Check out our New Publishers' Select for Free Articles

Applied Surface Science (v.256, #20)

Editorial Board (pp. ii).

Reconnaissance of the specific surface of vapour grown carbon micro and nanofibres as a main controller of the sorption of hydrogen by A. Madroñero; A. Asenjo; C. Gil; M. Jaafar; A. López (pp. 5797-5802).

The influence of the hydrogen content in several physical aspects of carbonaceous microfibres obtained from a mixture of hydrogen and hydrocarbon gas is examinated in this study. The hydrogen content is evaluated behalf a measurement of the fibres density. These changes of content depend on the manufacturing process and further treatments of the fibres. The surface energy is established after contact angle evaluation. There is not a clear relation between the surface energy and the porosity, which is a very relevant parameter in order to establish the hydrogen storage capacity of all materials.The fibres have been evaluated using Kelvin probe force microscopy (KPFM), which provides a map of the surface potential. These measurements suggest a relation between the surface potential and the hydrogen adsorbed in the surface of the fibres.

Keywords: Atomic force microscopy; Interface states; Physical adsorption; Surface energy; Thermal desorption; Carbon; Hydrogen atom

Electrical properties of the CdTe back contact: A new chemically etching process based on nitric acid/acetic acid mixtures by Junfeng Han; Chunjie Fan; C. Spanheimer; Ganhua Fu; Kui Zhao; A. Klein; W. Jaegermann (pp. 5803-5806).

The performance of the back contact is one of the major issues of CdTe solar cell research. Standard nitric–phosphoric (NP) acid chemical etching before metallization is widely used to improve contact formation. However, previous studies of this traditional etching method indicated a blocking Schottky barrier at the back contact, and a roll-over phenomenon was found in the J– V curves of the CdTe solar cells. In this work, a new etching solution, i.e. a nitric–acetic (NA) acid was employed. The etching rate was slow and a Te-rich layer was formed on the surface, which was less than 1nm. The CdTe solar cell with this new etching method showed no roll-over phenomenon and displayed a good ohmic back contact performance. XPS analysis demonstrated that the back contact barrier height was close to those of CdTe with standard NP etching. A possible mechanism was presented for the improvement of back contact properties.

Keywords: CdTe; Back contact; NA etching

XPS study of the surface chemistry on AZ31 and AZ91 magnesium alloys in dilute NaCl solution by Lei Wang; Tadashi Shinohara; Bo-Ping Zhang (pp. 5807-5812).

The surface chemistry on AZ31 and AZ91 magnesium alloys was characterized by X-ray photoelectron spectroscopy (XPS) in the corrosion and the passivation zones. In the corrosion zone, the presence of Mg(OH)₂ and MgCO₃ species was found in the outer surface, whereas, in the inner layer, the co-existence of Mg(OH)₂, MgO and MgCO₃ species was observed for both alloys. The presence of Al³⁺ in the surface electrolyte to form Al₂O₃/Al(OH)₃ and the formation of carbonate product provide a better passivation on the surfaces and retard the chloride-induced corrosion on the materials in the passivation zone.

Keywords: Magnesium; AZ31 and AZ91 alloys; Corrosion; Passivation; XPS

Vacancy-induced room-temperature ferromagnetism in ZnO rods synthesized by Ni-doped solution and hydrothermal method by Zhenhua Yu; Shihui Ge; Yalu Zuo; Guowei Wang; Feng Zhang (pp. 5813-5817).

Pure ZnO and Ni-doped ZnO rods have been prepared by hydrothermal method at a temperature of 120°C. The morphological, structural, magnetic and optical properties of the as-prepared rods were investigated by means of field emission scanning electron microscopy, X-ray diffraction, vibrating sample magnetometer and photoluminescence. All the samples are radial-grown hexagon rods with diameter from 470 to 720nm and length of 4–6μm. X-ray diffraction shows that the rods have single crystalline wurtzite structure without other impurity phases. The pure ZnO rods and Ni-doped ZnO rods have ferromagnetism at room temperature, and the special saturation magnetization deduces with the increasing diameter of rods. These results reveal that the saturation magnetization of the ZnO rods depends on the surface-to-volume ratio of rods rather than the Ni doping concentrations. The photoluminescence spectra studies show the same diameter dependences of oxygen vacancies as that of magnetization, which demonstrates that oxygen vacancies at surface of rods play an important role in introducing ferromagnetism. The annealing in rich oxygen and reducing atmospheres confirms this argument further.

Keywords: ZnO; Hydrothermal; Oxygen vacancy

Formation of titania composite coatings on carbon steel by plasma electrolytic oxidation by Yunlong Wang; Zhaohua Jiang; Zhongping Yao (pp. 5818-5823).

Titania composite coatings were prepared on carbon steel by plasma electrolytic oxidation in silicate electrolyte and aluminate electrolyte with titania powers doping in the electrolytes. The microstructure of the coatings was characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The properties of the coatings including bond strength, thickness, thermal shock resistance and corrosion resistance varying with the quantities of titania powers in the electrolytes were studied. Investigation results revealed that the coating obtained in silicate electrolyte was composed of anatase-TiO₂, rutile-TiO₂ crystal phases and some Fe, Si, P elements; coating obtained in aluminate electrolyte consisted of anatase-TiO₂, Al₂TiO₅ and some Fe, P elements. Coatings obtained in two types of electrolytes show porous and rough surface. With increasing the concentration of titania powers in the electrolytes, the coating surface first became more compact and less porous and then became more porous and coarse. The bond strength and thickness were not strongly affected by concentration of titania powers in electrolytes. The valves were 23MPa and for 66μm for coatings obtained in aluminate electrolyte, and 21MPa and 35μm for coatings obtained in silicate electrolyte. Coatings obtained in silicate electrolyte showed a little better thermal shock resistance than those obtained in aluminate electrolyte and the best coatings were obtained with middle concentration of titania powers in the electrolytes. All coated samples showed better corrosion resistance than the substrate in 3.5wt% NaCl solution. The best coatings were also obtained with middle concentration of titania powers doping in both electrolytes whose corrosion current density was decreased by 2 orders of magnitude compared with the substrate.

Keywords: Plasma electrolytic oxidation; Titania; Steel; Corrosion resistance

The fabrication of superhydrophobic copper films by a low-pressure-oxidation method by Ming-De Pei; Bo Wang; Er Li; Xue-hong Zhang; Xue-mei Song; Hui Yan (pp. 5824-5827).

The lotus-leaf-like superhydrophobic copper was fabricated by a facile two-step method without the chemical modification, on which the water contact angle can reach 158° and the water-sliding angle is less than 10°. Reversible superhydrophobicity to superhydrophilicity transition was observed and controlled by alternation of UV irradiation and dark storage. More interestingly, the superhydrophobic surface exhibits superoleophilicity and all those properties can be well used in reversible switch, separating the water and oil and so on.

Keywords: Superhydrophobic; The contact angle; The sliding angle; Superoleophilicity

Laser Shock Processing of 6061-T6 Al alloy with 1064nm and 532nm wavelengths by G. Gomez-Rosas; C. Rubio-Gonzalez; J.L. Ocaña; C. Molpeceres; J.A. Porro; M. Morales; F.J. Casillas (pp. 5828-5831).

Laser Shock Processing (LSP) has been proposed as a competitive alternative technology to classical treatments for improving fatigue and wear resistance of metals. We present a configuration and results in the LSP concept for metal surface treatments in underwater laser irradiation at 532nm and 1064nm. The purpose of the work is to compare the effect of both wavelengths on the same material. A convergent lens is used to deliver 1.2J/pulse (1064nm) and 0.9J/pulse (532nm) in a 8ns laser FWHM pulse produced by 10Hz Q-switched Nd:YAG laser with spots of a 1.5mm in diameter moving forward along the work piece. A LSP configuration with experimental results using a pulse density of 2500pulses/cm² and 5000pulses/cm² in 6061-T6 aluminum samples are presented. High level compressive residual stresses are produced using both wavelengths. It has been shown that surface residual stress level is comparable to that achieved by conventional shot peening, but with greater depths. This method can be applied to surface treatment of final metal products.

Keywords: Laser Shock Processing; Compressive residual stress

Optical and electrical properties of Y₂O₃ thin films prepared by ion beam assisted deposition by Jian Leng; Zhinong Yu; Yuqiong Li; Dongpu Zhang; Xiaoyi Liao; Wei Xue (pp. 5832-5836).

