Applied Surface Science (v.256, #24)

Characterization of ZrO2-promoted Cu/ZnO/nano-Al2O3 methanol steam reforming catalysts by Samuel D. Jones; Luke M. Neal; Michael L. Everett; Gar B. Hoflund; Helena E. Hagelin-Weaver (7345-7353).
Three Cu/ZnO/ZrO2/Al2O3 methanol reforming catalysts were investigated using X-ray photoelectron spectroscopy (XPS). The catalysts which contained ZrO2 from a monoclinic nanoparticle ZrO2 precursor exhibit both a higher activity toward the methanol steam reforming reaction and a lower CO production rate compared to catalysts composed of an XRD-amorphous ZrO2 produced by impregnation using a Zr(NO3)2 precursor. The presence of a monoclinic phase appears to result in an increased charge transfer between the Zr and Cu species, as evidenced by a relatively electron-rich ZrO2 phase and a partially oxidized Cu species on reduced catalysts. This electron deficient Cu species is more reactive toward the methanol reforming reaction and partially suppresses CO formation through the reverse water gas shift or methanol decomposition reactions.
Keywords: Methanol steam reforming; Copper catalyst; Cu/ZnO/ZrO2/Al2O3; Hydrogen production; Nanoparticle zirconia; XPS;

To improve the anterior surface biocompatibility of hydrophobic acrylic intraocular lens (IOL) in a convenient and continuous way, poly(ethylene glycol)s (PEGs) were immobilized by atmospheric pressure glow discharge (APGD) treatment using argon as the discharge gas. The hydrophilicity and chemical changes on the IOL surface were characterized by static water contact angle and X-ray photoelectron spectroscopy to confirm the covalent binding of PEG. The morphology of the IOL surface was observed under field emission scanning electron microscopy and atomic force microscopy. The surface biocompatibility was evaluated by adhesion experiments with platelets, macrophages, and lens epithelial cells (LECs) in vitro. The results revealed that the anterior surface of the PEG-grafted IOL displayed significantly and permanently improved hydrophilicity. Cell repellency was observed, especially in the PEG-modified IOL group, which resisted the attachment of platelets, macrophages and LECs. Moreover, the spread and growth of cells were suppressed, which may be attributed to the steric stabilization force and chain mobility effect of the modified PEG. All of these results indicated that hydrophobic acrylic IOLs can be hydrophilic modified by PEG through APGD treatment in a convenient and continuous manner which will provide advantages for further industrial applications.
Keywords: Intraocular lens; Surface modification; Poly(ethylene glycol); Atmospheric pressure glow discharge; Biocompatibility;

N-type Bi2Te2.7Se0.3 thermoelectric thin films with thickness 800 nm have been deposited on glass substrates by flash evaporation method at 473 K. Annealing effects on the thermoelectric properties of Bi2Te2.7Se0.3 thin films were examined in the temperature range 373–573 K. The structures, morphology and chemical composition of the thin films were characterized by X-ray diffraction, field emission scanning electron microscope and energy dispersive X-ray spectroscopy, respectively. Thermoelectric properties of the thin films have been evaluated by measurements of the electrical resistivity and Seebeck coefficient at 300 K. The Hall coefficients were measured at room temperature by the Van der Pauw method. The carrier concentration and mobility were calculated from the Hall coefficient. The films thickness of the annealed samples was measured by ellipsometer. When annealed at 473 K, the electrical resistivity and Seebeck coefficient are 2.7 mΩ cm and −180 μV/K, respectively. The maximum of thermoelectric power factor is enhanced to 12 μW/cm K2.
Keywords: Bi2Te2.7Se0.3; Thin film; Electrical transport properties; Annealing; Flash evaporation;

The effect of substrate bias on X-ray photoelectron spectroscopy (XPS) study of nitrogen incorporated amorphous carbon (a-C:N) films embedded with nanoparticles deposited by filtered cathodic jet carbon arc technique is discussed. High resolution transmission electron microscope exhibited initially the amorphous structure but on closer examination the film was constituted of amorphous phase with the nanoparticle embedded in the amorphous matrix. X-ray diffraction study reveals dominantly an amorphous nature of the film. A straight forward method of deconvolution of XPS spectra has been used to evaluate the sp3 and sp2 contents present in these a-C:N films. The carbon (C 1s) peaks have been deconvoluted into four different peaks and nitrogen (N 1s) peaks have been deconvoluted into three different peaks which attribute to different bonding state between C, N and O. The full width at half maxima (FWHM) of C 1s peak, sp3 content and sp3/sp2 ratio of a-C:N films increase up to −150 V substrate bias and beyond −150 V substrate bias these parameters are found to decrease. Thus, the parameters evaluated are found to be dependent on the substrate bias which peaks at −150 V substrate bias.
Keywords: XPS; Filtered cathodic jet carbon arc; Nanoparticle; a-C:N; Substrate bias;

Development of electroless Ni–Zn–P/nano-TiO2 composite coatings and their properties by S. Ranganatha; T.V. Venkatesha; K. Vathsala (7377-7383).
Ni–Zn–P–TiO2 composite coatings were successfully obtained on low carbon steel by electroless plating technique. Deposits were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive analysis (EDS) studies. The hardness and microstructure of as plated and heat treated Ni–Zn–P and Ni–Zn–P–TiO2 composite coatings were analyzed. The change in microstructure and higher hardness was noticed for heat treated composite. The corrosion resistance behavior of as plated and heat treated Ni–Zn–P and Ni–Zn–P–TiO2 coatings was investigated by anodic polarization, Tafel plots and electrochemical impedance spectroscopic (EIS) studies in 3.5 wt% NaCl solution. The composite coating exhibited enhanced corrosion resistance property over Ni–Zn–P coating.
Keywords: Electroless Ni–Zn–P–TiO2; Composites; Metal matrix; Coatings; Corrosion; Microstructure;

Atomic oxygen erosion resistance of polyimide/ZrO2 hybrid films by Fei Xiao; Kai Wang; Maosheng Zhan (7384-7388).
A series of polyimide/zirconia (PI/ZrO2) hybrid films were synthesized based on zirconium n-butoxide, pyromellitic acid dianhydride (PMDA) and 4,4′-oxydianiline (ODA) by a sol–gel process. The atomic oxygen (AO) exposure tests were carried out using a ground-based atomic oxygen effects simulation facility. The effects of ZrO2 content on the morphology and structure evolvement of PI/ZrO2 hybrid films were investigated using field emission scanning electron microscopy (FE-SEM) and X-ray photoelectron spectrometer (XPS), respectively. The results indicated that a zirconia-rich layer was formed on the polyimide film sourcing from the zirconium n-butoxide after AO exposure, which decreased the erosion rate and obviously improved the AO resistance of polyimide films.
Keywords: Polyimide; Zirconia; Atomic oxygen; XPS; Low earth orbit;

A fluorine-contained copolymer ultra-thin film: Stability and electrochemical corrosion behavior by Jia Luo; Jinchun Cheng; Xiaoning Dong; Yijun Liu; Guosheng Huang; Junyan Zhang (7389-7394).
A novel fluorine-contained random copolymer (2,3,4,5,6-pentafluorostyrene)-r-poly(4-vinyl benzocyclobutene) (P(PFSt-r-4-VBCB)) was synthesized, and then spin-coated onto Si substrates followed by thermal cross-linking to produce the copolymer ultra-thin films. Although the surface modification with the P(PFSt-r-4-VBCB) film was simple and did not rely on special surface chemical reactions, the film could decrease the surface energy significantly, more importantly; the film demonstrated excellent stability and corrosion resistance. This random copolymer film could find broad applications in modifying various solid surfaces to enhance the properties such as corrosion resistance and solvent resistance.
Keywords: Copolymer; Ultra-thin film; Electrochemical corrosion; Surface modification;

Fe + 50 wt.% WC composite coating was prepared by laser induction hybrid rapid cladding (LIHRC) on steel substrate. The phase and microstructure of the composite coating were investigated by X-ray diffraction (XRD), environmental scanning electron microscope (ESEM) and energy dispersive spectrum (EDS). The results showed that WC particles were dissolved almost completely to precipitate the coarse herringbone M6C eutectic carbides and the fine dendritic M6C carbides, and that the partially dissolved WC particles with an alloyed reaction layer were occasionally observed in the whole coating. The phases of the composite coating were composed of supersaturated solid solution α-Fe, retained austenite, Fe3C, W2C, M6C and M7C3. The microstructure evolution in the composite coating was represented by the transformation of three parts such as Fe-based metallic matrix, dispersed carbides and incompletely dissolved WC particles. The microhardness of Fe-based WC composite coating was three times much higher than that of the substrate, but was relatively lower than that of Ni-based WC composite coating by LIHRC.
Keywords: Laser induction hybrid rapid cladding (LIHRC); Coating; Fe-based WC; Eutectic carbides; Microstructure;

