Beam Exposure Dependence and Mechanisms of Photon-stimulated Desorption from Alkali Fluorides

Photon-stimulated desorption experiments were performed on the (001) face of LiF for photon energies near the F(2s) and Li(ls) edges (from 37 to 72 eV). There are structures in the F+ yield above the F(2s) edge which are absent in the Li+ spectrum, differences in detail in the Li+ and F+ yields near the Li(ls) edge, and considerable broadening of the desorption yields as compared to the bulk photoabsorption spectrum. The first observation of a strong x-ray, and visible, beam exposure dependence of ion yields from LiF and NaF is also presented. These results are discussed in terms of electronic and defect properties of alkali halides.