Layer Dependent Ferroelectricity and Electromechanically Coupled Polarization in Two-Dimensional 1T'-ReS2.

Two-dimensional (2D) van der Waals (vdW) materials with sliding ferroelectricity exhibit an enormous potential for next-generation nanodevices. Among these, 1T'-ReS2 with an ultralow symmetry stands out as a pivotal candidate. However, the fundamental scientific mechanism underlying sliding ferroelectricity in 1T'-ReS2 remains poorly understood due to the complexity of its crystal structure. By integrating STEM, DFT calculations, and KPFM, this work resolves the correlation between AA/AB stacking and polarization in 1T'-ReS2. PFM and STEM characterizations further reveal that the observed ferroelectric-like PFM signals originate from flexoelectric-like wrinkles rather than from intrinsic ferroelectric switching. Finally, device measurements provide evidence of sliding ferroelectricity in even-layer AB-stacked ReS2 and demonstrate its application potential.