Chemical Interface Damping by Electrochemical Gold Oxidation

Chemical interface damping is a change in the effective collision frequency of conduction band electrons in metal originating from a chemical change in the metal interface. In this work, we present in situ ellipsometric measurements that reveal the chemical interface damping effect from the electrochemical oxidation of single-crystal and polycrystalline gold films. We observed an increase in collision frequency of up to 21 meV for single-crystalline gold. To compare with literature results obtained with thiols and metal oxides on gold nanoparticles, we normalize the collision frequency by the electron mean free path to the surface of the structure. We show that electrochemical gold oxidation provides a stronger effect on the collision frequency than these coatings. Similar ellipsometric experiments have previously been conducted to investigate the optical properties of gold oxide but without taking chemical interface damping into account. The change in reflection from the oxidation of gold was solely attributed to the oxide coating. We also show that the chemical interface damping effect saturates at a larger effective oxide thickness, which is attributed to the stabilization of the gold-oxide interface. Our results are important for the design of optoelectronic and photochemical experiments involving nanostructured gold. Electrochemical gold oxidation can be used to significantly change the optical response of such structures and to increase the efficiency of the light–matter interaction.