Topographic and Spectroscopic Characterization of Electronic Edge States in CVD Grown Graphene Nanoribbons
Minghu Pan,1 E. Costa Girão,2,7,8 Xiaoting Jia,4 Sreekar Bhaviripudi,4 Qing Li,1 Jing Kong,5 V. Meunier,2,3 and Mildred S. Dresselhaus5,6
1-Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
2-Dept. Physics, Astronomy, & Applied Physics, and
3-Dept. Materials Science & Engineering, Rensselaer Polytechnic Institute, Troy, New York
4-Dept. Materials Science & Engineering, and
5-Dept. Electrical Engineering & Computer Science, and
6-Dept. Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts
7-Departamento de Fisica, Universidade Federal do Ceará, Caixa Postal 6030, Fortaleza, Ceará, 60455-900, Brazil
8-Departamento í de Física, Universidade Federal do Piauí, Teresina, Piauí, 64049-550, Brazil
This work proposes that defects at the edge of graphene nanoribbons (GNRs) grown by chemical-vapor-deposition (CVD) dramatically alter the electronic properties of GNRs. The first observation of an atomically resolved defective edge structure for CVD-grown GNRs is reported. These ribbons exhibit highly crystalline structures with well-defined, clean edges. First-principles calculations, combined with scanning tunneling spectroscopy (STS), reveal spin-split edge states induced by electron-electron Coulomb repulsion at ribbon edges, which are significantly affected by local edge defects.
We used STM to analyze the relationship between edge shapes and electronic structures in CVD-grown GNRs. Single-layered GNRs, from several to 100 nm wide and up to 1 μm long, were studied. High-resolution STS images highlight highly crystalline nanoribbon structures with well-defined, clean edges. Theoretical calculations indicate clear spin-split edge states induced by electron-electron Coulomb repulsion. Edge defects can significantly modify these edge states, and different edge structures at each side of a single ribbon produce asymmetric electronic edge states. A reconstructed edge structure composed of 5-7 member rings exhibits the best match with experimental results, suggesting defects at the edge of CVD-grown GNRs. This work suggests that by modifying the local edge structure (using methods such as Joule heating) the electronic edge states of GNRs can be controlled.
This work will be published in Nano Letters (DOI: 10.1021/nl204392s). This research was conducted at the Center for Nanophase Materials Sciences, which is sponsored at Oak Ridge National Laboratory by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy. The work at MIT was done under ONR-N00014-09-1-1063 (X.J., M.S.D., and J.K.) while S.B. and J.K. acknowledge the support from National Science Foundation NSF DMR 0845358. E.C.G. acknowledges support from the Brazilian agencies CNPq and CAPES (process 0327-10-7).