Helical polymers on Au (111) surface: the initial step for bottom-up growth of chevron-type graphene nanoribbons

A graphene nanoribbon of precise size and shape, which is critical for controlling its electronic properties and future device applications, can be synthesized by bottom-up growth on coinage metal surfaces. The initial step for this growth is the polymerization of the precursor molecules on the surface. For the growth of the chevron-type GNR, the precursor monomer, 6,11-dibromo-1,2,3,4-tetraphenyltriphenylene, has a complicated atomic structure with different configurations, depending on the helical chiralities rendered by the phenyl ring orientations. We investigate the polymerization step by combining ab initio simulations and experimental STM measurements, identifying the packing and the adsorption geometry of helical polymers on the Au surface. The effects of C-H and C-F bonds will also be discussed. Our results will help in exploring different precursors and understanding the growth mechanism.