Response of oxides to ion bombardment: the difference between inert and reactive ions

Abstract

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 [Vertóti 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 +, O 2 +, N 2 +, and N 2O + are compared using X-ray photoelectron spectroscopy for a number of oxide pairs with similar stoichiometries and electronic structures: B 2O 3 and Al 2O 3, SiO 2 and GeO 2, ZrO 2 and TiO 2, V 2O 5 and Nb 2O 5. 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 N 2 + 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.