Fig. 6. Surface wrinkles across 120° DWs owing to the 3D stacking in 3R β’-In₂Se₃.

a, b Atomic-resolution cross-sectional STEM images with the structure models overlaid, and polarized-light images showing multidomain patterns, with AFM topographic images taken from the highlighted regions, for 2H (a) and 3R (b) β’-In₂Se₃ crystals. 3R β’-In₂Se₃ displays a majority of 60° DWs and minor 120° DWs, with surfaces wrinkles across 120° DWs as revealed by the surface profile in the lower-left inset. In contrast, 60° DWs in the same region have the flat surface. c Schematic drawing of the 120° domain pattern in 3R β’-In₂Se₃, showing surface wrinkles across 120° DWs with a 2.50° out-of-plane (OOP) mosaic tilt. The associated in-plane (IP) tilt is ~0.97° (see Supplementary Fig. 8). The IP strain is indicated by double-headed arrows and the shear strain by single-headed arrows. d Reciprocal space map with 2θ/ω scan around (0 0 0 15) reflections. The two reflections indicate the OOP mosaic tilt due to the shear strain illustrated in c. The directions of the shear strain with respect to the IP strain are indicated in the lower left inset by single-headed arrows.