Effect of annealing temperature on the photocatalytic activity of WO3 for O2 evolution

Commercial WO₃ powder was annealed in air at four different temperatures and characterized by XRD and BET. The samples were used for the photooxidation of H₂O to O₂ under visible light irradiation (λ > 420 nm) in the presence of IO₃⁻ and the evolved gases were analyzed by gas chromatography. The results showed that the WO₃ photocatalyst of monoclinic phase, which was obtained by annealing at 750 °C for 4 h, displayed the best activity in terms of O₂ evolution among all the samples. Moreover, the activity was also found to be slightly affected by the grain size of the WO₃ samples.     

Vibrational spectroscopy characterization of magnetron sputtered silicon oxide and silicon oxynitride films

Vibrational (infrared and Raman) spectroscopy has been used to characterize SiO_xN_y and SiO_x films prepared by magnetron sputtering on steel and silicon substrates. Interference bands in the infrared reflectivity measurements provided the film thickness and the dielectric function of the films. Vibrational modes bands were obtained both from infrared and Raman spectra providing useful information on the bonding structure and the microstructure (formation of nano-voids in some coatings) for these amorphous (or nanocrystalline) coatings. X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) analysis have also been carried out to determine the composition and texture of the films, and to correlate these data with the vibrational spectroscopy studies. The angular dependence of the reflectivity spectra provides the dispersion of vibrational and interference polaritons modes, what allows to separate these two types of bands especially in the frequency regions where overlaps/resonances occurred. Finally the attenuated total reflection Fourier transform infrared measurements have been also carried out demonstrating the feasibility and high sensitivity of the technique. Comparison of the spectra of the SiO_xN_y films prepared in various conditions demonstrates how films can be prepared from pure silicon oxide to silicon oxynitride with reduced oxygen content.     

Observation of electron weak localization and correlation effects in disordered graphene

We have studied the electron transport properties of a disordered graphene sample, where the disorder was intentionally strengthened by Ga⁺ ion irradiation. The magneto-conductance of the sample exhibits a typical two-dimensional electron weak localization behavior, with electron-electron interaction as the dominant dephasing mechanism. The absence of electron anti-weak localization in the sample implies strong intersublattice and/or intervalley scattering caused by the disorders. The temperature and bias-voltage dependencies of conductance clearly reveal the suppression of conductance at low energies, indicating opening of a Coulomb gap due to electron-electron interaction in the disordered graphene sample. Supported by the National Natural Science Foundation of China (Grant Nos. 10774172 and 10874220), and the National Basic Research Program of China from the MOST (Grant No. 2006CB921304)     

Surface morphology and composition of c-, a- and m-sapphire surfaces in O2 and H2 environments

This paper reports that monitoring the composition of the c(0 0 0 1), a(11–20) and m(10–10) sapphire surfaces is essential for a proper interpretation of the surface morphologies obtained after annealing at 1253 and 1473 K in ArH₂ or ArO₂ atmospheres. Our experimental investigations, which have used Auger electron spectroscopy (AES) and atomic force microscopy (AFM) on the surfaces of 99.99% pure sapphire wafers, have led to the following original conclusions: (i) Calcium segregates at the c-surface of sapphire both under ArO₂ and ArH₂. (ii) Potassium adsorption enhances the kinetics of step-bunching on the c-surface under ArO₂. (iii) The step edges on the a-surface may develop a comb-like morphology made of parallel strips along the [10–10] direction. (iv) At 1253 K, clean m-surfaces may be stable. (v) Under ArH₂, alumina surface diffusion is much slower than under ArO₂ for all surface orientations, the surface concentration of impurities is low, and the Al–O ratio of the AES signals at the surface is significantly larger.     

NO dissociation and N2 production in the presence of co-adsorbed SO2 and D2 on Pt(3 3 2)

NO dissociation and subsequent N₂ production in the presence of co-adsorbed S¹⁸O₂ and D₂ on the surface of stepped Pt(3 3 2) were studied using Fourier transform infra red reflection–absorption spectroscopy (FTIR-RAS) combined with thermal desorption spectroscopy (TDS). Reduction of NO by D (D₂ is adsorbed dissociatively on Pt surfaces) proceeds to a limited extent, because this reaction is rate-controlled by NO dissociation and the supply of D atoms at the higher surface temperatures at which NO dissociation becomes significant (350 K and higher). NO–D reaction is suppressed in the presence of S¹⁸O₂, depending significantly on the S¹⁸O₂ coverage and the competition between the reactions NO–D and S¹⁸O₂–D. When the supply of D₂ is limited, e.g., 0.1 L in this study, the presence of S¹⁸O₂ suppresses the NO–D reaction. With a sufficient supply of D₂, e.g., 0.4 L and higher, D-atom competing reactions do not play a role any more because the reactions of both NO and S¹⁸O₂ with D proceed only to a very limited extent. As such, generation of O atoms from S¹⁸O₂ dissociation is the main reaction that leads to the suppression in NO dissociation and consequently, N₂ production.It is also concluded that the presence of S¹⁸O₂ does not seriously poison the active sites on the Pt surface, providing that there is a sufficient D supply to remove O atoms from both NO dissociation and S¹⁸O₂ dissociation.     

