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Applied Surface Science (v.256, #22)

Editorial Board (pp. ii).

Naproxen drug delivery using periodic mesoporous silica SBA-15 by Dáša Halamová; Mária Badaničová; Vladimír Zeleňák; Taťána Gondová; Ulla Vainio (pp. 6489-6494).

In this paper, we present the release of naproxen from hexagonal periodic mesoporous silica SBA-15, which serves as a drug delivery system. Naproxen, the well-known nonsteroidal anti-inflammatory drug (NSAID), was loaded into the pores of SBA-15 silica modified with aminopropyl groups. The physicochemical properties of the modified sample (A-SBA-15/napro) were compared with the unmodified SBA-15 mesoporous silica loaded with the drug (SBA-15/napro). The kinetic of the naproxen release into the physiological solution was studied. The released amount of naproxen represented 90.7% from the unmodified SBA-15 in 72h, while from the sample A-SBA-15/napro the released amount represented about 80.9%. The prepared materials were characterized by nitrogen adsorption/desorption, Small angle X-ray scattering (SAXS), Fourier-transform infrared spectroscopy (FT-IR) and the thermoanalytical methods (TG/DTA). Thin layer chromatography (TLC) was used for quantitative determination of the released naproxen.

Keywords: Mesoporous silica; Naproxen; Controlled release; Drug delivery

Theoretical study of Ni adsorption on the GaN(0001) surface by Rafael González-Hernández; William López; César Ortega; María Guadalupe Moreno-Armenta; Jairo Arbey Rodríguez (pp. 6495-6498).

First-principles pseudo-potential calculations within density-functional theory framework are performed in order to study the structural and electronic properties of nickel adsorption and diffusion on a GaN(0001)-2×2 surface. The adsorption energies and potential energy surfaces are investigated for a Ni adatom on the Ga-terminated (0001) surface of GaN. This surface is also used to study the effect of the nickel surface coverage. The results show that the most stable positions of a Ni adatom on GaN(0001) are at the H₃ sites and T₄ sites, for low and high Ni coverage respectively. In addition, confirming previous experimental results, we have found that the growth of Ni monolayers on the GaN(0001) surface is possible.

Keywords: Density-functional calculations; Gallium nitride; Chemisorption; Surface diffusion

Ageing of plasma-mediated coatings with embedded silver nanoparticles on stainless steel: An XPS and ToF-SIMS investigation by S. Zanna; C. Saulou; M. Mercier-Bonin; B. Despax; P. Raynaud; A. Seyeux; P. Marcus (pp. 6499-6505).

Nanocomposite thin films (∼170nm), composed of silver nanoparticles enclosed in an organosilicon matrix, were deposited onto stainless steel, with the aim of preventing biofilm formation. The film deposition was carried out under cold plasma conditions, combining radiofrequency (RF) glow discharge fed with argon and hexamethyldisiloxane and simultaneous silver sputtering. XPS and ToF-SIMS were used to characterize Ag-organosilicon films in native form and after ageing in saline solution (NaCl 0.15M), in order to further correlate their lifetime with their anti-fouling properties. Two coatings with significantly different silver contents (7.5% and 20.3%) were tested. Surface analysis confirmed the presence of metallic silver in the pristine coating and revealed significant modifications after immersion in the saline solution. Two different ageing mechanisms were observed, depending on the initial silver concentration in the film. For the sample exhibiting the low silver content (7.5%), the metal amount decreased at the surface in contact with the solution, due to the release of silver from the coating. As a result, after a 2-day exposure, silver nanoparticles located at the extreme surface were entirely released, whereas silver is still present in the inner part of the film. The coating thickness was not modified during ageing. In contrast, for the high silver content film (20.3%), the thickness decreased with immersion time, due to significant silver release and matrix erosion, assigned to a percolation-like effect. However, after 18 days of immersion, the delamination process stopped and a thin strongly bounded layer remained on the stainless steel surface.

Keywords: Plasma deposit; Surface characterization; Ageing; Silver nanoparticles; Organosilicon films

Structure evolution from nanocolumns to nanoporous of nitrogen doped amorphous carbon films deposited by magnetron sputtering by Bin Zhang; Yuanlie Yu; Zhou Wang; Junyan Zhang (pp. 6506-6511).

Different nitrogen doped amorphous carbon (CNx) films were obtained by magnetron sputtering of carbon target in argon and nitrogen atmosphere at the increasing negative bias voltages from 0 to 150V. The films structures have experienced great change, from the novel column to nanoporous structure at the bias voltage of 0V to the porous structure at 150V. The proposed growth process was that the CNx nuclei grew at 0V acted as the “seeds” for the growth of the nanocolumns, and ion etching effects at 150V induced the formation of nanoporous structures. Furthermore, a comparison study showed that the field emission properties of the CNx films were related with the introduction of the nitrogen atoms, the size and concentration of sp² C clusters and the surface roughness. The films with rougher surface have lower threshold field.

Keywords: Nanocolumn structure; Nanoporous structure; Field emission properties

Low-temperature oxidation of SiC surfaces by supercritical water oxidation by Takashi Futatsuki; Taro Oe; Hidemitsu Aoki; Naoyoshi Komatsu; Chiharu Kimura; Takashi Sugino (pp. 6512-6517).

The oxidation process on silicon carbide (SiC) surfaces is important for wide bandgap power semiconductor devices. We investigated SiC oxidation using supercritical water (SCW) at high pressure and temperature and found that a SiC surface can be easily oxidized at low temperature. The oxidation rate is 10nm/min at 400°C and 25MPa, equal to that of conventional thermal dry oxidation at 1200°C. Low-temperature oxidation should contribute to improved performance in future SiC devices. Moreover, we found that SCW oxidation at 400°C forms a much smoother SiO₂/SiC interface than that obtained by conventional thermal dry oxidation. A higher oxidation rate and smaller microroughness are achieved at a lower oxidation temperature owing to the high density of oxidizers under SCW conditions.

Keywords: SiC; FET; Oxide; Supercritical water; Near-critical water; High pressure; High temperature; Microroughness; Buffer layer

Synthesis of anodizing composite films containing superfine Al₂O₃ and PTFE particles on Al alloys by Suiyuan Chen; Chen Kang; Jing Wang; Changsheng Liu; Kai Sun (pp. 6518-6525).

Anodized composite films containing superfine Al₂O₃ and PTFE particles were prepared on 2024 Al alloy using an anodizing method. The microstructures and properties of the films were studied by scanning electron microscopy, optical microscopy and X-ray diffraction. Friction wear tests were performed to evaluate the mechanical properties of the composites. Results indicate that the composite films with reinforced Al₂O₃ and PTFE two-particles have reduced friction coefficients and relatively high microhardness. The friction coefficient can be as small as 0.15, which is much smaller than that of an oxide film prepared under the same conditions but without adding any particles (0.25), while the microhardness can reach as high as 404 HV. When rubbed at room temperature for 20min during dry sliding friction tests, the wear loss of the film was about 16mg, which is about the half of that of the samples without added particles. The synthesized composite films that have good anti-wear and self-lubricating properties are desirable for oil-free industrial machinery applications.

Keywords: Anodizing composite films; Particle-reinforcement; Wear; Self-lubricating properties

Optical and structural studies on Ba(Mg_1/3Ta_2/3)O₃ thin films obtained by radiofrequency assisted pulsed plasma deposition by N.D. Scarisoreanu; A.C. Galca; L. Nedelcu; A. Ioachim; M.I. Toacsan; E. Morintale; S.D. Stoica; M. Dinescu (pp. 6526-6530).

Single-phase Ba(Mg_1/3Ta_2/3)O₃ thin films were prepared by radiofrequency plasma beam assisted pulsed laser deposition (RF-PLD) starting from a bulk ceramic target synthesized by solid state reaction. Atomic force microscopy, X-ray diffraction and spectroscopic ellipsometry were used for morphological, structural and optical characterization of the BMT thin films. The X-ray diffraction spectra show that the films exhibit a polycrystalline cubic structure. From spectroscopic ellipsometry analysis, the refractive index varies with the thin films deposition parameters. By using the transmission spectra and assuming a direct band to band transition a band gap value of ≈4.72eV has been obtained.

Keywords: PACS; 81.15.Fg 77.55.−g 78.66.−wBMT; RF-PLD; XRD; Ellipsometry

Microstructure and electrical properties of Mn-doped barium strontium titanate thin films prepared on copper foils by Yanhua Fan; Shuhui Yu; Rong Sun; Lei Li; Yansheng Yin; Ka-Wai Wong; Ruxu Du (pp. 6531-6535).

Ba0.7−_xSr_0.3Mn_xTiO₃ ( x=0, 0.025, 0.05) thin films have been prepared on copper foils using sol–gel method. The films were processed in an atmosphere with low oxygen pressure so that the substrate oxidation is avoided and the formation of the perovskite phase is allowed. XRD and SEM results showed that Mn doping enhanced the crystallization of the perovskite phase in the films. The Mn substitution prevents the reduction of Ti⁴⁺ to Ti³⁺, which is supported by XPS analysis. The Ba0.7−_xSr_0.3Mn_xTiO₃ film with x=0.025 (BSMT25) exhibits preferred dielectric behavior and a lower leakage current density among the three thin films. The dielectric constant and loss of the BSMT25 film are 1213.5 and 0.065 at 1MHz and around zero field, which are mostly desired for embedded capacitor applications. The mechanism of Mn doping on improving the electrical properties of barium strontium titanate (BST) thin films was investigated.

Keywords: Thin films; Sol–gel growth; Microstructure; Electrical properties

Functional and optical properties of Au:TiO₂ nanocomposite films: The influence of thermal annealing by M. Torrell; L. Cunha; A. Cavaleiro; E. Alves; N.P. Barradas; F. Vaz (pp. 6536-6542).

A set of nanocomposite thin films consisting of Au nanoclusters dispersed in a TiO₂ dielectric matrix was deposited by reactive magnetron sputtering, and subjected to thermal annealing in vacuum, at temperatures ranging from 200 to 800°C. The obtained results show that the structure and the size of Au clusters, together with the matrix crystallinity, changed as a result of the annealing, and were shown to be able to change the optical properties of the films and keeping good mechanical properties, opening thus a wide number of possible applications. The crystallization of the gold nanoclusters induced by the annealing was followed by a systematic change in the overall coating behaviour, namely the appearance of surface plasmon resonance (SPR) behaviour. This effect enables to tailor the thin films reflectivity, absorbance and colour coordinates, contributing to the importance of this thin film system. The different attained optical characteristics (reflectance values ranging from interference to metallic-like behaviours and colour varying for interference rainbow-like to several tones of red-brownish), associated with a reasonable mechanical resistance of the coatings (good adhesion to different substrates and hardness values ranging from 5 to 7.5GPa), induce the possibility to use this film system in a wide range of decorative applications.

Keywords: Decorative thin films; Gold; Surface plasmon resonance; TiO; ₂; Mechanical properties

One step synthesis of vertically aligned ZnO nanowire arrays with tunable length by Gang Meng; Xiaodong Fang; Weiwei Dong; Ruhua Tao; Yiping Zhao; Zanhong Deng; Shu Zhou; Jingzhen Shao; Liang Li (pp. 6543-6549).

