ELECTRON-EMISSION IN SLOW COLLISIONS OF ALKALI IONS WITH ALKALATED W(110) SURFACES

We report the energy spectra of the collision-induced electron emission after slow (200 eV to 2 keV) alkali ion (Li through Cs) collisions with partially alkali-covered W(110) surfaces. Particular emphasis is directed to the study of the symmetrical combinations M+ colliding with M/W (M = Li, Na, K, Cs). Inter- and intra-atomic Auger processes dominate the spectra in all cases at energies below 1 keV. We observe in particular (1) Auger de-excitation of excited neutral projectile valence states producing electrons with energies below 5 eV, and (2) the creation of inner shell vacancies (Li 1s-1 and M n p-1 with n = 2, 3, 5 for M = Na, K and Cs, respectively) giving rise to interatomic (Auger de-excitation and capture) as well as to intra-atomic (auto-ionization) Auger-type processes both in the projectile- and the ad-alkali atom. A consistent analysis of the results is possible within a promotion model suitably modified in order to take into account charge transfer processes between the surface and the projectile.