Secondary electron yield of air-exposed ALD-Al2O3 coating on Ag-plated aluminum alloy

Abstract

Abstract Secondary electron yield (SEY) of air-exposed metals tends to be increased because of air-formed oxide, hydrocarbon, and other contaminants. This enhances the possibility of secondary electron multipacting in high-power microwave systems, resulting in undesirable occurrence of discharge damage. Al2O3 coatings have been utilized as passive and protective layers on device packages to provide good environmental stability. We employed atomic layer deposition (ALD) to produce a series of uniform Al2O3 coatings with appropriate thickness on Ag-plated aluminum alloy. The secondary electron emission characteristics and their variations during air exposure were observed. The escape depth of secondary electron needs to exceed the coating thickness to some extent in order to demonstrate SEY of metallic substrates. Based on experimental and calculated results, the maximum SEY of Ag-plated aluminum alloy had been maintained at 2.45 over 90 days of exposure without obvious degradation by applying 1 nm Al2O3 coatings. In comparison, the peak SEY of untreated Ag-plated aluminum alloy grew from an initial 2.33 to 2.53, exceeding that of the 1 nm Al2O3 sample. The ultra-thin ALD-Al2O3 coating substantially enhanced the SEY stability of metal materials, with good implications for the environmental dependability of spacecraft microwave components.