Quantum confinement in few layer SnS nanosheets.

Orthorhombic tin monosulfide (SnS) consists of layers of covalently bound Sn and S atoms held together by weak van der Waals forces and is a stable two-dimensional material with potentially useful properties in emerging applications such as valleytronics. Large-scale sustainable synthesis of few-layer (e.g., 1-10 layers) SnS is a challenge, which also slows progress in understanding their properties as a function of number of layers. Herein we describe solvothermal synthesis of SnS in water or ethylene glycol. The latter yields a flower-like morphology where the petals are SnS nanoplates and sonication and separation of these flowers via differential centrifugation yields 1-10 layer SnS nanoplates. The direct optical absorption edges of these SnS nanoplates blue-shift due to quantum confinement from 1.33 to 1.88 eV as the thickness (number of layers) is decreased from ∼5 nm (10 layers) to ∼2 nm (4 layers).