报告摘要：
     The edges of layered materials have unique properties that substantially differ from the body regions. In this work, we perform a systematic Raman study of the edges of various layered materials (MoS2, WS2, WSe2, PtS2, and black phosphorus). The Raman spectra of the edges feature newly observed forbidden Raman modes, which are originally undetectable from the body region. By selecting the edge type and the polarization directions of the incident and scattered light, all forbidden Raman modes are distinctly detected. Optical simulations show that the edges of layered materials drastically distort the electromagnetic fields of both the incident and scattered light, so that the light interacts with the edges in a distinct way, which differs from its interactions with the body regions. We expect this work to contribute to a comprehensive understanding of the Raman spectroscopy of layered materials and to facilitate future exploration of the optical properties of edges. [1]
    The crystal structure and physical properties of two-dimensional transition metal dichalocogenides (TMDs) are substantially dependent on the filling of d orbitals of transition metal. Group-10 TMDs have been revealed with widely tunable bandgap, high mobility and good stability. We demonstrate layer-dependent semiconductor-to-semimetal evolution of 2D PtSe2. Few-layer PtSe2 field-effect transistor shows high room-temperature mobility (~210 cm2V-1s-1) in a back-gated configuration on SiO2/Si, comparable to that of BP. Bulk PtSe2 device exhibits the metallic-like conductivity (6.64×105 S/m). The characteristics of widely tunable bandgap of PtSe2 allows it to be effectively response to near-infrared light. Furthermore, our results showed that PtSe2 has much better air-stability (over 1 year) than BP. [2]-[3]

[1] Science Advances, 2018, 2018, 4, eaau6252
[2] Advanced Materials, 2016, 28(12), 2399-2407.

[3] Advanced Materials, 2017, 29, 1604230

报告人简历：
Dr. Yang Chai is an Associate Professor at the Hong Kong Polytechnic University. He is the vice president of Physical Society of Hong Kong, and the Chair of IEEE ED/SSC Hong Kong Chapter. He joined the Department of Applied Physics in the Hong Kong Polytechnic University in 2012. He is a recipient of RGC Early Career Award in 2014, the IEEE Distinguished Lecturer since 2016, and the Semiconductor Science and Technology Early Career Research Award in 2017. His current research interest includes low-dimensional material for electron devices.

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