Applied Surface Science (v.256, #16)

The electrochemical and mechanical properties of Ti incorporated amorphous carbon films in Hanks’ solution by Chunfu Hong; Jiangping Tu; Dongguang Liu; Ruiling Li; Changdong Gu (4859-4866).
Ti incorporated amorphous carbon (a-C) films with variant Ti contents were prepared by the unbalanced magnetron sputtering process. Scanning electron microscopy, ultraviolet Raman spectroscopy, X-ray photoelectron spectroscopy and transmission electron microscopy were used to characterize the microstructure of a-C films. The hardness and lubricated tribological properties were assessed using nanoindentation and ball-on-disk tribometer. As the Ti content in a-C films increases from 0 to 15.2 at.%, the sp 3 volume fraction, the internal stress and the hardness of the films decreases gradually, while the disorder of sp 2 bond increases. The electrochemical tests reveal that the a-C films with lower than 1.5 at.% Ti possess good corrosion resistance in Hanks’ solution, while the a-C film with 15.2 at.% Ti is susceptible to crevice corrosion. The reduced friction of the a-C films is due to the sp 2 bonded film surface and boundary lubrication of the Hanks’ solution. The a-C film with 3.1 at.% Ti exhibits the best wear resistance in Hanks’ solution among the studied films.
Keywords: Amorphous carbon; Electrochemistry; Lubricated wear; Microstructure; Hank's solution;

Water and oil repellency of flexible silica-coated polymeric substrates by Chien-Te Hsieh; Yu-Shun Cheng; Shu-Min Hsu; Jia-Yi Lin (4867-4872).
A facile coating technique was used for the one-step creation of silica-sphere layers onto flexible polypropylene (PP) substrates, which showed the enhanced repellency toward liquid droplets with different surface tensions, ranging from 25.6 to 72.3 mN/m. One-step solution preparation comprised the homogenous mixing of colloidal silica nanospheres and perfluoroalkyl methacrylic copolymer, and the resulting F-silica slurry was subsequently deposited over the PP films, which showed good adhesion. The flexible silica-coated polymeric film displayed a remarkable repellency toward water and oil drops, when compared with the F-coated PP flat film. The silica-stacking layers on the PP substrate generated a roughened surface, owing to the creation of bionic surface hierarchically combined with multiple-scale architecture. To clarify this, the wetted fraction was determined from Cassie–Baxter equation, and the work of adhesion, based on Young–Duprè equation, was used to examine the sliding ability of the resulting polymeric films. The cross-cut test incorporated with film bending proved the excellent adherence between silica layer and PP substrate. A satisfactory durability in water and oil immersions for 10 days showed that the resulting PP film possesses strong adhesion and better repellency for a long period, confirming a promising commercial feasibility.
Keywords: Polymeric substrate; Water repellency; Oil repellency; Work of adhesion; Silica sphere; Contact angle;

Morphology and microstructure of patterned nickel incorporated amorphous carbon films by simple pyrolysis by Shanhong Wan; Yuanlie Yu; Junyan Zhang; Liping Wang (4873-4878).
A simple but novel pyrolysis technique for the fabrication of nickel incorporated diamond-like carbon films with ring-like pattern was presented. Without using any template under ambient atmospheric pressure, nickel incorporated diamond-like carbon films exhibited some regular ring-like patterns on the films surface dependent on the nickel content to some extent, characterized by scanning electron microscopy. Compared with pure carbon films, nickel incorporation greatly enhanced carbon films graphitization. Besides the influence of the treatment temperature, the formation of the as-deposited films with ring-like patterns was also closely related to the synergy of the catalysis effect of nickel particles and the induction to reduce surface tension.
Keywords: Diamond-like carbon film; Pyrolysis; Pattern; Surface tension;

Growth and characterization of Cd1−x Zn x Te thin films prepared from elemental multilayer deposition by Rajiv Ganguly; Sumana Hajra; Tamosha Mandal; Pushan Banerjee; Biswajit Ghosh (4879-4882).
Cd1−x Zn x Te is a key material for fabrication of high-energy radiation detectors and optical devices. Conventionally it is fabricated using single crystal growth techniques. The method adopted here is the deposition of elemental multilayer followed by thermal annealing in vacuum. The multilayer structure was annealed at different temperatures using one to five repetitions of Cd–Zn–Te sequence. X-ray diffraction pattern for the multilayer with five repetitions revealed that annealing at 475 °C yielded single-phase material compared to other annealing conditions. EDX spectroscopy was carried out to study the corresponding compositions. Photoluminescence properties and change of resistance of the multilayer under illumination were also studied. The resistivity of the best sample was found to be a few hundreds of Ω cm.
Keywords: CZT; Multilayer; Vapor deposition; X-ray diffraction; Luminescence;

GaN nanowires have been successfully synthesized on Si(1 1 1) substrates by magnetron sputtering through ammoniating Ga2O3/Cr thin films at 950 °C. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), FT-IR spectrophotometer, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (TEM), and photoluminescence (PL) spectrum were carried out to characterize the microstructure, morphology, and optical properties of GaN samples. The results demonstrate that the nanowires are single-crystal GaN with hexagonal wurtzite structure and high-quality crystalline, have the size of 30–80 nm in diameter and several tens of microns in length with good emission properties. The growth direction of GaN nanowires is perpendicular to the fringe of (1 0 1) plane. The growth mechanism of GaN nanowires is also discussed in detail.
Keywords: GaN nanowires; Magnetron sputtering; Microstructure; Growth mechanism;

