Abstract: Metal oxide thin film materials, including SnO2, TiO2, WO3, MoO3, ZnO, have been widely studied for gas sensing applications. However, new gas-sensing materials with distinct and diverse characteristics for new sensing applications such as electronic nose are still being explored. Presently, gas sensing properties of other metal oxides have not yet been extensively explored. Chromium oxide is an interesting metal oxide for gas sensor because of its temperature stability and moderate electrical conductivity. Nevertheless, there have been very few studies on gas sensing behaviors of this material. In this work, chromium oxide thin films were systematically studied by reactive sputtering with varying sputtering parameter including oxygen flow rate. Structural characterization by means of scanning electron microscopy and X-ray diffraction reveals that the films have sub-micometer grain-size with Rhombohedral phase of Cr2O3. Gas-sensing performances of sputtered chromium oxide thin film have been characterized toward ethanol and acetylene sensing. It was found that chromium oxide thin films exhibit p-type conductivity with increased resistance when exposed to ethanol and acetylene, which are reducing gases. In addition, sensitivity to both acetylene and ethanol tend to improve as oxygen flow rate increases. Furthermore, the chromium oxide thin films exhibit high sensitivity at moderate temperature of 250-300 °C with minimum operating temperature of 200 °C.
Abstract: Platinum impregnated ZnO tetrapods were prepared and studied for the detection of ethanol vapor. ZnO tetrapods were synthesized by oxidation reaction technique by heating a mixer of zinc powder (99.99%) and hydrogen peroxide solution (30 wt.%) at 1,000oC in air. Platinum was impregnated by dropping hydrogen hexachloroplatinate (IV) hydrate, H2Cl6Pt.aq, solution with different concentration on ZnO tetrapods and then, heated at 350oC for 1 hr. The platinum impregnated ZnO tetrapods were characterized by field emission scanning electron microscopy (FE-SEM) and energy dispersive spectroscopy (EDS) for morphology and chemical composition, respectively. The particles were observed on the surface of ZnO tetrapods. The EDS spectrum suggested that the particles were platinum. Platinum impregnated ZnO tetrapods were tested ethanol sensing properties under ethanol concentration of 50-1,000 ppm. The ethanol sensing results indicated that the sensitivity of the sensors depended on the platinum impregnated concentration. Moreover, the sensors based on platinum impregnated ZnO tetrapods of 0.035 wt.% exhibited higher sensitivity compare to those of non-impregnation ZnO tetrapods.
Abstract: ZnO nanostructures were synthesized by thermal oxidation reaction from zinc powder and then impregnated by gold colloid. The gold colloid was prepared by chemical reduction technique and had red color. The heating temperature and sintering time of thermal oxidation were 700 °C and 24 hours, respectively under oxygen atmosphere. The morphology of ZnO nanostructures and ZnO impregnated gold colloid were studied by field emission scanning electron microscope (FE-SEM). The diameter and length of pure ZnO and ZnO impregnated gold colloid were about the same value and were in the range of 100-500 nm and 2.0-7.0 µm, respectively. The ethanol sensing properties of ZnO impregnated by gold colloid were tested in ethanol atmosphere at ethanol concentrations of 1000 ppm and at an operating temperature of 260-360 °C. It was found that the sensitivity and response time were improved for gold impregnated sensor with an optimum operating temperature of 300°C due to the enhanced reaction between the ethanol and the adsorbed oxygen at an optimum temperature.
Abstract: Cadmium sulphide (CdS) thin films have been deposited by chemical bath deposition method (CBD) on CdTe substrates. The temperature of the deposition was varied from 40 oC to 70oC under stirring, pH of complexing agent about 10-11.5 and doping by CdCl2. The morphology was composed of small columnar crystals, characterized by SEM. The crystallographic structure contains a mixture of hexagonal and cubic structures were study by TEM. The energy gap values 2.395 eV were found calculated by reflectance spectra using UV-VIS spectrometer. This study showed the correlation of deposition temperature, grain size, energy gap and observed some properties of CdS nanocrystal in the films.
Abstract: Iron phthalocyanine (FePc) thin films prepared by thermally evaporated from as received and purified powders were studied. The molecular interaction between FePc thin films and acetone vapor was studies by X-ray photoemission spectroscopy (XPS) and optical absorption spectrometer. The core level XPS spectra and optical absorption spectra showed slightly different between the spectra before and after acetone exposure. For FePc film evaporated with purified powder, only the Fe 2p3/2 spectra at about 712 eV appeared and the height of peak dramatically decreased. Iron K-edge X-ray absorption near edge structure (XANES) spectra was used to investigate iron atom in as received and purified powders and also study the interaction between FePc molecule and methanol vapor. The X-ray diffraction pattern of as received, annealed and purified FePc powder were investigated to study the crystal reformation and Raman spectroscopy was used to investigate iron atom vibration in as received FePc film.
