Valence excitation in RHEED

Electron energy-loss spectroscopy (EELS) has proven to be a powerful method for studying the electronic structure and performing microanalyses of materials in a transmission electron microscope (see for example, Egerton (1986)). In conjunction with imaging of thin films by TEM and STEM, EELS has permitted chemical analysis of small specimen regions with high spatial resolution. The analysis of energy-loss edges for inner-shell excitation has allowed the determination of valence states of atoms from the energy-loss near-edge structure (ELNES) and determination of the local environments of atoms from the extended energy-loss fine structure (EXELFS). The use of EELS in the glancing incidence, surface-reflection mode for bulk samples is an attractive topic since the penetration of the electron beam into the surface, in general, is just a few atomic layers. This is the technique of high-energy reflection electron energy-loss spectroscopy (REELS). The analysis of the composition and structure of thin surface layers can form an important adjunct to high-resolution surface imaging by REM, or in combination with scanning REM (SREM), microdiffraction and secondary electron (SE) imaging, which are possible with STEM instruments.