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Applied Surface Science (v.254, #7)

Effect of graded interlayer on the mode I edge delamination by residual stresses in multilayer coating-based systems by X.C. Zhang; B.S. Xu; H.D. Wang; Y.X. Wu (pp. 1881-1889).

The mode I edge delamination could be initiated due to the presence of the interfacial peeling stresses near the edges of the multilayered systems due to the material mismatches between the adjacent layers. However, the exact peeling stress distributions could not be obtained by using the existing analytical and numerical models. It was proposed recently that the peeling moment resulting from the localized peeling stresses could be used to characterize mode I edge delamination. In this paper, the effect of the graded interlayer on the mode I edge delamination by thermal residual stresses in multilayer coating-based systems was investigated. Following the previous analysis approaches, the exact closed-form solutions for the peeling moments at individual interfaces and the curvatures for bilayer system, typical thermal barrier coating (TBC) system and TBC-based system with a graded interlayer inserted between the metallic layer and the ceramic layer were, respectively, derived. Case studies showed that the edge delamination by thermal stress could be impeded by properly selecting the coating materials and individual layer thicknesses. These studies may provide some important insights for developing fail-safe designing methodologies for multilayered systems.

Keywords: PACS; 05.70.−a; 62.20.−x; 65.70.+yResidual stress; Edge delamination; Interfacial peeling stress; Multilayered coating-based system; Graded interlayer

Characteristics of Co-filled carbon nanotubes by Te-Hua Fang; Kuan-Hua Chen; Win-Jin Chang (pp. 1890-1894).

The Co-filled carbon nanotubes (CNTs) film was produced on silicon substrate by electron cyclotron resonance microwave plasma chemical vapor deposition (ECR-CVD). The effects of different plasma powers of 200, 300, 400 and 500W, on the morphology, structure and electrical properties of the CNTs film, were studied. The results showed that the surface density of the vertical nanotubes decreased when the plasma power was higher than 200W. When plasma power of 300W was used, the ends of the metal-filled carbon nanotubes (MF-CNTs) became straighter and more uniform. The Co-filled CNTs grown at 300 and 400W had a current discharge at the applied voltages of 30 and 40V, respectively. In addition, the surface morphology and the structure of the CNTs film were examined using scanning electron microscopy (SEM) and high-resolution field emission gun transmission electron microscopy (TEM). Energy dispersive X-ray spectroscopy (EDXS) analyses were performed to identify the composition of the material inside the CNTs.

Keywords: Metal-filled carbon nanotubes; ECR-CVD; Electrical property

Calculus removal on a root cement surface by ultrashort laser pulses by Johan F. Kraft; Kasper Vestentoft; Bjarke H. Christensen; Henrik Løvschall; Peter Balling (pp. 1895-1899).

Ultrashort-pulse-laser ablation of dental calculus (tartar) and cement is performed on root surfaces. The investigation shows that the threshold fluence for ablation of calculus is a factor of two to three times smaller than that of a healthy root cement surface. This indicates that ultrashort laser pulses may provide an appropriate tool for selective removal of calculus with minimal damage to the underlying root cement. Future application of an in situ profiling technique allows convenient on-line monitoring of the ablation process.

Keywords: PACS; 42.62.Be; 78.47.+p; 87.50.HjLaser ablation; Ultrashort laser pulses; Dentistry; Calculus

Nonlinear optical properties of Au/ZnO nanoparticle arrays by Tingyin Ning; Yueliang Zhou; Hong Shen; Heng Lu; Zhihui Sun; Lingzhu Cao; Dongyi Guan; Dongxiang Zhang; Guozhen Yang (pp. 1900-1903).

The triangular-shaped Au/ZnO nanoparticle arrays were fabricated on fused quartz substrate using nanosphere lithography. The structural characterization of the Au/ZnO nanoparticle arrays was investigated by atomic force microscopy. The absorption peak due to the surface plasmon resonance of Au particles at the wavelength of about 570nm was observed. The nonlinear optical properties of the nanoparticle arrays were measured using the z-scan method at a wavelength of 532nm with pulse duration of 10ns. The real and imaginary part of third-order nonlinear optical susceptibility, Re χ⁽³⁾ and Im χ⁽³⁾, were determined to be 1.15×10⁻⁶ and −5.36×10⁻⁷esu, respectively. The results show that the Au/ZnO nanoparticle arrays have great potential for future optical devices.

Keywords: PACS; 42.70.−a; 61.46.−w; 78.67.−n; 81.07.−bNanoparticle arrays; Optical nonlinearity; Nanosphere lithography; z; -Scan

Synthesis and electron paramagnetic resonance study of a nitroxide free radical covalently bonded on aminopropyl-silica gel by Madalina Tudose; Titus Constantinescu; Alexandru T. Balaban; Petre Ionita (pp. 1904-1908).

A solid spin-labeled material was obtained starting from 2-chloro-3,5-dinitro- N-(4-(2,2,6,6-tetramethyl-piperidine-1-oxyl)-benzamide) and aminopropyl-silica gel. Stability tests showed that even after several months the spin-labeled material had the same properties as immediately after synthesis. EPR properties of the TEMPO-derivatized silica were studied as a function of solvent polarity and temperature. Rotational correlation times were calculated from EPR spectra and correlated with solvent characteristics and temperature. Polar solvents induce a fast motion of the spin-label, clearly seen in the EPR spectra by the apparition of the well-known TEMPO radical triplet. The solid spin-labeled (dry) sample showed a high interspin interaction, which can be disrupted not only by different (liquid) solvents, but also by absorption of different solids, like cyclodextrins, dendrimers or polyethyleneglycols. Also, changes induced by the temperature were studied in the case of toluene wet sample. From 150 to 370K, the spectrum is changing from a slow motion spectrum type to a fast motion regime. The preparative procedures to obtain the spin-labeled silica as well as some of its parameters are described.

Keywords: TEMPO; Spin-labeled silica gel; EPR; Free radical

Synthesis of FeCo nanoparticles by pulsed laser deposition in a diffusion cloud chamber by P.L. Ong; S. Mahmood; T. Zhang; J.J. Lin; R.V. Ramanujan; P. Lee; R.S. Rawat (pp. 1909-1914).

Magnetic FeCo nanoparticles were successfully synthesized in a diffusion cloud chamber setup within pulsed laser deposition (PLD) equipment. The variation of morphology and size of FeCo nanoparticles with the number of laser pulses, ambient gas pressure and temperature gradient was studied. It was observed that the morphology of the nanoparticles changes from “cloud-like” fractal clusters to particle chains; average particle size increased at higher argon gas pressure. Increasing the temperature gradient considerably reduced the agglomeration of the nanoparticles. Nanoparticles deposited using the diffusion cloud chamber are found to be crystalline.

Keywords: Nanoparticles; FeCo; Pulsed laser deposition; Diffusion cloud chamber

Biological functionalization and fluorescent imaging of carbon nanotubes by Zuxun Xu; PingAn Hu; Shimin Wang; Xianbao Wang (pp. 1915-1918).

Biofunctionalization and manipulating of carbon nanotubes (CNTs) is important for biomedical research and application. Cy5 labeled goat anti-rabbit IgG (anti-IgG-Cy5) is chemically bonded to CNTs via a two-step process of diimide-activated amidation. This process can avoid the intermolecular connection of proteins. Fluorescent imaging of CNTs in aqueous solution has been demonstrated using anti-IgG-Cy5 immobilized CNTs (IgG-CNTs) as the model. The biologically functionalized carbon nanotubes (f-CNTs) in solution have been observed successfully using fluorescence microscopy. The fluorescent image of highly oriented f-CNTs is obtained at first time. The influencing factors on fluorescent imaging including oxidation duration, background noise and reactant concentration are discussed.

Keywords: Functionalization; Fluorescent imaging; Carbon nanotubes

Influence of porous morphology on optical dispersion properties of template free mesoporous titanium dioxide (TiO₂) films by P. Sudhagar; R. Sathyamoorthy; S. Chandramohan (pp. 1919-1928).

