제목: Ab initio Study of Growth and Electronic Structure of 2D Materials: Graphene, h-BN, and TMDs
연사: 홍석륜 교수( 세종대 물리학과 )
초록: Two-dimensional (2D) materials such as graphene, hexagonal boron nitride (h-BN), transition metal dichalcogenides (TMDs) have attractive physical and chemical properties in relation to the application of nanodevices. To understand the growth and electronic structure of these 2D materials, we have performed density functional theory calculations.
First, to understand the growth of graphene in its initial stage on the oxide substrates, we investigate binding behaviors of carbon atoms on the substrates. Noticeably, at least one carbon atom of the carbon structure binds to an oxygen atom of the surfaces due to strong C-O binding. 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. We also study the edge-functionalization of armchair graphene nanoribbons (AGNRs) with pentagonal-hexagonal edge structures. The edge-functionalized (5,6)-AGNRs with some substitutional atoms opens a band gap, similarly to the defect-free AGNRs. The overall electronic structures of edge-functionalized (5,6)-AGNRs depend on the number of electrons at edges, supplied by substitutional atoms.
Next, we investigate vacancy structures with triangular shape to understand their formation and growth in single 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. We also study the intercalation between zigzag GNR (ZGNR) and h-BN sheet to find its effect on electronic properties of the ZGNR/h-BN heterostructure. The intercalated impurity atoms are more stable at the edge than in the middle region. Especially, the nickel atom has the smallest energy difference between two embedding positions, which means that the Ni atom is relatively easy to intercalate in the structure.
Finally, we investigate the reduction of the Fermi level pinning (FLP) occurring at metal-TMD interfaces by atomic passivation on the metal surface. Passivating atoms prevent the direct contact between Au(111) and MoS2, and thus FLP at Au-MoS2 interfaces is reduced by weak interaction between atom-passivated Au(111) and MoS2. FLP is greatly reduced at sulfur-passivated Au-MoS2 interfaces with the smallest binding energy. Furthermore, fluorine-passivated Au(111) can form ohmic contact with MoS2, representing almost zero Schottky barrier height (SBH). We suggest that SBH can be controlled depending on the passivating atoms on Au(111).
일시 및 장소: 2017년 5월 11일(목) 오후 4시 30분, 베어드홀 103호