Advanced Materials Research Vol. 802

Abstract: n-Type nanocrystalline FeSi₂/intrinsic Si/p-type Si heterojunctions were successfully fabricated by FTDCS and their forward current-voltage characteristics at low temperatures were analyzed on the basis of thermionic emission theory. The analysis of J-V characteristics exhibits an increase in the ideality factor and a decrease in the barrier height at low temperatures. The values of ideality factor were estimated to be 2.26 at 300 K and 9.29 at 77 K. The temperature dependent ideality factor together with the constant value of parameter A indicated that a trap assisted multi-step tunneling process is the dominant carrier transport mechanism in this heterojunction. At high voltages, the current transport mechanism is dominated by SCLC process.

Abstract: Sn doped ZnPc films were deposited on intrinsic Si and glass substrates by organic source thermal co-evaporation technique with different deposition rates. Optical properties and electronic structure were characterized by UV-Vis spectroscopy and X-ray photoelectron spectroscopy (XPS) respectively. The UV-Vis results showed that phase transition of ZnPc from α-phase to β-phase occurred when Sn:ZnPc deposition rate is 0.3:0.7 or higher. XPS results indicated that the outer s electron of Sn atom is transferred to the ZnPc. Broadening of the C 1s spectra is observed with the increasing of Sn deposition rate. This broadening corresponds to the change of molecular environment surrounding carbon atoms in the Sn-doped ZnPc films.

Abstract: We present characterization and thermoelectric properties of oxide thermoelectric materials of P-Ca₃Co₄O₉ and N-CaMnO₃ synthesized by solid state reaction method and sintering in air. The crystalline structure was measured by x-ray diffraction (XRD) and confirmed by transmission electron microscope (TEM). The powder size and gran size of P-Ca₃Co₄O₉ and N-CaMnO₃ were observed by scanning electron microscope (SEM). The electrical resistivity and Seebeck coefficient are measured. It was found that, the P-Ca₃Co₄O₉shows the point symmetry groups in three dimensions require of monoclinic system and N-CaMnO₃ shows cubic system corresponding with TEM results. The powder size and grain size were obtained mean values of 1-3 µm. The electrical resistivity and Seebeck coefficient were obtained for P-Ca₃Co₄O₉and for N-CaMnO₃ at 360 K.

Abstract: The Mg₂Si compound was synthesized by the solid state reaction method. The powder precursors of Mg and Si were thoroughly mixed in ballmilling for 24 hr in an argon atmosphere. Mixed powder was pressed at 170MPa and sintered at 800 °C for 6 hr in an argon atmosphere. The sinter powder was crushed in mortar for 1 hr. The crystal structure and microstructure were measured and observed by using XRD and SEM. The microstructure and the crystal structure were analyzed. TheMg₂Si shows single phase, cubic structure and particle size about 1-10 mm.

Abstract: The polycrystalline of sodium cobalt oxide (Na_0.5CoO₂) was synthesized by solid state reaction method and sintering method. The microstructure was composed of powder size and crystal structure. The Seebeck coefficient and electrical resistivity are measured. We found that the concentration of sodium ions sandwiched between two neighboring CoO₂ layers played a crucial role in transport properties. The results showed small particle size, single phase and orthorhombic structure. The Seebeck coefficient of Na_0.5CoO₂ increased as the temperature increased. The electrical resistivity was decreased as temperature decreased from the range 300-500 K.

Abstract: The PbTe has been prepared by pressing and annealing method in argon atmosphere. The PbTe sample was obtained single phase and cubic structure. The Seebeck coefficient, the electrical resistivity, thermal conductivity measured by steady state method and evaluated dimensionless figure merit at room temperature. The values of Seebeck coefficient, the electrical resistivity, thermal conductivity and dimensionless figure merit are about -260 µV/K, 3 mΩcm, 0.5 W/m K and ~ 0.35 respectively at 420 K.

Abstract: Crystal structure of Zn_0.96Al_0.02Ga_0.02O was analyzed by X-Ray diffraction (XRD) technique and the microstructure was observed by scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The XRD results showed single phase and hexagonal structure a = b = 3.24982 Å, and c = 5.20661 Å. The SEM and TEM results showed the grain size of material arrangement changed after sintering and TEM diffraction pattern confirmed hexagonal crystal structure of Zn_0.96Al_0.02Ga_0.02O after sintering.

Abstract: Solid state pH-sensor device with high efficiency has successfully prepared by using TiN thin film as sensing membrane of extended gate field effect transistor (EG-FET) device. This research has described the physical properties and sensing characteristics of TiN membrane thin film which deposited on SiO₂/Si substrate through reactive D.C. magnetron sputtering system. Thenanocrytal-TiNwith anatasestructure depended on substrate heating conditions was revealed from glancing angle x-ray diffraction. The I_DS-V_GS measurement in the standard buffer solutions showed that the sensitivity of fabricated TiN-EGFET pH deviceis 59.82mV/pH.

Abstract: Anatase TiO₂ powders used as photocatalysts were prepared by ball milling process at various milling time and annealed in nitrogen atmosphereat different temperatures. Commercial TiO₂ powders were ball-milled with ethanol at room temperature. After ball milling process, the samples were annealed in nitrogen atmosphere. The particle sizes and surface area of milled powders were measured by particle analyzer and Brunauer Emmet Teller method(BET). Effect of milling time and annealing temperature on structural properties of TiO₂ powders was investigated by X-ray diffraction(XRD) and scanning electron microscope(SEM). The degradation of aquous RhB dye by ball-milled TiO₂ powder photocatalyst was investigated under UV light irradiation. Comparing to P-25, TiO₂ powder prepared via ball milling process at 24 hr demonstrated significant enhancement in its photocatalytic activity under UV light due to the increasing active surface area after ball milling process.

Abstract: Tantalum oxide (Ta₂O₅) thin films, 100 nm thick were deposited by D.C. reactive magnetron sputtering system at different operated pressure on unheated p-type silicon (100) wafer and 304 stainless substrates. Their crystalline structure, film surface morphology and optical properties, as well as anticorrosive behavior, were investigated. The structure and morphology of films were characterized by grazing-incidence X-ray diffraction (GIXRD) and atomic force microscopy (AFM). The optical properties were determined by spectroscopic ellipsometry (SE). The corrosion performances of the films were investigated through potentiostat and immersion tests in 1 M NaCl solutions. The results showed that as-deposited Ta₂O₅ thin films were amorphous. The refractive index varied from 2.06 to 2.17 (at 550 nm) with increasing operated pressure. The corrosion rate of Ta₂O₅ thin film improves as the operated pressure decreases. The Ta₂O₅ thin films deposited at 3 mTorr operated pressure could be exhibited high performance anticorrosive behavior.