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.

Magnetic field superimposed cold field emission gun under extreme-high vacuum

“…The 90% decrease time was prolonged to 900 min from 290 min in the previous study. 10 This longer decrease time indicates that the pressure around the emitter was lower than that in the previous study in spite of the existence of the preaccelerator magnetic lens. The variation in the probe current was calculated as (I max À I min )/I mean , where I max , I min , and I mean are the maximum, minimum, and average current.…”

“…The behavior of the current variations was similar to that found in the previous study. 10 However, the time span of current decrease took one day because of the pressure reduction to 3 Â 10 À10 Pa. The probe current stayed almost constant for more than 10 h during the initial period of the measurement.…”

“…To obtain images with constant contrast, the stability of the probe current, which is at the center of emission cone and is used for imaging, is more important than the stability of the total current. In our previous study, 10 we reduced the pressure of a conventional FEG from 10 À8 to 10 À9 Pa by employing a nonevaporative getter (NEG) pump. With this gun, we obtained stable probe currents in which the 90% decrease time was 290 min.…”

A stable LaB6 nanoneedle field-emission point electron source

“…3b). 33 It should also be noted that the W(310) emission was operated at an EHV of 10 À9 Pa while the LaB 6 nanoneedle was operated at an ultrahigh vacuum (UHV) of 10 À7 Pa. We expect the LaB 6 nanoneedle to show even more stable emissions when it is operated in an EHV of 10 À9 Pa. The recovery and reproducibility of stable emission current aer exposure to air are also essential for practical applications and this has been veried by experimental measurements using a controlled procedure.…”

Surface characterization of zirconia-coated tungsten Schottky emitters by using RHEED, AES, and TOF-SIMS

“…Their performance strongly depends on the quality of their electron sources [1]. Currently, the Schottky emitter [2,3] and Cold-field emitter [4][5][6] have been used as point electron sources with high brightness, high stability, and low energy spread. The zirconiacoated-tungsten (Zr/O/W) Schottky emitter, developed by Swanson et al [7,8], provides us with a particularly good balance of brightness (about 5× 10 7 A/cm 2 /sr at 5 kV), lifetime (in excess of 15,000 hours), and energy spread (about 0.4 eV) [3].…”