This paper focuses the influence of porous morphology on the microstructure and optical properties of TiO₂ films prepared by different sol concentration and calcination temperatures. Mesoporous TiO₂ thin films were prepared on the glass substrates by sol–gel dip coating technique using titanium (IV) isopropoxide. Porous morphology of the films can be regulated by chemical kinetics and is studied by scanning electron microscopy. The optical dispersion parameters such as refractive index ( n), oscillator energy ( E_d), and particle co-ordination number ( N_c) of the mesoporous TiO₂ films were studied using Swanepoel and Wemple–DiDomenico single oscillator models. The higher precursor concentration (0.06M), films exhibit high porosity and refractive index, which are modified under calcination treatment. Calcinated films of low metal precursor concentration (0.03M) possess higher particle co-ordination number ( N_c=5.05) than that of 0.06M films ( N_c=4.90) due to calcination at 400°C. The lattice dielectric constant ( E_∞) of mesoporous TiO₂ films was determined by using Spintzer model. Urbach energy of the mesoporous films has been estimated for both concentration and the analysis revealed the strong dependence of Urbach energy on porous morphology. The influence of porous morphology on the optical dispersion properties also has been explained briefly in this paper.

Keywords: PACS; 61.43.Gt; 78.66.Bz; 81.40.EfMesoporous TiO; ₂; thin films; Calcination effect; Optical dispersion parameters; Urbech energy

Morphological and surface compositional changes in poly(lactide-co-glycolide) tissue engineering scaffolds upon radio frequency glow discharge plasma treatment by Ivan Djordjevic; Leanne G. Britcher; Sunil Kumar (pp. 1929-1935).

Chemical functionalisation of polymeric scaffolds with functional groups such as amine could provide optimal conditions for loading of signalling biomolecules over the entire volume of the porous scaffolds. Three-dimensional (both surface and bulk) functionlisation of large volume scaffolds is highly desirable, but preferably without any change to the basic morphological, structural and bulk chemical properties of the scaffolds. In this work, we have carried out and compared treatments of poly(lactide-co-glycolide) tissue engineering scaffolds by two methods, that is, a wet chemical method using ethylenediamine and a glow discharge plasma method using heptylamine as a precursor. The samples thus prepared were analysed by scanning electron microscopy and X-ray photoelectron spectroscopy. The plasma treatment generated amide and protonated amine (NH⁺) groups which were present in the bulk and on the surface of the scaffold. Amination also occurred for the wet chemical treatments but the structural and chemical integrity were adversely affected.

Keywords: PACS; 87.68+z; 52.77−jXPS; SEM; Poly(lactide-co-glycolide); Tissue engineering; Plasma polymerisation; Surface characterization

Is gold always chemically passive? by Maëlenn Aufray; Alain André Roche (pp. 1936-1941).

When epoxy-amine liquid mixtures are applied onto metallic substrates (such as Al, Ti, Sn, Zn, Fe, Cr, Cu, Ag, Ni, and Au), concomitant amine chemisorption and metallic surface dissolution occur, leading to organo-metallic complex formation. The interphase formation was studied, using two different amines as hardener (IsoPhoroneDiAmine and DiEthyleneTriAmine). If the complex concentration within the liquid amine or epoxy-amine prepolymer was higher than its solubility limit, the complexes will crystallize. Sharp needle-like crystals were only observed with metal–IPDA organo-metallic complexes. A lot of metals are widely used as reactive substrates with gold as a reference, which is considered chemically inert. It is misleading, since it will be shown in this article that gold reacts with amine, just as the other metals.

Keywords: Chemisorption; Diffusion and migration; Surface chemical reaction; Gold; Solid–liquid interfaces; Epoxy; Amine; Metal–polymer interphase

Preparation and characterization of SiO₂/ZrO₂/Ag multicoated microspheres by Xiaoyun Ye; Yuming Zhou; Yanqing Sun; Jing Chen; Zhiqiang Wang (pp. 1942-1946).

A new type of multicoated silica/zirconia/silver (SiO₂/ZrO₂/Ag) core-shell composite microspheres is synthesized in this paper. In the process, ZrO₂-decorated silica (SiO₂/ZrO₂) core-shell composites were firstly fabricated by the modification of zirconia on silica microspheres through the hydrolysis of zirconium precursor. Subsequently, on SiO₂/ZrO₂ composite cores, silver nanoparticles were introduced via ultrasonic irradiation and acted as “Ag seeds” for the formation of integrate silver shell by further reduction of silver ions using formaldehyde as reducer. The resulting samples were characterized by transmission electron microscopy, X-ray diffraction, Fourier-transform infrared, energy-dispersive X-ray, and UV–vis spectroscopy, indicating that zirconia and silver layers were successfully coated on the surfaces of silica microspheres.

Keywords: SiO; ₂; /ZrO; ₂; Silver; Composite; Transmission electron microscopy; X-ray diffractometry

Synthesis of GaN nanowires on gold-coated SiC substrates by novel pulsed electron deposition technique by M. Lei; H. Yang; P.G. Li; W.H. Tang (pp. 1947-1952).

A two-step approach for macro-synthesis of GaN nanowires was developed in this study. GaN nanoparticles were firstly synthesized through a facile solid-state reaction using an organic reagent dicyandiamide (C₂N₄H₄) and Ga₂O₃ as precursors. Subsequently, single-crystalline wurtzite GaN nanowires were grown on gold-coated 6H-SiC substrates via novel pulsed electron deposition (PED) technique using the as-prepared GaN nanoparticles as target, which provides a new route employing nanoparticles as precursors to fabricate GaN nanowires. It is found that pulsed electron ablation induced Ga and N plasma directly towards the gold-coated substrate to initialize the vapor–liquid–solid (VLS) growth processes. The morphological and structural properties were investigated in detail and Raman scattering spectrum of these nanowires presented some new features.

Keywords: GaN; Nanowire; Pulsed electron deposition technique; Raman scattering spectroscopy

Effect of substrate temperature on the structural, optical and electrical properties of dc magnetron sputtered tantalum oxide films by S.V. Jagadeesh Chandra; S. Uthanna; G. Mohan Rao (pp. 1953-1960).

dc reactive magnetron sputtering technique was employed for deposition of tantalum oxide films on quartz and silicon substrates by sputtering of pure tantalum target in the presence of oxygen and argon gases under various substrate temperatures in the range 303–973K. The variation of cathode potential with the oxygen partial pressure was systematically studied. The influence of substrate temperature on the chemical binding configuration, crystal structure and optical properties was investigated. X-ray photoelectron spectroscopic studies indicated that the films formed at oxygen partial pressures ≥1×10⁻⁴mbar were stoichiometric. The Fourier transform infrared spectroscopic studies revealed that the films formed up to substrate temperatures <673K showed a broad absorption band at 750–1000cm⁻¹ and a sharp band at 630cm⁻¹ indicated the presence of amorphous phase while at higher substrate temperatures the appearance of bands at about 810 and 510cm⁻¹ revealed the polycrystalline nature. The effect of substrate temperature on the electrical characteristics of Al/Ta₂O₅/Si structure was investigated. The dielectric constant values were in the range 17–29 in the substrate temperature range of 303–973K. The current–voltage characteristics showed modified Poole–Frenkel conduction mechanism with a tendency for reduction of the compensation level. The optical band gap of the films decreased from 4.44 to 4.25eV and the refractive index increased from 1.89 to 2.25 with the increase of substrate temperature from 303 to 973K.

Keywords: Tantalum oxide; Dielectric; Optical; Electrical

Preparation, structural and photoluminescent properties of CeO₂:Eu³⁺ films derived by Pechini sol–gel process by Hai Guo; Yanmin Qiao (pp. 1961-1965).

In this study, CeO₂ and CeO₂:Eu films were prepared by a simple Pechini sol–gel process and dip-coating method. CeO₂ were successfully synthesized by hydrolysis of cerium nitrate. Thermogravimetric analysis was used to study the thermal chemical properties of sol–gel powder. Structural properties of CeO₂ films annealed at different temperature ranging from 400 to 900°C were investigated by X-ray diffraction, field emission scanning electron microscopy, and Fourier transform infrared spectroscopy. Luminescent properties of CeO₂:Eu³⁺ films were investigated by excitation and emission spectra. Our results show that CeO₂ is a good host material for rare earth ions doping and Pechini sol–gel process is a useful method to derive high quality, macrocrack free, pure and doped CeO₂ films.

