Large Conductance Modulation of Gold Thin Films by Huge Charge Injection via Electrochemical Gating

By using an electrochemical gating technique with a new combination of polymer and electrolyte, we were able to inject surface charge densities n2D as high as 3.5×10¹⁵ e/cm² in gold films and to observe large relative variations in the film resistance, ΔR/R^', up to $10%$ at low temperature. ΔR/R^' is a linear function of n2D---as expected within a free-electron model---if the film is thick enough (≥25 nm); otherwise, a tendency to saturation due to size effects is observed. The application of this technique to 2D materials might allow extending the field-effect experiments to a range of charge doping where large conductance modulations and, in some cases, even the occurrence of superconductivity are expected.