We studied computationally the relative stability of PtML/WC(0 0 0 1) [pseudomorphic monolayer of Pt(1 1 1) on WC(0 0 0 1)] interfacial structures using a density functional slab model approach. The work of adhesion was calculated for six different interfacial structures, taking into account both W- and C-terminations of the carbide. The results show that the optimal interfacial structure of PtML/WC(0 0 0 1) is the W-terminated WC(0 0 0 1) with Pt atoms adhesion on the hcp site (W-hcp). The nature of metal/carbide bonding for the W-hcp interfacial geometry was determined on the basis of the partial density of states (PDOS). Adsorption of atomic hydrogen and dissociation of the hydrogen molecule on the W-hcp PtML/WC(0 0 0 1) was investigated and compared to that on Pt(1 1 1). It is found that the most favorable H2 dissociation channels need similar activation energies of 5.28 and 4.93 kJ/mol on PtML/WC(0 0 0 1) and Pt(1 1 1), respectively, with the release of considerable reaction energies. Furthermore, adsorption of CO on the W-hcp PtML/WC(0 0 0 1) and Pt(1 1 1) was also investigated. The results indicate that PtML/WC(0 0 0 1) is much less susceptible to CO poisoning than Pt(1 1 1), especially at the low coverage of CO.
Keywords: Density functional theory; Dissociation; Hydrogen molecule; Monoxide carbon; Carbide;

Using the effective mass and parabolic band approximations and a variational procedure we have calculated the combined effects of intense laser radiation, hydrostatic pressure, and applied electric field on shallow-donor impurity confined in cylindrical-shaped single and double GaAs–Ga1−x Al x As QD. Several impurity positions and inputs of the heterostructure dimensions, hydrostatic pressure, and applied electric field have been considered. The laser effects have been introduced by a perturbative scheme in which the Coulomb and the barrier potentials are modified to obtain dressed potentials. Our findings suggest that (1) for on-center impurities in single QD the binding energy is a decreasing function of the dressing parameter and for small dot dimensions of the structures (lengths and radius) the binding energy is more sensitive to the dressing parameter, (2) the binding energy is an increasing/decreasing function of the hydrostatic pressure/applied electric field, (3) the effects of the intense laser field and applied electric field on the binding energy are dominant over the hydrostatic pressure effects, (4) in vertically coupled QD the binding energy for donor impurity located in the barrier region is smaller than for impurities in the well regions and can be strongly modified by the laser radiation, and finally (5) in asymmetrical double QD heterostructures the binding energy as a function of the impurity positions follows a similar behavior to the observed for the amplitude of probability of the noncorrelated electron wave function.
Keywords: Intense laser effects; Quantum wells; Hydrostatic pressure; Electric field; Impurity;

Electrodeposition of nickel/SiC composites in the presence of cetyltrimethylammonium bromide by Ewa Rudnik; Lidia Burzyńska; Łukasz Dolasiński; Maciej Misiak (7414-7420).
Electrodeposition of SiC particles with nickel matrix in the presence of cetyltrimethylammonium bromide (CTAB) at two current densities was carried out. Surface chemistry (amount of acidic and basic superficial groups, surface charge, Ni2+ and Br adsorption) of the SiC powder in the presence of various CTAB amounts (0–1.1 mM) was studied. Cationic surfactant inhibited adsorption of cations and enhanced adsorption of anions on the positive charged carbide surface, but Br/Ni2+ molar ratios for adsorbed ions were higher than in the bath. It was attributed to the CTAB adsorption realized predominantly by hydrophobic interactions between aliphatic chain of the molecule and SiC surface with the positive head group of CTA+ pointed toward the bulk solution. Increased SiC incorporation to the composite coating with CTAB addition was observed. Correlation between current efficiency and Br/Ni2+ molar ratios for ions adsorbed on SiC was found. The influence of CTAB concentration on the cathodic polarization curves was also determined. Structure of the composite coatings was studied by microscopic observations. Microhardness of the fine-grained metal matrix composites was also determined.
Keywords: Nickel; Silicon carbide; Composite; Electrodeposition; Surfactant; Adsorption;

In most laser material processing, material removal by different mechanisms is involved. Here, application of acoustic signals with thermoelastic (below threshold) and breakdown origin (above threshold) together with plasma plume analysis as a simple monitoring system of interaction process is suggested. In this research the interaction of pulse CO2 laser with 200 ns duration and maximum energy of 1.3 J operating at 1 Hz with austenitic stainless steel (316-L) is reported. The results showed that the non-linear point of the curve can serve as a useful indicator of melting fluence threshold (in this case ≈830 J cm−2) with corresponding temperature calculated using plasma plume analysis. Higher acoustic amplitudes and larger plasma plume volume indicates more intense interaction. Also, analysis showed that a phase explosion process with material removal (ejecta) in the form of non-adiabatic (i.e., d t  ≫  α −1) is at play after laser pulse is ended. Also, SEM photographs show different surface quality medication at different laser intensities, which indicates the importance of recoil momentum pressure and possibly electrons and ions densities in heat transfer. Finally, electrochemical test indicate an improved corrosion resistance for laser treated samples compared to untreated ones.
Keywords: CO2 laser; Stainless steel; Monitoring; Acoustic; Plasma plume;

Development of hydrogel microstructures on single-walled carbon nanotube films by Cheng Ai Li; Kwi Nam Han; Minh-Phuong Ngoc Bui; Xuan-Hung Pham; Gi Hun Seong (7428-7433).
In this study, the development of polyethylene glycol (PEG) hydrogel microstructures led to the micropatterning of single-walled carbon nanotube (SWCNT) films. Polyethylene glycol was patterned in a process analogous to photolithography in order to manufacture high-density arrays of micrometer-scale hydrogel wells on SWCNT film surfaces. These microwells were composed of hydrophobic SWCNT films surrounded by hydrophilic PEG hydrogel walls. Effects of PEG hydrogel microstructures on the micropatterning of SWCNT films were systematically investigated under different substrates prepared with 3-(trichlorosilyl)propyl methacrylate or octadecyltrichlorosilane solution. A characterization of protein adsorption and an electrochemiluminescence (ECL) reaction were performed to evaluate the biocompatible and electrical efficiency of the patterned SWCNT films in various applications. The proteins selectively adhered to the SWCNT surface inside the microwells, while adherent proteins were absent from the hydrogel walls. In the ECL reaction, the SWCNT films patterned with PEG hydrogel exhibited good, stable ECL behavior, a sign that patterned SWCNT films can be used as flexible and transparent electrodes.
Keywords: Single-walled carbon nanotube films; Polyethylene glycol hydrogel; Micropatterning; Photopolymerization; Electrochemiluminescence;

GaAs surface passivation by plasma-enhanced atomic-layer-deposited aluminum nitride by M. Bosund; P. Mattila; A. Aierken; T. Hakkarainen; H. Koskenvaara; M. Sopanen; V.-M. Airaksinen; H. Lipsanen (7434-7437).
A low-temperature passivation method for GaAs surfaces is investigated. Ultrathin AlN layers are deposited by plasma-enhanced atomic-layer-deposition at 200  ° C on top of near-surface InGaAs/GaAs quantum well structures. A significant passivation effect is seen as shown by up to 30 times higher photoluminescence intensity and up to seven times longer lifetime compared to uncoated reference samples. The improved optical properties are accompanied by a redshift of the quantum well photoluminescence peak likely caused by a combination of the nitridation of the GaAs capping layer and a surface coupling effect.
Keywords: GaAs passivation; Plasma-enhanced ALD; Aluminum nitride;

Co-sensitized quantum dot solar cell based on ZnO nanowire by J. Chen; J. Wu; W. Lei; J.L. Song; W.Q. Deng; X.W. Sun (7438-7441).
An efficient photoelectrode is fabricated by sequentially assembled CdS and CdSe quantum dots (QDs) onto a ZnO-nanowire film. As revealed by UV–vis absorption spectrum and scanning electron microscopy (SEM), CdS and CdSe QDs can be effectively adsorbed on ZnO-nanowire array. Electrochemical impedance spectroscopy (EIS) measured demonstrates that the electron lifetime for ZnO/CdS/CdSe (13.8 ms) is calculated longer than that of ZnO/CdS device (6.2 ms), which indicates that interface charge recombination rate is reduced by sensitizing CdSe QDs. With broader light absorption range and longer electron lifetime, a power conversion efficiency of 1.42% is achieved for ZnO based CdS/CdSe co-sensitized solar cell under the illumination of one Sun (AM 1.5G, 100 mW cm−2).
Keywords: Quantum dot; Solar cell; CdS; CdSe; ZnO nanowire;

