title: Ultra-narrow metallic armchair graphene nanoribbons.
abstract: Graphene nanoribbons (GNRs)-narrow stripes of graphene-have emerged as promising building blocks for nanoelectronic devices. Recent advances in bottom-up synthesis have allowed production of atomically well-defined armchair GNRs with different widths and doping. While all experimentally studied GNRs have exhibited wide bandgaps, theory predicts that every third armchair GNR (widths of N=3m+2, where m is an integer) should be nearly metallic with a very small bandgap. Here, we synthesize the narrowest possible GNR belonging to this family (five carbon atoms wide, N=5). We study the evolution of the electronic bandgap and orbital structure of GNR segments as a function of their length using low-temperature scanning tunnelling microscopy and density-functional theory calculations. Already GNRs with lengths of 5 nm reach almost metallic behaviour with ∼100 meV bandgap. Finally, we show that defects (kinks) in the GNRs do not strongly modify their electronic structure.
authors.affiliation: Department of Applied Physics, Aalto University School of Science, PO Box 15100, Aalto 00076, Finland.
authors.forename: Amina
authors.initials: A
authors.lastname: Kimouche
authors.affiliation: COMP Centre of Excellence, Department of Applied Physics, Aalto University School of Science, PO Box 11100, Aalto 00076, Finland.
authors.forename: Mikko M
authors.initials: MM
authors.lastname: Ervasti
authors.affiliation: Department of Applied Physics, Aalto University School of Science, PO Box 15100, Aalto 00076, Finland.
authors.forename: Robert
authors.initials: R
authors.lastname: Drost
authors.affiliation: Department of Chemistry, Aalto University School of Chemical Technology, PO Box 16100, Aalto 00076, Finland.
authors.forename: Simo
authors.initials: S
authors.lastname: Halonen
authors.affiliation: COMP Centre of Excellence, Department of Applied Physics, Aalto University School of Science, PO Box 11100, Aalto 00076, Finland.
authors.forename: Ari
authors.initials: A
authors.lastname: Harju
authors.affiliation: Department of Chemistry, Aalto University School of Chemical Technology, PO Box 16100, Aalto 00076, Finland.
authors.forename: Pekka M
authors.initials: PM
authors.lastname: Joensuu
authors.affiliation: Department of Applied Physics, Aalto University School of Science, PO Box 15100, Aalto 00076, Finland.
authors.forename: Jani
authors.initials: J
authors.lastname: Sainio
authors.affiliation: Department of Applied Physics, Aalto University School of Science, PO Box 15100, Aalto 00076, Finland.
authors.forename: Peter
authors.initials: P
authors.lastname: Liljeroth