ELECTRON-EMISSION IN LOW-ENERGY GRAZING COLLISIONS OF C+ IONS WITH W(110) PARTIALLY COVERED BY ALKALI ATOMS

Electron energy spectra of slow (50 eV) C+ ions colliding under grazing incidence with clean and partially alkalated (Li, Na, K, Cs) W(110) surfaces are reported. The spectra can be interpreted as due to various inter- and intra-atomic Auger processes occurring in the vicinity of the surface: for clean W(110) hardly any electrons are observed. For small alkali coverages the emission is due to Auger capture involving two electrons from the surface. For sufficiently large alkali coverages the resonant capture of one or two electrons from the surface leads to the formation of core-excited states of the neutralized projectile (beyond 0.3 monolayer alkali coverage in terms of a completed monolayer, typically) and Feshbach resonances of the configuration C-*(2s(2)2p3l3l') (beyond 0.5 monolayer K or Cs coverage). These states manifest themselves by their decay via Auger deexcitation and autodetachment, respectively. The availability of three multiplet states of the C(2s(2)2p2) configuration into which Auger processes can take place produces richly structured spectra. In addition we report the ion scattering spectra (ISS) of the C- ions scattered into 90-degrees as a function of the coverage of W(110) by alkali atoms.