Length control of ZnO nanowire arrays is a valuable concern for both fundamental research and future device application. In this article, vertically aligned ZnO nanowire arrays were synthesized by a seed layer catalyzed vapor phase transport method in a single experiment cycle. The length of these nanowire arrays exhibits a quasi-continuous evolution. It was found that the type and flow rate of carrier gas have a significant influence on the length modulation of ZnO arrays along the tube. A feasible route to tune the length of ZnO nanowire arrays from several micrometers to nearly 100μm could be achieved by adjusting proper deposition position and carrier gas.

Keywords: ZnO nanowire arrays; Vapor phase transport; Length tuning

New bio-cleaning strategies on porous building materials affected by biodeterioration event by Federica Valentini; Alessia Diamanti; Giuseppe Palleschi (pp. 6550-6563).

In this paper, a new bio-cleaning procedure based on the glucose oxidase (GOx) has been applied on the travertine and peperino substrata to remove the biological patina (i.e., biofilm). Glucose oxidase, used as a model enzyme system, is able to produce in situ H₂O₂ (the cleaning agent having oxidizing properties) by the enzymatic reaction at room temperature. The travertine and peperino samples came from the Villa Torlonia in Rome (Italy), and an analytical diagnosis on them was performed applying several analytical techniques, such as the differential interference contrast microscopy (DIC), the optical microscope (OM), the Fourier transform infrared spectroscopy (FT-IR) and the X-ray fluorescence (XRF) that evidence the presence of biofilms on the substrata. Better results were obtained on the travertine samples in terms of the cleaning efficiency and the absence of the etching effect on the surface, eventually induced by the peroxide molecule. These results could be explained in terms of the different porosities of the two kinds of stone materials, according to the BET data. A comparative study was also performed to validate the new bio-cleaning procedure, using both traditional approaches based on saturated (NH₄)₂CO₃ solution and EDTA in buffer solution and the enzyme lipase treatments. Among all, the cleaning procedure via GOx shows the best result, probably because the enzyme controls the concentration of the H₂O₂ in situ and also retains the H₂O₂ preferentially on the surface (where the biological patina is present) depending on the porosity of the substrata. A synergistic effect, with other enzymes such as lipase and protease, combined with the biocompatibility of the enzymatic treatments, could represent a new way for a higher cleaning efficiency to apply on different stone substrata.

Keywords: Stone materials; Biodeterioration; Bio-cleaning; GOx biocatalyst

Investigation of growth mechanism of nano-scaled cadmium sulfide within titanium dioxide nanotubes via solution deposition method by Rongjun Pan; Yucheng Wu; Kongyong Liew (pp. 6564-6568).

The growth mechanism of cadmium sulfide nanomaterials, including nanodots, nanotubes, and nanorods, within titanium dioxide nanotubes via solution deposition method was investigated. The materials obtained were characterized by field emission scanning electron microscopy, UV–visible spectroscopic and photoelectrochemical techniques. The results revealed that: (1) the concentration of ions introduced into the tubes influenced the morphology of the cadmium sulfide obtained: at low concentration, defects on the tube walls induce heterogeneous nucleation hence cadmium sulfide was observed attaching to the walls; at high concentration, particle aggregation occur due to negligible repulsion between the nuclei resulting in sedimentation of cadmium sulfide particles; (2) cadmium sulfide prefers to grow on seeds formed initially, so that nanodots or nanotubes and nanorods were formed at low and at high concentrations respectively; (3) the order of ions introduction also influences the morphology of cadmium sulfide formed within the tubes, (4) the photoresponse of the obtained nanomaterials was extended efficiently; and (5) the photoelectrochemical properties were strongly influenced by both the amount and the morphology of the deposited CdS sensitizer.

Keywords: Growth mechanism; Cadmium sulfide; Titanium dioxide nanotube arrays; Solution deposition

Origin of HfO₂/GaAs interface states and interface passivation: A first principles study by Weichao Wang; Ka Xiong; Geunsik Lee; Min Huang; Robert M. Wallace; Kyeongjae Cho (pp. 6569-6573).

First principles calculations of HfO₂/GaAs interfaces indicate that the interface states originate from the charge mismatch between HfO₂ and GaAs surfaces. We find that a model neutral interface (HfO₂ and GaAs surfaces terminated with two O and one Ga atoms per surface unit cell) removes gap states due to the balance of the interface charge. F and H can neutralize the HfO₂/GaAs interface resulting in useful band offsets, thus becoming possible candidates to passivate the interface states.

Keywords: PACS; 73.20.At; 71.20.NrHfO; ₂; /GaAs interface; Fermi level pinning; Electronegativity (EN)

Effect of solid surface on the formation of thin confined lubricating film of water with micro-content of oil by Liran Ma; Jianbin Luo; Chenhui Zhang (pp. 6574-6579).

The formation of confined film between two contacting surfaces is significant for evaluating the lubricating ability of liquid. A micro-content of oil in water was experimentally demonstrated to be significantly effective to the film formation of water, which was much thicker than predicted by elastohydrodynamic lubrication theory. The effect of solid surface characteristics on the liquid film confined in a nanogap has been investigated. The film forming performances of such films were presented. The work of adhesion between two different phases was calculated, and the competitive wetting behaviours of water and oil on different solid surfaces were employed to understand the film formation mechanism.

Keywords: Confined film; Water; Micro-content of oil; Solid surface

Preparation and characterization of antibacterial Au/C core–shell composite by Yan-Hong Gao; Nian-Chun Zhang; Yu-Wen Zhong; Huai-Hong Cai; Ying-liang Liu (pp. 6580-6585).

An environment-friendly oxidation–reduction method was used to prepare Au/C core–shell composite using carbon as core and gold as shell. The chemical structures and morphologies of Au/C core–shell composite and carbon sphere were characterized by X-ray diffraction, transmission electron microscope, energy dispersion X-ray spectrometry (EDS) and X-ray photoelectron spectroscopy (XPS). The antibacterial properties of the Au/C core–shell composite against Escherichia coli ( E. coli), Staphylococcus aureus ( S. aureus) and Candida albicans ( C. albicans) were examined by the disk diffusion assay and minimal inhibition concentration (MIC) methods. In addition, antibacterial ability of Au/C core–shell composite was observed by atomic force microscope. Results demonstrated that gold homogeneously supported on the surface of carbon spheres without aggregation and showed efficient antibacterial abilities.

Keywords: Carbon spheres; Au/C; Core–shell structure; Antibacterial activity; Composite

Electrical, structural and surface properties of fluorine doped tin oxide films by V. Bilgin; I. Akyuz; E. Ketenci; S. Kose; F. Atay (pp. 6586-6591).

Fluorine (F) incorporated polycrystalline SnO₂ films have been deposited onto glass substrates by ultrasonic spray pyrolysis technique. To possess information about the electrical properties of all films, their electrical conductivities were investigated depending on the temperature, and their activation and trap energies were analyzed. The crystalline structure, surface properties and elemental analysis of the SnO₂ films were examined to determine the effect of the F element. After all investigations, it was concluded that each fluorine incorporation rate has a different and important effect on the physical properties, and SnO₂:F (3at%) films were found to be the most promising sample for energy conversion devices, especially as conducting electrode in solar cells with its improved structural and electrical properties as compared to others.

Keywords: SnO; ₂; :F films; Ultrasonic spray pyrolysis; Electrical properties; XRD; SEM; EDS

Inter-diffusion study in MgO tunneling magneto-resistive (TMR) system by XPS by G.H. Yu; Xilin Peng (pp. 6592-6595).

In this paper, we investigated the elemental inter-diffusion in MgO TMR system, namely, between MgO barrier and free layer (CoFeB, NiFe or their combination) interface and the oxygen diffusion into the capping layers (Ta, Ru, TaN) at elevated temperatures using simple sheet film stack to simplify the results interpretation. Boron, cobalt, iron, and nickel show various diffusion tendencies into the MgO barrier after annealing the sheet film stack. Oxygen has different penetration depth into single CoFeB free layer upon annealing under N₂+Ar protective atmosphere for different capping layers. Ru and TaN capping layer provide much better O₂ diffusion barrier, compared with Ta capping layer. This could potentially change the boron segregation tendency at free layer and capping layer interface and thus affect the interface crystallization process and lattice matching between the crystallized CoFeB free layer and the MgO(001) barrier layer. All these effects will impact the overall TMR performance.

Keywords: TMR; MgO; Inter-diffusion; XPS; CoFeB

Enhanced field emission properties of screen-printed doubled-walled carbon nanotubes by polydimethylsiloxane elastomer by Hui Ding; Tao Feng; Zhejuan Zhang; Kai Wang; Min Qian; Yiwei Chen; Zhuo Sun (pp. 6596-6600).

Field emission (FE) properties of double-walled carbon nanotubes (DWCNTs) treated by polydimethylsiloxane (PDMS) elastomer with different heating temperature have been systematically studied. The current density of treated DWCNT films decreases with the increase of heating temperature. The screen-printed DWCNTs treated by PDMS elastomer with drying temperature 150°C for 20min have the best FE performance with a marvelous field enhancement factor ( β=20194). The optimized FE performance is attributed to the morphological change of DWCNT films after PDMS elastomer treatment and the change of separation energy for the CNT-substrate interface. It is proved that the PDMS treatment is a facile and effective method for field emission display (FED) application, especially for low-temperature FED preparation.

Keywords: Double-walled carbon nanotube; Field emission; Elastomer; Post-treatment

Characterization of nanocrystalline SnO₂ thin film fabricated by electrodeposition method for dye-sensitized solar cell application by A.Y. El-Etre; S.M. Reda (pp. 6601-6606).

Nanocrystalline SnO₂ thin film was prepared by cathodic electrodeposition–anodic oxidation and its structure was characterized by X-ray diffraction, SEM, UV–visible absorption and nitrogen adsorption–desorption by BET method. The obtained film has a surface area of 137.9m²/g with grain sized of 24nm. Thus the prepared SnO₂ thin film can be applied as an electrode in dye-sensitized solar cell. The SnO₂ electrode was successfully sensitized by Erythrosin dye and photoelectrochemical measurements indicate that the cell present short-circuit photocurrent ( J_sc) of 760μA/cm², fill factor (FF=0.4), photovoltage ( V_oc=0.21V) and overall conversion efficiency ( η) of 0.06% under direct sun light illumination. The relatively low fill factor and photovoltage are attributed to the reduction of triodiode by conduction band electrons and intrinsic properties of SnO₂.

Keywords: Nanocrystalline; SnO; ₂; Cathodic electrodeposition; Erythrosin; Dye-sensitized solar cell

Influence of substrate temperature on structures and dielectric properties of pyrochlore Bi_1.5Zn_1.0Nb_1.5O₇ thin films prepared by pulsed laser deposition by Xiaohua Zhang; Wei Ren; Peng Shi; Aifeng Tian; Hong Xin; Xiaofeng Chen; Xiaoqing Wu; Xi Yao (pp. 6607-6611).

The influence of substrate temperature on structural and dielectric properties of cubic pyrochlore Bi_1.5Zn_1.0Nb_1.5O₇ (BZN) thin films prepared by pulsed laser deposition process has been investigated. BZN thin films were deposited on Pt/Ti/SiO₂/Si(100) substrate and in situ annealed at 700°C. The results indicate that the substrate temperature has a significant effect on the structural and dielectric properties of BZN thin films. The films exhibit a cubic pyrochlore structure in the substrate temperature range from 550°C to 700°C and at the annealing temperature of 700°C. With further increase of substrate temperature to 750°C, the phases of Bi₂O₃, BiNbO₄ and Bi₅Nb₃O₁₅ can be detected in the XRD pattern due to the Zn loss. The dielectric constant and loss tangent of the films deposited at 650°C are 192 and 6×10⁻⁴ at 10kHz, respectively. The tunability is 10% at a dc bias field of 0.9MV/cm.

