Scattering of 4 keV Ne+, Na+ and F+ ions from a NaCl (1 0 0) surface under a small angle of incidence. Angular distributions and charge fractions

Multiple excitation of Fuchs–Kliewer phonons by Ne+ions back-scattered by the LiF(100) surface at grazing incidence

“…However, for the Ne + → Ne 0 scattering process additional broadening effects are to be expected, because: (i) there is an inhomogeneous broadening associated with the spread of the position of the neutralization site of Ne + along its path close to the surface; (ii) the screening of an F 0 point defect involves a broad spectrum of surface phonons of all momenta, whereas the coherent FK state, solely excited in the reflected Ne + peak, involves Q vectors predominantly in the forward direction around some average value with negligible dispersion effects. This effect works in the direction of equalizing the widths of the two peaks; (iii) the LiF valence band from which the transferred electron originates has a width of over 3 eV [32]; disregarding the fact that the transition probability decreases for the deeper band states, the convolution with a 1.5 eV band half-width would raise the peak FWHM to 6.6 eV; (iv) the energy defect E in (1) has an uncertainty of at least 1 eV, depending on whether the Auger neutralization process creates an exciton or a free electron, as discussed in section 2 (such excitonic and secondary electron emissions accompanying positive-ion neutralization have been reported in [31,[33][34][35][36][37], but not for the present Ne + experiment [1]).…”