▎ 摘　　要

The discovery of electric field induced band gap opening in bilayer graphene opens a new door for making semiconducting graphene without aggressive size scaling or using expensive substrates. However, bilayer graphene samples have been limited to mu m(2) size scale thus far, and synthesis of wafer scale bilayer graphene poses a tremendous challenge. Here we report homogeneous bilayer graphene films over at least a 2 in. x 2 in. area, synthesized by chemical vapor deposition on copper foil and subsequently transferred to arbitrary substrates. The bilayer nature of graphene film is verified by Raman spectroscopy, atomic force microscopy, and transmission electron microscopy. Importantly, spatially resolved Raman spectroscopy confirms a bilayer coverage of over 99%. The homogeneity of the film is further supported by electrical transport measurements on dual-gate bilayer graphene transistors, in which a band gap opening is observed in 98% of the devices.