Density functional theory insights into NO gas sensing of Ti-doped ZnO monolayer with oxygen vacancy

Abstract

The objective of this study was to investigate the adsorption of NO gas molecules on both pure and Ti-doped defective ZnO monolayers, along with their potential application as NO gas sensors, using first-principles density functional theory. To account for electronic interactions, we incorporated the Hubbard potential for d-orbitals. Our findings reveal that the pure ZnO monolayer exhibits minimal interaction with the NO gas molecule. In contrast, the NO gas molecule adsorbed on the ZnO monolayer with an oxygen vacancy defect shows a higher adsorption energy of −0.720 eV and increased charge transfer compared to the pure ZnO monolayer, suggesting that the presence of an oxygen vacancy enhances the adsorption capacity. Furthermore, the NO gas molecule is strongly chemisorbed onto both the Ti-doped ZnO monolayer and the Ti-doped defective ZnO monolayer, with high adsorption energies of −2.057 and −2.154 eV, respectively. The most significant changes in electrical conductivity are observed in the Ti-doped ZnO monolayer, indicating enhanced sensitivity. While Ti doping improves sensitivity, the oxygen vacancy leads to non-selective adsorption of both NO and O2. Work function analysis shows that Ti doping lowers the work function, making the Ti-doped ZnO monolayer more responsive to NO adsorption in terms of work function changes. The ZnO monolayer with an oxygen vacancy demonstrates stability in oxygen-poor conditions, whereas the Ti-doped ZnO monolayer maintains stability under oxygen-rich conditions. Overall, these results suggest that doping the ZnO monolayers with Ti and creating an oxygen vacancy are effective strategies for enhancing NO gas sensing properties.