RESPONSE OF OXIDES TO ION-BOMBARDMENT - THE DIFFERENCE BETWEEN INERT AND REACTIVE IONS

The loss of O from oxides bombarded by chemically neutral ions, i.e. inert gas ions, is widely documented. It is, however, still not possible to relate with certainty such loss to the basic properties of the oxides, namely to such factors as mass, surface binding energy, bulk binding energy, volatility, mass transport, Gibbsian segregation, or electric fields. Even the most basic response of all, namely chemically random behavior [Vertoti et al., Surf. Interf. Anal. 19 (1992) 291), has an unestablished importance. The present work further develops our approach to the problem. The effects of 1-5 keV bombardment with Ar+, O2+, N2+, and N2O+ are compared using X-ray photoelectron spectroscopy for a number of oxide pairs with similar stoichiometries and electronic structures: B2O3 and Al2O3, SiO2 and GeO2, ZrO2 and TiO2, V2O5 and Nb2O5. Minor O loss occurred with the first five and major loss with the last three. What is important, however, is that the loss was consistently higher for N2+ than Ar+ impact, yet the overall anion content, expressed as the sum O + N, remained largely unchanged. We take this result as demonstrating a prominent role for chemically random behavior, i.e. the relative strengths of the M-O and M-N bonds did not enter.