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MPhil Thesis Presentation 
Fabrication of BN Encapsulated FET Devices Using Atomically Thin 2D Materials
Speaker Mr Yuanwei Wang
Department of Physics, The Hong Kong University of Science and Technology
Date 24 July 2017 (Monday)
Time 16:00 - 17:00
Venue Room 4475 (Lifts 25-26), HKUST
In recent years atomically thin 2D materials like graphene, boron nitride (BN), transition metal dichalcogenides (TMDC) or black phosphorus (BP) have drawn a lot of attention because of their marvelous properties. In this thesis, variety of different two dimensional devices were fabricated and measured to explore their properties of these materials. And the production methods of these devices were also detailedly described and throughly discussed.
Several high quality black phosphorus samples encapsulated with boron nitride thin films were successfully fabricated. An additional strong Raman peak around 5cm􀀀1 above the A1 g mode in the Raman spectrums were observed and investigated. It was believed that this was caused by the strong inter-layer coupling in BP samples, which also result in its surface atoms to vibrate at a higher frequency than the atoms in its inner layers. And because in my samples, the BP flakes are sandwiched by atomically smooth BN films, and without interference of exposure to the environment, such signal was able to be pick up and recored for the first time. The transport property of monolayer Rhenium Diselenide (ReSe2) were also measured at different temperature with a few devices assembled with van derWaals heterostructure. Because most of time ordinary metals contact with ReSe2 will result in a huge Schottky barrier that makes low temperature measurement almost impossible. So in this work few layer graphene flakes were used for contact instead. With its tunable Fermi level and high carrier concentration, such gate-tunable graphene electrodes can greatly reduced the Schottky barrier height in theory. And experimental data has confirmed this presumption. The devices have showed a record high mobility reading at low temperature. More importantly, such method could also be used in other 2D materials’ low temperature characterization. An important implications for future works and applications.