▎ 摘　　要

We report capacitance measurements in top-gated graphene sheets as a function of charge carrier density. A measurement method using an LC-circuit provides high sensitivity to small capacitance changes and hence allows the observation of the quantum part of the capacitance. The extracted density of states has a finite value of 1 x 10(17) m(-2) eV(-1) in the vicinity of the Dirac point, which is in contrast to the theoretical prediction for ideal graphene. We attribute this discrepancy to fluctuations of the electrostatic potential with a typical amplitude of 100 meV in our device.