Direct synthesis of bilayer graphene on silicon dioxide substrates

Graphene layers were synthesized on silica and 90, 300, 400 and 700 nm thick silicon dioxide films by chemical vapor deposition at semi-atmospheric pressure environment, using controlled mixtures of hydrogen, argon and methane gases. The effects of the methane flux and the total pressure on the homogeneity of the graphene layers were investigated. The samples were characterized by Raman spectroscopy and mapping, X-ray photoelectron spectroscopy and optical transmittance measurements. The latter method was used to determine the number of graphene layers of the samples. Scanning electron microscopy, atomic force microscopy was carried out to study the surface uniformity and electrical measurements were also performed. Our results indicate that large area, a homogeneous nanocrystalline graphene layer can be obtained with an appropriate choice of synthesis parameters. Raman spectroscopy results indicate turbostratic graphene bilayers were obtained.