Berlin 2008 – scientific programme
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O: Fachverband Oberflächenphysik
O 89: Metal Substrates: Epitaxy and Growth
O 89.12: Talk
Friday, February 29, 2008, 12:15–12:30, MA 041
Incommensurate epitaxy of graphene on Ir(111) — •Alpha N’Diaye, Johann Coraux, Carsten Busse, and Thomas Michely — II. Physikalisches Institut, Universität zu Köln
Graphene can epitaxially be grown on Ir(111) by thermal decomposition of hydrocarbons. Due to the incommensurate lattices of graphene and the underlying Ir(111) surface, a large supercell moiré with a periodicity of 25 Å emerges. Despite the incommensurability of the two lattices, graphene grows well ordered on Ir(111) with the dense packed iridium [1 1 0] direction parallel to the [1 1 20] of graphene.
We present two ways of preparing graphene on Ir(111). One method employs preadsorption of ethylene (C2H4) and subsequent thermal decomposition. This yields a high graphene island. The average island size can be controlled by temperature, while the coverage is fixed to about 20 % of the surface area. Based on the analysis of the evolution of graphene flake size distribution with time and temperature, we propose the coalescence of graphene flakes as a coarsening mechanism.
The second method is based on continuous exposure of the hot Ir(111) surface to ethylene. At the chosen temperatures (between 970 K and 1320 K) ethylene decomposes on iridium, but not on graphene. This process is suited to covering the whole surface with one layer of graphene. Nucleation of graphene flakes takes place exclusively at step edges.
Epitaxial perfection increases with the domain size. The domain size is crucially dependent on the preparation temperature. At 1320 K this size exceeds the micrometer scale.