Synthesis and growth mechanisms of (3,1)-graphene nanoribbons on Cu(111): insights from STM and DFT analysis

We present a comprehensive study on the bottom-up synthesis of chiral (3,1)-graphene nanoribbons (GNRs) on Cu(111) using two analogous precursors, 10,10'-dibromo-9,9'-bianthryl (DBBA) and bianthracene (BA). Through a temperature-programmed growth strategy supported by scanning tunnelling microscopy, we investigate the role of precursor diffusion, polymerization, and cyclodehydrogenation in GNR formation. Our results show that DBBA predominantly forms bisanthene due to restricted surface diffusion and premature cyclodehydrogenation, rendering it unsuitable for extended ribbon growth. In contrast, BA exhibits significantly higher surface mobility, leading to the formation of polyanthracene chains, which subsequently transform into long (3,1)-GNRs upon controlled annealing. We identify cyclodehydrogenation at chain termini as a key factor limiting ribbon length. Our findings provide new insights into optimizing growth conditions for extended GNRs on Cu(111), paving the way for their integration into future electronic and spintronic applications.