Keywords: PACS; 81.20.F; 78.66CeO; ₂; :Eu film; Pechini sol–gel; Luminescent properties; FE-SEM

Nanocrystalline soft ferromagnetic Ni–Co–P thin film on Al alloy by low temperature electroless deposition by A. Abdel Aal; A. Shaaban; Z. Abdel Hamid (pp. 1966-1971).

Soft ferromagnetic ternary Ni–Co–P films were deposited onto Al 6061 alloy from low temperature Ni–Co–P electroless plating bath. The effect of deposition parameters, such as time and pH, on the plating rate of the deposit were examined. The results showed that the plating rate is a function of pH bath and the highest coating thickness can be obtained at pH value from 8 to10. The surface morphology, phase structure and the magnetic properties of the prepared films have been investigated using scanning electron microscopy (SEM), X-ray diffraction analysis (XRD) and vibrating magnetometer device (VMD), respectively. The deposit obtained at optimum conditions showed compact and smooth with nodular grains structure and exhibited high magnetic moments and low coercivety. Potentiodynamic polarization corrosion tests were used to study the general corrosion behavior of Al alloys, Ni–P and Ni–Co–P coatings in 3.5% NaCl solution. It was found that Ni–Co–P coated alloy demonstrated higher corrosion resistance than Ni–P coating containing same percent of P due to the Co addition. The Ni–Co–P coating with a combination of high corrosion resistance, high hardness and excellent magnetic properties would be expected to enlarge the applications of the aluminum alloys.

Keywords: Electroless Ni–Co–P; Ferromagnetic coatings; Thin films; Al alloy

Scanning probe studies of water nucleation on aluminum oxide and gold surfaces by N. Missert; R.G. Copeland (pp. 1972-1976).

The nucleation of nanoscale water at surfaces in humid environments is sensitive to several factors, including the details of the surface morphology, ability of the surface to hydrate and the presence of contaminants. Tapping mode atomic force microscopy was used to investigate the nucleation process as a function of relative humidity (RH) on passive aluminum and gold thin films. Films exposed to the ambient environment prior to RH exposure showed discrete structures with lateral sizes ranging from 10 to 100nm only at RH>70%. These structures formed preferentially at grain boundaries, triple points and regions with significant topography such as protruding grains. The morphology of the passive aluminum surface is permanently altered at the sites where discrete structures were observed; nodules with heights ranging from 0.5 to 2nm persist even after reducing the RH to <2%. The gold surface does not show such a permanent change in morphology after reducing the RH. Passive aluminum films exposed to high RH immediately after growth (e.g. no ambient exposure) do not show discrete structures even at the highest RH exposures of 90%, suggesting a hydrophilic surface and the importance of surface hydrocarbon contaminants in affecting the distribution of the water layer.

Keywords: PACS; 68.08−p; 68.08 BcInterfacial water; AFM; Aluminum; Corrosion; Surface hydrocarbon

The effect of controlled ion bombardment on the electronic structure of the Si(001) surface by K.R. Roos; J. Lozano; J.H. Craig Jr. (pp. 1977-1980).

We have studied the effects of controlled ion bombardment on the electronic structure of the Si(001) surface. The surface was exposed to various doses of Ar⁺ ions accelerated towards the surface at 500eV. X-ray photoelectron spectroscopy (XPS) spectra of the irradiated H-terminated Si(001) surface reveal the appearance of peaks that are associated with the presence of cleaved Si bonds. Ultraviolet photoelectron spectroscopy (UPS) spectra of the irradiated Si(001)2×1 surface show that the dimer dangling-bond surface state decays monotonically with increasing dose. These results, coupled with previous scanning tunneling microscopy (STM) studies, indicate that the breaking of dimers, and possibly the creation of adatom-like defects, during ion irradiation are responsible for the changes in the electronic structure of the valence band for this surface.

Keywords: Silicon; Ion bombardment; X-ray photoelectron spectroscopy; Ultraviolet photoelectron spectroscopy; Surface defects; Surface electronic phenomena

Investigation of sol–gel derived HfO₂ on 4H-SiC by Kang Ji Wang; Kuan Yew Cheong (pp. 1981-1985).

Deposition of HfO₂ films on n-type 4H-SiC substrates by sol–gel spin-on coating technique has been performed and the physical and electrical characteristics of this film as a function of annealing temperature (550, 750, and 850°C for 30min) have been reported. The physical properties of the film have been characterized using a Filmetrics and X-ray diffractometer, while conduction atomic force microscope and semiconductor parameter analyzer were used for electrical characterization. Phase transformation has been revealed in the oxide as the annealing temperature changed. Refractive index, relative density, dielectric constant of the film, and oxide–semiconductor interface trap density have been extracted and related to the leakage current through the oxide. It has been recorded that, oxide annealed at 700°C has demonstrated the lowest leakage current and the best oxide reliability. The reasons of these observations have been explained.

Keywords: High dielectric constant material; Silicon carbide; Hafnium oxide; Sol–gel spin-on coating

Multi-level relief structures in sol–gel and photoresist fabricated by laser ablation and analyzed with coherence probe microscopy by E. Neiss; M. Flury; P. Gérard; L. Mager; J.-L. Rehspringer; A. Fort; P. Montgomery; J. Fontaine; T. Engel; A. Benatmane (pp. 1986-1992).

The demand in the field of microtechnology to create multi-level structures with sufficient resolution has been growing in recent years, particularly in micro-optics. Using the well-known laser ablation technique, the behaviour of different hybrid organic/inorganic homemade sol–gel materials and of a standard commercial photoresist are investigated with a KrF laser emitting at 248nm with nanosecond pulses. The aim consists of rapidly transferring relief patterns at low cost. The experimental set-up and procedure combined with the versatile profilometry technique of coherence probe microscopy (CPM) for rapid analysis are presented; the fabrication issues are discussed and compared with ablation of quartz and polymers. The materials calibration curves, which demonstrate the achievement of the present work, are presented.

Keywords: Laser micromachining; Multi-level structure; Sol–gel; Coherence probe microscopy

Effects of growth temperature on Li–N dual-doped p-type ZnO thin films prepared by pulsed laser deposition by Y.Z. Zhang; J.G. Lu; Z.Z. Ye; H.P. He; L.P. Zhu; B.H. Zhao; L. Wang (pp. 1993-1996).

Li–N dual-doped p-type ZnO (ZnO:(Li,N)) thin films have been prepared by pulsed laser deposition. The introduction of Li and N was confirmed by secondary ion mass spectrometry measurements. The structural, electrical, and optical properties as a function of growth temperature were investigated in detail. The lowest room-temperature resistivity of 3.99Ωcm was achieved at the optimal temperature of 450°C, with a Hall mobility of 0.17cm²/Vs and hole concentration of 9.12×10¹⁸cm⁻³. The ZnO:(Li,N) films exhibited good crystal quality with a complete c-axis orientation, a high transmittance (about 90%) in the visible region, and a predominant UV emission at room temperature. The two-layer-structure p-ZnO:(Li,N)/n-ZnO homojunctions were fabricated on a sapphire substrate. The current–voltage characteristics exhibited the rectifying behavior of a typical p–n junction.

Keywords: PACS; 61.72.V; 73.61.G; 81.15.FZnO; p-Type conductivity; Li–N dual-doping method; Pulsed laser deposition

Berkovich nanoindentation and deformation mechanisms in GaN thin films by Chien-Huang Tsai; Sheng-Rui Jian; Jenh-Yih Juang (pp. 1997-2002).

The deformation mechanisms of GaN thin films obtained by metal-organic chemical vapor deposition (MOCVD) method were studied using nanoindentation with a Berkovich diamond indenter, micro-Raman spectroscopy and the cross-sectional transmission electron microscopy (XTEM) techniques. Due to the sharpness of the tip of Berkovich indenter, the nanoindentation-induced deformation behaviors can be investigated at relatively lower load and, hence, may cover wider range of deformation-related phenomena over the same loading range. The load–displacement curves show the multiple “pop-ins” during nanoindentation loading. No evidence of nanoindentation-induced phase transformation and cracking patterns were found up to the maximum load of 300mN, as revealed from the micro-Raman spectra and the scanning electron microscopy (SEM) observations within the mechanically deformed regions. In addition, XTEM observation performed near the cross-section of the indented area revealed that the primary deformation mechanism in GaN thin film is via propagation of dislocations on both basal and pyramidal planes. The continuous stiffness measurement (CSM) technique was used to determine the hardness and Young's modulus of GaN thin films. In addition, analysis of the load–displacement data reveals that the values of hardness and Young's modulus of GaN thin films are 19±1 and 286±25GPa, respectively.

