W/Mo/Cr Doping Modulates the Negative–Positive Inversion Gas Sensing Behavior of VO₂(M1)

The anomalous gas sensing behavior has garnered significant attention from researchers, prompting a re-evaluation of the gas sensing theory. This work focuses on inversion gas sensing behavior induced by element doping. W/Mo/Cr-doped VO₂(M1) samples are synthesized, and their sensing behaviors are investigated. The results show that the elements can modulate the sensing behavior with an opposite orientation. The sensing behavior in the opposite orientation is attributed to the extent of the reduced Fermi level of VO₂(M1) after doping. W-doped VO₂(M1) maintains a resistance-decreased sensing behavior (-n). In contrast, the decrease in Fermi level results in the formation of a Schottky barrier between the gas-absorbed Mo/Cr-doped VO₂(M1) and the electrode. The formation of Schottky barriers leads to the inversion sensing behavior, which feedbacks as an increased resistance (-p). This study offers a novel perspective on the gas sensing theory.