Local electronic structure of atomically-precise graphene nanoribbon heterojunctions

Graphene nanoribbons (GNRs) are one-dimensional strips of graphene that exhibit novel electronic and magnetic properties. Bottom-up synthesis of GNRs via self-assembly of molecular precursors yields nanoribbons with atomic-scale structural control, thus allowing precise tuning of properties such as bandgap, edge chirality, and heteroatom doping. Here we report the local electronic structure characterization of bottom-up GNR heterojunctions fabricated from a only single type of molecular precursor. Using this new molecule, bottom-up GNRs were grown that incorporate sacrificial carbonyl groups along their edges. Subsequent thermal annealing of the GNRs after growth was used to induce removal of the carbonyl groups through a bond cleavage process. STM spectroscopy shows that these segments have different electronic properties, thus allowing formation of Type II heterojunctions with atomically well-defined interfaces. Experimental bandedge energy level alignment and wave function distributions are consistent with first principles theoretical simulations for this bottom-up heterojunction system.