title: Tuning nonlinear optical absorption properties of WS₂ nanosheets.
abstract: To control the optical properties of two-dimensional (2D) materials is a long-standing goal, being of both fundamental and technological significance. Tuning nonlinear optical absorption (NOA) properties of 2D transition metal dichalcogenides in a cost effective way has emerged as an important research topic because of its possibility to custom design NOA properties, implying enormous applications including optical computers, communications, bioimaging, and so on. In this study, WS2 with different size and thickness distributions was fabricated. The results demonstrate that both NOA onset threshold, F(ON), and optical limiting threshold, F(OL), of WS2 under the excitation of a nanosecond pulsed laser can be tuned over a wide range by controlling its size and thickness. The F(ON) and F(OL) show a rapid decline with the decrease of size and thickness. Due to the edge and quantum confinement effect, WS2 quantum dots (2.35 nm) exhibit the lowest F(ON) (0.01 J cm(-2)) and F(OL) (0.062 J cm(-2)) among all the samples, which are comparable to the lowest threshold achieved in graphene based materials, showing great potential as NOA materials with tunable properties.
authors.affiliation: Department of Applied Physics and Materials Research Center, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China. yuen.tsang@polyu.edu.hk.
authors.forename: Hui
authors.initials: H
authors.lastname: Long
authors.forename: Lili
authors.initials: L
authors.lastname: Tao
authors.forename: Chun Yin
authors.initials: CY
authors.lastname: Tang
authors.forename: Bo
authors.initials: B
authors.lastname: Zhou
authors.forename: Yuda
authors.initials: Y
authors.lastname: Zhao
authors.forename: Longhui
authors.initials: L
authors.lastname: Zeng
authors.forename: Siu Fung
authors.initials: SF
authors.lastname: Yu
authors.forename: Shu Ping
authors.initials: SP
authors.lastname: Lau
authors.forename: Yang
authors.initials: Y
authors.lastname: Chai
authors.forename: Yuen Hong
authors.initials: YH
authors.lastname: Tsang