  Graphene has recently attracted a great deal of interest in both academia and
industry because of its unique electronic and optical properties [1,2], as well
as its chemical, thermal, and mechanical properties. The superb characteristics
of graphene make this material one of the most promising candidates for various
applications, such as ultrafast electronic circuits [1] and photodetectors [2],
clean and renewable energy [3], and rapid single-molecule DNA sequencing [4,5].
The electronic properties of the graphene system rely heavily on the number of
graphene layers [6] and effects on the coupling with the underlying substrate.
Graphene can be produced by mechanical exfoliation of graphite, solution
approaches [7,8], thermal decomposition of SiC [9,10], and chemical vapor
deposition/segregation on catalytic metals [11-17]. Despite significant
progress in graphene synthesis, production with fine control over the thickness
of the film remains a considerable challenge. Here, we report on the synthesis
of nearly 100% coverage of single-layer graphene on a Ni(111) surface with
carbon atoms diffused from a highly orientated pyrolytic graphite (HOPG)
substrate. Our results demonstrate how fine control of thickness and structure
can be achieved by optimization of equilibrium processes of carbon diffusion
from HOPG, segregation from Ni, and carbon diffusion at a Ni surface. Our
method represents a significant step toward the scalable synthesis of graphene
films with high structural qualities and finely controlled thicknesses and
toward realizing the unique properties of graphene.
