Fig. 1: Out-of-plane vacancy-defect gradient visualized by electron ptychography.

a Schematic illustration of the multislice electron ptychography for depth sectioning of a PtTe₂ sample. During ptychographic reconstruction, the sample is divided into 15 slices and each slice is ~2 nm in thickness. b, c The summed phase images of [001] PtTe₂ over 15 slices taken from orange, blue, gray, and green rectangles of Supplementary Fig. 8c, respectively. The scale bar is 5 Å. The yellow arrows marked in c denote the V_Te due to a relatively weak mapping intensity. d The corresponding profiles of phase intensity taken from atomic columns marked with blue, gray and green rectangles in c respectively. e Te phase mapping in the selected 29-layer PtTe₂ film from near the substrate to near the top surface. Light and dark colors denote the low and high V_Te concentration, respectively. The light/dark distinction of mapping results indicates the inhomogeneous distribution of V_Te. The colorbar denotes the Te phase intensity with the unit of rad. The substrate is schematically shown. The scale bar is 1 nm. f The relative phase intensity variation of the Te/Pt in each PtTe₂ layer, which is extracted from Supplementary Fig. 11. The intensity is normalized by the maximum intensity. The error bars are generated from the standard deviations of the Te/Pt ratio.