Effect of the surface processing on the secondary electron yield of Al alloy samples

In this study we have investigated the relation between the secondary electron yield (SEY) and the surface chemical state for technical Al alloy samples cut from the inner walls of the Petra III storage ring. SEY curves measured after prolonged electron beam irradiation at 500 eV showed maximum values (δ_max⁡) between 1.8 and 1.5. By combining x-ray photoelectron spectroscopy with SEY measurements, we have been able to relate the surface chemical composition to the δ_max⁡ values for the “as-received” surface (δ_max⁡=2.7), for the electron beam conditioned sample (δ_max⁡=1.8-1.5), and after substantially removing the surface contaminating layer by means of Ar⁺ ion sputtering (δ_max⁡=1.3). Our detailed chemical analysis shows that the SEY strongly increases in the presence of the thin surface oxide film which unavoidably forms on the clean Al alloy sample under electron beam irradiation even in ultrahigh vacuum conditions, and suggests that the high reactivity of pure Al and Al alloys to oxygen could be the cause of the difference among the SEY values measured in different ultrahigh vacuum environments.