Pongsri Mangkorntong

Orthorhombic Molybdenum Trioxide Whiskers by Vapor Transport Method

Orthorhombic MoO3 whiskers have been grown by using vapor transport method. High-quality, transparent and colorless MoO3 plate-like whiskers are obtained inside alumina furnace tube with high aspect ratio of 20–30 for the growth time of 1 h. The length and the width of whiskers are directly proportional to growth time. The location that whiskers occurred is an evidence of vapor-solid growth mechanism by sublimation. From characterization, MoO3 whiskers exhibit a near-perfect single crystal with high purity of orthorhombic phase, smooth morphology, and indirect band gap of 2.98 eV. MoO3 whisker has also been demonstrated as a gas sensor toward ethanol vapor.

Ethanol Sensor Based on Au-doped ZnO Nanostructures

Ethanol sensing characteristics of ethanol sensor based on Au-doped ZnO nanostructures were studied. Au-doped ZnO nanostructures with 5% gold by weight were prepared by thermal oxidation technique. The sintering time was varied for 6 hours and 24 hours. The wire-like or belt-like nanostructures with the sharp ends outward from microparticles were observed. The diameter and length of ZnO nanostructures are in the range of 250-750 nm and 1.7-7.0 mum, respectively, with the average diameter of 500 nm. EDS spectrum shows Au signal confirming incorporation of Au into ZnO nanostructures. For 24 hours sintering time, the diameter and length of ZnO nanostructures are 170-500 nm and 2.0-7.0 jim, respectively, with the average diameter of 330 nm. The average diameter for 24 hours sintering time is smaller than that of 6 hours sintering time. The response and recovery characteristics of Au-doped ZnO nanostructures upon exposure to ethanol concentration of 1000 ppm at different operating temperatures suggest that the sensitivity depend on operating temperatures. It is found that the highest sensitivity is 88 at 280 degC for 6 hours sintering time and about 170 at 300-320 degC for 24 hours sintering time. The longer sintering times the higher the sensitivity. The enhancement of sensitivity for longer sintering time may be explained in terms of the smaller size of nanostructures due to the increase of effective surface for absorption of ethanol on the surface.