The emerging two-dimensional (2D) platinum disulfide (PtS₂) has driven increasing attentions due to its high electron mobility, good air-stability, and strong interlayer interaction which leads to a widely tunable electronic structure. However, a detailed study on its covalent-like layer-dependent properties remains infant. Herein, we demonstrate the successful production of ultrathin 1T-PtS₂ ribbons with thickness centralized almost at monolayer 1L–4L and large domain size up to 210 µm on Au foils using chemical vapor deposition (CVD) technique, which enables macro- and microscopic study of its extraordinary layer-dependent features with precise control of the number of layers. Using electron energy loss spectroscopy (EELS) and optical pump-probe spectroscopy (OPPS), we reveal that both the electron and ultrafast optical absorption signals of the as-grown 2D PtS₂ show strong nonlinear layer-dependent responses which manifest discriminated transition in 1L–4L PtS₂ ribbons. The layer-dependent nonlinear response of 2D PtS₂ can be well interpreted in the frame of calculated electron and phonon structures. These achievements offer a platform for successfully fabricating large-sized ultrathin 2D PtS₂ and facilitating our knowledge about its electronic and optoelectronic properties.

Owing to its anisotropic optical and electrical properties, rhenium diselenide (ReSe₂) has garnered considerable attention recently as a candidate material for polarization-sensitive photodetectors. However, the direct and controllable synthesis of large-sized ReSe₂ with a uniform thickness is still a great challenge. Herein, we have refined the synthesis method to obtain uniform monolayer ReSe₂ flakes with a size of up to ~ 106 μm on sapphire via an ambient-pressure chemical vapor deposition technique using Na promoter from sodium chloride. Interestingly, optical pump-probe spectroscopy revealed a fast switching from saturable absorption (SA) to absorption enhancement (AE) in subpicosecond time scale, followed by a slower decay induced by exciton recombination. Furthermore, both AE and SA signals exhibited clear angular dependence with a periodicity of 180°, which reflected the dichroism in nonlinear absorption dynamics. In addition, the photocarrier dynamics including free-carrier transport and subpicosecond relaxation due to exciton formation or surface trapping was probed using time resolved terahertz spectroscopy. We believe that our study serves as a reference for atomically controlled synthesis of large-sized ReSe₂ and provides useful insights on its optoelectronic properties for novel device applications.