Check out our New Publishers' Select for Free Articles

Applied Surface Science (v.255, #15)

Chemical etching investigation of polycrystalline p-type 6H-SiC in HF/Na₂O₂ solutions by Noureddine Gabouze; Aissa Keffous; Tahar Kerdja; Yasmine Belaroussi (pp. 6751-6756).

In this work, an experimental study on the chemical etching reaction of polycrystalline p-type 6H-SiC was carried out in HF/Na₂O₂ solutions. The morphology of the etched surface was examined with varying Na₂O₂ concentration, etching time, agitation speed and temperature. The surfaces of the etched samples were analyzed using scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) Fourier transform infrared spectroscopy (FT-IR) and photoluminescence. The surface morphology of samples etched in HF/Na₂O₂ is shown to depend on the solution composition and bath temperature. The investigation of the HF/Na₂O₂ solutions on 6H-SiC surface shows that as Na₂O₂ concentration increases, the etch rate increases to reach a maximum value at about 0.5M and then decreases. A similar behaviour has been observed when temperature of the solution is increased. The maximum etch rate is found for 80°C. In addition, a new polishing etching solution of 6H-SiC has been developed. This result is very interesting since to date no chemical polishing solution has been developed on the material.

Keywords: Silicon carbide; Chemical etching; SEM

The effect of some triazole derivatives as inhibitors for the corrosion of mild steel in 1M hydrochloric acid by Shengtao Zhang; Zhihua Tao; Weihua Li; Baorong Hou (pp. 6757-6763).

Corrosion inhibition by some new triazole derivatives on mild steel in 1M hydrochloric acid solutions has been investigated by weight loss test, electrochemical measurement, scanning electronic microscope analysis and quantum chemical calculations. The results indicate that these compounds act as mixed-type inhibitors retarding the anodic and cathodic corrosion reactions and do not change the mechanism of either hydrogen evolution reaction or mild steel dissolution. The studied compounds following the Langmuir adsorption isotherm, and the thermodynamic parameters were determined and discussed. The effect of molecular structure on the inhibition efficiency has been investigated by ab initio quantum chemical calculations. The electronic properties such as highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO) energy levels, energy gap (LUMO–HOMO), dipole moment and molecular orbital densities were calculated.

Keywords: PACS; 81.65. KnAdsorption; Corrosion inhibition; EIS; Quantum chemical calculations

Plasma treatment of polypropylene fabric for improved dyeability with soluble textile dyestuff by Necla Yaman; Esen Özdoğan; Necdet Seventekin; Hakan Ayhan (pp. 6764-6770).

The impact of plasma treatment parameters on the surface morphology, physical–chemical, and dyeing properties of polypropylene (PP) using anionic and cationic dyestuffs were investigated in this study. Argon plasma treatment was used to activate PP fabric surfaces. Activated surfaces were grafted different compounds: 6-aminohexanoic acid (6-AHA), acrylic acid (AA), ethylendiamine (EDA), acryl amide (AAMID) and hexamethyldisiloxane (HMDS). Compounds were applied after the plasma treatment and the acid and basic dyeing result that was then observed, were quite encouraging in certain conditions. The possible formed oxidizing groups were emphasized by FTIR and ATR and the surface morphology of plasma treated PP fibers was also investigated with scanning electron microscopy (SEM).PP fabric could be dyed with acid and basic dyestuffs after only plasma treatment and plasma induced grafting, and fastnesses of the dyed samples were satisfactory.

Keywords: Polypropylene; Surface functionality; Plasma treatment; Acid dyestuff; Basic dyestuff

Self-assembly of silanated poly(ethylene glycol) on silicon and glass surfaces for improved haemocompatibility by Zhang Guo; Sheng Meng; Wei Zhong; Qiangguo Du; Laisheng L. Chou (pp. 6771-6780).

Surface immobilization of poly(ethylene glycol) (PEG) is an effective method to produce a material surface with protein repulsive property. This property could be made permanent by using covalent grafting of the PEG molecules onto material surfaces. In this study, self-assembled monolayers (SAMs) of PEG on silicon-containing materials (silicon chip and glassplate) were obtained through a one-step coating procedure of one kind of silanated PEG molecules made through the reaction between monomethoxy PEG and 3-isocyanatopropyltriethoxysilane. Atomic force microscopy (AFM) and water static contact angle measurement were employed to investigate the surface topography and wettability of the PEGylated material surfaces. The changes in the topography and the water contact angle of the surfaces with time of incubation in PBS solution were also measured. The results revealed that stable and uniform self-assembled monolayers of PEG could be formed on silicon or glass surfaces by simply soaking the substrates in the solution of silanated PEGs. The covalent coupling of PEGs to the substrates was also confirmed. In order to evaluate the stability of the SAMs, blood compatibility of the modified glassplate surface was evaluated by measuring full blood activated partial thromboplastin time (APTT), prothrombin time (PT), and thrombin time (TT), as well as by scanning electron microscopy (SEM) analysis of the appearance of adherence and denaturation of blood platelets onto the glassplate. The silanated PEGs were shown to have good effect on the protein-repulsion as well as haemocompatibility of the substrates.

Keywords: PACS; 81.65.−b; 81.15.−z; 87.85.jjAtomic force microscopy; Blood compatibility; Self-assembled monolayer; Silanated PEG

Enhancing the crystallinity and surface roughness of sputtered TiO₂ thin film by ZnO underlayer by Feng Huang; Bin Xie; Bingjun Wu; Lei Shao; Ming Li; Haiqian Wang; Yousong Jiang; Yizhou Song (pp. 6781-6785).

TiO₂ and TiO₂/ZnO double layer films were sputtered on glass substrates. It was found that a thin ZnO underlayer is helpful for tailoring the microstructure and surface morphology of the TiO₂ film. By applying a 70-nm-thick ZnO underlayer, a TiO₂ thin film of 100nm in thickness with well crystallized anatase phase and rough surface was successfully fabricated without heating the substrate. Relatively high photo-catalytic activity and good hydrophilic properties were observed in such TiO₂/ZnO double layer films.

Keywords: Titanium oxide; Zinc oxide; Photo-catalysis; Sputtering; Super-hydrophilic

CdS thin films obtained by thermal treatment of cadmium(II) complex precursor deposited by MAPLE technique by Andrei Rotaru; Anna Mietlarek-Kropidłowska; Catalin Constantinescu; Nicu Scărişoreanu; Marius Dumitru; Michal Strankowski; Petre Rotaru; Valentin Ion; Cristina Vasiliu; Barbara Becker; Maria Dinescu (pp. 6786-6789).

Thin films of [Cd{SSi(O–Bu^t)₃}(S₂CNEt₂)]₂, precursor for semiconducting CdS layers, were deposited on silicon substrates by Matrix-Assisted Pulsed Laser Evaporation (MAPLE) technique. Structural analysis of the obtained films by Fourier transform infrared spectroscopy (FTIR) confirmed the viability of the procedure. After the deposition of the coordination complex, the layers are manufactured by appropriate thermal treatment of the system (thin film and substrate), according to the thermal analysis of the compound. Surface morphology of the thin films was investigated by atomic force microscopy (AFM) and spectroscopic-ellipsometry (SE) measurements.

Keywords: Cadmium(II) coordination compound; MAPLE; Precursor for CdS layers; Thermal treatment; Spectroscopic-ellipsometry

Argon laser induced changes to the carbonate content of enamel by M.J. Ziglo; A.E. Nelson; G. Heo; P.W. Major (pp. 6790-6794).

Argon laser irradiation can be used to cure orthodontic brackets onto teeth in significantly less time than conventional curing lights. In addition, it has been shown that the argon laser seems to impart a demineralization resistance to the enamel. The purpose of this study was to use surface science techniques to ascertain if this demineralization resistance is possibly a result of a decrease in the carbonate content of enamel. Eleven mandibular third molars previously scheduled for extraction were collected and used in the present study. The teeth were sectioned in two and randomly assigned to either the argon laser (457–502nm; 250mWcm⁻²) or the control (no treatment) group. The sections assigned to the argon laser group were cured for 10s and analyzed. To exaggerate any potential changes the experimental sections were then exposed to a further 110s of argon laser irradiation. Surface analysis was performed using X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The results showed no statistically significant change in the carbonate content of enamel after argon laser irradiation ( p>0.05). Thus, it is suggested that any demineralization resistance imparted to the enamel surface by argon laser irradiation is not due to alterations in carbonate content.

Keywords: Argon laser; Enamel; Molar; Carbonate; Calcium hydroxyapatite

Preparation and characterization of poly(lactic acid)-grafted TiO₂ nanoparticles with improved dispersions by Yan-Bing Luo; Xiu-Li Wang; Da-Yun Xu; Yu-Zhong Wang (pp. 6795-6801).

Poly(lactic acid) (PLA)-grafted TiO₂ particles were prepared by in situ melt polycondensation of lactic acid onto the surface of TiO₂ nanoparticles. The resulting products were characterized by FTIR, XPS, TG-FTIR, XRD analysis and electron microscopy observation so as to have a better understanding of bonding between the graft polymer and nanoparticles. New characteristic peaks of Ti–carboxylic coordination bond, the changes in the relative intensities of the infrared absorption bands of graft polymer and the two decomposition stage of PLA-grafted TiO₂ confirmed that PLA was grafted on the surface of TiO₂ nanoparticles. By attachment of PLA, the PLA-grafted TiO₂ samples exhibited much better dispersion and a slightly larger particle size than bare TiO₂ particles. PLA-grafted TiO₂ nanoparticles will find wide applications in biomedical and eco-friendly materials, especially as fillers in PLA matrix.