Electrochemical behavior of cobalt from 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid by Caina Su; Maozhong An; Peixia Yang; Hongwei Gu; Xinghua Guo (4888-4893).
The electrodeposition of metallic cobalt from a 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid was investigated. The electrochemical behavior of Co(II) in the ionic liquid on a platinum working electrode at 60 °C was studied by cyclic voltammetry and chronoamperometry. The results from the cyclic voltammetry showed that the electrodeposition of metallic Co in the ionic liquid was an irreversible process and controlled by the diffusion of Co(II) on a platinum working electrode. The average value of αn α was calculated to be 0.35 and the diffusion coefficient (D 0) of Co(II) was calculated to be 1.76 × 10−8  cm2/s at 60 °C. Chronoamperometric results indicated that the electrodeposition of Co on a platinum working electrode followed the mechanism of instantaneous nucleation and three-dimensional growth with diffusion-controlled. The cobalt plating was uniform, dense, shining in appearance with good adhesion to the platinum substrate at 60 °C. The scanning electron microscope (SEM) micrographs were used to confirm that the cobalt plating was denser and finer at 60 °C. Energy dispersive X-ray analysis (EDAX) profile showed that the obtained plating was pure cobalt. X-ray diffraction (XRD) pattern indicated that there was a preferred orientation direction and the average size of cobalt grains was 40 nm.
Keywords: Electrodeposition; Cobalt; Ionic liquid; Diffusion coefficient; Nucleation;

Due to the considerable scientific and commercial interest in poly(ethylene glycol) (PEG) grafted solid surfaces for biomedical applications, it is important to characterize the properties and behaviour of these modified surfaces. In this study, we applied a unique method to predict the magnitude of interactive forces exerted between a globular protein and PEG-grafted matrices. Carboxyl functionalized solid matrices were covalently grafted with PEG-amine derivatives at varying PEG surface concentrations and layer thicknesses by controlling the grafting reaction parameters. X-ray photoelectron spectroscopy was used to characterize these PEG-grafted matrices using the standard overlay model. A detailed and systematic correlation between PEG layer thickness and the distance between the grafted PEG chains resulted in valuable information regarding protein interactions with these PEG-grafted matrices. Finally, this predicted interaction behaviour was validated with fluorescent images obtained from fluorescein isothiocyanate-labelled Cytochrome c-conjugated solid matrices using confocal laser scanning microscopy.
Keywords: PEG; XPS; Conformation; Covalent grafting; Surface characterization; Protein interactions; FITC labelling;

Enhanced dielectric properties of lead barium zirconate thin films by manganese doping by Xihong Hao; Jiwei Zhai; Jing Zhou; Xiaowei Li; Xiwen Song; Shengli An (4902-4905).
(Pb0.5Ba0.5)ZrO3 (PBZ) and 1 mol% Mn-doped (Pb0.5Ba0.5)ZrO3 (Mn-PBZ) sol were successfully fabricated, and corresponding thin films were deposited on Pt(1 1 1)/TiO2/SiO2/Si(1 0 0) substrates by spin-coating method. Effects of Mn doping on the microstructure and electrical properties of PBZ thin films were investigated systemically. X-ray diffraction patterns showed that both films had a polycrystalline perovskite structure, and that the degree of (1 1 1) orientation were increased by Mn doping. Dielectric measurements illustrated that Mn-doped PBZ thin films not only had a larger dielectric constant, but also possessed a smaller dielectric loss. Accordingly, the tunability and the figure of merit of PBZ films were improved by Mn doping.
Keywords: Lead barium zirconate; Doping; Microstructure; Dielectric properties;

High temperature materials are necessary for the design of primary heat shields for future reusable space vehicles re-entering atmospheric planet at hypersonic velocity. During the re-entry phase on earth, one of the most important phenomena occurring on the heat shield is the recombination of atomic oxygen and this phenomenon is more or less catalyzed by the material of the heat shield. PM 1000 is planned to be use on the EXPERT capsule to study in real conditions its catalycity. Before the flight, it is necessary to perform measurements on ground test facility. Experimental data of the recombination coefficient of atomic oxygen under air plasma flow were obtained in the diffusion reactor MESOX on pre-oxidized PM 1000, for two total pressures 300 and 1000 Pa in the temperature range (850–1650 K) using actinometry and optical emission spectroscopy. In this investigation, the evolution of the recombination coefficient is dependent of temperature, pressure level and also of the chemical composition of the surface leading to one order of magnitude for a given temperature. The recombination coefficient is increasing with temperature and also dependent on the static pressure. The surface change due to the plasma exposure is inspected with SEM, XRD and XPS. As chromium oxide is the main part of the oxide layer formed during the oxidation in air plasma conditions, a sintered Cr2O3 sample was elaborated from powders to compare the data of the recombination coefficient obtained on PM 1000. Pre- and post-test analyses on the several materials were carried out using SEM, WDS, XRD and XPS.
Keywords: Intermetallics; Oxidation; Atom recombination; Heat and plasma treatment; Aerospace use;

Preferred orientations in nano-gold/silica/silicon interfaces by Sanjeev Vasisht; John Shirokoff (4915-4923).
Gold in contact with silicon substrates Si(1 0 0), Si(1 1 1), and SiO2 is studied by thermal evaporation and annealing in N2 using the modified sphere-plate technique. The final orientation distribution of crystalline Au films grown on Si substrate systems that incorporate a native amorphous oxide layer of silica and Au on amorphous silica (SiO2 glass) substrates is influenced by preferred orientations and twinning. Experimental evidence suggests that the orientation of Au{1 1 1} close packed planes (multiply twinned) was found to be of low-energy as the annealing temperature was increased to 530 °C and 920 °C. Additional orientations were observed for Au{1 0 0} on Si(1 0 0) substrates and Au{1 0 0}, {1 1 0}, and {3 1 1} on SiO2 substrates. After annealing at 920 °C the size distribution of the gold particles was determined to be within the range of 20–800 nm while the morphology of gold surface appears spherical to faceted in character. These results show similarities to recent findings for smaller nano-size 1D particles, islands and thin Au films on silicon annealed over lower temperature ranges.
Keywords: Solid–solid interfaces; Nano-micro-crystals; Preferred orientations; XRD; Pole figures; SEM; AFM;

