Fig. 1: Cross-sectional Transmission Electron Microscopy (TEM) analysis of monoclinic CrI₃ with rhombohedral-type stacking faults.

a Schematic of cross-sectional TEM samples showing the graphite-encapsulated CrI₃ crystal on a Si/SiO₂ substrate. b Experimental selected area electron diffraction (SAED) along [010] crystal zone axis. Some diffraction signals are labeled with a parallelogram overlay. c, d Simulated SAED pattern (top) and side-view (bottom) of monoclinic and rhombohedral phase stacking of CrI₃, respectively. e High-Angle Annular Dark-Field Scanning Transmission Electron Microscopy (HAADF-STEM) image of cross-sectional CrI₃ sample. The inset shows the fast Fourier transform of the image. The orange arrows indicate the interlayer shift with a scheme of the atomic configuration included for clarification. f Zoomed-in STEM image (left) and elemental mapping (right) of Cr (green) and I (red) with Energy-Dispersive X-ray Spectroscopy (EDX). g Zoomed-in SAED with indexed diffraction signals. h Exemplary HAADF-STEM image of CrI₃ with a rhombohedral-type (R-type) stacking fault with layers labeled through 1–4 for guidance. The red dashed box indicates the R-type stacking fault, and the orientation of the arrows is used to highlight the change in stacking order throughout the layers. i Top-view atomic model showing the honeycomb configuration of the Cr atoms at layers 1-4 in (h) with an inserted R-type fault in monoclinic CrI₃. Cr atoms are colored following those at (h).