Damage structure in the ionic crystal LiF irradiated with swift heavy ions

In many insulators, swift heavy ions in the MeV to GeV energy regime create latent tracks characterized by irreversible structural and chemical change s. Based on a large data set, the present report will give a detailed descr iption of the damage structure and defect morphology of ion tracks in lithi um fluoride. The results were obtained by different complementary technique s including optical absorption spectroscopy, small-angle X-ray scattering ( SAXS), chemical etching, scanning force microscopy, and surface profilometr y. In a large cylindrical halo of several tens of nanometers around the ion trajectory, single defects such as F- and F-2-centers are evidenced by opt ical absorption spectroscopy, similar to the damage known from conventional irradiations. Above a critical electronic stopping power of the ions of ar ound 10 ke\llnm, new effects occur, namely the formation of more complex de fects in a very small core region with a radius of 1-2 nm. The damage in th is zone is responsible for a characteristic anisotropic X-ray scattering an d for chemical etching. Several observations indicate that this core consis ts of a quasi-cylindrical discontinuous array of complex defect aggregates (presumably small Li colloids, molecular fluorine and vacancy clusters). Pr ofilometer measurements reveal substantial ion-induced volume expansion, Th is swelling can be assigned to a track radius of about 5-10 nm, an intermed iate zone between the track core and the halo, and appears at a much lower threshold of around 4 keV/nm. Track data (radii and threshold) linked to th e core and to swelling can be described within the frame of the thermal spi ke model assuming two different criteria, namely quenching of a vapor and a melt phase, respectively created along the ion path. O 2000 Elsevier Scien ce B.V. All rights reserved.In many insulators, swift heavy ions in the MeV to GeV energy regime create latent tracks characterized by irreversible st ructural and chemical changes. Based on a large data set, the present repor t will give a detailed description of the damage structure and defect morph ology of ion tracks in lithium fluoride. The results were obtained by diffe rent complementary techniques including optical absorption spectroscopy, sm all-angle X-ray scattering (SAXS), chemical etching, scanning force microsc opy, and surface profilometry. In a large cylindrical halo of several tens of nanometers around the ion trajectory, single defects such as F- and Fa-c enters are evidenced by optical absorption spectroscopy, similar to the dam age known from conventional irradiations. Above a critical electronic stopp ing power of the ions of around 10 keV/nm, new effects occur, namely the fo rmation of more complex defects in a very small core region with a radius o f 1-2 nm. The damage in this zone is responsible for a characteristic aniso tropic X-ray scattering and for chemical etching. Several observations indi cate that this core consists of a quasi-cylindrical discontinuous array of complex defect aggregates (presumably small Li colloids, molecular fluorine and vacancy clusters). Profilometer measurements reveal substantial ion-in duced volume expansion, This swelling can be assigned to a track radius of about 5-10 nm, an intermediate zone between the track core and the halo, an d appears at a much lower threshold of around 4 keV/nm. Track data (radii a nd threshold) linked to the core and to swelling can be described within th e frame of the thermal spike model assuming two different criteria, namely quenching of a vapor and a melt phase, respectively created along the ion p ath. (C) 2000 Elsevier Science B.V. All rights reserved.