Generation of electron beams by low–temperature field emission

Abstract

AbstractA method is proposed of generating a fine electron beam which has an excellent monochromaticity and high brightness by using an extremely low temperature and high electric field. This paper describes the actual apparatus based on the proposal. If the cathode of the apparatus is kept at an extremely low temperature (about 4K), theoretically, the possibility exists of making the energy spread as small as of the order of 0.01 eV, while the energy spread of a conventional electron beam at room temperature with a high electric field is of the order of 0.1 eV. The prototype apparatus assembled consists of a 3‐electrode type electron emission system, the main part containing a retarding potential energy analyzer and a vacuum chamber (about 10−9 Torr) made of stainless steel. Polycrystal tungsten wire is used for the cathode. The reduction of the energy spread was not achieved for the theoretical value, because of the deposits on the tip surface due to the residual gas (notably oxygen) at the extremely low temperature (cooled by liquid helium). At a low temperature (cooled by liquid nitrogen), however, the energy spread was improved by 25% compared with that at room temperature. This shows a possible improvement of the energy spread by cooling the cathod as expected.