Performance of MgO/Au cermet films as secondary electron emission cold cathodes

The performance of MgO/Au cermet films as secondary electron emission cold cathodes was tested in a crossed‐field amplifier (CFA) tube until it showed signs of cathode insufficiency. Only 5–25% of the original cermet thickness (4000 Å) was left. Although heavy C coverage was observed, which degraded the secondary electron emission (delta), the primary cause of tube failure was the erosion of the cermet film under electron and ion bombardment. The mechanism and dissociation rate for MgO was determined in electron‐stimulated desorption measurements. A threshold for O+ ion desorption at the Mg 2p level demonstrated that MgO dissociates by the Knotek‐Feibelman mechanism with a yield of 1 × 10−7 O+ ions desorbed per incident electron. Various aspects of cathode erosion during CFA operation were considered and evaluated using a combination of experimental data and theoretical calculations. The results indicate that electrons and ions are both important sources of film erosion and limit the use of MgO/Au cermet films in practical CFA tube applications.