Key Engineering Materials Vols. 609-610

Abstract: Since ZnO is a wide band gap (3.37 eV) semiconductor with a large exitonic binding energy (60 meV), it has been considered as a candidate for various applications, such as ultraviolet (UV) light emitting diodes and laser diodes. For the applications of ZnO-based optoelectronic devices, it is necessary to produce n and p type ZnO films with the high quality. Since ZnO is naturally n-type semiconductor material due to intrinsic defects, such as oxygen vacancies, zinc interstitials, etc., it is easy to produce n-type ZnO with high quality. However, it is difficult to produce low-resistive and stable p-type ZnO due to its asymmetric doping limitations and the self-compensation effects of the intrinsic defects. According to the theoretical studies, p-type ZnO can be realized using group-V dopants substituting for O, such as N, P and As. Among them, N has been suggested to be an effective acceptor dopant candidate to achieve p-type ZnO, because that nitrogen has a much smaller ionic size than P and As and the energy level of substitutional N_O is lower than that of substitutional P_O and As_O. Transparent p-type ZnO: N thin films have been fabricated using the pulsed laser deposition method at deposition temperatures 800 °C under the O₂ and N₂ mixing pressure 6Pa. N-doped ZnO films were deposited on sapphire substrate using metallic zinc (99.999%) as target. The structural, optical and electrical properties of the films were examined by XRD, UV-visit spectra and Hall effect measurement. We found that thin film contain the hexagonal ZnO structure. The Hall effect measurement revealed that the carrier concentration is 5.84×10¹⁸ 1/ cm³, and Hall mobility is 0.26 cm^2/Vs, electrical resistivity is 4.12ohm-cm. Film thickness is 180nm. Besides, Visible light transmittance is more than 80%, and calculative band-gap is 3.1 eV, which is lower than ZnO.

Abstract: Cork flooring maintains the natural qualities of cork, showing the unique and elegant natural patterns, and also has series of advantages such as thermal insulation, sound insulation, moisture barrier, insulation, and no static. Ultraviolet (UV) curable coatings have no volatile organic compounds, little environmental pollution, fast curing, and are suitable for high speed automated production, which is the development of environmentally friendly wood floor coatings. In this paper, the UV-curable wooden coatings for floor were interfacially modified with nanosilica. The process parameters were optimized by orthogonal experiments, and the overall performance of wood flooring UV coating was obtained. The mechanical properties of the coating (hardness, adhesion and impact strength), resistance to liquid properties (resistance to aqueous sodium chloride solution, resistance to aqueous sodium hydroxide solution, resistance to alcohol, resistance to blue and black ink, resistance to sauce) and gloss were tested. It was found that wood flooring UV coating had good performance, hardness reached 3H, adhesion reached one grade, impact strength was 40 kgcm, and fluid-resistant performance (120 h) of coating reached one grade when the nanosilica content was 0.50%~0.70%, the drying time was 2 min, and medium pressure mercury UV lamp was 3. The gloss results showed that gloss of wood flooring UV coatings decreased with the increase of nanosilica content. When the nanosilica content was 0.50%~0.70%, the gloss value was in the vicinity of 35%, showing a matte gloss. This study provides new perspectives in wood flooring UV coating for industrial applications.

Abstract: In this paper, RuO₂-CB/MVQ composites were prepared through following steps. First, the nanoruthenium particles had been prepared by solvent thermo-deoxidization ways. Secondly, the nanoRuO₂ particles had been formed by oxidation reaction of nanoruthenium particles in air. Thirdly, the carbon black/silicone rubber mixed rubber was prepared by solvent mixing. Fourthly, the nanoruthenium particles were mixed into carbon black/silicone rubber mixed rubber by rubbing dispersion. Finally, vulcanization molding was carried out at certain preasure and temperature. The piezoresistive properties of CB/MWQ composite materials were tested with pressure-resistance testing systems designed ourselves. The test results showed that suitable amounts of RuO₂ could enhance the stability and creep of piezoresistive properties of CB/MWQ composite materials. The microstructure of CB/MWQ composite materials were analyzed with SEM and TEM. The characterization results showed that nanoRuO₂ particles dispersed in composite materials in nanolevel. These nanostructure could improve conductive net of carbon black, and reinforce crosslink net of silicone rubber. These factors had advantage to the stability of piezoresistive properties of CB/MWQ composite materials.

