Strain Modulation by van der Waals Coupling in Bilayer Transition Metal Dichalcogenide

Abstract

Manipulation of lattice strain is emerging as a powerful means to modify the properties of low-dimensional materials. Most approaches rely on external forces to induce strain, and the role of interlayer van der Waals (vdW) coupling in generating strain profiles in homobilayer transition metal dichalcogenide (TMDC) films is rarely considered. Here, by applying atomic-resolution electron microscopy and density functional theory calculations, we observed that a mirror twin boundary (MTB) modifies the interlayer vdW coupling in bilayer TMDC films, leading to the development of local strain for a few nanometers in the vicinity of the MTB. Interestingly, when a single MTB in one layer is "paired" with another MTB in an adjacent layer, interlayer-induced strain is reduced when the MTBs approach each other. Therefore, MTBs are not just 1D discontinuities; they can exert localized 2D strain on the adjacent lattices.

A machine perspective of atomic defects in scanning transmission electron microscopy

“…Both the moment method and the model‐based method require initial positions for the algorithm to proceed. However, determining the number of atomic columns is challenging in multiphase material systems, such as bilayer MoSe 2 with coexistence of 2H and 3R phases, due to the need to specify multiple sets of basis vectors in the preprocessing stage. Recently this problem has been overcome by successfully implementing Bayesian statistics to extract the optimal number of atomic columns and positions in low signal‐to‐noise ratio (SNR) STEM images .…”

“…In 2010, Krivanek et al successfully mapped out carbon and oxygen atoms in a monolayer boron nitride (BN) using STEM. Since then, a plethora of atomic defects in various 2D material systems under different growth conditions have been intensively studied . Atomically doped 2D transition metal dichalcogenides (TMDCs) with other transition metal or chalcogen atoms such as Mo x W 1‐x X 2 (X = S, Se) and MSe 2(1‐x) S 2x (M = Mo, W) have been reported to tune the bandgap of the alloy systems.…”

“…Left panel: Selected milestones in the timeline of STEM imaging of 2D materials' defects (blue). Adapted with permission from Reference Copyright 2010, Springer Nature, Reference Copyright 2013, Springer Nature, Reference Copyright 2014, Springer Nature, Reference Copyright 2017, Wiley‐VCH, Reference Copyright 2018, American Chemical Society. Right panel: Selected landmarks in the timeline of machine learning and its application in materials science.…”

“…[3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] Atomically doped 2D transition metal dichalcogenides (TMDCs) with other transition metal or chalcogen atoms such as Mo x W 1-x X 2 (X = S, Se) [5][6][7][8] and MSe 2(1-x) S 2x (M = Mo, W) [9][10][11][12] have been reported to tune the bandgap of the alloy systems. Various grain boundaries [13][14][15][16][17][18][19][20][21][22][23][24][25] show distinct optical, electrical, magnetic, and catalytic properties. Herein, structural defects or external dopants are able to endow a broad range of promising applications in 2D materials based on the defect topology and density, such as nanoelectronics, 26 optoelectronics, 26 valleytronics, 27 catalysis, 28,29 and so on.…”

Real-space light-reflection mapping of atomically thin WSe2 flakes revealing the gradient local strain

“…Recently, many studies have been reported on the strain effect of 2D layered materials [10][11][12]. This effect has been proved that the optical band gap can be tuned by up to several hundred meV/% in atomically thin TMDs by local strain [13].…”