Control of carrier type and density in exfoliated graphene by interface engineering

Air-stable, n-doped or p-doped graphene sheets on a chip were achieved by modifying the substrates with self-assembled layers of silane and polymer. The interfacial effects on the electronic properties of graphene were investigated using micro-Raman and Kelvin probe force microscopy (KPFM). Raman studies demonstrated that the phonon vibrations were sensitive to the doping level of graphene on the various substrates. Complementary information on the charge transfer between the graphene and substrate was extracted by measuring the surface potential of graphene flakes using KPFM, which illustrated the distribution of carriers in different graphene layers as well as the formation of dipoles at the interface. The Fermi level of single layer graphene on the modified substrates could be tuned in a range from-130 to 90 mV with respect to the Dirac point, corresponding to the doped carrier concentrations up to 1012 cm^-2.