Atomic-Level Dynamics of Point Vacancies and the Induced Stretched Defects in 2D Monolayer PtSe 2 .

Monolayer PtSe 2 holds great potential in extending 2D devices functionality, but their atomic-level-defect study is still limited. Here, we investigate the atomic structures of lattice imperfections from point to stretched 1D defects in 1T-PtSe 2 monolayers, using annular dark-field scanning transmission electron microscopy (ADF-STEM). We show Se vacancies (V Se ) have preferential sites with high beam-induced mobility. Diverse divacancies form with paired V Se . We found stretched linear defects triggered by dynamics of V Se that altered strain fields, distinct from the line vacancies in 2H-phase 2D materials. The paired V Se stability and formation possibility of vacancy lines are evaluated by density functional theory. Lower sputtering energy in PtSe 2 than that in MoS 2 can cause larger possibility of atomic loss compared to diffusion required for creating V Se lines. This provides atomic insights into the defects in 1T-PtSe 2 and shows how a deviated 1D structure is embedded in a 2D system without losing atom lines.