ENDOR Study of a <111> Interstitial Defect in LiF

Abstract

Results of (electron-nuclear double-resonance) measurements and analysis of a (lll)-oriented defect in pure LiF are presented. This paramagnetic defect is produced at low temperatures by x-ray or electron irradiation. The ENDOR hyperfine constants from 11 nonequivalent sets of lattice nuclei have been obtained by fitting the ENDOR spectrum to a spin Hamiltonian. Results of this ENDOR study show that this (111) defect is equivalent to an interstitial fluorine atom that has the form of a negatively charged diatomic molecule ¥o~, centered on a negative-ion site, with its molecular axis oriented along a (111) direction.

Creation of nanosize defects in LiF crystals under 5- and10−MeVAu ion irradiation at room temperature

“…24,26 The center of a latent image undergoes transformation into a large colloid particle during the development of a photographic image. To understand the reasons of the reciprocity law failure between the intensity and duration of irradiation in LiF in the case of low fluxes ͑long irradiation time͒, it should be taken into account that the hopping diffusion of H interstitials ͑interstitial fluorine atoms͒ starts already at 50-60 K. 5,7,8 The recombination of H centers with F and F 2 centers, which are immobile at RT, causes the restoration of a regular lattice. On the other hand, it is shown 7,23 that a pair association of two H interstitials in the form of a trihalide molecule is stable at RT, thus, providing the existence of two F centers ͑F and H centers are created in the form of F-H pairs of complementary defects͒.…”

“…[5][6][7] A Frenkel pair consists of an F center ͑an electron in the field of an anion vacancy͒ and an H center, which is a dihalide F 2 − molecule located at one anion site and oriented along one of the ͗111͘ directions. 8 Radiation damage in alkali halides under heavy ion irradiation strongly depends on the energy loss, irradiation temperature, and dose ͑fluence͒. [9][10][11] Irradiation with ions having an energy loss above a critical threshold of 6 -10 keV/ nm leads to a complex track structure with nanosize damage in the central part of the track ͑core͒ and color centers in a larger damage zone of several tens of nanometers ͑halo͒ around the ion path.…”