Y₂O₃ thin films were deposited by ion beam assisted deposition (IBAD) and the effects of fabrication parameters such as substrate temperature and ion energy on the structure, optical and electrical properties of the films were investigated. The results show that the deposited Y₂O₃ films had less optical absorption, larger refractive index, and better film crystallinity with the increase of substrate temperature or ion energy. The as-deposited Y₂O₃ films without ion-beam bombardment had larger relative dielectric constant ( ɛ_r) and the ɛ_r decreased with time even over by 40%, while the ɛ_r of films prepared with high ion energy had less changes, only less than 3%. Also, with the increase of ion energy, the electrical breakdown strength and the figure of merit increased.

Keywords: Y; ₂; O; ₃; Ion beam assisted deposition (IBAD); Optical properties; Electrical properties

Microstructure and age characterization of Cu–15Ni–8Sn alloy coatings by laser cladding by Zhang Hui; He Yizhu; Yuan Xiaomin; Pan Ye (pp. 5837-5842).

The present work has investigated the influence of direct aging treatment on the precipitation sequence and properties of the Cu–15Ni–8Sn alloy coatings prepared by laser cladding. The experimental results show that the tendency of Sn segregation in the conventional Cu–15Ni–8Sn solidification microstructure is effectively relieved. Before aging, there are only two phases in the coating: the α-Cu solid solution dendrites with 7wt.% Sn solubility, and a small fraction of Sn-enriched δ-phase at the interdendrites in rapid solidified microstructure. After the coating was directly aged at 370°C without traditional solution pretreatment, the α-Cu solid solution dendrites experience precipitations in the order of pure spinodal decomposition, DO₂₂-ordered structure and discontinue γ-DO₃. The microhardness of the coating treated by direct aging reached 390 HV 0.5, which was higher than that treated by conventional solution and aging process owing to the solidified fine grains and hardening effect of spinodal decomposition. In addition, the Sn-enriched δ-phase at the interdendrites also decomposes to laminar discontinuous precipitated γ-DO₃ phase after aging. Precipitation sequence and properties of the clad coatings change obviously during the direct aging treatment.

Keywords: Laser cladding; Cu–15Ni–8Sn alloy; Component segregation; Aging treatment; Spinodal decomposition

A simple pathway to ordered silica nanopattern from self-assembling of block copolymer containing organic silicon block by Qi Wang; Jinghui Yang; Weiwei Yao; Ke Wang; Rongni Du; Qin Zhang; Feng Chen; Qiang Fu (pp. 5843-5848).

Self-assembly of block copolymer is an effective strategy to prepare periodic structures at nanoscale. In this paper an unique and very simple method to prepare inorganic silica nanopattern is demonstrated from self-assembling of poly(styrene- block-dimethylsiloxane) (PS- b-PDMS) on the surface of silicon wafer. To simplify the patterning process, at first we obtain highly ordered PDMS microdomains, which are covered with PS layer by controlling solvent vapor annealing conditions. Following exposure to UV/O₃ irradiation, nanopatterned surface consisting of silicon oxide is fabricated directly via selectively etching PS phase and converting PDMS phase into silicon oxide. As tuning the composition of the block copolymer, hexagonally packing dot and straight stripe pattern can be obtained. Finally, the time evolution from spheres morphology to aligned long cylinders is discussed. These results hold promise for nanolithography and the fabrication of nanodevices.

Keywords: Block copolymers; Self assembling; Silicon oxide

Characterization of native and anodic oxide films formed on commercial pure titanium using electrochemical properties and morphology techniques by Sahar A. Fadl-allah; Q. Mohsen (pp. 5849-5855).

Potentiostatically anodized oxide films on the surface of commercial pure titanium (cp-Ti) formed in sulfuric (0.5M H₂SO₄) and in phosphoric (1.4M H₃PO₄) acid solutions under variables anodizing voltages were investigated and compared with the native oxide film. Potentiodynamic polarization and electrochemical impedance spectroscopy, EIS, were used to predicate the different in corrosion behavior of the oxide film samples. Scanning electron microscope, SEM, and electron diffraction X-ray analysis, EDX, were used to investigate the difference in the morphology between different types of oxide films. The electrochemical characteristics were examined in phosphate saline buffer solution, PSB (pH 7.4) at 25°C. Results have been shown that the nature of the native oxide film is thin and amorphous, while the process of anodization of Ti in both acid solutions plays an important role in changing the properties of passive oxide films. Significant increase in the corrosion resistance of the anodized surface film was recorded after 3h of electrode immersion in PSB. On the other side, the coverage ( θ) of film formed on cp-Ti was differed by changing the anodized acid solution. Impedance results showed that both the native film and anodized film formed on cp-Ti consist of two layers. The resistance of the anodized film has reached to the highest value by anodization of cp-Ti in H₃PO₄ and the inner layer in the anodized film formed in both acid solutions is also porous.

Keywords: Titanium; Anodic oxide films; Native film; Impedance (EIS); SEM; EDX

Catalytic performance of grafted Al-MCM-41 in hydroisomerization of n-dodecane by Xinyu Chen; Min Jia; Guozhu Liu; Xiangwen Zhang; Li Wang; Zhentao Mi (pp. 5856-5861).

Pt/Al-MCM-41 samples with constant metal loading but various Si/Al ratios were prepared by reacting pure silica MCM-41 with different concentrations of polyaluminum chloride (PAC) aqueous solutions. It is observed that the molar ratio of Si/Al decreases from 24.3 to 11.2 when increase the PAC concentration from 0.1M to 2.0M. A better retention of structural integrity could be seen when the PAC concentration is below 1.0M. The Lewis acid increases while incorporating aluminum into the framework of MCM-41, while the Brönsted acid reaches a maximum value when the PAC concentration is 1.0M. Hydroisomerization of n-dodecane was carried out over these Pt/Al-MCM-41 samples. It is demonstrated that increasing the aluminum content generally can trigger a higher n-dodecane conversion, but a lower isomers selectivity due to the increasing strong Brönsted acid sites. And the Pt/Al-MCM-41 post-synthesized by the PAC concentration at 1.0M shows highest isomers selectivity and yield corresponding to the maximum medium Brönsted acid quantities (24.15μmol/g).

Keywords: Al-MCM-41; Post-synthesis; Polyaluminum chloride; Hydroisomerization

Preparation of flower-like Cu₂O nanoparticles by pulse electrodeposition and their electrocatalytic application by Yong-e Gu; Xu Su; Yongling Du; Chunming Wang (pp. 5862-5866).

A pulsed electrodeposition technique based on a multipulse sequence of potentials of equal amplitude, duration and polarity was employed for preparation of highly dispersed flower-like cuprous oxide (Cu₂O) nanoparticles. The morphology analysis of the particles using scanning electron microscope (SEM) reveals that the flower-like particles were from sequential growth of Cu₂O along the (111) direction on the cubic Cu₂O (100). The structure and the chemical composition of the deposits were characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Optical property and band gap of the Cu₂O was investigated using UV/vis diffuse reflection spectra (DRS), and the measured value of energy gap is 2.18eV. The dark and light open circuit potential–time characterization study showed that the flower-like Cu₂O nanoparticles exhibited good photoelectric response. Cyclic voltammetry carried out in the presence of p-nitrophenol (p-NP) shows that the electrocatalytic performance of the Cu₂O particles for the reduction of p-NP, which was characterized by a cathodic peak at around −0.6V. The influence of the incidence of light on the electrocatalysis is also discussed.

Keywords: Flower-like Cu; ₂; O; Pulse electrodeposition; Electrocatalysis; p-nitrophenol

Optimization of covalent antibody immobilization on macroporous silicon solid supports by R. Dev Das; S. Maji; S. Das; C. RoyChaudhuri (pp. 5867-5875).

In this paper, optimization of the protocol for covalent antibody immobilization on macroporous silicon solid supports of various porosities, which is recently being employed as a promising substrate for biosensors, has been reported. Covalent binding of antibody has been carried out by silanization and crosslinker attachment on the substrate. For maximum antibody immobilization on macroporous silicon, all the individual processes have been separately optimized for the first time in terms of treatment time, pH, concentration, incubation time and others with the help of optical density measurements. The optimum treatment of the surface after every step has been further reconfirmed by detailed EDX analysis, SEM measurements and contact angle measurements. It has been observed that the density of antibody binding increases with increasing porosity and for a 70% porosity macroporous sample it is almost three times more than that of planar silicon which is significantly higher than the previous comparative reports on planar silicon and macroporous silicon. The amount of properly oriented HIgG antibodies has been estimated by quantification of the alkaline phosphate conjugated protein A binding by optical density measurements.

Keywords: Macroporous silicon; Optimum antibody immobilization; High binding density; SEM; EDX; Contact angle

Multilayer growth of BaTiO₃ thin films via pulsed laser deposition: An energy-dependent kinetic Monte Carlo simulation by Z. Zhu; X.J. Zheng; W. Li (pp. 5876-5881).

