Ultra-narrow metallic armchair graphene nanoribbons

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 =3 m +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. Graphene nanoribbons have potential applications as nanoscale wires, though experimentally studied ribbons display wide bandgaps. Here, the authors synthesise the narrowest armchair graphene nanoribbon predicted to have metallic behaviour and show these ribbons—5 carbon atoms wide—indeed display almost metallic behaviour.