An Anomalous Formation Pathway for Dislocation-Sulfur Vacancy Complexes in Polycrystalline Monolayer MoS2

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Two-dimensional (2D) molybdenum disulfide (MoS2) exhibits direct bandgap semiconducting properties, making it a material of significant interest.
• Experimental observations of sulfur vacancy concentrations in monolayer MoS2 are highly variable, contrasting with theoretical predictions of low formation energy.

Purpose of the Study:

• To investigate the structures and energetics of vacancies and interstitials in both grain boundaries (GB) and grain interiors (GI) of monolayer MoS2.
• To uncover the anomalous formation pathway for dislocation-double sulfur vacancy (V2S) complexes in MoS2.

Main Methods:

• Density functional theory (DFT) calculations were employed to study defect structures and energetics.
• Analysis focused on vacancy and interstitial configurations within grain boundaries and grain interiors of monolayer MoS2.

Main Results:

• An anomalous pathway for the formation of dislocation-double sulfur vacancy (V2S) complexes was identified.
• A (5|7) defect in S-polar grain boundaries can convert to a (4|6) defect, which acts as both a dislocation and a double sulfur vacancy.
• This dislocation character enables the complex to migrate into the grain interior via thermal activation, carrying the double vacancy.

Conclusions:

• The findings explain the prevalence of single sulfur vacancies (VS) in exfoliated MoS2 and double sulfur vacancies (V2S) in chemical vapor deposition (CVD)-grown MoS2.
• The study reproduces observed grain boundary patterns in CVD-grown MoS2.
• The revealed sulfur vacancy formation pathway offers critical insights for controlling the quality of monolayer MoS2.