Fig. 1: Reflection contrast imaging of ferroelectric domains in few-layer 3R-MoS₂.

a Optical micrograph of a 3R-MoS₂ flake on Si/SiO₂/hBN. Topographical steps and edges of the bottom hBN have been marked by white dotted lines. b Surface potential map within the area enclosed by the black rectangle in (a). Two domains, marked by ∘ and □, can be identified by the difference in contrast. c. Integrated intensity map of ΔR/R at the X_A spectral region, i.e., from 1906 to 1918 meV (gray bar in inset of d). d Low-temperature reflectance contrast spectra from various spatial locations marked by symbols of corresponding color in c (black - 5L domain I, red - 5L domain II, and blue - 7L). Inset shows high-resolution spectra collected from domain I and II. e, f Two crystal configurations of 5L 3R-MoS₂ overlayed on layer-projected K_{V B} and K_CB band-edges. To first order, the band edge variation along Z and the degeneracies, highlighted for the XM-XM-MX-XM stacking by dotted lines, result from the ferroelectricity-induced electrostatic considerations (SI Figs. S12, 13 for other configurations). Arrows represent polarization vectors at the interfaces.