| AVS 64th International Symposium & Exhibition | |
| Vacuum Technology Division | Monday Sessions |
| Session VT+MN-MoM |
| Session: | Progress with Measurement in Vacuum |
| Presenter: | Keigo Kasuya, Hitachi, Ltd., Japan |
| Authors: | K. Kasuya, Hitachi, Ltd., Japan T. Ohshima, Hitachi, Ltd., Japan S. Katagiri, Hitachi, Ltd., Japan T. Kawasaki, Hitachi, Ltd., Japan |
| Correspondent: | Click to Email |
In the presence of a strong electric field, electrons are emitted from sharply pointed cathodes at room temperature. This cold field emission (CFE) process provides a prominent electron beam with high brightness and a low energy spread, so CFE emitters are used extensively in a variety of electron microscopes.
One of the important challenges for CFE is stabilizing the emission current. The adsorption of residual gases on the emitter increases the surface work function and decreases the emission current over time. Additionally, surface sputtering by ions causes irregular current fluctuations.
One way to stabilize emission current is to reduce the pressure around the electron gun. This decreases incident gases and ions hitting the emitter and slows the current decrease. We reduced the pressure of an electron gun from 10-8 to 10-10 Pa by using non-evaporative getter (NEG) pumps [1]. This stabilized the emission current so that it was almost constant over a 24 hour period. The 90% decrease time, the time it takes the current to fall to 90% of the initial value, was increased from 10 minutes to 1280 minutes. In addition, the maximum emission current was increased from 30 μA to 1000 μA. With this gun, operators can use electron microscopes without the need for emission current adjustment.
By applying this technology, we developed a 1.2 MV high voltage transmission electron microscope [2]. The electron gun is equipped with a preaccelerator magnetic lens for enhancing the effective brightness of the electron beam. The pressure of the gun was 3X10-10 Pa, and a stable emission current was obtained. The microscope achieved the world’s highest spatial resolution of 43 pm.
Part of this research was funded by a grant from the Japan Society for the Promotion of Science (JSPS) through the “Funding Program for World-Leading Innovative R&D on Science and Technology (FIRST Program),” initiated by the Council for Science and Technology Policy (CSTP).
[1] K. Kasuya et al., J. Vac. Sci. Technol. B, 34, 042202 (2016).
[2] K. Kasuya et al., J. Vac. Sci. Technol. B, 32, 031802 (2014).