Structural and morphological study of ZnO thin films electrodeposited on n-type silicon by N. Ait Ahmed; G. Fortas; H. Hammache; S. Sam; A. Keffous; A. Manseri; L. Guerbous; N. Gabouze (7442-7445).
In this work, we report on the electrodeposition of ZnO thin films on n-Si (1 0 0) and glass substrates. The influence of the deposition time on the morphology of ZnO thin films was investigated. The ZnO thin films were characterized by X-ray diffraction (XRD), energy dispersive X-ray (EDS) and scanning electron microscopy (SEM). The results show a variation of ZnO texture from main (0 0 2) at 10 min to totally (1 0 1) at 15 min deposition time. The photoluminescence (PL) studies show that both UV (∼382 nm) and blue (∼432 nm) luminescences are the main emissions for the electrodeposited ZnO films. In addition, the film grown at 15 min indicates an evident decrease of the yellow-green (∼520 nm) emission band comparing with that of 10 min. Finally, transmittance spectra show a high transmission value up to 85% in the visible wavelength range. Such results would be very interesting for solar cells applications.
Keywords: Silicon; Morphology; Electrodeposition; Zinc oxide; Diffraction;

Effect of mesh patterning with UV pulsed-laser on optical and electrical properties of ZnO/Ag–Ti thin films by K.S. Kao; D.L. Cheng; S.H. Chang; P.T. Hsieh; H.S. Chin; H.K. Lin (7446-7450).
In this study, the ZnO/Ag–Ti structure for transparence conducting oxide (TCO) is investigated by optimizing the thickness of the Ag–Ti alloy and ZnO layers. The Ag–Ti thin film is deposited by DC magnetron sputtering and its thicknesses is well controlled. The ZnO thin film is prepared by sol–gel method using zinc acetate as cation source, 2-methoxiethanol as solvent and monoethanolamine as solution stabilizer. The ZnO film deposition is performed by spin-coating technique and dried at 150 °C on Corning 1737 glass. Due to the conductivity of ZnO/Ag–Ti is dominated by Ag–Ti, the sheet resistance of ZnO/Ag–Ti decrease dramatically as the thickness of Ag–Ti layer increases. However, the transmittances of ZnO/Ag–Ti become unacceptable for TCO application after the thickness of Ag–Ti layer beyond 6 nm. The as-deposited ZnO/Ag–Ti structure has the optical transmittance of 83% @ 500 nm and the low resistivity of 1.2 × 10−5  Ω-cm. Furthermore, for improving the optical and electrical properties of ZnO/Ag–Ti, the thermal treatment using laser is adopted. Experimental results indicate that the transmittance of ZnO/Ag–Ti is improved from 83% to 89% @ 500 nm with resistivity of 1.02 × 10−5  Ω-cm after laser drilling. The optical spectrum, the resistance, and the morphology of the ZnO/Ag–Ti will be reported in the study.
Keywords: Transparent conducting oxide; ZnO; Ag–Ti; Laser patterning;

Superhydrophobic and transparent zinc oxide (ZnO) thin films were deposited by a simple and cost effective spray pyrolysis technique (SPT) onto the glass substrates at 723 K from an aqueous zinc acetate precursor solution. The solution concentration was varied from 0.1 to 0.4 M and its effect on structural, morphological, wetting and optical properties of ZnO thin films was studied. The synthesized films were found to be polycrystalline, with preferential growth along c-axis. A slight improvement in the crystallite size and texture coefficient is observed as the concentration of the solution is increased. SEM micrographs show the uniform distribution of spherical grains of about 60–80 nm grain size. The films were specular and highly transparent with average transmittance of about 85%. The spectrum shows sharp absorption band edge at 381 nm, corresponding to optical gap of 3.25 eV. The samples of texture coefficient less than 90% and roughness less than 75 nm are hydrophobic and above these values they become superhydrophobic in nature. The hydrophobicity coupled with high transmittance is of great importance in commercial application such as transparent self-cleaning surfaces, anti-fog, anti-snow, fluid microchips and microreactors.
Keywords: Thin films; Zinc oxide; X-ray diffraction; SEM; Optical properties; Contact angle;

A novel surface cleaning method for chemical removal of fouling lead layer from chromium surfaces by Kh. Gholivand; M. Khosravi; S.G. Hosseini; M. Fathollahi (7457-7461).
Most products especially metallic surfaces require cleaning treatment to remove surface contaminations that remain after processing or usage. Lead fouling is a general problem which arises from lead fouling on the chromium surfaces of bores and other interior parts of systems which have interaction with metallic lead in high temperatures and pressures. In this study, a novel chemical solution was introduced as a cleaner reagent for removing metallic lead pollution, as a fouling metal, from chromium surfaces. The cleaner aqueous solution contains hydrogen peroxide (H2O2) as oxidizing agent of lead layer on the chromium surface and acetic acid (CH3COOH) as chelating agent of lead ions. The effect of some experimental parameters such as acetic acid concentration, hydrogen peroxide concentration and temperature of the cleaner solution during the operation on the efficiency of lead cleaning procedure was investigated. The results of scanning electron microscopy (SEM) showed that using this procedure, the lead pollution layer could be completely removed from real chromium surfaces without corrosion of the original surface. Finally, the optimum conditions for the complete and fast removing of lead pollution layer from chromium surfaces were proposed. The experimental results showed that at the optimum condition (acetic acid concentration 28% (V/V), hydrogen peroxide 8% (V/V) and temperature 35 °C), only 15-min time is needed for complete removal of 3 g fouling lead from a chromium surface.
Keywords: Metallic surface cleaning; Fouling lead; Chemical removal; Cleaner solution; Chelating agents;

Cr-modified silicide coatings were prepared on a Ti–Nb–Si based ultrahigh temperature alloy by Si–Cr co-deposition at 1250 °C, 1350 °C and 1400 °C for 5–20 h respectively. It was found that both coating structure and phase constituents changed significantly with increase in the co-deposition temperature and holding time. The outer layers in all coatings prepared at 1250 °C for 5–20 h consisted of (Ti,X)5Si3 (X represents Nb, Cr and Hf elements). (Ti,X)5Si4 was found as the only phase constituent in the intermediate layers in both coatings prepared at 1250 °C for 5 and 10 h, but the intermediate layers in the coatings prepared at 1250 °C for 15 and 20 h were mainly composed of (Ti,X)5Si3 phase that was derived from the decomposition of (Ti,X)5Si4 phase. In the coating prepared at 1350 °C for 5 h, single (Ti,X)5Si3 phase was found in its outmost layer, the same as that in the outer layers in the coatings prepared at 1250 °C; but in the coatings prepared at 1350 °C for 10–20 h, (Nb1.95Cr1.05)Cr2Si3 ternary phase was found in the outmost layers besides (Ti,X)5Si3 phase. In the coatings prepared at 1400 °C for 5–20 h, (Nb1.95Cr1.05)Cr2Si3 ternary phase was the single phase constituent in their outmost layers. The phase transformation (Ti,X)5Si4  → (Ti,X)5Si3  + Si occurred in the intermediate layers of the coatings prepared at 1350 and 1400 °C with prolonging co-deposition time, similar to the situation in the coatings prepared at 1250 °C for 15 and 20 h, but this transformation has been speeded up by increase in the co-deposition temperature. The transitional layers were mainly composed of (Ti,X)5Si3 phase in all coatings. The influence of co-deposition temperature on the diffusion ability of Cr atoms was greater than that of Si atoms in the Si–Cr co-deposition processes investigated. The growth of coatings obeyed inverse logarithmic laws at all three co-deposition temperatures. The Si–Cr co-deposition coating prepared at 1350 °C for 10 h showed a good oxidation resistance due to the formation of SiO2 and Nb, Cr-doped TiO2 scale after oxidation at 1250 °C for 10 h.
Keywords: Ti–Nb–Si based ultrahigh temperature alloy; Coating structure; Phase constituents; Cr-modified silicide coating; Pack cementation process;

A facile, low-temperature, and low-cost chemical route has been developed to prepare ZnO nanowire and nanosphere compound structures. The morphology, structure, and composition of the yielded products have been examined by field-emission scanning electron microscopy, transmission electron microscopy, and X-ray diffraction measurements. We have systematically investigated the optical properties of the ZnO nanostructures by micro-Raman, photoluminescence, and transmission spectroscopy. The results demonstrate that the yielded ZnO nanostructures possess good optical quality with high light absorption. We have further successfully employed the obtained ZnO compound nanostructures in dye-sensitized solar cells. The light-to-electricity conversion results show that the compound nanostructure exhibits a significant enhancement of short-circuit current density due to the increased surface area and light scattering in the compound nanostructures. The present chemical route provides a simple way to synthesize various compound nanostructures with high surface area for nanodevice applications.
Keywords: Nanostructures; Semiconductors; Chemical synthesis; Photoconductivity and photovoltaics;

