Raman spectra of graphene exfoliated on insulating crystalline substrates

We have investigated single layer, bilayer and few-layer graphene exfoliated on SiO 2 and on single crystal surfaces of SrTiO 3 , Al 2 O 3 and TiO 2 using Raman spectroscopy. The typical 'fingerprint' 2 D peak turns out to be indicative of the number of graphene layers independent of the substrate material. The morphological quality of the graphene is as good as on SiO 2 substrates for all the materials. We find evidence for substrate-induced changes due to doping. With most substrates, hole doping is observed, but with SrTiO 3 we have identified a dielectric substrate with which electron accumulation in graphene can be achieved.