Electrons from intra- and inter-atomic Auger processes in low-energy He 2+ collisions with partially alkalated W(110) surfaces

Abstract

Electron energy spectra from He 2+ (100 eV) ions colliding under grazing incidence with partially alkali(Na, Cs)-covered W(110) surfaces are reported as a function of the alkali coverage θ (0 ⩽ θ ⩽ 1 ML). For clean W(110) the sequence of electronic transitions during the collision is similar as reported previously for other clean metals. For θ > 0.4 ML He 2+ is preferentially neutralized into He ∗∗ via He +∗(n = 3) states by two-step resonant capture of two electrons. Electrons are mainly emitted by Auger de-excitation of He +∗(n = 3 → 2) and autoionization of He ∗∗ to He + at this stage. In a second step the He + ions produced in the cours neutralization process again capture resonantly one or two electrons. Auger de-excitation of He ∗ and autodetachment of He −∗( 2S) then primarily give rise to electron emission whereby He neutrals in the ground state are formed. It is furthermore concluded that in a major portion of the collision events three electrons are emitted.