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

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 pre vious measurements of the Ni system: the influence of adsorbates, in partic ular 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 f ound to play an important rule in determining the population of the differe nt 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 soli d (bulk or surface) determine the efficiency of the population of individua l atomic levels and the energy distribution of the atoms in these electroni c states. Analyzing the experimental data. the contribution of inelastic pr ocesses to elastic cascade sputtering for clean, oxidized, and carbonized s urfaces, at room temperature and up to 800 degrees C as well as for various azimuthal angles could be determined and has finally led to a coherent des cription of the sputtering-excitation process for low-lying excited Ni atom s: the emission of an ionic core and subsequent electron capture into excit ed states.