Center for Functional Nanomaterials Seminar

Graphene, a single sheet of carbon sp2 bonded carbon, can be grown by pyrolytic decomposition of ethene (C2H4) on Ir(111). We show that despite the weak bonding a variety of properties and applications arise from the interplay of epitaxial graphene on Ir(111) with its substrate.
Graphene on Ir(111) forms a moire superstructure with a periodicity of 25.3 Ã. Making use of the vernier effect, we show that graphene is slightly contracted on Ir(111) and estimate the bending radius of a graphene sheet on an iridium step.
Cooling a graphene layer after growth at high temperatures gives rise to compressive stress. We show with STM and LEEM that this stress is partly relieved by the formation of wrinkles (Fig.1).
The electronic structure shows that the dirac cone is preserved in graphene on Ir(111). The substrate induces a small p-doping shifting the dirac point about 0.1eV above the fermi level. Additionally, the superperiodic potential coined onto the band structure of graphene by the moire gives rise to replica cones and minigaps in the band structure.
The moire acts as a template for the growth of regular cluster arrays.
The binding of metal atoms occurs through a local rehybridization of graphene from sp2 to a diamond like sp3 configuration so that clusters nucleate and grow in the regular periodicity of the moire superstructure. For Ir as the average cluster size can be tuned from 4.5 to 130 atoms This approach allows to grow cluster lattices of various metals including W, Pt, Re or bimetallic clusters from Ir/Fe and Ir/Au e.g. with in average 75 atoms and an Ir/Fe ratio of 1/6.5.