Evidence for the Stopping of Slow Ions by Excitations of Optical Phonons in Insulators

The energy loss of Ne⁺ ions with keV energies scattered under grazing incidence from a LiF(001) surface is studied with a time-of-flight technique. Since charge exchange in front of the wide-band-gap insulator is widely suppressed, the energy loss of slow ions moving in front of the solid can be investigated under specific interaction conditions. From the theoretical analysis of data we find evidence for an energy loss mechanism based on the excitations of optical phonons in the insulator.