Effects of low work-function lanthanum oxides on stable electron field emissions from nanoscale emitters

Abstract

Nanoscale electron field emitters are known to produce more stable electron emissions than conventional emitters. This has been attributed to size effects; nanoscale emitters can operate with a small emission current and a low extraction voltage, which reduces the bombardment of residual gas ions on the emitter tip. However, our experiments discovered that nanoscale LaB₆ emitters had extremely stable emissions, suggesting that chemical effects are present in addition to size effects. This suggests that during operations, a material other than LaB₆ may be deposited on the surface of the tip to enhance the stability of emissions. Therefore, we searched for possible materials theoretically within the La–B–O ternary system and found that lanthanum oxides (LaO) and oxygen-deficient La₂O₃ (La₂O_3−x) had good electrical conductivity and a low work function comparable to that of LaB₆. These lanthanum oxides are chemically less reactive to residual gases than LaB₆. Thus, if they are present on the LaB₆ surface, they could stabilize electron emissions without diminishing the emission performance. These findings suggest that lanthanum oxides could be used for electron field emitters.