Differential probability for surface and volume electronic excitations in Fe, Pd and Pt

The normalized differential mean free path for volume scattering and the differential surface excitation probability for medium energy electrons travelling in Fe, Pd and Pt are extracted from reflection electron energy loss spectra (REELS). This was achieved by means of a recently introduced procedure in which two REELS spectra taken under different experimental conditions are simultaneously deconvoluted. In this way, it is possible to obtain the unique reconstruction for the surface and volume single scattering loss distribution. The employed method is compared with a procedure that is frequently used for this purpose [S. Tougaard, I. Chorkendorff, Phys. Rev. B 35 (1987) 6570]. It is shown, both theoretically and through analysis of model spectra as well as experimental data that the approach by Tougaard and Chorkendorff does not result in a single scattering loss distribution. Rather, it gives a mixture of surface, bulk and mixed scattering of any order.