Infrared Spectroscopic Probe of Charge Distribution in Gated Multilayer Graphene: Evidence of Nonlinear Screening

We characterize the charge distribution in ion-gated turbostratic multilayer graphene employing broadband infrared transmittance spectroscopy. The experimental results evince the nonlinear screening of graphene and are in agreement with a theoretical model that accounts for the electrostatic coupling between the layers and the quantum capacitance of the graphene. We find that descriptions of charge distributions in these systems in the high-density regimes accessed experimentally via the formation of an electric double layer must include the capacitance of the multilayer graphene channel, which varies with charge and thickness. Specifically, the graphene-channel capacitance increases with thickness but tends to saturate after three layers, underscoring graphene's qualities for ultrathin charge-storage applications. Through accurate determination of the layer-resolved carrier density in multilayer graphene, this sensitive technique may prove useful for the study of charge distributions in other two-dimensional multilayer devices.