Atomically Sharp Dual Grain Boundaries in 2D WS₂ Bilayers

Abstract

It is shown that tilt grain boundaries (GBs) in bilayer 2D crystals of the transition metal dichalcogenide WS 2 can be atomically sharp, where top and bottom layer GBs are located within sub-nanometer distances of each other. This expands the current knowledge of GBs in 2D bilayer crystals, beyond the established large overlapping GB types typically formed in chemical vapor deposition growth, to now include atomically sharp dual bilayer GBs. By using atomic-resolution annular dark-field scanning transmission electron microscopy (ADF-STEM) imaging, different atomic structures in the dual GBs are distinguished considering bilayers with a 3R (AB stacking)/2H (AA′ stacking) interface as well as bilayers with 2H/2H boundaries. An in situ heating holder is used in ADF-STEM and the GBs are stable to at least 800 °C, with negligible thermally induced reconstructions observed. Normal dislocation cores are seen in one WS 2 layer, but the second WS 2 layer has different dislocation structures not seen in freestanding monolayers, which have metal-rich clusters to accommodate the stacking mismatch of the 2H:3R interface. These results reveal the competition between maintaining van der Waals bilayer stacking uniformity and dislocation cores required to stitch tilted bilayer GBs together. Bilayer Grain Boundaries

Atomic Structure of Dislocations and Grain Boundaries in Two-Dimensional PtSe2

“…The ADF-STEM images in Figure 4a,b show a monolayer GB with a tilt angle of 34°, which develops along a nanoscale meandering pathway, extending along two directions with turning angles of 120°, illustrated by blue and purple lines separately in Figure 4c, similar to other 2D TMDs. 53,54 In accordance with the 30°GB in Figures 2 and 3, the dislocation cores along the same extending direction are connected in a staggered arrangement (see the short red lines representing the connection between two sequential dislocations in Figure 4c). The GBs along angle β of 68°are also connected by stepped 5|7 +Se dislocation cores with a small deviation angle (φ) of ∼10°, resembling that in the 30°GB in Figure 3c.…”

Few-Layer WS2–WSe2 Lateral Heterostructures: Influence of the Gas Precursor Selenium/Tungsten Ratio on the Number of Layers

“…The structures in both domains display a hexagonal arrangement, and the bilayer WS 2 and WSe 2 were AB stacked in our experiment (Figure S9). ,− The SAED of the interface shows that each diffraction is composed of a pair of diffraction peaks (Figure b), representing WS 2 and WSe 2 respectively . The high-magnification HAADF-STEM image of the bl–mo WSe 2 homojunction interface is shown in Figure c, in which the bilayer WSe 2 is brighter than monolayer WSe 2 .…”

A ReaxFF Force Field for 2D-WS2 and Its Interaction with Sapphire

“…Grain boundaries (GB) are ubiquitous topological line defects observed in WS 2 crystalline films and play a crucial role in modulating material properties. ,− For example, recent studies reveal the 1D metallic behavior of 60° grain boundaries, ,, which strongly modify the electronic properties of 2D materials in interesting ways that may contradict the common belief that GBs always have detrimental effects on the optoelectronic properties of crystalline films . Conversely, understanding the strong interplay between crystal growth and grain boundaries in controlling the morphological structure of growth fronts and coalescing grains is vital to fabricating highly single-crystalline films.…”