Small bandgap in atomically precise 17-atom-wide armchair-edged graphene nanoribbons

Bottom-up synthesis of graphene nanoribbons (GNRs) may open new possibilities in future electronic devices owing to their tunable electronic structure, which depends strongly on their well-defined width and edge geometry. For instance, armchair-edged GNRs (AGNRs) exhibit width-dependent bandgaps. However, the bandgaps of AGNRs synthesized experimentally so far are relatively large, well above 1 eV. Such a large bandgap may deteriorate device performance due to large Schottky barriers and carrier effective masses. Here, we describe the bottom-up synthesis of AGNRs with smaller bandgaps, using dibromobenzene-based precursors. Two types of AGNRs with different widths, namely 17 and 13 carbon atoms, were synthesized on Au(111), and their atomic and electronic structures were investigated by scanning probe microscopy and spectroscopy. We reveal that 17-AGNRs have the smallest bandgap, as well as the smallest electron/hole effective mass, among bottom-up AGNRs reported so far. The successful synthesis of 17-AGNRs is a significant step toward the development of GNR-based electronic devices

Author Correction: Small bandgap in atomically precise 17-atom-wide armchair-edged graphene nanoribbons

An amendment to this paper has been published and can be accessed via a link at the top of the paper

Experimental and Theoretical Investigations of Surface-Assisted Graphene Nanoribbon Synthesis Featuring Carbon–Fluorine Bond Cleavage

Edge-fluorinated graphene nanoribbons are predicted to exhibit attractive structural and electronic properties, which, however, still need to be demonstrated experimentally. Hence, to provide further experimental insights, an anthracene trimer comprising a partially fluorinated central unit is explored as a precursor molecule, with scanning tunneling microscopy and X-ray photoelectron spectroscopy analyses, indicating the formation of partially edge-fluorinated polyanthrylenes <i>via</i> on-surface reactions after annealing at 350 °C on Au(111) under ultrahigh-vacuum conditions. Further annealing at 400 °C leads to the cyclodehydrogenation of partially edge-fluorinated polyanthrylenes to form graphene nanoribbons, resulting in carbon–fluorine bond cleavage despite its high dissociation energy. Extensive theoretical calculations reveal a defluorination-based reaction mechanism, showing that a critical intermediate structure, obtained as a result of H atom migration to the terminal carbon of a fluorinated anthracene unit in polyanthrylene, plays a crucial role in significantly lowering the activation energy of carbon–fluorine bond dissociation. These results suggest the importance of transient structures in intermediate states for synthesizing edge-fluorinated graphene nanoribbons

Experimental and Theoretical Investigations of Surface-Assisted Graphene Nanoribbon Synthesis Featuring Carbon–Fluorine Bond Cleavage

Edge-fluorinated graphene nanoribbons are predicted to exhibit attractive structural and electronic properties, which, however, still need to be demonstrated experimentally. Hence, to provide further experimental insights, an anthracene trimer comprising a partially fluorinated central unit is explored as a precursor molecule, with scanning tunneling microscopy and X-ray photoelectron spectroscopy analyses, indicating the formation of partially edge-fluorinated polyanthrylenes <i>via</i> on-surface reactions after annealing at 350 °C on Au(111) under ultrahigh-vacuum conditions. Further annealing at 400 °C leads to the cyclodehydrogenation of partially edge-fluorinated polyanthrylenes to form graphene nanoribbons, resulting in carbon–fluorine bond cleavage despite its high dissociation energy. Extensive theoretical calculations reveal a defluorination-based reaction mechanism, showing that a critical intermediate structure, obtained as a result of H atom migration to the terminal carbon of a fluorinated anthracene unit in polyanthrylene, plays a crucial role in significantly lowering the activation energy of carbon–fluorine bond dissociation. These results suggest the importance of transient structures in intermediate states for synthesizing edge-fluorinated graphene nanoribbons