Intra- and inter-atomic auger processes in collisions of low energy He, He, He* (2, S, 2S) and Li with Li covered W(110) surfaces

Electron spectra from He, He and Li (10 to 1500 eV) ions colliding under grazing incidence with Li covered W (110) surfaces are reported. The results are compared with those obtained from thermal collisions of (2S; 2S) metastable He atoms. In these collisions 1 s vacancies are either produced during the collision event (energetic He (Li) collisions) or are brought into the collision (slow He (He, He*) collisions). Population of the 2 s orbitals by two electrons produces states which decay by intraatomic Auger processes: we observe autoionization of He** (2 s) and Li** (1 s 2 s) as well as autodetachment of He* (1 s 2 s). Alternatively the 1 s-holes in the projectile or target (Li) can be filled by Auger processes involving one or two surface electrons. The processes leading to electron emission are studied as a function of the Li coverage in the submonolayer region (0≦Θ≦1 Ml) and as a function of the projectile energy. It is concluded that with one or two 1 s vacancies present in the projectile the double capture of two surface electrons constitutes an important process responsible for electron emission of low work function surfaces. © 1992 Springer-Verlag.