Fig. 4. Edge study of PbI₂.

ADF-STEM image of a typical intrinsic edges of two different monolayer PbI₂ flakes just after deposition on the graphene and b sharp zigzag-faceted edges of the monolayer PbI₂ flake after electron beam irradiation. The arrows show the clustering of the atoms after having been sputtered out of the edges. The yellow boxes show the faceted zigzag edge formation from the intrinsic edges after the damage from electron beam. c ADF-STEM images showing I- and Pb-terminated zigzag termination. The two insets in the image shown with white and pink boxes show the high resolution of the areas with same color annotation that have I- and Pb-terminated edges. The line profile of the regions marked in orange and green boxes confirms the position of the lead and iodide in the honeycomb structure. d, e The line profile of the orange and green boxes shown in c, in the direction of 1–2 and 3–4. f High-resolution ADF-STEM image of the area shown under red box in c. g High-resolution ADF-STEM image of the area shown under blue box in c. h, i Time-lapse ADF-STEM image of the edge at t = 0 s and t = 30 s of electron beam exposure. The red arrow indicates the ejection of the electrons from the edges due to the damage from the electron beam, leading to ‘unzipping’ of the chain, maintaining the zigzag edge of the flakes. j–l Time-lapse series of ADF-STEM images recorded after 1 min of electron beam exposure. The yellow annotations show the edge-terminated bonds at the edge at t = 0 s, which starts reconstructing in k, annotated with blue. After 2 min, (l) the edge was fully reconstructed, as shown with growing blue annotated region. The scale bars in h–l correspond to 1 nm.