Keywords: PACS; 61.46.Df; 87.85.jjTiO; ₂; nanoparticle; Poly(lactic acid); Graft; FTIR; XPS

Epitaxial SiC formation induced by medium energy ions on Si(111) at room temperature by Praveen Kumar; Lekha Nair; Santanu Bera; B.R. Mehta; S.M. Shivaprasad (pp. 6802-6805).

In the search for silicon technology compatible substrate for III-nitride epitaxy, we present a proof-of-concept for forming epitaxial SiC layer on Si(111). A C/Si interface formed by ion sputtering is exposed to 100–1500eV Ar⁺ ions, inducing a chemical reaction to form SiC, as observed by core-level X-ray photoelectron spectroscopy (XPS). Angle dependent XPS studies shows forward scattering feature that manifest the epitaxial SiC layer formation, while the valence band depicts the metal to insulator phase change.

Keywords: X-ray photoelectron spectroscopy; Silicon carbide; Ion beam induced reactions; Reaction threshold

Controlling geometric and electronic properties of highly ordered CuPc thin films by T. Toader; G. Gavrila; J. Ivanco; W. Braun; D.R.T. Zahn (pp. 6806-6808).

Geometric and electronic properties of ordered copper phthalocyanine (CuPc) thin films grown on hydrogen- and antimony-passivated Si(111) surfaces have been studied using near edge X-ray absorption fine structure (NEXAFS) and photoemission spectroscopy. The H- and Sb-passivations of vicinal Si surfaces resulted in different molecular orientations in thick films, namely upright and near lying molecules, respectively. In the absence of the vicinality, the molecules on the Sb-passivated surface changed towards upright orientation. The work function of the films was monitored during the growth and correlated with the molecular orientation.

Keywords: PACS; 61.10.Ht; 68.37.Ps; 68.55.Jk; 71.20.Rv; 73.20.At; 79.60.−iOrganic semiconductors; Phthalocyanine; Photoemission; NEXAFS; Molecular film growth; Molecular orientation

Surface morphology and optical properties of ZnO epilayers grown on Si(111) by metal organic chemical vapor deposition by S.C. Hung; P.J. Huang; C.E. Chan; W.Y. Uen; F. Ren; S.J. Pearton; T.N. Yang; C.C. Chiang; S.M. Lan; G.C. Chi (pp. 6809-6813).

Heteroepitaxial ZnO epilayers were grown on Si(111) substrates using a vertical geometry atmospheric pressure metal organic chemical vapor deposition (AP-MOCVD) system. The growth temperature was varied from 550°C to 650°C in steps of 25°C. The ZnO growth rate and surface morphology were strong functions of the growth temperature and ranged from ∼0.16μm/h to 1.36μm/h. The surface morphology of the ZnO films changed from granular to sharp tips as the growth temperature increased. The effect of buffer thickness was also examined, and was found to have a strong effect on the optical properties of the ZnO. An optimized growth condition for ZnO epilayers was found at 625°C, producing a FWHM in the room temperature photoluminescence (PL) spectrum of 4.5nm and a preferred growth orientation along the (002) direction.Transmission electron microscopy images and selected area diffraction patterns showed excellent crystalline quality of both the buffer and ZnO overlayer. When non-optimized growth temperatures were employed, post-growth annealing was found to greatly enhance the ratio of band-edge to deep level emission.

Keywords: ZnO; Surface morphology

Electrodeposition of platinum nanoclusters on type I collagen modified electrode and its electrocatalytic activity for methanol oxidation by Yujing Sun; Lanlan Sun; Fugang Xu; Cunlan Guo; Zhelin Liu; Yue Zhang; Tao Yang; Zhuang Li (pp. 6814-6818).

We firstly reported a novel polymer matrix fabricated by type I collagen and polymers, and this matrix can be used as nanoreactors for electrodepositing platinum nanoclusters (PNCs). The type I collagen film has a significant effect on the growth of PNCs. The size of the platinum nanoparticles could be readily tuned by adjusting deposition time, potential and the concentration of electrolyte, which have been verified by field-emitted scanning electron microscopy (FE-SEM). Furthermore, cyclic voltammetry (CV) has demonstrated that the as-prepared PNCs can catalyze methanol directly with higher activity than that prepared on PSS/PDDA film, and with better tolerance to poisoning than the commercial E-TEK catalyst. The collagen–polymer matrix can be used as a general reactor to electrodeposit other metal nanostructures.

Keywords: Platinum nanoclusters; Type I collagen; Electrodeposition; Electrocatalyst

Particulate assisted growth of ZnO nanorods and microrods by pulsed laser deposition by T. Premkumar; P. Manoravi; B.K. Panigrahi; K. Baskar (pp. 6819-6822).

Zinc oxide (ZnO) thin films were deposited on the gallium nitride (GaN) and sapphire (Al₂O₃) substrates by pulsed laser deposition (PLD) without using any metal catalyst. The experiment was carried out at three different laser wavelengths of Nd:YAG laser ( λ=1064nm, λ=532nm) and KrF excimer laser ( λ=248nm). The ZnO films grown at λ=532nm revealed the presence of ZnO nanorods and microrods. The diameter of the rods varies from 250nm to 2μm and the length varies between 9 and 22μm. The scanning electron microscopy (SEM) images of the rods revealed the absence of frozen balls at the tip of the ZnO rods. The growth of ZnO rods has been explained by vapor–solid (V–S) mechanism. The origin of growth of ZnO rods has been attributed to the ejection of micrometric and sub-micrometric sized particulates from the ZnO target. The ZnO films grown at λ=1064nm and λ=248nm do not show the rod like morphology. X-ray photoelectron spectroscopy (XPS) has not shown the presence of any impurity except zinc and oxygen.

Keywords: PACS; 81.15.Fg; 68.55.−a; 61.10.Nz; 78.55.EtPulsed laser deposition; Zinc oxide; SEM; X-ray photoelectron spectroscopy

Effects of polyethylenimine on morphology and property of ZnO films grown in aqueous solutions by Xiulan Hu; Yoshitake Masuda; Tatsuki Ohji; Kazumi Kato (pp. 6823-6826).

Morphologies and properties of well-aligned ZnO films were controlled using zinc nitrate-hexamethylenetetramine aqueous solutions with the addition of polyethylenimine as a surfactant. Porous and dense ZnO films were fabricated with and without polyethylenimine, respectively. The addition of polyethylenimine proceeded to form porous ZnO whiskers film by preferential adsorption to nonpolar crystal faces and modifications of the surface free energy and growth rate. Dense ZnO film showed high transmittance of 80%, and low intensity of fluorescence and photo-induced current. Porous ZnO whiskers film showed low transmittance of 70%, while high intensity of fluorescence and high photo-induced current were detected because the porous ZnO nanowhisker film possessed a large interior surface area which can capture large amounts of DNA molecules labeled with dye molecules on the surface of ZnO crystals. High performance dye-sensitized sensors can be produced using ZnO whisker films prepared from an aqueous solution.

Keywords: Aqueous solution; ZnO film; Morphology; Transmittances; Fluorescence; Photocurrent

In vitro evaluation of bioactivity of CaO–SiO₂–P₂O₅–Na₂O–Fe₂O₃ glasses by Rajendra Kumar Singh; G.P. Kothiyal; A. Srinivasan (pp. 6827-6831).

Glasses with compositions 41CaO(52− x)SiO₂4P₂O₅· xFe₂O₃3Na₂O (2≤ x≤10mol.%) were prepared by melt quenching method. Bioactivity of the different glass compositions was studied in vitro by treating them with simulated body fluid (SBF). The glasses treated for various time periods in SBF were evaluated by examining apatite formation on their surface using grazing incidence X-ray diffraction, Fourier transform infrared reflection spectroscopy, scanning electron microscopy and energy dispersive spectroscopy techniques. Increase in bioactivity with increasing iron oxide content was observed. The results have been used to understand the evolution of the apatite surface layer as a function of immersion time in SBF and glass composition.

Keywords: PACS; 81.05.Pj; 87.64.Je; 87.68.+z; 61.10.KwBioactive glasses; Iron oxide; In vitro tests; Apatite layer; Surface morphology

The effects of strain on STM lithography on HS-ssDNA/Au (111) surface by Fan Chen; Anhong Zhou; Haeyeon Yang (pp. 6832-6839).

Scanning tunneling microscopy (STM) lithography was utilized to investigate a 12-mer HS-ssDNA self-assembled Au (111) surface. Under low sample bias and high tunneling current, the repeated scanning resulted in the growth of nanostripes. The stripe orientation, the stripe width, and the spacer width between adjacent nanostripes were found to be dependent on their relative locations from dislocation points where two adjacent gold terraces overlap. The stripe and the spacer width also vary with the distance from these points. The results indicate that such stripes may reflect the strain distributions and the release pathway along the Au surfaces. The results also suggest that the presence of HS-ssDNA molecules enhances the lithography processes on the gold surface by acting as force transmitters.

