title: Size-dependent nonlinear optical properties of atomically thin transition metal dichalcogenide nanosheets.
abstract: Size-dependent nonlinear optical properties of modification-free transition metal dichalcogenide (TMD) nanosheets are reported, including MoS2 , WS2 , and NbSe2 . Firstly, a gradient centrifugation method is demonstrated to separate the TMD nanosheets into different sizes. The successful size separation allows the study of size-dependent nonlinear optical properties of nanoscale TMD materials for the first time. Z-scan measurements indicate that the dispersion of MoS2 and WS2 nanosheets that are 50-60 nm thick leads to reverse saturable absorption (RSA), which is in contrast to the saturable absorption (SA) seen in the thicker samples. Moreover, the NbSe2 nanosheets show no size-dependent effects because of their metallic nature. The mechanism behind the size-dependent nonlinear optical properties of the semiconductive TMD nanosheets is revealed by transient transmission spectra measurements.
authors.affiliation: State Key Laboratory of Applied Organic Chemistry, College of Chemistry and Chemical Engineering, Key Laboratory of Special Function Materials and Structure Design, Ministry of Education, Lanzhou University, Lanzhou, 730000, P.R. China.
authors.forename: Kai-Ge
authors.initials: KG
authors.lastname: Zhou
authors.forename: Min
authors.initials: M
authors.lastname: Zhao
authors.forename: Meng-Jie
authors.initials: MJ
authors.lastname: Chang
authors.forename: Qiang
authors.initials: Q
authors.lastname: Wang
authors.forename: Xin-Zhi
authors.initials: XZ
authors.lastname: Wu
authors.forename: Yinglin
authors.initials: Y
authors.lastname: Song
authors.forename: Hao-Li
authors.initials: HL
authors.lastname: Zhang
keywords: layered materials; liquid-phase separation; nonlinear optical materials; structure-property relationships; thin films