Influence of substrate dielectric permittivity on local capacitive behavior in graphene

Graphene deposited on silicon dioxide (DG-SiO2) and high-kappa dielectric strontium titanate (DG-STO) are investigated for electrostatic properties by local capacitance measurements carried out with Scanning Capacitance Spectroscopy (SCS). The quantum capacitance associated with 2DEG in graphene showed significant increase for DG-STO as a function of Fermi level (E-F) as compared to that for DG-SiO2. The quantum capacitance, being a fundamental property of graphene 2DEG, is not expected to vary with substrate dielectric properties in the absence of any interaction. However, the observed increase in quantum capacitance in our case is predominantly due to the enhanced effectively biased area in DG-STO. We suggest that this effect is a consequence of better dielectric screening of commonly observed charged impurities, on graphene and/or at the graphene/substrate interface, by the use of high permittivity substrate.