STRUCTURAL SURFACE INVESTIGATION WITH LOW-ENERGY BACKSCATTERED ELECTRONS

We review the structural results obtained through the analysis of inel astically backdiffused electrons from a solid surface. Thanks to the a mount of experimental and theoretical evidences, the physical mechanis m underlying the EELFS (Extended Energy Loss Fine Structure) features beyond a ionization edge seems now well accepted in terms of an EXAFS- like effect. We have found strong evidence that among the most probabl e scattering events, namely: single inelastic diffusion, energy loss p receded or followed by diffraction events supplied by the lattice, the main channel of interaction with a core electron is essentially const ituted by inelastic followed by diffraction processes. The energy loss process occurs at a very small diffusion angle from the primary beam direction and this explains the capability of low-energy electrons to induce dipole transitions on the scattering matrix element of a core e lectron. The EXFAS (EXtended Fine Auger Structure) signal, detected at kinetic energy greater than that of the Auger transitions, increases the usefulness of the elemental Auger spectroscopy as a local structur al tool. Some efforts should be devoted in future to elucidating bette r the physical process. The combination of the EELFS and EXFAS techniq ues may help to give a wider description of a number of surface and in terface effects.