Keywords: Cubic pyrochlore Bi; _1.5; Zn; _1.0; Nb; _1.5; O; ₇; Thin films; Pulsed laser deposition; Dielectric tunability

Characterization of amorphous organic thin films, determination of precise model for spectroscopic ellipsometry measurements by Azadeh Farahzadi; Maryam Beigmohamadi; Phenwisa Niyamakom; Stephan Kremers; Nico Meyer; Michael Heuken; Matthias Wuttig (pp. 6612-6617).

The optical properties of tris(8-hydroxyquinoline) aluminum (Alq₃), N,N′-diphenyl-N,N′-bis(1-naphthyl)-1-1′biphenyl-4,4″diamine (α-NPD) and other amorphous organic materials for OLEDs application, e.g. 4,4-bis(2,2-diphenyl vinyl)-1,1-biphenyl (DPVBI) and Spiro-DPVBI have been studied by multi-angle spectroscopic ellipsometry (SE). The thin films of these materials have been deposited by organic vapor phase deposition (OVPD). The structural characterization has been performed using atomic force microscopy (AFM) and X-ray reflectometry (XRR). Comparison of the measurements using these different independent techniques enables the precise determination of the optical model for dielectric function of these thin films. The detail analyses on Alq₃ and α-NPD show that the Kim model with Gaussian broadening provides a significantly better fit to the ellipsometry data than the frequently used harmonic oscillator model. This conclusion is further proved by performing similar measurements on other amorphous organic samples for OLEDs application, e.g. DPVBI and Spiro-DPVBI. This result can be explained by the characteristic features of electronic states in organic molecules.

Keywords: Optical properties; Amorphous organic materials; OLEDs characterization

Improved electrical and interfacial properties of RF-sputtered HfAlO_x on n-GaAs with effective Si passivation by P.S. Das; A. Biswas (pp. 6618-6625).

In this paper, we present the effects of ultrathin Si interfacial layer on the physical and electrical properties of GaAs MOS capacitors fabricated using RF-sputtered HfAlO_x gate dielectric. It is found that HfAlO_x/Si/n-GaAs stack exhibits excellent electrical properties with low frequency dispersion (∼4.8%), hysteresis voltage (0.27V) and interface trap density (1.3×10¹²eV⁻¹cm⁻²). The current density of 3.7×10⁻⁵A/cm² is achieved with an equivalent-oxide-thickness of 1.8nm at V_FB+1V for Si-passivated HfAlO_x films on n-GaAs. X-ray photoelectron spectroscopy (XPS) analysis shows that the suppression of low-k interfacial layer formation is accomplished with the introduction of ultrathin Si interface control layer (ICL). Thus the introduction of thin layer of Si between HfAlO_x dielectrics and GaAs substrate is an effective way to improve the interface quality such as low frequency dispersion, hysteresis voltage and leakage current. Additionally, current conduction mechanism has been studied and the dominant conduction mechanisms are found to be Schottky emission at low to medium electric fields and Poole–Frenkel at high fields and high temperatures under substrate injection. In case of gate injection, the main current conduction at low field is found to be the Schottky emission at high temperatures.

Keywords: GaAs; High-k; XPS; Interfacial characteristic; Current conduction mechanism

Synthesis of nanoporous silicon carbide ceramics by thermal evaporation process by Jian Wei (pp. 6626-6629).

New nanoporous β-SiC ceramics were synthesized by a simple thermal evaporation method with commercial silicon powder and activated carbon fragments. The results of scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy and X-ray diffraction indicated that the microstructure of the β-SiC nanoporous ceramics was uniform and consistent with the pore size of 50–100nm. The β-SiC nanocrystal grains of 50–200nm were accumulated together to form a nanopore network. The formation mechanism was attributed to a template synthesis process, in which activated carbon fragments were employed as the template and they reacted with vaporized silicon through a vapor–solid way.

Keywords: Nanoporous; Carbide; Ceramics; Template

Au nanoparticles in PMMA matrix: In situ synthesis and the effect of Au nanoparticles on PMMA conductivity by Eda Yilmaz; Sefik Suzer (pp. 6630-6633).

Thin PMMA films with and without gold nanoparticles were subjected to ±10V d.c. and a.c. (square wave) excitations in various frequencies while recording their XPS spectra, and the resulting differences due to charging were examined. Both pure PMMA films and films containing gold nanoparticles showed charging shifts, but those of pure PMMA were more extensive than of PMMA containing gold nanoparticles, suggesting enhanced conductivity, induced by the incorporated gold nanoparticles. Non-charging behavior for these films was also observed with the increase of gold nanoparticle concentration. Gold nanoparticles were in situ synthesized and photo-patterned within the polymer films by UV irradiation.

Keywords: Au-nanoparticles; PMMA matrix; In situ synthesis; Charging

Structure and corrosion resistance of nickel foils deposited in a vertical gravity field by Ting Liu; Zhancheng Guo; Zhi Wang; Mingyong Wang (pp. 6634-6640).

The effects of vertical gravity fields on the structural characteristics of electrodeposited Ni foils were investigated in a centrifuge. Analysis by atomic force microscopy (AFM) shows that the surface roughness of Ni foils reduces from 37.6nm to 8.1nm with the increase of gravity coefficient ( G) from 1 to 354. Furthermore, the roughness of Ni foils deposited at G=62 evolves much more slowly than that deposited at G=1. The study of the textural perfection by X-ray diffractiometry (XRD) reveals that the degree of (200) preferred orientation parallel to the substrate plane is lowered by the vertical gravity field. Randomly oriented deposits are obtained in the vertical gravity field while deposits with uniaxial texture are obtained in the natural gravity field. Due to these variations in the structure, the Ni foils obtained in the vertical gravity field exhibit improved corrosion resistance.

Keywords: Vertical gravity field; Electrodeposition; Nickel foil; Structure; Corrosion

XPS analysis for degraded Y₂SiO₅:Ce phosphor thin films by E. Coetsee; J.J. Terblans; H.C. Swart (pp. 6641-6648).

X-ray photoelectron spectroscopy (XPS) results were obtained for standard Y₂SiO₅:Ce phosphor powders as well as undegraded and 144h electron degraded Y₂SiO₅:Ce pulsed laser deposited (PLD) thin films. The two Ce 3d peaks positioned at 877.9±0.3 and 882.0±0.2eV are correlated with the two different sites occupied by Ce in the Y₂SiO₅ matrix. Ce replaced the Y in the two different sites with coordination numbers of 9 and 7. The two Ce 3d XPS peaks obtained during the thin film analysis were also correlated with the luminescent mechanism of the broad band emission spectra of the Y₂SiO₅:Ce X₁ phase. These two different sites are responsible for the two main sets of cathodoluminescent (CL) and photoluminescence (PL) peaks situated at wavelengths of 418 and 496nm. A 144h electron degradation study on the Y₂SiO₅:Ce thin film yielded an increase in the CL intensity with a second broad emission peak emerging between 600 and 700nm. XPS analysis showed the presence of SiO₂ on the surface that formed during prolonged electron bombardment. The electron stimulated surface chemical reaction (ESSCR) model is used to explain the formation of this luminescent SiO₂ layer.

Keywords: Y; ₂; SiO; ₅; :Ce; CL; XPS; Electron degradation

Phase explosion induced by high-repetition rate pulsed laser by Jinghua Han; Yaguo Li; Qiuhui Zhang; Yuqing Fu; Weixing Fan; Guoying Feng; Liming Yang; Xudong Xie; Qihua Zhu; Shouhuan Zhou (pp. 6649-6654).

The characteristics and mechanisms of the damage to absorbing glass with high-repetition laser pulses (several kHz) are discussed. The results show that: (1) in the range of comparatively low-repetition rate, the damage is characterized by material melting and a small crater on the surface of substrate; (2) with the increase in repetition rate, a bigger and deeper crater is surrounded by re-deposition and crystalline granules originating from the cooling of vapor; and (3) the crater, surrounded by evaporation and an large number of solid particulates which is obviously the characters of phase explosion, becomes even bigger and deeper when the repetition rate is further increased. We modeled the temperature distribution in different repetition rate regime and found that heat accumulation plays a significant role in damage process. Because of the temperature dependence of damage mechanism, the temperature of the area irradiated by laser beam will ramp up with increasing the repetition rate, which triggers the melting and evaporation of dielectrics and phase explosion successively. Our results may benefit the understanding of laser-induced damage in optical materials.

Keywords: PACS; 81.15.Fg; 61.80.Ba; 68.35.RhAbsorbing glass; Laser-induced breakdown; Phase explosion; High-repetition rate pulsed laser

Growth of Ni–Mn–Ga high-temperature shape memory alloy thin films by magnetron sputtering technique by C. Liu; H.W. Mu; L.X. Gao; W.J. Ma; X. An; Z.Y. Gao; W. Cai (pp. 6655-6659).

Ni–Mn–Ga thin films have been fabricated by using magnetron sputtering technique under various substrate negative bias voltages. The effect of substrate negative bias voltage on the compositions and surface morphology of Ni–Mn–Ga thin films was systematically investigated by energy dispersive X-ray spectrum and atomic force microscopy, respectively. The results show that the Ni contents of the thin films increase with the increase of the substrate negative bias voltages, whereas the Mn contents and Ga contents decrease with the increase of substrate negative bias voltages. It was also found that the surface roughness and average particle size of the thin films remarkably decrease with the increase of substrate negative bias voltages. Based on the influence of bias voltages on film compositions, a Ni₅₆Mn₂₇Ga₁₇ thin film was obtained at the substrate negative bias voltage of 30V. Further investigations indicate that the martensitic transformation start temperature of this film is up to 584K, much higher than room temperature, and the film has a non-modulated tetragonal martensitic structure at room temperature. Transmission electron microscopy observations reveal that microstructure of the thin film exhibits an internally (111) type twinned substructure. The fabrication of Ni₅₆Mn₂₇Ga₁₇ high-temperature shape memory alloy thin film will contribute to the successful development of microactuators.

Keywords: Shape memory alloy (SMA); Sputtering; Thin films; Ni–Mn–Ga

Development of TREN dendrimers over mesoporous SBA-15 for CO₂ adsorption by Margandan Bhagiyalakshmi; Sang Do Park; Wang Seog Cha; Hyun Tae Jang (pp. 6660-6666).

Mesoporous SBA-15 was synthesized using rice husk ash (RHA) as the silica source and their defective Si–OH groups were grafted with tris(2-aminoethyl) amine (TREN) dendrimers generation through step-wise growth technique. The X-ray diffraction (XRD) and nitrogen adsorption/desorption results of parent SBA-15 obtained from RHA, suggests its resemblance with SBA-15 synthesized using conventional silica sources. Furthermore, the nitrogen adsorption/desorption results of SBA-15/TREN dendrimer generations (G1–G3) illustrates the growth of dendrimer inside the mesopores of SBA-15 and their CO₂ adsorption capacity was determined at 25°C. The maximum CO₂ adsorption capacity of 5–6 and 7–8wt% over second and third dendrimer generation was observed which is discernibly higher than the reported melamine and PAMAM dendrimers. The experimental CO₂ adsorption capacity was found to be less than theoretically calculated CO₂ adsorption capacity due to inter and intra molecular amidation as result of steric hindrance during the dendrimer growth. These SBA-15/TREN dendrimer generations also exhibit thermal stability up to 350°C and CO₂ adsorption capacity remains unaltered upon seven consecutive runs.

