▎ 摘　　要

Tin oxides and tin (SnOx-Sn) compound films were thermally evaporated onto chemical vapor deposition (CVD)-grown graphene films to obtain improved nitrogen dioxide (NO2) gas sensitivity. The effects of the vacuum annealing and ultraviolet (UV) ozone (O-3) exposure of the bare graphene films prior to the thermal evaporation on the SnOx-Sn films' sensitivities, bonding states, and surface morphologies were investigated. With increasing annealing time, the coverage of the SnOx-Sn nanoparticles on the graphene increased and the p to n sensitivity transition occurred when n-type SnOx-Sn nanoparticles became dominant instead of the p-type graphene films for sensors without O-3 exposure. Meanwhile, the opposite p-type sensitivity response was dominant with increasing annealing time for the O-3-treated sensors. The chemisorbed Sn on the graphene generated by O-3 exposure was oxidized by highly reactive NO2, resulting in a p-type doping effect, which would lead to n-to p-type sensitivity transition when the hole concentration exceeded the initial electron concentration of the n-type SnOx-Sn compound films. Vacuum annealing and O-3 exposure also exhibited a tremendous influence on the SnOx-Sn films' surface morphologies, which could be responsible for the subsequent sensitivity dependence.