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The growth of controlled 1D carbon-based nanostructures on metal surfaces isa multistep process whose path, activation energies and intermediate metastablestates strongly depend on the employed substrate. Whereas this process has beenextensively studied on gold, less work has been dedicated to silver surfaces,which have a rather different catalytic activity. In this work, we present anexperimental and theoretical investigation of the growth of poly-$p$-phenylene(PPP) chains and subsequent narrow graphene ribbons starting from4,4''-dibromo-$p$-terphenyl molecular precursors deposited at the silversurface. By combing scanning tunneling microscopy (STM) imaging and densityfunctional theory (DFT) simulations, we describe the molecular morphology andorganization at different steps of the growth process and we discuss thestability and conversion of the encountered species on the basis of calculatedthermodynamic quantities. Unlike the case of gold, at the debromination step weobserve the appearance of organometallic molecules and chains, which can beexplained by their negative formation energy in the presence of a silver adatomreservoir. At the dehydrogenation temperature the persistence of intercalatedBr atoms hinders the formation of well-structured graphene ribbons, which areinstead observed on gold, leading only to a partial lateral coupling of the PPPchains. We numerically derive very different activation energies for Brdesorption from the Ag and Au surfaces, thereby confirming the importance ofthis process in defining the kinetics of the formation of molecular chains andgraphene ribbons on different metal surfaces.

On-surface synthesis and evolution of self-assembled poly($p$-phenylene) chains on Ag(111): a joint experimental and theoretical study