XPS analysis of electrically stressed alumina

The importance of reliable high voltage performance of ceramic samples in vacuum dictates the use of surface analysis for better understanding of flashover phenomenon. XPS analysis was used with three types of alumina samples, raw, chemically cleaned and metallised, in the course of studying the electric and optical performance of ceramic insulators under high electric field in vacuum. Two sapphire samples were also used for the purpose of comparison. The aim is to identify the effect of surface conditions, cleaning and metallisation, on the high field performance of insulators. XPS results indicated clear differences between the three types, which are reflected in the electro-optical performance of the samples examined. A systematic analysis of the sapphire sample, non-metallised (raw and chemically cleaned) and metallised alumina samples was carried out before and after the gradual application of electric fields up to 15 MV/m in high vacuum. The results obtained for chemically cleaned and metallised samples are similar as far as the variation of the main components, before and after the application of electrical fields. Carbon and oxygen atomic concentrations changed after the application of voltage in an adverse way to that for raw samples. Impurities were found in some of the samples, which explained their unexpected I-V characteristic behaviour. With the aid of other techniques, including electro-optical studies, a better understanding of the electronic behaviour of the ceramics was obtained.