Templating Effect of Different Low-Miller-Index Gold Surfaces on the Bottom-Up Growth of Graphene Nanoribbons

This work is focused on the structural control ofgraphene nanoribbons (GNRs) and intermediate polymeric wires[poly(p-phenylene), PPP] during their thermoactivated bottom-upsynthesis from room temperature to 480 °C. The first step of thesynthesis relies on the Ullmann coupling between 4,4″-dibromo-p-terphenyl (DBTP) molecular precursor units that lead to PPPwires in the temperature range between 170 and 200 °C. Thermalannealing at higher temperatures (360−480 °C) triggers the PPPlateral fusion to yield GNRs. We systematically studied thedeposition of DBTP on the three main low-Miller-index goldsurfaces, i.e., Au(100), Au(110), and Au(111), to elucidate thetemplating effects of such surfaces due to the pronouncedanisotropy of their reconstructions via a multitechnique approach (scanning tunneling microscopy, X-ray photoelectronspectroscopy, and low-energy electron diffraction). The best results are obtained on Au(100) in terms of (i) GNR length (up to 80nm), (ii) narrow width distribution (only 6- and 9-GNRs), (iii) long-range order, and (iv) excellent alignment along thereconstruction. Au(111) produces longer GNRs than Au(100) but poorer molecular ordering. Concerning PPP wires, they are stablewithin a wide temperature range and exhibit an interesting improvement of the long-range order with increasing temperature onAu(100), but the best overall organization and unidirectionality have been achieved on Au(110).