ELASTIC-SCATTERING AND INTERFERENCE OF BACKSCATTERED PRIMARY, AUGER AND X-RAY PHOTOELECTRONS AT HIGH KINETIC-ENERGY - PRINCIPLES AND APPLICATIONS

Similarities in the diffraction of electrons generated from Point sources in single-crystal materials are discussed and related to the underlying physics associated with the various emission processes. It is shown that despite considerable differences in origin, Auger electrons, X-ray photoelectrons, and primary electrons that are incoherently backscattered exhibit essentially the same diffraction modulations when emitted from the same material at comparable, high kinetic energies. This result occurs because the high degree of forward peaking associated with electron-atom scattering at large kinetic energies selects only lower-order interference fringes at small scattering angles which are rather insensitive to the emission mechanism or the angular momentum of the prescattered final state. Despite these similarities, Auger and X-ray photoelectrons retain the important and distinctive property of atom specificity, a property not generally possessed by backscattered primary electrons. This property can considerably simplify structure determinations of multi-element material surfaces. Although not generally atom-specific, incoherent backscattered electron diffraction offers the advantage of very rapid data acquisition when compared to Auger and X-ray photoelectron diffraction. Similarities between the three techniques are brought together under the unifying theme of secondary electron holography. In this approach, the investigator can view a secondary electron diffraction pattern as a hologram of the surface, and can, with proper care, directly extract atomic positions in the near-surface region by appropriately Fourier transforming the hologram. Recent case studies of both conventional secondary electron diffraction and holography are discussed, and comparisons between the two approaches are made.