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.
Highlights
Graphene nanoribbons (GNRs)—narrow stripes of graphene—have emerged as promising building blocks for nanoelectronic devices
More realistic calculations predict the presence of a bandgap, but it should remain much smaller than that found in armchair GNRs of the other families[7]
The experimental results are corroborated by density-functional theory (DFT) calculations that are used to identify the fingerprints of molecular orbitals as a function of the GNR length
Summary
Graphene nanoribbons (GNRs)—narrow stripes of graphene—have emerged as promising building blocks for nanoelectronic devices. More sophisticated models taking into account, for example, edge relaxation predict non-vanishing but small bandgaps[8,13] These narrow armchair GNRs with narrow or vanishing bandgaps would form ideal molecular wires to be used as interconnects in molecular scale circuitry. More realistic calculations predict the presence of a bandgap, but it should remain much smaller than that found in armchair GNRs of the other families[7] We confirm these theoretical predictions and measure experimentally a B100 meV bandgap in long GNRs using low-temperature scanning tunnelling microscopy (STM). This near-metallic regime is already reached in GNRs of six perylene monomer units, that is, with lengths longer than 5 nm. This suggest that these GNRs would form ideal interconnects in molecular scale electronic circuitry
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