Nanospectroscopy highlights

The complex interaction between graphene and a support with non-threefold symmetry may result in a peculiar film morphology and structure. On the square Ir(100) we discovered flat and buckled graphene phases that coexist at room temperature; they form stripe-shaped domains which relieve the strain accumulated after cooling the film below growth temperature. In the buckled phase, a small fraction of the carbon atoms chemisorbs to the substrate, originating a textured structure with exceptionally large one-dimensional ripples of nm periodicity. The two graphene phases exhibit distinctively different electronic structure. By imaging emission from graphene's π-band at the reciprocal space K point, photoemission microscopy enabled a direct comparison of the local density of states (DOS) of flat and buckled graphene. The low intensity observed in

the latter points to the disruption of the Dirac cones. This result was confirmed by theory, which also revealed that the metallic-like character of the buckled phase does not originate from strain or rippling, but rather from the chemisorption to the substrate. The novelty highlighted in our study is that the change in the graphene DOS at the Dirac point is due to the chemisorption of just a small fraction of the atoms in the unit cell.

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Rippling and bonding of a graphene superlattice on Ir(100);
A. Locatelli, C. Wang, C. Africh, N. Stojić, T.O. Menteş, G. Comelli, N. Binggeli;
ACS Nano 7, 6955–6963 (2013);
doi: 10.1021/nn402178u.