Contact angle measurements on poly(tetrafluoroethylene) (PTFE) surface were carried out for the systems containing ternary mixtures of cetyltrimethylammonium bromide (CTAB) and p-(1,1,3,3-tetramethylbutyl)phenoxypoly(ethylene glycols), Triton X-100 (TX100) and Triton X-165 (TX165). The aqueous solution of ternary surfactant mixtures were prepared by adding the third surfactant to the binary mixture of the surfactants where the synergetic effect in the reduction of the surface tension of water was determined, to compare the influence of the third surfactants on the values of surface tension of this binary mixture and the values of the contact angle on PTFE. The obtained results and calculations indicate that the ternary mixtures of CTAB + TX165 (αCTAB = 0.2, γ LV  = 60 and 50 mN/m) + TX100 (C  = 10−8 to 10−2  M) have the biggest efficiency of the reduction of contact angle of water on PTFE in comparison to aqueous solutions of the single surfactants and their binary and ternary mixtures. Also in the case of all studied ternary mixtures of surfactants at concentrations of the bulk phase corresponding to unsaturated monolayer at water–air interface the adsorption of surfactants at PTFE–water interface is different than that at water–air interface, but is the same at concentrations near the critical micelle concentration (CMC). Thus the linear dependences between γ LV  cos  θ  −  γ LV and cos  θ  − 1/γ LV, in the range of concentration studied for all systems confirm the same adsorption at two interfaces only at C near the CMC.
Keywords: Cationic surfactant; Nonionic surfactant; Ternary mixtures of surfactants; Poly(tetrafluoroethylene); Wettability;

Substrate temperature influence on the trombogenicity in amorphous carbon nitride thin coatings by D.S. Galeano-Osorio; S. Vargas; L.M. López-Córdoba; R. Ospina; E. Restrepo-Parra; P.J. Arango (7484-7489).
Carbon nitride thin films were obtained through plasma assisted physical vapor deposition technique by pulsed arc, varying the substrate temperature and investigating the influence of this parameter on the films hemocompatibility. For obtaining approaches of blood compatibility, environmental scanning electron microscopy (ESEM) was used in order to study the platelets adherence and their morphology. Moreover, the elemental chemical composition was determined by using energy dispersive spectroscopy (EDS), finding C, N and O. The coatings hemocompatibility was evaluated by in vitro thrombogenicity test, whose results were correlated with the microstructure and roughness of the films obtained.During the films growth process, the substrate temperature was varied, obtaining coatings under different temperatures, room temperature (T room), 100 °C, 150 °C and 200 °C. Parameters as interelectrodic distance, voltage, work pressure and number of discharges, were remained constant. By EDS, carbon and nitrogen were found in the films.Visible Raman spectroscopy was used, and it revealed an amorphous lattice, with graphitic process as the substrate temperature was increased. However, at a critical temperature of 150 °C, this tendency was broken, and the film became more amorphous. This film showed the lowest roughness, 2 ± 1 nm. This last characteristic favored the films hemocompatibility. Also, it was demonstrated that the blood compatibility of carbon nitride films obtained were affected by the I D/I G or sp3/sp2 ratio and not by the absolute sp3 or sp2 concentration.
Keywords: Carbon nitride films; Hemocompatibility; Raman spectroscopy; Roughness; Substrate temperature;

Bias voltage effect on the structure and property of chromium copper–diamond-like carbon multilayer films fabricated by cathodic arc plasma by Jui-Yun Jao; Sheng Han; Li-Shin Chang; Chi-Lung Chang; Yu-Ching Liu; Han C. Shih (7490-7495).
Chromium copper–diamond-like carbon (Cr:Cu)-DLC films were deposited onto silicon and by cathodic arc evaporation process using chromium (Cr) and copper (Cu) target arc sources to provide Cr and Cu in the Me-DLC. Acetylene reactive gases were the carbon source and activated at 180 °C at 13 mTorr, and a substrate bias voltage was varied from −50 V to −200 V to provide the (Cr:Cu)-DLC structure. The structure, interface, and chemical bonding state of the produced film were analyzed by transmission electron microscope (TEM), IR Fourier transform (FTIR) spectra, and X-ray photoelectron spectroscopy (XPS). The results showed that the Cr-containing a-C:H/Cu coatings exhibited an amorphous layer of DLC:Cr layer and a crystalline layer of Cu multilayer structure. The profiles of sp3/sp2 (XPS) ratios corresponded to the change of microhardness profile by varying the pressure of the negative DC bias voltage. These (Cr:Cu)-DLC coatings are promising materials for soft substrate protective coatings.
Keywords: Diamond-like carbon; TEM; Cathodic arc evaporation; Multilayer;

Iron oxide thin films were prepared by spray pyrolysis technique (SPT) at various substrate temperatures (T sub ) and different deposition time. X-ray diffraction (XRD) analysis showed that, at T sub  ≥ 350 °C, a single phase of α-Fe2O3 film is formed which has the rhombohedral structure. Moreover, the crystallinity was improved by increasing T sub . The effect of T sub as well as deposition time on the optical dispersion of these films has been investigated. The optical transmittance and reflectance measurements were performed by using spectrophotometer in the wavelength range from 300 to 2500 nm. The refractive index was determined by using Murmann's exact equation. It was observed that, the refractive index increased with increasing in both the T sub and film thickness. The optical dispersion parameters have been evaluated and analyzed by using Wemple–Didomenico equation. The obtained results showed that, the dielectric properties have weak dependencies of growth temperature and film thickness. At T sub  ≥ 350 °C, the average values of oscillator energy, E o and dispersion energy, E d were found to be 5.96 and 34.08 eV. While at different thickness, the average values of dispersion energies were found to be 3.93 and 17.08 eV. Also, the average values of oscillator strength S o and single resonant frequency ω o were estimated 10.78 × 1013  m−2 and 5.99 × 1015  Hz, while at different thickness were evaluating 4.81 × 1013  m−2 and 6.11 × 1015  Hz. Furthermore, the optical parameters such as wavelength of single oscillator λ o , plasma frequency ω p , and dielectric constant ɛ have been evaluated. The carrier concentration N opt by using Drud's theory was obtained the range of 5.07 × 1025  m−3 to 1.04 × 1026  m−3.
Keywords: Optical dispersion; Iron oxide; Spray pyrolysis; Thin films;

Wood is a valuable building material, but it is susceptible to degradation if left unprotected especially when using less durable species. Protection is commonly achieved by applying a suitable finish that should exhibit sufficient penetration, good adhesion and resistance to photo-degradation and weathering. The performance of wood coatings is largely influenced by the adhesion between the coating and substrate and any degradation of the substrate will also affect the coating. The aim of this study was to determine the degree to which the substrate degrades despite the coating and adds to the ageing of the coating from the interface. This effect can be expected to differ for soft- and hardwoods. Coated wood samples from pine and meranti wood – a soft- and hardwood – were irradiated with UV-B light to detect surface changes at various length scales and to assess the impact of the underlying wood substrate on the ageing performance of a commercially available acrylic coating. Surface modifications were determined with atomic force microscopy, Fourier transform infrared spectroscopy, colour spectroscopy, static contact angle and a surface roughness profiler.
Keywords: Surface properties; UV ageing; Roughness; Polarity; Hardness; Surface colour;

The oxidation behaviors of powder metallurgy (PM) Rene95 Ni-based superalloy in the temperature range of 800–1000 °C are investigated in air by virtue of isothermal oxidation testing, X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy. The results show that the oxidation kinetics follows a square power law as the time extends at each temperature. The oxidation layers are detected to be composed of Cr2O3, TiO2 and a small amount of NiCr2O4. The cross-sectional morphologies indicate that the oxidation layer consists of three parts: Cr-rich oxide layer, Cr and Ti duplex oxide layer, and oxidation affected zone. Theoretical analyses of oxidation kinetics and thicknesses of oxidation layers confirm that the activation energy of oxidation of PM Rene95 superalloy is 165.32 kJ mol−1 and the oxidation process is controlled by diffusions of oxygen, Cr, and Ti. Accordingly, a diffusion-controlled mechanism is suggested to understand the oxidation behaviors of PM Rene95 superalloy at elevated temperatures.
Keywords: Nickel based superalloys; Powder metallurgy; Oxidation; Diffusion; Rene95;

Crystalline coiled carbon nano/micro fibers in thin film form have been synthesized via direct current plasma enhanced chemical vapor deposition (PECVD) on copper substrates with acetylene as a carbon precursor at 10 mbar pressure and 750 °C substrate temperature. The as-prepared samples were characterized by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). XRD pattern as well as selected area electron diffraction (SAED) pattern showed that the samples were crystalline in nature. SEM and HRTEM studies showed that as synthesized coiled carbon fibers are having average diameter ∼100 nm and are several micrometers in length. The as-prepared samples showed moderately good electron field emission properties with a turn-on field as low as 1.96 V/μm for an inter-electrode distance 220 μm. The variation of field emission properties with inter-electrode distance has been studied in detail. The field emission properties of the coiled carbon fibrous thin films are compared with that of crystalline multiwalled carbon nanotubes and other carbon nanostructures.
Keywords: Carbon coil; Chemical vapor deposition; Field emission;

