Role of Au surface step edge on bottom-up growth of atomically precise graphene nanoribbons: First-principles study*

The formation of energy gap in graphene can be understood as a critical problem for graphene electronic device application. One of the way to introduce the band gap is use of graphene nanoribbons (GNR). Especially, the bottom-up growth can produce high quality and atomically precise armchair GNR, but their length is limited up to few tens nm. For the GNR growth, 10,10$'$-dibromo-9,9$'$-bianthryl (DBBA) precursor molecules polymerize on Au surface at 470 Kelvin and resultant poly-anthracene becomes into GNR by surface assisted cyclodehydrogenation at 670 Kelvin. In order to obtain much longer GNR, understanding of the formation of poly-anthracene is necessary. In this study, we investigated the adsorption of DBBA, poly-anthracene and GNR on Au surfaces by means of first-principles calculations using PHASE code. The effect of van der Waals interaction was included by the semi-empirical method by Grimme. To discuss the effect of surface morphology, we considered the flat Au(111) and stepped Au(443). We found that DBBA and poly-anthracene are stable at the step edges. These results should be an origin of recently reported growth of spacially aligned GNR on Au(887) stepped surfaces.