Ar-ion bombardment effects on ZrO2 surfaces

Chemical, compositional, and electronic changes induced by 3-keV Ar+ sputtering in ZrO2 have been quantitatively studied by use of x-ray photoemission spectroscopy. It is shown that 3-keV Ar+ bombardment leads to a gradual buildup of an oxygen depletion layer which has been quantitatively characterized by its thickness (∼1.2 nm), averaged composition (∼ZrO), and in-depth distribution of the different oxide phases that originate during the process. In addition, the electronic distribution at the valence band of both thermally grown and Ar+-bombarded ZrO2 was also determined by x-ray photoemission spectroscopy. Thermally grown ZrO2 was shown to exhibit significant photoemission in the band gap, probably due to defects. Ar+ bombardment of those surfaces caused a broadband emission at 2.3 eV above the top of the valence band as well as significant changes in the O 2p region of the valence band which are associated with the above-mentioned changes in surface composition. The Zr 4d contribution to the valence band of the altered layer could also be estimated. This contribution increases with Ar+ sputtering and accounts not only for the whole emission band in the gap but also significantly for the photoemision in the O 2p energy range