Self-Assembly of Supra-Molecular Systems on Graphene or Graphite

Abstract

Self-assembled monolayers oer excellent opportunities to increase our understanding of fundamental aspects of self-organization, interfacial phenomena and structure property relationships. The ability to tailor molecules with precisely dened and well-controlled structure combined with experiments based on self-assembled monolayers, provides a possibility for a more fundamental understanding of phenomena like ordering and growth, aected by competing intermolecular, molecular-substrates and molecule-solvent interactions.

In this context, the scanning tunneling microscopy and spectroscopy and atomic force microscopy were used for the study of the self-assembly of hydrogen bonding and -conjugated molecules into structurally organized monolayers on graphene and graphite. Besides the formation mechanism of self-assembled structures, potential use of the resulting patterns in applications such as electronic nano-wires, were investigated by spatial mapping of the electronic states. For the oligothiophene based conjugated molecules used in our study, the experiments showed the formation of 1D supramolecular chains with a continuous electronic density of states, which tentatively suggests that within such molecular chains, conjugation of electrons is preserved.

Moreover, our experiments suggest that, although graphene and graphite have identical chemical composition and nearly the same crystal lattice parameters at the surface, graphite adsorbs molecules much more strongly than graphene. Weak electronic coupling at the graphene-molecules interface provides the possibility to image and "see" unperturbed intrinsic molecular orbitals, and to distinguish unambiguously individual molecular segments. Our results have important implications for the use of graphene for future device applications that require electronic decoupling between adsorbates and substrates.