Keywords: Mesoporous silica; SBA-15; CO; ₂; adsorption; Dendrimer; TREN

Effect of surface roughness on leakage current and corrosion resistance of oxide layer on AZ91 Mg alloy prepared by plasma electrolytic oxidation by Bongyoung Yoo; Ki Ryoung Shin; Duck Young Hwang; Dong Heon Lee; Dong Hyuk Shin (pp. 6667-6672).

The influence of the surface roughness of Mg alloys on the electrical properties and corrosion resistance of oxide layers obtained by plasma electrolytic oxidation (PEO) were studied. The leakage current in the insulating oxide layer was enhanced by increasing the surface roughness, which is a favorable characteristic for the material when applied to hand-held electronic devices. The variation of corrosion resistance with surface roughness was also investigated. The corrosion resistance was degraded by the increasing surface roughness, which was confirmed with DC polarization and impedance spectroscopy. Pitting corrosion on the passive oxide layer was also analyzed with a salt spray test, which showed that the number of pits was not affected by the surface roughness when the spray time reached 96h.

Keywords: Mg alloy; Plasma electrolytic oxidation; Corrosion; Surface roughness

Effect of a LaSrCoO₃ buffer layer on Pb1−_xLa_xTi1− x_/4O₃ films studied by polarized Raman spectroscopy by W.L. Zhu; J.L. Zhu; Y.S. Luo; J.G. Zhu; D.Q. Xiao; R.T. Li; G. Pezzotti (pp. 6673-6677).

A confocal Raman investigation of Pb1−_xLa_xTi1− x_/4O₃ (PLT) thin films grown by RF magnetron sputtering on PbO_x/Pt/Ti/SiO₂/Si substrates with an intermediate LaSrCoO₃ (LSCO) layer was performed. The influence of the LaSrCoO₃ buffer layer was analyzed taking advantage of the observed Raman spectral band variation, which varied according to different manufacturing procedures. In the presence of a LSCO layer, the A1(1TO) Raman mode, which was indicative of tetragonal distortion, was pronouncedly enhanced, and a slight deviation from the (001) plane of the film was observed from the angular dependence of the polarized Raman spectral intensity. Furthermore, the spectral band variation as well as the residual stress along the in-depth direction was measured in the film from cross-sectional spectral line scans. This latter measurement showed a relaxation of the lattice mismatch in the presence of LSCO and PbO layers.

Keywords: PACS; 81.15.Cd; 87.64.Je; 68.55.JkPolarized Raman spectroscopy; Thin films; Lead titanate

Catalytic performance of Mn₃O₄ and Co₃O₄ nanocrystals prepared by sonochemical method in epoxidation of styrene and cyclooctene by Azadeh Askarinejad; Mojtaba Bagherzadeh; Ali Morsali (pp. 6678-6682).

A simple sonochemical method was developed to synthesis uniform sphere-like Co₃O₄ and Mn₃O₄ nanocrystals. Epoxidation of styrene and cyclooctene by anhydrous tert-butyl hydroperoxide over the prepared Co₃O₄ and Mn₃O₄ nanocatalysts was investigated. The results of conversion activity were compared with bulk Co₃O₄ and Mn₃O₄. Under optimized reaction conditions, the nanocatalysts showed a superior catalytic performance as compared to the bulk catalysts. Powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and BET surface area, were used to characterize and investigate the nanocatalysts.

Keywords: Epoxidation; Styrene; Cyclooctene; Co; ₃; O; ₄; and Mn; ₃; O; ₄; nanocatalysts; Sonochemistry

Preparation and dispersive mechanism of highly dispersive ultrafine silver powder by Guiquan Guo; Weiping Gan; Jian Luo; Feng Xiang; Jinling Zhang; Hua Zhou; Huan Liu (pp. 6683-6687).

Using ascorbic acid as the reducing agent, AgNO₃ as the source of Ag, the ultrafine silver powder was prepared by liquid-phase reduction method. The optimal conditions to prepare the ultrafine silver powder were obtained by studying the effects of following factors, such as the selection of dispersant, the doses of dispersant and pH, on the dispersibility of silver powder under other constant conditions. The pure ultrafine silver powder with quasi-spherical shape and mean size of 1.15μm was synthesized under the optimal conditions of polyvinyl alcohol (PVA) as disperser, PVA/AgNO₃ mass ratio of 4:100 and pH 7 while maintaining other conditions exactly in the same circumstances, such as AgNO₃ concentration of 0.20molL⁻¹, ascorbic acid concentration of 0.15molL⁻¹ and reaction temperature of 40°C. The ultrafine silver powder was characterized by SEM and XRD. And a PVA dispersive mechanism for preparing highly dispersive ultrafine silver powder, proved by the ultraviolet spectra, is that PVA absorbed on the surface of silver particles by coordination bond preventing the silver particles from diffusion and aggregation. In addition, the steric effect may help to reduce aggregation.

Keywords: Ultrafine silver powder; Preparation; Highly dispersive; Dispersive mechanism

Platinum catalyst on ordered mesoporous carbon with controlled morphology for methanol electrochemical oxidation by Ling-Bin Kong; Heng Li; Jing Zhang; Yong-Chun Luo; Long Kang (pp. 6688-6693).

Ordered mesoporous carbons CMK-3 with various morphologies are synthesized by using various mesoporous silica SBA-15 as template and then support to prepare Pt/CMK-3 catalyst. The obtained catalysts are compared in terms of the electrocatalytic activity for methanol oxidation in sulfuric acidic solutions. The structure characterizations and electrochemical analysis reveal that Pt catalysts with the CMK-3 support of large particle size and long channel lengths possess larger electrochemical active surface area (ECSA) and higher activity toward methanol oxidation than those with the other two supports. The better performance of Pt/CMK-3 catalyst may be due to the larger area of electrode/electrolyte interface and larger ECSA value of Pt catalyst, which will provide better structure in favor of the mass transport and the electron transport.

Keywords: Methanol oxidation; Ordered mesoporous carbon; Platinum; Morphology

Enhanced light output of InGaN LEDs with a roughened p-GaN surface using different TMGa flow rates in p-AlGaN layer by P.C. Tsai; W.R. Chen; Y.K. Su; C.Y. Huang (pp. 6694-6698).

We have demonstrated the enhancement of light output of InGaN-based blue light-emitting diodes (LEDs) using different trimethylgallium (TMGa) flow rates in the growth of p-AlGaN epilayer to facilitate a rougher p-GaN surface. It is found that higher output power can be achieved from the LEDs with rougher surface morphologies when the TMGa flow rate ( R_TMGa) is increased up to 60sccm during p-Al_0.05Ga_0.95N epilayer growth. Such a rough surface obtained at higher R_TMGa is attributed to the fact that the vertical growth rate is faster than the lateral growth rate, thus, leading to the facet of crystal growth focuses mainly in the vertical direction. The output power of devices biased at 20mA is 15.4, 15.9, 17.5, and 18.9mW for TMGa flow rates of 10, 20, 40, and 60sccm, respectively.

Keywords: PACS; 77.55.Px; 78.55.Cr; 81.15.GhGaN; Light-emitting diodes (LEDs); Light extraction efficiency; Surface roughness

Hydrophobic vertically aligned carbon nanotubes on Corning glass for self cleaning applications by Ian Y.Y. Bu; Shu Pei Oei (pp. 6699-6704).

Vertically aligned carbon nanotubes were prepared by Plasma enhanced chemical vapor deposition (PECVD) on inexpensive Corning glass substrates using different under layers. The samples were functionalised by a simple 1H,1H-2H,2H perfluorodecyl-trichlorosilane (FDTS) and hexane mixture. The surface roughness of the CNTs and protective FDTS coating provides an ideal hydrophobic surface of around 141°. Auger spectroscopy analysis was performed to confirm fluorination of the sample. It was also found titanium provides a suitable under layer support for Ni catalyst due to the wetability of the two elements.

Keywords: Low temperature; Hydrophobic; Carbon nanotube; Vertically aligned

Preparation and enhanced visible light-driven catalytic activity of ZnO microrods sensitized by porphyrin heteroaggregate by Xiangqing Li; Ying Cheng; Shizhao Kang; Jin Mu (pp. 6705-6709).

An inorganic–organic composite (ZnO/TAPPI–CoTPPS) composed of ZnO microrods and nano-heteroaggregates containing tetrakis(4-trimethylaminophenyl) porphyrin (TAPPI) and tetrakis(4-sulfonatophenyl) porphyrin cobalt(II) (CoTPPS), has been achieved by a simple mixing method. From the solid diffuse reflectance UV–vis spectrum of ZnO/TAPPI–CoTPPS, it can be observed that the Soret band of the porphyrin heteroaggregate of ZnO/TAPPI–CoTPPS is blue-shifted in comparison with that of the pure TAPPI–CoTPPS heteroaggregate while the Q bands are red-shifted, which demonstrates that there exists some interaction between the porphyrin heteroaggregate and ZnO. In addition, the photodegradation of rhodamine B (RhB) in water catalyzed by ZnO/TAPPI–CoTPPS was investigated at room temperature. Under visible light irradiation ( λ≥420nm), the photocatalytic activity of the ZnO/TAPPI–CoTPPS composite was higher than those of the porphyrin monomers modified ZnO composite and pure ZnO.

Keywords: Porphyrin heteroaggregate; ZnO; Composite; Photocatalysis

Surface modification of polyacrylonitrile film by anchoring conductive polyaniline and determination of uricase adsorption capacity and activity by Gülay Bayramoğlu; Ayşegul Ü. Metin; M. Yakup Arıca (pp. 6710-6716).

Polyacrylonitrile (PAN) films were modified with chemical polymerization of conductive polyaniline (PANI) in the presence of potassium dichromate as an oxidizing agent. The effect of aniline concentration on the grafting efficiency and on the electrical surface resistance of PAN and (PAN/PANI)-1–3 composite film was investigated. The surface resistances of the conductive composite films were found to be between 6.32 and 0.97kΩ/cm. As the amount of grafted PANI increased on the PAN films, the electrical resistance of composite film decreased. The PAN/PANI composite films were also characterized using SEM and FTIR. The changes in the surface properties of the films were characterized by contact angle measurements. As expected, the PAN, PAN/PANI and PAN/PANI-uricase immobilized films, exhibited different contact angle values and surface free energy due to different interactive functional groups of the films.The conductive films were well characterized and used for immobilization of uricase. The amount of adsorbed enzyme increases with the increase of surface concentration of grafted fibrous polyaniline polymer. The maximum amount of immobilized enzyme onto composite film containing 2.4% PANI was about 216μg/cm² (i.e., PAN/PANI-3). The immobilized uricase was reused 24 times in batch wise assay in a day. Finally, the immobilized uricase enzyme system was successfully fabricated and applied to determine the uric acid level in human serum samples.