The main purpose of this study is to develop trivalent chromium, Cr(III), conversion coatings on aluminum alloys. The influence of Cr(III) concentration and immersion time on structures and anticorrosive performance of the coatings has been investigated. Corrosion behaviors of the coatings were evaluated in a 0.5 M H2SO4 aqueous solution at room temperature using potentiodynamic polarization. The structure and valence state of the coatings were examined by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The addition of Cr(III) ions to the conversion bath considerably changes structures and compositions of the coatings. The coatings with Cr oxides possess a denser and thinner structure. Moreover, the corrosion resistance of Cr(III) coatings tends to decline with increasing immersion time due to the dissolution of coatings in the dipping period. According to XPS analysis, the Cr(III) conversion coatings are composed of Cr2O3, Cr(OH)3, Al2O3, Al(OH)3, ZrO2, Zr(OH)4, AlF3, and ZrF4, but no hexavalent chromium component in the coatings. The result indicates that the coatings prepared in the solution with 0.01 M Cr(III) for 5 min have the smoothest and densest structure and the best anticorrosive performance among all of conversion coatings in this work.
Keywords: Trivalent chromium conversion coating; Aluminum alloys; Corrosion resistance; Chromic sulfate; Immersion time;

Water condensation on zinc surfaces treated by chemical bath deposition by R.D. Narhe; Wenceslao González-Viñas; D.A. Beysens (4930-4933).
Water condensation, a complex and challenging process, is investigated on a metallic (Zn) surface, regularly used as anticorrosive surface. The Zn surface is coated with hydroxide zinc carbonate by chemical bath deposition, a very simple, low-cost and easily applicable process. As the deposition time increases, the surface roughness augments and the contact angle with water can be varied from 75° to 150°, corresponding to changing the surface properties from hydrophobic to ultrahydrophobic and superhydrophobic. During the condensation process, the droplet growth laws and surface coverage are found similar to what is found on smooth surfaces, with a transition from Cassie-Baxter to Wenzel wetting states at long times. In particular, it is noticeable in view of corrosion effects that the water surface coverage remains on order of 55%.
Keywords: Superhydrophobic surface; Condensation; Coalescence; Chemical bath deposition; Corrosion;

Characterization of ZnO thin film synthesized on alumina-rich spinel substrate by magnetron sputtering by Huili Tang; Jun Xu; Hongjun Li; Yongjun Dong; Yinzhen Wang; Feng Wu (4934-4937).
Zinc oxide (ZnO) thin film has been epitaxially grown on (1 1 1) Mg0.4Al2.4O4 substrate by RF-magnetron sputtering. In resonant Raman scattering, higher-order longitudinal optical phonon modes were clearly observed, revealing high optical quality of the ZnO film. Optical absorption indicated a visible exciton absorption at room temperature. The near band edge emission showed a red shift due to the shrinkage of the band gap with increasing the temperature.
Keywords: ZnO thin film; Semiconductor compounds; Magnetron sputtering;

Microstructures and tribological properties of plasma sprayed WC–Co–Cu–BaF2/CaF2 self-lubricating wear resistant coatings by Jianhui Yuan; Yingchun Zhu; Heng Ji; Xuebing Zheng; Qichao Ruan; Yaran Niu; Ziwei Liu; Yi Zeng (4938-4944).
A promising WC–Co–Cu–BaF2/CaF2 self-lubricating wear resistant coating was deposited via atmospheric plasma spraying (APS) process by using homemade feedstock powders composed of WC–Co, Cu and BaF2/CaF2 eutectic. The as-prepared cermet coatings had better frictional behavior comparing with the WC–Co coating. Moreover, the often-occurred decarburization of WC in APS process was noticeably improved due to the binding of copper and BaF2/CaF2 phase, which not only offered effective solid lubrication, but also acted as bind phases to mend the microstructure and protected WC from decomposition. The optimized specimen contained 10 wt.% Cu and 10 wt.% BaF2/CaF2 in a WC–Co matrix, which had excellent frictional and wear performance. The wear mechanism of the self-lubricating wear resistant coating was discussed with the microstructures, compositions and mechanical properties of the composite materials in detail.
Keywords: Wear; Plasma spraying; BaF2/CaF2; Coatings;

Effects of mesoporous structure and UV irradiation on in vitro bioactivity of titania coatings by Ya-Ping Guo; Hai-Xiong Tang; Yu Zhou; De-Chang Jia; Cong-Qin Ning; Ya-Jun Guo (4945-4952).
Mesoporous titania coatings (MTCs) with a pore size of 4.75 nm were prepared on Ti6Al4V substrates by a sol–gel process, and then irradiated with UV light at room temperature for 2 h. The effects of mesoporous structure and UV irradiation on the in vitro bioactivity were investigated. Simulated body fluid (SBF) tests reveal that the MTCs exhibit a high apatite-forming ability, which may be attributed to the following reasons: (i) the BET surface area of the MTCs is ∼190 m2/g, resulting in a greater density of Ti–OH groups than that without mesoporous structure; (ii) theoretical analysis reveals that the mesoporous structure can improve the driving force and nucleation rate of apatite precipitation in SBF. As compared with the MTCs, the UV-irradiated coatings do not exhibit any change in phase components and surface morphologies. However, the apatite-forming ability is higher on the UV irradiation coatings than on the MTCs because of the increase of Ti–OH groups and the improvement of wettability after UV irradiation. In addition, the investigation of the MG63 cell proliferation on the both substrates was performed. The results indicate that the MTCs before and after UV irradiation exhibit a good biocompatibility and are fit for the MG63 cell proliferation.
Keywords: Titania coating; Mesoporous structure; UV irradiation; Bioactivity; Cell proliferation;

The critical velocity for particle deposition in cold spraying is a key parameter, which depends not only on the material type, but also the particle temperature and oxidation condition. The dependency of deposition efficiency of cold spray Cu particles on the particle temperature and surface oxidation was examined. The effect of particle surface oxide scales on the interfacial microstructure and adhesive strength of the cold-sprayed Cu coatings was investigated. The results show that the deposition efficiency significantly increases with increasing the gas temperature but decreases with augmenting the oxygen content of the starting powder. The oxide inclusions at the interfaces between the deposited particles inhibit the effective bonding of fresh metals and remarkably lower the bond strength of the deposited Cu coatings on steel.
Keywords: Cold spraying; Copper coatings; Oxidation; Critical velocity; Adhesive strength;

