Temporary negative ion formation in interactions of low-energy inert gas ions (He⁺, Ne⁺) with Cs-adsorbed Cu(111) surfaces

Low-energy (0.5-1 keV) inert gas ions (He⁺, Ne⁺) have been used to investigate the interaction of ions with Cs-covered Cu(111) surfaces. Electron spectra from the interaction were obtained for grazing angles of incidence. From the energy and angular distributions of emitted electrons, it can be confirmed that the sharp electron peaks with excitation energies of 19.32±0.08 and 16.15±0.08 eV are caused by the decays of He*^-(1s2s^{2 2}S) and Ne*^-(2p⁵3s^{2 2}P) states, respectively. It was also found that negative ion resonances take place on the incoming trajectories far above the surface ion cores. The one-step two-electron capture has been proposed to explain the formation of negative-ion resonances. © 1995.