High Fractions of Negative Ions in Grazing Scattering of Fast Oxygen Atoms from a LiF(100) Surface

Oxygen atoms and ions with energies ranging from 2 to 100 keV are scattered at grazing angles of incidence from a LiF(100) surface. We analyze the charge states of the scattered beams as a function of the projectile energy. The most striking result of our study is the observation of negative ion fractions of up to about 70%. We interpret these large fractions of ${\mathrm{O}}^{-}$ ions to capture in binary-type collisions of fluorine $2p$ electrons from the target and the subsequent suppression of loss for these captured electrons due to the energy gap of the insulator.