CoO(100) and CoO(100)/Co₃O₄ Fuchs-Kliewer Phonon Spectra

The CoO(100) HREELS spectrum has been reported with features that, atypically, cannot be attributed to known phonon losses. This article presents both HREELS Fuchs-Kliewer phonon spectra and XPS spectra of both stoichiometric CoO(100) and of this substrate exposed to oxygen gas. CoO(100) O 1s and Co 2p binding energies, and Co 2p satellite structure, were comparable to literature values. As expected, the stoichiometric CoO(100) surface yielded one fundamental phonon loss (∼69.4 meV) with additional losses only at integral multiples of this value. Exposure of the CoO surface to oxygen results in additional losses attributed to the oxidation of the near-surface region, with the single loss phonon varying in energy with oxygen partial pressure. Higher oxide phase results, including XPS spectra, have similarities to those reported for Co₃O₄. Regardless of the nature of the higher oxide overlayer, the present results demonstrate that with respect to fundamental phonon mode and n-multiple losses, the CoO(100) surface HREELS spectrum is comparable to other rock-salt transition metal monoxides, with additional HREELS spectrum features indicating a deviation in the CoO(100) surface stoichiometry.