Stabilities and electronic properties of monolayer MoS2 with one or two sulfur line vacancy defects

Abstract

Stimulated by the recent experimental observation that single sulfur vacancies in monolayer MoS₂ are mobile under the electron beam and easily agglomerate into the sulfur line vacancy defects [Phys. Rev. B: Condens. Matter Mater. Phys., 2013, 88, 035301], the stabilities and electronic properties of monolayer MoS₂ with one or two staggered sulfur line vacancy defects (SV or DV), along the armchair or zigzag direction (AC–SV, AC–DV or ZZ–SV, ZZ–DV), have been investigated systematically by first-principles calculations. It is found that: (1) The ZZ-types (ZZ–SV and ZZ–DV) are more stable at different line vacancy densities than the AC-types (AC–SV and AC–DV), which is in good agreement with previous experimental findings. (2) More interestingly, it is predicted from our numerical calculations that, in the same ZZ-types, the ZZ–DV is more stable than the ZZ–SV, indicating that two separate ZZ–SV line vacancy defects tend to move closely to each other for coalescing into a ZZ–DV, which is in contrast to the AC-type with AC–SV being a little more stable than the AC–DV. (3) The monolayer MoS₂ with the AC–SV or AC–DV are both semiconductors with a direct or an indirect band gap, respectively, both of which are significantly smaller than that of the perfect monolayer. (4) Furthermore, the out-of-plane distortion induced by strain release in the monolayer MoS₂ with ZZ–SV or ZZ–DV is more severe than that with the AC-type, which can further considerably decrease the system's gap value or even make the gap nearly closed. Our calculation results will be helpful in future nanoelectronics and nanoelectromechanics based on MoS₂ materials.