Keywords: PACS; 68.35.Gy; 68.37.Ef; 81.16.Nd; 87.14.gk; 81.16.DnScanning tunneling microscopy; Lithography; DNA; Strain; Self-assembly

Surface modification of polymethyl methacrylate intraocular lenses by plasma for improvement of antithrombogenicity and transmittance by Lihua Zhang; Di Wu; Yashao Chen; Xiaoli Wang; Guowei Zhao; Haiyan Wan; Changzheng Huang (pp. 6840-6845).

To improve antithrombogenicity and reduce ultraviolet transmittance, polymethyl methacrylate intraocular lenses (PMMA IOLs) were pretreated with Ar plasma and combined with heparin (Hp), with polyglycol (PEG) and with both Hp and PEG in a plasma atmosphere. The resulting modified PMMA IOLs denoted as PEG–PMMA, Hp–PMMA and Hp–PEG–PMMA were characterized by attenuated total reflectance Fourier transfer infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), ultraviolet–visible spectroscopy (UV–vis), contact angle (CA) and platelet adhesion experiments. The results indicated that Hp and PEG had been successfully immobilized onto the surfaces of PMMA IOLs. Antithrombogenicity was improved remarkably and ultraviolet transmittance was reduced as well.

Keywords: Plasma treatment; PMMA IOL; Surface modification; Antithrombogenicity; UV transmittance

Generation of a stable surface concentration of amino groups on silica coated onto titanium substrates by the plasma enhanced chemical vapour deposition method by Endre J. Szili; Sunil Kumar; Roger St. C. Smart; Nicolas H. Voelcker (pp. 6846-6850).

This report describes the amino functionalisation of the surface of plasma enhanced chemically vapour deposited silica films (PECVD-SiO₂), which were coated onto titanium substrates. Amino groups were linked to PECVD-SiO₂ via 3-aminpropyl triethoxysilane (APTES). We showed that the APTES functionalised PECVD-SiO₂ surfaces contained a high packing density of amino groups (67–92 NH₂ groups per nm²), indicative of a multilayered and highly cross-linked APTES film. 65–66% of the original surface concentration of APTES was retained on the PECVD-SiO₂ surface after incubation under physiological conditions, indicating that APTES films are relatively stable on PECVD-SiO₂ in these environments. The stability of the amino groups obtained on PECVD-SiO₂ in this study is much higher compared to other hydroxyl-bearing materials, such as titanium. Therefore, PECVD-SiO₂ films may find use as functional biomaterial coatings and as intermediate adhesion layers in silanisation processes.

Keywords: 3-Aminopropyl triethoxysilane; Plasma enhanced chemical vapour deposition; Silica; Titanium

The structure and molecular orientation of polytetrafluoroethylene coatings deposited from active gas phase by Alexander A. Rogachev; Sigitas Tamulevičius; Alexander V. Rogachev; Maxim A. Yarmolenko; Igoris Prosycevas (pp. 6851-6856).

The molecular structure of polytetrafluoroethylene (PTFE) coatings deposited on aluminium substrates was investigated by the method of attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR). It has been shown experimentally that PTFE coatings deposited by the electron-beam dispersion method have molecular orientation and are ordered nonmonotonously during the process of coating growth. Maximum order and orientation of molecules along the normal to the substrate are observed in an interfacial layer located within up to 100nm to the substrate. The observed morphological and orientation features of the formed layers were explained using the proposed adsorption–diffusion mechanism of polymer coating formation.

Keywords: Active gas phase; Electron-beam dispersion; Thin film; Polytetrafluoroethylene; Molecular orientation

Patterning on single crystalline silicon by laser scanning and alkaline etching by Takashi Hosono; Hitoshi Tokura (pp. 6857-6861).

The applicability of laser processing for small-lot micro-electromechanical system devices is discussed in this paper. This simple process could replace conventional complex processes designed with mass production in mind. Ablation, protrusions or surface modification is revealed to occur by argon ion laser scanning into silicon. Which of them occurs depends on the laser power. It is found that the protrusions are covered by a thin layer of oxide; however, oxidation of the modified surface is not established even though some results suggest it. Surface modification is more applicable to surface patterning than coarse protrusion is because the laser-modified surface can be used as a mask in KOH etching to make sharp patterns. The applicability of this method is indicated by demonstrating pattern width control, patterning over a large area and the fabrication of a 16-bit linear scale.

Keywords: Laser processing; Surface patterning; KOH etching; Oxide layer

High-temperature oxidation studies of cold-sprayed Ni–20Cr and Ni–50Cr coatings on SAE 213-T22 boiler steel by Niraj Bala; Harpreet Singh; Satya Prakash (pp. 6862-6869).

The high-temperature oxidation behavior of cold-sprayed Ni–20Cr and Ni–50Cr coatings on SAE 213-T22 boiler steel has been investigated at 900°C in air under cyclic heating and cooling conditions for 50 cycles. The kinetics of oxidation of coated and bare boiler steel has been established with the help of weight change measurements. It was observed that all the coated and bare steels obeyed parabolic rate law of oxidation. X-ray diffraction, FE-SEM/EDAX and X-ray mapping techniques were used to analyse the oxidation products of the coated and uncoated boiler steel. The uncoated steel suffered corrosion in the form of intense spalling and peeling of its oxide scale, which was perhaps due to the formation of unprotective Fe₂O₃ oxide scale. Both the coatings showed better resistance to the air oxidation as compared to the uncoated steel. The Ni–50Cr coating was found to be more protective than the Ni–20Cr-coated steel. The formation of oxides and spinels of nickel and chromium may be contributing to the development of air oxidation resistance in the coatings.

Keywords: High-temperature oxidation; Cold spraying; Ni–20Cr; Ni–50Cr; Oxide scales; Boiler steel

The unexpected formation of Au δ⁺–Si δ⁻ by the resonance neutralization of Ar⁺ during the low energy bombardment of Au nanoparticles on c-Si by De-Quan Yang; Edward Sacher (pp. 6870-6874).

Nanoscale Au layers, with irregular porosities, have been formed by the low energy Ar⁺ bombardment of Au nanoparticles that were sputter-deposited onto native oxide-covered Si surfaces. High-resolution field emission scanning electron microcopy (FE-SEM) and X-ray photoelectron spectroscopy (XPS) have been used to characterize the formation and evolution of the nanoporous layer. Under Ar⁺ bombardment, the Au nanoparticles that were initially deposited were observed to flatten and spread across the native oxide surface, without diffusing, finally coalescing at their edges to form a nanoporous film having irregular pore dimensions. XPS showed that this evolution was accompanied by the loss of Au as a result of sputtering. The formation of such porous films necessitates strong interfacial bonding to avoid the lateral diffusion of the Au nanoparticles, and their ultimate coalescence into larger nanoparticles.We demonstrated that Ar⁺ beam bombardment invariably caused the formation of Au δ⁺–Si δ⁻ bonding, rather than the expected Au δ⁻–Si δ⁺ bonding, and we explain this to be due to the resonance neutralization of the Ar⁺ beam on impacting the Au layer. We also reveal that the presumed formation of AuSi_x is not quantifiable by XPS, due to the superposition of the chemical shift of the Au nanoparticles with that of the quantum size effect, during Au loss on sputtering.

Keywords: Ar; ⁺; beam bombardment; Au nanoparticles; Interfacial bond formation; Resonance neutralization

Interface adhesion properties of functional coatings on titanium alloy formed by microarc oxidation method by Y.M. Wang; L.X. Guo; J.H. Ouyang; Y. Zhou; D.C. Jia (pp. 6875-6880).

Three functional coatings (namely Al-C, Si-P-Al and P-F-Al coating) were fabricated by microarc oxidation method on Ti6Al4V alloy in different aqueous solutions. The microstructure, phase and chemical composition of coatings were investigated using scanning electron microscope, X-ray diffraction and energy dispersive spectroscopy. The interface adhesion failure mode of the coating is revealed by shear, tensile and thermal shock methods. The coatings exhibit high adhesion strength by the quantitative shearing test, registering as 110, 70, and 40MPa for Al-C, Si-P-Al and P-F-Al coating, respectively. The tensile test of the coated samples shows that microarc oxidation treatment does not significantly deteriorate mechanical properties of substrate titanium alloy. The observations of the coating failure after subjected to the identical tensile elongation of 3.0% are well in agreement with those results of the shear test. The thermal cycle test indicates that all the coatings have good anti-thermal shocking properties.

Keywords: Microarc oxidation; Coatings; Microstructure; Mechanical properties; Adhesion

Structure, morphology and properties of Fe-doped ZnO films prepared by facing-target magnetron sputtering system by Changzheng Wang; Zhong Chen; Ying He; Lanying Li; Dong Zhang (pp. 6881-6887).

We have prepared a series of ZnO films with various concentrations of Fe dopant by using facing-target magnetron sputtering system and investigated their structure, morphology, optical properties and magnetic properties by means of the X-ray diffraction, Raman spectrometer, X-ray photoelectron spectroscopy, scanning electron microscope, UV–vis spectrophotometer, spectrofluorophotometer and vibrated sample magnetometer, respectively. The results showed Fe was in 2+ valence state in film. With increasing the concentration of Fe dopant the crystal quality deteriorated gradually and an increasing compressive stress occurred in ZnO films. All the grains grew with a columnar form along the [002] direction and the average size of grains decreased monotonically as the concentration of Fe dopant increased. The calculated results indicated that the band gap of films decreased with the increment of the concentration of Fe dopant, which resulted in the red-shift of violet emission peak. Moreover, the intensity of violet emission peak increased with the increment of Fe concentration because of the interface trap existing in depletion regions located at the ZnO grains boundaries. When the concentration of Fe dopant was smaller than 0.028, the films exhibited paramagnetic properties while the films displayed weak ferromagnetic properties when the concentration of Fe dopant increased to 0.041.

