In order to meet the needs of electron emitter’s surface study

a simple and convenient AES apparatus has been made. Some oxide cathodes and active Ni substrates were studied by means of this apparatus.lt was observed that the relative atomic concentration of Ba and Sr changed significantly before and after activation. And this change is related to the surface segregation of the activating agents in active Ni. A fully-activated cathode has greater amount of BaO than SrO in the coating surface layer and "excess" Ba also appears in this region.