Ammonia-gas nitriding of AISI 304 austenitic stainless steel was studied at temperatures higher than 800 °C using SEM and X-ray diffraction. The result showed that S-phase, an expanded austenite, was formed even at such high temperatures due to a high nitriding potential of ammonia gas. The equilibrium phase, CrN was formed through a decomposition of S-layer in two different modes; the one was through continuous precipitation of particles at the surface-side of S-layer due to a higher nitriding potential; the other through a discontinuous(-like) precipitation at the austenite interface-side, producing a fine lamellar structure of austenite and CrN. The γ-phase in the surface-side resulting from the precipitation of CrN particles subsequently transformed into Fe4N because of a fast enrichment of N atoms and a limited mobility of Cr atoms at the surface-side. A coarse lamellar structure made of austenite and Cr2N was developed in front of fine lamellae composed of austenite and CrN by the decomposition of supersaturated austenite through a discontinuous precipitation via grain boundary movement.
Keywords: Gas-nitriding; Nitride-layer; Expanded austenite; Stainless steel; High temperature;

The objective of this study is to investigate how the surface characteristics of indium phosphide (InP) can be modified through the use of atomic hydrogen (H*) cleaning and silicon interfacial control layers (Si ICL), prior to the deposition of MgO dielectric layers. X-ray photoelectron spectroscopy (XPS) analysis shows that the InP native oxide can be successfully removed using atomic hydrogen cleaning at a substrate temperature of 300 °C. However, atomic force microscopy (AFM) images display evidence for the growth of metallic In island features after H* cleaning, and subsequent deposition of MgO thin films on the H* cleaned surface resulted in high levels of interfacial indium oxide growth. It has also been shown that the deposition of thin (∼1 nm) Si layers on InP native oxide surfaces results in the transfer of oxygen from the InP substrate to the Si ICL and the formation of Si–InP bonds. XPS analysis indicates that MgO deposition and subsequent 500 °C annealing results in further oxidation of the Si layer. However, no evidence for the re-growth of interfacial In or P oxide species was observed, in contrast to observations on the H* cleaned surface.
Keywords: III–V semiconductors; InP; Atomic hydrogen; Si control layers; MgO;

The microgravity and high magnetic field simulated by a superconducting magnet were used to investigate the dynamics of deposition mechanisms of hydroxyapatite (HAp) on the surface of Ti-6Al-4V samples. The HAp coatings were derived by a self-assembly-induced biomineralization method in simulated body fluid. The experimental results showed that the amount and growth rate of HAp deposition in the simulated microgravity condition were far less than those in the gravity field, as were those in the high magnetic field compared with those outside the magnet. This may provide insight into the bone loss of astronauts in spaceflight from the viewpoint of the dynamic balance between HAp nucleation, deposition and decomposition on the surface of substrates.
Keywords: Simulated microgravity; Deposition; Hydroxyapatite; Bone loss in space;

Zinc-ion implanted and deposited titanium surfaces reduce adhesion of Streptococccus mutans by Juan Xu; Gang Ding; Jinlu Li; Shenhui Yang; Bisong Fang; Hongchen Sun; Yanmin Zhou (7540-7544).
While titanium (Ti) is a commonly used dental implant material with advantageous biocompatible and mechanical properties, native Ti surfaces do not have the ability to prevent bacterial colonization. The objective of this study was to evaluate the chemical composition and bacterial adhesive properties of zinc (Zn) ion implanted and deposited Ti surfaces (Zn–PIIID–Ti) as potential dental implant materials. Surfaces of pure Ti (cp–Ti) were modified with increasing concentrations of Zn using plasma immersion ion implantation and deposition (PIIID), and elemental surface compositions were characterized by X-ray photoelectron spectrometry (XPS). To evaluate bacterial responses, Streptococcus mutans were seeded onto the modifiedTi surfaces for 48 h and subsequently observed by scanning electron microscopy. Relative numbers of bacteria on each surface were assessed by collecting the adhered bacteria, reculturing and counting colony forming units after 48 h on bacterial grade plates. Ti, oxygen and carbon elements were detected on all surfaces by XPS. Increased Zn signals were detected on Zn–PIIID–Ti surfaces, correlating with an increase of Zn-deposition time. Substantial numbers of S. mutans adhered to cp–Ti samples, whereas bacterial adhesion on Zn–PIIID–Ti surfaces signficantly decreased as the Zn concentration increased (p  < 0.01). In conclusion, PIIID can successfully introduce Zn onto a Ti surface, forming a modified surface layer bearing Zn ions that consequently deter adhesion of S. mutans, a common bacterium in the oral environment.
Keywords: Zinc; Pure titanium; Surface modification; Anti-bacterial property; Streptococcus mutans;

Nanolubrication of sliding components in adaptive optics used in microprojectors by Bharat Bhushan; Hyungoo Lee; Satish C. Chaparala; Vikram Bhatia (7545-7558).
Integrated microprojectors are being developed to project a large image on any surface chosen by the users. For a laser-based microprojector, a piezo-electric based adaptive optics unit is adopted in the green laser architecture. The operation of this unit depends on stick-slip motion between the sliding components. Nanolubrication of adaptive optics sliding components is needed to reduce wear and for smooth operation. In this study, a methodology to measure lubricant thickness distribution with a nanoscale resolution is developed. Friction, adhesion, and wear mechanisms of lubricant on the sliding components are studied. Effect of actual composite components, scan direction, scale effect, temperature, and humidity to correlate AFM data with the microscale device performance is studied.
Keywords: Microprojector; Green laser; Lubricants; Adhesion; Friction; Thickness mapping; Atomic force microscopy;

Aluminum nanoparticles were synthesized by pulsed laser ablation of Al targets in ethanol, acetone, and ethylene glycol. Transmission Electron Microscope (TEM) and Scanning Electron Microscope (SEM) images, Particle size distribution diagram from Laser Particle Size Analyzer (LPSA), UV–visible absorption spectra, and weight changes of targets were used for the characterization and comparison of products. The experiments demonstrated that ablation efficiency in ethylene glycol is too low, in ethanol is higher, and in acetone is highest. Comparison between ethanol and acetone clarified that acetone medium leads to finer nanoparticles (mean diameter of 30 nm) with narrower size distribution (from 10 to 100 nm). However, thin carbon layer coats some of them, which was not observed in ethanol medium. It was also revealed that higher ablation time resulted in higher ablated mass, but lower ablation rate. Finer nanoparticles, moreover, were synthesized in higher ablation times.
Keywords: Aluminum nanoparticles; Laser ablation; Liquid media; Ablation time;

Silicon nanowires for ‘turn-on’ fluorescence detection of Zn(II) by Wenfeng Xu; Lixuan Mu; Haitao Yuan; Taiping Zhang; Wensheng Shi (7565-7569).
The surface of the silicon nanowire was covalently modified with silane derivative of acenaphthene to form a ‘turn-on’ fluorescence sensor for Zn(II). The fluorescent intensities of the sensor were linearly increased with the increment of the Zn(II) concentration in the range of 0.0–20 μM, and a good selectivity and sensitivity to Zn(II) were obtained. Differently from conventional Zn(II) ion fluorescence sensor, the present sensor could be repeatedly used and exhibit a facilitation in practical application.
Keywords: Silicon nanowires; Chemosensor; Fluorescence enhancement; Modification;

In this paper the effect of the laser field on the nonlinear optical properties of a square quantum well under the applied electric field is investigated theoretically. The calculations are performed in saturation limit using the density matrix formalism and the effective mass approach. Our results show that the laser field considerably effects the confining potential of the quantum well and thus the nonlinear optical properties.
Keywords: Quantum well; Intersubband transition; Nonlinear optical properties;

Adsorption of parent nitrosamine (NA) on 5T and 10T cluster models of H–ZSM-5 catalyst has been theoretically investigated using quantum chemical B3LYP and MP2 methods. Three stable complexes (AC) were found on the potential energy surface of interaction between NA and cluster models of H–ZSM-5. NA can interact not only with acidic site of zeolite via the lone electron pair on nitrogen and oxygen atoms (O(N)⋯HZO) but also with the oxygen atoms of the framework via the hydrogen atoms of NH2 group (NH⋯O) as well. However, the Lewis acidity of zeolite framework is the dominating factor in the interaction between NA and zeolite. The calculated adsorption enthalpy of NA on 5T and 10T clusters of H–ZSM-5 catalyst at ONIOM(MP2/6-311++G(d,p):HF/6-31+G(d)) level ranges from −19.73 to −40.33 and −63.81 to −73.73 kJ/mol, respectively. Adsorption energy for AC complexes increases in going from B3LYP method to MP2 one. The results of atoms in molecules (AIM) calculations showed that NH5⋯O interactions have electrostatic character, whereas O(N)⋯HZ interactions have partially covalent nature. The results of natural bond orbital (NBO) analysis showed that charge transfer occurs from NA to H–zeolite cluster.
Keywords: 5T and 10T cluster models; Nitrosamine–H–ZSM-5 complexes; NBO; AIM;