Keywords: PACS; 68.55.−a; 71.55.Gs; 74.25.Gz; 74.25.Ha; 81.16.MkFe-doped ZnO films; Structure; Morphology; Properties; Facing-target magnetron sputtering system

Low-phosporous nickel-coated carbon microcoils: Controlling microstructure through an electroless plating process by H. Bi; K.C. Kou; A.E. Rider; K. Ostrikov; H.W. Wu; Z.C. Wang (pp. 6888-6893).

Carbon microcoils (CMCs) have been coated with a nickel–phosphorus (Ni–P) film using an electroless plating process, with sodium hypophosphite as a reducing agent in an alkaline bath. CMC composites have potential applications as microwave absorption materials. The morphology, elemental composition and phases in the coating layer of the CMCs and Ni-coated CMCs were investigated by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD), respectively. The effects of process parameters such as pH, temperature and coating time of the plating bath on the phosphorus content and deposition rate of the electroless Ni–P coating were studied. The results revealed that a continuous, uniform and low-phosphorous nickel coating was deposited on the surface of the CMCs for 20min at pH 9.0, plating bath temperature 70°C. The as-deposited coatings with approximately 4.5wt.% phosphorus were found to consist of a mix of nano- and microcrystalline phases. The mean particle size of Ni–P nanoparticles on the outer surface of the CMCs was around 11.9nm. The deposition rate was found to moderately increase with increasing pH, whereas, the phosphorous content of the deposit exhibited a significant decrease. Moreover, the material of the coating underwent a phase transition between an amorphous and a crystalline structure. The thickness of the deposit and the deposition rate may be controlled through careful variation of the coating time and plating bath temperature.

Keywords: Carbon microcoils; Electroless plating; Coating; Microstructure; Chemical vapor deposition

Improving blood-compatibility of titanium by coating collagen–heparin multilayers by J.L. Chen; Q.L. Li; J.Y. Chen; C. Chen; N. Huang (pp. 6894-6900).

This work deals with improving the blood-compatibility of titanium by coating it with heparin (Hep) and collagen (Col) using a layer-by-layer (LBL) self-assembly technique. In the work described here, LBL-produced Hep–Col film growth is initialized by deposition of a layer of positively charged polyl-Lysine (PLL) on a titanium surface, which is negatively charged after treatment with NaOH, followed by formation of a multilayer thin film formed by alternating deposition of negatively charged heparin and positively charged collagen utilizing electrostatic interaction. The chemical composition, wettability, surface topography, mass and thickness of the film were investigated by Fourier transform infrared spectroscopy, water contact angle measurement, scanning electron microscopy, atomic force microscopy, electronic analytical semi-microbalances, and XP stylus profilometry. The in vitro platelet adhesion and activation were investigated by a static platelet adhesion test probing the lactate dehydrogenase (LDH) release of adherent platelets after lysis and by a P-selectin assay. The clotting time was examined by activated partial thromboplastin time (APTT) and prothrombin time (PT) assays. All obtained data showed that the LBL film can significantly decrease platelet adhesion and activation, and prolong clotting time of APTT and PT compared to untreated titanium. LBL-produced Hep–Col films on titanium display more excellent anticoagulation performance than on the surface of titanium.

Keywords: Layer-by-layer self-assembly; Blood-compatibility; Heparin; Collagen

Vacancy diffusion in Cu ∑=5[001] twist grain boundary by Yan-Ni Wen; Jian-Min Zhang; Wan-Min Yang; Ke-Wei Xu (pp. 6901-6906).

Both the formation energies and the diffusive activation energy of a single vacancy migrating intra- and inter-layer in the first four atomic planes near Cu ∑=5[001] twist GB have been investigated by means of MD in conjunction with MAEAM. The effects of the GB on the vacancy formation and migration are only to the third layer. The vacancy is favorable to be formed on the un-coincident site in the first, second and third layers near the GB plane and this case is enhanced successively following the third, second and first layers. A single vacancy either on un-coincident site or on coincident site in the forth, third and second layers is favorable to migrate to un-coincident site (its first-nearest-neighbor) in its adjacent layer near the GB. But for the first layer, the favorable migration path of the vacancy on the un-coincident site is between un-coincident sites of the first layer or to its nearest-neighbor of the first layer in the rotating grain, which is not the case for the vacancy on the coincident site ‘1’ that is migrated difficultly. So, there are collective tendency of the vacancy in the GB.

Keywords: Cu; Vacancy; MAEAM; Diffusion; Grain boundary

Effect of titanium powder assisted surface pretreatment process on the nucleation enhancement and surface roughness of ultrananocrystalline diamond thin films by Debabrata Pradhan; I. Nan Lin (pp. 6907-6913).

A superior, easy and single-step titanium (Ti) powder assisted surface pretreatment process is demonstrated to enhance the diamond nucleation density of ultrananocrystalline diamond (UNCD) films. It is suggested that the Ti fragments attach to silicon (Si) surface form bond with carbon at a faster rate and therefore facilitates the diamond nucleation. The formation of smaller diamond clusters with higher nucleation density on Ti mixed nanodiamond powder pretreated Si substrate is found to be the main reason for smooth UNCD film surface in comparison to the conventional surface pretreatment by only nanodiamond powder ultrasonic process. The X-ray photoelectron spectroscopic study ascertains the absence of SiC on the Si surface, which suggests that the pits, defects and Ti fragments on the Si surface are the nucleation centers to diamond crystal formation. The glancing-incidence X-ray diffraction measurements from 100nm thick UNCD films evidently show reflections from diamond crystal planes, suggesting it to be an alternative powerful technique to identify diamond phase of UNCD thin films in the absence of ultra-violet Raman spectroscopy, near-edge X-ray absorption fine structure and transmission electron microscopy techniques.

Keywords: Diamond nucleation; Microwave plasma CVD; Glancing-incidence XRD; X-ray photoelectron spectroscopy; Atomic force microscopy

Preparation and characterization of Cobalt Sulfophthalocyanine/TiO₂/fly-ash cenospheres photocatalyst and study on degradation activity under visible light by Pengwei Huo; Yongsheng Yan; Songtian Li; Huaming Li; Weihong Huang (pp. 6914-6917).

Cobalt Sulfophthalocyanine (CoSPc) sensitized TiO₂ sol samples were prepared through a Sol–Gel method using Cobalt Sulfophthalocyanine as a sensitizer. Loading and modified floating photocatalyst was prepared by hydrothermal method using fly-ash cenospheres as a carrier. The properties of the samples were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and UV–vis diffuse reflectance spectrum (DRS). Photocatalytic activity was studied by degrading wastewater of methylene blue under visible light. The results indicate that the fly-ash cenospheres are covered by modified TiO₂ film which composed of the anatase, brookite and rutile misch crystal phase. CoSPc/TiO₂/fly-ash cenospheres samples have good catalytic activity under visible light, and have strong absorbency during 600–700nm. The sensitization of CoSPc can enhance visible light catalytic activity of TiO₂/fly-ash cenospheres. The degradation rate of methylene blue reaches 73.36% in 180min under the visible light illumination. But too much CoSPc can decrease its catalytic activity.

Keywords: PACS; 81.15.−z; 82.50.HPSol–Gel method; Low temperature; Hydrothermal method; CoSPc/TiO; ₂; /fly-ash cenospheres; Photocatalysis

The peculiarities of the low-energy ion scattering by polycrystal targets by F.F. Umarov; N.N. Bazarbaev; F.G. Djurabekova (pp. 6918-6923).

In the present work, experimental and computer simulation studies of low-energy ( E₀=80–500eV) Cs⁺ ions scattering on Ta, W, Re target surfaces and K⁺ ions scattering on Ti, V, Cr target surfaces have been performed for more accurate definition of mechanism of scattering, with a purpose of evaluation of an opportunity of use of slow ions scattering as a tool of surface layers analysis. The choice of the targets was based on the fact that the ratios of atomic masses of target atoms and ions μ= m₂/ m₁ were almost the same for all cases considered and greater than 1 (direct mass ratio) however, the difference of binding energies of target atoms in the cases of Cs⁺ and K⁺ scattering was almost twice as much. It has been noticed that the dependencies of the relative energy retained by scattering ions at the maximum of energy distribution versus the initial energy E_m/ E₀ ( E₀) have a similar shape in all cases. The relative energy retained by scattering ions increases while the initial energy of incidence ions decreases. The curves are placed above each other relative to the binding energies of target atoms, to show what this says about the influence of binding energy on a process of scattering of low-energy ions. The correlation between value of energy change maintained by an ion for different values of E₀ in the case of scattering by targets with different masses of atoms and its binding energies is experimentally established. The contrary behavior of the E_m/ E₀ ( E₀) dependencies concerning the target atom binding energy quantity E_b for cases with direct ( μ>1) and inverse ( μ<1) mass ratio of colliding particles is established. The comparison of experimental energy distributions with calculated histograms shows that the binary collision approximation cannot elucidate the abnormally great shift in the maxima of relative energy distributions towards greater energy retained by scattering ions.

