A Novel Mechanism Based on Oxygen Vacancies to Describe Isobutylene and Ammonia Sensing of p-Type Cr2O3 and Ti-Doped Cr2O3 Thin Films

Gas sensors based on metal oxide semiconductors (MOS) have been widely used for the detection and monitoring of flammable and toxic gases. In this paper, p-type Cr<inf>2</inf>O<inf>3</inf> and Ti-doped Cr<inf>2</inf>O<inf>3</inf> (CTO) thin films were synthesized using an aerosol-assisted chemical vapor deposition (AACVD) method. Detailed analysis of the thin films deposited, including structural information, their elemental composition, oxidation state, and morphology, was investigated using XRD, Raman analysis, SEM, and XPS. All the gas sensors based on pristine Cr<inf>2</inf>O<inf>3</inf> and CTO exhibited a reversible response and good sensitivity to isobutylene (C<inf>4</inf>H<inf>8</inf>) and ammonia (NH<inf>3</inf>) gases. Doping Ti into the Cr<inf>2</inf>O<inf>3</inf> lattice improves the response of the CTO-based sensors to C<inf>4</inf>H<inf>8</inf> and NH<inf>3</inf>. We describe a novel mechanism for the gas sensitivity of p-type metal oxides based on variations in the oxygen vacancy concentration.