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

Abstract

Grain boundaries (GBs) are important structural defects that have significant influence on the electronic structure and magnetic properties of transition-metal dichalcogenides (TMDs). However, reports on GBs in lower-symmetry T″-structure TMDs, especially on their local electronic structures, are rare. Here, we report a systematic study of intrinsic coherent GBs in monolayer ReSe2, a representative T″-structure TMD with anisotropy and intriguing electrical properties, via a combination of atomic-resolution scanning transmission electron microscopy (STEM) imaging and first-principles calculations. These coherent GBs feature a coherent Se sublattice and unchanged Re–Se (and Se–Re) local coordination. Based on the saturation of the Re–Re bond, the GBs are divided into three categories: those with saturated Re–Re bonds (3 Re–Re bonds per Re atom), denoted as α-GBs; those with truncated Re4 chains but intact Re4 clusters (β-GBs); and those with broken Re4 clusters (γ-GBs). The intact configurations of the α-GBs enable them to form easily, and they possess semiconductor characteristics inherited from the pristine ReSe2 monolayer. Interestingly, the introduction of both β-GBs and γ-GBs leads to the emergence of local magnetic moment, arising from the Re 5d xz atomic orbitals around the boundaries. Moreover, the GBs with broken Re–Re bonds (β- and γ-GBs) exhibit subtle differences in spin-polarized in-gap states, demonstrating the strong dependency of the electronic properties on the precise atomic structure of the GBs. These results are of fundamental importance in understanding lower-symmetry TMDs and the structure–property relationships in two-dimensional materials.

Sub‐Nanometer Electron Beam Phase Patterning in 2D Materials

“…Phase transitions in uniform phase domains aside, the patterning approach is also applied to grain boundaries (GB) [ 21 , 22 ] of the T’’ phase ReS 2 monolayers. Prevailing deep energy states in the bandgaps are spatially found at GBs of the ReS 2 monolayer, [ 21 ] which induce Fermi level pinning and greatly lower the carrier mobility across GBs.…”

Probing Functional Structures, Defects, and Interfaces of 2D Transition Metal Dichalcogenides by Electron Microscopy

“…Reproduced with permission. [ 69 ] Copyright 2021, American Chemical Society. g,h) Atomic‐resolution ADF images of the edge structures with or without reconstructions along the directions of the Mo‐zigzag chain g) and the S‐zigzag chain h) in monolayer MoS 2 .…”

“…[ 68 ] In addition to the extensively studied hexagonal 1H‐MoS 2 , a systematic investigation of GBs in ReSe 2 with a lower‐symmetric 1T″ phase revealed that GBs can be categorized based on the saturation of the Re−Re bond (Figure 2f). [ 69 ] While the synthesis of wafer‐scale single‐crystal TMDs without any GBs has already been realized through epitaxy on crystalline substrates, [ 61b–d ] the precise control of GBs with different types and densities is still in its infancy.…”

“…f) Atomic-resolution ADF images of GBs in monolayer ReSe 2 with the corresponding structural models. Reproduced with permission [69]. Copyright 2021, American Chemical Society.…”

Regulating the electronic and magnetic properties of 1T′-ReS2 by fabricating nanoribbons and transition-metal doping: a theoretical study

“…14,16 The Re–Re atoms in monolayer 1T′-ReS 2 form rhombus with an angle of ∼119.8° between the a and b axes. 14,17,18 The diamond-shaped chains induce in-plane anisotropy and interlayer decoupling effects, both of which lead to the unique electronical properties in 1T′-ReS 2 . Therefore, 1T′-ReS 2 has a wide range of applications in infrared sensing, 19 strain sensors, 20,21 photodetectors 22 and battery anode materials.…”