Point defects in the 1T′ and 2H phases of single-layer MoS2 : A comparative first-principles study

Abstract

The metastable $1{T}^{\ensuremath{'}}$ phase of layered transition metal dichalcogenides has recently attracted considerable interest due to electronic properties, possible topological phases, and catalytic activity. We report a comprehensive theoretical investigation of intrinsic point defects in the $1{T}^{\ensuremath{'}}$ crystalline phase of single-layer molybdenum disulfide ($1{T}^{\ensuremath{'}}\text{\ensuremath{-}}{\mathrm{MoS}}_{2}$) and provide comparison to the well-studied semiconducting $2H$ phase. Based on density functional theory calculations, we explore a large number of configurations of vacancy, adatom, and antisite defects and analyze their atomic structure, thermodynamic stability, and electronic and magnetic properties. The emerging picture suggests that, under thermodynamic equilibrium, $1{T}^{\ensuremath{'}}\text{\ensuremath{-}}{\mathrm{MoS}}_{2}$ is more prone to hosting lattice imperfections than the $2H$ phase. More specifically, our findings reveal that the S atoms that are closer to the Mo atomic plane are the most reactive sites. Similarly to the $2H$ phase, S vacancies and adatoms in $1{T}^{\ensuremath{'}}\text{\ensuremath{-}}{\mathrm{MoS}}_{2}$ are very likely to occur while Mo adatoms and antisites induce local magnetic moments. Contrary to the $2H$ phase, Mo vacancies in $1{T}^{\ensuremath{'}}\text{\ensuremath{-}}{\mathrm{MoS}}_{2}$ are expected to be an abundant defect due to the structural relaxation that plays a major role in lowering the defect formation energy. Overall, our study predicts that the realization of high-quality flakes of $1{T}^{\ensuremath{'}}\text{\ensuremath{-}}{\mathrm{MoS}}_{2}$ should be carried out under very careful laboratory conditions but at the same time the facile defects introduction can be exploited to tailor physical and chemical properties of this polymorph.