Unveiling the formation of epitaxial graphene on cobalt

PEEM and LEEM enabled imaging the structural transformation that graphene on cobalt undergoes at temperatures above 500°C, from a rotationally-incoherent, defective layer to an epitaxial one.The structural transformation takes place via the growth and propagation of mesoscopic carbidic islands and involves the dissolution and recondensation of carbon.
M. Jugovac et al., Carbon 152, 489-496 (2019).

The CVD growth of graphene on cobalt has been researched intensively and a variety of different outcomes has been found, depending much on the conditions used. Despite similarities with the related graphene/Ni(111) system, the route for establishing viable protocols for epitaxial growth has proven not to be as straightforward as it could be expected on plain geometrical arguments. Most notably, a structural transformation has been found to occur in graphene, which induces its recrystallization upon annealing. Yet, the microscopic mechanisms behind the epitaxy of graphene on cobalt and their relation to the CVD process remain still unclear. In the present work, we address the structural transition from a rotationally incoherent, defective graphene layer formed at low temperatures to a high crystalline quality epitaxial one on a cobalt substrate. To do this, we use an array of powerful methods based on cathode lens microscopy,

offering high structural and chemical sensitivity. We find that the transformation takes place via the growth and propagation of mesoscopic carbidic islands. We identify the underlying mechanism for the formation of epitaxial graphene to involve the dissolution and recondensation of carbon within these regions. The activation energy of the process is estimated to be 1.84 ± 0.11 eV, indicating that the carbon detachment is the rate-limiting step.

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Role of carbon dissolution and recondensation in graphene epitaxial alignment on cobalt; M. Jugovac, F. Genuzio, E.G. Lazo, N. Stojic, G. Zamborlini, V. Feyer, T.O. Menteş, A. Locatelli, C.M. Schneider;
Carbon 152, 489-496 (2019); doi: 10.1016/j.carbon.2019.06.033;

Ultima modifica il Giovedì, 18 Luglio 2019 16:10