Secondary ion emission from binary alloy systems. Part I: O ⁺₂ bombardment

Abstract

We have studied the emission of positive atomic ions from five binary alloys: Cr-Ni, Fe-Ni, Cu-Ni, Pd-Ni, and Ag-Pd, all under O+2 bombardment. Significant enhancement and suppression of ionization probabilities due to the presence of the second alloy component were observed. The alloying effect follows two general rules. 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+, while 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+. X-ray photoemission studies of the O+2 bombarded alloy surfaces connect the general rules with the enhanced oxidation of B and the suppressed oxidation of A in the alloys. All the cases that deviate from the rules originate from insufficient oxygen for oxidation resulting from the self-limiting nature of oxidation by O+2 bombardment.