The group of Low Energy Electron Microscopy as a part of the Electron Optics Department deals with the instrumentation and applications of the cathode lens mode in the scanning electron microscope [1]. 

Primary beam electrons of a high energy are decelerated by negative bias of the sample to very low energy electron probe. Reflected and transmitted electrons are then accelerated to the detectors [2]. The probe diameter is nearly of a constant size through the whole energy range as the cathode lens is a very good corrector of aberrations under the wavelength of electrons varying within several orders of magnitude down to very low energies. 

At low energies the interaction volume of electrons inside a target diminishes making hence the method highly surface sensitive. Below about 50 eV plenty of contrast mechanisms given by the crystal orientation and its electronic structure can be studied. The transmitted signal at units of electronvolts can be observable especially with two dimensional crystals.  

1. Müllerová I., Frank L.: Scanning low energy electron microscopy. In: Advances in imaging and electron physics 128 (2003), ed. by Hawkes P., New York, Elsevier Science, 309-443. 

2. Müllerová I., Matsuda K., Hrnčiřík P., Frank.L.: Enhancement of SEM to scanning LEEM. Surface Science 601 (2007) 4768-4773.

 

For further reading on Low Energy Electron Transmission see: