High emission current of 1000 μA at 4 × 10−10 Pa from W⟨310⟩ cold field emitter in electron gun

Abstract

Total cold field emission (CFE) current has generally been limited to 30 μA because a higher current may initiate a vacuum arc that destroys the emitter. However, high emission current is needed to reduce the operation time in analytical electron microscopy and to further enhance the brightness of CFE. The authors achieved a total emission current of 1000 μA by reducing the pressure around the electron gun to 4 × 10−10 Pa. This high emission current was achieved without initiating a vacuum arc apparently because the number of ions striking the emitter surface was reduced. While a high angular current density of 1670 μA/sr was obtained at 1000 μA, current fluctuation occurred during the initial “plateau region” period of the probe current, and this needs to be investigated. This fluctuation is attributed to surface adsorption of gases emitted by electron stimulated desorption (ESD). Evaluation of the effect of introducing dominant ESD gases, namely, H2 or CO, on the current fluctuation revealed that the adsorption of H2 maintained the plateau region while the adsorption of CO caused current fluctuation in the plateau region.