Au-nanoparticle incorporated oxide thin film materials demonstrate significant promise as functional sensor materials for high temperature optical gas sensing in severe environments relevant for fossil and nuclear based power generation. The Au/yttria-stabilized zirconia (YSZ) system has been extensively studied in the literature and serves as a model system for fundamental investigations that seek to better understand the mechanistic origin of the plasmonic gas sensing response. In this work, X-ray photoelectron spectroscopy techniques are applied to Au/YSZ films in an attempt to provide further experimental evidence for a proposed sensing mechanism involving a change in free carrier density of Au nanoparticles due to charge transfer. Published by Elsevier B.V.