Abstract
The adsorption characteristics of different environmental gas molecules such as HF, CO, CO(2), SO(2), H(2)S, NH(3), NO and NO(2) on the surface of a CuBr monolayer have been studied using DFT+U calculations with Grimme scheme DFT-D2 for accurate description of the long-range interactions (van der Waals). Our findings indicate that the CuBr monolayer (ML) exhibits high sensitivity to CO, SO(2), H(2)S, NH(3), NO and NO(2), as evidenced by their strong adsorption energies and significant charge transfer. In contrast, HF and CO(2) molecules show weak adsorption on the CuBr ML, due to their low adsorption energies and minimal charge transfer. High diffusion energy barriers for gas molecules (CO, CO(2), NH(3) and NO(2)) indicate that they are less mobile and tend to remain stable at their adsorption sites. Conversely, low diffusion energy barriers (HF, SO(2), H(2)S and NO) suggest that a lesser amount of energy needs to be expended and gases can move easily across the surface of the substrate. The band structure and partial density of states calculations reveal that the electronic properties of the CuBr ML are altered due to the contributions of the orbitals of the gas molecules (C-p and O-p of CO, F-p of HF, O-p of CO(2), S-p of H(2)S, N-p of NH(3), S-p and O-p of SO(2), N-p and O-p of NO and NO(2)) and CuBr ML (Cu-p, Cu-d, Br-p). The charge density difference and Bader charge analysis indicate that the gas molecules (CO, HF, SO(2), CO(2), NO and NO(2)) either act as charge acceptors or donors (H(2)S and NH(3)). The work function variations of the CuBr ML before and after adsorption and significant changes in the conductivity verify the high sensitivity of CO, SO(2), H(2)S, NH(3), NO and NO(2) with the CuBr ML. The band gap variations (before and after adsorption) are small for HF, CO, CO(2), H(2)S and NH(3) whereas large variations in band gap for SO(2), NO and NO(2) reveal that the CuBr ML is quite selective to these three gases. The recovery time for gas molecules desorption from CuBr ML is reduced to a reasonable recovery time by increasing the temperature from ambient to 500 K with UV exposure. Thus our theoretical results indicate that the CuBr ML is a promising candidate as a gas sensor for sensing applications of CO, SO(2), H(2)S, NH(3) NO and NO(2) with high sensitivity and selectivity.