Figure 2: HAADF-STEM imaging of franckeite.
From: Exfoliation of natural van der Waals heterostructures to a single unit cell thickness
(a) High-resolution image of the crystal lattice viewed along the [001] direction (plan view of the basal plane). The scale bar corresponds to 1 nm. (b) Cross-sectional image of the layering viewed along the [100] direction. The scale bar corresponds to 5 nm. (c) Corresponding EDXS elemental intensity maps with the two-axis scale bar corresponding to 1 nm. (d) Proposed structure model of franckeite, with the relative size of atoms corresponding to their brightness in HAADF. (e) Atomic-resolution image of the cross-section for a few-layer crystal. The inset shows overlaid franckeite structure, the scale bar corresponds to 1 nm. (f) Corresponding EDXS concentration profiles showing compositional variation both between and within the individual layers. In contrast, no compositional variations are detected for the crystal viewed along the [001] direction. The pink dashed lines are a guide for the eye correlating the EDXS profile with the cross-sectional HAADF. The grey solid lines are a guide for the eye correlating the concentration peaks (Pb and Sn) and troughs (S).
