The role of oxygen and fluorine in the electron emission of some kinds of cathodes

Abstract

Experiments have proved that lowering of the work function of a cathode by adsorbing both oxygen and electropositive metallic elements on its surface may be more effective than by adsorbing simply the metallic element. However, the role played by oxygen is not yet completely clear. In this paper we first discuss briefly the situation of the thermionic cathode. Then the role of oxygen or fluorine in the activation of the negative electron affinity GaAs photocathode is discussed. Emphasis will be placed on the atomic core potential field of the surface atoms of the cathode, the bonding state of the surface adsorption layer (Cs or O), and the transfer of electron charges in the surface atoms. The conclusion is drawn that an appropriate quantity of oxygen adsorbed on the cathode surface would be essential to result in a better dispenser cathode and also high quantum yield negative electron affinity photocathodes, while fluorine would play an important part in the electron emission stability.