Simulations of particles which are emitted in laser ablation have been performed by the method of Direct Simulation Monte Carlo to investigate the deposition profiles of the emitted particles. The influences of the temperature, pressure and stream velocity of the initial evaporated layer formed during laser ablation process on the profile of the deposited film have been examined. It is found that the temperature gives a minor influence on the deposition profile, whereas the stream velocity and the pressure of the initial evaporated layer have a greater impact on the deposition profile. The energy in the direction of surface normal (E ) and that in the parallel direction of the surface (E ||) are shown to increase and decrease, respectively after the laser irradiation due to collisions between the emitted particles, and this trend is magnified as the pressure increases. As a consequence, the stream velocity in the direction of surface normal increases with the increase in the pressure. A mechanism of the phenomenon that a metal with a lower sublimation energy shows a broader angular distribution of emitted particles is presented. It is suggested that low density of evaporated layer of a metal with a low sublimation energy at its melting point decreases the number of collisions in the layer, leading to the low stream velocity in the direction of surface normal, which results in the broader deposition profile of the emitted particles.
Keywords: Angular distribution; Pulsed laser deposition; Direct Simulation Monte Carlo; Sublimation energy;

Undoped and lithium (Li)-doped ZnO films were prepared by sol–gel method using spin coating technique. The effects of Li content on the crystallinity and morphological properties of ZnO films were assessed by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). XRD patterns of the films showed the hexagonal wurtzite type polycrystalline structure and that the incorporation of lithium leads to substantial changes in the structural characteristics of ZnO films. The SEM and AFM measurements showed that the surface morphology of the films was affected from the lithium incorporation. The wrinkle network was observed on the surface from both SEM and AFM results for undoped ZnO. The wrinkle structure disappeared with increasing Li content. The absorption spectra of the ZnO and 5% Li-doped ZnO (LZO5) films were carried out between 140 and 400 K temperatures. The optical band gap of ZnO and LZO5 films (calculated at various temperatures) showed a linear dependence on the temperature. The absolute zero value optical band gap and the rate of change of the band gap with temperature of the ZnO and LZO5 films were found to be 3.339 and 3.322 eV, and 2.95 × 10−4 and 1.60 × 10−4  eV/K, respectively. The transport mechanisms in the ZnO and LZO5 films have been investigated by analyzing of the temperature (80–300 K) dependence of the conductivity. The activation energies of the ZnO film increased with Li content.
Keywords: Li-doped ZnO; Sol–gel method; X-ray diffraction; Temperature dependence of band gap; Conductivity;

Heterojunction light emitting diodes fabricated with different n-layer oxide structures on p-GaN layers by magnetron sputtering by Bo Hyun Kong; Won Suk Han; Young Yi Kim; Hyung Koun Cho; Jae Hyun Kim (4972-4976).
We grew heterojunction light emitting diode (LED) structures with various n-type semiconducting layers by magnetron sputtering on p-type GaN at high temperature. Because the undoped ZnO used as an active layer was grown under oxygen rich atmosphere, all LED devices showed the EL characteristics corresponding to orange-red wavelength due to high density of oxygen interstitial, which was coincident with the deep level photoluminescence emission of undoped ZnO. The use of the Ga doped layers as a top layer provided the sufficient electron carriers to active region and resulted in the intense EL emission. The LED sample with small quantity of Mg incorporated in MgZnO as an n-type top layer showed more intense emission than the LED with ZnO, in spite of the deteriorated electrical and structural properties of the MgZnO film. This might be due to the improvement of output extraction efficiency induced by rough surface.
Keywords: Zinc oxide; Light emitting diodes; Sputtering; Heterojunction;

Low energy repetitive miniature plasma focus device as high deposition rate facility for synthesis of DLC thin films by E. Ghareshabani; R.S. Rawat; R. Verma; S. Karamat; S. Sobhanian (4977-4983).
Diamond-like carbon (DLC) films were deposited on Si (1 0 0) substrate using a low energy (219 J) repetitive (1 Hz) miniature plasma focus device. DLC thin film samples were deposited using 10, 20, 50, 100 and 200 focus shots with hydrogen as filling gas at 0.25 mbar. The deposited samples were analyzed by XRD, Raman Spectroscopy, SEM and XPS. XRD results exhibited the diffraction peaks related to SiO2, carbon and SiC. Raman studies verified the formation amorphous carbon with D and G peaks. Corresponding variation in the line width (FWHM) of the D and G positions along with change in intensity ratio (I D/I G) in DLC films was investigated as a function of number of deposition shots. XPS confirmed the formation sp2 (graphite like) and sp3 (diamond like) carbon. The cross-sectional SEM images establish the 220 W repetitive miniature plasma focus device as the high deposition rate facility for DLC with average deposition rate of about 250 nm/min.
Keywords: Plasma focus; Diamond-like carbon thin films; Raman spectroscopy; XPS;

Protein immobilization capacity and covalent binding coverage of pulsed plasma polymer surfaces by Yongbai Yin; Daniel Bax; David R. McKenzie; Marcela M.M. Bilek (4984-4989).
Three carbon surfaces were deposited using pulsed plasma enhanced chemical vapour deposition method: a low and a high nitrogen-containing plasma polymer surfaces and a diamond-like carbon surface. The surfaces were analysed using both X-ray photoelectron spectroscopy (XPS) technique and the enzyme-linked immunosorbent assay (ELISA) method combining with sodium dodecyl sulphate (SDS) cleaning to investigate the capacity and covalent binding of the immobilized proteins. A good correlation was found on quantification of remaining protein after SDS cleaning using the ELISA method and the XPS technique. All surfaces had similar initial capacity of protein attachment but with large different resistance to SDS cleaning. The analysis showed that the high nitrogen-containing plasma polymer was the best biocompatible material due to its highest resistance to SDS cleaning, i.e. with the highest quantity (∼80%) of proteins bound covalently.
Keywords: Plasma polymerized surface; Protein immobilization; X-ray photoelectron spectroscopy; Enzyme-linked immunosorbent assay; SDS cleaning; Tropoelastin;

