Low Coverage of Long Graphene Nanoribbons by On-surface Double Layer Polymerization on Au(111)

Abstract The controlled surface annealing by steps of 50°C of graphene nanoribbon (GNR) precursors on Au(111) is characterized, during the GNR on-surface synthesis, using low-temperature ultrahigh vacuum scanning tunneling microscopy and dI/dV spectroscopy. The initial monomer coverage is increased up to 3 monolayers (MLs) and annealed at every 50°C. After the first annealing step, the monomers self-organize into 2 ML islands and, then, the Ullmann coupling reaction takes place in both 1st and 2nd MLs. An optimal initial monomer coverage of ~ 1.5 ML is necessary for reaching a final GNR length distribution up to 50 nm and a low surface coverage of 0.4 ML required for single GNR molecule experiments.