The Mobile and Pinned Grain Boundaries in 2D Monoclinic Rhenium Disulfide

Abstract

In bulk crystals, the kinetics of dislocations is usually hindered by the twining boundaries (TB) or grain boundaries (GB), rendering the well-known grain boundary strengthening effects. Nevertheless, here it is found that in 2D rhenium disulfide (ReS 2), twinning is much easier than dislocation slip. Consequently, the highly mobile TBs or GBs are inversely pinned by the relatively immobile dislocations. Due to the strong in-plane covalent bonding, the GBs in high-symmetry 2D materials such as graphene which consists of defects are immobile at room temperature. In contrast, in monoclinic 2D ReS 2 several types of GBs (including TBs) can be readily generated and driven by mechanical loading. A complete library of the GBs in 2D ReS 2 is established by the (in situ) atomic-scale transmission electron microscopy (TEM) characterizations and density functional theory (DFT) calculations. The twinning (shear) stresses for 2D ReS 2 are estimated as low as 4-30 MPa, one or two orders of magnitude lower than the traditional bulk materials. Full elucidation on the GB structures and especially the intriguing GB kinetics in such anisotropic 2D materials are of fundamental importance to understand the structure-property relationships and develop strain-tunable applications for 2D materials in future.

Ferroelastic–Ferroelectric Multiferroicity in van der Waals Rhenium Dichalcogenides

“…This is also consistent with previous reports that the TB is observed in low-energy methods, e.g., crack generation [18] and molecule intercalation, [19] while other types of TBs are observed in highenergy methods, e.g., electron beam irradiation. [13,17]…”

“…[ 29,30 ] Specifically, the coherent TBs, including the planes (100), (010), , and , where the bonds in the Re 4 cluster must change their conformation, are not generated, but two types of domain wall structures— TB formed preferentially with only change in the direction of bridge bonds and (110) TB formed with the shift of the bridge bonds at the opposite ends of the cluster to one side without change in the bonds of Re 4 clusters—are experimentally observed. [ 17 ] In other words, although each orientation state is energetically equivalent, the difference in energy cost to form TB induces priority order in switching among orientation states. This is also consistent with previous reports that the TB is observed in low‐energy methods, e.g., crack generation [ 18 ] and molecule intercalation, [ 19 ] while other types of TBs are observed in high‐energy methods, e.g., electron beam irradiation.…”

“…Recent studies on the reconstruction of ReS 2 and ReSe 2 using various methods, e.g., electron beam irradiation, [13,17] crack generation, [18] and intercalation of molecules, [19] suggest the possibility of domain switching by strain, but the direct relation between external stress and domain reconstruction is still obscure. Here, we report intrinsic ferroelastic-ferroelectric multiferroicity in single-crystalline van der Waals rhenium dichalcogenides (ReX 2 ).…”

Realizing the Intrinsic Anisotropic Growth of 1T′ ReS2 on Selected Au(101) Substrate toward Large‐Scale Single Crystal Fabrication

“…Take ReS 2 as an example, its monoclinic distorted octahedral (1T′) structure renders it optically and electrically biaxial, and thus endows it strong 2D in‐plane anisotropic properties and the accompanied brand new applications. [ 16–24 ] However, several recent studies have revealed that Re4‐chain reconstruction occurs easily with diverse manners during ReS 2 growth process, which brings plenty of sub‐domains and GBs in each ReS 2 domain, [ 25–29 ] as schematically shown in the top row of Figure . Accordingly, these sub‐domains with different lattice orientations lead to the optical and electrical properties varying dramatically in each ReS 2 domain, and the GBs seriously degrade its electrical transport properties.…”

Diverse Spin-Polarized In-Gap States at Grain Boundaries of Rhenium Dichalcogenides Induced by Unsaturated Re–Re Bonding

“…The GB configurations are expected to be more complex, because of the lower symmetry for the T″ structures. Although the formation mechanism and kinetics of several GBs in ReS 2 have been demonstrated, 34,35 a systemic classification of GBs in T″ structures and studies on the corresponding electronic and magnetic properties are still lacking. Herein, we systematically investigate the intrinsic coherent GBs of monolayer ReSe 2 and their electronic structures, using a combination of atomic-resolution STEM imaging 36 and firstprinciples calculations.…”