Secondary ion emission from binary alloy systems. Part II: Ar¹ bombardment with O₂ absorption

Abstract

The emission of positive atomic ions from Cu-Ni, Pd-Ni, and Ag-Pd alloys was studied under Ar+ bombardment with saturated O2 adsoprtion. In line with other published data on Cr-Fe, Cr-Ni, and Fe-Ni alloys, these studies all agree well with two general rules porposed previously for O+2 bombardment. The first rule states that for an alloy A-B, where A forms a stronger oxide bond than B, the presence of A enhances the emission of B+, and the presence of B suppresses the emission of A+. The second rule states that the presence of A sharpens the energy distribution of B+ while the presence of B broadens the energy distribution of A+. The experimental data fit the rules with better consistency than for the case of O+2 bombardment except in cases of low oxygen sticking coefficients on the alloy surfaces. The success of the general rules is linked with the enhanced oxidation of B and the suppressed oxidation of A in the alloy. X-ray photoemission studies of the oxidized surfces support this explanation. Further evidence of an energy-dependent ionization probability of Ni+ from pure Ni provides a consistent explanation of the second general rule.