  From both fundamental and technical points of view, a precise control of the
layer number of graphene samples is very important. To reach this goal, atomic
scale mechanisms of multilayer graphene growth on metal surfaces should be
understood. Although it is a geometrically favorable pathway to transport
carbon species to interface and then form a new graphene layer there,
penetration of a graphene overlayer is not a chemically straightforward
process. In this study, the possibility of different active species to
penetrate a graphene overlayer on Cu(111) surface is investigated based on
first principles calculations. It is found that carbon atom penetration can be
realized via an atom exchange process, which leads to a new graphene growth
mechanism. Based on this result, a bilayer graphene growth protocol is proposed
to obtain high quality samples. Such a penetration possibility also provides a
great flexibility for designed growth of graphene nanostructures.