Keywords: Conductive polymer; Polyaniline; Contact angle; Surface energy; Adsorption; Uricase

Solvent effects on adsorption of CO over CuCl(111) surface: A density functional theory study by Riguang Zhang; Lixia Ling; Baojun Wang; Wei Huang (pp. 6717-6722).

DFT calculations have been performed to investigate the effect of dielectric responses of the solvent environment on the CO adsorption over CuCl(111) surface by using COSMO (conductor-like solvent model) model in Dmol³. Different dielectric constants, including vacuum, liquid paraffin, methylene chloride, methanol and water solution, are considered. The effects of solvent model on the structural parameters, adsorption energies and vibrational frequency of CO adsorption over CuCl(111) surface have been investigated. The calculation results suggest that solvent effects can improve the stability of CO adsorption and reduce the intensity of C–O bond, which might mean that solvent is in favor of C–O bond activation and improve the reaction activity of oxidative carbonylation in a slurry reactor.

Keywords: Carbon monoxide; CuCl(1; 1; 1); Solvent effects; Adsorption; Density functional theory

Multi-walled carbon nanotube supported Pd and Pt nanoparticles with high solution affinity for effective electrocatalysis by Weichun Ye; Haiyuan Hu; Hong Zhang; Feng Zhou; Weimin Liu (pp. 6723-6728).

Multi-walled carbon nanotubes (MWCNTs) are easily wrapped with a functional biopolymer—polydopamine (Pdop) through self-polymerization of dopamine in a mild basic solution. The MWCNTs@Pdop exhibits long term dispersivity in water for at least one month. The Pdop has large capacity to coordinate [PdCl₄]²⁻ and [PtCl₆]²⁻ that upon reduction transform to corresponding metal nanoparticles. The nanoparticles strongly adhere to Pdop layer and can be used for the electrooxidation of haydrazine and methanol, respectively. Compared to Pd and Pt supported on unmodified MWCNTs, the Pd and Pt nanoparticle decorated on MWCNTs@Pdop exhibit much higher electrocatalytic activity and enhanced stability.

Keywords: Water-soluble; Carbon nanotubes; Polydopamine; Electrocatalysis

Characteristics and self-cleaning effect of the transparent super-hydrophobic film having nanofibers array structures by Kyungjun Lee; Sungnam Lyu; Sangmin Lee; Youn Sang Kim; Woonbong Hwang (pp. 6729-6735).

Transparent super-hydrophobic films were fabricated using the PDMS method and silane process, based on anodization in phosphoric acid. Contact angle tests were performed to determine the contact angle of each film according to the anodizing time. Transmittance tests also were performed to obtain the transparency of each TPT (trimethylolpropane propoxylate triacrylate) replica film according to the anodizing time. The contact angle was determined by studying the drop shape, and the transmittance was measured using a UV-spectrometer. The contact angle increases with increasing anodizing time, because increasing pillar length can trap more air between the TPT replica film and a drop of water. The transmittance falls with increasing anodizing time because the increasing pillar length causes a scattering effect. This study shows that the pillar length and transparency are inversely proportional. The TPT replica film having nanofibers array structures was better than other films in aspect of self-cleaning by doing quantitative experimentation.

Keywords: Nanostructure; Super-hydrophobicity; Self-cleaning; Transparency; Nanofiber; Anodic aluminum oxide (AAO)

Superhydrophobic cotton fabric fabricated by electrostatic assembly of silica nanoparticles and its remarkable buoyancy by Yan Zhao; Yanwei Tang; Xungai Wang; Tong Lin (pp. 6736-6742).

Highly hydrophilic cotton fabrics were rendered superhydrophobic via electrostatic layer-by-layer assembly of polyelectrolyte/silica nanoparticle multilayers on cotton fibers, followed with a fluoroalkylsilane treatment. The surface morphology of the silica nanoparticle-coated fibers, which results in the variety of the hydrophobicity, can be tailored by controlling the multilayer number. Although with the static contact angle larger than 150°, in the case of 1 or 3 multilayers, the fabrics showed sticky property with a high contact angle hysteresis (>45°). For the cotton fabrics assembled with 5 multilayers or more, slippery superhydrophobicity with a contact angle hysteresis lower than 10° was achieved. The buoyancy of the superhydrophobic fabric was examined by using a miniature boat made with the fabric. The superhydrophobic fabric boat exhibited a remarkable loading capacity; for a boat with a volume of 8.0cm³, the maximum loading was 11.6 or 12.2g when the boat weight is included. Moreover, the superhydrophobic cotton fabric showed a reasonable durability to withstand at least 30 machine washing cycles.

Keywords: Cotton fabrics; Superhydrophobic; Layer-by-layer assembly; Self-cleaning; Water-repellency

Epitaxial ZnO films grown on ZnO-buffered c-plane sapphire substrates by hydrothermal method by Hai-Yan Shan; Jie Li; Shuai Li; Qing-Yu Zhang (pp. 6743-6747).

ZnO films are hydrothermally grown on ZnO-buffered c-plane sapphire substrates at a low temperature of 70°C. A radio-frequency (RF) reactive magnetron sputtering has been used to grow the ZnO buffer layers. X-ray diffraction, scanning electron microscopy, and room temperature photoluminescence are carried out to characterize the structure, morphology and optical property of the films. It is found that the films are stress-free. The epitaxial relationship between the ZnO film and the c-plane sapphire substrate is found to be ZnO (0001)||Al₂O₃ (0001) in the surface normal andZnO[101¯0]||Al2O3[112¯0] in plane. Sapphire treatment, as such acid etching, nitridation, and oxidation are found to influence the nucleation of the film growth, and the buffer layers determine the crystalline quality of the ZnO films. The maximum PL quantum efficiency of ZnO films grown with hydrothermal method is found to be about 80% of single-crystal ZnO.

Keywords: PACS; 81.10.Dn; 68.55.−a; 71.55.GsZnO films; Epitaxial relationship; Sapphire treatment; Hydrothermal growth; Optical property

Electronic states of a hydrogenic impurity in a zinc-blende GaN/AlGaN quantum well by M. Pattammal; A. John Peter (pp. 6748-6752).

Binding energies of ground and a few low lying excited states of a hydrogenic donor confined in a zinc-blende GaN/AlGaN quantum well are investigated. They are computed within the framework of single band effective mass approximation, by means of a variational approach. The donor states are investigated with the various impurity positions as a function of well width. The calculations have been carried out with the inclusion of conduction band non-parabolicity through the energy dependent effective mass. The variational solutions have been improved by using a two-parametric trial wavefunction. The results seem better and good agreement with the other investigators. To support our results, we observe that the values of variational parameters are consistent when two parameter wave function is used. We find that the inclusion of non-parabolic effects leads to more binding for all the values of well width and is significant for narrow wells. The results are compared with the existing available literature.

Keywords: PACS; 73.22.−f; 73.21.La ;71.55.−iHydrogenic donor impurity; Electronic states; Semiconductor nano-structures

Experimental, density function theory calculations and molecular dynamics simulations to investigate the adsorption of some thiourea derivatives on iron surface in nitric acid solutions by K.F. Khaled (pp. 6753-6763).

The effects of thiourea derivatives, namely N-methyl thiourea (MTU), N-propyl thiourea (PTU) and N-allyl thiourea (ATU) on the corrosion behaviour of iron in 1.0M solution of HNO₃ have been investigated in relation to the concentration of thiourea derivatives. The experimental data obtained using the techniques of weight loss, Tafel polarization and electrochemical impedance spectroscopy, EIS. The results showed that these compounds revealed a good corrosion inhibition, (ATU) being the most efficient and (MTU) the least. Computational studies have been used to find the most stable adsorption sites for thiourea derivatives. This information help to gain further insight about corrosion system, such as the most likely point of attack for corrosion on iron (110), the most stable site for thiourea derivatives adsorption and the binding energy of the adsorbed layer. The efficiency order of the inhibitors obtained by experimental results was verified by theoretical analysis.

Keywords: Corrosion inhibition; Impedance; Monte Carlo simulation; Adsorption; Molecular simulation

In situ investigation of ice formation on surfaces with representative wettability by Long Yin; Qiang Xia; Jian Xue; Shuqing Yang; Qingjun Wang; Qingmin Chen (pp. 6764-6769).

In this work, we have prepared a series of samples with five representative surface wettabilities: i.e. superhydrophilic, hydrophilic, critical, hydrophobic and superhydrophobic. These samples were in situ observed the freezing process of water droplets on clean and artificially contaminated surfaces to investigate the relationship between surface wettability and ice formation. Ice accretion was also tested by spraying supercooled water to samples at different horizontal inclination angles (HIA). Surface topography was proved to be essential to the icing through heterogeneous nucleation. However, the correlation between surface wettability and ice formation was not observed. Finally, we found that the superhydrophobic surface clearly exhibited reduced ice accumulation in the initial stage of ice formation associated with the lower sliding angle (SA) of water droplets.

Keywords: Superhydrophobic; Contact angle; Surface topography; Ice accretion

Influence of high-pressure hydrogen treatment on structural and electrical properties of ZnO thin films by Chunye Li; Hongwei Liang; Jianze Zhao; Qiuju Feng; Jiming Bian; Yang liu; Rensheng Shen; Wangcheng Li; Guoguang Wu; G.T. Du (pp. 6770-6774).

ZnO thin films were treated by high-pressure hydrogen (H₂). Scanning electron microscope (SEM) images show that the surface morphology of ZnO films has been changed significantly by H₂ treatment. X-ray diffraction patterns show that the Zn(OH)₂ phases formed after H₂ treatment. The X-ray photoelectron spectroscopy results indicate that H atoms were doped into the surface of ZnO by forming H–O–Zn bond. The phenomenon shows that it is easy to form O–H bond in ZnO rather than H interstitial atom under high-pressure hydrogen circumstance.

Keywords: ZnO; MOCVD; High-pressure H; ₂; Zn(OH); ₂

Effects of pulse electrodeposition parameters on the properties of Ni–TiO₂ nanocomposite coatings by S.A. Lajevardi; T. Shahrabi (pp. 6775-6781).

The aim of this study is to investigate the effects of pulse electrodeposition parameters on the properties of nickel–titania composite coatings electrodeposited from a nickel Watts type bath. The effects of average current density, frequency and duty cycle on the surface morphology, crystal size, preferred orientation of the deposits and the amount of embedded nano-TiO₂ particles in the composite coatings were investigated. The results represented the optimum amount of average current density (e.g., 4Adm⁻²) for obtaining the highest volume percentage of the incorporated titania particles and subsequently the maximum microhardness. Moreover, by increasing the frequency up to 10Hz while reducing the duty cycle to 10% at constant peak current density, the volume percentage of particles increased to about 7% which is almost twice as much the volume percentage as deposited particles in direct current method. According to the results the composite coating exhibited obviously [100]+[211] as preferred orientation at low pulse frequency and the diffraction intensity of the [211] fiber orientation is increased, probably due to the pH increase adjacent to the electrolyte/cathode interface at higher frequencies. Also, it has been found that by reduction in the duty cycle, more titania particles were incorporated in the composite coatings and this promoted the nickel crystals growth on [100] planes and consequently the coatings preferred orientation changed from the [211] to [100]+[211] planes.