Keywords: PACS; 79.20.RfIon–surface interaction; Low-energy heavy ions scattering; Energy spectra; Binding energy; Mass ratio of colliding particles; Non-binary mechanism of scattering; Many-particle interactions; Dynamic Monte-Carlo computer simulation method

Synthesis of intrinsic fluorescent polypyrrole nanoparticles by atmospheric pressure plasma polymerization by Ping Yang; Jing Zhang; Ying Guo (pp. 6924-6929).

Intrinsic fluorescent polypyrrole (ppy) nanoparticles with different shapes were fabricated by atmospheric pressure plasma polymerization. Gradient electrical field and polarization of active particles in the plasma induce change of shape of nanoparticles from spherical to rod, when the plasma power varied from 5W to 10W. Both X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) results suggest that the atmospheric pressure plasma polymerization process (APPP) at the power of 5W and 10W can help to preserve the integrity of the structure of monomer due to the predominant role of radical polymerization in APPP at these powers. However, when the plasma power increased to 20W, the ring structure of some pyrroles was destroyed, owing to existence of higher energy species. The polypyrrole nanoparticles exhibit the peak fluorescence around 415nm. Fluorescent results show that the fluorescent properties of polypyrrole nanoparticles are related to the particle size of the polymer. The bigger particles would have more enlarged room for exciton diffusion, resulting in lower fluorescence intensity and red shift of the fluorescent peak.

Keywords: PACS; 52.50.Dg; 82.33.Xj; 82.35.Cd; 61.46.Df; 81.65.−bAtmospheric pressure plasma polymerization; Polypyrrole nanoparticles; Fluorescence

Emission characteristics, crystalline phase and composition of vapor-transport-equilibrated Er:LiNbO₃ crystal codoped with 6mol% MgO by De-Long Zhang; Bei Chen; Hong-Li Liu; Yu-Ming Cui; E.Y.B. Pun (pp. 6930-6938).

Polarized downconversion, 980-nm-upconversion and near-infrared emission characteristics of vapor-transport-equilibrated (VTEed) bulk Er (0.4mol%)/MgO (6mol%)-codoped LiNbO₃ crystals were investigated. The downconversion and upconversion visible emissions display similar VTE effects including the drop of emission intensity and the weakening of polarization dependence. At 0.98 and 1.5μm regions, the VTE has a weak effect on the emission intensity, but a strong effect on the spectral shape. The crystalline phases in these bulk Er/Mg-codoped VTE crystals are determined by comparing their infrared emission characteristics with those of pure ErNbO₄ powder and locally Er-doped MgO (4.5mol%):LiNbO₃ crystal. The results show that the Er³⁺ ions present in these bulk Er/Mg-codoped VTE crystals as a mixture of Er:LiNbO₃ and ErNbO₄ phases. The percentages of the ErNbO₄ phase contained in these VTE crystals were evaluated from the 1531 and 1536nm characteristic absorption areas. The contents of constituent elements were determined by chemical analysis.

Keywords: PACS; 42.70.Hj; 81.10.Bk; 78.55.HxEr:Mg:LiNbO; ₃; Vapor-transport-equilibration; Er; ³⁺; emission; Crystalline phase; Composition

Kinetic study of interfacial solid state reactions in the Ni/4H–SiC contact by Z. Zhang; J. Teng; W.X. Yuan; F.F. Zhang; G.H. Chen (pp. 6939-6944).

Investigation of the relatively low temperature reaction between Ni nanolayer film and 4H–SiC substrate provides valuable insights into studies of the fundamental properties of SiC Schottky diodes. A quantitative description of chemical kinetics of Ni/SiC contact formation has been studied via deposition of about 50nm Ni film on 4H–SiC (Si terminated surface) by magnetron sputtering and subsequent annealings at temperatures of 500–700°C. X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM) and Auger electron spectroscopy (AES) techniques were used to investigate the interface reaction products upon annealing and element distribution across the reaction layer. It is found that the thermodynamically stable silicide Ni₂Si begins to form at the contact interface as a result of sample annealing above 600°C, which associated with producing carbon distributed at the surface and at the interface of the silicide with the SiC substrate. The kinetic process is described to mainly include the solid state interface reactions and the diffusion of components through the produced layer of silicides. When the diffusion layer is thick enough (more than 100nm), the kinetic feature is thought to be diffusion controlled, which follows the parabolic law. The active energy of Ni silicide formation was derived as (135.0±19.51)kJmol⁻¹.

Keywords: PACS; 68.55.−a; 81.15.Cd; 82.65+r4H–SiC; Interfacial reaction; Chemical kinetics

Investigation of the structure and surface characteristics of Cu–Ni–M(III) mixed oxides (M=Al, Cr and In) prepared from layered double hydroxide precursors by Hui Wang; Xu Xiang; Feng Li; David G. Evans; Xue Duan (pp. 6945-6952).

The Cu–Ni–M(III) mixed oxides (M=Al, Cr and In) were prepared by calcination of layered double hydroxide precursors with Cu²⁺/Ni²⁺/M³⁺ ratio of 1/2/1. The materials were characterized by means of powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR), thermogravimetric-differential thermal analysis (TG-DTA), X-ray photoelectron spectroscopy (XPS) and low temperature N₂ adsorption–desorption experiments. The results indicated that calcination of precursors at 500°C gave rise to mixed metal oxides including simple oxides and composite oxides, and the composition distributions of obtained oxides depended on the nature of trivalent cation in precursors. Under mild experimental conditions (atmospheric pressure and 25°C), oxidation of aqueous phenol solutions by hydrogen peroxide exhibited that the Cr-containing mixed oxide achieved the highest conversion of phenol owing to the presence of more amount of composite oxide phase containing active copper centers, while the aluminum-containing one could significantly enhance deep oxidation of phenol into smaller molecules owing to the presence of more surface oxygen species.

Keywords: Metal oxides; Microstructure; Precursor; Surface

Optical properties of zinc peroxide and zinc oxide multilayer nanohybrid films by Dániel Sebők; Tamás Szabó; Imre Dékány (pp. 6953-6962).

Zinc peroxide and zinc oxide nanoparticles were prepared and self-assembled hybrid nanolayers were built up using layer-by-layer (LbL) technique on the surface of glass substrate using the layer silicate hectorite and an anionic polyelectrolyte, sodium polystyrene sulfonate (PSS). Light absorption, interference and morphological properties of the hybrid films were studied to determine their thickness and refractive index. The influence of layer silicates and polymers on the self-organizing properties of ZnO₂ and ZnO nanoparticles was examined. X-ray diffraction revealed that ZnO₂ powders decomposed to ZnO (zincite phase) at relatively low temperatures (less than 200°C). The optical thickness of the films ranged from 190 to 750nm and increased linearly with the number of layers. Band gap energies of the ZnO₂/hectorite films were independent from the layer thickness and were larger than that of pure ZnO₂ nanodispersion. Decomposition of ZnO₂ to ZnO and O₂ at 400°C resulted in the decrease of the band gap energy from 3.75 to 3.3eV. Concomitantly, the refractive index increased in correlation with the formation of the zincite ZnO phase. In contrast, the band gap energies of the ZnO₂/PSS hybrid films decreased with the thickness of the nanohybrid layers. We ascribe this phenomenon to the steric stabilization of primary ZnO₂ particles present in the confined space between adjacent layers of hectorite sheets.

Keywords: ZnO; ₂; nanoparticles; ZnO nanohybrid films; Optical properties; Optical interference; Band gap energy; Self-assembly

DRIFTS study of different gas adsorption for CO selective oxidation on Cu–Zr–Ce–O catalysts by Chen Shengzhou; Hanbo Zou; Zili Liu; Weiming Lin (pp. 6963-6967).

The adsorptions of different gases (CO, H₂ and O₂) in the hydrogen-rich gas on the co-precipitated Cu–Zr–Ce–O catalyst were discussed and the active sites were ascertained with infrared spectroscopy technique. It was shown that the adsorption strength of CO was stronger than that of O₂ or H₂. Hydrogen and CO were competitive adsorption and the coexistence H₂ and CO on the surface accelerated the rate of CO desorption. Adsorbed H₂ could convert into geminal OH groups on the ceria surface at high temperatures in the absence of oxygen, while it was easy to form surface hydroxyl groups at low temperatures and condensed to physical water with increasing desorption temperature in the existence of oxygen. The adsorption of CO₂ was strong and it could transform into thermal stable carbonate species even in the reaction conditions. The active sites of the Cu–Zr–Ce–O catalyst were Cu²⁺ and Cu⁺, mainly the latter. The oxygen defect sites could be formed on the Cu–Zr–Ce–O catalyst surface through dehydration and decarboxylation.

Keywords: CO selective oxidation; Cu–Zr–Ce–O catalyst; DRIFTS; Gas adsorption

Corrosion protection of Mg/Al alloys by thermal sprayed aluminium coatings by A. Pardo; P. Casajús; M. Mohedano; A.E. Coy; F. Viejo; B. Torres; E. Matykina (pp. 6968-6977).

