On-Surface Synthesis of Graphene Nanoribbons: Photoelectron Spectroscopy Reveals Impact of Substrate Reactivity

Graphene nanoribbons (GNRs) show favorable electronic and optical properties due to their excellent stability at ambient conditions and are suitable materials for nanoscale electronic devices. 10,10′-Dibromo-9,9′-bianthracene (DBBA) has proven to be a suitable precursor for on-surface synthesis of GNRs because it shows a manifold of temperature-assisted reactions like dehalogenation, debromination, or Ullman-coupling on metal surfaces. We use DBBA to conduct a thorough investigation across a wide temperature range (170–750 K) and to track the formation process of 7-graphene nanoribbons (7-GNRs) on Au(111), Ag(111), and Cu(111) substrates by utilizing X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). The reaction pathways exhibit a strong dependence on the substrate reactivity: on Au(111), the reactions require annealing and 7-GNRs are formed at 560 K; on Ag(111), debromination occurs at 400 K and 7-GNRs are achieved at 695 K; and on Cu(111), the robust chemical interaction at the interface leads to the debromination upon deposition (at 170 K) and the final product is formed at 750 K. Overall, we demonstrate that DBBA serves as a valuable precursor to GNRs, while the metal substrates play a crucial role to effect the growth behavior of organic materials