Dislocation motion and grain boundary migration in two-dimensional tungsten disulphide

Abstract

Dislocations have a significant effect on mechanical, electronic, magnetic and optical properties of crystals. For a dislocation to migrate in bulk crystals, collective and simultaneous movement of several atoms is needed. In two-dimensional crystals, in contrast, dislocations occur on the surface and can exhibit unique migration dynamics. Dislocation migration has recently been studied in graphene, but no studies have been reported on dislocation dynamics for two-dimensional transition metal dichalcogenides with unique metal-ligand bonding and a three-atom thickness. This study presents dislocation motion, glide and climb, leading to grain boundary migration in a tungsten disulphide monolayer. Direct atomic-scale imaging coupled with atomistic simulations reveals a strikingly low-energy barrier for glide, leading to significant grain boundary reconstruction in tungsten disulphide. The observed dynamics are unique and different from those reported for graphene. Through strain field mapping, we also demonstrate how dislocations introduce considerable strain along the grain boundaries and at the dislocation cores.

Bandgap tunability at single-layer molybdenum disulphide grain boundaries

“…4, the MoS 2 lattice orientation changes gradually through the GB without obvious periodicity break and visible defects, suggesting that the strain effect could be the primary reason for the bandgap decrease. As expected, the effects are significantly larger for the GB with 18°misorientation angle than for the GB with 3°misorientation, which is reasonable as a larger mismatch would induce a larger strain field 47 .…”

“…Thus, due to the growth and annealing processes, the GB defects are in fact healed over a much wider region than that considered in simpler models. As discussed below, we believe that this GB defects are accommodated mainly through the lattice distortions that result in a strain field 47 , instead of through energetically unfavourable deep gap states. For the case of 3°GB in Fig.…”

“…Focusing on the GB with 18°m isorientation, we discuss the two possible mechanisms contributing to the decrease of the electronic bandgaps as a function of d. As with previous observations 20,41,[48][49][50][51] , the bandgap of SL MoS 2 is very sensitive to strain, which is thereby first considered here. Line dislocation defects at GBs are well known to be able to create a local strain field 47,52 . A recent study on the GBs of monolayer WS 2 suggests that the strain field can extend over several nanometres from the dislocation cores and are at maxima at the dislocation cores where tensile and compressive strains intermix 47 .…”

“…Line dislocation defects at GBs are well known to be able to create a local strain field 47,52 . A recent study on the GBs of monolayer WS 2 suggests that the strain field can extend over several nanometres from the dislocation cores and are at maxima at the dislocation cores where tensile and compressive strains intermix 47 . Since strain is certainly present at and close to the GBs due to the lattice distortions (Supplementary Figure 2), we attribute the change in bandgap with d to strain, the magnitude of which decreases as d increases.…”

Engineering the Electronic Properties of Two‐Dimensional Transition Metal Dichalcogenides by Introducing Mirror Twin Boundaries

“…TEM images of the grain boundaries at the merged flakes have been reported by various groups. [13,14,25] Moreover, the electronic structure of the GBs were studied using scanning tunneling microscopy (STM). [26,27] Importantly, mirror twin boundaries (MTBs) with particular atomic structures between regions with 60° relative orientation have been repeatedly reported.…”