Ethanol Sensing Property of Tetrapods Prepared by Thermal Oxidation of Zn and TiO2 Mixture

Abstract

Tetrapods of Zn and TiO2 mixture have been synthesized through the thermaloxidation technique. The mixed powder was placed into Al2O3 crucible, and then heated infurnace at 1000??C for a few minutes. The Al2O3 crucible was taken out from the furnace, andthe white wool products were observed. The white wool products were examined byFE-SEM, EDS, and XRD for morphology, chemical composition, crystal structure, andphase formation. FE-SEM result revealed that the white wool products composed oftetrapods with single crystalline and had two different shapes, round tip and sharp tip. Theround tip tetrapods had the length of 1???2 ??m and the diameter of 160???280 nm, while thesharp tip tetrapods had the length of 3???13 ??m and the diameter ranging from 330???470 nm.The EDS attached to the FE-SEM was performed on one leg of tetrapod and indicated Ti, O,and Zn elements. The atomic concentration of Ti was less than 1 at. %. XRD result indicatedthat the tetrapods exhibited hexagonal wurtzite ZnO phase (a = 3.247 ?? and c = 5.175 ??) andsmall phase fraction of face-centered cubic Zn2TiO4 phase (a = 4.479 ??). The tetrapods werefabricated as the ethanol sensor and tested under the ethanol ambient of 50-1000 ppm at thevarious operating temperature. Our tetrapod sensors exhibited the sensitivity 20 times higherthan that of pure ZnO tetrapods, prepared by the same method. The tetrapod sensors showedhigh resistance when exposed in air; however, its resistance dropped sharply when exposedin ethanol, indicating n-type property of metal oxide semiconductor. The sensor sensitivitywas a function of the ethanol concentration and the operating temperature. The highestsensitivity was measured to be 23.6 under ethanol concentration of 1000 ppm at operatingtemperature of 300??C.

Keywords: Ethanol sensor, tetrapods, ZnO, thermal oxidation, crystal growth.