Photoelectron Emission of TiN-coated Alumina Excited by Ultraviolet Light

Surface breakdown of solid insulator in vacuum is initiated by surface charging which is strongly influenced by electron emission properties of the insulator. In this study, photoelectron emission of alumina exited by vacuum ultraviolet light is observed using an electron emission microscope (EEM). As a result, photoelectron emissions of 99.7% purity alumina ceramic named HA997, sapphire (single crystal alumina) and TiN-coated sapphire intermittently took place at isolated individual sites on its surface, while that of conductive material is a continuous emission. The discrete emission of the insulator samples is probably caused by the positive surface charging after the electron emission. It is found that the number of the photoelectron emission sites of HA997 is higher than that of sapphire. Since TiN is often coated on alumina for reducing SEE coefficients, photoelectron emission sites of TiN-coated sapphire were also investigated. The results show that the number of the emission sites is almost same as that of uncoated sapphire. Furthermore, the relationship between photoelectron emission properties and surface charging is also discussed