High Resolution Electron Energy Loss Spectroscopy (HREELS)
High resolution electron energy loss spectroscopy (HREELS) is a surface science technique to study e.g. molecular vibrations of adsorbates and other surface related excitations (e.g. plasmons). A highly monochromatized (dE~0.5 meV), sharp beam of electrons is directed at a surface. While most of the electrons are reflected from the surface, some of them interact more intensely and loose a certain amount of energy by exciting surface plasmons or molecular vibrations. These electrons have accordingly a lower kinetic energy and can also be detected in off-specular directions (i.e. not in the main beam of reflected electrons). From the exact amount of lost energy and the direction under which these electrons leave the surface one, can deduce the details of the vibrational degrees of the freedom of the examined surface.