As key building blocks for nanoelectronics, graphene nanoribbons (GNRs) have attracted considerable interest over the past two decades. Atomically precise GNRs can be synthesized on Au(111) via on-surface reactions of 10, 10′-9, 9′-bianthryl (DBBA) in two sequential steps: (i) debromination and (ii) cyclodehydrogenation. Despite extensive efforts, the catalytic role of the gold substrate and the physical origin of the adatom effect remain debated, largely due to a lack of electronic-structure-level understanding. Here, we present a comprehensive DFT-D3 study of GNRs on the Au(111) surface by evaluating the energy profiles under four different conditions [vacuum, isolated Au atom, Au(111) surface, and Au adatom on Au(111)]. By combining barrier calculations with electronic-structure analyses, we find that the catalytic effect originates from charge transfer from the C–H (or C–Br) σ bond to the Au adatom, which weakens the bond and lowers the barrier. At 470 K, debromination (barrier 0.753 eV) is kinetically favored, leading to surface-stabilized biradical intermediates that readily couple. Upon heating to 670 K, a thermally activated Au adatom originating from the Au(111) surface lowers the energy barrier of dehydrogenation from 2.650 eV (bare surface) to 2.295 eV. Quantitative transition state theory estimates give half-lives consistent with experimental reaction times (microseconds for debromination at 470 K; hours for cyclodehydrogenation at 670 K). Consequently, we propose that the gold adatom plays a crucial catalytic role in the dehydrogenation process during GNR formation on the Au(111) surface.

Close

PrevNext

View figure in article

• Growth
• Graphene
• Nanoribbon
• First-principles calculations