Vacancy impacts on electronic and mechanical properties of MX2 (M = Mo, W and X = S, Se) monolayers

Monolayers of transition metal dichalcogenides (TMD) exhibit excellent mechanical and electrical characteristics. Previous studies have shown that vacancies are frequently created during the synthesis, which can alter the physicochemical characteristics of TMDs. Even though the properties of pristine TMD structures are well studied, the effects of vacancies on the electrical and mechanical properties have received far less attention. In this paper, we applied first-principles density functional theory (DFT) to comparatively investigate the properties of defective TMD monolayers including molybdenum disulfide (MoS2), molybdenum diselenide (MoSe2), tungsten disulfide (WS2), and tungsten diselenide (WSe2). The impacts of six types of anion or metal complex vacancies were studied. According to our findings, the electronic and mechanical properties are slightly impacted by anion vacancy defects. In contrast, vacancies in metal complexes considerably affect their electronic and mechanical properties. Additionally, the mechanical properties of TMDs are significantly influenced by both their structural phases and anions. Specifically, defective diselenides become more mechanically unstable due to the comparatively poor bonding strength between Se and metal based on the analysis of the crystal orbital Hamilton population (COHP). The outcomes of this study may provide the theoretical knowledge base to boost more applications of the TMD systems through defect engineering.