Keywords: Composite coatings; Electrodeposition; Pulse current; Titania particles; Morphology; Preferred orientation

Microstructure and microhardness analysis of the hexagonal oxides formed on the surface of the AISI 304 stainless steel after Nd:YAG pulsed laser surface melting by C.Y. Cui; X.G. Cui; Y.K. Zhang; K.Y. Luo; Q. Zhao; J.D. Hu; Z. Liu; Y.M. Wang (pp. 6782-6786).

The laser surface melting (LSM) technique was adopted to modify the surface layer microstructure of the AISI 304 stainless steel in this paper. The results showed that the hexagonal morphologies have been successfully fabricated on the surface after LSM. These hexagons had side lengths of about 0.5–1μm and were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), field emission scanning electron microscope (FESEM) and high resolution transmission electron microscope (HRTEM). It was proved by the XRD that the stainless steel surface mainly consisted of γ-Fe, Cr₂O₃, Fe₂O₃ and some manganese oxides. The FESEM micrographs showed that the hexagonal oxides were regular hexagons in geometry. The HRTEM micrographs also indicated the presence of the hexagons on the surface of the stainless steel. The spacing values were calculated from the HRTEM micrograph and the SAED pattern, and the hexagonal oxide phases determined by these spacing values were consistent with those verified by the XRD. After LSM, the microhardness of the stainless steel was significantly improved.

Keywords: LSM; Stainless steel; Hexagon; Morphology; HRTEM; Microhardness

Film forming kinetics and reaction mechanism of γ-glycidoxypropyltrimethoxysilane on low carbon steel surfaces by Lixia Yang; Jun Feng; Wenguang Zhang; Jun-e Qu (pp. 6787-6794).

The film forming kinetics and reaction mechanism of γ-GPS on low carbon steel surfaces was investigated by FTIR-ATR, AFM, NSS and theoretical calculation method. The results from experimental section indicated that the reaction of γ-GPS on low carbon steel surfaces followed the conventional reaction mechanism, which can be described as reaction (I) (Me (Metal)–OH+HO–Si→Me–O–Si+H₂O) and reaction (II) (Si–OH+Si–OH→Si–O–Si+H₂O). During film forming process, the formation of Si–O–Fe bond (reaction (I)) exhibited oscillatory phenomenon, the condensation degree of silanol monomers (reaction (II)) increased continuously. The metal hydroxyl density had significant influence on the growth mechanisms and corrosion resisting property of γ-GPS films. The results from theoretical calculation section indicated that the patterns of reaction (I) and reaction (II) were similar, involving a nucleophilic attack on the silicon center. The formation of Si–O–Fe bond (reaction (I)) was kinetically and thermodynamically preferred, which had catalytic effect on its condensation with neighboring silanol monomers (reaction (II)). Our DFT calculations were good consistent with the experimental measurements.

Keywords: γ-Glycidoxypropyltrimethoxysilane; Silane films; Film forming kinetics; Metal

Pyridine-thermal synthesis and high catalytic activity of CeO₂/CuO/CNT nanocomposites by Dengsong Zhang; Hailing Mai; Lei Huang; Liyi Shi (pp. 6795-6800).

Carbon nanotubes (CNTs) were controllably coated with the uninterrupted CuO and CeO₂ composite nanoparticles by a facile pyridine-thermal method and the high catalytic performance for CO oxidation was also found. The obtained nanocomposites were characterized by transmission electron microscopy, scanning electron microscopy, X-ray diffraction as well as X-ray photoelectron spectroscopy. It is found that the CuO/CeO₂ composite nanoparticles are distributed uniformly on the surface of CNTs and the shell of CeO₂/CuO/CNT nanocomposites is made of nanoparticles with a diameter of 30–60nm. The possible formation mechanism is suggest as follows: the surface of CNTs is modified by the pyridine due to the π–π conjugate role so that the alkaline of pyridine attached on the CNT surface is more enhanced as compared to the one in the bulk solvent, and thus, these pyridines accept the proton from the water molecular preferentially, which result in the formation of the OH⁻ ions around the surface of CNTs. Subsequently, the metal ions such as Ce³⁺ and Cu²⁺ in situ react with the OH⁻ ions and the resultant nanoparticles deposit on the surface of CNTs, and finally the CeO₂/CuO/CNT nanocomposites are obtained. The T₅₀ depicting the catalytic activity for CO oxidation over CeO₂/CuO/CNT nanocomposites can reach ∼113°C, which is much lower than that of CeO₂/CNT or CuO/CNT nanocomposites or CNTs.

Keywords: Carbon nanotubes; Composites; Coating

Chemical quenching of positronium in Fe₂O₃/Al₂O₃ catalysts by C. Li; H.J. Zhang; Z.Q. Chen (pp. 6801-6804).

Fe₂O₃/Al₂O₃ catalysts were prepared by solid state reaction method usingα-Fe₂O₃ andγ-Al₂O₃ nano powders. The microstructure and surface properties of the catalyst were studied using positron lifetime and coincidence Doppler broadening annihilation radiation measurements. The positron lifetime spectrum shows four components. The two long lifetimesτ3 andτ4 are attributed to positronium annihilation in two types of pores distributed inside Al₂O₃ grain and between the grains, respectively. With increasing Fe₂O₃ content from 3wt% to 40wt%, the lifetimeτ3 keeps nearly unchanged, while the longest lifetimeτ4 shows decrease from 96ns to 64ns. Its intensity decreases drastically from 24% to less than 8%. The Doppler broadening S parameter shows also a continuous decrease. Further analysis of the Doppler broadening spectra reveals a decrease in the p-Ps intensity with increasing Fe₂O₃ content, which rules out the possibility of spin-conversion of positronium. Therefore the decrease ofτ4 is most probably due to the chemical quenching reaction of positronium with Fe ions on the surface of the large pores.

Keywords: Fe; ₂; O; ₃; /Al; ₂; O; ₃; Catalyst; Positronium; Quenching

Self-assembled octadecyltrichlorosilane monolayer formation on a highly hydrated silica film by A. Poda; A. Anderson; W.R. Ashurst (pp. 6805-6813).

A MVD silica layer that consists of a highly hydrated surface favorable for organosilane surface reaction is investigated. The MVD silica layer lacks free surface silanol groups while supporting a more extensive adsorbed water layer as compared to oxidized Si(100). Octadecyltrichlorosilane monolayers (OTS) deposited on the MVD silica layer are found to follow the same mechanisms of growth and exhibit properties comparable to those formed on oxidized Si(100) surfaces. The growth process of octadecylsiloxane films is investigated as a function of immersion time and temperature by utilizing ATR-FTIR, ellipsometry, contact angle analysis, and AFM. The MVD silica layer is shown to support an ordered interfacial water structure that is more tightly bound due to a higher degree of hydrogen bonding associated with the hydroxylated surface. The importance of interfacial water on the OTS film formation process is highlighted and the role of free OH groups on the adsorption mechanism is diminished. It is shown that OTS films can be formed on a highly hydrated surface comparable to those formed on oxidized Si(100) surfaces.

Keywords: Self-assembled monolayer; Interfacial water layer; Octadecyltrichlorosilane; MVD silica layer

Photoluminescence and Raman analysis of novel ZnO tetrapod and multipod nanostructures by Zhiwei Peng; Guozhang Dai; Weichang Zhou; Peng Chen; Qiang Wan; Qinglin Zhang; Bingsuo Zou (pp. 6814-6818).

Novel ZnO tetrapod and multipod nanostructures were successfully synthesized in bulk quantity through thermal evaporation method. The morphologies and structures of the ZnO nanostructures were characterized by scanning electron microscopy, X-ray diffraction and transmission electron microscopy. The results revealed that the ZnO nanostructures consisted of tetrapods and multipods with tower-like legs. The ZnO nanostructures were of high purity and were well crystallized with wurtzite structure. The preferred growth direction of legs was found to be the [0001] direction. Possible growth mechanisms were proposed for the formation of the ZnO nanostructures. Room temperature photoluminescence (PL) spectra showed that the as-synthesized ZnO nanostructures had a strong green emission centered at 495nm and a weak ultraviolet emission at 383nm. Raman spectroscopy was also adopted to explore the structural quality of the ZnO nanostructures.

Keywords: PACS; 78.55.−m; 81.05.Dz; 81.10.Aj; 81.10.BkZnO; Nanostructures; Crystal growth; Photoluminescence

Crystallization and surface segregation in CuIn_0.7Ga_0.3Se₂ thin films on Cu foils grown by pulsed laser deposition by Yeon Hwa Jo; Bhaskar Chandra Mohanty; Yong Soo Cho (pp. 6819-6823).

This work reports unexpected crystallization and segregation behavior of CuIn_0.7Ga_0.3Se₂ (CIGS) thin films deposited on flexible Cu foils by pulsed laser deposition. A composite-type microstructure containing nanometer-scaled CIGS crystallites embedded in amorphous Cu-rich matrix is observed even at the high temperature of 500°C. The findings are attributed to very fast condensation of the ablated species and random nucleation induced from the amorphous matrix. Cu-rich particulates tend to precipitate on the film surface, and their average size, shape, number density and composition exhibit a strong dependence on the substrate temperature up to 500°C. The similar crystallization properties of the films on Cu foils and glass substrates are noticeable to the use of Cu foils for flexible solar cells.

Keywords: Chalcopyrite; CIGS; Pulsed laser deposition; Solar cells

Surface hydrophobic modification of ultra-fine aluminum silicate by mechanically grinding and heating by Liaosha Li; Xue Ren; Weixiao Jia; Jibin Liu; Jing Zhu (pp. 6824-6828).

Highly hydrophobic ultra-fine aluminum silicate can be obtained by mechanically grinding and heating both aluminum silicate particles and octadecoic acid. The results showed that the organic modifier was adsorbed on the surface of aluminum silicate particles where a little new organic group was generated, and the hydrophobicity of ultra-fine aluminum silicate powder was enhanced. Grafting reaction was mainly carried out in heating process. Due to both grinding and heating, the modifier spread on the surface of particle completely and bonded with Si to form Si–O–C, and with Al to form acyl alumina in bidentate coordination. As a result, a highly hydrophobic layer was formed on the powder surface. However, it was unsuitable for heating temperature to exceed 180°C, or else the layer would be destroyed. All the above points represent a useful effort for surface-grafting modification of powder particles. In this study, a novel method as a reference was provided on the surface-grafting modification of powder particles.

Keywords: Grind; Hydrophobic modification; Ultra-fine aluminum silicate; Octadecoic acid

Effect of nickel doping on structural, optical and electrical properties of TiO₂ nanoparticles by sol–gel method by K. Karthik; S. Kesava Pandian; N. Victor Jaya (pp. 6829-6833).

Nickel-doped anatase TiO₂ nanoparticles have been prepared by sol–gel method. The X-ray powder diffraction study reveals that all the prepared samples have pure anatase phase tetragonal system. The average crystallite size of the prepared sample is 14nm, when found through transmission electron microscope. A strong frequency dependence of both dielectric constant ( ɛ′) and dielectric loss (tan δ) were observed for various dopant levels at room temperature in the frequency range of 42Hz to 5MHz. At low frequency, the piling up of mobile charge carriers at the grain boundary produces interfacial polarization giving rise to high dielectric constant. The asymmetric shape of frequency dependence of the dielectric loss for the primary relaxation process is observed for each concentration. From the ac conductivity studies, the reduction in conductivity may arise due to the decreasing particle with the increase in Ni-dopant level.

