Selective Growth of Ferroelectric Ultrathin Nonlayered γ‐In 2 Se 3

Abstract Indium selenide (In 2 Se 3 ) has received increasing interest due to its diverse polytypes and associated polytype‐dependent ferroelectric properties, making it one of the promising platforms guiding the development of ultrathin ferroelectric nanodevices. To date, α‐, β‐, and β'‐phase In 2 Se 3 have been well studied, but nonlayered γ‐In 2 Se 3 remains underexplored because of sophisticated formation paths and minor energy differences with other phases. Therefore, understanding the growth mechanisms and electronic structures of γ‐In 2 Se 3 is crucial to present the full roadmap of the In x Se y family. Herein, a precursor‐guided chemical vapor deposition (CVD) method is proposed to selectively grow ultrathin γ‐In 2 Se 3 crystals with a nonlayered, vacancy‐ordered screw form (VOSF) structure. The sublimation temperature of precursors plays a critical role in selectively synthesizing α‐, β‐, and γ‐phase In 2 Se 3 using different precursors (In 2 Se 3 , In 2 O 3 , InCl 3 ). Ex situ scanning transmission electron microscopy (STEM) reveals a γ‐In 2 Se 3 ‐to‐InSe phase transition at 600 °C, consecutively triggered by interlayer bonds broken, vacancy reorganization and removal of Se atoms. Away from existing literature, only out‐of‐plane ferroelectricity in γ‐In 2 Se 3 , driven by vertical off‐center displacements of Se atoms, is detected. Therefore, a full spectrum of In 2 Se 3 ’s polytypes, particularly nonlayered ferroelectric γ‐In 2 Se 3 , is selectively obtained, presenting great potential for next‐generation In 2 Se 3 ‐based polytypes‐dependent nanoelectromechanical and memory devices.