Mechanism for the Large Conductance Modulation in Electrolyte-gated Thin Gold Films

TL;DR

This paper reveals that large conductance changes in electrolyte-gated gold films are primarily due to reversible surface oxidation and reduction, not electric double layer charging, challenging previous assumptions about the gating mechanism.

Contribution

The study demonstrates that surface redox reactions, rather than electric double layer formation, dominate conductance modulation in electrolyte-gated gold films.

Findings

Reversible oxidation/reduction causes large conductance changes.

Electric double layer capacitance accounts for less than 10% of the effect.

XANES confirms surface redox as the main mechanism.

Abstract

Electrolyte gating using ionic liquid electrolytes has recently generated considerable interest as a method to achieve large carrier density modulations in a variety of materials. In noble metal thin films, electrolyte gating results in large changes in sheet resistance. The widely accepted mechanism for these changes is the formation of an electric double layer with a charged layer of ions in the liquid and accumulation or depletion of carriers in the thin film. We report here a different mechanism. In particular, we show using x-ray absorption near edge structure (XANES) that the previously reported large conductance modulation in gold films is due to reversible oxidation and reduction of the surface rather than the charging of an electric double layer. We show that the double layer capacitance accounts for less than 10\% of the observed change in transport properties. These results represent a significant step towards understanding the mechanisms involved in electrolyte gating.