In this study, we report on the mechanical properties, failure and fracture modes in two cases of engineering materials; that is transparent silicon oxide thin films onto poly(ethylene terephthalate) (PET) membranes and glass-ceramic materials. The first system was studied by the quazi-static indentation technique at the nano-scale and the second by the static indentation technique at the micro-scale. Nanocomposite laminates of silicon oxide thin films onto PET were found to sustain higher scratch induced stresses and were effective as protective coating material for PET membranes. Glass-ceramic materials with separated crystallites of different morphologies sustained a mixed crack propagation pattern in brittle fracture mode.
Keywords: Fracture; Failure; Nanoindentation; Nanoscratch; Silicon oxide film; Glass-ceramic material;

Ni, Ag, and Pt-based Al-doped ZnO (AZO) films have been deposited as transparent conductivity layers on quartz by RF magnetron sputtering and characterized by X-ray diffraction, Hall measurement, optical transmission spectroscopy, scanning electron microscopy (SEM). The deposition of thicker metal layer in double layers resulted in lowering the effective electrical resistivity with a slight reduction of their optical transmittance. A film consisting of AZO (250 nm)/Ni (2 nm) double structure, exhibits a sheet resistance of 21.0 Ω/sq, a high transmittance of 76.5%, and characterize good adhesion to substrate. These results make the satisfactory for GaN-based light-emitting diodes (LEDs) and solar cells with metal-based AZO double films as current spread layers.
Keywords: Al-doped ZnO; Double layer; Transparent conductive oxide; Magnetron sputtering;

A density functional theory (DFT) study of graphene synthesis from graphite oxidation and exfoliation is presented. The calculated DFT results for O adsorption predict C=O as a most stable bond on the graphene oxide (GO) sheet. The obtained exfoliation energy for the graphene and the GO are 143 and ∼70 mJ/m2 that verify easier exfoliation of the graphite oxide compared with the graphite. Furthermore, the DFT results show that for decreasing the exfoliation energy of the GO at least two layers of the graphite should be oxidized during the oxidation process.
Keywords: Graphene; Density functional theory; Exfoliation;

Field emission properties of carbon nanotube cathodes produced using composite plating by Fang-Hsing Wang; Tzu-Ching Lin; Shien-Der Tzeng; Ching-Tien Chou (7600-7605).
Field emission properties of carbon nanotube field emission cathodes (CNT-FECs) produced using composite plating are studied. The experiment uses a CNT suspension and electroless Ni plating bath to carry out composite plating. The CNTs were first purified by an acid solution, dispersed in a Ni electrobath, and finally co-deposited with Ni on glass substrates to synthesize electrically conductive films. Field emission scanning electron microscopy and Raman spectroscopy results show that the field emission characteristics and graphitic properties of CNT-FECs depend on the pH value of the electrobath. Experiments show that the optimum electrobath pH value is 5.4, achieving a field emission current density of 1.0 mA/cm2 at an applied electric field of 1.5 V/μm. The proposed CNT-FECs possess good field emission characteristics and have potential for backlight unit application in liquid crystal displays.
Keywords: Carbon nanotube(CNT); Field emission; Composite plating; pH value;

Improvement of organic solar cells by flexible substrate and ITO surface treatments by Yuang-Tung Cheng; Jyh-Jier Ho; Chien-Kun Wang; William Lee; Chih-Chiang Lu; Bao-Shun Yau; Jhen-Liang Nain; Shun-Hsyung Chang; Chiu-Cheng Chang; Kang L. Wang (7606-7611).
In this paper, surface treatments on polyethylene terephthalate with polymeric hard coating (PET-HC) substrates are described. The effect of the contact angle on the treatment is first investigated. It has been observed that detergent is quite effective in removing organic contamination on the flexible PET-HC substrates. Next, using a DC-reactive magnetron sputter, indium tin oxide (ITO) thin films of 90 nm are grown on a substrate treated by detergent. Then, various ITO surface treatments are made for improving the performance of the finally developed organic solar cells with structure Al/P3HT:PCBM/PEDOT:PSS/ITO/PET. It is found that the parameters of the ITO including resistivity, carrier concentration, transmittance, surface morphology, and work function depended on the surface treatments and significantly influence the solar cell performance. With the optimal conditions for detergent treatment on flexible PET substrates, the ITO film with a resistivity of 5.6 × 10−4  Ω cm and average optical transmittance of 84.1% in the visible region are obtained. The optimal ITO surface treated by detergent for 5 min and then by UV ozone for 20 min exhibits the best WF value of 5.22 eV. This improves about 8.30% in the WF compared with that of the untreated ITO film. In the case of optimal treatment with the organic photovoltaic device, meanwhile, 36.6% enhancement in short circuit current density (J sc) and 92.7% enhancement in conversion efficiency (η) over the untreated solar cell are obtained.
Keywords: Polyethylene terephthalate (PET); Flexible solar cells; Indium tin oxide (ITO); Work function; Conversion efficiencies;

The pack-boronizing of pure vanadium under a controlled atmosphere by Mehmet Tarakci; Yucel Gencer; Adnan Calik (7612-7618).
Pack boronizing of pure vanadium was performed at 1100 °C for 4, 8, 12 and 16 h under a controlled atmosphere. Characterization of the boride formed on the surface of pure vanadium was carried out by metallographic techniques, profilometry, SEM-EDS, XRD and microhardness measurements. The metallographic studies revealed that a single boride layer with dense, compact and relatively smooth morphology was formed on the surface of pure vanadium. The interface between boride layer and base metal was wavy in nature. The formation of only the VB2 phase on pure vanadium was confirmed by surface and cross-sectional XRD analysis. The microhardness of the boride layer was approximately 3700 HV for all boriding times. Fracture toughness of the boride layer was evaluated using Vickers indentation, giving the value of 2.1–5.9 and 1.7–3.4 MPa m1/2 for Palmqvist and median/radial approaches, respectively. Thickness of the boride layer increased almost parabolically from about 23 to 50 μm with boriding time. Surface roughness of the coating was relatively increased from approximately 0.58 to 2.25 μm by boriding duration.
Keywords: Vanadium diboride; Pack boronizing; Boriding of pure vanadium; Fracture toughness;

Fabrication of an intelligent superhydrophobic surface based on ZnO nanorod arrays with switchable adhesion property by Xiaotao Zhu; Zhaozhu Zhang; Xuehu Men; Jin Yang; Xianghui Xu (7619-7622).
The superhydrophobic ZnO surface possessing water adhesive reversibility is fabricated by a facile method. The as-prepared surface is low adhesive; however, after being irradiated by UV light through a photomask, it becomes highly adhesive. A water droplet can suspend on the irradiated surface. Further annealing the irradiated surface, water droplets can roll on the surface again. Reversible transition between the high adhesive pinning state and low adhesive rolling state can be realized simply by UV illumination and heat treatment alternately. The adhesion transition is attributed to the adsorption/desorption of surface hydroxyl groups and the organic chains rearrangement on the top surfaces of ZnO.
Keywords: ZnO nanorod arrays; Superhydrophobic; Switchable adhesion; Intelligent;

Defects, stress and abnormal shift of the (0 0 2) diffraction peak for Li-doped ZnO films by Yow-Jon Lin; Mu-Shan Wang; Chia-Jyi Liu; Hsueh-Jung Huang (7623-7627).
The effect of changes in Li content on the structural property of sol–gel Li-doped ZnO films was investigated in this study. The observed changes of the Li incorporation-induced strain along c-axis are closely related to the different ratios between the concentrations of Li interstitials (Lii) and Li substituting for Zn (LiZn) in the films. According to the observed results from X-ray diffraction (XRD) and photoluminescence measurements, we found that the domination of the dissociative mechanism in the Li-doped ZnO films led to transformation from LiZn to Lii, involving the formation of Zn vacancies (VZn). In addition, the interaction between these defects (that is, LiZn, Lii, VZn and oxygen vacancy) and the crystal structure may lead to the abnormal shift of the (0 0 2) diffraction peak position determined from XRD measurements.
Keywords: ZnO; XRD; Defect; Photoluminescence; Doping;

