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

摘要

Electrolyte gating using ionic liquid electrolytes has recently generatedconsiderable interest as a method to achieve large carrier density modulationsin a variety of materials. In noble metal thin films, electrolyte gatingresults in large changes in sheet resistance. The widely accepted mechanism forthese changes is the formation of an electric double layer with a charged layerof ions in the liquid and accumulation or depletion of carriers in the thinfilm. We report here a different mechanism. In particular, we show using x-rayabsorption near edge structure (XANES) that the previously reported largeconductance modulation in gold films is due to reversible oxidation andreduction 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 theobserved change in transport properties. These results represent a significantstep towards understanding the mechanisms involved in electrolyte gating.