Subnanometer WS2 pores

Nanomaterials Nanopores in monolayers of transition metal dichalcogenides such as molybdenum disulfide (MoS2) and tungsten disulfide (WS2) have potential applications in molecular separations, but how small can the pores be made? For example, defects created by removal of single Mo atoms from MoS2 are refilled by mobile Mo atoms. Ryu et al. used electron-beam irradiation in a transmission electron microscope to remove single W atoms from a monolayer WS2 sheet. At 500°C, which is sufficient to allow some sulfur vacancy migration, bond rearrangements created either smaller triangular or larger circular subnanometer pores that were stabilized in part through W–W bonding and by bond rotations about the pore periphery. The triangular holes were less stable and, under irradiation, evolved into the circular structures. ACS Nano 10.1021/acsnano.8b07051 (2018).