Highly Selective and Sensitive Resistive and Schottky Diode Sensor for Nitrogen-Containing Gas Based on Monolayer Penta-HgO₂

Highly sensitive and reusable sensors for detecting harmful gas molecules are particularly important to reduce their harmful impacts on human health and the natural environment. Based on the density functional theory calculations, the adsorption properties and sensing performances of the monolayer penta-HgO₂ material for nitrogen-containing toxic gas molecules (N₂O, NH₃, NO₂, and NO) were thoroughly explored. The adsorptions of NH₃, NO₂, and NO (N₂O) on the monolayer penta-HgO₂ substrate are characterized by high (low) adsorption energy, significant (little) charge transfer, and short (long) adsorption distance, showing chemisorption (physisorption) properties. In addition, the band gap of penta-HgO₂ decreases significantly after adsorbing NO₂ and NO, resulting in a substantial increase in electrical conductivity. Meanwhile, due to the adsorption of NO, the substrate also generates an obvious magnetic moment. In this study, an efficient strategy to predict the direction and extent of charge transfer between the absorbed gas and substrate material is put forward by comparing the Fermi level and band edge positions of the adsorbent to the frontier molecular orbitals of the adsorbate. Furthermore, we propose a highly efficient resistive gas sensor based on the penta-HgO₂ monolayer material for detecting NO₂ and NO due to the obvious variations of the electronic structure and resultant prominent changes in the conductivity. Particularly, a Schottky diode sensor by fabricating a contacted interface between the penta-HgO₂ monolayer and an Ag metal is designed according to the significantly changed work functions. The types and barrier heights of the metal-semiconductor contact (Ag-HgO₂) are modulated by the adsorption of NO₂ or NO. Different current signals can be observed when a bias voltage of 0.4 eV is applied, enabling the selective identification of NO₂ and NO. Additionally, the short recovery time after adsorbing NO₂ and NO demonstrates the reusability of the sensor. The theoretical results of this study provide valuable insights for accelerating the discovery of potential sensing materials and promote innovative resistive sensors or Schottky diode sensors based on the pentagonal monolayer material for detecting nitrogen-containing gases.