Two-dimensional (2D) van der Waals semiconductors such as monolayer MoS2 and WSe2 are an attractive building block for novel photonic devices due to their strongly excitonic character. Monolayer transition metal dichalcogenides exhibit strong excitonic absorption due to band nesting  and allow exploration of hybrid quasi-particle states such as plexcitons  through strong dipole-dipole coupling . The first part of this talk will focus on their approaches to realizing electrical generation, manipulation, and detection of excitons and their complexes based on various van der Waal heterostructures. Specifically, he will discuss how MIS-type heterostructures allow electrically tunable excitonic electroluminescence  and electro-optic upconversion in linear optics regime. They demonstrate that hexagonal boron nitride can serve as a unipolar tunnel barrier that allows hot carrier injection and energy harvesting. Their results reveal that interlayer charge transfer dynamics is tunable with electrical bias and competes with thermalization of hot photocarriers leading to distinct optoelectronic response at high photon energy excitation. The second part will discuss their recent discovery of a novel monolayer MoS2 growth mechanism based on vapor-liquid-solid conversion . They show that alkali metal plays a key role in reducing the melting point of the precursors and triggering the vapor-liquid-solid mode, yielding epitaxial growth of monolayer nanoribbons.
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- W. Zhao et al. “Exciton-plasmon coupling and electromagnetically induced transparency in monolayer semiconductors hybridized with Ag nanoparticles” Adv. Mater. 28, 2709 (2016).
- D. Kozawa et al. “Efficient interlayer energy transfer via 2D dipole coupling in MoSe2/WS2 heterostructures” Nano Lett. 16, 4087 (2016).
- S. Wang et al. “Efficient carrier-to-exciton conversion in field emission tunnel diodes based on MIS-type van der Waals heterostack” Nano Lett. 17, 5156 (2017).
- S. Li, et al. “Vapor-liquid-solid growth of monolayer MoS2 nanoribbons” Nat. Mater. 17, 535 (2018).
Dr. Eda received his M.Sc. in Materials Science and Engineering from Worcester Polytechnic Institute in 2006 and Ph.D. in the same discipline from Rutgers University in 2009. He became a Newton International Fellow of the Royal Society of the UK and worked at Imperial College London. Dr. Eda joined the National University of Singapore as an Assistant Professor of Physics and Chemistry, and a member of the Centre for Advanced 2D Materials (CA2DM) in 2011. He is a recipient of the Singapore National Research Foundation (NRF) Research Fellowship and many awards including the Singapore National Academy of Science (SNAS) Young Scientist Award, University Young Researcher Award, and IPS Omicron Nanotechnology Award. He is an Associate Editor of npj 2D Materials and Applications. He also formerly served as an Editorial Board Member for Scientific Reports. Dr. Eda investigates a wide range of condensed matter physical properties of two-dimensional (2D) materials. His research focuses on the extraordinary photophysical properties of atomically thin van der Waals compounds and their potential applications in novel photonic devices. He has co-authored > 100 peer-reviewed papers including 7 invited review/perspective articles and a book chapter. His work has been cited over 29,000 times (h-index of 51) as of Jan 2019.