Stabilization of a tungsten ⟨310⟩ cold field emitter

Abstract

Cold-field-emission current from a tungsten ⟨310⟩ emitter in a scanning electron microscope (SEM) gun, evacuated by an ion pump and a supplementary nonevaporative getter pump, was stabilized. It was verified that the probe current from a local (310) crystal plane exhibits different time variations in comparison to that of total current. As for the probe current under a pressure of 2×10−9 Pa, a stable plateau region—which lasted about 4 h—appeared just after flashing of the emitter. By observing emission patterns, it was verified that these different emission characteristics are originated from the anisotropy of current decay in accordance with crystal planes. With low-temperature “mild flashings” at 700 °C, the plateau region was extended to 12 h, which is long enough for practical SEM application. The superior properties of the plateau region, namely, high current, low noise, and small current variation, will enhance the performance and usability of electron microscopes.