Prediction of a Kinetic Pathway for Fabricating the Narrowest Zigzag Graphene Nanoribbons on Cu(111)

The narrowest zigzag graphene nanoribbons (nZGNRs) consisting of linearly fused benzene rings have distinctly superior electronic and spintronic properties; yet, to date, fabrication of nZGNRs via bottom-up self-assembly remains a daunting challenge. Here, based on first-principles calculations, we propose a kinetic pathway for growing nZGNRs on Cu(111) using 1,4-dibromo-2,5-bis­(bromomethyl)­benzene precursors. We show that such a precursor molecule can readily adsorb on Cu(111), accompanied by easy detachment of the four Br substituents. As building blocks for the formation of the nZGNRs, the resulting C₈H₆ radicals have high diffusional and rotational mobilities on the substrate. Two such radicals can fuse into an nZGNR-like dimer via covalent bond formation by overcoming a kinetic barrier of ∼1.00 eV, with the unsaturated C atoms properly located to allow additional C₈H₆ radicals to join and elongate the nZGNR. We further examine possible competing byproducts and find that the yields of nZGNRs can be enhanced with proper choices of the substrates. As a comparative study, the precursor molecule of 1,4-bis­(bromomethyl)­benzene has also been investigated and found to be less desirable in forming the nZGNRs. These findings provide a highly appealing route toward the fabrication of nZGNRs for potential applications in nanoelectronics and spintronics.