Synthesis and gas sensitivity of In-doped ZnO nanoparticles

Undoped and In-doped ZnO nanoparticles were produced by renovated hybrid induction and laser heating (HILH) in this study from Zn-In alloy, with different mole ratios, as the raw material in a flowing mixed gas atmosphere of Ar + O-2. The morphological characteristics, phase microstructure, and chemical state of In-doped ZnO nanoparticles were investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The change in the electrical resistance of thick film based on the In-doped ZnO nanoparticles and their gas sensitivities to volatile organic compounds (VOCs), benzene, acetone, ethyl alcohol, toluene, and xylene, as a function of temperature were measured in the temperature range of 200-500degreesC, and compared with the undoped thick film. The results showed that the In-doped ZnO has lower resistance and higher sensitivity than that of the undoped ZnO. This was probably due to the fact that the In3+ ions, replacing the Zn2+ ions in the ZnO lattice, resulted in an increase of the concentration of free electrons followed by an increase of the adsorbed oxygen. Among the types of In-doped ZnO, 4.58 at % In-doped ZnO had the lowest resistance, and had the highest sensitivity. On increasing the concentration of In into ZnO, its resistance increased, while the sensitivity decreased. The sensitivity of the 4.58 at % In-doped ZnO to VOCs was in the order of acetone > alcohol > xylene > toluene > benzene at an operating temperature of 420degreesC. (C) 2003 Kluwer Academic Publishers.