Electron spectroscopy in SEM and STEM

Low energy electrons, in the energy range 0-2 keV, are very useful in surface science. Both secondary (0-100 eV nominally) and Auger (50-2 keV) electrons can be used as analytic signals in ultra-high vacuum (UHV) scanning (SEM) and scanning transmission (STEM) electron microscopes. This paper briefly reviews some ongoing projects, which are aimed at improving the spatial resolution and information content of these signals. Both secondary electron imaging (SEI) and Auger electrons spectroscopy (AES) have a long history. Reviews of AES and its microscopic counterpart scanning Auger microscopy (SAM) have been given previously in this International Conference Series; over the intervening period AES/SAM instruments have become widely available commercially. Simply biassing the sample up to a few hundred volts (-ve) has lead to a new technique (biassed-SEI) which is sensitive at the sub-monolayer level. In general biassing the sample is a useful additional experimental variable. It can be used to visualize thin films and surface topography, including steps; it can also be used to distinguish spectral features (eg Auger peaks) from the sample from those due to stray electrons, and to place such features in the best energy region for the electron spectrometer.