In situ edge engineering in two-dimensional transition metal dichalcogenides

Exerting synthetic control over the edge structure and chemistry of two-dimensional (2D) materials is of critical importance to direct the magnetic, optical, electrical, and catalytic properties for specific applications. Here, we directly image the edge evolution of pores in Mo 1 −x W x Se 2 monolayers via atomic-resolution in situ scanning transmission electron microscopy (STEM) and demonstrate that these edges can be structurally transformed to theoretically predicted metastable atomic configurations by thermal and chemical driving forces. Density functional theory calculations and ab initio molecular dynamics simulations explain the observed thermally induced structural evolution and exceptional stability of the four most commonly observed edges based on changing chemical potential during thermal annealing. The coupling of modeling and in situ STEM imaging in changing chemical environments demonstrated here provides a pathway for the predictive and controlled atomic scale manipulation of matter for the directed synthesis of edge configurations in Mo 1 − x W x Se 2 to achieve desired functionality. The unique properties of 2D materials are affected by the discontinuities posed by the structure’s edge. Here, using atomic-resolution scanning transmission electron microscopy and ab initio molecular dynamics simulations, the authors image and explain the formation of specific edge structures on Mo 1 − x W x Se 2 monolayers under different chemical conditions.