Fig. 1: The crystal structure and characterization of γ-GaSe.
From: Emergence of ferroelectricity in a nonferroelectric monolayer
a Schematic top and side view of the γ-GaSe structure. The orange and green spheres refer to the Ga atoms and Se atoms, respectively. The orange rhombus shadow indicates a primitive cell in the top view. Each quadruple layer (QL) contains four atomic layers in the order of Se-Ga-Ga-Se layers, and three QLs form a unit cell (dashed rectangle). b Raman spectrum of γ-GaSe nanoflake. c XRD pattern of the γ-GaSe crystal (upper panel) and the corresponding XRD standard card (lower panel, PDF#65-2112). d, e XPS spectrum of Ga 3d and Se 3d core orbital peaks took on the γ-GaSe nanoflake, respectively. The small circles represent the fitting result of the experimental data (red curves), decomposed into doublet peaks (olive and blue curves).