Field emission pressure sensors with non-silicon membranes by N. Badi; A.M. Nair; A. Bensaoula (4990-4994).
We report on the fabrication of cold cathode emitter and the design parameter simulation of a functional field emission-based pressure sensor. This device comprises a membrane made of metallic compound acting as the anode in front of a flat cold cathode emitter. First, the mechanical deflection of a diaphragm under selected input pressures is modeled. The current density distribution in the deflected diaphragm is then calculated using realistic field emission characteristics from fabricated sulfur doped boron nitride (S-BN) cold cathode device. The total current output was found by integrating the measured current density of the fabricated electron emitter device over the entire diaphragm area of the membrane as function of external pressure. The results show that conventional silicon membranes would pose problems when implemented in a real field emission device, and show how the use of unconventional materials (i.e., TiN) can help overcome these problems.
Keywords: Pressure sensor; Electron field emission; Boron nitride; COMSOL multiphysics;

Study of the morphological evolution of ZnO nanostructures on various sapphire substrates by J.P. Kar; S.N. Das; J.H. Choi; T.I. Lee; J.M. Myoung (4995-4999).
Zinc oxide (ZnO) nanostructures were grown on A-, C- and R-plane sapphires by metal organic chemical vapor deposition (MOCVD) technique. The shape of nanostructures was greatly influenced by the underlying sapphire substrate. Vertical aligned nanowires were observed on A- and C-plane sapphires, whereas the nanopencils were grown on R-plane sapphire. A correlation between the morphological and optical properties of the nanostructures has been established, where the morphological and structural characteristics are responsible for the evolution of optical properties. The nanowires, grown on C-plane sapphires, have shown superior optical properties. Comparatively higher photo-induced wettability transition has also been observed for ZnO nanostructures on R-plane sapphire.
Keywords: ZnO; Nanostructures; Metal organic chemical vapor deposition; Morphological and optical properties;

The drug-eluting stents have been regarded as a milestone in inhibiting the restenosis of coronary arteries. However, adverse reactions caused by bare-metal stents and non-biodegradable polymer coatings may result in some clinical problems. In this study, a new tacrolimus-eluting stent coated with biodegradable poly(1,3-trimethylene carbonate) (PTMC) is developed. The structures are characterized by Fourier transform infrared (FTIR) analysis, and the wettability is measured by contact angle assay. The biological behaviors are evaluated by the in vitro platelets adhesion test, APTT test, the human umbilical cord artery smooth muscle cells (HUCASMCs), 4′,6-diamidine-2-phenylindole (DAPI) and actin immunofluorescence staining, MTT colorimetric assay. These results show that after blending tacrolimus into PTMC, the anticoagulant behavior is improved, and the adhesion and proliferation of HUCASMCs on samples are inhibited. This work aims to find one kind of surface erosion biodegradable polymers that can be applied as drug-eluting stent coatings.
Keywords: Poly(1,3-trimethylene carbonate); Drug-eluting stent; Surface erosion; Smooth muscle cell; Tacrolimus;

Highly ordered Ag nanorod arrays were successfully fabricated using a simple chemical deposition method with the assistance of porous alumina membrane (PAM) template. The products were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). Ag+ ions in the PAM nanochannels were reduced by acetaldehyde reagent and resulting in the formation of rod array structures. It is found that the diameter of the Ag nanorods is determined by the PAM template, and the length of the Ag nanorods is depended on the reaction temperature. The growth mechanism of the Ag nanorod arrays is investigated in the study.
Keywords: Ag; Nanorod arrays; Chemical deposition; PAM template;

Roughness evolution of Si surfaces upon Ar ion erosion by V.I.T.A. de Rooij-Lohmann; I.V. Kozhevnikov; L. Peverini; E. Ziegler; R. Cuerno; F. Bijkerk; A.E. Yakshin (5011-5014).
We studied the roughness evolution of Si surfaces upon Ar ion erosion in real time. Following the theory of surface kinetic roughening, a model proposed by Majaniemi was used to obtain the value of the dynamic scaling exponent β from our data. The model was found to explain both the observed roughening and the smoothening of the surfaces. The values of the scaling exponents α and β, important for establishing a universal model for ion erosion of (Si) surfaces, have been determined. The value of β proved to increase with decreasing ion energy, while the static scaling exponent α was found to be ion energy independent.
Keywords: X-ray scattering; Ion erosion; Dynamic scaling; Si;

Morphology and antimony segregation of spangles on batch hot-dip galvanized coatings by Shu Peng; Jintang Lu; Chunshan Che; Gang Kong; Qiaoyu Xu (5015-5020).
Spangles produced by batch hot-dip galvanizing process have a rougher surface and a greater surface segregation of alloying element compared with those in continuous hot-dip galvanizing line (CGL), owing to the cooling rate of the former is much smaller than that of the later. Therefore, typical spangles on a batch hot-dipped Zn–0.05Al–0.2Sb alloy coating were investigated. The chemical, morphological characterization and identification of the phases on the spangles were examined by scanning electron microscopy (SEM), backscattered electron imaging (BSE), atomic force microscopy (AFM), energy dispersive spectroscopy (EDS) and X-ray diffraction analysis (XRD). The results showed that the coating surface usually exhibited three kinds of spangles: shiny, feathery and dull spangle, of which extensively antimony surface segregation was detected. The nature of precipitate on the coating surface was identified as β-Sb3Zn4, The precipitated β-Sb3Zn4 particles distributed randomly on the shiny spangle surface, both β-Sb3Zn4 particles and dentritic segregation of antimony dispersed in the dendritic secondary arm spacings of the feathery spangle and on the whole dull spangle surface. The dentritic segregation of antimony and precipitation of Sb3Zn4 compound are discussed by a proposed model.
Keywords: Hot-dip galvanizing; Spangle; Coating; Sb3Zn4; Surface segregation;

