Enhancement of Ethanol Sensing Properties by Alloying ${\rm TiO}_{2}$ With ZnO Tetrapods

The Ti_xZn_1-xO tetrapods were synthesized using simple thermal oxidation method from Zn and TiO₂ mixture. The tetrapods exhibited single crystalline hexagonal wurtzite structure with the prefer growth direction of [0002] along the legs. The sensors based on Ti_xZn_1-xO tetrapods were fabricated and investigated the ethanol sensing properties. The FE-SEM, HRTEM, SAED, XRD, and RS results suggested that Ti_xZn_1-xO alloy was formed with a slightly decrease of c-axis lattice parameter. The decrease of sensor resistance under ethanol atmosphere was observed and suggested that the Ti_xZn_1-xO tetrapods possessed n-type property of semiconductor similar to ZnO. The Ti_xZn_1-xO tetrapod sensors exhibited higher sensitivity than that of pure ZnO tetrapod sensors for entire ethanol concentration with optimum operating temperature of 300°C. Thus, the enhancement of sensitivity due to alloying TiO₂ with the ZnO tetrapods was observed and maybe explained by an increase of adsorbed oxygen ions due to substitution of Ti atom into Zn atom. Also, the slope value of the plot between log(S-1) and log C suggested that adsorbed oxygen ion species at the surface of the Ti_xZn_1-xO tetrapods was O^2- which was same as pure ZnO tetrapods. Finally, these results have an important implication for a development of ethanol sensors based on metal oxide semiconductors for alcohol breath analyzer.