Self-doped nanocolumnar vanadium oxides thin films for highly selective NO2 gas sensing at low temperature

Abstract

Vanadium dioxide (VO2) as strong correlated oxide has been intensively studied due to the unique properties accompanied by metal-insulator transition (MIT) near room temperature. Their extrinsic electrical and optical transformations on MIT have been greatly attracted in many potential applications. In this study, we propose to apply an intrinsic electrical property of VO2 in metallic phase as doping agent of chemiresistive sensor. Self-doped nanocoulmnar vanadium oxides (SNVO) thin films are simply fabricated by glancing angle deposition without any template and chemical additives. The nanocolumnar VO2 thin films were deposited by e-beam evaporator, and then the SNVO with residual VO2 in V2O5 nanocolums were synthesized by an air atmosphere annealing, which are composed of dominant oxidized V2O5 which plays a sensing role on the surface and the residual VO2 with self-doping effect inside nanocolumns. Especially at low temperature (150°C), SNVO sensor shows an ultra-high performance (Rgas/Rair>100) to NO2 (5ppm) gas. It is supposed that the residual VO2 which shows metallic properties above Mott transition temperature (∼67°C) acts as an intrinsic electron donor by pseudo-free electron, which helps adsorption of oxygen ions on the surface and extends the depletion region of few nanometers of narrow necks between nanocolumns.