Liquid Exfoliation Few-Layer SnSe Nanosheets with Tunable Band Gap

Two-dimensional (2D) materials have recently drawn tremendous attention because of their novel properties and potential applications in high-speed transistors, solar cells, and catalysts. Few-layer SnSe is a new member of the 2D family with excellent performance in optoelectronic and thermoelectric devices. It is necessary to synthesize few-layer SnSe nanosheets in large scale for various applications. In this work, we develop a scalable liquid-phase exfoliation method to synthesize high-quality crystalline SnSe nanosheets. The morphology and microstructure of SnSe nanosheets are systematically investigated with high-resolution transmission electron microscopy, atomic force microscopy, and Raman spectroscopy. The thinnest nanosheets are bilayered. The optical absorption properties of SnSe nanosheets from near-infrared to ultraviolet light are studied. It is worth noting that the band gap of the nanosheets monotonically increases with the reduction of the nanosheet thickness. The electronic structure of SnSe nanosheets with various thicknesses is calculated by first-principles calculations, the evolution of the band gap as a function of the nanosheet thickness is confirmed, and the mechanism of the band gap evolution is discussed. Our work paves the way for the scalable synthesis of 2D SnSe with tunable optical absorption and band gap, which has potential for use in photoelectronic and photocatalytic applications.