The Atomic and Electronic Structure of 0° and 60° Grain Boundaries in MoS2

Abstract

We have investigated atomic and electronic structure of grain boundaries in monolayer MoS2, where relative angles between two different grains are 0 and 60 degree. The grain boundaries with specific relative angle have been formed with chemical vapor deposition growth on graphite and hexagonal boron nitride flakes; van der Waals interlayer interaction between MoS2 and the flakes restricts the relative angle between two different grains of MoS2. Through scanning tunneling microscopy and spectroscopy measurements, we have found that the perfectly stitched structure between two different grains of MoS2 was realized in the case of the 0 degree grain boundary. We also found that even with the perfectly stitched structure, valence band maximum and conduction band minimum shows significant blue shift, which probably arise from lattice strain at the boundary.

Grain-Boundary-Induced Strain and Distortion in Epitaxial Bilayer MoS2 Lattice

“…Due to the hexagonal symmetry of the underlying sapphire template, the orientation of growing domains is controlled to a great extent through a van der Waals epitaxy. However, the lack of inversion symmetry in a monolayer MoS2 implies that growing domains with 0º rotation between them can get stitched without any defects, 34 whereas domains that are 60 twins always result in a grain boundary (GB). Therefore, in highly epitaxial MoS2, the GBs are overwhelmingly dominated by 60 twin boundaries.…”

“…While a translational mismatch could be present between grains with the same orientation, it can also be relaxed through their sliding on an ultra-flat crystalline substrate, resulting in a well-stitched, defect-free boundary. 34 In this work, we investigate the morphology of MoS 2 layers grown on two-inches sapphire substrates using the molybdenum hexacarbonyl and dihydrogen sulfide metal organic CVD (MOCVD) precursors. During the growth, the MoS 2 crystals develop a preferential in-plane orientation and, therefore, form a representative system to study inevitable disorder events in such an epitaxial system.…”

“…In a single layer of MX 2 , certain grain boundaries dominate the boundary structures due to the absence of inversion symmetry, particularly grain boundaries that occur between 60° rotational twinned crystals. While a translational mismatch could be present between grains with the same orientation, it can also be relaxed through their sliding on an ultra-flat crystalline substrate, resulting in a well-stitched, defect-free boundary …”

Large area chemical vapour deposition grown transition metal dichalcogenide monolayers automatically characterized through photoluminescence imaging

“…The density of grain boundaries can be reduced through epitaxial growth of the TMD islands on substrates with hexagonal symmetry, such as hBN [26][27][28] , mica 29 , c-plane sapphire 30,31 and graphene 32 . On these substrates, van der Waals interlayer interaction promotes the relative alignment despite the, often large, lattice mismatch 33 . In CVD the morphology of islands can be controlled to a degree by altering the local ratio of the transition metal and chalcogen atoms around a nucleation point.…”

Illuminating Invisible Grain Boundaries in Coalesced Single-Orientation WS2 Monolayer Films

“…As achieving large-area monolayer films becomes possible, it is more critical to uncover defects that arise from synthesis, such as grain boundaries (GBs) or point defects, and to understand the underlying physics behind their formation. With this understanding, we can further engineer defects and alleviate obstacles to single crystallinity. − …”