  Chemical interface damping is a change in the effective collision frequency
of conduction band electrons in metal originating from a chemical change of the
metal interface. In this work, we present in-situ ellipsometric measurements
that reveal the chemical interface damping effect from electrochemical
oxidation of single crystal and polycrystalline gold films. We observe an
increase in collision frequency of up to 21 meV for single-crystalline gold. To
compare to 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 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 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.
