Capture and loss of valence electrons during low energy H+ and H- scattering from LaB6(100), Cs/Si(100), graphite and LiCl

The mechanism of electron attachment to low-energy (100 eV) protons has bee n investigated during scattering from graphite, Si(100), LaB6(100), and LiC l. The primary H+ ion survives neutralization when scattered from highly io nized target species, such as Cs+, La3+, Li+, and Cl-, existing on the topm ost surface layer. In terms of H- ion formation at the metal and semiconduc tor surfaces, multiple scattering from the solid is dominant relative to si ngle surface scattering because the former has a much larger cross-section than the latter, indicating that H- is caused by the non-local resonant tun neling process. At the LiCl surface, on the other hand, a close atomic enco unter with individual target ions is found to be important for H- ion forma tion. This is because the non-local resonance process is prohibited due to the existence of the large band gap and the charge state of scattered hydro gen is determined by the transient chemisorption state very close to the su rface. (C) 1999 Elsevier Science B.V. All rights reserved.