UV-induced desorption of oxygen at the TiO2 surface for highly sensitive room temperature O2 sensing

TiO2 was widely considered as a promising material for gas sensing. However, developing TiO2 based O2 sensors working at room temperature is still challenging owing to the difficulties of desorbing oxygen adatoms from the TiO2 surface. Here, the influence of the UV irradiation on the desorption of the surface oxygen on the TiO2 films was investigated by using the atmosphere dependent electric transport, Kelvin probe microscopy and x-ray photoelectron spectroscopy. A lasting high conductivity and high Fermi level of the TiO2 film were observed after the UV irradiation in vacuum, which can be drastically suppressed by a subsequent O2 gas exposure. Thus the UV induced desorption of the surface oxygen is evidenced. Moreover a surface charge transfer model is proposed based on DFT calculations to account for the photodesorption mechanism. Utilizing such effect, the film conductivity was increased and the adsorption sites were actively recovered upon UV irradiation, thereby greatly enhanced the O2 gas sensitivity. Our findings provided a way to optimize the performance of the O2 sensors at room temperature with low cost and high efficiency.