An energy-dependent kinetic Monte Carlo approach was proposed to simulate the multilayer growth of BaTiO₃ thin films via pulsed laser deposition, in which the four steps, such as the deposition of atoms, the diffusion of adatoms, the bonding of adatoms, and the surface migration of adatoms, were considered. Distinguishing with the traditional solid-on-solid (SOS) model, the adatom bonding and the overhanging of atoms, according to the perovskite structure, were specially adopted to describe the ferroelectric thin film growth. The activation energy was considered from the interactions between the ions, which were calculated by Born–Mayer–Huggins (BMH) potential. From the simulation the relative curves of the each layer coverage and roughness vs total coverage were obtained by varying the parameter values of the incident kinetic energy, laser repetition rate and mean deposition rate. The relationship between growth modes and the different parameters was also acquired.

Keywords: Kinetic Monte Carlo simulation; Multilayer; BaTiO; ₃; thin film; Pulsed laser deposition; Growth mode

Modified titanium surface with gelatin nano gold composite increases osteoblast cell biocompatibility by Young-Hee Lee; Govinda Bhattarai; Santosh Aryal; Nan-Hee Lee; Min-Ho Lee; Tae-Gun Kim; Eun-Chung Jhee; Hak-Yong Kim; Ho-Keun Yi (pp. 5882-5887).

This study examined the gelatin nano gold (GnG) composite for surface modification of titanium in addition to insure biocompatibility on dental implants or biomaterials. The GnG composite was constructed by gelatin and hydrogen tetrachloroaurate in presence of reducing agent, sodium borohydrate (NabH₄). The GnG composite was confirmed by UV–VIS spectroscopy and transmission electron microscopy (TEM). A dipping method was used to modify the titanium surface by GnG composite. Surface was characterized by scanning electron microscopy (SEM) and energy dispersive X-ray (EDX). The MC-3T3 E1 cell viability was assessed by trypan blue and the expression of proteins to biocompatibility were analyzed by Western blotting. The GnG composite showed well dispersed character, the strong absorption at 530nm, roughness, regular crystal and clear C, Na, Cl, P, and Au signals onto titanium. Further, this composite allowed MC-3T3 E1 growth and viability compared to gelatin and pure titanium. It induced ERK activation and the expression of cell adherent molecules, FAK and SPARC, and growth factor, VEGF. However, GnG decreased the level of SAPK/JNK. This shows that GnG composite coated titanium surfaces have a good biocompatibility for osteoblast growth and attachment than in intact by simple and versatile dipping method. Furthermore, it offers good communication between cell and implant surfaces by regulating cell signaling and adherent molecules, which are useful to enhance the biocompatibility of titanium surfaces.

Keywords: Gelatin nano gold composite; Titanium modification; Cell signaling; Cell adherent molecules; Biocompatibility; Dental implant

Mechanical strength and hydrophobicity of cotton fabric afterSF6 plasma treatment by K. Kamlangkla; B. Paosawatyanyong; V. Pavarajarn; Jose H. Hodak; Satreerat K. Hodak (pp. 5888-5897).

Surface treatments to tailor fabric properties are in high demand by the modern garment industry. We studied the effect of radio-frequency inductively coupledSF6 plasma on the surface characteristics of cotton fabric. The duration of the treatment and theSF6 pressure were varied systematically. We measured the hydrophobicity of treated cotton as a function of storage time and washing cycles. We used the weight loss (%) along with the etching rate, the tensile strength, the morphology changes and the hydrophobicity of the fabric as observables after treatments with different plasma conditions. The weight loss remains below 1% but it significantly increases when the treatment time is longer than 5min. Substantial changes in the surface morphology of the fiber are concomitant with the increased etching rate and increased weight loss with measurable consequences in their mechanical characteristics. The measured water absorption time reaches the maximum of 210min when theSF6 pressure is higher than 0.3Torr. The water contact angle (149°) and the absorption time (210min) of cotton treated with extreme conditions appear to be durable as long as the fabric is not washed. X-ray photoelectron spectroscopy analysis reveals that the water absorption time of the fabric follows the same increasing trend as the fluorine/carbon ratio at the fabric surface and atom density of fluorine measured by Ar actinometer.

Keywords: PACS; 52.77.DqCotton; Plasma processing; Mechanical properties

TiCN/TiNbCN multilayer coatings with enhanced mechanical properties by J.C. Caicedo; C. Amaya; L. Yate; M.E. Gómez; G. Zambrano; J. Alvarado-Rivera; J. Muñoz-Saldaña; P. Prieto (pp. 5898-5904).

Enhancement of mechanical properties by using a TiCN/TiNbCN multilayered system with different bilayer periods ( Λ) and bilayer numbers ( n) via magnetron sputtering technique was studied in this work. The coatings were characterized in terms of structural, chemical, morphological and mechanical properties by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and nanoindentation. Results of the X-ray analysis showed reflections associated to FCC (111) crystal structure for TiCN/TiNbCN films. AFM analysis revealed a reduction of grain size and roughness when the bilayer number is increased and the bilayer period is decreased. Finally, enhancement of mechanical properties was determined via nanoindentation measurements. The best behavior was obtained when the bilayer period ( Λ) was 15nm ( n=200), yielding the highest hardness (42GPa) and elastic modulus (408GPa). The values for the hardness and elastic modulus are 1.6 and 1.3 times greater than the coating with n=1, respectively. The enhancement effects in multilayer coatings could be attributed to different mechanisms for layer formation with nanometric thickness due to the Hall-Petch effect; because this effect, originally used to explain the increase in hardness with decreasing grain size in bulk polycrystalline metals, has also been used to explain hardness enhancements in multilayers taking into account the thickness reduction at individual single layers that make the multilayered system. The Hall-Petch model based on dislocation motion within layers and across layer interfaces, has been successfully applied to multilayers to explain this hardness enhancement.

Keywords: PACS; 61.05.c; 62.20.Qp; 68.65.AcMultilayer coatings; Magnetron sputtering; Mechanical properties

Deposition and microstructure characterization of atmospheric plasma-sprayed ZnO coatings for NO₂ detection by Chao Zhang; Marc Debliquy; Hanlin Liao (pp. 5905-5910).

This work studied the possibility of using a sensor based on plasma-sprayed zinc oxide (ZnO) sensitive layer for NO₂ detection. The atmospheric plasma spray process was employed to deposit ZnO gas sensing layer and the obtained coating structure was characterized by scanning electron microscopy and X-ray diffraction analysis. The influences of gas concentration, working temperature, water vapor in testing air on NO₂ sensing performance of the ZnO sensors were studied. ZnO sensors showed a good sensor response and selectivity to NO₂ at an optimal working temperature.

Keywords: Plasma spraying; Coating; ZnO; Gas sensor; NO; ₂

Modification of palygorskite surface by organofunctionalization for application in immobilization of H₃PW₁₂O₄₀ by Lixia Zhang; Qingzhe Jin; Jianhua Huang; Yuanfa Liu; Liang Shan; Xingguo Wang (pp. 5911-5917).

Modified palygorskite with 3-aminopropyltriethoxysilane (KH550) and N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (KH792) were used as adsorbent supports for adsorption of 12-phosphotungstic acid (H₃PW₁₂O₄₀, HPW). The effect of some factors, such as adsorbent dosage, contact time, initial HPW concentration and temperature, was investigated. The experimental data were well fitted with the pseudo-second-order kinetic model and the Langmuir adsorption isotherm model at all studied temperatures. The physicochemical properties of the solids were characterized by using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis–simultaneous differential thermal analysis (TGA–SDTA), and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy analysis techniques. The characteristic results indicated that silylated-Pa was a suitable support for adsorption of HPW; and HPW was finely and effectively distributed on silylated-Pa and retained partly strong Bronsted acidity.

Keywords: Palygorskite; Heteropolyacid; Adsorption; Kinetic; Isotherms

Sinterability studies on K_0.5Na_0.5NbO₃ using laser as energy source by Xiaoyong Tian; Anne Dittmar; Jörg Melcher; Jürgen G. Heinrich (pp. 5918-5923).

The sinterability of K_0.5Na_0.5NbO₃ (KNN) ceramics by a laser beam has been investigated in the present research. A 100W CO₂ laser with a beam diameter of 0.6mm has been used to sinter the KNN specimens prepared on a uniaxial pressing machine. The relations between laser power and thickness of densified layer, crystallographic structures and phase compositions have been studied. A comparison has been made between laser and furnace sintered KNN samples according to the SEM, XRD and XRF results. The possibility of KNN used for the layer-wise laser direct sintering 3D components has been confirmed in this paper.

Keywords: Laser sintering; Piezoelectric ceramics; Texture engineering; Surface treatment

Characteristics of solid aerosols produced by optical catapulting studied by laser-induced breakdown spectroscopy by F.J. Fortes; J.J. Laserna (pp. 5924-5928).

