Topic:Electronic Structure of Atomically Precise Graphene Nanoribbon
Time: 02:00PM, Apr. 05th (Wednesday)
Location: Conference Room B, BLDG 909-1F
Abstract
Recent advances in on-surface chemistry enable the fabrication of graphene nanoribbons (GNRs) with atomically precision, opening the door to tailoring their electronic properties to the needs of specific applications [1]. This method uses properly designed small molecules as building blocks forming atomically precise GNRs after thermally activated coupling reactions, which has been demonstrated to deliver control over width and edge termination of GNRs at atomic level. Due to quantum confinements and edge effects, the electronic properties of GNRs depend crucially on their detailed atomic structure. Theory calculations at different levels show that GNRs with armchair edges exhibit a semiconducting band gap which oscillates with increased width. Even more intriguing are GNRs with zigzag edges, which are predicted to host spin-polarized edge states. Although a significant number of theoretical studies have investigated on a wide of graphene nanostructures, experimental results are scarce and largely affected by limited structural precision and/or pronounced interaction with the supporting substrate.
Here, we thoroughly investigate several atomically precise GNRs fabricated via on-surface synthesis method: armchair GNRs of width N=7 [2], armchair GNR heterostructures [3], zigzag GNRs of width N=6 [4], and a new type of GNRs with decorated five-membered rings at edges [5]. By combining the electronic characterization through scanning tunneling spectroscopy and first principles calculations with non-contact atomic microscopy images, where one can directly ‘see’ the atomic structure, we are able to give unprecedented insights into the relation between atomic and electronic structure of graphene nanostructures. To understand the ribbon-metal substrate interaction, we put particular emphasis to electronically decouple GNRs from the metal substrate, on which they are grown. Through STM-based multistep manipulation routine, the GNRs are successfully transferred onto insulating substrates, enabling the access of their intrinsic electronic properties. Our data unambiguously answer some of the fundamental questions of GNRs at atomic level, e.g., the value of band gap of armchair GNRs, energy splitting of magnetic edge states, substrate-ribbon interactions etc.
Biography
Wang Shiyong
12/2013-now: Postdoc in Roman Fasel’s group
Empa-Swiss Federal Laboratories for Materials Science and Technology
CH-8600 Dubendorf
Switzerland
Tel. 0041791720067
Email: Shiyong.wang@empa.ch
Education:
Ph.D in Physics (with Prof. Lin Nian)09/2009-09/2013Hong Kong University of Science and Technology
B.S. in Electronic Information Science & Technology09/2005-07/2009University of Electronic Science and Technology of China
Selected publications:
5. On-surface synthesis of graphene nanoribbons with zigzag edge topology
P. Ruffieux, S. Wang, B. Yang, C. Sánchez-Sánchez, J. Liu, T. Dienel, L. Talirz, P. Shinde, C. A. Pignedoli, D. Passerone, T. Dumslaff, X. Feng, K. Müllen, R. Fasel,Nature 531, 489 (2016) (Co-first author).
4.Giant energy splitting at atomically precise zigzag edges
S. Wang, L. Talirz, C. Pignedoli, X. Feng, K. Müllen R. Fasel, P. Ruffieux, Nature Comm., 11507 (2016).
S. Wang, L. Z. Tan, W. Wang, S. G. Louie, N. Lin, Phys. Rev. Lett. 113, 196803 (2014).
2.Visualization and Manipulation of Individual Dopant States in Single Conjugated Oligomers
S. Wang, W. Wang, N. Lin, ACS Nano 6, 3401 (2012).
1. Resolving band structure evolution and defect-induced states of single conjugated oligomers by scanning tunneling microscopy and tight-binding calculations
S. Wang, W. Wang, N. Lin, Phys. Rev. Lett. 106, 206803 (2011).
Contact: Prof. Lifeng Chi