Tuning the Bandgap of Exfoliated InSe Nanosheets by Quantum Confinement

Strong quantization effects and tuneable near-infrared photoluminescence emission are reported in mechanically exfoliated crystals of γ-rhombohedral semiconducting InSe. The optical properties of InSe nanosheets differ qualitatively from those reported recently for exfoliated transition metal dichalcogenides and indicate a crossover from a direct to an indirect band gap semiconductor when the InSe flake thickness is reduced to a few nanometers. The discovery of single-atomic layer graphene1 has led to a surge of interest in other anisotropic crystals with strong in-plane bonds and weak, van der Waals-like, inter-layer coup­ling.2 A variety of two-dimensional (2D) crystals with high crystalline quality and…