Layer-Dependent Band Structure of Ternary Metal Chalcogenides: Thickness-Controlled Hexagonal FeIn₂S₄

Two-dimensional (2D) transition metal dichalcogenides have received considerable attention due to their exotic electrical, chemical, and physical properties. Here, we report a layer-dependent band structure of a 2D semiconducting ternary metal chalcogenide (TMC), hexagonal FeIn2S4 (hFIS), which is prepared through thickness-controlled colloidal solution synthesis. The controlled dissociation rate of chalcogen precursors caused the growth of the different thicknesses of hFIS, which is coincident with mechanisms established in conventional 2D nanomaterial colloidal synthesis. The various thickness-dependent band structures of hFIS were investigated from the corresponding optical band gap and redox potentials. The unveiled layer-dependent band structure of hFIS showed band gaps of approximately 1.02, 1.26, and 1.52 eV, corresponding to synthesis of the 7–8, 5–6, and 2–3 layers, respectively. This study will contribute to the exploration of other layer-dependent TMCs (MIn2X4, M = Fe, Co, Mn, and Zn and X = S, Se, and Te) for new optical and electronic device applications.