We have studied large areas of (√3×√3)R30° graphene commensurate with a Pt(111) substrate. A combination of experimental techniques with ab initio density functional theory indicates that this structure is related to a reconstruction at the Pt surface, consisting of an ordered vacancy network formed in the outermost Pt layer and a graphene layer covalently bound to the Pt substrate. The formation of this reconstruction is enhanced if low temperatures and polycyclic aromatic hydrocarbons are used as molecular precursors for epitaxial growth of the graphene layers.

New nanoarchitectures can be built from polycyclic aromatic hydrocarbons (PAHs) by exploiting the capability of some metal surfaces of inducing cyclodehydrogenation reactions. This bottom-up approach allows the formation of nanostructures with different dimensionality from the same precursor as a consequence of the diffusion and coupling of the PAHs adsorbed on the surface. In this work we present a thorough study, by means of a combination of X-ray Photoemission Spectroscopy, Near-Edge X-ray Absorption Fine Structure and Scanning Tunneling Microscopy with first principle calculations, of the structural and chemical transformations undergone by pyridyl-substituted dibenzo[5]helicene on three coinage surfaces, namely Cu(110), Cu(111) and Au(111). Upon annealing, on-surface chemical reactions are promoted affecting the adsorbate/substrate and the molecule/molecule interactions. This thermally induced process favours the transformation from diffusing isolated molecules to polymeric nanographene chains and finally to N-doped graphene. IntroductionNew organic materials have the potential of substituting silicon-based technology in electronic devices, and are already widely spread in organic light emitting diodes (OLED) and in new designs of solar cells. Surface-mediated chemical modification of polycyclic aromatic hydrocarbons (PAHs), emerges as an excellent way to synthesize novel nanostructures, with a precise control of their composition and of their electronic properties. Moreover, this bottom-up approach may allow controlling a specific reaction path at the atomic level, leading to tailored reaction outcomes. In particular, thermally induced (cyclo)dehydrogenation (and/or dehalogenation) of PAHs followed by covalent coupling on transition metal surfaces may result in the synthesis of new zero-, one-and two-dimensional nanoarchitectures.