Nikorn 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.

Zn2TiO4 Nanostructures Prepared by Thermal Oxidation Method

Zn2TiO4 nanostructures were synthesized by the thermal oxidation method. Zn with 0, 10, 20, and 30 mol% TiO2 mixed powder were blended in polyvinyl alcohol and coated on an alumina substrate to form thick films. The thick films were heated at temperature of 600, 700, and 800°C under normal atmosphere for 24 hrs. FE-SEM images showed belt-liked nanostructures with the length of 0.3-30 µm, the width of 30-1800 µm, and the thickness ranging in the order of nm. Ti was incorporated into the nanostructures with ZnO to form Zinc titanate compound, indicated by EDS. Raman spectra and XRD results suggested that phase of Zinc titanate is cubic Zn2TiO4. The oxidation temperature and TiO2 content are critical to the phase quality of the nanostructures.

Ethanol Sensing Characteristics of ZnO Nanostructures Impregnated by Gold Colloid

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.

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.

CuO nanostructure by oxidization of copper thin films

CuO nanostructures were synthesized by oxidizing copper thin films. The copper thin film was grown on alumina substrates by evaporation copper powder at pressure of 0.04 mtorr. The copper thin films were then oxidized 800, and 900oC for 12, 24 and 48 hr, respectively. The obtained CuO nanostructures were investigated by Energy Dispersive Spectroscopy (EDS), Field Emission Scanning Electron Microscope (FE-SEM) image, and X-Ray Diffraction (XRD). The diameter of CuO nanostructure is around 100-600 nanometers and it is depends on oxidation reaction time and temperature. These CuO nanostructures have a potential application for nanodevices such as nano gas sensor or dye-sensitized solar cells.