Abstract: Interaction between organic solvent vapors, zinc phthalocyanine (ZnPc) and copper phthalocyanine (CuPc) coated on quartz crystal resonators were investigated for various types of organic solvent vapors including acetone, propanol, ethanol, tetrahydrofuran, methanol, nail lacquer remover, 100 Pipers and Masterblend whiskies. The major different features of the resonance frequency shift as a function of time were extracted in order to employ in gas sensor. The sensor consists of ZnPc or CuPc thin film with the thickness of ~300 nm coated on quartz crystal with resonance frequency of 2 MHz. It used as a transducer by convert the surface adsorption into the frequency shift. When the odor interacts with ZnPc or CuPc layer, the quartz frequency normally decreases from the fundamental frequency due to the additional mass on quartz surface. The different types of organic solvent have different sensitivity to the thin film and these changing lead to the different frequency shift characteristics. The frequency shift were collected and the selected data points at the time of 5, 10, 15, 20, 70, 75, and 80 minutes after dropping alcohol were used to extract the feature by using the principal component analysis (PCA) in order to classify the type of alcohol. The PCA can be used to identify the major characteristic difference of various organic solvent interactions. The main features can be identified by the amount of the frequency shift and the decay characteristics.
Abstract: The oxide content in Al powder has a significant effect on the expansion and stability of Al foams produced using a direct gas blowing method. The optimum level of oxide content is expected to be between 0.3 and 0.9 wt.% to enable large foam expansion.
Abstract: Transparent glass with composition 65LiNbO3-35SiO2 was fabricated via the conventional melt-quenching technique. Glass-ceramics containing nanoscale (less than 100 nm) rhombohedral lithium niobate crystals were successfully produced by annealing the respective glass at various temperatures (600, 650 700 and 975 °C) for 1 h. The result of optical transmission spectra shows that the quenched sample is optically transparent. Transparent samples should possess crystals << 200 nm and have a narrow distribution of crystal sizes.
Abstract: Porous Clay Heterostructures (PCHs) have been prepared by the surfactant-directed assembly of mesostructured silica within the two-dimensional interlayer galleries of clays. The PCH is an interesting material to use as entrapping system such as ethylene scavenger, owing to its high surface area with uniform and specific pore size. In the present work, the PCH was synthesized within the galleries of Na-bentonite clay by the polymerization of tetraethoxysilane (TEOS) in the presence of surfactant micelles. In addition, a mesoporous clay with organic-inorganic hybrid (HPCH) is modified via co-condensation reaction of TEOS with methyltriethoxysilane (MTS) to enhance hydrophobicity of PCH material for entrapping system. According to pore characterization, PCHs have surface areas of 421-551 m2/g, an average pore diameter in the supermicropore to small mesopore range of 4.79-5.02 nm, and a pore volume of 0.57-0.66 cc/g while HPCHs have surface areas of 533-966 m2/g, an average pore diameter of 4.28-6.38 nm, and a pore volume of 0.42-0.77cc/g.
Abstract: Electrospinning is common used in manufacturing ultrafine fibers from a polymer solution. With a high specific surface area, high porosity and good biocompatibility, the elecrospun membranes have extensive applications as biomaterials such as tissue scaffolds and for drug delivery. Silk fibroins (SF), gelatin (G) both have good biocompatibility and are non-toxic. And in previous literature, gelatin nanofiber can be successfully prepared by electrospinning, which was dissolved in formic acid. Tencel, which is extracted from wood pulp, is biodegradable, has a smooth fiber structure, can protect wounds and is irritation-free. Consequently, SF, G and Tencel are widely used in biomedical applications, such as for wound dressings and scaffolds for tissue engineering and so on. In this study, we discussed the applications of different shapes of electrospun membrane such as film, web. After that, the electrospun membrane was combined with Tencel nonwoven to fabricate composite nonwoven. Electrospinning of SF/ G was performed using formic acid as the spinning solvent. Parameters, such as electrical field (15~11 kV), spinning distance (15~7 cm), and volume ratio of SF and G, were analyzed to investigate their effects on electrospinnability and morphology of nanofiber membranes. The morphology of electrospun SF/ G nanofibers was investigated by scanning electron microscopy (SEM). Analytical demonstrate that the optimal electrospinning condition was fibers with an average diameter of 200–300 nm.