Preliminary study for the construction of a low-energy electron-diffraction apparatus using a high-tension source

Abstract

This paper is a study towards the construction of a low-energy electron-diffraction apparatus using a Johansson objective for its optical system. A theoretical study in Gaussian approximation shows that the diffraction pattern is formed in the focus plane of the objective; its dimensions do not depend on the electron energy. By computing courses of electron trajectories, a more accurate investigation is carried out. A variation of 100 eV in electron energy induces broadening less than 7% in the diffraction pattern. The size of each spot in the pattern is lower than 0.6 mm, while the aperture of the primary beam is lower than 1.6 mm. The objective is shown to carry out by itself the filtering of the secondary electrons, the better this filtering the smaller the aperture radius. This study points out important advantages in using this device for the diffraction of low-energy electrons—advantages which were first perceived in preliminary experiments.