LAUSR

Indium selenide (In2Se3) 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 In2Se3 have been well studied, but nonlayered γ-In2Se3 remains underexplored because of sophisticated formation paths and minor energy differences with other phases. Therefore, understanding the growth mechanisms and electronic structures of γ-In2Se3 is crucial to present the full roadmap of the InxSey family. Herein, a precursor-guided chemical vapor deposition (CVD) method is proposed to selectively grow ultrathin γ-In2Se3 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 In2Se3 using different precursors (In2Se3, In2O3, InCl3). Ex situ scanning transmission electron microscopy (STEM) reveals a γ-In2Se3-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-In2Se3, driven by vertical off-center displacements of Se atoms, is detected. Therefore, a full spectrum of In2Se3's polytypes, particularly nonlayered ferroelectric γ-In2Se3, is selectively obtained, presenting great potential for next-generation In2Se3-based polytypes-dependent nanoelectromechanical and memory devices.