Publications in Scientific Journals:

W.S.M. Werner:
"Differential surface and volume excitation probability of medium-energy electrons in solids";
Physical Review B, 74 (2006), 07542101 - 07542114.

English abstract:
A procedure is developed to rigorously decompose experimental loss spectra of medium-energy50 eV-50 keV electrons reflected from solid surfaces into contributions due to surface and volume electronicexcitations. This can be achieved by analysis of two spectra acquired under different experimental conditions,e.g., measured at two different energies and/or geometrical configurations. The input parameters of this procedurecomprise the elastic scattering cross section and the inelastic mean free path for volume scattering. Thenormalized differential inelastic mean free path as well as the differential surface excitation probability areretrieved by this procedure. Reflection electron energy loss spectroscopy REELS data for Si, Cu, and Au aresubjected to this procedure and the retrieved differential surface and volume excitation probabilities are comparedwith data from the literature. The present results are compared with earlier proposed procedures in whichsurface excitations are neglected, in particular the deconvolution formula by Tougaard and Chorkendorff Phys.Rev. B 35, 6570 1987 that is frequently employed for this purpose. It is shown that application of the latterprocedure to realistic REELS spectra that always contain a significant contribution due to surface excitationsdoes not lead to a single scattering loss distribution of any kind, but rather yields a mixture of contributions ofelectrons that have suffered an arbitrary number of surface and bulk collisions. Therefore, quantitative interpretationof the retrieved loss distributions is troublesome. On the other hand, the results using the procedureproposed in the present work exhibit satisfactory quantitative agreement with theoretical calculations andverify the commonly accepted model for medium energy electron transport in solids with unprecedented detail.

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