On Contamination on Electrode Surfaces and Electric Field Limitations

Broad area electrodes, especially in technical systems, are contaminated by oxides, adsorbates, and dust in mean thicknesses between 1 and 100 nm depending on surface preparation. These contaminants yield electric field limitations in three respects: (1) adsorbates and dust enhance the field emission of electrons (FE); (2) oxides, adsorbates and dust n enhance the secondary electron emission (SEE); and (3) oxides, adsorbates and dust show stimulated desorption of molecules and ions under electron, photon, or ion impact. Because of these enhancements, more electric field energy is transferred to the kinetic energy of electrons and ions, enhancing secondary processes such as electron emission and desorption of molecules and ions. Thus, electric field limitations and breakdown phenomena are encountered already at field levels as low as 106. V/m, where clean surfaces don't show field limitations and breakdown phenomena.