Optical catapulting (OC) constitutes an effective method to transport small amounts of different materials in the form of a solid aerosol. In this report, laser-induced breakdown spectroscopy (LIBS) is used for the analysis of those aerosols produced by OC. For this purpose, materials were catapulted using a Q-switch Nd:YAG laser. A second Q-switch Nd:YAG laser was used for LIBS analysis of the ejected particles. Data processing of aerosols was conducted using conditional data analysis. Also, the standard deviation method was used for the qualitative identification of the ejected particles. Two modes of interaction in OC (OC with focused or defocused pulses) have been evaluated and discussed. LIBS demonstrates that the distribution (spreading) of the ejected particles along the propagation axis increased as a function of the interpulse delay time. The mass density and the thickness of the target also play an important role in OC-LIBS.

Keywords: Laser-induced breakdown spectroscopy; LIBS; Optical catapulting; Solid aerosol; Shock wave

A density functional theory study of CH₄ dehydrogenation on Co(111) by Zhijun Zuo; Wei Huang; Peide Han; Zhihong Li (pp. 5929-5934).

The dehydrogenation of CH₄ on the Co(111) surface is studied using density functional theory calculation (DFT). It is found that CH₄ is favored to dissociate to CH₃ and then transforms to CH₂ and CH by sequential dehydrogenation, and CH₄ activation into CH₃ and H is the rate-determining step on the Co(111) surface. CH₂ is quite unstable on Co(111) surface. CH dehydrogenation into C and H is difficult. CH₃ and H prefer to adsorb on 3-fold hollow hcp and fcc sites, and CH₂, CH and C prefer to adsorb on hcp sites.

Keywords: DFT; Adsorption; CH; ₄; Co(1; 1; 1); Dehydrogenation

pH-controlled silicon nanowires fluorescence switch by Lixuan Mu; Wensheng Shi; Taiping Zhang; Hongyan Zhang; Guangwei She (pp. 5935-5938).

Covalently immobilizing photoinduced electronic transfer (PET) fluorophore 3-[N, N-bis(9-anthrylmethyl)amino]-propyltriethoxysilane (DiAN) on the surface of silicon nanowires (SiNWs) resulted a SiNWs-based fluorescence switch. This fluorescence switch is operated by adjustment of the acidity of the environment and exhibits sensitive response to pH at the range from 8 to 10. Such response is attributed to the effect of pH on the PET process. The successful combination of logic switch and SiNWs provides a rational approach to assemble different logic molecules on SiNWs for realization of miniaturization and modularization of switches and logic devices.

Keywords: Silicon nanowires; Optical switch; Surface modification

Microstructure and mechanical properties of alumina coatings prepared by double glow plasma technique by Hongbing Liu; Jie Tao; Jiang Xu; Zhaofeng Chen; Xinyi Luo (pp. 5939-5945).

Low-temperature growth (600°C) of α-Al₂O₃ coatings on the stainless steel substrate by double glow plasma technique was achieved. The compositions and microstructures of the coatings prepared at different oxygen flow rates were characterized, respectively, by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectrometry. A phenomenological mechanism for the formation of the Al₂O₃ ceramic coatings during the oxidation process was proposed on the basis of the experimental results. It was obvious that the oxygen flow rates had a great effect on the surface structure of the prepared Al₂O₃ coatings. The dense and smooth Al₂O₃ coatings were prepared at the oxygen flow rate of 15sccm. In addition, the correlations between the mechanical properties of Al₂O₃ coating and oxygen flow rates were also discussed. The coating prepared at 15sccm oxygen flow rate exhibited the best mechanical properties with a maximum hardness of 31GPa and elastic modulus of 321GPa. The corresponding critical load of scratch adherence for this sample was 47N.

Keywords: Double glow plasma; Co-deposition of aluminum and oxygen; α-Al; ₂; O; ₃; Adhesion; Hardness

Study of n⁺ type porous GaAs by photoluminescence spectroscopy: Effect of the etching time on the deep levels by T. Abdellaoui; M. Daoudi; A. Bardaoui; R. Chtourou (pp. 5946-5951).

Photoluminescence (PL) analysis is used to study porous layers elaborated by electrochemical etching of n⁺ Si-doped GaAs substrate with different etching times. Temperature and power dependence photoluminescence (PL) studies were achieved to characterize the effect of the etching time on the deep levels of the n⁺ Si-doped GaAs. The energy emission at about 1.46eV is attributed to the band-to-band (B–B) (e–h) recombination of a hole gas with electrons in the conduction band. The emission band is composed of four deep levels due to the complex of (V_AsSi_GaV_Ga), a complex of a (Ga vacancy – donor – As vacancy), a (Si_Ga–V_Ga³⁻) defect or Si clustering, and a (gallium antisite double acceptor-effective mass donor pair complex) and which peaked, respectively, at about (0.94, 1, 1.14, and 1.32eV). The PL intensity behavior as function of the temperature is investigated, and the experimental results are fitted with a rate equation model with double thermal activation energies.

Keywords: Porous GaAs; Electrochemical etching; Photoluminescence; Deep levels; Thermal activation energy

Occurrence of particle debris field during focused Ga ion beam milling of glassy carbon by Qin Hu; William O’Neill (pp. 5952-5956).

To explore the machining characteristics of glassy carbon by focused ion beam (FIB), particles induced by FIB milling on glassy carbon have been studied in the current work. Nano-sized particles in the range of tens of nanometers up to 400nm can often be found around the area subject to FIB milling. Two ion beam scanning modes – slow single scan and fast repetitive scan – have been tested. Fewer particles are found in single patterns milled in fast repetitive scan mode. For a group of test patterns milled in a sequence, it was found that a greater number of particles were deposited around sites machined early in the sequence. In situ EDX analysis of the particles showed that they were composed of C and Ga. The formation of particles is related to the debris generated at the surrounding areas, the low melting point of gallium used as FIB ion source and the high contact angle of gallium on glassy carbon induces de-wetting of Ga and the subsequent formation of Ga particles. Ultrasonic cleaning can remove over 98% of visible particles. The surface roughness ( R_a) of FIB milled areas after cleaning is less than 2nm.

Keywords: Focused ion beam (FIB); Glassy carbon; Milling; Nano-particles; Ultrasonic; Cleaning

Effect of source temperature on the morphology and photoluminescence properties of ZnO nanostructures by Khalifa Al-Azri; Roslan Md Nor; Y.M. Amin; Majid. S. Al-Ruqeishi (pp. 5957-5960).

ZnO nanostructures have been synthesized by heating a mixture of ZnO/graphite powders using the thermal evaporation and vapor transport on Si(100) substrates without any catalyst and at atmospheric argon pressure. The influence of the source temperature on the morphology and luminescence properties of ZnO nanostructures has been investigated. ZnO nanowires, nanoflowres and nanotetrapods have been formed upon the Si(100) substrates at different source temperatures ranging from 1100 to 1200°C. Room temperature photoluminescence (PL) spectra showed increase green emission intensity as the source temperature was decreased and ZnO nanowires had the strongest intensity of UV emission compared with other nanostructures. In addition, the growth mechanism of the ZnO nanostructures is discussed based on the reaction conditions.

Keywords: Nanostructures; ZnO; Photoluminescence

Aqueous phase Ag nanoparticles with controlled shapes fabricated by a modified nanosphere lithography and their optical properties by Yujun Song; Hani E. Elsayed-Ali (pp. 5961-5967).

We have developed a modified nanosphere lithography (NSL) process to fabricate surface-confined Ag nanoparticles (NPs) with controlled shapes. NPs with different shapes, such as triangular, quadrilateral, pentagon or trapezoidal with rounded tips or edges, can be fabricated by this process. These Ag NPs can be dislodged into water forming NPs in an aqueous environment. The developed process results in better NP shape retaining than those obtained using the routine NSL process. The UV–vis absorption of the surface-confined Ag NPs show distinct blue shift and reduced intensity after surface modification. The NPs produced by the modified NSL and dislodged in water have significantly less density of debris as observed by transmission electron microscopy and UV–vis absorption spectrum.

Keywords: Nanoparticles; Silver; Fabrication; Aqueous; Nanosphere lithography; Surface plasmon resonance

A variable charge molecular dynamics study of the initial stage of nickel oxidation by S. Garruchet; O. Politano; P. Arnoux; V. Vignal (pp. 5968-5972).

