Electronic excitation, luminescence and particle emission : Studying ion-induced phenomena in ToF-MEIS

Abstract: Medium energy ion scattering (MEIS) is an experimental technique for the high-resolution depth profiling of thin films. Commonly, ions with energies between several ten to a few hundred keV are employed as probes, and backscattered particles are detected. Apart from scattering, keV ions can upon their interaction with matter induce luminescence, electron emission and the sputtering of neutrals and ions. However, research on this secondary particle emission in the medium energy regime is scarce. Thus, this thesis aims to perform a systematic analysis of 1) ion-induced photon emission and 2) the sputtering of positive ions in a time-of-flight (ToF) MEIS set-up. A significant fraction of photons exhibits energies of only a few eV, which is on the order of typical valence transitions in solids. The dependence of the photon yield on several experimental parameters is studied. By analysing the dependence on the employed geometry, it is concluded that photons are produced along the whole trajectory of the incident ion. Furthermore, the photon yield shows a strong material dependence, which seems to be subject to matrix effects. To study the sputtering process, mass spectrometry was integrated into an existing ToF-MEIS set-up. The secondary ions exhibit very low initial kinetic energies and, therefore, need to be accelerated by a sufficiently high voltage. Then, atomic and molecular ions originating both from the employed target material and surface contaminations can be detected. Whereas experimental evidence suggests a predominantly electronic sputtering process for species adsorbed to the surface, target bulk constituents seem to be sputtered by nuclear collision cascades.