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Special CAMP: Study of Growth and Electronic Structure of 2D Materials

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Suklyun Hong, Sejong University, Seoul, South Korea
30 June 2015 from 3:30 PM to 4:30 PM
339 Davey Laboratory
Contact Name
Jorge Sofo
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Two-dimensional (2D) materials such as graphene, hexagonal boron nitride (h-BN), and transition metal dichalcogenides (TMDs) have attractive physical properties in relation to the application of nanodevices. To understand the growth and electronic structure of those 2D materials, we have performed density functional theory calculations.

First, to understand the growth of graphene in its initial stage on the oxide substrates such as sapphire and magnesium oxide, we investigate binding behaviors of carbon atoms on the oxide surfaces. Carbon atoms form chain-like or distorted graphene-like structures on the surfaces because of the strong binding between carbon atoms. Noticeably, at least one carbon atom of the carbon structure binds to an oxygen atom of the surfaces due to strong binding between carbon and oxygen atoms. These theoretical results combined with the experimental ones may imply that carbon atoms on the oxide substrates form the nanocrystalline graphite structure rather than a perfect graphene, within a limited area.

Next, we investigate adsorption behaviors of h-BN flakes on the copper surface to study the initial stage of growth by the chemical vapor deposition method. By increasing the number of adsorbed B and N atoms, we study formation behaviors of the BN flakes with triangular, linear, and hexagonal shapes on the copper surface. We find that the formation of BN flake in a triangular shape is most favorable on the surface. On the other hand, we investigate several defect structures with triangular shape to understand the formation and growth of defects in single h-BN sheet because researchers observed atomic defect structures with triangle shape in a free-standing h-BN sheet. We find that the defects with nitrogen-terminated zigzag-type edges are most stable and maintain their shapes when the defects grow in the sheet.

Then, we study electronic properties of molybdenum disulfide (MoS2) nanostructures with adsorbed atoms and molecules due to possible applications of gas sensors or detectors. Contrary to the case of 2D MoS2 monolayer surface, some molecules such as CO, NO, and O2 are bound well to the edges of armchair MoS2 nanoribbons. We find that the adsorption states make the band gap narrower. Finally, the formation of carbon-based composites is discussed in relation to available experiments.