Direct growth of bilayer graphene on SiO₂ substrates by carbon diffusion through nickel

Here we report a transfer-free method of synthesizing bilayer graphene directly on SiO(2) substrates by carbon diffusion through a layer of nickel. The 400 nm nickel layer was deposited on the top of SiO(2) substrates and used as the catalyst. Spin-coated polymer films such as poly(methyl methacrylate), high-impact polystyrene or acrylonitrile-butadiene-styrene, or gas-phase methane were used as carbon sources. During the annealing process at 1000 °C, the carbon sources on the top of the nickel decomposed and diffused into the nickel layer. When cooled to room temperature, bilayer graphene was formed between the nickel layer and the SiO(2) substrates. The nickel films were removed by etchants, and bilayer graphene was then directly obtained on SiO(2), eliminating any transfer process. The bilayer nature of the obtained graphene films on SiO(2) substrates was verified by Raman spectroscopy and transmission electron microscopy. The Raman spectroscopy mapping over a 100 × 100 μm(2) area indicated that the obtained graphene is high-quality and bilayer coverage is approximately 70%.