Influence of adsorbates, crystal structure, and target temperature on the sputtering yield and kinetic-energy distribution of excited Ni atoms

Abstract

We present results for the emission of secondary Ni atoms in the electronic ground state and some excited metastable states under ion bombardment. In particular, we address some of the most urgent questions resulting from previous measurements of the Ni system: the influence of adsorbates, in particular oxygen, on the excitation, the influence of the crystal structure and orientation, and possible temperature effects. A direct comparison between sputtering under identical experimental conditions from polycrystalline and single crystal targets has been performed. Inelastic processes have been found to play an important role in determining the population of the different electronic levels of sputtered atoms. The density of states of the solid and the overlap of the electronic wave functions of the atom and the solid (bulk or surface) determine the efficiency of the population of individual atomic levels and the energy distribution of the atoms in these electronic states. Analyzing the experimental data, the contribution of inelastic processes to elastic cascade sputtering for clean, oxidized, and carbonized surfaces, at room temperature and up to $800\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ as well as for various azimuthal angles could be determined and has finally led to a coherent description of the sputtering-excitation process for low-lying excited Ni atoms: the emission of an ionic core and subsequent electron capture into excited states.