The oxidation of nickel single crystals is investigated by using variable charge molecular dynamics. The simulations are performed on three nickel low-index surfaces ((100), (110) and (111)) at temperatures between 300K and 950K. The results show that the shape of the oxidation kinetics is independent of the crystallographic orientation and the temperature under the present conditions. The oxide thin film grows according to an island growth mode, this initial stage of oxidation can be divided in three steps: ( i) the dissociative chemisorption step ( ii) the oxide island nucleation and ( iii) the lateral growth of the island. The first step is slowdown/speedup by the surface orientation and temperature. Finally, the simulations show the onset of an oxide layer.

Keywords: Molecular dynamics; Oxidation; Nickel; Oxygen

Fabrication of hydrophobic alumina aerogel monoliths by surface modification and ambient pressure drying by Lina Wu; Yudong Huang; Zhijiang Wang; Li Liu; Huifang Xu (pp. 5973-5977).

Hydrophobic crack-free alumina aerogel monoliths were fabricated by –Si(CH₃)₃ (trimethylsilyl substituent) modification of alcogels followed by an ambient pressure drying procedure. One-step solvent exchange and surface modification were simultaneously progressed by immersing alumina alcogels in trimethylmethoxysilane (TMMOS)/hexane solution. It is found that the hydrophobic property of alumina aerogels is affected by the contents of TMMOS from the measurements of contact angle and Fourier transform infrared spectrometry. Thermogravimetry/differential scanning calorimetry analyses reveal that the modified aerogels maintain their hydrophobic behavior up to a temperature of 260°C. The structure and morphology of the obtained hydrophobic alumina aerogels were characterized by the measurements of N₂ physical adsorption and scanning electron microscopy, which showed that they were highly porous materials with narrow slit-like pore geometry and a high degree of pore size uniformity.

Keywords: Hydrophobic; Alumina aerogel; Surface modification; Siloxane

Surface tailoring of SiO₂ nanoparticles by mechanochemical method based on simple milling by Jinbin Lin; Hongling Chen; Licheng Yao (pp. 5978-5984).

An appropriate modifying agent is obviously important with regard to the surface treatment of nanoparticles. Moreover, a right physical mixer that can provide enough energy to break up the secondary structure (aggregate and agglomerate) of nanoparticles is absolutely critical to the modification as well. However, it is not easy to give consideration to both of them during the process of modification. As is often the case, we tend to take care of the modifying agent but lose sight of the physical mixer. In this paper, hybrid particles of SiO₂/2,4-Diisocyanatotoluene (SiO₂/TDI) and SiO₂/2,4-Diisocyanatotoluene/hydroxyl silicone oil (SiO₂/TDI/(PDMS-OH)) were fabricated by mechanochemical method based on simple milling. The prepared hybrid particles (SiO₂/TDI and SiO₂/TDI/(PDMS-OH)) were characterized by infrared spectroscopy (FT-IR), static contact angle (CA), water sorption measurement, thermal analysis (TGA and DSC) and transmission electron microscopy (TEM). FT-IR spectra and thermal analysis (DSC) results demonstrate that TDI together with PDMS-OH is chemically anchored to the surface of nano-SiO₂. TGA results show that the grafting density of TDI is as high as 2.62 TDI/nm², while the grafting density of PDMS-OH is 0.0156 PDMS-OH/nm². Deduced from static contact angle (CA) and water sorption measurement, both hybrid particles exhibit strong hydrophobic (140^o for SiO₂/TDI and 144^o for SiO₂/TDI/(PDMS-OH)) after modification. TEM images reveal that hybrid particles (SiO₂/TDI and SiO₂/TDI/(PDMS-OH)) prepared by ball milling method exhibit much better miscibility and dispersibility in PDMS matrix when compared with those particles prepared by a common mixing device.

Keywords: Nano-SiO2; Hybrid particles; Surface modification; Mechanochemical

Investigation on cracking behavior of Ni-based coating by laser-induction hybrid cladding by Yongjun Huang; Xiaoyan Zeng (pp. 5985-5992).

Based on the experiments of laser-induction hybrid cladding by powder feeding, the cracking behavior of Ni-based coating and solidification characteristic in molten pool were investigated. The results indicate that the hybrid cladding is effective to prevent from cracking in Ni-based coating. With the increase of induction energy density, the tensile stress and crack rate decrease obviously. When the induction energy density arrives at 36J/mm², the free-cracks coating can be achieved. In laser-induction hybrid cladding, the martensite can be eliminated in the heat affected zone and the phase transformation stress is little. Moreover, the molten pool is solidified through two directions such as the coating surface and coating/substrate interface, i.e., firstly the top and bottom in molten pool are solidified, and then the middle in molten pool is solidified. Therefore, in hybrid cladding, the peak value of tensile stress is located in the middle of coating, which is different from that in laser cladding. This distribution status of residual stress is greatly helpful to restrict the cracks of Ni-based coating in laser-induction hybrid cladding.

Keywords: Cracking behavior; Coating; Laser-induction hybrid cladding; Residual stress

Atomistic study of deposition process of Al thin film on Cu substrate by Yongzhi Cao; Junjie Zhang; Tao Sun; Yongda Yan; Fuli Yu (pp. 5993-5997).

In this paper we report molecular dynamics based atomistic simulations of deposition process of Al atoms onto Cu substrate and following nanoindentation process on that nanostructured material. Effects of incident energy on the morphology of deposited thin film and mechanical property of this nanostructured material are emphasized. The results reveal that the morphology of growing film is layer-by-layer-like at incident energy of 0.1–10eV. The epitaxy mode of film growth is observed at incident energy below 1eV, but film-mixing mode commences when incident energy increase to 10eV accompanying with increased disorder of film structure, which improves quality of deposited thin film. Following indentation studies indicate deposited thin films pose lower stiffness than single crystal Al due to considerable amount of defects existed in them, but Cu substrate is strengthened by the interface generated from lattice mismatch between deposited Al thin film and Cu substrate.

Keywords: Deposition; Thin film; Indentation; Molecular dynamics

Evaluation of the substrate effect on indentation behavior of film/substrate system by J.S. Wang; X.J. Zheng; H. Zheng; Z. Zhu; S.T. Song (pp. 5998-6002).

A method to evaluate the substrate effect quantitatively in film indentation is proposed. For the thin film deposited on the substrate, the power function relationship is used to describe the loading curve of the film indentation behavior. The loading curve exponent of the power function which is the fitting parameter can reflect the substrate effect quantitatively. The finite element method is used to simulate the nanoindentation process of the film/substrate system. The loading curve exponent can be obtained from the simulation results. A substrate effect factor based on the loading curve exponent is defined to characterize the effect of the substrate on film indentation. Meanwhile, the dimensionless function of the loading curve exponent related with the material properties and indentation depth is obtained. The results can be helpful to the measurement of the mechanical properties of thin films by means of nanoindentation.

Keywords: Substrate effect; Nanoindentation; Finite element method; Dimensionless analysis

Ultrathin Mo/MoN bilayer nanostructure for diffusion barrier application of advanced Cu metallization by Bin Zhao; Kefei Sun; Zhenlun Song; Junhe Yang (pp. 6003-6006).

Ultrathin Mo (5nm)/MoN (5nm) bilayer nanostructure has been studied as a diffusion barrier for Cu metallization. The Mo/MoN bilayer was prepared by magnetron sputtering and the thermal stability of this barrier is investigated after annealing the Cu/barrier/Si film stack at different temperatures in vacuum for 10min. The failure of barrier structure is indicated by the abrupt increase in sheet resistance and the formation of Cu₃Si phase proved by X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS). High resolution transmission electron microscopy (HRTEM) examination suggested that the ultrathin Mo/MoN barrier is stable and can prevent the diffusion of Cu at least up to 600°C.

Keywords: Mo/MoN; Bilayer nanostructure; Diffusion barrier; Thermal stability

Interfacial reaction of silver ultra-thin film deposited on interpenetrating polymer network substrate by liquor-phase reduction by Dongyan Tang; Yudi Guo; Xiaohong Zhang; Yuelong Yin (pp. 6007-6012).

The interfacial reaction, metal transformations, and nonmetal bond types of silver ultra-thin film deposited on polyurethane (PU) based interpenetrating polymer networks (IPN) substrate by the liquor-phase reduction at room temperatures were studied by atomic force microscope (AFM), X-ray photoelectron spectroscopy (XPS) and attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). The IPN substrate was prepared by dip-pulling precursors onto a silicon wafer or a glass plate, followed by solidification at room temperature. The interpenetrate structures of IPN with two crosslinked networks restricted the aggregation of silver during the reduction and deposition. The devised –OH terminal group in PU simplified the determination of reactive site in IPN and reinforced the adhesion between IPN and silver through interfacial reaction. The XPS results, which matched well with the ATR-FTIR results, verified the chemical reactive site of PU in IPN with silver in the oxide state.

