Vacancy-induced structural, electronic and optical properties of Hf2CO2 MXene

Abstract

Two-dimensional materials have been widely studied in recent years due to their excellent properties. In this paper, we investigate the structural, electronic and optical properties of pristine and vacancy defect Hf2CO2 using first-principles calculations. The results indicate that O-vacancy (VO) is energetically more favorable than C-vacancy (VC) and Hf-vacancy (VHf) using analysis of vacancy formation energy and energetic stability. The introductions of VC and VHf result in the transition from semiconductor to metal, while introduction of VO makes the bandgap of the pristine Hf2CO2 (PH) monolayer decrease. The introduction of VHf and VC also results in occurrence of localized defect states. The introduction of VO effectively enhances the photocatalytic efficiency of the Hf2CO2 with VO (Hf2CO2-VO) monolayer. The PH and Hf2CO2-VO monolayers are semiconductors and have high optical conductivity, strong absorption and reflectivity at 2.5 eV. The charge transfer is also explored.