Dynamics of Electric Double Layer Formation and Dissipation in Polyethylene Oxide:LiClO4 on Graphene Transistors

A convenient tool for exploring the electronic properties of two-dimensional (2D) materials is the formation of an electric double layer (EDL). The EDL is formed at the interface between the 2D material and an electrolyte where cations or anions induce image charge in the 2D material, doping it n- or p-type respectively. This approach is powerful because it can induce ultrahigh sheet carrier densities up to 10¹⁴ cm^-2, surpassing traditional gate oxides by more than one order of magnitude. To extend the use of EDL doping beyond basic materials exploration to practical devices, what is needed is a better understanding of the dynamics of EDL formation/dissipation. In this work, epitaxial graphene Hall bar devices are gated with a solid polymer electrolyte, polyethylene oxide (PEO):LiClO₄. Hall measurements are used to quantify sheet carrier density and mobility in the electrolytic-gate bias range of ± 2 V. Ion dynamics of EDL formation and dissipation are measured as a function of temperature. At an electrolyte thickness of 1 μm, the room temperature EDL formation time (~1 – 100 s) is longer than the dissipation time (~10 ms). The EDL dissipation is modeled by a stretched exponential decay, and the temperature-dependent dissipation times are described by the Vogel-Fulcher-Tammann equation, reflecting the coupling between polymer and ion mobility. The measured temperature-dependent relaxation times qualitatively agree with COMSOL multiphysics simulations of time-dependent ion transport in the presence of an applied field. Additional results showing EDL response to pulsed bias measurements will also be presented.

This work was supported in part by the Center for Low Energy Systems Technology (LEAST), one of six centers of STARnet, a Semiconductor Research Corporation program sponsored by MARCO and DARPA.