Grain-Boundary-Induced Strain and Distortion in Epitaxial Bilayer MoS2 Lattice

Grain boundaries between 60° rotated and twinned crystals constitute the dominant type of extended line defects in two-dimensional transition metal dichalcogenides (2D MX2) when grown on a single crystalline template through van der Waals epitaxy. The two most common 60° grain boundaries in MX2 layers, i.e., β- and γ-boundaries, introduce distinct distortion and strain into the 2D lattice. They impart a localized tensile or compressive strain on the subsequent layer, respectively, due to van der Waals coupling in bilayer MX2 as determined by combining atomic resolution electron microscopy, geometric phase analysis and density functional theory. Based on these observations, an alternate route to strain engineering through controlling intrinsic van der Waals forces in homo-bilayer MX2 is proposed. In contrast to commonly used external means, this approach enables localized application of strain to tune electronic properties of the 2D semiconducting channel in ultra-scaled nanoelectronic applications.