The protective features of thermal sprayed Al-coatings applied on AZ31, AZ80 and AZ91D magnesium/aluminium alloys were evaluated in 3.5wt.% NaCl solution by electrochemical and gravimetric measurements. The changes in the morphology and corrosion behaviour of the Al-coatings induced by a cold-pressing post-treatment were also examined. The specimens were characterized by scanning electron microscopy, energy dispersive X-ray analysis and low-angle X-ray diffraction. The as-sprayed Al-coatings revealed a high degree of porosity and poor corrosion protection, which resulted in galvanic acceleration of the corrosion of the magnesium substrates. The application of a cold-pressing post-treatment produced more compact Al-coatings with better bonding at the substrate/coating interface and higher corrosion resistance regardless of the nature of the magnesium alloy.

Keywords: Magnesium; Aluminium coatings; Corrosion; Thermal spraying

Controlling growth of ZnO rods by polyvinylpyrrolidone (PVP) and their optical properties by S.F. Wei; J.S. Lian; Q. Jiang (pp. 6978-6984).

ZnO rods with different morphologies were synthesized through a wet chemical method by addition of polyvinylpyrrolidone (PVP). By adjusting the concentration of the additive in the growth solution, we can control the diameter, ratio of length to diameter and density of ZnO rods. FESEM images showed that the rods in nanoscale could be obtained at the polyvinylpyrrolidone concentration of 1.0mM. Meanwhile, the resonant Raman scattering and photoluminescence spectra showed that the crystalline quality and the optical property of ZnO rods were improved through moderate addition of polyvinylpyrrolidone (concentration of 1.0mM) in the growth solution. In addition, the possible mechanism of the PVP effect on the growth of ZnO rods was discussed based on the FT-IR spectra.

Keywords: ZnO rods; Polyvinylpyrrolidone; Nanoscale; Resonant Raman scattering; Photoluminescence

Auger and photoluminescence analysis of ZnO nanowires grown on AlN thin film by Ramin Yousefi; Burhanuddin Kamaluddin; Mahmood Ghoranneviss; Fatemeh Hajakbari (pp. 6985-6988).

ZnO nanowires were grown on AlN thin film deposited on the glass substrates using a physical vapor deposition method in a conventional tube furnace without introducing any catalysts. The temperature of the substrates was maintained between 500 and 600°C during the growth process. The typical average diameters of the obtained nanowires on substrate at 600 and 500°C were about 57 and 22nm respectively with several micrometers in length. X-ray diffraction and Auger spectroscopy results showed Al diffused from AlN thin film into the ZnO nanowires for the sample grown at 600°C. Photoluminescence of the nanowires exhibits appearance of two emission bands, one related to ultraviolet emission with a strong peak at 380–382nm, and the other related to deep level emission with a weak peak at 503–505nm. The ultraviolet peak of the nanowires grown at 500°C was blue shifted by 2nm compared to those grown at 600°C. This shift could be attributed to surface effect.

Keywords: PACS; 71.55.Gs; 78.55.EtZnO nanowires; AlN thin film; Diffusion; Photoluminescence; Auger spectroscopy

Engineering the Maxwell–Wagner polarization effect by T. Prodromakis; C. Papavassiliou (pp. 6989-6994).

Layered structures, when supporting the Maxwell–Wagner polarization mechanism, exhibit very large effective electric permittivity and thus can be used for miniaturizing purposes. However, the large interfacial dimensions evolved, limit the Maxwell–Wagner polarization at relatively low frequencies. Any element or mechanism that causes a spatial variation of charge density, contributes to the dielectric susceptibility of a medium. Thus, intentionally planted polarization states can be used for further exploiting the Maxwell–Wagner polarization mechanism.

Keywords: Maxwell–Wagner polarization; Slow-wave mode; Dielectric loading

Tip–surface interactions at redox responsive poly(ferrocenylsilane) (PFS) interface by AFM-based force spectroscopy by Hong Jing Chung; Jing Song; G. Julius Vancso (pp. 6995-6998).

Poly(ferrocenylsilanes) (PFS) belong to the class of redox responsive organometallic polymers. Atomic force microscopy (AFM)-based single molecule force spectroscopy (SMFS) was used earlier to study single chain PFS response and redox energy driven single chain PFS molecular motors. Here we present further AFM investigations of force interactions between tip and a grafted PFS surface under potential control in electrochemical redox cycles. Typical tip–Au interaction is considered as reference in the force measurements. First the electrostatic component in the diffused double layer (DL) in NaClO₄ electrolyte environment was considered for a “grafted to” PFS, which dominated the interplay between the tip and sample surface. The DL forces can also hinder the physisorption of PFS chain onto the tip when the voltage was applied at −0.1V. On the other hand, if the tip contacted the PFS surface prior to the electrochemical process, physisorption of PFS chains governed the overall interaction regardless of subsequently applied surface potential. In addition, prolonged contact time, t_c, may also contribute to the stability of tip–PFS bridging and detection of electrostatic forces between the tip–PFS interface. The results showed that tip–substrate interaction forces without PFS grafts have negligibly small force contributions under similar, electrochemically controlled, conditions used in single PFS chain based molecular motors.

Keywords: AFM force spectroscopy; Poly(ferrocenylsilane) (PFS)

Tribological properties of silicate materials on nano and microscale by Ph. Tordjeman; N. Morel; M. Ramonda (pp. 6999-7004).

We studied the friction properties of four model silicate materials at the nanoscale and microscale. From nanotribology, we characterized the tribological properties at single asperity contact scale and from microtribology, we characterized the tribological properties at multi asperity contact scale. First, for each material we measured chemical composition by XPS, Young's modulus by acoustical microscopy and roughness σ by atomic force microscopy (AFM). Second, we measured the nanofriction coefficients with an AFM and the microfriction coefficients with a ball probe tribometer, for three hardnesses of the ball probe. We identified one friction mechanism at the nanoscale (sliding friction) and two friction mechanisms at the microscale (sliding friction and yielding friction). Comparison of the nano and microfriction coefficients at the same sliding friction regime shown, that the tribological properties of these materials didn’t depend on roughness.

Keywords: Nanotribology; Microtribology; Silicate materials; Roughness

Defect effect on tribological behavior of diamond-like carbon films deposited with hydrogen diluted benzene gas in aqueous environment by Jin Woo Yi; Se Jun Park; Myoung-Woon Moon; Kwang-Ryeol Lee; Seock-Sam Kim (pp. 7005-7011).

This study examined the friction and wear behavior of diamond-like carbon (DLC) films deposited from a radio frequency glow discharge using a hydrogen diluted benzene gas mixture. The DLC films were deposited on Si (100) and polished stainless steel substrates by radio frequency plasma-assisted chemical vapor deposition (r.f.-PACVD) at hydrogen to benzene ratios, or the hydrogen dilution ratio, ranging from 0 to 2.0. The wear test was carried out in both ambient and aqueous environments using a homemade ball-on-disk type wear rig. The stability of the DLC coating in an aqueous environment was improved by diluting the benzene precursor gas with hydrogen, suggesting that hydrogen dilution during the deposition of DLC films suppressed the initiation of defects in the film and improved the adhesion of the coating to the interface.

Keywords: DLC; Hydrogen dilution; Aqueous environment; Spallation wear; Defect

Characterization of CdTe films with in situ CdCl₂ treatment grown by a simple vapor phase deposition technique by Araceli Rios Flores; R. Castro-Rodríguez; J.L. Peña; N. Romeo; A. Bosio (pp. 7012-7016).

A unique vapor phase deposition (VPD) technique was designed and built to achieve in situ CdCl₂ treatment of CdTe film. The substrate temperature was 400°C, and the temperature of CdTe mixture with CdCl₂ source was 500°C. The structural and morphological properties of CdTe have been studied as a function of wt.% CdCl₂ concentration by using X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM) and atomic force microscopy (AFM). XRD measurements show that the presence of CdCl₂ vapor induces (111)-oriented growth in the CdTe film. SEM measurements have shown enhance growth of grains, in the presence of CdCl₂. From AFM the roughness of the films showed a heavy dependence on CdCl₂ concentration. In the presence of 4% CdCl₂ concentration, the CdTe films roughness has a root mean square (rms) value of about 275Å. This value is about 831Å for the non-treated CdTe films.

Keywords: PACS; 81.15.Kk; 81.15.−z; 81.05.Dz; 68.37.Hk; 68.37.Ps; 61.05.cp In situ; CdCl; ₂; treatment; Solar cells CdS/CdTe; Vapor phase deposition

Effect of substrate annealing on the quality of pulsed laser deposited Zn1−_xMg_xO thin films by Gaurav Shukla; Alika Khare (pp. 7017-7020).

The annealing effects of sapphire substrate before deposition on the quality of epitaxial Zn1−_xMg_xO thin films grown by pulsed laser deposition are reported. Our Experimental results indicate that the surface quality of Zn1−_xMg_xO thin films and hexagonal columnar growth is improved on the annealed sapphire substrate at high temperatures due to formation of atomic terraces on the substrate surface. The photoluminescence signals also increases with the increasing annealing temperature of the substrate.

Keywords: Thin films; Deposition; Epitaxial growth

Synthesis of nearly monodisperse nanoparticles in alcohol: A pressure and solvent-induced low-temperature strategy by Guozhu Li; Xianyu Li; Wenchao Peng; Xiaobin Fan; Guoliang Zhang; Fengbao Zhang (pp. 7021-7027).

