▎ 摘　　要

We present a systematic study of grain size and carrier mobility behaviour in polycrystalline graphene films grown on copper substrates with various surface roughness values. We first observe that as the surface roughness of the substrate decreases, the graphene grain size increases significantly, thus decreasing the density of grain boundaries. Then, using field-effect transistor structures, we confirm that as the substrate roughness decreases, carrier mobility values in graphene increase, whatever the channel length of the transistor. For a substrate rms roughness around 5 nm (measured on a 10 x 10 mu m(2) field) and using a fast growth process (similar to 40 min), we obtain mobility values as high as similar to 6900 cm(2) Vs(-1) for electrons and similar to 6000 cm(2) Vs(-1) for holes in polycrystalline graphene with a small grain size of similar to 12-14 mu m.