  Atomically precise graphene nanoribbons (GNRs) have a wide range of
electronic properties that depend sensitively on their chemical structure.
Several types of GNRs have been synthesized on metal surfaces through selective
surface-catalyzed reactions. The resulting GNRs are adsorbed on the metal
surface, which may lead to hybridization between the GNR orbitals and those of
the substrate. This makes investigation of the intrinsic electronic properties
of GNRs more difficult, and also rules out capacitive gating. Here we
demonstrate the formation of a dielectric gold chloride adlayer that can
intercalate underneath GNRs on the Au(111) surface. The intercalated gold
chloride adlayer electronically decouples the GNRs from the metal and leads to
a substantial hole doping of the GNRs. Our results introduce an easily
accessible tool in the in situ characterization of GNRs grown on Au(111) that
allows for exploration of their electronic properties in a heavily hole-doped
regime.
