Size-dependent nonlinear optical properties of atomically thin PtS₂ nanosheet

To manipulate the nonlinear optical absorption (NOA) properties of layered two dimensional (2D) materials by simple and cost-effective methods is an attractive research topic as the NOA properties can be further optimized for various potential applications, such as compact optical switchers, pulsed laser generation, optical limiters, and biosensors. In this work, the NOA response of the novel group 10 transition metal dichalcogenide (TMD), platinum disulfide (PtS₂) is investigated with respect to different PtS₂ flakes size and thickness for the first time. Four PtS₂- NMP suspensions with modified size and thickness distribution were successfully fabricated. The average flake size and thickness ranged from about 565 nm to 110 nm and 30 nm–10 nm, respectively. Z-scan measurement shows that the NOA response of PtS₂ depends heavily on the flake size and thickness. As the layer thickness and lateral size of the PtS₂ nanosheets reduced, the widened bandgap and increased active nanosheet edges will facilitate the photon absorption and lead to an enhancement of the RSA effect. However, sustained elevation of the RSA effect will reach a saturation threshold, and the RSA response will become weaker afterwards. A variation of the NOA performance from an initial weakening of RSA response, and followed by switching to saturable absorption (SA) is observed in the Z-scan test as the flake size and thickness become lower from S3000 to S9000 PtS₂ samples. This work has demonstrated a significant modification of NOA properties of the PtS₂, which can further be utilized in various applications.