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P. Lackner, Z. Zou, S. Mayr, U. Diebold, M. Schmid:
"Using photoelectron spectroscopy to observe oxygen spillover to zirconia";
Physical Chemistry Chemical Physics, 21 (2019), 17613 - 17620.

X-ray photoelectron spectroscopy (XPS) of five-monolayer-thick ZrO2films reveals a core level bindingenergy difference of up to 1.8 eV between the tetragonal and monoclinic phase. This difference isexplained by positively charged oxygen vacancies in the tetragonal films, which are slightly reduced. Dueto the large band gap of zirconia (E5-6 eV), these charges shift the electron levels, leading to higherbinding energies of reduced tetragonal films w.r.t. fully oxidized monoclinic films. These core level shiftshave the opposite direction than what is usually encountered for reduced transition metal oxides. Thevacancies can be filledviaoxygen spillover from a catalyst that enables O2dissociation. This can beeither a metal deposited on the film, or, if the film has holes, the metallic (in our case, Rh) substrate.Our study also confirms that tetragonal ZrO2is stabilizedviaoxygen vacancies and shows that the XPSbinding energy difference between O 1s and Zr 3d solely depends on the crystallographic phase

http://dx.doi.org/10.1039/c9cp03322