MODULATED ELECTRON-EMISSION - THE EFFECT OF ELASTIC AND INELASTIC ELECTRONS ON CORE-LEVEL IONIZATION

We investigated the elastic and inelastic contributions to the focusin g and defocusing properties of low-index Fe atomic chains on keV elect ron beams. To this end, we measured the intensity of the 2p-ionization loss signal from a thin Co film buried in a Fe matrix as a function o f the incidence angle of the electron beam for different values of the beam energy. The angular anisotropy of the measured signal, A(z), dir ectly measures the focusing effect at the depth z where the Co marker is located. The maximum (102%) in A(z) occurs at z = 5 scatterers; at about 12 scatterers below the surface the anisotropy is still 86%. The intensity anisotropy of the 2p-ionization loss we measured is compare d to that of the Co LMM Auger signal and to single-scattering cluster calculations, It has been found that a finite spatial extension of the ionization region has to be taken into account to reproduce the exper imental results. The relative weight of elastic and inelastic contribu tions to the 2p core-level ionization cross section has been evaluated as a function of depth and electron energy.