Keywords: Interfacial reaction; Liquor-phase reduction; Silver; Interpenetrating polymer networks (IPN); X-ray photoelectron spectroscopy (XPS); Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR)

Electrical and ferromagnetic properties of Tb-doped indium–tin oxide films fabricated by sol–gel method by Yalu Zuo; Shihui Ge; Zhenhua Yu; Shiming Yan; Xueyun Zhou; Li Zhang (pp. 6013-6017).

The electrical and ferromagnetic properties of (In0.9−_xTb_xSn_0.1)₂O₃ and (In0.99−_yTb_0.01Sn_y)₂O₃ films fabricated by sol–gel method have been investigated. All the films show room temperature ferromagnetism. The magnetic moment per Tb ion of (In0.9−_xTb_xSn_0.1)₂O₃ films first increases and then decreases with the increasing Tb content. The variation of conductivity with Tb content is coincident with that of the magnetic moment. Furthermore, the conductivity and magnetic moment variations with Sn content y in (In0.99−_yTb_0.01Sn_y)₂O₃ films also have the similar trend. These results imply that the ferromagnetism may originate from the carrier-mediated mechanism.

Keywords: Sol–gel method; Carrier-mediated mechanism; Tb-doped indium–tin oxide

3′-Hydroxy-4-methoxychalcone as a potential antibacterial coating on polymeric biomaterials by P.M. Sivakumar; Geetha Iyer; Lavanya Natesan; Mukesh Doble (pp. 6018-6024).

Antimicrobial property of chalcone coated high density polyethylene (HDPE), low density polyethylene (LDPE), polypropylene (PP) and polyurethane (PU) against Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa is reported here. The presence of chalcone on the surface was confirmed from fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Bacterial adhesion decreased considerably on all the coated surfaces. Bacterial adhesion was highest on PU surface (most hydrophobic) and lowest on HDPE (most hydrophilic) surface. Chalcone seems to damage the membrane of the bacteria as well as exhibit slimicidal activity. Reasonably good correlation was observed between the CFU (Colony Forming Units) ratio (it is defined as the ratio of CFU on coated surface to the chalcone uncoated surface) at the 24th hour against both hydrophobicity of the microorganism and roughness of the coated polymeric surfaces. Increasing roughness of the polymer and hydrophobicity of the microorganisms were positively and negatively correlated respectively with CFU ratio. Hence, the chalcone coated polymers can be used in the development of newer biomaterials.

Keywords: 3′-Hydroxy-4-methoxychalcone; Bacterial adhesion; Slimicidal activity; Contact angle; Surface roughness

On tuning the orientation of grains of spray pyrolysed ZnO thin films by T.V. Vimalkumar; N. Poornima; C. Sudha Kartha; K.P. Vijayakumar (pp. 6025-6028).

Effect of varying spray rate on the structure and optoelectronic properties of spray pyrolysed ZnO film is analysed. ZnO films were characterised using different techniques such as X-ray diffraction (XRD), photoluminescence, electrical resistivity measurement, and optical absorption. The XRD analysis proved that, with the increase in spray rate, orientation of the grains changed from (101) plane to (002) plane. The films exhibited luminescence in two regions—one was the ‘near band-edge’ (NBE) (∼380nm) emission and the other one was the ‘blue-green emission’ (∼503nm). Intensity of the blue-green emission decreased after orientation of grains shifted to (002) plane. Scanning electron microscope (SEM) analysis of the films asserts that spray rate has major role in improving the crystallographic properties of the films. Moreover resistivity of the films could be lowered to 2.4×10⁻²Ωcm without any doping or post-deposition annealing.

Keywords: ZnO; Spray pyrolysis; Plane orientation; Sheet resistivity; Photoluminescence

Immobilization of metalloporphyrins on P(4VP-co-St)/SiO₂ by the quaternarization reaction by Ruixin Wang; Weizhou Jiao; Baojiao Gao (pp. 6029-6034).

Poly(4vinylpyridine-co-styrene) (P(4VP-co-St)) was grafted on silica gel particles in the manner of “grafting from”, and the grafting particle P(4VP-co-St)/SiO₂ was gained. The chloromethylation reaction for the tetraphenylporphyrin (TPP) was performed using a chloromethylation reagent, 1,4-bis(chloromethyoxy)butane which was uncarcinogenic, and the tetra-chloromethylphenyl-porphyrin (TMCPP) was prepared. Then, the quaternization reaction between the benzyl chloride groups on TMCPP and pyridine groups of the grafted P(4VP-co-St) macromolecules occurred and the bonding of TMCPP on the particles P(4VP-co-St)/SiO₂ was realized, resulting in the functional composite-type particles TMCPP-P(4VP-co-St)/SiO₂. Subsequently, the metallation of the bonded particles TMCPP-P(4VP-co-St)/SiO₂ was carried out via the coordination reaction between TMCPP-P(4VP-co-St)/SiO₂ and metal salt, resulting in the supported metalloporphyrin (MP) catalysts MP-P(4VP-co-St)/SiO₂. The supported catalysts were characterized by UV–Vis spectra. The effects of various factors on the bonding process of TMCPP on P(4VP-co-St)/SiO₂ were studied in detail. In addition, the catalytic activity of the supported catalysts MP-P(4VP-co-St)/SiO₂ have been studied in oxidation process of ethyl benzene with molecular oxygen to acetophenone without the use of sacrificial co-reductant. The experimental results showed that the tetra-chloromethylphenyl-porphyrin (TMCPP) could be successfully bonded onto the P(4VP-co-St)/SiO₂ surfaces by means of the quaternization reaction between TMCPP and the pyridine groups on grafted P(4VP-co-St) macromolecules. The supported catalysts MP-P(4VP-co-St)/SiO₂ exhibited the fine catalytic activity. Moreover, the supported cobalt porphyrin was more active than the supported iron and manganese porphyrins.

Keywords: 4-Vinylpyridine; Graft polymerization; SiO; ₂; Metalloporphyrin; Quaternarization reaction; Immobilization

Adsorption of nonpolar benzene derivatives on single-walled carbon nanotubes by Ching-Ju Monica Chin; Mei-Wen Shih; Hen-Jer Tsai (pp. 6035-6039).

The adsorption of benzene, toluene, and chlorobenzene on single-walled carbon nanotubes (SWCNTs) with and without acid oxidation was conducted to investigate the influences of derivative groups on benzene rings and functional groups from SWCNTs on adsorption by SWCNTs. The SWCNTs of high purity were chosen and moderate acid oxidation was performed so that the surface physical properties remained unchanged after acid oxidation and the influences of acid oxidation on adsorption were only contributed from the modification of the surface chemistry of SWCNTs. The oxygen-containing surface groups introduced by acid oxidation obstructed the interactions between functional groups of nonpolar benzene derivatives and C-rings of SWCNTs significantly. The dispersive interaction between the partially positive H⁺ of the methyl group and the oxygen-containing surface groups slightly increased the adsorption of toluene on oxidized SWCNTs at high solution pH. The thermodynamic of adsorption was also studied at different temperatures.

Keywords: Benzene derivatives; Carbon nanotubes (CNTs); π–π Interactions

Ferromagnetism driven by cation vacancy in GaN thin films and nanowires by Anlong Kuang; Hongkuan Yuan; Hong Chen (pp. 6040-6046).

The first-principles calculations have been performed to understand the origin of magnetism in undoped GaN thin films. The results show that Ga vacancy, rather than that of N contributes the observed magnetism, and the magnetic moments mainly come from the unpaired 2 p electrons at nearest-neighbor N atoms of the Ga vacancy. Calculations and discussions are also extended to bare and passivated GaN nanowires, We find that per Ga vacancy on the surface sites products the total magnetic moment of 1.0μB while that inside of the nanowires can lead to the formation of a net moment of 3.0μB. The coupling between two Ga vacancies is also studied and we found that the coupling is ferromagnetic coupling. The surface passivation with hydrogen is shown to strongly enhance the ferromagnetism. Our theoretical study not only demonstrates that GaN nanowire can be magnetic even without transition-metal doping, but also suggests that introducing Ga vacancy is a natural and an effective way to fabricate low-dimensional magnetic GaN nanostructures.

Keywords: First-principles; Nanowire; Vacancy; Spin-density

Effect of dielectric barrier discharge on semiconductor Si electrode surface by Changquan Wang; Guixin Zhang; Xiangning He (pp. 6047-6052).

Electrode materials and shapes affected the discharge modes. Meanwhile, the discharge has influence upon electrode surface. In order to study the effect of discharge on semiconductor electrode, the experiments were carried out using single crystal Si wafer as high voltage electrode of atmospheric pressure dielectric barrier discharge in air. The effects of dielectric barrier discharge on Si electrode surface are analyzed by means of field emission scanning electron microscope (FESEM) and X-ray photoelectron spectroscopy (XPS). The results show that surface roughness and oxidation increase with discharge time, while surface nitridation is not observed on Si electrode surface. It is different from Cu electrode. The difference is due to different chemical reactions between electrode surface and air plasma but could also be ascribed to the different analysis techniques used.

