Ar-ion bombardment effects on ZrO2 surfaces.

Abstract

Chemical, compositional, and electronic changes induced by 3-keV ${\mathrm{Ar}}^{+}$ sputtering in ${\mathrm{ZrO}}_{2}$ have been quantitatively studied by use of x-ray photoemission spectroscopy. It is shown that 3-keV ${\mathrm{Ar}}^{+}$ bombardment leads to a gradual buildup of an oxygen depletion layer which has been quantitatively characterized by its thickness (\ensuremath{\sim}1.2 nm), averaged composition (\ensuremath{\sim}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 ${\mathrm{Ar}}^{+}$-bombarded ${\mathrm{ZrO}}_{2}$ was also determined by x-ray photoemission spectroscopy. Thermally grown ${\mathrm{ZrO}}_{2}$ was shown to exhibit significant photoemission in the band gap, probably due to defects. ${\mathrm{Ar}}^{+}$ 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 ${\mathrm{Ar}}^{+}$ 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.