Measurements and microscopic model of quantum capacitance in graphene

Metal-oxide-semiconductor (MOS) structures based on graphene were fabricated with ultrathin Y2O3 films as the top gate oxide. While the quantum capacitance of graphene was measured using the MOS structure and shown to agree well with theory for ideal graphene at large channel potential, it deviates significantly from theory near the Dirac point. A general microscopic capacitance model is developed and used to describe the quantum capacitance anomaly near the Dirac point. Excellent agreement with experiment results was achieved using this model and key parameters including potential fluctuation and local carrier density fluctuation were retrieved.