  Graphene is a very promising material for nanoelectronics applications due to
its unique and remarkable electronic and thermal properties. However, when
deposited on metallic electrodes the overall thermal conductivity is
significantly decreased. This phenomenon has been attributed to the mismatch
between the interfaces and contact thermal resistance. Experimentally, one way
to improve the graphene/metal contact is thorough high-temperature annealing,
but the detailed mechanisms behind these processes remain unclear. In order to
address these questions, we carried out fully atomistic reactive molecular
dynamics simulations using the ReaxFF force field to investigate the
interactions between multi-layer graphene and metallic electrodes (nickel)
under (thermal) annealing. Our results show that the annealing induces an
upward-downward movement of the graphene layers, causing a pile-driver-like
effect over the metallic surface. This graphene induced movements cause a
planarization (thermal polishing-like effect) of the metallic surface, which
results in the increase of the effective graphene/metal contact area. This can
also explain the experimentally observed improvements of the thermal and
electric conductivities.
