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 $\mathrm{F}\mathrm{}\left(2s\right)\mathrm{}$ and $\mathrm{Li}\mathrm{}\left(1s\right)\mathrm{}$ edges (from 37 to 72 eV). There are structures in the ${\mathrm{F}}^{+}$ yield above the $\mathrm{F}\mathrm{}\left(2s\right)\mathrm{}$ edge which are absent in the ${\mathrm{Li}}^{+}$ spectrum, differences in detail in the ${\mathrm{Li}}^{+}$ and ${\mathrm{F}}^{+}$ yields near the $\mathrm{Li}\mathrm{}\left(1s\right)\mathrm{}$ 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.