Nearly monodisperse nanoparticles were synthesized by an environmentally benign low-temperature (140–180°C) method involving pressure-induced decomposition of metal oleates in alcohol. XRD and TEM were employed in the characterization of the samples. In this study, Fe₃O₄, CoO, MnO, CoFe₂O₄, MnFe₂O₄, and a mixture of Ni, NiO, Ni₂O₃ nanoparticles, exhibiting various shapes and assemblies, were obtained.

Keywords: Synthesis; Nanoparticles; Shape; Assemble

Low-temperature growth of polycrystalline Ge thin film on glass by in situ deposition and ex situ solid-phase crystallization for photovoltaic applications by Chao-Yang Tsao; Jürgen W. Weber; Patrick Campbell; Per I. Widenborg; Dengyuan Song; Martin A. Green (pp. 7028-7035).

Poly-crystalline germanium (poly-Ge) thin films have potential for lowering the manufacturing cost of photovoltaic devices especially in tandem solar cells, but high crystalline quality would be required. This work investigates the crystallinity of sputtered Ge thin films on glass prepared by in situ growth and ex situ solid-phase crystallization (SPC). Structural properties of the films were characterized by Raman, X-ray diffraction and ultraviolet–visible reflectance measurements. The results show the transition temperature from amorphous to polycrystalline is between 255°C and 280°C for in situ grown poly-Ge films, whereas the transition temperature is between 400°C and 500°C for films produced by SPC for a 20h annealing time. The in situ growth in situ crystallized poly-Ge films at 450°C exhibit significantly better crystalline quality than those formed by solid-phase crystallization at 600°C. High crystalline quality at low substrate temperature obtained in this work suggests the poly-Ge films could be promising for use in thin film solar cells on glass.

Keywords: Poly-crystalline germanium; Thin film; Sputtering; Solid-phase crystallization

Mineralization of surfactant functionalized multi-walled carbon nanotubes (MWNTs) to prepare hydroxyapatite/MWNTs nanohybrid by Qinggang Tan; Ke Zhang; Shuying Gu; Jie Ren (pp. 7036-7039).

Multi-walled carbon nanotubes (MWNTs) were well dispersed in water and functionalized by adding surface active agent (i.e., sodium dodecyl sulfate, SDS). Subsequently, biomimetic mineralization was carried out on the SDS functionalized MWNTs by using an alternate soaking process (ASP) in the Ca/P solutions. As-prepared samples were characterized by transmission electron microscope, infrared spectrum and X-ray diffraction. The results show that nano-HA crystals were formed on the SDS functionalized MWNTs and the mineralized MWNTs remained a dispersing state. As-prepared HA–MWNTs nanohybrid combining the osteconductive property of HA and the excellent mechanical property of MWNTs will provide a promising material for bone tissue engineering.

Keywords: Multi-walled carbon nanotubes; Surface active agent; Mineralization; Hydroxyapatite

Study on the hydrophobic surfaces prepared by two-step sol–gel process by Shi-Ing Huang; Yi-Ju Shen; Hui Chen (pp. 7040-7046).

In this study, the two-step sol–gel process was used to prepare hydrophobic coating films on the glass substrates. The first step was to add hydrogen chloride into TEOS (tetraethoxysilane) solution, and then the second step was to add ammonia into the above reacted solution. We adopted different amount of hydrogen chloride and ammonia to control the sol–gel reaction and observed the change of the viscosity, gelatin period of the solution and contact angles of the coating films. By this method, we created a surface with roughness and then the hydroxyl groups were terminated by adding trimethylchlorosilane (TMCS) to produce a hydrophobic coating layer. The amount of the acid, base and water added in the solution influenced the reaction rate and resulted in the aggregation and condensation of the particles to form rough surfaces. Consequently, the rough surfaces made by aggregation and condensation of the large particles, which were modified by TMCS resulted in higher contact angles (>140°). In this study, a surface with contact angle 150° was obtained.

Keywords: Hydrophobic; Sol–gel; TEOS; Viscosity; Contact angle

Investigations on Fe³⁺ doped polyvinyl alcohol films with and without gamma (γ)-irradiation by G. Vijaya Kumar; R. Chandramani (pp. 7047-7050).

This paper deals with the preparation of pure and ferric chloride (FeCl₃) doped polyvinyl alcohol (PVA) films by solution casting method. Optical and electrical properties were systematically investigated. We have found the decrease in optical band gap energy of PVA films on doping FeCl₃. The optical band gap energy values in the present work are found to be 3.10eV for pure PVA, 2eV for PVA:Fe³⁺ (5mol%), 1.91eV for PVA:Fe³⁺(15mol%) and 1.8eV for PVA:Fe³⁺(25mol%). Direct current electrical conductivity ( σ) of pure, FeCl₃ doped PVA films in the temperature range 70–127°C has been studied. At 387K dc electrical conductivity of pure PVA film is 5.5795μΩ⁻¹cm⁻¹, PVA:Fe³⁺ (5mol%) film is 10.0936μΩ⁻¹cm⁻¹ and γ-Irradiated PVA:Fe³⁺ (5mol%) film for 900CGY/min is 22.1950μΩ⁻¹cm⁻¹. The result reveals the enhancement of the electrical conductivity with γ-irradiation. FT-IR study signifies the intermolecular hydrogen bonding between Fe³⁺ ions of FeCl₃ with OH group of PVA.

Keywords: Polyvinyl alcohol; Fe; ³⁺; ions; Dc electrical conductivity

Preparation and properties of electroless Ni–P–SiO₂ composite coatings by D. Dong; X.H. Chen; W.T. Xiao; G.B. Yang; P.Y. Zhang (pp. 7051-7055).

Dispersible SiO₂ nanoparticles were co-deposited with electroless Ni–P coating onto AISI-1045 steel substrates in the absence of any surfactants in plating bath. The resulting Ni–P/nano-SiO₂ composite coatings were heat-treated for 1h at 200°C, 400°C, and 600°C, respectively. The hardness and wear resistance of the heat-treated composite coatings were measured. Moreover, the structural changes of the composite coatings before and after heat treatment were investigated by means of X-ray diffraction (XRD), while their elemental composition and morphology were analyzed using an energy dispersive spectrometer (EDS) and a scanning electron microscope (SEM). Results show that co-deposited SiO₂ particles contributed to increase the hardness and wear resistance of electroless Ni–P coating, and the composite coating heat-treated at about 400°C had the maximum hardness and wear resistance.

Keywords: Electroless plating; Ni–P alloy coating; SiO; ₂; nanoparticles; Composite coating; Hardness; Wear resistance

Initial oxidation of duplex stainless steel by Črtomir Donik; Aleksandra Kocijan; Djordje Mandrino; Irena Paulin; Monika Jenko; Boris Pihlar (pp. 7056-7061).

Three different techniques were used to produce thin oxide layers on polished and sputter-cleaned duplex stainless-steel samples. These samples were exposed to 10⁻⁵mbar of pure oxygen inside the vacuum chamber, exposed to ambient conditions for 24h, and plasma oxidized. The oxide layers thus produced were analysed using XPS depth profiling in order to determine the oxide layers’ compositions with depth. We found that all the techniques produce oxide layers with different traces of metallic components and with the maximum concentration of chromium oxide shifted towards the oxide-layer–bulk-metal interface. A common characteristic of all the oxide layers investigated is a double-oxide stratification, with regions closer to the surface exhibiting higher concentrations of iron oxide and those more in-depth exhibiting higher concentrations of chromium oxide. A simple non-destructive Thickogram procedure was used to corroborate the thickness estimates for the thinnest oxide layers.

Keywords: Duplex stainless steel; Stainless steel; Oxidation; XPS; Thickogram; Plasma oxidation

High temperature corrosion behaviour of some Fe-, Co- and Ni-base superalloys in the presence of Y₂O₃ as inhibitor by Harpreet Singh; Gitanjaly; Surendra Singh; S. Prakash (pp. 7062-7069).

High temperature corrosion is accelerated degradation of materials at higher temperatures of operation caused by the presence of a deposit of salt or ash. Inhibitors and fuel additives have been investigated with varying success to control this type of corrosion. In this work, effect of an oxide additive namely Y₂O₃ on the hot corrosion behaviour of some superalloys viz Superfer 800H (alloy A), Superco 605 (alloy B) and Superni 75 (alloy C) has been investigated in an Na₂SO₄–60%V₂O₅ environment at 900°C for 50 cycles. Each cycle consisted of 1h heating in a Silicon Carbide Tube Furnace followed by 20min cooling in ambient air. Weight data were taken by an electronic balance having an accuracy of 0.01mg after each cycle. Subsequently, the exposed alloys were characterized by XRD, SEM and EPMA analyses to evaluate the role of the oxide additive. In the Na₂SO₄–60%V₂O₅ environment, the corrosion rate for the Co-base alloy was found to be highest, whereas that for the Ni-base Superni 75 the lowest. Superficially applied Y₂O₃ was observed to be useful in reducing the high temperature corrosion of the alloys. It was found to be most effective for the alloy A for which the oxide scale was continuous and rich in protective Cr. Alloy B showed the formation of medium size scale rich in Cr and Co. The oxide scale for the alloy C contained mainly Cr and Ni.

Keywords: High temperature corrosion; Superalloys; Inhibitors; Oxide additives; Oxide scales

Junction characteristics of C₆₀/polycarbonate blend on Si substrate by S.S. Sharma; B. Tripathi; M. Singh; D. Bhatnagar; Y.K. Vijay (pp. 7070-7072).

