Research Article Issue
Nonlinear electronic and ultrafast optical signatures in chemical vapor-deposited ultrathin PtS2 ribbons
Nano Research 2022, 15 (5): 4366-4373
Published: 24 February 2022

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.

Research Article Issue
Salt-assisted growth and ultrafast photocarrier dynamics of large-sized monolayer ReSe2
Nano Research 2020, 13 (3): 667-675
Published: 12 February 2020

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.

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