Vacuum ultraviolet reflectivities of LiF, NaF, and KF

High-resolution normal-incidence (9°) reflectivities of lithium-fluoride, sodium-fluoride, and potassium-fluoride single crystals were investigated between 6 and 35 eV at room temperature, 100 and 30 K using a minicomputer-controlled vacuum ultraviolet reflectometer at the Winconsin Synchrotron Radiation Facility. Data were taken on surfaces cleaved and maintained in high vacuum. Reflectivity data were Kramers-Kronig analyzed to yield the dielectric functions of the materials and various energy and temperature derivatives were calculated as an aid to interpretation. In all materials, considerable new structure is reported with broad, general agreement with earlier work on LiF and KF. We report the first reflectivity data between 12 and 35 eV for NaF. Computed values of $-\mathrm{Im}\left(\frac{1}{\epsilon }\right)$ were in good agreement with electron-energy-loss experiments of Creuzburg. It is only possible to provide detailed interpretation of optical features in special cases, but a general discussion is provided in the conventional framework.