Imaging the polarization state in few-layer 3R-MoS₂ with Kelvin Probe Force Microscopy

Recently, rhombohedral-stacked (R-stacked) transition metal dichalcogenides (TMDs) have attracted much attention due to the novel ferroelectricity phenomenon occurring at their interfaces which can potentially be used in memory and optoelectronic devices. Since the spontaneous polarization direction is governed by stacking orders, a bilayer R-stacked TMD can be switched between two opposite polarization states. On the other hand, the polarization state in a thicker flake can be interesting as more than one interface is involved. Here we probe the polarization state by imaging the surface potential in few-layer 3R-MoS₂ flakes with Kelvin Probe Force Microscopy (KPFM). We find that multiple polarization states induced by different stacking configurations can coexist in a flake. Furthermore, the substrate doping can contribute to distinguishing those ideally degenerate polarization states. In all, our results reveal the stacking disorder in few-layer R-stacked MoS₂ flakes.