Point defects in the 1$T'$ and 2$H$ phases of single-layer MoS$_2$: A comparative first-principles study

TL;DR

This study uses first-principles calculations to compare point defects in the 1$T'$ and 2$H$ phases of single-layer MoS$_2$, revealing differences in defect stability, magnetic properties, and reactivity relevant for material applications.

Contribution

It provides a comprehensive theoretical comparison of intrinsic point defects in 1$T'$-MoS$_2$ and 2$H$-MoS$_2$, highlighting defect formation energies and magnetic effects.

Findings

1$T'$-MoS$_2$ is more prone to hosting lattice imperfections than 2$H$-MoS$_2$.

S vacancies and adatoms are likely in both phases, while Mo vacancies are more abundant in 1$T'$-MoS$_2$.

Defects can be exploited to tailor the material's physical and chemical properties.

Abstract

The metastable 1$T'$ phase of layered transition metal dichalcogenides has recently attracted considerable interest due to electronic properties, possible topological electronic phases and catalytic activity. We report a comprehensive theoretical investigation of intrinsic point defects in the 1$T'$ crystalline phase of single-layer molybdenum disulfide (1$T'$-MoS$_2$), and provide comparison to the well-studied semiconducting 2$H$ phase. Based on density functional theory calculations, we explore a large number of configurations of vacancy, adatom and antisite defects and analyse their atomic structure, thermodynamic stability, electronic and magnetic properties. The emerging picture suggests that, under thermodynamic equilibrium, 1$T'$-MoS$_2$ is more prone to hosting lattice imperfections than the 2$H$ 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 2$H$ phase, S vacancies and adatoms in 1$T'$-MoS$_2$ are very likely to occur while Mo adatoms and antisites induce local magnetic moments. Contrary to the 2$H$ phase, Mo vacancies in 1$T'$-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$T'$-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.