Keywords: PACS; 62.20.−x; 68.37.Hk; 68.37.Lp; 81.15.GhMOCVD; GaN; Nanoindentation; Multiple pop-ins; Micro-Raman spectroscopy; Focused ion beam; Transmission electron microscopy

Stable multilayer thin films composed of gold nanoparticles and lysozyme by Yan-lei Su; Chao Li (pp. 2003-2008).

It needs appropriately attractive forces to construct multilayer thin films by layer-by-layer (LBL) assembly technique. It is feasible to prepare multilayer thin films on glass slides with negatively charged gold nanoparticles and positively charged lysozyme through the electrostatic LBL assembly technique. The gold nanoparticles/lysozyme multilayer thin films are highly stable; immersion in 0.1M HCl, NaOH, and surfactant sodium dodecyl sulfate aqueous solutions cannot destroy the films. The highly stable gold nanoparticles/lysozyme multilayer thin films have potential application in long-term antibacterial coating.

Keywords: Gold nanoparticle; Lysozyme; Film; Stability; Antibacterial coating

Fabrication of superhydrophobic surfaces on engineering material surfaces with stearic acid by Qi Wang; Bingwu Zhang; Mengnan Qu; Junyan Zhang; Deyan He (pp. 2009-2012).

Via a simple wet chemical etching followed by stearic acid modification, the presence of synergistic binary structures at micro- and nanometer scales and stearic acid bestows superhydrophobic property on steel and aluminum alloy surfaces. The as-prepared surfaces show superhydrophobic not only for pure water but also for corrosive liquids such as acid, basic and salt solutions. The stable superhydrophobicity of steel and aluminum alloy surfaces will extend their applications as engineering materials.

Keywords: Superhydrophobicity; Chemical etching; Alloy; Wettability

Properties of Dy-doped ZnO nanocrystalline thin films prepared by pulsed laser deposition by Huiming Huang; Yangjun Ou; Sheng Xu; Guojia Fang; Meiya Li; X.Z. Zhao (pp. 2013-2016).

Highly transparent conductive Dy₂O₃ doped zinc oxide (ZnO)1–_x(Dy₂O₃)_x nanocrystalline thin films with x from 0.5% to 5% have been deposited on glass substrate by pulsed laser deposition technique. The structural, electrical and optical properties of Dy₂O₃ doped thin films were investigated as a function of the x value. The experimental results show that the Dy concentration in Dy-doped ZnO thin films has a strong influence on the material properties especially electrical properties. The resistivity decreased to a minimum value of 5.02×10⁻⁴Ωcm with x increasing from 0.5% to 1.0%, then significantly increased with the further increasing of x value. On the contrary, the optical direct band gap of the (ZnO)1–_x(Dy₂O₃)_x films first increased, then decreased with x increasing. The average transmission of Dy₂O₃ doped zinc oxide films in the visible range is above 90%.

Keywords: Doped zinc oxide; Pulsed laser deposition; Thin film; Transparent-conductive oxide

Electrochromic properties of nano-structured nickel oxide thin film prepared by spray pyrolysis method by Sheng-Hui Lin; Fu-Rong Chen; Ji-Jung Kai (pp. 2017-2022).

In this study, we present a simple method to improve the electrochromic properties of a nickel oxide thin film. The method involves a three-step process—(a) conducting indium tin oxide (ITO) nano-particles were first sprayed onto a conducting substrate to form a porous nano-structured ITO layer, (b) nickel oxide film was then deposited onto the nano-structured ITO layer by a spray pyrolysis technique, and (c) the substrate, ITO nano-particles layer and nickel oxide film were annealed at high temperature of 300°C to improve adhesion of these three layers. The microstructure of the resulting electrochromic cell was investigated using scanning electron microscopy. It is evident that the nickel oxide film covers the surface of the ITO nano-particle layer and forms a nano-structured nickel oxide (NSNO) film. The switching time and contrast were characterized by Autolab PGSTAT12 potentiostat and Jasco V-570 spectrophotometer. The results suggest that the transmittance contrast and switching time of NSNO are slightly superior to those of a conventional nickel oxide (CNO) film. However, the cycling durability of NSNO can be much better than that of CNO.

Keywords: PACS; 61.46.Df; 78.40.HaNickel oxide; Nano-structured; Electrochromic; Spray pyrolysis

Catalytic decomposition of trichloroethylene over Pt-/Ni-catalyst under microwave heating by Hideaki Takashima; Martin Karches; Yoshinori Kanno (pp. 2023-2030).

Microwave (MW)-activated catalytic reactor system was studied and the results were compared with that of a conventional system based on the thermal activation method. Trichloroethylene (TCE) was decomposed under various MW-powers supply. Results showed that there is an optimum film thickness that was loaded on supports in MW heating system. The threshold may be within 1–3μm. Lower temperature cannot activate the catalyst, while higher temperature results in carbon deposition and catalyst deactivation. This means that the dechlorination reaction needs to fix an optimum film MW-power supply in order to avoid the deposition of carbon on the surface of the active phase. MW-activated system is also worth compensating the conventional system in VOCs decomposition reaction.

Keywords: PACS; 81.16.Hc; 73.61.At; 84.40.−x; 82.30.Lp; 72.30.+qCatalysis in nanotechnology; Electrical conductivity of metals thin films; Microwave technology; Decomposition reactions; Skin effect

Nanostructures on SiC surface created by laser microablation by L. Fedorenko; A. Medvid’; M. Yusupov; V. Yukhimchuck; S. Krylyuk; A. Evtukh (pp. 2031-2036).

Silicon carbide (SiC), as it is well-known, is inaccessible to usual methods of technological processing. Consequently, it is important to search for alternative technologies of processing SiC, including laser processing, and to study the accompanying physical processes. The work deals with the investigation of pulsed laser radiation influence on the surface of 6H–SiC crystal. The calculated temperature profile of SiC under laser irradiation is shown. Structural changes in surface and near-surface layers of SiC were studied by atomic force microscopy images, photoluminescence, Raman spectra and field emission current–voltage characteristics of initial and irradiated surfaces. It is shown that the cone-shaped nanostructures with typical dimension of 100–200nm height and 5–10nm width at the edge are formed on SiC surface under nitrogen laser exposure ( λ=0.337μm, t_p=7ns, E_p=1.5mJ). The average values of threshold energy density 〈 W_thn〉 at which formation of nanostructures starts on the 0001 and0001¯surfaces of n-type 6H–SiC(N), nitrogen concentration n_N≅2×10¹⁸cm⁻³, are determined to be 3.5J/cm² and 3.0J/cm², respectively. The field emission appeared only after laser irradiation of the surface at threshold voltage of 1000V at currents from 0.7μA to 0.7mA. The main role of the thermogradient effect in the processes of mass transfer in prior to ablation stages of nanostructure formation under UV laser irradiation (LI) was determined. We ascertained that the residual tensile stresses appear on SiC surface as a result of laser microablation. The nanostructures obtained could be applied in the field of sensor and emitting extreme electronic devices.

Keywords: PACS; 81.16.Mk, 81.07.Bc, 79.20.DsSilicon carbide; Laser ablation; Nanostructures; Field emission; Photoluminescence; Raman spectra

Effect of hydroxylamine hydrochloride on the floral decoration of zinc oxide synthesized by solution method by Rizwan Wahab; S.G. Ansari; Young Soon Kim; Gilson Khang; Hyung-Shik Shin (pp. 2037-2042).

