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PhD Thesis Presentation
Electrical and Optical Characterizations of Atomically-Thin Layered Materials
Speaker Mr Gen Long
Department of Physics, The Hong Kong University of Science and Technology
Date 17 January 2018 (Wednesday)
Time 14:00
Venue Room 4472 (Lifts 25-26), HKUST

Systematic studies are performed to explore the electronic, optical, and magnetic features of three 2D materials, namely, black phosphorus (BP), graphene, and manganese thiophosphite.

Charge density wave phase transition is demonstrated on the surface of electrostatically doped multilayer graphene when the Fermi level approaches the M points in the first Brillouin zone of graphene band structure. Ionic liquid gating technique is applied to tune the Fermi surface to M points because of the ultrahigh efficiency to induce charge carriers. The occurrence of charge density wave phase transition is demonstrated by electronic transport and optical measurements in electrostatically doped multilayer graphene.

A four-step strategy is performed to access the quantum Hall regime in BP. The charge carrier scattering mechanism is first explored. The localization effects from the charged impurities hinder the high charge carrier mobility. Then, a new device fabrication process is developed by protecting BP flakes with hexagonal boron nitride under vacuum. The polarities of BP conducting channels are controlled by contact metals engineering. High-quality ambipolar devices are achieved in BP 2D system. Finally, ambipolar quantum Hall effect is observed in BP. Critical parameters, such as effective mass, Lande g-factor, spin-susceptibility, and quantum life time, are extracted. Specifically, an asymmetric transport behavior is observed between spin-up and spin-down charge carriers in BP.

A systematic experimental study on an antiferromagnetic honeycomb lattice of MnPS3 is performed. The crystal structure of MnPS3 is identified by high-resolution scanning transmission electron microscopy. Layer-dependent angle-resolved polarized Raman fingerprints of the MnPS3 crystal are obtained. Temperature dependences of anisotropic magnetic susceptibility of MnPS3 crystal are measured in superconducting quantum interference device. Magnetic parameters, such as effective magnetic moment, are extracted from the mean field approximation model.