Growth of Large‐Sized 2D Ultrathin SnSe Crystals with In‐Plane Ferroelectricity

Tin (II) selenide (SnSe) is an emerging 2D material with many intriguing properties, such as record-high thermoelectric figure of merit (ZT), purely in-plane ferroelectricity, and excellent nonlinear optical properties. To explore these functional properties related applications, a crucial step to develop controllable routes synthesize large-area, ultrathin, high-quality SnSe crystals. Physical vapor deposition (PVD) constitutes reliable method SnSe, however, effects various growth parameters have not yet been systematically investigated, current PVD-synthesized flakes are often thick (>10 nm) small lateral sizes (<10 µm). In this work, crystals synthesized via low-pressure PVD, which display ferroelectric domains observed by piezoresponse force microscopy polarization-dependent reflection spectroscopy. Detailed studies regarding the roles further carried out, including substrate pre-annealing, duration, temperature, pressure, enable rationally optimize obtain up ≈23.0 µm thicknesses down ≈2.0 nm (3–4 layers). This work paves way for controlled large-area facilitating future exploration interesting multiferroic applications atomic thickness.