Keywords: PACS; 52.40.Hf; 61.82.Fk; 52.80.MgDielectric barrier discharge; Semiconductor electrode; Air plasma; Power supply

Metal oxide buffer layer for improving performance of polymer solar cells by Zhouying Zhao; Ranganath Teki; Nikhil Koratkar; Harry Efstathiadis; Pradeep Haldar (pp. 6053-6056).

We report the application of aluminum doped ZnO (ZnO:Al) layer as a buffer on ITO glass for fabrication of non-inverted polymer solar cells. The ZnO:Al thin film was deposited using DC magnetron sputtering, with the thickness being varied from 23 to 100nm. The devices showed most discernible improvements in their efficiencies when a thin layer of ZnO:Al film of thickness ∼40nm was introduced. The observed enhancement in short circuit current density and open circuit voltage is likely attributed to the role of the ZnO:Al film as an optical tuner and an interfacial diffusion barrier. The result suggests that a metal oxide layer inserted between ITO and polymer layers can be a route for improving both efficiency and stability of polymer solar cells.

Keywords: ZnO; Metal oxide; Optical tuner; Buffer; Polymer solar cells

Experimental determination of valence band offset at PbTe/Ge(100) interface by synchrotron radiation photoelectron spectroscopy by C.F. Cai; H.Z. Wu; J.X. Si; W.H. Zhang; Y. Xu; J.F. Zhu (pp. 6057-6059).

The band offset at the interface of PbTe/Ge (100) heterojunction was studied by the synchrotron radiation photoelectron spectroscopy. A valence band offset of Δ E_V=0.07±0.05eV, and a conduction band offset of Δ E_C=0.27±0.05eV are concluded. The experimental determination of the band offset for the PbTe/Ge interface should be beneficial for the heterojunction to be applied in new optoelectronic and electronic devices.

Keywords: SRPES; PbTe/Ge heterojunction; Band offsets

A facile method to modify carbon nanotubes with nitro/amino groups by Li Wang; Shouai Feng; Jianghong Zhao; Jianfeng Zheng; Zhijian Wang; Li Li; Zhenping Zhu (pp. 6060-6064).

Nitro groups (–NO₂) have been introduced on the surface of multi-walled carbon nanotubes (MWCNTs) by treatment with a mixture of concentrated H₂SO₄/HNO₃ solution at low temperature (60°C). Such a low-temperature treatment simultaneously can well prevent MWCNTs from the structural damage. From the nitro-modified MWCNTs, MWCNTs can be readily modified with amino groups by reduction of nitro groups. The prepared amino-modified MWCNTs are highly soluble in polar solvents such as dimethylformamide (DMF), alcohol and acetone. Further, as a demonstration, MWCNTs can be functionalized with guest objects, provided by the strong bonding ability of amino groups.

Keywords: MWCNTs; Nitro groups; Amino groups; Mixed acid; Low temperature; Perylene derivative

Influence of process time on microstructure and properties of 17-4PH steel plasma nitrocarburized with rare earths addition at low temperature by M.F. Yan; R.L. Liu (pp. 6065-6071).

17-4PH stainless steel was plasma nitrocarburized at 430°C for different time with rare earths (RE) addition. Plasma RE nitrocarburized layers were studied by optical microscope, scanning electron microscope equipped with an energy dispersive X-ray analyzer, X-ray diffraction, microhardness tests, pin-on-disc tribometer and anodic polarization tests. The results show that rare earths atoms can diffuse into the surface of 17-4PH steel. The modified layer depths increase with increasing process time and the layer growth conforms approximately to the parabolic law. The phases in the modified layer are mainly of γ′-Fe₄N, nitrogen and carbon expanded martensite (α′_N) as well as some incipient CrN at short time (2h). With increasing of process time, the phases of CrN and γ′-Fe₄N increase but α′_N decomposes gradually. Interestingly, the peaks of γ′-Fe₄N display a high (200) plane preferred orientation. The hardness of the modified specimen is more than 1340HV, which is about 3.7 times higher than that of untreated one. The friction coefficients and wear rates of specimens can be dramatically decreased by plasma RE nitrocarburizing. The surface hardness and the friction coefficients decrease gradually with increasing process time. The corrosion test shows that the 8h treated specimen has the best corrosion resistance with the characterization of lower corrosion current density, a higher corrosion potential and a large passive region as compared with those of untreated one.

Keywords: Low temperature plasma nitrocarburizing; Rare earths (RE); Microstructure; Wear; Corrosion

Controlled growth of superhydrophobic films by sol–gel method on aluminum substrate by Shixiang Lu; Yiling Chen; Wenguo Xu; Wei Liu (pp. 6072-6075).

Superhydrophobic surface was prepared by sol–gel method on aluminum substrate via immersing the clean pure aluminum substrate into the solution of zinc nitrate hexahydrate (Zn(NO₃)₂·6H₂O) and hexamethylenetetraamine (C₆H₁₂N₄) at different molar ratios and unchanged 0.04mol/L total concentration, then heated at 95°C in water bath for 1.5h, subsequently modified with 18 alkanethiols or stearic acid. When the molar ratios of Zn(NO₃)₂·6H₂O and C₆H₁₂N₄ were changed from 10:1 to 1:1 the contact angle was higher than 150°. The best prepared surface had a high water contact angle of about 154.8°, as well as low angle hysteresis of about 3°. The surface of prepared films using Zn(NO₃)₂·6H₂O and C₆H₁₂N₄ composed of ZnO and Zn–Al LDH, and Al. SEM images of the film showed that the resulting surface exhibits different flower-shaped wurtzite zinc oxide microstructure and porous Zn–Al LDH. The special flowerlike and porous architecture, along with the low surface energy leads to the surface superhydrophobicity.

Keywords: Superhydrophobic; Sol–gel; Water contact angle

Synthesis and characterization of ZnO–Ag core–shell nanocomposites with uniform thin silver layers by Fei Li; Yuliang Yuan; Junyang Luo; Qinghua Qin; Jianfang Wu; Zhen Li; Xintang Huang (pp. 6076-6082).

This paper presents an investigation on the synthesis and characterization of ZnO–Ag core–shell nanocomposites. ZnO nanorods were employed as core material for Ag seeds, and subsequent nucleation and growth of reduced Ag by formaldehyde formed the ZnO–Ag core–shell nanocomposites. The ZnO–Ag nanocomposites were annealed at different temperature to improve the crystallinity and binding strength of Ag nanoparticles. The morphology, microstructure and optical properties of the ZnO–Ag core–shell nanocomposites were characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, ultraviolet–visible (UV–vis) absorption and photoluminescence measurement. It was demonstrated that very small face-center-cubic Ag nanoparticles were coated on the surface of ZnO nanorods. The ultraviolet absorption and surface plasmon absorption band of ZnO–Ag core–shell nanocomposites exhibited some redshifts relative to pure ZnO nanorods and monometallic Ag nanoparticles. The coating of Ag nanocrystals onto the ZnO nanorods completely quenched the photoluminescence. These observations reflected the strong interfacial interaction between ZnO nanorods and Ag nanoparticles. The effect of Ag coating thickness on the morphology and optical properties of ZnO–Ag core–shell nanocomposites was also investigated. Moreover, the growth mechanism of ZnO–Ag core–shell nanocomposites was also proposed and discussed in detail.

Keywords: PACS; 81.07.Bc; 81.16.Be; 61.46.HkZnO–Ag; Core–shell; Ultraviolet–visible absorption; Photoluminescence; Growth mechanism

Synthesis, characterization and antimicrobial activity of copper and zinc-doped hydroxyapatite nanopowders by Vojislav Stanić; Suzana Dimitrijević; Jelena Antić-Stanković; Miodrag Mitrić; Bojan Jokić; Ilija B. Plećaš; Slavica Raičević (pp. 6083-6089).

Antimicrobial materials based on hydroxyapatite are potentially attractive in a wide variety of medical applications. The synthesis of copper and zinc-doped hydroxyapatite was done by neutralization method. This method consists of dissolving CuO or ZnO in solution of H₃PO₄, and the slow addition to suspension of Ca(OH)₂ for obtaining monophasic product. Characterization studies from XRD, SEM, TEM and FTIR spectra showed that particles of all samples are of nano size and they do not contain any discernible crystalline impurity. The quantitative elemental analysis showed that the copper and zinc ions fully incorporated into the hydroxyapatite. The antimicrobial effects of doped hydroxyapatite powders against pathogen bacterial strains Escherichia coli, Staphylococcus aureus and pathogen yeast Candida albicans were tested in solid and liquid media. Quantitative test in liquid media clearly showed that copper and zinc-doped samples had viable cells reduction ability for all tested strains.

