Characterization of nonlinear screening in ionic liquid gated graphene multilayers via infrared spectroscopy*

We quantify charge distributions in turbostratic few-layer graphene combining broadband infrared transmittance spectroscopy and analytical models. We show that the non-invasive experimental technique provides layer-resolved charge density profiles in regimes of interest for energy storage applications accessed using ionic-liquid gating. More importantly, we obtain unambiguous evidence of nonlinear screening of graphene which varies with thickness and charge density. Our results present good agreement with our theoretical model that accounts for the electrostatic coupling between layers and quantum capacitance of graphene. The proposed capacitor network model suggests that the effective channel capacitance increases with multilayer thickness but saturates after three layers, underscoring graphene’s qualities for ultrathin charge storage applications. Our work suggests that the combination of ionic liquid gating and infrared transmission spectroscopy may prove useful to the study of charge distributions in two-dimensional material systems.