Be3N2 thin films have been grown on Si(1 1 1) substrates using the pulsed laser deposition method at different substrate temperatures: room temperature (RT), 200 °C, 400 °C, 600 °C and 700 °C. Additionally, two samples were deposited at RT and were annealed after deposition in situ at 600 °C and 700 °C. In order to obtain the stoichiometry of the samples, they have been characterized in situ by X-ray photoelectron (XPS) and reflection electron energy loss spectroscopy (REELS). The influence of the substrate temperature on the morphological and structural properties of the films was investigated using scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD). The results show that all prepared films presented the Be3N2 stoichiometry. Formation of whiskers with diameters of 100–200 nm appears at the surface of the films prepared with a substrate temperature of 600 °C or 700 °C. However, the samples grown at RT and annealed at 600 °C or 700 °C do not show whiskers on the surface. The average root mean square (RMS) roughness and the average grain size of the samples grown with respect the substrate temperature is presented. The films grown with a substrate temperature between the room temperature to 400 °C, and the sample annealed in situ at 600 °C were amorphous; while the αBe3N2 phase was presented on the samples with a substrate temperature of 600 °C, 700 °C and that deposited with the substrate at RT and annealed in situ at 700 °C.
Keywords: Laser ablation; Be3N2; Thin films; Whiskers;

Ion recognition-based separation techniques have received much attention because of their high selectivity for target ions. In this study, we have prepared a novel ion imprinted polymer (IIP) to remove nickel ions with high selectivity. The imprinted polymer was prepared by copolymerization of 2-hydroxy ethyl methacrylate (HEMA) with nickel vinylbenzoate complex in the presence of ethylene glycol dimethacrylate (EGDMA) as a crosslinker. The polymerization was carried out in bulk with free radical initiation using 2-methoxy ethanol as a solvent and porogen. The adsorbed nickel was completely eluted with 15 mL of 1 M HCl. Control polymer was also prepared by similar experimental conditions without using imprint ion. The above synthesized polymers were characterized by surface area measurements, FT-IR, microanalysis and SEM analysis. The adsorption capacity of IIP and CP was found to be 1.51 and 0.65 mmol g−1, respectively. The optimal pH for quantitative enrichment was 6.5. Nature of eluent, eluent concentration and eluent volume were also studied. The relative selectivity factor (α r) values of Ni(II)/Zn(II), Ni(II)/Cu(II) and Ni(II)/Co(II) were 78.6, 111.1 and 91.6, respectively. Five replicate determinations of 30 μg L−1 of Ni(II) gave a mean absorbance of 0.067 with a relative standard deviation of 1.06%. The lowest concentration determined by GTA-AAS below which the recovery becomes non-quantitative is 6 μg L−1. IIP was tested for removal of Ni(II) from sea water sample.
Keywords: Ion imprinted polymer; 4-Vinylbenzoic acid; Ni(II); Solid phase extraction;

The pure-shear mode solidly mounted resonator based on c-axis oriented ZnO film by Da Chen; Jingjing Wang; Yan Xu; Dehua Li; Zhaoxin Li; Hongwei Song (7638-7642).
In this paper, we fabricate a pure-shear mode film bulk acoustic resonator based on c-axis oriented ZnO film. The resonator is consisted of an in-plane electrode, a highly c-axis oriented ZnO film and a SiO2/W Bragg reflector. The shear mode wave is excited by the lateral electric field. The resonator works in a pure-shear mode with the resonance frequency near 1.5 GHz and the Q-factor of 479 in air. There is no obvious longitudinal mode resonance in the frequency response, which can be explained that the electric field component normal to the surface is very weak and the Bragg reflector has the effective frequency selectivity for the shear mode. Importantly for sensors, the immersion into de-ionized water and glycerol liquid still allows for a Q-factor up to 335 and 220, respectively. This resonator shows the potential as mass loading sensors for biochemical application.
Keywords: Film bulk acoustic resonator; Shear mode; ZnO film; Mass loading sensor;

Adsorption and dissociation of molecular hydrogen on Pt/CeO2 catalyst in the hydrogen spillover process: A quantum chemical molecular dynamics study by Farouq Ahmed; Md. Khorshed Alam; Ryuji Muira; Ai Suzuki; Hideyuki Tsuboi; Nozomu Hatakeyama; Akira Endou; Hiromitsu Takaba; Momoji Kubo; Akira Miyamoto (7643-7652).
Ultra accelerated quantum chemical molecular dynamics method (UA-QCMD) was used to study the dynamics of the hydrogen spillover process on Pt/CeO2 catalyst surface for the first time. The direct observation of dissociative adsorption of hydrogen on Pt/CeO2 catalyst surface as well as the diffusion of dissociative hydrogen from the Pt/CeO2 catalyst surface was simulated. The diffusion of the hydrogen atom in the gas phase explains the high reactivity observed in the hydrogen spillover process. Chemical changes, change of adsorption states and structural changes were investigated. It was observed that parallel adsorption of hydrogen facilitates the dissociative adsorption leading to hydrogen desorption. Impact with perpendicular adsorption of hydrogen causes the molecular adsorption on the surface, which decelerates the hydrogen spillover. The present study also indicates that the CeO2 support has strong interaction with Pt catalyst, which may cause an increase in Pt activity as well as enhancement of the metal catalyst dispersions and hence increasing the rate of hydrogen spillover reaction.
Keywords: Hydrogen spillover; Quantum chemical molecular dynamics; Catalyst surface;

The nucleation and growth of diamond on ultra-thin Cr/Al and Ti/Al interlayered stainless steel substrates were investigated. The metal interlayers were produced by ion beam sputtering deposition and consisted of an outer layer of 20 nm Cr or Ti and an inner layer of 30 nm Al, respectively. During the microwave plasma-enhanced chemical vapor deposition process, the inner Al diffuses into steel surface and forms Fe–Al compounds, while the outer Cr or Ti is carburized and transformed into corresponding carbides. These two ultra-thin dual metal interlayers are effective in suppressing the graphite soot formation on steel surfaces. Nevertheless, continuous diamond thin film is difficult to be obtained due to severe buckling and fragmentation deformation induced by residual stress.
Keywords: Diamond thin film; Chemical vapor deposition; Steel; Ultra-thin interlayer; Adhesion;

In this study, we examined the tensile and fracture behaviors of multi-walled carbon nanotube (MWCNT) reinforced epoxy nanocomposites with and without moisture absorption. The MWCNT/epoxy nanocomposites were fabricated using 0.1 wt.% unmodified, oxidized, and silanized MWCNTs and were kept in seawater for over 15 weeks. Silane-modified specimens demonstrated greater tensile strength, elastic modulus, and transmittance than unmodified or acid-modified specimens, irrespective of moisture absorption. Compared to dry nanocomposites, moisture absorption decreased the tensile strength and elastic modulus for each surface modification. Fracture behavior showed similar tendencies as tensile test results. However, the fracture toughnesses of oxidized and silanized MWCNT/epoxy nanocomposites were not notably different, whereas unmodified specimens had much lower fracture toughnesses, irrespective of moisture absorption. Moisture absorption may have caused degradation resulting in weak interfacial bonding due to epoxy swelling.
Keywords: Multi-walled carbon nanotubes (MWCNTs); Moisture absorption; Surface modification; Tensile strength; Fracture toughness;

A study of AFM-based scratch process on polycarbonate surface and grating application by Chul Hyun Choi; Dong Jin Lee; Jun-Ho Sung; Min Woo Lee; Seung-Gol Lee; Se-Geun Park; El-Hang Lee; Beom-Hoan O (7668-7671).
We report on the possibility of applying atomic force microscope (AFM) lithography to draw micro/nano-structures on the surface of a polycarbonate (PC) substrate. We also fabricated a grating structure on the PC surface using the scratch method. An AFM silicon tip coated with a diamond layer was utilized as a cutting tool to scratch the surface of the sample. In order to obtain pattern depth deeper than the control method of interaction force, we used a scanner movement method which the sample scanner moves along the Z-axis. A grating of 100 μm × 150 μm was fabricated by the step and repeat method wherein the sample stage is moved in the direction of the XY-axis. The period and the depth of the grating are 500 and 50 nm, respectively. Light of 632.8 nm wavelength was diffracted on the surface of the PC substrate.
Keywords: AFM; Nanolithography; Polymer substrate; Grating structure;

Wetting properties of silica plates contacted with dipalmitoylphosphatidylcholine (DPPC) or DPPC/enzyme (phospholipase PLA2) in NaCl solution were determined by thin layer wicking and with a help of Washburn equation. The wicking experiments were performed both for bare plates and the silica plates precontacted overnight with the probe liquid saturated vapors the silica plates, as well as untreated and DPPC (or DPPC/enzyme) treated. Adsorption of DPPC on original silica plates increases a bit hydrophobic character of silica surface in such a way that hydrocarbon chains are directed outwards and the polar part towards the silica surface. However, after the enzyme action the products of DPPC hydrolysis by PLA2 (palmitic acid and lysophosphatidylcholine) increase again hydrophilic character of silica surface (an increase in acid–base interactions, γ s A B ).The changes of silica surface wettability are evidently dependent on the time of enzyme contacting with DPPC in NaCl solution. Although, the changes of total surface free energy of silica after treatment with DPPC/enzyme solution are minor about 2–6 mJ/m2, the changes of the electron-donor ( γ s − ) and Lifshitz–van der Waals ( γ s L W ) component of the surface free energy are noticeable. Despite, these results are somehow preliminary, it seems that thin layer wicking method is an interesting tool for investigation of the effect of adsorbed DPPC on hydrophobicity/hydrophilicity of silica surface and influence of enzyme PLA2 action.
Keywords: SiO2 plates; DPPC; Phospholipase A2 enzyme; Wetting properties; Washburn equation;

