Point Defects and Grain Boundaries in Rotationally Commensurate MoS2 on Epitaxial Graphene

Abstract

With reduced degrees of freedom, structural defects are expected to play a greater role in two-dimensional materials in comparison to their bulk counterparts. In particular, mechanical strength, electronic properties, and chemical reactivity are strongly affected by crystal imperfections in the atomically thin limit. Here, ultra-high vacuum (UHV) scanning tunneling microscopy (STM) and spectroscopy (STS) are employed to interrogate point and line defects in monolayer MoS2 grown on epitaxial graphene (EG) at the atomic scale. Five types of point defects are observed with the majority species showing apparent structures that are consistent with vacancy and interstitial models. The total defect density is observed to be lower than MoS2 grown on other substrates, and is likely attributed to the van der Waals epitaxy of MoS2 on EG. Grain boundaries (GBs) with 30° and 60° tilt angles resulting from the rotational commensurability of MoS2 on EG are more easily resolved by STM than atomic force microscopy at similar scales due to the enhanced contrast from their distinct electronic states. For example, band gap reduction to ~0.8 eV and ~0.5 eV is observed with STS for 30° and 60° GBs, respectively. In addition, atomic resolution STM images of these GBs are found to agree well with proposed structure models. This work offers quantitative insight into the structure and properties of common defects in MoS2, and suggests pathways for tailoring the performance of MoS2/graphene heterostructures via defect engineering.

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• Large spin-orbit splitting of deep in-gap defect states of engineered sulfur vacancies in monolayer WS2
• How Substitutional Point Defects in Two-Dimensional WS${}_2$ Induce Charge Localization, Spin-Orbit Splitting, and Strain
• Superlubricity of epitaxial monolayer WS2 on graphene
• Molecular Beam Epitaxy of 2D-layered Gallium Selenide on GaN substrates
• Point defects in the 1$T^{\prime }$ and 2$H$ phases of single-layer MoS${}_2$: A comparative first-principles study
• Chemical trends of deep levels in van der Waals semiconductors
• Band Bending and Valence Band Quantization at Line Defects in MoS${}_2$
• Resonant and Bound States of Charged Defects in Two-Dimensional Semiconductors
• Direct Visualization of Electric Field induced Structural Dynamics in Monolayer Transition Metal Dichalcogenides
• Microstructure and Elastic Constants of Transition Metal Dichalcogenide Monolayers from Friction and Shear Force Microscopy
• Intra-Domain Periodic Defects in Monolayer MoS${}_2$
• The Atomic and Electronic structure of 0° and 60° grain boundaries in MoS2
• Microscopic mechanism of van der Waals heteroepitaxy in the formation of MoS2/hBN vertical heterostructures
• Defects, band bending and ionization rings in MoS2
• Low-Temperature Annihilation Rate for Quasi-Localized Excitons in Monolayer MoS2
• Bandgap closing at the screw dislocations of WS2 spirals