  We report that graphene films with thickness ranging from 1 to 7 layers can
be controllably synthesized on the surface of polycrystalline copper by a
chemical vapour deposition method. The number of layers of graphene is
controlled precisely by regulating the flow ratio of CH4 and H2, the reaction
pressure, the temperature and the reaction time. The synthesized graphene films
were characterized by scanning electron microscopy, transmission electron
microscopy, selected area electron diffraction, X-ray diffraction and Raman
spectroscopy. In addition, the graphene films transferred from copper to other
substrates are found to have a good optical transmittance that makes them
suitable for transparent conductive materials.
