high substrate bias was applied. The enhancement of the ratio was due to ion effects.

Keywords: PACS; 68.43.−h; 81.15.Gh; 87.64.JeHydrocarbon; Hydrogen; Infrared spectroscopy; Plasma processing

Properties of the roughness in NiFe/FeMn exchange-biased system by V.P. Nascimento; E.C. Passamani; A. Biondo; V.B. Nunes; E. Baggio Saitovitch (pp. 6248-6254).

X-ray reflectivity and atomic force microscopy analyses were performed in the Si/WTi (7nm)/NiFe (5nm)/FeMn (13nm)/WTi (7nm) exchange-biased system prepared by magnetron sputtering. Layer-by-layer analyses were done in order to have interfacial roughness parameters quantitatively. X-ray reflectivity results indicate that the successive layer deposition gives rise to a cumulative roughness. In addition, the atomic force microscopic images analyses have revealed that the roughness enhancement caused by the successive layer deposition can be associated with an appearance of a longer wavelength roughness induced by the NiFe layer deposition.

Keywords: PACS; 81.15.Cd; 75.70.Cn; 68.35.Ct; 61.10.Eq; 68.37.PsMagnetron sputtering; Exchange bias; Interface roughness; X-ray reflectivity; AFM

Properties of ZnO thin films grown on Si substrates in vacuum and oxygen ambient by pulsed laser deposition by Jie Zhao; Lizhong Hu; Weifeng Liu; Zhaoyang Wang (pp. 6255-6258).

Epitaxial ZnO thin films have been synthesized directly on Si(111) substrates by pulsed laser deposition (PLD) in vacuum. The reflection high-energy electron diffraction (RHEED) indicates that streaky patterns can be clearly observed from the ZnO epilayers prepared at 600 and 650°C, revealing a two-dimensional (2D) growth mode. While the ZnO thin film deposited in oxygen ambient shows ring RHEED pattern. There is a compressive in-plane stress existing in the ZnO epitaxial film, but a tensile one in the polycrystalline film. Compared with the ZnO epilayer, the ZnO polycrystalline film shows more intense ultraviolet emission (UVE) with a small full width at half maximum (FWHM) of 89meV. It is suggested that the atomically flat epilayers may be powerfully used as transitive stratums to grow high-quality ZnO films suitable for the fabrication of optoelectronic devices.

Keywords: PACS; 61.14.Hg; 81.05.Dz; 78.55.EtZnO; Pulsed laser deposition; Reflection high-energy electron diffraction; X-ray diffraction; Photoluminescence

Crystallization and surface morphology evolution of erbium fluoride films on different substrates by W.T. Su; B. Li; L. Yin; L. Yang; D.Q. Liu; F.S. Zhang (pp. 6259-6263).

Erbium fluoride (ErF₃) films were thermally deposited on Ge(111), Si(001) and copper mesh grid with different substrate temperature. X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterize the structure and morphology of the films. The structure of ErF₃ films deposited on germanium and silicon changed from amorphous to crystalline with increasing the substrate temperature, while the crystallization temperature of the films on silicon is higher than that of on germanium. The infrared optical properties of the films change greatly with the evolution of crystal structure. It is also found that the morphology of ErF₃ film on Ge(111) at 200°C is modulated by the stress between the substrate and film. The SEM and TEM results confirmed that the ErF₃ films on copper mesh grid were crystalline even at 100°C. Interestingly, the ErF₃ films show flower-like surface morphology when deposited on copper mesh at 200°C. The crystallization temperature ( T_c) of ErF₃ films on the three substrates has the relation which isTccopper3 films on different substrates.

Keywords: PACS; 61.43.Er; 81.15.Ef; 68.55.Ac; 68.55.JkErF; ₃; films; Thermal deposition; Crystallization temperature; Surface morphology

Deposition of silver nanoparticles on silica spheres via ultrasound irradiation by Xiaoyun Ye; Yuming Zhou; Jing Chen; Yanqing Sun (pp. 6264-6267).

Silver-decorated silica spheres of submicrometer-sized silica spheres with a core-shell structure were obtained based on a seed-mediated growth process, where silver nanoparticles were firstly formed from reducing Ag⁺ to Ag⁰ in N, N-dimethylformamide (DMF) in the presence of poly(vinylpyrrolidone) (PVP) as protective agent under ultrasound irradiation, followed by the growth of silver shell served silver nanoparticles as nucleation sites and formaldehyde as reducer. The results revealed that the terms of PVP addition and ultrasonic surroundings had great influence on the fabrication of silver seeds.

Keywords: Silica; Silver; Nanoparticle; Deposition; Ultrasound

The effect of polymer coatings on switching behavior and cycling durability of Pd/Mg–Ni thin films by S. Bao; Y. Yamada; M. Okada; K. Yoshimura (pp. 6268-6272).

Although Pd-capped Mg–Ni alloy switchable mirror thin films have potential applications in smart windows and optical switches, they degrade quickly and cannot be switched after about 150 cycles. This must be improved for practical use. In this study, we tested several polymer coatings on the surface of Pd/Mg₄Ni switchable mirror thin films as a protective membrane and evaluated the optical switching property and durability. The polymer membrane is able to suppress the oxidization of Mg because it has an excellent gas separation characteristic. Polymer coating extended the switching durability of samples to about 1000 cycles. In addition, the transmittance of the thin film in the transparent state is improved by the coating.

Keywords: PACS; 71.20.Lp; 73.61.At; 68.47.Mn; 68.43.Mn; 68.55.−aSwitchable mirror; Polymer; Metal hydride; Gasochromism; Ni–Mg alloy

Erratum to “Pressure induced anisotropy of electrical conductivity in polycrystalline molybdenum disulfide” [Appl. Surf. Sci. 252 (2006) 7941–7947] by V. Sánchez; E. Benavente; V. Lavayen; C. O’Dwyer; C.M. Sotomayor Torres; G. González; M.A. Santa Ana (pp. 6273-6273).

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Applied Surface Science (v.253, #14)