title: Exciton-dominated optical response of ultra-narrow graphene nanoribbons.
abstract: Narrow graphene nanoribbons exhibit substantial electronic bandgaps and optical properties fundamentally different from those of graphene. Unlike graphene--which shows a wavelength-independent absorbance for visible light--the electronic bandgap, and therefore the optical response, of graphene nanoribbons changes with ribbon width. Here we report on the optical properties of armchair graphene nanoribbons of width N=7 grown on metal surfaces. Reflectance difference spectroscopy in combination with ab initio calculations show that ultranarrow graphene nanoribbons have fully anisotropic optical properties dominated by excitonic effects that sensitively depend on the exact atomic structure. For N=7 armchair graphene nanoribbons, the optical response is dominated by absorption features at 2.1, 2.3 and 4.2 eV, in excellent agreement with ab initio calculations, which also reveal an absorbance of more than twice the one of graphene for linearly polarized light in the visible range of wavelengths.
authors.affiliation: Institute of Experimental Physics, Johannes Kepler University, 4040 Linz, Austria.
authors.forename: Richard
authors.initials: R
authors.lastname: Denk
authors.affiliation: Institute of Experimental Physics, Johannes Kepler University, 4040 Linz, Austria.
authors.forename: Michael
authors.initials: M
authors.lastname: Hohage
authors.affiliation: Institute of Experimental Physics, Johannes Kepler University, 4040 Linz, Austria.
authors.forename: Peter
authors.initials: P
authors.lastname: Zeppenfeld
authors.affiliation: Empa, Swiss Federal Laboratories for Materials Science and Technology, 8600 Dübendorf, Switzerland.
authors.forename: Jinming
authors.initials: J
authors.lastname: Cai
authors.affiliation: Empa, Swiss Federal Laboratories for Materials Science and Technology, 8600 Dübendorf, Switzerland.
authors.forename: Carlo A
authors.initials: CA
authors.lastname: Pignedoli
authors.affiliation: Empa, Swiss Federal Laboratories for Materials Science and Technology, 8600 Dübendorf, Switzerland.
authors.forename: Hajo
authors.initials: H
authors.lastname: Söde
authors.affiliation: 1] Empa, Swiss Federal Laboratories for Materials Science and Technology, 8600 Dübendorf, Switzerland [2] Department of Chemistry and Biochemistry, University of Bern, 3012 Bern, Switzerland.
authors.forename: Roman
authors.initials: R
authors.lastname: Fasel
authors.affiliation: Max Planck Institute for Polymer Research, 55128 Mainz, Germany.
authors.forename: Xinliang
authors.initials: X
authors.lastname: Feng
authors.affiliation: Max Planck Institute for Polymer Research, 55128 Mainz, Germany.
authors.forename: Klaus
authors.initials: K
authors.lastname: Müllen
authors.affiliation: CNR-Nanoscience Institute, S3 Center, 41125 Modena, Italy.
authors.forename: Shudong
authors.initials: S
authors.lastname: Wang
authors.affiliation: CNR-Nanoscience Institute, S3 Center, 41125 Modena, Italy.
authors.forename: Deborah
authors.initials: D
authors.lastname: Prezzi
authors.affiliation: CNR-Nanoscience Institute, S3 Center, 41125 Modena, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Ferretti
authors.affiliation: 1] CNR-Nanoscience Institute, S3 Center, 41125 Modena, Italy [2] Department of Physics, Mathematics, and Informatics, University of Modena and Reggio Emilia, 41125 Modena, Italy.
authors.forename: Alice
authors.initials: A
authors.lastname: Ruini
authors.affiliation: 1] CNR-Nanoscience Institute, S3 Center, 41125 Modena, Italy [2] Department of Physics, Mathematics, and Informatics, University of Modena and Reggio Emilia, 41125 Modena, Italy.
authors.forename: Elisa
authors.initials: E
authors.lastname: Molinari
authors.affiliation: Empa, Swiss Federal Laboratories for Materials Science and Technology, 8600 Dübendorf, Switzerland.
authors.forename: Pascal
authors.initials: P
authors.lastname: Ruffieux