טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentAbu Saleh Sameer
SubjectStructure and Reactivity of Heavy-Ion Tracks in Dielectric
Solids
DepartmentDepartment of Chemistry
Supervisor Professor Yehuda Eyal


Abstract

     Ion damage trails, latent ion tracks, created by swift heavy ions in dielectric solids exhibit remarkable chemical reactivity, and thus can be preferentially etched, opened, and radially enlarged by attack with suitable corrosive solutions. With the advent of techniques that allow selective track coating or filling with active elements or molecules, ion tracks have proven attractive containment and template structures for fabrication of materials and devices of nanoscopic width. However, resolving the nature of track formation processes under intense electronic energy deposition, and understanding the resulting track characteristics of importance for track applications, have been hampered by the lack of knowledge of the morphology of the latent ion tracks.

     Employing small-angle X-ray scattering combined with an original track structure model, we have derived for the first time the core structure of latent tracks created by GeV U, Pb, and Au ions in polyimide, polycarbonate, {100} LiF, and {100} muscovite. Complementary information has been obtained by transmission electron microscopy. All derived structures have clearly singled out the mechanisms responsible for track formation. In addition, employing brief etching treatments combined with scanning force microscopy and high-resolution scanning electron microscopy, we have derived for the first time the morphology of pits etched along ion tracks in {100} LiF and {111} CaF2. This study has shed light on the factors that control track etchability.

     Latent tracks in polyimide and polycarbonate are characterized by 64-69 % density decreases along the centers of ~6 nm diameter track cores. Latent tracks in {100} LiF are characterized by 49-74% electron density decreases along the center of ~3 nm diameter track cores. Latent tracks in {100} muscovite are characterized by ~4% density decreases along ~8-10 nm diameter cores. Track formation in the former 3 substrates has been attributed to local ion-induced radiolysis, followed by removal of gaseous and volatile alteration products, most likely via the low density tracks. The materials removed from the tracks in LiF are most likely fluorine gas and liquid Li. We have attributed track formation in muscovite to ion-induced thermal dehydration.

     Ion track etch pits in {100} LiF and in {111} CaF2 possess the 4-fold and the 3-fold symmetries of the irradiated crystal faces, respectively, and pit surfaces that are relatively stable crystal planes. This cleavage-like mechanism clearly indicates that etching is controlled both by radiation effects and by surface energies of crystal faces.