A MODEL STUDY OF THE EXTENDED FINE-STRUCTURE IN THE SECONDARY-ELECTRON SPECTRA OF SOLIDS

A theory describing the extended oscillations in secondary-electron (S E) spectra and their connections with the short-range atomic structure in solids is developed. We investigate the two main mechanisms for th e occurrence of SEs: direct knocking out of SEs from the core level by primary electrons, and a second-order process, called autoionization, going through excitation of a core-level electron into some intermedi ate states followed by emission of the final SEs. Interference of a di rect wave and waves reflected from neighbouring atoms are considered b oth in the final and in the intermediate states. We derive the cross s ections for SEs created in single crystals and polycrystals. In the la tter case the signal is described by the two EXAFS-like oscillating fu nctions which are controlled by the final and intermediate energies. T he intermediate wave diffraction is described by the EXAFS-like backsc attering in all cases. The extended fine structure is expressed, in ab explicit form, in terms of coordinates and the scattering characteris tics of neighbouring atoms, which opens up new possibilities for obtai ning information on the short-range atomic structure near surfaces.