Temperature-dependent photoluminescence (PL) from Si nanodots with Al2O3 surface passivation layers was studied. The Si nanodots were grown by low pressure chemical vapor deposition and the Al2O3 thin films were prepared by atomic layer deposition (ALD), respectively. The BOE (Buffer-Oxide-Etch) treatment resulted in the damaged surface of Si nanodots and thus caused dramatic reduction in the PL intensity. Significant enhancement of the PL intensity from Si nanodots after the deposition of Al2O3 thin films was observed over a wide temperature range, indicating the remarkable surface passivation effect to suppress the non-radiative recombination at the surface of Si nanodots. The results demonstrated that the Al2O3 surface passivation layers grown by ALD are effectually applicable to nanostructured silicon devices.
Keywords: Si nanodot; Atomic layer deposition; Surface passivation layer; Photoluminescence; Aluminum oxide (Al2O3);

The present work estimates, using a kinetic model, the growth kinetics of Fe2B boride layers generated at the surface of a gray cast iron via the powder-pack boriding considering three different temperatures (1173, 1223 and 1273 K) and four treatment times (2, 4, 6 and 8 h). By the use of the mass balance equation at the (Fe2B/substrate) interface under certain assumptions and considering the effect of the boride incubation time, it was possible to estimate the corresponding parabolic growth constant in terms of two parameters α C up F e 2 B and β(T) depending on the boron content in the Fe2B phase and on the process temperature, respectively. The mass gain at the material surface and the instantaneous velocity of the (Fe2B/substrate) interface were also estimated. A fairly good agreement was observed between the experimental parabolic growth constants taken from a reference work (Campos-Silva et al., Characterization of boride layers formed at the surface of gray cast irons, Kovove Mater. 47 (2009) 1–7.) and the simulated values of the parabolic growth constants. Furthermore, the boride layer thicknesses were predicted and experimentally verified for three process temperatures and four treatment times.
Keywords: Powder-pack boriding; Boride layers; Growth kinetics; Incubation time; Parabolic growth constant;

The impact of the ZrO2/La2O3 film thickness ratio and the post deposition annealing in the temperature range between 400 °C and 600 °C on the electrical properties of ultrathin ZrO2/La2O3 high-k dielectrics grown by atomic layer deposition on (1 0 0) germanium is investigated. As-deposited stacks have a relative dielectric constant of 24 which is increased to a value of 35 after annealing at 500 °C due to the stabilization of tetragonal/cubic ZrO2 phases. This effect depends on the absolute thickness of ZrO2 within the dielectric stack and is limited due to possible interfacial reactions at the oxide/Ge interface. We show that adequate processing leads to very high-k dielectrics with EOT values below 1 nm, leakage current densities in the range of 0.01 A/cm2, and interface trap densities in the range of 2–5 × 1012  eV−1  cm−2.
Keywords: ALD; High-k; ZrO2; La2O3; MOS; Germanium;

Tetrakis(ethylmethylamido)hafnium and water are commonly used precursors for atomic layer deposition of HfO2. Using reflection absorption infrared spectroscopy with a buried-metal-layer substrate, we probe surface species present during typical deposition conditions. We observe evidence for thermal decomposition of alkylamido ligands at 320 °C. Additionally, we find that complete saturation of the SiO2 substrate occurs in the first cycle at ≈100 °C whereas incomplete coverage is apparent even after many cycles at higher temperatures. The use of this technique as an in situ diagnostic useful for process optimization is demonstrated.
Keywords: Atomic layer deposition; Hafnium dioxide; In situ diagnostics; Infrared spectroscopy;

Registration markers are crucial in connecting scanning tunneling microscope (STM) lithographed nano- and atomic-scale devices to the outside world. In this paper we revisit an ultra high vacuum annealing method with a low thermal budget that is fully compatible with etched registration markers and results in clean 2 × 1 reconstructed Si(1 0 0) surfaces required for STM lithography. Surface contamination is prevented by chemically stripping and reforming a protective silicon oxide layer before transferring the sample to the vacuum system. This allows for annealing temperatures of only 900 °C, where normally carbon contaminants result in the formation of SiC clusters on the surface at annealing temperatures below 950 °C. Reactive ion etched marker structures with an etch depth of 60 nm and a typical lateral dimension of only 150 nm survive a 900 °C flash anneal.
Keywords: Silicon; STM; Surface preparation; Relocation markers;

Growth of TiO2 coating on wood surface using controlled hydrothermal method at low temperatures by Jian Li; Haipeng Yu; Qingfeng Sun; Yixing Liu; Yongzhi Cui; Yun Lu (5046-5050).
This paper examines the growth of anatase TiO2 coating on a wood surface through the hydrolysis of tetrabutyl orthotitanate (TBOT) in different conditions, using a controlled hydrothermal method at low temperatures. Energy disperse X-ray analysis and Fourier transform infrared spectroscopy analysis confirm that the growth of TiO2 coating on a wood surface is bonded to hydrocarbon chains. Several reaction factors that influence the morphologies and amount of TiO2 present on wood surface were also investigated. As observed from the scanning electron microscopy images, the morphology and content of TiO2 grown on a wood surface could be controlled under appropriate reaction conditions. Approximately 32.6% TiO2 content on a wood surface could be obtained when specific conditions are applied.
Keywords: Hydrothermal method; Titanium dioxide; Wood; Surface; Coating;

H2S-sensing properties of Pt-doped mesoporous indium oxide by Jinchun Tu; Nan Li; Xiaoyong Lai; Yue Chi; Yujie Zhang; Wei Wang; Xiaotian Li; Jixue Li; Shilun Qiu (5051-5055).
Pt-doped mesoporous indium oxide (In2O3) has been successfully obtained by a simple and effective in situ nanocasting method. The resultant samples were characterized by XRD, FE-SEM, TEM, N2 physisorption, XPS and EDX. The gas sensing properties for hydrogen sulfide (H2S) of the Pt-doped mesoporous In2O3 specimens were also examined. The results exhibit those In2O3 specimens possess much higher response to H2S even at low concentration of 2 ppm and a lower optimum working temperature of 150 °C. A possible mechanism was also provided to explain the improvement of the sensing properties.
Keywords: H2S; Sensors; Mesoporous materials; Nanomaterials;