Effect of the structure-directing agent on the floral (depicting flower) morphological variation of ZnO is systematically studied and presented here. Flowery decorated (resembling flower) zinc oxide structure composed of hexagonal nanorods (sharp tips and wider bases) was synthesized at 90°C using zinc acetate dihydrate and sodium hydroxide at various concentrations of hydroxylamine hydrochloride for 12h by solution method. Single crystalline nature with the wurtzite hexagonal phase remained unaltered with increasing concentration of hydroxylamine hydrochloride while the morphology changes from nanorod to plate like structure. Photoelectron spectroscopic measurement presented spectra close to the standard bulk ZnO, with an O 1s peak composed of surface adsorbed OH group, O²⁻ in the oxygen vacancies on ZnO structure and ZnO. At higher concentration (0.8M), surface adsorbed OH group increases while other component decreases because of the changes in the nucleation and surface energy. Results clearly indicate that hydroxylamine hydrochloride works as a structure-directing agent without affecting other properties.

Keywords: Structure-directing agent; ZnO; Solution method

Spectral studies of thin films based on poly( N-vinylcarzole) and red dopant by Aiwei Tang; Feng Teng; Sha Xiong; Yanbing Hou (pp. 2043-2047).

Organic light-emitting diodes were fabricated with a structure of indium–tin-oxide (ITO)/poly( N-vinylcarzole)(PVK):4-(dicyanom-ethylene)-2- t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4 H-pyran (DCJTB)/8-tris-hydroxyquinoline aluminum (Alq₃)/lithium fluoride (LiF)/Al. The energy transfer from PVK to Alq₃ then to DCJTB and the charge trapping processes were investigated by employing the photoluminescence (PL) and electroluminescence (EL) spectra. With increasing thickness of the Alq₃ layer, the PL and EL emission from PVK were decreased gradually, which indicated that the effective energy transfer occurred from PVK to Alq₃ and then from Alq₃ to DCJTB. At the same time, we found that the exciton recombination zone could be adjusted by controlling the Alq₃ layer thickness and the applied voltages. The effects of different DCJTB concentrations on the optical and electrical characteristics of the devices were investigated, and an obvious red-shift was observed with the DCJTB dopant concentrations increasing in the PL and EL spectra.

Keywords: Light-emitting diodes; Electroluminescence; PVK; DCJTB; Energy transfer

Liquid crystal deposition on poled, single crystalline lithium niobate by S.C. Bharath; K.R. Pimputkar; A.M. Pronschinske; T.P. Pearl (pp. 2048-2053).

For the purpose of elucidating the mechanisms for molecular organization at poled ferroelectric surfaces, single crystalline lithium niobate (LN), ‘Z-cut’ along the (0001) plane, has been prepared and characterized and subsequently exposed to liquid crystal molecules. As a model system we chose to study the anchoring of 4- n-octyl-4′-cyanobiphenyl (8CB) to LN. Liquid crystalline films are of interest because of their useful electronic and optical properties as well as chemical sensing attributes. Low-energy electron diffraction (LEED), atomic force microscopy (AFM), surface contact angle measurements (CA), and X-ray photoelectron spectroscopy (XPS) were used to characterize the surface of lithium niobate as well as the nature of 8CB films grown on the surface. Atomically flat LN surfaces were prepared as a support for monolayer thick, 8CB molecular domains. 8CB liquid crystal molecules were deposited by an ambient vaporization technique and the films were analyzed using XPS and CA. Understanding electrostatic anchoring mechanisms and thin film organization for this molecule on uniformly poled surfaces allows for a fuller appreciation of how molecular deposition of other polarizable molecules on periodically poled and patterned poled lithium niobate surfaces would occur.

Keywords: PACS; 68.08.Bc; 68.43.−h; 68.47.GhLithium niobate; Ferroelectric; Surface; Liquid crystal; Monolayer

Enhanced diamond nucleation on copper substrates by graphite seeding and CO₂ laser irradiation by Y.X. Han; H. Ling; J. Sun; M. Zhao; T. Gebre; Y.F. Lu (pp. 2054-2058).

Diamond nucleation on copper (Cu) substrates was investigated by graphite seeding and CO₂ laser irradiation at initial stages of the combustion-flame deposition. A graphite aerosol spray was used to generate a thin layer of graphite powders (less than 1μm) on Cu substrates. The graphite-seeded Cu substrates were then heated by a continuous CO₂ laser to about 750°C within 1min. It was found that diamond nucleation density after this treatment was more than three times as much as that on the virgin Cu substrates. As a consequence, diamond films up to 4μm were obtained in 5min. The enhancement of diamond nucleation on the graphite-seeded Cu substrates was attributed to the formation of defects and edges during the etching of the seeding graphite layers by the OH radicals in the flame. The defects and edges served as nucleation sites for diamond formation. The function of the CO₂ laser was to rapidly heat the deposition areas to create a favorable temperature for diamond nucleation and growth.

Keywords: PACS; 81.05.Uw; 81.15.Gh; 81.20.KaNucleation; Diamond films; Copper; Combustion flame; Laser irradiation

Probability of ionization of sputtered particles as a function of their energy by Yu. Kudriavtsev; A. Villegas; S. Gallardo; R. Asomoza (pp. 2059-2066).

In this study we have investigated how the probability of ionization of sputtered Si atoms to form negative ions depends on the energy of the atoms. We have determined the ionization probability from experimental SIMS energy distributions using a special experimental technique, which included de-convolution of the energy distribution with an instrumental transmission function, found by separate measurements.We found that the ionization probability increases as a power law ∼ E^0.677 for particles sputtered with energies of 0–10eV, then becomes a constant value (within the limits of experimental error) for particles sputtered with energies of 30–100eV. The energy distributions of Si⁻ ions, measured under argon and cesium ion sputtering, confirmed this radical difference between the yields from low and high-energy ions.To explain these results we have considered ionization mechanisms that are different for the low energy atoms (<10eV) and for the atoms emitted with higher energy (>30eV).

Keywords: SIMS; Secondary ion yield; Energy distribution; Escape depth

Age-induced oxide on cleaved surface of layered GaSe single crystals by S.I. Drapak; S.V. Gavrylyuk; Z.D. Kovalyuk; O.S. Lytvyn (pp. 2067-2071).

It is shown that a long-term keeping of a layered gallium monoselenide at room temperature results in formation of the intrinsic oxide at a cleaved surface of semiconductor. It is found that the chemical compositions of the intrinsic oxide at the surfaces of the intentionally undoped and doped samples of GaSe are different. The electrical properties of the GaSe-intrinsic oxide system are presented. It is established that intrinsic oxide films at the surface of GaSe are characterized by current instability with N-type current–voltage characteristic. The influence of relative humidity on changes of capacitance and surface resistivity of the intrinsic oxide is also discussed.

Keywords: PACS; 68.47.Fg; 61.10.−i; 87.64.Dz; 47.55.dr; 77.84.Bw; 73.61.−r; 07.07.DfGallium selenide; Intrinsic oxide; X-ray diffraction (XRD); Atomic force microscopy (AFM); Electrical properties; Humidity sensing

Self-assembled InAs island formation on GaAs (110) by metalorganic vapor phase epitaxy by A. Aierken; T. Hakkarainen; M. Sopanen; J. Riikonen; J. Sormunen; M. Mattila; H. Lipsanen (pp. 2072-2076).

Formation of self-assembled InAs 3D islands on GaAs (110) substrate by metal organic vapor phase epitaxy has been investigated. Relatively uniform InAs islands with an average areal density of 10⁹cm⁻²are formed at 400° C using a thin InGaAs strain reducing (SR) layer. No island formation is observed without the SR layer. Island growth on GaAs (110) is found to require a significantly lower growth temperature compared to the more conventional growth on GaAs (100) substrates. In addition, the island height is observed to depend only weakly on the growth temperature and to be almost independent of the V/III ratio and growth rate. Low-temperature photoluminescence at 1.22eV is obtained from the overgrown islands.

Keywords: PACS; 68.37.Ps; 78.67.Hc; 81.05.Ea; 81.15.Gh; 81.16.DnSelf-assemble; MOVPE; InAs island; GaAs (1; 1; 0)

Influence of hydrothermally modified γ-Al₂O₃ on the properties of NiMo/γ-Al₂O₃ catalyst by Juncheng Li; Lan Xiang; Xu Feng; Zhanwen Wang (pp. 2077-2080).

