Rapid and reliable thickness identification of two-dimensional nanosheets using optical microscopy

The physical and electronic properties of ultrathin two-dimensional (2D) layered nanomaterials are highly related to their thickness. Therefore, the rapid and accurate identification of single-and few-to multilayer nanosheets is essential to their fundamental study and practical applications. Here, a universal optical method has been developed for simple, rapid, and reliable identification of single-to quindecuple-layer (1L-15L) 2D nanosheets, including graphene, MoS₂, WSe₂, and TaS₂, on Si substrates coated with 90 or 300 nm SiO₂. The optical contrast differences between the substrates and 2D nanosheets with different layer numbers were collected and tabulated, serving as a standard reference, from which the layer number of a given nanosheet can be readily and reliably determined without using complex calculation or expensive instrument. Our general optical identification method will facilitate the thickness-dependent study of various 2D nanomaterials and expedite their research toward practical applications.