The nanocrystal thin films of zinc oxide doped by Al (ZnO:Al) were deposited by dc reactive magnetron sputtering on the glass substrates, in the pressure range of 33–51 Pa. From the X-ray diffraction patterns, the nanocrystalline structure of ZnO:Al films and the grain size were determined. The optical transmission spectra depend from the sputtering pressure, but their average value was 90% in the range from 33 Pa to 47 Pa. Also, the sputtering pressure changes the optical band gap of ZnO:Al films, which is highest for films deposited at 37 Pa, 40 Pa and 47 Pa. The obtained films at room temperature have a sheet resistance of 190 Ω/cm2 which increases with time, but the films annealed at temperature of 400 °C have constant resistance. The surface morphology of the films was studied by Scanning electron microscopy. XPS spectra showed that the peak of O1s of the as-deposited films is smaller than the peak of the annealed ZnO:Al films.
Keywords: Zinc oxide films; Magnetron sputtering; Transmission spectra and sheet resistance;

The wavelet analysis method has been extensively employed to analyze the surface structures and evaluate the surface roughness. In this work, however, the wavelet analysis method was introduced to decompose and reconstruct the sampled surface profile signals in the cutting direction that achieved by SPDT (single point diamond turning) operation, and the surface profile signals in tool feeding direction were reconstructed with the approximate harmonic functions directly. And moreover, the orthogonal design method, i.e. the combination design of general rotary method, was resorted to model the variations of the independent frequency and amplitude of different simulated harmonic signals in the cutting and tool feeding directions. As expected resultantly, a novel 3D surface topography modeling solution was established, which aims to predict and modify the finished KDP (potassium dihydrogen phosphate or KH2PO4) crystal surfaces. The validation tests were carried out finally under different cutting conditions, and the collected average surface roughness in any case was compared with the corresponding value as predicted. The results indicated the experimental data were well consistent with the predictions, and only an average relative error of 11.4% occurred in predicting the average surface roughness.
Keywords: KDP crystal; Wavelet analysis; Modeling; 3D topography; Surface roughness;

Nickel di-silicide formation induced by RTA process at 850 °C for 60 s in the Ni/Si(1 0 0) systems are investigated as a function of the initial Ni film thickness of 7–89 nm using XRD, RBS, SEM, X-SEM and AFM. Based on the XRD and RBS data, in the silicide films of 400–105 nm, NiSi and NiSi2 silicide phases co-exist, indicating that Ni overlayer is completely transformed to NiSi and NiSi2 silicide phases. SEM reveals that these films consist of large grains for co-existence of NiSi2 and NiSi phases, separated from one another by holes, reflecting that NiSi2 grows as islands in NiSi matrix. These films have low sheet resistance, ranging from 1.89 to 5.44 Ω/□ and good thermal stability. For thicknesses ≤ 80 nm RBS yields more Si-rich silicide phases compared to thicker films, whereas SEM reveals that Si-enriched silicide islands with visible holes grow in Si matrix. As the film thickness decreases from 400 to 35 nm, AFM reveals a ridge-like structure showing a general trend of decreasing average diameter and mean roughness values, while sheet resistance measurements exhibit a dramatic increase ranging from 1.89 to 53.73 Ω/□. This dramatic sheet resistance increase is generated by substantial grain boundary grooving, followed by island formation, resulting in a significant phase transformation from NiSi2-rich to Si-rich silicide phases.
Keywords: Nickel di-silicide; Rapid thermal annealing (RTA); Thickness-dependent silicide formation; Sheet resistance; XRD; RBS; SEM; X-SEM and AFM techniques;

Annealing effect on CdS/SnO2 films grown by chemical bath deposition by H. Metin; S. Erat; S. Durmuş; M. Ari (5076-5081).
The extensive investigation of the annealing effect in nitrogen atmosphere on the structural optical and electrical properties of chemically deposited CdS films on SnO2 has been performed. The as-deposited film shows 2.45 eV band gap (E g) and decreases with increasing annealing temperature. The film annealed at 623 K having pure hexagonal phase (a  = 4.14 Å, c  = 6.71 Å for [1 0 0] plane) and E g  = 2.36 eV shows 10 times higher conductivity for all temperature range, and shows two different activation energies E a  = 0.114 eV and E a  = 0.033 eV for the temperature range 395 K ≤  T  ≤ 515 K and 515 K ≤  T  ≤ 585 K, respectively. The structural parameters such as dislocation density, strain and optical parameters such as absorption and extinction coefficient are calculated and compared for all the films.
Keywords: CdS; SnO2; Optical properties; Electrical properties;

A comparative study of surface energy data from atomic force microscopy and from contact angle goniometry by Dimitrios A. Lamprou; James R. Smith; Thomas G. Nevell; Eugen Barbu; Corinne Stone; Colin R. Willis; John Tsibouklis (5082-5087).
Forces of adhesion have been measured for interactions involving self-assembled monolayers or polymer-film structures that had each been deposited onto a gold-coated glass substrate and a probing, gold-coated cantilever. The data have been fitted into mathematical models that allow the calculation of surface energy by considering the work done for the separation of the identically coated contacting surfaces. These values of surface energy are in close agreement with those from corresponding contact angle determinations, highlighting the potential usefulness of the technique for the study of surfaces at a resolution level approaching 1000 atoms. Comparative studies show that the employment of the atomic force microscopy technique may be preferable for the study of samples that are susceptible to penetration by liquids or for investigations under conditions that exceed the useful limits of conventional probing techniques involving liquids.
Keywords: Surface energy; Atomic force microscopy; Alkanethiols; Self-assembly; Goniometry;

