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Growth and atomic structure of graphene on Ir(332)

The growth of large-scale uniform graphene on flat Ir(111) is today well established. The graphene produced by thermally activated catalytic decomposition of ethylene forms a (9.32 x 9.32) moiré superstructure. The moiré structure gives rise to superperiodic potential which forms replica bands and opens minigaps in the π-band of graphene (Dirac cone). Motivated by the possibility to further modify the Dirac cone, e.g. by additional 1D periodic potential introduced by substrate, we have studied the growth and performed scanning tunnelling microscopy (STM) and low energy electron diffraction (LEED) investigation of graphene on vicinal Ir(332) surface. The structural properties of graphene grown by temperature controlled growth (TPG) and chemical vapour deposition (CVD) by varying sample temperature and ethylene pressure have been characterized. LEED results show that the growth process alters the long-range uniformity and 1.1 nm periodicity characteristic for a pristine Ir(332) surface, which is upon graphene growth characterized by new periodicity of much smaller length. STM study of the topology shows that periodic narrower steps are formed but also flat (111) areas, indicating the reshaping of the substrate by step bunching. The width of new formed terraces and degree of step order can be influenced by sample temperature during CVD. We have identified at least three distinct rotational variants of graphene resulting in different moiré patterns. With the insight in the atomic arrangement of carbon lattice on terraces and at the step edges a link between moiré pattern and edge properties is established.

graphene; Ir(332); step bunching; step edge; CVD; TPG; STM

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