Substrate-Controlled Synthesis of 5-Armchair Graphene Nanoribbons

5-Armchair graphene nanoribbons (5-AGNRs) have been successfully synthesized through the on-surface reaction of 1,4,5,8-tetrabromonaphthalene (TBN) on Ag(111) and characterized by scanning tunneling microscopy. Silver-naphthalene chains are observed as intermediate states toward the formation of 5-AGNRs. A similar reaction of TBN has been conducted on Cu(111), but no 5-AGNRs are obtained. Disordered amorphous products prevail on Cu(111) upon high-temperature annealing (600 K), which is tentatively explained by the strong aryl-Cu bonds. Scanning tunneling spectroscopy measurements of 5-AGNRs on Ag(111) reveal three prominent peaks at bias voltages of -0.3, 1.0, and 1.5 V, determining that the apparent band gap is 1.3 eV.