▎ 摘　　要

We report on graphene films grown by atmospheric pressure chemical vapor deposition on bulk and thin film nickel. Carbon precipitation on the polycrystalline grains is controlled by the methane concentration and substrate cooling rate. It is found that graphene grows over multiple grains, with edges terminating along the grain boundaries and with dimensions directly correlated to the size of the underlying grains. This greatly restricts the resulting graphene size (<10 mu m) in the thin film growth, whereas monolayer graphene with linear dimensions of hundreds of micrometers takes up the great majority of the surface overlayers on the bulk nickel (>50%). In addition, the number of layers can be better controlled in the bulk growth. Characterizations of the graphene sheets using transmission electron microscopy, Raman spectroscopy, and transport measurements in the field-effect configuration are also discussed.