Fabrication of three-dimensional network of ZnO tetratpods and its response to ethanol

A three-dimensional network of ZnO tetrapods was fabricated on a quartz substrate. The interconnected tetrapods, having legs with length of several μm and diameter in the 0.1–1 μm range, were synthesized via a simple thermal oxidation reaction. Zn powder was heated in a furnace at a temperature of 900 °C and was made to react with air and water vapor. The content of water vapor in air was found to control the adherence onto the substrate and the morphology of the deposited layers. The layers developed a grain structure or a porous structure made of interconnected tetrapods, depending on the content of water vapor in air. The network of tetrapods which was obtained for a small content of water vapor formed a highly porous layer with a high surface to volume ratio. The tetrapod network was tested as a gas sensing element by measuring changes in its electrical resistance upon exposure to ethanol. The responses to ethanol were investigated as a function of the layer temperature and the ethanol concentration. The optimum temperature of the tetrapod network layer was found to be 400 °C, at which ethanol concentration as low as 0.5 ppm was easily detected. The tetrapod network exhibited a 10-fold increase in sensitivity when compared with a ZnO polycrystalline thick film.