Low-energy electron diffraction with energy resolution

Abstract

Low-energy electron diffraction (LEED) is a well established technique for evaluation of the surface atom arrangement. The information is derived from the elastically scattered electrons. Usually the thermal diffuse background between diffraction spots is assumed to be constant and subtracted as a constant. For spot profile analysis, which provides the arrangement of units like islands or domains, the elastic intensity has to be measured throughout the Brillouin zone. The usual LEED systems (with energy resolution of some eV) cannot distinguish between elastic and thermal diffuse scattering. For that purpose a new instrument has been developed. We combined the deflection unit from a high-resolution LEED system with 127° analyzer from a high-resolution electron energy loss spectrometer (EELS) in a suitable manner. The new instrument was checked with the Si(111), Al(111), and Al(111)+O2 surface. The energy resolution (ΔE=6.7 meV) allows separation of a large fraction of phonon losses. The momentum resolution (transfer width 150 nm) is the same as other high-resolution LEED systems. As a result the first LEED system with both high momentum and high energy resolution is presented (ELS-LEED).