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

Abstract

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.