Density functional theory insight towards high sensitivity for NO, NO2 and O2 over monolayer SnO

Abstract

Density functional theory calculations are performed here to evaluate the changes in the band structure, density of states, adsorption energy and charge transfer for the monolayer SnO after adsorbing multifarious gas molecules, including CH4, CO, CO2, H2, H2O, NH3, N2, NO2, NO and O2. The optimum binding position between gas molecules and monolayer SnO is confirmed by calculating their adsorption energy, and the result shows that the monolayer SnO has the strongest adsorption capacity for NO, NO2 and O2 among these gas molecules, which illustrates that SnO is prone to select above three molecules in adsorption. The adsorbability of these three molecules can be attributed to the shorter distance of critical adsorption, the greater sensitivity of electron band structure and the larger charge transfer. Especially, the adsorption energy of O2 is as high as 1.69 eV and the average electron obtained by each O2 from the base is high up to 1 e-. The selectivity and sensitivity demonstrate that the monolayer SnO can be considered as a possible gas sensor material to detect the concentration of above-mentioned three gases in the mixed gases. Moreover, the valence band and the conduction band of monolayer SnO are not obviously changed after adsorbing CH4, CO, CO2, H2, H2O, NH3 or N2; in contrast, the impurity levels appear in the band gap when NO, NO2 or O2 is adsorbed and they can obviously reduce the band gap.