Scanning Microwave Microscopy of Polarization Domain Boundaries in 2D SnSe

Scanning microwave microscopy (SMM) allows for nanoscale characterization of in-plane polarization domains in 2D atomic-layered SnSe. Previous SMM studies found significantly higher conductivity at domain boundaries than in the domain interior. Here, we successfully use SMM to distinguish 90 degrees and 180 degrees domain boundaries not revealed by polarized optical microscopy or atomic force microscopy. Quantitative analysis results in significantly higher conductivity in 180 degrees domain boundaries than in 90 degrees domain boundaries and, in turn, inside domains. We attribute the enhanced conductivity to polarization-induced two-dimensional electron or hole gas similar to that in GaN high-electron mobility transistors. This work demonstrates SMM's efficacy for non-destructive, in situ monitoring of 2D materials and devices.