Role of Oxygen Vacancies in the Electrical Properties of WO3−x Nano/Microrods with Identical Morphology

Tungsten oxide (WO3−x) crystalline nano/microrods with identical morphology but different contents of oxygen vacancies were prepared by thermally evaporating fixed amount of WO3 powder in reductive atmosphere from different amounts of S power at 1150°C in a vacuum tube furnace, in which both sources were loaded in separate ceramic boat. With increasing amount of S powder, a series of tungsten oxides, WO3, WO2.90, W19O55 (WO2.89), and W18O49 (WO2.72), could be obtained. And devices were fabricated by screen-printing the obtained WO3−x crystals on ceramic substrates with Ag-Pd interdigital electrodes. With increasing content of oxygen vacancies, the devices fabricated with WO3−x crystals present a negative to positive resistance response to relative humidity. Under dry atmosphere, for the devices with increasing x, the strong response to light changed from short to long wavelength; under light irradiation, the conducting ability of the devices was enhanced, due to the more efficient separation and transportation of the photogenerated carriers; and under simulated solar irradiation, the photocurrent intensity of the W18O49 device was roughly 8 times, about 500 times, and even 1000 times larger than that of the W19O55, WO2.90, and WO3 one, respectively. With the versatile optoelectrochemical properties, the obtained WO3−x crystals have the great potential to prepare various humidity sensors and optoelectrical devices.

Fine Tungsten Powder Obtained with Blue Tungsten Oxide through the Hydrogen Reduction

Fine tungsten powder is prepared with blue tungsten oxide (BTO) through the hydrogen reduction. The samples were characterized with the scanning electron microscope (SEM), fisher sub-sieve sizer (FSSS) and the particulate size description analyzer (PSDA). Fine tungsten powder is easily obtained when the reduction temperature is low. With the increasement of the reduction temperature, the grain size of tungsten powder becomes coarse. The increase of the weight of BTO in the ceramic boat leads to the increasement of the thickness of its bed. Therefore, the weight of BTO in the ceramic boat ought to reduce if fine tungsten powder is prepared. Fine tungsten powder can be obtained when the hydrogen flow increases.

Fabrication and Structural and Optical Characterizations of GaN Nano and Micro Structures Grown by Thermal Evaporation Method

Gallium Nitride (GaN) nano and micro structures were grown on different substrates, such as ceramic boat and alumina plate using thermal evaporation method with commercial GaN powder under the flow of Argon (Ar) gas atmosphere. Micro structural studies by scanning electron microscopy (SEM) revealed the role of different substrates in the nucleation of the GaN nano and micro wires and ribbons. Additional structural and optical characterizations were performed using energy-dispersive X-ray spectroscopy (EDX) and photoluminescence (PL) spectroscopy. Results indicated that the nanowires and nanoribbons are of single-crystal hexagonal GaN and are more and less orderly in their growth with different substrates. The quality of growth of the GaN nanowires and nanoribbons for different substrates is highly dependent on the lattice mismatch between the nanowires and their substrates and it also depends on the conditions of the growth.

Synthesis and Photoluminescence Properties of Novel SnO2 Zigzag Nanoribbons

Novel single-crystalline SnO2 zigzag nanoribbons have been successfully synthesized by chemical vapour deposition. Sn powder in a ceramic boat covered with Si plates was heated at 1100°C in a flowing argon atmosphere to get deposits on a Si wafers. The main part of deposits is SnO2 zigzag nanoribbons. They were characterized by means of X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM) and selected-area electron diffraction (SAED). SEM observations reveal that the SnO2 zigzag nanoribbons are almost uniform, with lengths near to several hundred micrometers and have a good periodically tuned microstructure as the same zigzag angle and growth directions. Possible growth mechanism of these zigzag nanoribbons was discussed. A room temperature PL spectrum of the zigzag nanoribbons shows three peaks at 373nm, 421nm and 477nm.The novel zigzag microstructures will provide a new candidate for potential application.