ELECTRONIC-STRUCTURE OF STOICHIOMETRIC AND AR-BOMBARDED ZRO2 DETERMINED BY RESONANT PHOTOEMISSION()

The electronic properties of thermally grown ZrO2 thin films before an d after Ar+ bombardment have been studied with resonant photoemission spectroscopy using synchrotron radiation. For stoichiometric ZrO2 thin films the experimental valence-band spectra are in good agreement wit h the calculated density of states for bulk ZrO2. For both stoichiomet ric and Ar+-bombarded ZrO2 thin films, resonant photoemission from the valence band was observed when the photon energy was swept through th e Zr 4p-->4d transition energy. The resonant profile was found to exhi bit a maximum at hv=39 eV, followed by a second well-resolved broad ma ximum around 50 eV. The feature at 39 eV is consistent with resonant e nhancement of the Zr 4d states and has been used to identify those reg ions of the valence band with an important Zr 4d admixture. The result s are in good agreement with the calculated Zr 4d partial density of s tates. The intensity increase observed at hv similar to 45-50 eV is fo und to be associated with the nonbonding region of the valence band, a lthough a proper interpretation is needed. In addition, it was found t hat Ar+ bombardment induces electronic states in the band-gap region a nd changes in the O 2p valence band. Three distinct emission bands wer e identified in the band gap as a function of the Ar+ dose. They are a ssociated with the formation of oxygen vacancies and mixed oxidation s tates due to preferential sputtering of the oxygen atoms. Resonant pho toemission of these Ar+-bombarded films demonstrates both the cationic character of the band-gap states and the increase of the cationic con tribution to the O 2p valence band.