The influence of hydrothermal modification of γ-Al₂O₃ on the properties of NiMo/γ-Al₂O₃ catalyst was investigated in this paper. The experimental results showed that the use of the modified γ-Al₂O₃ in the preparation of the NiMo/γ-Al₂O₃ catalyst led to the increase of the dispersion of the surface Mo and Ni oxides, favored the formation of the poly-molybdates and promoted the reduction of the active Mo oxides owing to the increase of the surface acidity of the modified γ-Al₂O₃. Therefore, the NiMo/γ-Al₂O₃ catalyst supported on the modified γ-Al₂O₃ exhibited a higher hydrodenitrogenation (HDN) activity than that supported on the untreated γ-Al₂O₃ in the temperature range of 300–340°C.

Keywords: Hydrothermal modification; Dispersion; HDN; NiMo/γ-Al; ₂; O; ₃; catalyst

Properties of ZnO thin films grown on Si substrates by photo-assisted MOCVD by Xiangping Li; Baolin Zhang; Huichao Zhu; Xin Dong; Xiaochuan Xia; Yongguo Cui; Keke Huang; Guotong Du (pp. 2081-2084).

ZnO thin films were grown on (100) p-Si substrates by Photo-assisted Metal Organic Chemical Vapor Deposition (PA-MOCVD) using diethylzinc (DEZn) and O₂ as source materials and tungsten–halogen lamp as a light source. The effects of tungsten–halogen lamp irradiation on the surface morphology, structural and optical properties of the deposited ZnO films have been investigated by means of atomic force microscope (AFM), X-ray diffraction and photoluminescence (PL) spectra measurements. Compared with the samples without irradiation, the several characteristics of ZnO films with irradiation are improved, including an improvement in the crystallinity of c-axis orientation, an increase in the grain size and an improvement in optical quality of ZnO films. These results indicated that light irradiation played an important role in the growth of ZnO films by PA-MOCVD.

Keywords: PACS; 68.37.Ps; 78.55.Et; 81.05.Dz; 81.15.GhZnO films; Photo-assisted MOCVD; XRD spectra; Photoluminescence; AFM

Thin films prepared from tungstate glass matrix by B. Montanari; S.J.L. Ribeiro; Y. Messaddeq; M.S. Li; G. Poirier (pp. 2085-2089).

Vitreous samples containing high concentrations of WO₃ (above 40%M) have been used as a target to prepare thin films. Such films were deposited using the electron beam evaporation method onto soda-lime glass substrates. These films were characterized by X-ray diffraction (XRD), perfilometry, X-ray energy dispersion spectroscopy (EDS), M-Lines and UV–vis absorption spectroscopy. In this work, experimental parameters were established to obtain stable thin films showing a chemical composition close to the glass precursor composition and with a high concentration of WO₃. These amorphous thin films of about 4μm in thickness exhibit a deep blue coloration but they can be bleached by thermal treatment near the glass transition temperature. Such bleached films show several guided modes in the visible region and have a high refractive index. Controlled crystallization was realized and thus it was possible to obtain WO₃ microcrystals in the amorphous phase.

Keywords: PACS; 61.43.Er; 68.60.−p; 74.25.GzGlass; Tungsten; Thin film

Characterization of laser-generated silicon plasma by L. Torrisi; F. Caridi; D. Margarone; A. Borrielli (pp. 2090-2095).

A study of visible laser ablation of silicon, in vacuum, by using 3ns Nd:YAG laser radiation is reported. Nanosecond pulsed ablation, at an intensity of the order of 10¹⁰W/cm², produces high non-isotropic emission of neutrals and ionic species. Mass quadrupole spectrometry, coupled to electrostatic ion deflection, allows estimation of the energy distributions of the emitted species from plasma. Neutrals show typical Boltzmann-like distributions while ions show Coulomb–Boltzmann-shifted distributions depending on their charge state. Time-of-flight measurements were also performed by using an ion collector consisting of a collimated Faraday cup placed along the normal to the target surface. Surface profiles of the craters, created by the laser radiation absorption, permitted to study the ablation threshold and ablation yields of silicon in vacuum. The plasma fractional ionization, temperature and density were evaluated by the experimental data. A special regard is given to the ion acceleration process occurring inside the plasma due to the high electrical field generated at the non-equilibrium plasma conditions. The angular distribution of the neutral and ion species is discussed.

Keywords: PACS; 52.38.Mf; 52.70.NcLaser ablation; Silicon plasma; Plasma temperature; Electric field in plasma-laser

Influence of charge deposition in a field-emission display panel by Lei Wei; Xiaobing Zhang; Chaogang Lou; ZuoYa Zhu (pp. 2096-2101).

Field-emission displays (FEDs) have been studied intensively in recent years as a candidate for flat-display panels in the future. In a FED, electrons emit from field emitters. Some electrons may impinge on the insulator surface between cathode and gate electrodes and cause charging of that surface because the yield of secondary electron emission is usually not equal to one. The charging of the insulator walls between cathode and gate electrodes is one of the important factors influencing the performance of a FED. In this paper, a simulation program is used to calculate this charge deposition, electric field distribution and electron trajectories. From the change of the electric field upon charge deposition in the triode region, it is shown that the insulator surface is negatively charged at a low gate voltage, e.g. 20V. However, positive charge is deposited when the gate voltage is high, e.g. 100V. The simulations also show that the emission current will increase even further after coating the dielectric with a thin film of a material with a high-secondary emission coefficient such as MgO. If a cone-shaped dielectric aperture is used in a triode, the emission current will decrease after charge deposition. However, the focus performance of the electron beam is improving in this case.

Keywords: Field-emission display; Secondary emission; Triode; Surface charge; Field distribution; CNT; MgO

Synthesis of bimetallic systems using replacement reactions by Songrui Wang; Jian’an He; Jinglin Xie; Yuexiang Zhu; Youchang Xie; Jingguang G. Chen (pp. 2102-2109).

Series of bimetallic systems were prepared by replacement reactions and characterized by XRD and XPS. The results suggest that the ad-metals are monolayer dispersed on the surface of sub-metal in Pd(Pt, Cu)/Co(Ni) systems, while in Pd(Pt, Au)/Cu systems surface solid solution is formed. In Ag(Au)/Co(Ni) and Ag/Cu systems no interaction between the metals is observed just as in the simple mixture of the respective crystallites. The outermost electronic configurations, the atomic radius of the metals, and the low-preparation temperature seem to be important factors for the different states of these bimetallic catalysts.

Keywords: Bimetallic catalysts; Monolayer dispersion; Surface solid solution

The effect of contamination of dielectric target surfaces under electron irradiation by E.I. Rau (pp. 2110-2113).

The influence of the contamination film formed under the electron bombardment of the sample surface on the conditions of experimental studies using analytical electron-probe apparatus (scanning electron microscopes, X-ray microanalyzers) is considered. The accompanying artifacts, namely the decreased effective value of the secondary electron emission coefficient and the shifted value of the second crossover energy of primary electrons are calculated.

Keywords: PACS; 79.20.Hx; 29.30.EpSecondary electron emission; Insulators; Contamination; Second crossover energy point

Bottom and top AF/FM interfaces of NiFe/FeMn/NiFe trilayers by V.P. Nascimento; E.C. Passamani; A.D. Alvarenga; A. Biondo; F. Pelegrini; E. Baggio Saitovitch (pp. 2114-2119).

X-ray reflectivity analyses were performed in the Si/WTi (7nm)/NiFe (30nm)/FeMn (13nm)/NiFe (10nm)/WTi (7nm) exchange-biased system prepared by magnetron sputtering under three different argon working pressures. Layer-by-layer analyses were realized in order to obtain the interfacial roughness parameters quantitatively. For a fixed argon pressure, the root-mean-square roughness (including the atomic grading) of the upper (FeMn/NiFe) interface are greater than that for the lower one in all studied samples. Argon working pressure also has severe influence over the NiFe/FeMn interfaces, being more pronounced at the upper interfaces.

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

Effect of erbium interlayer on nickel silicide formation on Si(100) by W. Huang; Y.L. Min; G.P. Ru; Y.L. Jiang; X.P. Qu; B.Z. Li (pp. 2120-2123).