Keywords: Hydroxyapatite; Cu; Zn; Nanoparticle; Antimicrobial

CdS films deposited by chemical bath under rotation by A.I. Oliva-Avilés; R. Patiño; A.I. Oliva (pp. 6090-6095).

Cadmium sulfide (CdS) films were deposited on rotating substrates by the chemical bath technique. The effects of the rotation speed on the morphological, optical, and structural properties of the films were discussed. A rotating substrate-holder was fabricated such that substrates can be taken out from the bath during the deposition. CdS films were deposited at different deposition times (10, 20, 30, 40 and 50min) onto Corning glass substrates at different rotation velocities (150, 300, 450, and 600rpm) during chemical deposition. The chemical bath was composed by CdCl₂, KOH, NH₄NO₃ and CS(NH₂)₂ as chemical reagents and heated at 75°C. The results show no critical effects on the band gap energy and the surface roughness of the CdS films when the rotation speed changes. However, a linear increase on the deposition rate with the rotation energy was observed, meanwhile the stoichiometry was strongly affected by the rotation speed, resulting a better 1:1 Cd/S ratio as speed increases. Rotation effects may be of interest in industrial production of CdTe/CdS solar cells.

Keywords: Chemical bath deposition; Rotating substrate; CdS films; CdS properties

Numerical investigation on atomic oxygen undercutting of the protective polymer film using Monte Carlo approach by Yang Liu; Xue Liu; Guohui Li; Tao Li (pp. 6096-6106).

Atomic oxygen undercutting effect of the protective polymer film in low earth orbit space environment is a potential threat to vulnerable long duration exposure facility. A Monte Carlo computational model is developed to simulate the interactions between atomic oxygen undercutting course with polyimide film. Physical process of the atomic oxygen undercutting, the definition of parameters, the affected by atomic oxygen fluence, orbit angle, protection coating thickness and thermal assimilation and the additive anti-undercutting components as well as a new three-dimensional reaction probability are discussed in detail. Simulated results are in good agreement with flight experimental data. With the increment of the atomic oxygen fluence, all the undercutting profiles, the depth and the width increased. Maximum undercutting depth is always larger than maximum undercutting width and the larger thermal assimilation coefficient causes the smaller undercutting damage. Using three-dimensional reaction probability, maximum depth decreased by approximately 20% than that of 28.5° orbit angle.

Keywords: Polymer film; Atomic oxygen undercutting; Monte Carlo; Numerical simulation

Improved mechanical properties of hydroxyapatite/poly(ɛ-caprolactone) scaffolds by surface modification of hydroxyapatite by Yan Wang; Jing Dai; Qingchun Zhang; Yan Xiao; Meidong Lang (pp. 6107-6112).

Scaffolds comprising hydroxyapatite (HAP) or poly(ɛ-caprolactone)-grafted hydroxyapatite (g-HAP) and poly(ɛ-caprolactone) (PCL) were prepared using the thermally induced phase separation/salt leaching technique. The g-HAP nanoparticles were evaluated by Fourier Transformation Infrared Spectroscopy (FTIR) and thermal gravimetric analysis (TGA). Power X-ray Diffraction (XRD) patterns confirmed the successful grafting on the surface of HAP. The effects on mechanical strength, porosity and thermal property of scaffolds by the introduction of nanoparticles were extensively investigated. The compressive modulus of the scaffold was greatly improved by the addition of g-HAP nanoparticles. Especially the compressive modulus of the g-HAP/PCL scaffold containing 20wt% of g-HAP was 59.4% higher than that of the corresponding HAP/PCL scaffold.

Keywords: Scaffold; Poly(ɛ-caprolactone); Hydroxyapatite; Surface grafting; Mechanical property

Deposition and electrostatic removal of gaseous organic contaminants on substrate surfaces by Angus Shiue; Der-Chi Tien; Walter Den; Shih-Cheng Hu; Chia-Shao Hsu (pp. 6113-6116).

The adhesion behavior of di-n-butyl phthalate (DBP) onto different substrates (quartz, glass, and silicon) used as wafer surfaces was studied by using an in situ UV spectrophotometric technique. The results from the closed cell experiments revealed that greatest extent of DBP adhesion occurred on the quartz chip (0.154μgcm⁻²), followed in the order by the glass (0.054μgcm⁻²) and silicon (0.039μgcm⁻²). By means of the in situ spectrophotometric observation, application of an electrical field at 290Vcm⁻¹ in the cell proved to be effective in inducing charging of DBP aerosols, which were consequently attracted towards the electrodes. This method can be applied to wafer storage and transport equipments to prevent wafer contamination from material outgassing representative by DBP.

Keywords: UV spectrophotometer; Airborne molecular contamination; DBP; Electrostatic force

Effect of zinc nitrate concentration on the structural and the optical properties of ZnO nanostructures by Hee Yeon Yang; Se Han Lee; Tae Whan Kim (pp. 6117-6120).

ZnO nanorods and nanodisks were formed on indium-tin-oxide-coated glass substrates by using an electrochemical deposition method. Scanning electron microscopy images showed that the ZnO nanorods were transformed into nanodisks with increasing Zn(NO₃)₂ concentration. X-ray diffraction patterns showed that the ZnO nanostructures had wurzite structures. The full widths at half maxima of the near band-edge emission peak of photoluminescence spectra at 300K for ZnO nanorods were small, indicative of the high quality of the nanorods. These results indicate that the structural and the optical properties of ZnO nanostructures vary by changing Zn(NO₃)₂ concentration.

Keywords: PACS; 61.46.+w; 68.65.−k; 78.55.EtZnO nanorods; ZnO nanodisks; Zn(NO; ₃; ); ₂; Structural property; Optical property

Surface characterization of Pd/Ag23wt% membranes after different thermal treatments by A. Ramachandran; W.M. Tucho; A.L. Mejdell; M. Stange; H.J. Venvik; J.C. Walmsley; R. Holmestad; R. Bredesen; A. Borg (pp. 6121-6132).

Hydrogen permeation measurements of 1.5–10μm thick Pd/Ag23wt% membranes before and after thermal treatments at 300°C in air (both sides) or in the temperature range 300–450°C in N₂ (feed side) and Ar (permeate side) were performed. Accompanying changes in surface topography and chemical composition were subsequently investigated by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) depth profiling. For a 2μm thick membrane, the surface roughness increased for all annealing temperatures applied, while a temperature of 450°C was required for an increase in roughness of both membrane surfaces to occur for the 5μm membrane. The thickest membrane, of 10μm, showed changed surface roughness on one side of the membrane only and a slight decrease in hydrogen permeance after all heat treatments in N₂/Ar. X-ray photoelectron spectroscopy investigations performed after treatment and subsequent permeation measurements revealed segregation of silver to the membrane surfaces for all annealing temperatures applied. In comparison, heat treatment at 300°C in air resulted in significantly increased hydrogen permeance accompanied by increasing surface roughness. Upon exposure to oxygen, Pd segregates to the surface to form a 2–3nm thick oxide layer (PdO), with more complex segregation behavior after subsequent reduction and permeance measurements in pure hydrogen. The available permeance data for the Pd/Ag23wt% membranes after heat treatment in air at 300°C is found to depend linearly on the inverse membrane thickness, implying bulk limited hydrogen permeation for thicknesses down to 1.5–2.0μm.

Keywords: PdAg membranes; Hydrogen permeation; Surface topography; Segregation

Preparation and atomic oxygen erosion resistance of silica film formed on silicon rubber by sol–gel method by An Xing; Yuan Gao; Jungang Yin; Guangjuan Ren; Huitao Liu; Mianjun Ma (pp. 6133-6138).

Based on the characteristic that silicon coupling agents have the capability to develop ‘molecular bridge’ in the interface of organic materials and inorganic materials, silica films were prepared on the surface of flexible silicon rubber by sol–gel method and the optical transmittance of the sample before and after atomic oxygen irradiation was tested. The surface morphology and structure of silica films were investigated by scanning electronic microscope (SEM) and Fourier transformed infrared spectroscopy (FTIR). The results indicated that the silica sol could easily form a uniform thin film on the surface of silicon rubber pretreated by high concentration silicon coupling agents, and the inorganic silica films could combine with organic silicon rubber without obvious delamination on the interface.

Keywords: Silica film; Silicon rubber; Silicon coupling agent; Atomic oxygen

Sections

Personal tools

Applied Surface Science (v.256, #20)

Sections

Personal tools

Local resources

Applied Surface Science (v.256, #20)