Synchrotron radiation photoelectron spectroscopy and near-edge X-ray absorption fine structure study on oxidative etching of diamond-like carbon films by hyperthermal atomic oxygen by Masahito Tagawa; Kumiko Yokota; Akira Kitamura; Koji Matsumoto; Akitaka Yoshigoe; Yuden Teraoka; Kazuhiro Kanda; Masahito Niibe (7678-7683).
Surface structural changes of a hydrogenated diamond-like carbon (DLC) film exposed to a hyperthermal atomic oxygen beam were investigated by Rutherford backscattering spectroscopy (RBS), synchrotron radiation photoelectron spectroscopy (SR-PES), and near-edge X-ray absorption fine structure (NEXAFS). It was confirmed that the DLC surface was oxidized and etched by high-energy collisions of atomic oxygen. RBS and real-time mass-loss data showed a linear relationship between etching and atomic oxygen fluence. SR-PES data suggested that the oxide layer was restricted to the topmost surface of the DLC film. NEXAFS data were interpreted to mean that the sp2 structure at the DLC surface was selectively etched by collisions with hyperthermal atomic oxygen, and an sp3-rich region remained at the topmost DLC surface. The formation of an sp3-rich layer at the DLC surface led to surface roughening and a reduced erosion yield relative to the pristine DLC surface.
Keywords: Hydrogen; Diamond-like carbon; Atomic oxygen; sp2; sp3; NEXAFS; RBS;

Cobalt-supported alumina as catalytic film prepared by electrophoretic deposition for hydrogen release applications by R. Chamoun; U.B. Demirci; D. Cornu; Y. Zaatar; A. Khoury; R. Khoury; P. Miele (7684-7691).
Shaped catalysts are crucial for technological applications. In this context, we have developed Co–αAl2O3 catalyst films deposited over Cu plates to be used in hydrogen generation by hydrolysis of sodium borohydride NaBH4 in alkaline solution. The Co–αAl2O3 films were prepared by electrophoretic deposition according to six different routes. While five of them failed in fabricating adhering films, the sixth route, consisting of electrodepositing Co-impregnated αAl2O3, showed promising results. The as-obtained shaped catalysts were stable when hydrogen vigorously bubbled and catalyzed the NaBH4 hydrolysis with attractive hydrogen generation rates. These results open an alternative route for preparing shaped catalysts in this reaction.
Keywords: Cobalt-supported on alumina; Electrophoretic deposition; Hydrogen storage; Sodium borohydride;

Spatial and electronic structure of the Ni3P surface by Liangcai Zhou; Yi Kong; Yong Du; Jiong Wang; Yichun Zhou (7692-7695).
To understand the catalytic effect in the Ni–Ni3P for the growth of carbon nanostructures, the structural and electronic properties of Ni3P surface are calculated from first-principles calculations. The calculated surface energies for the (0 0 1)-Ni4P4-terminated surface, the (0 0 1)-Ni8-terminated surface, and the (1 1 0)-Ni8-terminated surface show that the (0 0 1)-Ni4P4-terminated surface is energetically more stable within the allowed range of the chemical potential of P. Through the analysis of the partial density of states of Ni and P atoms in surface and bulk states, respectively, it is further found that due to the bond contractions of the surface layer, the core-level shifts of P atoms in the (0 0 1)-Ni4P4-terminated surface make P atoms in the Ni3P particles act as a catalyst. Finally, the obtained results of the work function show that the (0 0 1)-Ni4P4-terminated surface has the largest work function when compared with the other two studied surfaces.
Keywords: Ni3P surface; Catalytic effect; First-principles calculations;

Effective method for preparation of oxide-free Ge2Sb2Te5 surface: An X-ray photoelectron spectroscopy study by Zheng Zhang; Jisheng Pan; Yong Lim Foo; Lina Wei-Wei Fang; Yee-Chia Yeo; Rong Zhao; Luping Shi; Tow-Chong Chong (7696-7699).
Cleaning the surfaces of the as-deposited Ge2Sb2Te5 was studied by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and X-ray diffraction (XRD). The mixed native oxides on the as-deposited Ge2Sb2Te5 surface can be easily removed by dipping Ge2Sb2Te5 in de-ionized water for 1 min, while the surface morphology remains unchanged after cleaning. Native oxides only re-grow after exposure to air for more than 4 min. Although dipping in water leads to a surface layer deficient in Ge and Sb, the surface composition of Ge2Sb2Te5 can recover to its stoichiometric value after annealing at 200 °C in vacuum. The phase remains amorphous at room temperature after dipping in water, and changes to fcc and hcp after annealing at 100 and 220 °C, respectively.
Keywords: Surface cleaning; XPS; Phase change; Ge2Sb2Te5;

The use of Reactive Ion Etching for obtaining “free” silica nano test tubes by Fatih Buyukserin; Charles R. Martin (7700-7705).
Silica nano test tubes are one-dimensional inorganic nanostructures with several biotechnological applications including biosensing, magnetic resonance imaging, and targeted cancer therapeutics. They are generally prepared by sol–gel deposition of silica to nanoporous alumina templates. Preparing samples composed of isolated free silica nano test tubes can be a challenging process due to the conformal coating of silica on the template. This causes the formation of a top-surface silica layer which laterally connects the nano test tubes. Herein, we detailed the use of Reactive Ion Etching to remove this top-surface silica layer which yields free silica nano test tubes with template dissolution. Compared with the mechanical polishing approach, Reactive Ion Etching treatment allows a fine manipulation ability of the surface material at the nanoscale level. When used excessively, Reactive Ion Etching causes an orifice closing phenomenon that may be employed to create novel one-dimensional nanocapsules.
Keywords: Reactive Ion Etching; Nanoporous alumina; Silica nano test tubes; Ar plasma; Surface sol–gel;

Influence of the physico-chemical properties of CeO2–ZrO2 mixed oxides on the catalytic oxidation of NO to NO2 by Idriss Atribak; Noelia Guillén-Hurtado; Agustín Bueno-López; Avelina García-García (7706-7712).
Commercial and home-made Ce–Zr catalysts prepared by co-precipitation were characterised by XRD, Raman spectroscopy, N2 adsorption at −196 °C and XPS, and were tested for NO oxidation to NO2. Among the different physico-chemical properties characterised, the surface composition seems to be the most relevant one in order to explain the NO oxidation capacity of these Ce–Zr catalysts. As a general trend, Ce–Zr catalysts with a cerium-rich surface, that is, high XPS-measured Ce/Zr atomic surface ratios, are more active than those with a Zr-enriched surface. The decrease in catalytic activity of the Ce–Zr mixed oxided upon calcinations at 800 °C with regard to 500 °C is mainly attributed to the decrease in Ce/Zr surface ratio, that is, to the surface segregation of Zr. The phase composition (cubic or t′′ for Ce-rich compositions) seems not to be a direct effect on the catalytic activity for NO oxidation in the range of compositions tested. However, the formation of a proper solid solution prevents important surface segregation of Zr upon calcinations at high temperature. The effect of the BET surface area in the catalytic activity for NO oxidation of Ce–Zr mixed oxides is minor in comparison with the effect of the Ce/Zr surface ratio.
Keywords: Ceria–zirconia; Mixed oxides; Ceria; XPS; NO to NO2 oxidation capacity;

Electrodeposition of novel Sn–Ni–Fe ternary alloys with amorphous structure by L. Sziráki; E. Kuzmann; M. El-Sharif; C.U. Chisholm; S. Stichleutner; G.B. Lak; K. Süvegh; E. Tatár; Z. Homonnay; A. Vértes (7713-7716).
Tin–nickel–iron (Sn–Ni–Fe) ternary alloys have been successfully prepared for the first time by electrochemical deposition. 57Fe and 119Sn conversion electron Mössbauer and PXRD investigations of these alloys showed that the alloys were dominated by new metastable phases which do no occur in the thermally prepared alloys and are not to be found in the corresponding equilibrium phase diagram. Essentially these ternary alloys proved to be amorphous and ferromagnetic.
Keywords: Electrodeposition; Amorphous alloy; Sn–Ni–Fe ternary alloy; Mössbauer spectroscopy;