Ethylene adsorption was studied by use of DFT/B3LYP with basis set 6-31G(d,p) in Gaussian’03 software. It was found that ethylene has adsorbed molecularly on all clusters with π adsorption mode. Relative energy values were calculated to be −50.86 kcal/mol, −20.48 kcal/mol, −32.44 kcal/mol and −39.27 kcal/mol for Ni13 nanocluster, Ni10(1 1 1), Ni13(1 0 0) and Ni10(1 1 0) surface cluster models, respectively. Ethylene adsorption energy is inversely proportional to Ni coordination number when Ni10(1 1 1), Ni13(1 0 0) and Ni10(1 1 0) cluster models and Ni13 nanocluster are compared with each other.
Keywords: Ni nanocluster; (1 1 1); (1 1 0); (1 0 0); Surface cluster model; DFT; Ethylene adsorption; Coordination number;

Reaction mechanism on reduction surface of mixed conductor membrane for H2 production by coal-gas by PeiJun Shen; WeiZhong Ding; YuDing Zhou; ShaoQing Huang (5094-5101).
The reaction mechanism on surface of BaCo0.7Fe0.2Nb0.1O3−δ membrane for reforming coal-gas was studied. The effects of metal particle on membrane surface were concluded. ‘Activation mechanism’ was proposed to be the key for enhancing oxygen permeation of membrane; while the catalyst-bed only takes charge of the reforming reaction. Though not as important as ‘activation mechanism’, the ‘space charge mechanism’ still affects the oxygen permeation of membrane. According to these mechanisms, the new design and surface-modifying strategy of membrane reactor were proposed.
Keywords: Mixed conductor membrane; BaCo0.7Fe0.2Nb0.1O3−δ ; Coal-gas reforming; Surface reaction;

Characteristics of ZnO:Al thin films co-doped with hydrogen and fluorine by Y.H. Kim; J. Jeong; K.S. Lee; J.K. Park; Y.J. Baik; T.-Y. Seong; W.M. Kim (5102-5107).
Fluorine and hydrogen co-doped ZnO:Al (AZO) films were prepared by radio frequency (rf) magnetron sputtering of ZnO targets containing 1 wt.% Al2O3 on Corning glass at substrate temperature of 150 °C with Ar/CF4/H2 gas mixtures, and the structural, electrical and optical properties of the as-deposited and the vacuum-annealed films were investigated. In as-deposited state, films with fairly low resistivity of 3.9–4 × 10−4  Ω cm and very low absorption coefficient below 900 cm−1 when averaged in 400–800 nm could be fabricated. After vacuum-heating at 300 °C, the minimum resistivity of 2.9 × 10−4  Ω cm combined with low absorption loss in visible region, which enabled the figure of merit to uplift as high as 4 Ω−1, could be obtained for vacuum-annealed film. It was shown that, unlike hydrogenated ZnO films which resulted in degradation upon heating in vacuum at moderately high temperature, films with fluorine addition could yield improved electrical properties mostly due to enhanced Hall mobility while preserving carrier concentration level. Furthermore, stability in oxidizing environment could be improved by fluorine addition, which was ascribed to the filling effect of dangling bonds at the grain boundaries. These results showed that co-doping of hydrogen and fluorine into AZO films with low Al concentration could be remarkably compatible with thin film solar cell applications.
Keywords: Transparent conducting oxide; ZnO; Co-doping; Fluorine; Hydrogen;

Detection of algae and bacterial biofilms formed on titanium surfaces using micro-Raman analysis by S. Ramya; R.P. George; R.V. Subba Rao; R.K. Dayal (5108-5115).
Biofouling is one of the major impediments in the use of titanium in sea-water cooled condensers of power plants, which is otherwise an excellent material with respect to corrosion resistance. Raman microscopic experiments were carried out on biofilms grown on titanium surfaces to find out the chemical composition of complex extracellular polymeric substances (EPS) in the biofilm. Though the spectral resolution of normal Raman experiments on these systems was very poor, it was improved when micro-SERS experiments were carried out using mono and bimetallic Ag and Cu colloids. It was observed that spatial distribution of polysaccharides was higher than that of proteins in algae biofilms formed on titanium matrix. Similar experiments were performed on laboratory cultured bacterial films of Pseudomonas aeruginosa. It was evidenced that algal and bacterial biofilms on titanium can be clearly distinguished with the help of Raman mapping coupled with SERS technique using bimetallic Ag/Cu colloids.
Keywords: Raman spectroscopy; Colloids; Biofouling; Biofilms; Characterization;

Modulation of the photoluminescence of Si quantum dots by means of CO2 laser pre-annealing by Yong-bin Chen; Yong Ren; Rong-ling Xiong; You-yuan Zhao; Ming Lu (5116-5119).
Si quantum dots (QDs) embedded in SiO2 can be normally prepared by thermal annealing of SiO x (x  < 2) thin film at 1100 °C in an inert gas atmosphere. In this work, the SiO x thin film was firstly subjected to a rapid irradiation of CO2 laser in a dot by dot scanning mode, a process termed as pre-annealing, and then thermally annealed at 1100 °C for 1 h as usual. The photoluminescence (PL) intensity of Si QD was found to be enhanced after such pre-annealing treatment. This PL enhancement is not due to the additional thermal budget offered by laser for phase separation, but attributed to the production of extra nucleation sites for Si dots within SiO x by laser irradiation, which facilitates the formation of extra Si QDs during the subsequent thermal annealing.
Keywords: Si quantum dots; Photoluminescence; Laser annealing;

It is shown that different highly oriented Pb(Zr0.52,Ti0.48)O3 films can be obtained on Pt/Ti/SiO2/Si substrate using a sol–gel technique. The effects of pyrolysis temperature on the orientation, phase composition and ferroelectric properties of the films are investigated. It is found the ferroelectric hysteresis loops of (1 1 1)-oriented film, (1 1 1) and (1 0 0) mix-oriented film can both be saturated when the external electric field is large enough, whereas the hysteresis loop of (1 0 0)-oriented film is difficult to saturate. The analysis of X-ray diffraction indicated the possibility of different phase composition in different oriented films under large film residual stress. Higher remnant polarization (53 μC/cm2) for (1 0 0)-oriented film can be attributed to its more tetragonal phase composition, which results in that the in-plane domain switching can continuously occur with external electric field increasing.
Keywords: Lead zirconate titanate films; Phase transitions; Orientation; Ferroelectric properties;