Transition from n- to p-type electrical conductivity induced by ethanol adsorption on α-tellurium dioxide nanowires

Tellurium oxide (TeO2) nanowires were synthesized by the thermal evaporation of tellurium metal in an oxygen atmosphere without the presence of any catalysts. The morphology, structure and composition of the prepared nanowires were studied by scanning electron microscopy, X-ray diffraction spectroscopy, micro-Raman scattering and energy-dispersive X-ray spectroscopy. The nanowires were found to have uniform morphology with diameters ranging from 60 to 600 nm and lengths up to several micrometers. They exhibit a well-crystalline structure consistent with tetragonal (α-phase) TeO2 crystal. An optical energy band gap of 3.48 eV for direct transition was estimated by UV–vis–NIR spectroscopy. Gas-sensing properties of samples were examined for different gases in dry air at the working temperature of 80–150 °C. In particular, the results obtained clearly show that the transition from n- to p-type conductivity is induced by the variation of the ethanol concentration. The samples were insensitive to CH4, NO and NO2 and showed a poor sensitivity to CO and NH3 in the investigated temperature and concentration ranges.