Keywords: Nanoparticle; Anatase TiO; ₂; Dielectric; Conductivity

Growth of b-axis oriented VO₂ thin films on glass substrates using ZnO buffer layer by Te-Wei Chiu; Kazuhiko Tonooka; Naoto Kikuchi (pp. 6834-6837).

VO₂ thin films are grown on glass substrates by pulsed laser deposition using vanadium metal as a target. In this study, a ZnO thin film was used as a buffer layer for the growth of VO₂ thin films on glass substrates. X-ray diffraction studies showed that the VO₂ thin film had b-axis preferential orientation on a c-axis oriented ZnO buffer layer. The thickness of the ZnO buffer layer and the oxygen pressure during VO₂ deposition were optimized to grow highly b-axis oriented VO₂ thin films. The metal-insulator transition properties of the VO₂ film samples were investigated in terms of infrared reflectance and electrical resistance with varying temperatures.

Keywords: VO; ₂; ZnO; Buffer layer; b; -Axis; Preferential orientation

Light radiation through a transparent cathode plate with single-walled carbon nanotube field emitters by E.S. Jang; J.C. Goak; H.S. Lee; S.H. Lee; J.H. Han; C.S. Lee; J.H. Sok; Y.H. Seo; K.S. Park; N.S. Lee (pp. 6838-6842).

In the conventional carbon nanotube backlight units (CNT-BLUs), light passes through the phosphor-coated anode glass plate, which thus faces closely the thin film transistor (TFT) backplate of a liquid crystal display panel. This configuration makes heat dissipation structurally difficult because light emission and heat generation occur simultaneously at the anode. We propose a novel configuration of a CNT-BLU where the cathode rather than the anode faces the TFT backplate by turning it upside down. In this design, light passes through the transparent cathode glass plate while heating occurs at the anode. We demonstrated a novel design of CNT-BLU by fabricating transparent single-walled CNT field emitters on the cathode and by coating a reflecting metal layer on the anode. This study hopefully provides a clue to solve the anode-heating problem which would be inevitably confronted for high-luminance and large-area CNT-BLUs.

Keywords: Field emission; Carbon nanotube; Backlight unit; Heat dissipation; Transparent cathode

Ammoxidation of carbon materials for CO₂ capture by M.G. Plaza; F. Rubiera; J.J. Pis; C. Pevida (pp. 6843-6849).

Ammoxidised carbons were produced from three different starting materials: an activated carbon obtained from wood by chemical activation using the phosphoric acid process, a steam activated peat-based carbon, and a char obtained from a low-cost biomass feedstock, olive stones. Nitrogen was successfully incorporated into the carbon matrix of the different materials, the amount of nitrogen uptake being proportional to the oxygen content of the precursor. At room temperature the CO₂ capture capacity of the samples was found to be related to the narrow micropore volume, while at 100°C other factors such as surface basicity took on more relevance. At 100°C all the ammoxidised samples presented an enhancement in CO₂ uptake compared to the parent carbons.

Keywords: Ammoxidation; Carbon materials; Adsorption; CO; ₂; capture

The influence of sputtering procedure on nanoindentation and nanoscratch behaviour of W–S–C film by Manish Roy; T. Koch; A. Pauschitz (pp. 6850-6858).

Sulphides of tungsten with its lamellar structure – whereby weak van der Waals forces act between the layers – are commonly believed to be responsible for their excellent self-lubricating properties. The present investigation is undertaken in order to explore the possibility of using this film for MEMS application. In order to achieve this objective, W–S–C films are deposited on 100Cr6 steel using radio frequency magnetron sputtering. Carbon was incorporated in the films via three different ways: (1) using a reactive gas (CH₄), (2) by co-sputtering from separate targets (WS₂ and C targets) and, (3) by co-sputtering from a C target embedded with WS₂ pellets. Microstructural features and mechanical properties of these films are evaluated with the help of scanning electron microscopy and nanoindentation. The topography, structural features and scratch behaviour are analysed using atomic force microscopy, X-ray diffraction and nanoindenter. It is noted that the film deposited by sputtering two targets exhibits the highest hardness due to high oxygen content. The highest elastic modulus pertains to the film deposited from the carbon target containing WS₂ pellets as this film has amorphous structure and the minimum porosity. The friction coefficient under scratching is the highest for reactively sputtered film whereas it is the minimum for the film deposited from the carbon target containing WS₂ pellets as this film has amorphous structure and the minimum roughness.

Keywords: Nanoindentation; Nanoscratch; Sputtering; W–S–C film

Surface modification of polypropylene non-woven fabric using atmospheric nitrogen dielectric barrier discharge plasma by Kunlei Wang; Wenchun Wang; Dezheng Yang; Yan Huo; Dezhen Wang (pp. 6859-6864).

In this paper, a dielectric barrier discharge operating in nitrogen at atmospheric pressure has been used to improve the surface hydrophilic property of polypropylene (PP) non-woven fabric. The changes in the hydrophilic property of the modified PP samples are investigated by the contact angle measurements and the variation of water contact angle is obtained as a function of the energy density; micrographs of the PP before and after plasma treatment are observed by scanning electron microscopy (SEM) and the chemical composition of the PP surface before and after plasma treatment is also analyzed by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The results show that the surface hydrophilic property of the PP samples is greatly improved with plasma treatment for a few seconds, as evidenced by the fact that the contact angle of the treated PP samples significantly decreases after plasma treatment. The analysis of SEM shows that the surface roughness of the treated PP samples increases due to bonding and etching in plasma processing. The analyses of FTIR and the C1s peak in the high-resolution XPS indicate that oxygen-containing and nitrogen-containing polar functional groups are introduced into PP surface in plasma processing. It can be concluded that the surface hydrophilic property of the modified PP samples has been obviously improved due to the introduction of oxygen-containing and nitrogen-containing polar groups and the increase of the surface roughness on the PP surface.

Keywords: Polypropylene; Surface modification; Dielectric barrier discharge; Atmospheric pressure; Hydrophilic property

A combined experimental and theoretical analysis of Fe-implanted TiO₂ modified by metal plasma ion implantation by Chung-Chih Yen; Da-Yung Wang; Ming-Huei Shih; Li-Shin Chang; Han C. Shih (pp. 6865-6870).

Photocatalyst titanium dioxide (TiO₂) thin films were prepared using sol–gel process. To improve the photosensitivity of TiO₂ at visible light, transition metal of Fe was implanted into TiO₂ matrix at 20keV using the metal plasma ion implantation process. The primary phase of the Fe-implanted TiO₂ films is anatase, but X-ray diffraction revealed a slight shift of diffraction peaks toward higher angles due to the substitutional doping of iron. The additional band gap energy levels were created due to the formation of the impurity levels (Fe–O) verified by X-ray photoelectron spectroscopy, which resulted in a shift of the absorption edge toward a longer wavelength in the absorption spectra. The optical band gap energy of TiO₂ films was reduced from 3.22 to 2.87eV with an increase of Fe ion dosages from 0 to 1×10¹⁶ions/cm². The band gap was determined by the Tauc plots. The photocatalysis efficiency of Fe-implanted TiO₂ was assessed using the degradation of methylene blue under ultraviolet and visible light irradiation. The calculated density of states for substitutional Fe-implanted TiO₂ was investigated using the first-principle calculations based on the density functional theory. A combined experimental and theoretical Fe-implanted TiO₂ film was formed, consistent with the experimentally observed photocatalysis efficiency of Fe-implanted TiO₂ in the visible region.

Keywords: Titanium dioxide; Metal plasma ion implantation; Densities of states; Band gap

ZnS thin film deposited with chemical bath deposition process directed by different stirring speeds by Y. Zhang; X.Y. Dang; J. Jin; T. Yu; B.Z. Li; Q. He; F.Y. Li; Y. Sun (pp. 6871-6875).

In this combined film thickness, scanning electron microscopy (SEM), X-ray diffraction and optical properties study, we explore the effects of different stirring speeds on the growth and optical properties of ZnS film deposited by CBD method. From the disclosed changes of thickness of ZnS film, we conclude that film thickness is independent of the stirring speeds in the heterogeneous process (deposition time less than 40min), but increases with the stirring speeds and/or deposition time increasing in the homogeneous process. Grazing incident X-ray diffraction (GIXRD) and the study of optical properties disclosed that the ZnS films grown with different stirring speeds show partially crystallized film and exhibit good transmittance (70–88% in the visible region), but the stirring speeds cannot give much effects on the structure and optical properties in the homogeneous process.

Keywords: ZnS; Stirring speed; Structure; Optical properties

The effect of working pressure on the chemical bond structure and hydrophobic properties of PET surface treated by N ion beams bombardment by Wanyu Ding; Dongying Ju; Weiping Chai (pp. 6876-6880).

Polyethylene terephthalate (PET) surface was bombarded by N ion beams at room temperature. Varying the working pressure of the ion beams, PET surfaces with different composition and properties were obtained. Characterization by X-ray photoelectron spectrometry showed that only on film surface, ester bonds, especially C–O bonds, were broken and N element chemical bonded with C. The influence depth was less than 5nm because of the lower ion energy (about 10³eV). Contact angle results revealed that with increasing the working pressure of ion beams, the contact angle of PET surface to pure water increased from 51° to 130°. With these results, one conclusion could be deduced that the hydrophilic and hydrophobic properties of PET surface could be influenced by N atom chemical bond with C, which in turn is controlled by the working pressure of N ion beams.

Keywords: Polyethylene terephthalate; Ion beams; XPS; Chemical bond; Contact angle

Optimization of VI/II pressure ratio in ZnTe growth on GaAs(001) by molecular beam epitaxy by Jie Zhao; Yiping Zeng; Chao Liu; Lijie Cui; Yanbo Li (pp. 6881-6886).

ZnTe epilayers were grown on GaAs(001) substrates by molecular beam epitaxy (MBE) at different VI/II beam equivalent pressure (BEP) ratios ( R_VI/II) in a wide range of 0.96–11 with constant Zn flux. Based on in situ reflection high-energy electron diffraction (RHEED) observation, two-dimensional (2D) growth mode can be formed by increasing the R_VI/II to 2.8. The Te/Zn pressure ratios lower than 4.0 correspond to Zn-rich growth state, while the ratios over 6.4 correspond to Te-rich one. The Zn sticking coefficient at various VI/II ratios are derived by the growth rate measurement. The ZnTe epilayer grown at a R_VI/II of 6.4 displays the narrowest full-width at half-maximum (FWHM) of double-crystal X-ray rocking curve (DCXRC) for (004) reflection. Atomic force microscopy (AFM) characterization shows that the grain size enlarges drastically with the R_VI/II. The surface root-mean-square (RMS) roughness decreases firstly, attains a minimum of 1.14nm at a R_VI/II of 4.0 and then increases at higher ratios. It is suggested that the most suitable R_VI/II be controlled between 4.0 and 6.4 in order to grow high-quality ZnTe epitaxial thin films.

Keywords: PACS; 81.05.Dz; 68.35.Bs; 68.55.Jk; 81.15.HiZnTe; Molecular beam epitaxy; Reflection high-energy electron diffraction; X-ray diffraction; Atomic force microscopy

Deposition of hydrogenated amorphous carbon nitride films by dielectric barrier discharge plasmas by Jinhai Niu; Lianlian Zhang; Zhihui Zhang; Dongping Liu; Yanhong Liu; Zhiqing Feng (pp. 6887-6892).

