Bottom-Up Fabrication and Bandgap Determination of N = 8 Armchair Graphene Nanoribbons

Armchair graphene nanoribbons (AGNRs) are increasingly recognized as a promising semiconducting material for future nanoelectronics applications. Theoretical predictions suggest that the 8-AGNR, with a width of 8 carbon atoms, is one such candidate. Significant effort has been spent to fabricate 8-AGNRs, but it remains challenging to establish an efficient 8-AGNR bottom-up synthesis protocol and to accurately determine the 8-AGNR bandgap. Here we report the synthesis and characterization of pristine 8-AGNRs via a bottom-up approach that combines solution-phase polymerization with on-surface synthesis. A tailored polymeric precursor was synthesized through A2B2-type Suzuki polymerization in solution, and was then deposited onto a Au(111) substrate using matrix-assisted direct (MAD) transfer. Annealing under ultrahigh vacuum conditions induced cyclodehydrogenation and resulted in the formation of structurally well-defined 8-AGNRs. Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) confirm the targeted 8-AGNR chemical structure and reveal a 0.74 ± 0.04 eV electronic bandgap on Au(111).