The response of thermally and optically stimulated luminescence from Al2O3:C to high-energy heavy charged particles

The thermoluminescence (TL) and optically stimulated luminescence (OSL) response of Al₂O₃ dosimeters to high-energy heavy charged particles (HCP) has been studied using the heavy ion medical accelarator at Chiba, Japan. The samples were Al₂O₃ single-crystal chips, of the type usually known as TLD-500, and Luxel^TM dosimeters (Al₂O₃:C powder in plastic) from Landauer Inc. The samples were exposed to ⁴He (150 MeV/u), ¹²C (400 MeV/u), ²⁸Si (490 MeV/u) and ⁵⁶Fe (500 MeV/u) ions, with linear energy transfer values covering the range from 2.26 to 189 keV/μm in water and doses from 1 to 100 mGy (to water). A ⁹⁰Sr/⁹⁰Y beta source, calibrated against a ⁶⁰Co secondary standard, was used for calibration purposes. For OSL, we used both continuous-wave OSL measurements (CW-OSL, using green light stimulation at 525 nm) and pulsed OSL measurements (POSL, using 532 nm stimulation from a Nd:YAG Q-switched laser). The efficiencies (η_HCP,γ) of the different HCPs at producing OSL or TL were observed to depend not only upon the linear energy transfer (LET) of the HCP, but also upon the sample type (single crystal chip or Luxel^TM) and the luminescence method used to define the signal—i.e. TL, CW-OSL initial intensity, CW-OSL total area, or POSL. Observed changes in shape of the decay curve lead to potential methods for extracting LET information of unknown radiation fields. A discussion of the results is given, including the potential use of OSL from Al₂O₃ in the areas of space radiation dosimetry and radiation oncology.     

Role of gallium wetting layer in high-quality ZnO growth on sapphire (0001) substrates

ZnO is a wide direct bandgap (Eg=3.37 eV at room temperature) II-VI compound semiconductor of wurtzite structure (a = 3.249 ? c = 5.207 ?. Compared to GaN and ZnS, ZnO has a larger exciton binding energy, ~60 meV (cf. ~25 meV for GaN and ~40 meV for ZnS), which is advantageous to realizing low-threshold excitonic lasers. Since optically pumped UV lasing of ZnO at room temperature was reported in 1997[1], much attention has been paid to the crystal quality improvement and p-type conduc…     

Microwave–assisted synthesis of <Emphasis Type="Italic">submicrometer</Emphasis> GaO(OH) and Ga<Subscript>2</Subscript>O<Subscript>3</Subscript> rods

Submicrometer sized gallium oxide hydroxide (GaO(OH)) and gallium oxide (Ga₂O₃) rods have been successfully fabricated on a large scale by refluxing an aqueous solution of Ga(NO₃)₃ and NH₄OH in a simple domestic microwave oven (DMO). The structures, morphologies, compositions and physical properties of the as–synthesized and calcined products have been characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), selected area energy dispersive X-ray spectroscopy (SAEDS), thermo gravimetric analysis (TGA), differential scanning calorimetry (DSC), and energy dispersive X-ray (EDX) analysis. TEM images show that submicrometer sized as–synthesized Ga O(OH) rods have diameters of 0.3–0.5 m and lengths of 3.2–3.5 m. The calcined product consists of submicrometer rods with diameters of 0.4–0.5 m and lengths of 5–5.5 m. XRD, EDX and SAED analysis together indicate that the as–synthesized product has an orthorhombic gallium oxide hydroxide (GaO(OH)) crystal structure, and that the calcined product is rhombohedral Ga₂O₃. A possible mechanism for the formation of submicrometer sized GaO(OH) rods is discussed briefly.     

Effects of barium on the nonlinear electrical characteristics and dielectric properties of SnO2-based varistors

The effects of barium on electrical and dielectric properties of the SnO_2·Co_2O_3·Ta_2O_5 varistor system sintered at 1250℃ for 60min were investigated. It is found that barium significantly improves the nonlinear properties. The breakdown electrical field increases from 378.0 to 2834.5V/mm, relative dielectric constant (at 1kHz) falls from 1206 to 161 and the resistivity (at 1kHz) rises from 60.3 to 1146.5kΩ·cm with an increase of BaCO_3 concentration from 0mol% to 1.00mol%. The sample with 1.00mol% barium has the best nonlinear electrical property and the highest nonlinear coefficient (α=29.2). A modified defect barrier model is introduced to illustrate the grain-boundary barrier formation of barium-doped SnO_{2}-based varistors.     

光电变色器件用纳米晶氧化钛薄膜的微结构与特性

纳米晶TiO2薄膜在光电变色器件中具有很重要的作用。它的微结构直接影响染料的吸附、光的散射以及电荷输运的特性。因此，探索TiO2薄膜的微结构(如粒径、表面形貌和厚度等)及光电性能是非常有意义的。采用电子束蒸发工艺制备了光电变色器件用纳晶TiO2薄膜，利用原子力显微镜、X射线衍射、俄歇电子能谱等手段对纳米晶TiO2薄膜的表面形貌、结晶状态及组分进行了分析。从理论上研究和讨论了纳米晶TiO2薄膜晶粒尺寸对光电性能的影响，并用量子限制效应解释了吸收光谱峰值波长随粒径减小而发生蓝移的现象。