HEAVY-ION-INDUCED MODIFICATION OF LITHIUM-FLUORIDE OBSERVED BY SCANNING FORCE MICROSCOPY

In order to study ion-induced damage in single crystals of lithium flu oride with scanning force microscopy (SFM), samples are irradiated wit h several, heavy-ion species with kinetic energy of 11.4 MeV per nucle on. As concluded from a previous analysis of ion tracks in LiF by opti cal absorption spectroscopy and small-angle X-ray scattering, single p oint defects occur in a track halo with a radius in the range 15-30 nm , whereas defect aggregates are formed in a track core region possessi ng a radius of only 1-2 nm. These aggregates can be attacked by chemic al etching if the energy loss along the ion trajectory surpasses a cri tical value of about 1 keV/Angstrom. SFM images of etched as well as u netched sample surfaces reveal new damage characteristics: etched ion- track profiles directed parallel to the ion trajectories exhibit a seq uence of single etch pits with an average distance between them of abo ut 140 nm. After exposure to heavy-ion irradiation at normal incidence , the unetched LiF surface is covered with round hillocks with a mean diameter of 55 (8) nm and heights of the order of 3 nm.