We report a study of the interface between fullerene (C₆₀) doped polycarbonate (PC) blends and n-type Si substrate. C₆₀ is usually an electron acceptor in interpenetrated networks and an electron transport in photovoltaic cells. We have studied that the guest–host approach to prepare C₆₀ doped polycarbonate blend. In this article, we report the I–V characteristics of C₆₀ doped polycarbonate/n-type Si junction and the annealing effect on these characteristics. In this junction, a nanocomposite of organic semiconductor fullerene (C₆₀), used as the active medium, with an inert polycarbonate matrix was spin coated on n-type Si substrate. We found that the C₆₀ shows the junction characteristics with n-type Si substrate. The knee voltage and dynamic resistance varies with concentration of C₆₀ as well as temperature. Ellipsometry studies showed the annealing effect on the refractive index and thickness of C₆₀ doped polycarbonate blend on n-type Si substrate. The optical micrographs show that fullerene (C₆₀) is spherical molecule and it is blend in the form of crystallites having size of micron order.

Keywords: Fullerene; Polycarbonate; Annealing; Ellipsometry; Refractive index

Preparation of superhydrophobic membranes by electrospinning of fluorinated silane functionalized poly(vinylidene fluoride) by Yingbo Chen; Hern Kim (pp. 7073-7077).

Fluorinated silane functionalized poly(vinylidene fluoride) (PVDF) is synthesized by graft polymerization of 3-trimethoxylpropyl methylacrylate with PVDF followed by coupling of fluorinated silanes. Flat membrane prepared using this functionalized PVDF has a water contact angle of 140°. Superhydrophobic PVDF membrane with a contact angle larger than 150° is prepared by the electrospinning of the fluorinated silane functionalized PVDF. The morphologies of the membranes are characterized using scanning electron microscopy. The surface composition of the membranes is analyzed using FTIR and the contact angles and water drops on the surface of the membrane are measured using video microscopy.

Keywords: PACS; 68.37−d; 81.05.Kf; 81.07.−bPolymer surfaces; Superhydrophobicity; Electrospinning; Nanofiber membrane

Chemical bond formation during laser bonding of Teflon^® FEP and titanium by Grigor L. Georgiev; Ronald J. Baird; Erik F. McCullen; Golam Newaz; Gregory Auner; Rahul Patwa; Hans Herfurth (pp. 7078-7083).

Teflon^® FEP (fluorinated ethylene propylene) is resistant to most chemical solvents, is heat sealable and has low moisture uptake, which make this polymer attractive as a packaging materials for electronics and implantable devices. Teflon^® FEP/Ti microjoints were fabricated by using focused infrared laser irradiation. Teflon^® FEP/Ti interfaces were studied by using X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and scanning electron microscopy coupled with energy dispersive spectroscopy (SEM–EDS). The XPS results give evidence for the formation of Ti–F bonds in the interfacial region. The AES and SEM–EDS results show that the chemical bond formation occurs only in the actual bond area. No evidence for chemical bond formation was found in the heat affected zone surrounding the laser bonds.

Keywords: Teflon; ^®; FEP/Ti interfaces; Laser fabrication; XPS; AES; EDS

Coating of carbon nanotubes on flexible substrate and its adhesion study by Abdelaziz Rahy; Pooja Bajaj; Inga H. Musselman; Soon Hyung Hong; Ya-Ping Sun; Duck J. Yang (pp. 7084-7089).

The primary goal of this project was to develop a flexible transparent conductor with 100Ω/sq and 90% transmittance in the wavelength range of 400–700nm on a flexible substrate. The best result achieved so far was 110Ω/sq at 88% transmittance using purified single-walled carbon nanotubes (SWNTs) coated on a polyethylene naphthalate (PEN) substrate. The secondary goal was to simplify the overall coating procedure; we successfully reduced the process from five (prior art method) to three steps utilizing a sonication method. We also found that the use of metallic SWNTs significantly improved the conductivity and transmittance compared with the use of mixed SWNTs, i.e., unseparated SWNTs. Furthermore, a possible adhesion mechanism between SWNTs and the surface of PEN was studied; we concluded that a π–π stacking effect and a hydrophobic interaction are the major contributing factors for SWNTs to adhere to the surface of the substrate.

Keywords: Conductive coating; Flexible substrate; Carbon nanotube; Adhesion

Optically active helical polyurethane@attapulgite composites: Effect of optical purity of S-1,1′-binaphthyl-2,2′-diol on infrared emissivity by Zhiqiang Wang; Yuming Zhou; Yanqing Sun; Zhenyu Mei; Yuee Miao (pp. 7090-7094).

Helical polyurethane@attapulgite (HPU@ATT) composites were prepared after the surface modification of the rod-like attapulgite (ATT). HPU@ATT composites based on S-1,1′-binaphthyl-2,2′-diol (S-BINOL) with different optical purity (O.P.) were characterized by Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and thermogravimetric analysis (TGA). The results indicate that the helical polyurethane has been successfully grafted onto the surfaces of the modified ATT without destroying the original crystalline structure of ATT. The rod-like nanoparticles were confirmed by transmission electron microscopy (TEM). Infrared emissivity values of HPU@ATT composites have been investigated, and the results indicate that the optical purity of monomer plays a very important role in the infrared emissivity for HPU@ATT owing to the effect of helical conformation and interchain hydrogen bonds. Along with the increased optical purity of S-BINOL, the infrared emissivity of HPU@ATT is reduced evidently. Infrared emissivity value of HPU@ATT based on S-BINOL with 100% optical purity is the lowest one (0.431).

Keywords: PACS; 81.07.Pr; 82.35.Np; 64.60.Qb; 78.66.Sq; 68.55.AcPolyurethane; Attapulgite; Helical structure; Optical purity; Infrared emissivity

One-step preparation of water-soluble single-walled carbon nanotubes by Li Zhang; Qing-Qing Ni; Yaqin Fu; Toshiaki Natsuki (pp. 7095-7099).

A novel one-step process using potassium persulfate (KPS) as oxidant is proposed in this paper to prepare water-soluble single-walled carbon nanotubes (SWNTs). The process without the need for organic solvents and acids is a low-cost, eco-friendly, facile method. Morphology observation by atomic force microscopy (AFM) indicates that the KPS-treated SWNTs were effectively debundled without obvious shortening in their length. The functional groups and thermal stability of the treated SWNTs were analyzed by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA). XPS results show that several functional groups such as potassium carboxylate (–COOK), carbonyl (–CO) and hydroxyl (–C–OH) groups were formed on the surfaces of the SWNTs, while the TGA results reveal that the quantity of the functional groups can reach to approximately 20%.

Keywords: Carbon nanotubes; Water-soluble; Potassium persulfate

Effect of Cu addition on whisker formation in tin-rich solder alloys under thermal shock stress by A. Skwarek; J. Ratajczak; A. Czerwinski; K. Witek; J. Kulawik (pp. 7100-7103).

This article focuses on the influence of thermal shocks and Cu addition on tin whiskers growth on the surface of tin-rich materials and alloys. The tests were carried out on real samples manufactured with classical PCB technology. Four Pb-free materials i.e. pure Sn, Sn99Cu1, Sn98Cu2 and Sn97Cu3 were tested from the point of view of susceptibility to whisker formation after thermal shocks. Results show that all tested materials were prone for whisker formation. Copper addition in coexistence with thermal shocks did not promote the growth of filament-like whiskers.

Keywords: Pb-free alloys; Whiskers; SEM; Thermal shocks

Diamond-like phase formation in an amorphous carbon films prepared by periodic pulsed laser deposition and laser irradiation method by Jaanus Eskusson; Raivo Jaaniso; Enn Lust (pp. 7104-7108).

Diamond-like carbon (DLC) films were fabricated by pulsed laser ablation of a liquid target. During deposition process the growing films were exited by a laser beam irradiation. The films were deposited onto the fused silica using 248nm KrF eximer laser at room temperature and 10⁻³mbar pressure. Film irradiation was carried out by the same KrF laser operating periodically between the deposition and excitation regimes. Deposited DLC films were characterized by Raman scattering spectroscopy. The results obtained suggested that laser irradiation intensity has noticeable influence on the structure and hybridization of carbon atoms deposited. For materials deposited at moderate irradiation intensities a very high and sharp peak appeared at 1332cm⁻¹, characteristic of diamond crystals. At higher irradiation intensities the graphitization of the amorphous films was observed. Thus, at optimal energy density the individual sp³-hybridized carbon phase was deposited inside the amorphous carbon structure. Surface morphology for DLC has been analyzed using atomic force microscopy (AFM) indicating that more regular diamond cluster formation at optimal additional laser illumination conditions (∼20mJ per impulse) is possible.

Keywords: Pulsed laser deposition; Diamond-like carbon; Liquid target; Thin film growth; Raman scattering spectroscopy; DLC

Erratum to “Using a chemical concept for reactivity for the interpretation of STM images of physisorbed molecules” [Appl. Surf. Sci. 253 (2007) 9047–9053] by Heiko Gawronski; Karina Morgenstern (pp. 7109-7109).

Sections

Personal tools

Applied Surface Science (v.255, #15)

Sections

Personal tools

Local resources

Applied Surface Science (v.255, #15)