Abstract: Sapphire (α-Al₂O₃) single crystal combines many good mechanical and optical properties that make it become the material of choice in a variety of modern Hi-Tech applications The use of CMP technique can produce high quality surface finishes at low cost and with fast material removal rates. In CMP process, nanoabrasive is very important parameters in determining the removal rate. In this paper, the influence mechanism of nanoabrasive on sapphire substrate CMP was analyzed deeply. The main kinetics processing was discussed in detail. According to sapphire substrate properties, alkali slurry was chosen and the mix of SiO₂ and Al₂O₃ sol was selected as nanoabrasive, and the particle size was 20~30nm. The results show that adding nanoalumina with the concentration of 20ml / L in the main abrasive can make the chemical action balance with the mechanical action in the CMP process, so that the substrate removal rate is well improved, and the surface roughness can be reduced to 0.236nm by adjusting the process parameters and slurry ratio. Such data meets the super smooth requirement and the optimal sapphire surface can be gotten. So such slurry with mixed abrasive can be as rough polishing slurry and can improve the polishing efficiency.

Abstract: We systematically study the componential and morphological characteristics of Cu₃N films induced by femtosecond laser irradiation on glass substrate. The experimental results demonstrate that with increase of laser power, significant changes on surface morphology can be observed, and coarse ripples structures present dominantly on film surfaces after irradiated by femtosecond laser. By XRD analysis of the treated sample area, componential evolutional process from the Cu₃N to Cu can be revealed at with increase of laser power, which provides an attracting application prospect in the field of utilizing microelectronic devices.

Abstract: The visible light photocatalytic degradation of methylene blue (MB) over N-doped TiO₂ (N-TiO₂) was investigated. The intermediate products of MB in the photocatalytic degradation process were analyzed by HPLC-MS technique. The results show that the cleavages of CS⁺=C and CN=C functional group in the central aromatic ring and the cleavage of N-C bond between the methyl group and nitrogen atom all can occur in the visible light photocatalytic degradation process over N-TiO₂, but MB is difficult to be mineralized completely to the inorganic products. A detailed degradation pathway of MB has been proposed on the basis of a careful identification of intermediate products.

Abstract: Thin TiO2 films in-situ growth on titanium alloy substrate were prepared in 0.05 mol/L H2SO4 electrolyte using the micro plasma oxidation method. The photocatalytic properties of the prepared thin TiO2 films were invested using Rhodamine B solution as a target pollutant. In order to improve the photocatalytic properties of the obtained TiO2 films, different content NH3·H2O was added into the H2SO4 electrolyte and obtained the N-doped TiO2 films photocatalyst. The influence of the doping ions on the crystal phase composition and microstructure of the TiO2 films were investigated by scanning electron microscopy (SEM) and X ray photoelectron spectroscopy (XPS). The results show that TiO2 films have uniformly grown closely on the surface of titanium substrate with pore size of 100-200 μm. The degradation efficiency of the TiO2 thin film prepared in H2SO4 + NH3·H2O is higher than that prepared with H2SO4, the degradation efficiency can reach 99% after 75 min, which increase about 10% than that of the H2SO4 eletrolyte.

Abstract: TiO₂ nanorod arrays (NRA) were synthesized via a facile hydrothermal method for preparing the dye-sensitized solar cells (DSSC). It was found that a post-thermal treatment facilitated enhancing the cell efficiency. The cells containing NRs underwent 500 °C annealing exhibited much higher efficiency than those un-sintered ones. Further, the internal resistance analysis was carried out to reveal the mechanism underlying the DSSC performance improvement. Specifically, the equivalent circuit model was employed to derivate the internal resistances, which was consistent with the experimental results. It was found that the sintered cells exhibited a higher series resistance and a lower shunt resistance than the un-sintered ones, suggesting the higher photocurrent density might result from the larger amount of dye loading.

Abstract: The synthesis of graphene using chemical vapor deposition (CVD) on patterned Cu thin films was studied. A series of experiments were carried out to optimize the CVD process of graphene synthesis on Cu thin films and the optimal growth conditions were obtained. Consequently, few-layer graphene which had been characterized by optical microscopy and Raman spectroscopy atomic was synthesized. Conductive atomic force microscopy (AFM) was used to measure the conductivity of metal-graphene contact samples and the result showed that the conductivity of CVD synthesized graphene on Cu thin films is higher than the transferred graphene on same Cu thin films, which was synthesized on 25 μm Cu foils by conventional CVD method.

Abstract: The Al₂O₃ is synthesized by detonation of mixed explosive, prepared by mixing RDX and aluminum hydroxide named as precursor of thermal decomposition. The production of detonation is analysed by XRD, TEM and DTA/TG. The curve of XRD indicates that the production are (α+γ)-Al₂O₃. The average crystal size of Al₂O₃ is 126nm calculated by the Scherrer equation. The photographs of TEM show that all granules of Al₂O₃ are spherical, and the average size of granule is 1000nm. The visible exothermic or endothermic peak does not appear on the curve of DTA from 50 to 1300 degree Centigrade. The curve of TG indicates that the production of detonation generates 12% weight loss from 50 to 1300 degree Centigrade.