H. Muller et al., ELECTRON-EMISSION IN SLOW COLLISIONS OF INERT-GAS AND REACTIVE IONS WITH W(110) PARTIALLY COVERED BY ALKALI ATOMS, Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms, 78(1-4), 1993, pp. 239-246
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.