ELECTRON-EMISSION IN SLOW COLLISIONS OF INERT-GAS AND REACTIVE IONS WITH W(110) PARTIALLY COVERED BY ALKALI ATOMS

Electron energy spectra from slow (50 to 1000 eV) collisions of inert gas (He+, He-2+ and Ar+) and reactive (H+, N+) ions colliding under gr azing incidence with W(110) surfaces are reported. The surface work fu nction is varied by the exposure of the W(110) surface to alkali atoms . For clean W(110) the sequence of electronic transitions during a slo w (50 eV, typically) collision is similar as reported for other clean metals: Auger capture processes involving two electrons from the surfa ce dominate for all projectiles. For sufficiently large coverages by a lkali atoms resonant capture of one or two surface electrons by the pr ojectiles leads to the formation of excited states of the projectiles with one or two electrons occupying valence orbitals. These states dec ay by Auger deexcitation (Penning ionization) and intra-atomic Auger p rocesses (autoionization and autodetachment), respectively. For the ca se of Ar+ ions colliding with W(110) partially covered by potassium it is demonstrated that core vacancies (Ar3p-1) are created during the c ollision provided the kinetic energy of the projectile surmounts about 300 eV. Contributions from both potential and kinetic emission can th en be seen in the spectra of the emitted electrons.