Density functional theory study of transitional metal-doped ZnO nanostructures for gas sensing: interaction of NH3 and NO2 with the doped ZnO surface

Abstract

Semiconductor oxide materials have gained popularity because of their good sensing performance, especially in terms of responsiveness, selectivity, fast response, and nontoxicity. Recently, zinc oxide (ZnO) has gained significant attention in sensing applications as an n-type semiconductor oxide material with a wide band gap of 3.34 eV. Its popularity stems from its cost-effective production, high electron mobility, and resistance to thermal changes. ZnO can be synthesized through various methods, including electrochemical anodizing, sol-gel, ultrasonic irradiation, spray pyrolysis, and hydrothermal techniques. Notably, the sensing characteristics of ZnO differ from other oxides and are influenced by the specific preparation method employed. Until now, ZnO has been used to detect various hazardous gases, including nitrogen dioxide, oxygen, nitrogen monoxide, carbon dioxide, hydrogen sulphide, ammonia, and formaldehyde. Sensitivity and gas selectivity issues are common problems with all semiconductor oxide-based sensors, however, enhancing gas performance and detection limits remains an open challenge. Additional techniques, including dopants, were incorporated to counteract these challenges. Density functional theory (DFT) is applicable in predicting the sensing properties and electronic structure of doped ZnO. In this study, the electronic transport performance and adsorption characteristics of NH3 and NO2 on doped ZnO we examined. Negative values of adsorption energy were found, suggesting that the adsorption process is thermodynamically favorable. It was observed that NH3 adsorption was more stable on the ZnO surface, whereas NO2 adsorption was favored on the Cu-doped ZnO surface.