To reveal the influence of erbium interlayer on the formation of nickel silicide and its contact properties on Si substrate, Er(0.5–3.0nm) and Ni(20nm) are successively deposited onto Si(100) substrate and are treated by rapid thermal annealing in pure N₂ ambient. The NiSi formation temperature is found to increase depending on the Er interlayer thickness. The formation temperature of NiSi₂ (700°C) is not influenced by Er addition. But with 2nm Er interlayer, the formed NiSi₂ is observed textured with preferred orientation of (100). During the formation of NiSi, Er segregates to the surface and little Er remains at the NiSi/Si(100) interface. Therefore, the Schottky barrier height of the formed NiSi/n-Si(100) contact is measured to be 0.635∼0.665eV which is nearly invariable with different Er addition.

Keywords: PACS; 73.30.+y; 73.40.Ns; 85.40.LsNi-silicide; Er interlayer; Schottky barrier

The role of strain in controlling the surface morphology of Al_xGa1−_xN following in situ treatment with SiH₄ and NH₃ by N. Ketteniss; R.A. Oliver; C. McAleese; M.J. Kappers; Y. Zhang; C.J. Humphreys (pp. 2124-2130).

Treatment of GaN with SiH₄ and NH₃ increases the size of surface pits associated with threading dislocations, allowing them to be easily imaged by atomic force microscopy. Here, we assess the effect of a similar treatment on Al_xGa1−_xN surfaces for x≤0.4. For relaxed Al_xGa1−_xN epilayers, an increase in the observed size and density of threading dislocation pits is observed. However, if the Al_xGa1−_xN is under tensile strain, the treatment results in the appearance of nanometre-scale surface hillocks. These hillocks may prevent observation of the dislocation pits. The hillocks are found to consist of crystalline Al_xGa1−_xN, and hence are suggested to be formed by strain driven etching or transformation of the surface by SiH₄ and NH₃.

Keywords: PACS; 81.15Kk; 68.37PsAlGaN; Atomic force microscopy; Threading dislocations

Superhydrophobic surfaces prepared from water glass and non-fluorinated alkylsilane on cotton substrates by Zhengxiong Li; Yanjun Xing; Jinjin Dai (pp. 2131-2135).

Superhydrophobic surfaces have been successfully prepared by sol–gel method using water glass as starting material. Such surfaces were obtained first by dip-coating the silica hydrosols prepared via hydrolysis and condensation of water glass onto cotton substrates, then the surface of the silica coating was modified with a non-fluoro compound, hexadecyltrimethoxysilane (HDTMS), to gain a thin film through self-assembly, superhydrophobicity with a water contact angle higher than 151° can be achieved. The morphology and surface roughness were characterized by SEM and AFM.

Keywords: PACS; 81.20.Fw; 81.16.Dn; 81.65.PsSuperhydrophobicity; Silica sol; Water glass; Non-fluorinated alkylsilane; Cotton fabrics

A computational analysis and suitability assessment of cold-gas dynamic spraying of glass-fiber-reinforced poly-amide 6 for use in direct-adhesion polymer metal hybrid components by M. Grujicic; B. Pandurangan; W.C. Bell; M. Daqaq; L. Ma; Norbert Seyr; Marc Erdmann; Jochen Holzleitner (pp. 2136-2145).

A transient non-linear dynamics computational analysis of cold-gas dynamic spraying (CGDS) of glass-fiber-reinforced poly-amide (nylon) 6 has been carried out using Ansys-Autodyn [Century Dynamics Inc., Ansys-Autodyn Version 11.0, User Documentation, Century Dynamics Inc. (a subsidiary of ANSYS Inc.), 2007] in order to assess the suitability of this spraying technology for coating of metal stampings used in polymer metal hybrid (PMH) load-bearing automotive component applications. In addition, the suitability of the CGDS is assessed with respect to a need for metal stamping surface preparation/treatment, the ability to deposit polymeric material without significant material degradation, the ability to selectively overcoat the metal stamping, the resulting magnitude of the polymer-to-metal adhesion strength, durability of the polymer/metal bond with respect to prolonged exposure to high-temperature/high-humidity and mechanical/thermal fatigue service conditions, and compatibility with the automotive body-in-white ( BIW) manufacturing process chain. The analysis revealed that CGDS can be considered as a viable technology for coating of metal stampings used in PMH load-bearing automotive component applications.

Keywords: CGDS; Polymer metal hybrids; Polymer metal adhesion; Automotive structural components; Polymer coating processes

Properties of Mg_xZn1−_xO thin films sputtered in different gases by Da-Yong Jiang; Ji-Ying Zhang; Ke-Wei Liu; Chong-Xin Shan; Yan-Min Zhao; Tong Yang; Bin Yao; You-Ming Lu; De-Zhen Shen (pp. 2146-2149).

Mg_xZn1−_xO alloy films were prepared on sapphire substrates using Ar and N₂ as the sputtering gases. The effect of the sputtering gas on the structural, optical and electrical properties of the Mg_xZn1−_xO films was studied. By using N₂ as the sputtering gas, the Mg_xZn1−_xO film shows p-type conductivity and the band gap is larger than that employing Ar as the sputtering gas. The reason for this phenomenon is thought to be related to the reaction between N–O or N–Zn, and the N-doping.

Keywords: Mg; _x; Zn; 1−; _x; O; Band gap; Raman; Electrical properties

Investigation of the interaction between electrical discharges and low resistivity silicon substrates by F. Soldera; G. Burdiles; U. Schmid; H. Seidel; F. Mücklich (pp. 2150-2157).

In this work the impact of single discharge pulses in air on single-crystalline, p-type silicon having a low bulk resistivity of 0.009–0.012Ωcm is investigated. Compared to platinum specimens, the craters in silicon have lateral dimensions which are about one order of magnitude larger despite comparable values for the melting point and the melting energy. This finding is attributed to the substantially higher bulk resistivity of silicon leading a higher energy input into the substrate when spark loaded. The energy generated by joule heating is, however, distributed across a larger area due to a current spreading effect. To study the impact of different surface properties on the sparking behaviour, the crater formation on the silicon substrate is investigated applying coatings with different material properties, such as sputter-deposited aluminium layers and thermally-grown silicon dioxide. In general, the crater characteristics formed on unmodified silicon is not influenced when a thin aluminium layer of 24nm is deposited. At higher film thickness above 170nm, the sparking energy is almost completely absorbed in the top layer with low influence on the underlying silicon substrate. In the case of a dielectric top layer with a thickness of 155nm, the formation of many small distinct craters is supported in contrast to a 500nm-thick SiO₂ film layer where the generation of a single crater with a large area is energetically favoured. A surface roughness of several nm on the silicon probes has no measurable effect on crater formation when compared to an original surface characteristic with values in the sub-nm range.

Keywords: Erosion; Electrical discharge; Bulk resistivity; Platinum; Silicon

Stable superhydrophobic surfaces over a wide pH range by Li Guo; Wenfang Yuan; Junping Li; Zhijie Zhang; Zemin Xie (pp. 2158-2161).

A stable superhydrophobic surface was fabricated by solidifying poly(epoxy-terminated polydimethylsiloxane- co-bisphenol A) [P(ETPDMS- co-BPA)] copolymer on a rough substrate. The low surface energy of the copolymer and the geometric structure at micrometer scale of the surface contribute to the superhydrophobic property. The as-prepared surface shows stable superhydrophobicity over a wide pH range (1–14) and the wettability is excellent stable to heating, water, corrosive solution and organic solvent treatments. The procedure is simple and time-saving as well as utilizing non-fluorine-containing compounds.

Keywords: PACS; 68.08.Bc; 68.35.Ct; 81.05.LgSuperhydrophobic; Stable; Epoxy-terminated polydimethylsiloxane; Bisphenol A

Real time investigation of the growth of silicon carbide nanocrystals on Si(100) using synchrotron X-ray diffraction by S. Milita; M. De Santis; D. Jones; A. Parisini; V. Palermo (pp. 2162-2167).

The growth of silicon carbide nanocrystals on Si(100) is studied by synchrotron surface X-ray diffraction (SXRD) during annealing at high temperature. A chemisorbed methanol monolayer is used as carbon source, allowing to have a fixed amount of carbon atoms to feed the growth. At room temperature, minor changes in the 2×1 reconstruction of silicon are observed due to the formation of Si–O–CH₃ and Si–H bonds from methanol molecules. When annealed at 500°C, carbon incorporation into the silicon leads only to local modifications of the surface structure. Above 600°C, tri-dimensional silicon carbide nanocrystals growth takes place, together with surface roughening and sharp decrease of domain sizes of the 2×1 reconstruction. The different processes taking place at each temperature are clearly distinguished and identified during the real time SXRD measurements.

