  The growth of graphene during Cu-catalyzed chemical vapor deposition was
studied using 12CH4 and 13CH4 precursor gasses. We suggest that the growth
begins by the formation of a multilayer cluster. This seed increases its size
but the growth speed of a particular layer depends on its proximity to the
copper surface. The layer closest to the substrate grows fastest and thus
further limits the growth rate of the upper layers. Nevertheless, the growth of
the upper layers continues until the copper surface is completely blocked. It
is shown that the upper layers can be removed by modification of the conditions
of the growth by hydrogen etching.
