Atomic-scale patterning in two-dimensional van der Waals superlattices.

Two-dimensional (2D) van der Waals superlattices comprised of two stacked monolayer materials have attracted significant interest as platforms for novel optoelectronic and structural behavior. Although studies are focused on superlattice fabrication, less effort has been given to the nanoscale patterning and structural modification of these systems. In this report, we demonstrate the localized layer-by-layer thinning and formation of nanopores/defects in 2D superlattices, such as stacked MoS2-WS2 van der Waals heterostructures and chemical vapor deposited bilayer WSe2, using aberration-corrected scanning transmission electron microscopy (STEM). Controlled electron beam irradiation is used to locally thin superlattices by removing the bottom layer of atoms, followed by defect formation through ablation of the second layer of atoms. The resulting defects exhibit atomically-sharp pore edges with tunable diameters down to 0.6 nm. Structural periodicities and focused STEM irradiation are also utilized to form close-packed nanopore arrays in superlattices with varying twist angles and commensurability. Applying these methods and mechanisms provides a forward approach in the atomic-scale patterning of stacked 2D nanodevices.