Keywords: PACS; 61.10.Nz; 68.47.FgX-ray diffraction; Semiconductor surfaces

Multifractal analysis of ITO thin films prepared by electron beam deposition method by Davood Raoufi; Hamid Reza Fallah; Ahmad Kiasatpour; Amir Sayid Hassan Rozatian (pp. 2168-2173).

In this work, we developed the multifractality and its formalism to investigate the surface topographies of ITO thin films prepared by electron beam deposition method for various annealing temperatures from their atomic force microscopy (AFM) images. Multifractal analysis shows that the spectrum width, Δ α (Δ α= α_max− α_min), of the multifractal spectra, f( α), can be used to characterize the surface roughness of the ITO films quantitatively. Also, it is found that the f( α) shapes of the as-deposited and annealed films remained left hooked (that is Δ f= f( α_min)− f( α_max)>0), and falls within the range 0.149–0.677 depending upon the annealing temperatures.

Keywords: PACS; 61.43.Hv; 68.55.JkITO thin film; Electron beam evaporation; Multifractal analysis; Surface roughness

Analyses of surface coloration on TiO₂ film irradiated with excimer laser by H.Y. Zheng; H.X. Qian; W. Zhou (pp. 2174-2178).

TiO₂ film of around 850nm in thickness was deposited on a soda-lime glass by PVD sputtering and irradiated using one pulse of krypton-fluorine (KrF) excimer laser (wavelength of 248nm and pulse duration of 25ns) with varying fluence. The color of the irradiated area became darker with increasing laser fluence. Irradiated surfaces were characterized using optical microscopy, scanning electron microscopy, Raman spectroscopy and atomic force microscopy. Surface undergoes thermal annealing at low laser fluence of 400 and 590mJ/cm². Microcracks at medium laser fluence of 1000mJ/cm² are attributed to surface melting and solidification. Hydrodynamic ablation is proposed to explain the formation of micropores and networks at higher laser fluence of 1100 and 1200mJ/cm². The darkening effect is explained in terms of trapping of light in the surface defects formed rather than anatase to rutile phase transformation as reported by others. Controlled darkening of TiO₂ film might be used for adjustable filters.

Keywords: PACS; 79.20.Ds; 52.50.Jm; 68.37.Hk; 87.64.JeExcimer laser; Titanium oxide; Surface coloration; Crack; Hydrodynamic ablation

Nanostructural and surface morphological evolution of chemically sprayed SnO₂ thin films by Saji Chacko; Ninan Sajeeth Philip; K.G. Gopchandran; Peter Koshy; V.K. Vaidyan (pp. 2179-2186).

Physical properties of a nanocrystalline thin film is greatly influenced by its morphological and structural evolution. We try to understand the transition of SnO₂ thin films from amorphous to nanocrystalline structure with XRD, IR, SEM, AFM and surface profiler studies. A 2D layer like structure resulting from quantum confinement is found for the films prepared at 400°C. We observed a new IR band at 530cm⁻¹ that was theoretically predicted and report it for the first time. A correlation of population of defects in SnO₂ films with change in lattice parameters and FWHM of IR bands are reported. The electric and optical properties of the films have been discussed.

Keywords: PACS; 52.70.kz; 63; 50.+x; 68; 37.; −; d; 68.37.Hk; 68.37.Ps; 81.15.; −; zOxygen vacancies; Structural and optical properties; IR band at 530; cm; ⁻¹; in SnO; ₂; thin films

Spray deposition of highly transparent fluorine doped cadmium oxide thin films by R.J. Deokate; S.M. Pawar; A.V. Moholkar; V.S. Sawant; C.A. Pawar; C.H. Bhosale; K.Y. Rajpure (pp. 2187-2195).

The cadmium oxide (CdO) and F:CdO films have been deposited by spray pyrolysis method using cadmium acetate and ammonium fluoride as precursors for Cd and F ions, respectively. The effect of temperature and F doping on the structural, morphological, optical and Hall effect properties of sprayed CdO thin films was investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), optical absorption and electrical measurement techniques. TGA and DTA studies, indicates the formation of CdO by decomposition of cadmium acetate after 250°C. XRD patterns reveal that samples are polycrystalline with cubic structure and exhibits (200) preferential orientation. Considerable broading of (200) peak, simultaneous shifting of corresponding Bragg's angle have been observed with respect to F doping level. SEM and AFM show the heterogeneous distribution of cubical grains all over the substrate, which are randomly distributed. F doping shifts the optical gap along with the increase in the transparency of CdO films. The Hall effect measurement indicates that the resistivity and mobility decrease up to 4% F doping.

Keywords: Cadmium oxide; Thin film; Spray pyrolysis; X-ray diffraction; Optical absorption; Resistivity

Synthesis of ZnO nanoparticles using nanosecond pulsed laser ablation in aqueous media and their self-assembly towards spindle-like ZnO aggregates by Chun He; Takeshi Sasaki; Yoshiki Shimizu; Naoto Koshizaki (pp. 2196-2202).

ZnO nanoparticles were fabricated by pulsed laser ablation (PLA) of a Zn metal in aqueous media, and aging effects on the morphology and photoluminescence properties of ZnO nanoparticles were investigated. The crystalline phase and particle morphology were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). It was found that small, well-defined ZnO nanoparticles were obtained by PLA of a Zn plate in aqueous media, and subsequent aging of the obtained ZnO nanoparticle suspension produced in cetyltrimethylammonium bromide (CTAB) solution led to the formation of spindle-like ZnO aggregates. However, in deionized water not the spindle-like ZnO aggregates but fluffy round aggregates were obtained. High-resolution transmission electron microscopic (HRTEM) observation indicated that the spindle-like ZnO aggregates were composed of many well-defined nanoparticles. Spindle-like aggregates exhibited strong exciton emission, while green emission could be suppressed via an aging process in the presence of CTAB. Moreover, thin films prepared by electrophoretic deposition (EPD) of ZnO nanoparticles after PLA in the presence of CTAB also possessed highly elongated aggregate structures that were possibly formed by surrounding the ZnO nanoparticles with double layers of CTAB molecules.

Keywords: ZnO nanoparticle; Pulsed laser ablation (PLA); Spindle-like ZnO aggregates; Aqueous media; Surfactant; Photoluminescence

Textured Al2024 alloy surface for super-hydrophobicity investigation by Lijuan Chen; Miao Chen; Huidi Zhou; Jianmin Chen (pp. 2203-2206).

To mimic the lotus leaf structure, micro- and nanometer honeycomb-like porous hierarchical microstructures were constructed on the Al2024 alloy surface in which the average diameter of micro-pores was ca. 10μm while those of nano-pores varied from 200 to 300nm. Super-hydrophobicity was achieved with a water contact angle of 158° and the sliding angle of 4° by modifying the textured surface with HFTHTMS (HFTHTMS=(heptadecafluoro-1,1,2,2-tetrahydrodecyl) trimethoxysilane).

Keywords: Wettability; Surface texture; Super-hydrophobic surfaces

Unidirectional variation of lattice constants of Al–N-codoped ZnO films by RF magnetron sputtering by Hu-Jie Jin; Sang-Hyun Oh; Choon-Bae Park (pp. 2207-2210).

Al–N-codoped ZnO films were fabricated by RF magnetron sputtering in the ambient of N₂ and O₂ on silicon (100) and homo-buffer layer, subsequently, annealed in O₂ at low pressure. X-ray diffraction (XRD) spectra show that as-grown and 600°C annealed films grown by codoping method are prolonged along crystal c-axis. However, they are not prolonged in (001) plane vertical to c-axis. The films annealed at 800°C are not prolonged in any directions. Codoping makes ZnO films unidirectional variation. X-ray photoelectron spectroscopy (XPS) shows that Al content hardly varies and N escapes with increasing annealing temperature from 600°C to 800°C.

Keywords: PACS; 71.55.Gs; 73.61.Ga; 78.66.HfMagnetron sputtering; Unstressed position; Codoping; Unidirectional variation

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Applied Surface Science (v.254, #7)

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Applied Surface Science (v.254, #7)