Hydrogenated amorphous carbon nitride (a-C:N:H) films were synthesized from CH₄/N₂, C₂H₄/N₂ and C₂H₂/N₂ mixtures using dielectric barrier discharge (DBD) plasmas. Atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) were used to characterize the surface morphology, bonding structure, and composition of the a-C:N:H films. The influences of plasma parameters (discharge pressure in the range of 25–1000Pa) and feed gases used on the composition and the structure of deposited films were systematically studied. The a-C:N:H films with the uniform surface structure were deposited by low-pressure DBD plasmas with various systems. Compared to the films deposited in C₂H₄/N₂ and C₂H₂/N₂ systems, the films deposited in the CH₄/N₂ system exhibit the relatively lower surface roughness and deposition rate. For all the films prepared in these three systems, increasing the discharge pressure leads to an increase in film surface roughness and deposition rate. Significant differences among the FTIR spectra of all deposited a-C:N:H films were also observed. Both FTIR and XPS spectra show that for all the films deposited in three different systems, increasing the N₂ fraction leads to a decrease in the H content of deposited a-C:N:H films and an increase in the N content. The properties of deposited films may change from those of polymerlike to diamond-like when the discharge pressure is increased. Correlations between the film properties and growth processes are discussed in this study.

Keywords: Dielectric barrier discharge; Hydrogenated amorphous carbon nitride films; FTIR; AFM; XPS

High-temperature application of the low-emissivity Au/Ni films on alloys by Zhibin Huang; Wancheng Zhou; Xiufeng Tang; Fa Luo; Dongmei Zhu (pp. 6893-6898).

The 200nm-thickness Ni film was imposed as the diffusion barrier layer between the Au film and the alloy substrate to improve the low-emissivity durability of the Au film at high temperature. The results show that the Au/Ni multilayer films still kept low emissivity after working at 600°C for 200h. It was concluded that the Ni interlayer effectively retarded the diffusion between gold film and the metal alloy below 600°C.

Keywords: PACS; 81.05.−t; 61.80.Ba; 68.60.−p; 66.30.NyLow emissivity; Diffusion barrier; Au/Ni multilayer films; High-temperature application

Calculation of the surface energy of fcc-metals with the empirical electron surface model by Baoqin Fu; Wei Liu; Zhilin Li (pp. 6899-6907).

The empirical electron surface model (EESM) based on the empirical electron theory and the dangling bond analysis method has been used to establish a database of surface energy for low-index surfaces of fcc-metals such as Al, Mn, Co, Ni, Cu, Pd, Ag, Pt, Au, and Pb. A brief introduction of EESM will be presented in this paper. The calculated results are in agreement with experimental and other theoretical values. Comparison of the experimental results and calculation values shows that the average relative error is less than 10% and these values show a strong anisotropy. As we predicted, the surface energy of the close-packed plane (111) is the lowest one of all index surfaces. For low-index planes, the order of the surface energies is γ(11₁₎< γ(10₀₎< γ(11₀₎< γ(21₀₎. It is also found that the dangling bond electron density and the spatial distribution of covalent bonds have a great influence on surface energy of various index surfaces.

Keywords: Surface energy; fcc-metals; Empirical electron theory; Valence electron structure; Dangling bond

5-(Perfluorooctylthio)acetamidofluorescein (5-FOAF) as a convenient tag for inspecting the surface coverage of fluorinated coatings by Yu-Ting Li; Huang-Han Chen; Boppudi Hari Babu; Ya-Yu Hsieh; Shu-Hui Chen (pp. 6908-6913).

Fluorinated compounds are commonly used for anti-stick coating but it is difficult to inspect the coverage of the coating without expensive instruments. Herein, we demonstrated that the 5-(perfluorooctylthio)acetamidofluorescein (5-FOAF) probe can be synthesized in one step and used as a testing reagent to inspect the fluorinated coating on silica- or metal-based surfaces. 5-FOAF is composed of a perfluoroalkyl domain, which has high specific affinity towards fluorinated compounds, and a fluorophore domain, which exhibits fluorescence emission visible by naked eyes. Thus, 5-FOAF will retain on the surface coated with fluorinated compounds but not on the un-coated surface and the emitted fluorescence from the retained tags serves as a semi-quantitative measure of the fluorine coverage across the surface. For this study, silica-based or metal-based surfaces were activated by silane chemistry and then coated with fluorinated compounds. The coating procedure was judiciously optimized to achieve a homogeneous coating. 5-FOAF probe was synthesized in-house and shown to retain on the fluorinated surface 2–5 times stronger than the bare surface. Moreover, by studying the retention on a non-fluoro hydrophobic substrate made of polydimethylsiloxane, the affinity of 5-FOAF with the fluorinated coating was confirmed to be specific and distinguishable from nonspecific hydrophobic interaction. In conclusion, we synthesized a novel chemical, 5-FOAF, and demonstrated its usefulness as a simple testing reagent for fluorinated coatings.

Keywords: Anti-sticking; Coating sensing; 5-FOAF; F-SAM; Fluorous affinity

Ni–P alloy–carbon black composite films fabricated by electrodeposition by Yosuke Suzuki; Susumu Arai; Morinobu Endo (pp. 6914-6917).

Ni–P alloy–carbon black (CB) composite films were fabricated by electroplating and their microstructures and properties were examined. The CB and phosphorus contents of the composite films were also investigated. The CB particles were found to be embedded in the Ni–P alloy matrix. The CB content in the deposits increased, reached a maximum value of 0.77mass% with increasing CB concentration in the bath up to 10gdm⁻³, and then decreased with a further increase in the CB concentration in the bath. Both before and after heat treatment, the composite films had higher hardnesses and lower friction coefficients than the Ni–P alloy films. Both before and after heat treatment, the friction coefficient of 0.77mass% CB composite films was about half that of Ni–P alloy films without CB.

Keywords: Carbon black; Ni–P alloy; Composite film; Electrodeposition

Laser ablation synthesis of indium oxide nanoparticles in water by N. Acacia; F. Barreca; E. Barletta; D. Spadaro; G. Currò; F. Neri (pp. 6918-6922).

Colloidal solutions of Indium oxide nanoparticles have been produced by means of laser ablation in liquids (LALs) technique by simply irradiating with a second harmonic (532nm) Nd:YAG laser beam a metallic indium target immersed in distilled water and varying the laser fluence up to 10Jcm⁻² and the ablation time up to 120min. At all the investigated fluences the vaporization process of the indium target is the dominant one. It produces a majority (>80%) of small size (<6nm) nanoparticles, with a very limited content of larger ones (size between 10 and 20nm). The amount of particles increases regularly with the ablation time, supporting the scalability of the production technique. The deposited nanoparticles stoichiometry has been verified by both X-ray photoelectron spectroscopy (XPS) and Energy Dispersive X-ray (EDX) analysis. Optical bandgap values of 3.70eV were determined by UV–vis absorption measurements. All these results confirm the complete oxidation of the ablated material.

Keywords: Indium oxide nanoparticles; Laser ablation in liquid; Morphology; Chemical composition

Effect of calendering on paper surface properties by P. Vernhes; M. Dubé; J.-F. Bloch (pp. 6923-6927).

Calendering of paper is an industrial finishing process designed to smoothen its surface so as to improve gloss as well as printability. In this article, we describe how calendering affects paper roughness on both microscopic and macroscopic length scales. We also discuss how these modifications relate to the morphology of the fibers composing the paper sheets. The characterization of the surface is carried out using an optical profilometer and two different species of fibers, as well as their mixture, are used. We first show that calendering induces modifications of the surface on all length scales measured and that these modifications are related by straightforward transformations. We also show that these results hold for papers formed from a mixture of fibers.

Keywords: Calendering; Different scales; Natural Fibers; Paper; Topography

Novel ultraviolet photoluminescence of ZnO/ZnGa₂O₄ composite layers by Qing Yang; Yu Saeki; Sotaro Izumi; Takao Nukui; Atsushi Tackeuchi; Akihiro Ishida; Hirokazu Tatsuoka (pp. 6928-6931).

ZnO/ZnGa₂O₄ composite layers were synthesized by simple thermal oxidation of ZnS substrates with gallium in the air. The continuous-wave and time-resolved photoluminescence measurements for the composites were performed at room temperature. It is found that the visible deep level emission from ZnO in ZnO/ZnGa₂O₄ composite layer was almost suppressed. In addition, the UV emission with long lifetime was also observed in comparison with that of pure ZnO layer without ZnGa₂O₄.

Keywords: PACS; 78.20.−e; 78.47.jd; 78.55.−m; 78.55.EtZnO/ZnGa; ₂; O; ₄; Ultraviolet photoluminescence; Relaxation; Thermal oxidation; Gallium

Novel synthesis and electrophoretic response of low density TiO–TiO₂–carbon black composite by Tingfeng Tan; Shirong Wang; Shuguang Bian; Xianggao Li; Yong An; Zhaojun Liu (pp. 6932-6935).

Novel low density TiO–TiO₂–carbon black composite was synthesized, which involved the deposition of inorganic coating on the surface of core–shell latex particles and subsequent removal of latex particles by calcination in high-purity nitrogen. The morphology and interior structure were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The images exhibited the composite had spherical shape and smooth surface, and the interior structure was hollow or porous. X-ray diffraction peaks (XRD) were mostly in agreement with the standard diffraction patterns of rutile TiO₂. In addition, the observed peaks at 2 θ of 43.5°, 50.6° and 74.4° can be indexed to (111), (200) and (220) planes of cubic phase TiO. The X-ray photoelectron spectroscopy (XPS) results indicated that composite consisted of carbon black, TiO and TiO₂. The apparent density of the composite was suitable to 1.62gcm⁻³, due to density matching with suspending media. Glutin–arabic gum microcapsules containing TiO–TiO₂–carbon black composite electrophoretic liquid were prepared via complex coacervation. The particles in the microcapsules showed excellent electrophoretic mobility under a DC field.

Keywords: Composites; Titanium oxide; Carbon black; Microencapsulation; Electrophoresis

Thermal stability of SiGe films on an ultra thin Ge buffer layer on Si grown at low temperature by Chengzhao Chen; Zhiwen Zhou; Yanghua Chen; Cheng Li; Hongkai Lai; Songyan Chen (pp. 6936-6940).

The thermal stability of SiGe films on an ultra thin Ge buffer layer on Si fabricated at low temperature has been studied. The microstructure and morphology of the samples were investigated by high-resolution X-ray diffraction, Raman spectra and atomic force microscopy, and using a diluted Secco etchant to reveal dislocation content. After thermal annealing processing, it is observed that undulated surface, threading dislocations (TDs) and stacking faults (SFs) appeared at the strained SiGe layer, which developed from the propagation of a misfit dislocation (MD) during thermal annealing, and no SFs but only TDs formed in strain-relaxed sample. And it is found that the SiGe films on the Ge layer grown at 300°C has crosshatch-free surface and is more stable than others, with a root mean square surface roughness of less than 2nm and the threading dislocation densities as low as ∼10⁵cm⁻². The results show that the thermal stability of the SiGe films is associated with the Ge buffer layer, the relaxation extent and morphology of the SiGe layer.

Keywords: PACS; 68.55.−a; 78.30.−j; 68.37. Ps; 62.40. +iThermal stability; SiGe; LT–Ge; Strain relaxation

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Applied Surface Science (v.256, #22)

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Applied Surface Science (v.256, #22)