Electron diffraction in UHV SEM, REM, and TEM

Abstract

Electron diffraction techniques are widely used in Surface Science, with the main aim of determining atomic positions in surface reconstructions and the location of adsorbed atoms. These techniques require an Ultra-high vacuum (UHV) environment. The use of a focussed beam in UHV electron microscopes in principle allows such techniques to be applied on a microscopic scale. Most obviously this has been achieved in the Low Energy Electron Microscope (LEEM), where the corresponding diffraction technique, LEED, can now be used to investigate local areas with different surface structures, and to follow both temperature and time evolution of these local structures. Some other geometries can be used to achieve similar goals. If the incident energy is raised, the incidence angle has to be moved from normal towards glancing, so that the 'perpendicular' energy is kept within the LEED range of 10-100 eV. Several reflection (REM) and scanning (SEM) instruments have been built with energies between 5 and lOOkeV. In general, the addition of RHEED to an UHV-SEM with Auger Electron Spectroscopy (AES) forms a very useful tool in Surface Science.