טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentSameer Abu Saleh
SubjectStructure of Ion Tracks in Dielectric Solids
DepartmentDepartment of Chemistry
Supervisor Professor Eyal Yehuda


Abstract

            Employing HRSEM (high-resolution scanning electron microscopy), we determined the nanometric etching diameter of latent tracks created by GeV heavy ions in the polymer polyimide (PI) and in LiF and CaF2 single crystals. Each experiment involved accelerator irradiation of a well-characterized specimen, a series of controlled short-term etching treatments, HRSEM measurements, and statistical analysis. Seven-year old U-ion (1.79 GeV) tracks in PI exhibited a mean etching diameter of 6.9 ± 1.4 nm, which essentially matches the mean core diameter of few-week old latent tracks as determined by transmission electron microscopy. Thus, the track region that manifests itself by a highly-elevated chemical reactivity coincides with the primary structurally-altered region of the track. Etching diameters of U-ion (2.36 GeV) and Bi-ion (1.76 GeV) track cores in {100} LiF and {111} CaF2 are 12.0 ± 4.3 nm and 8.3 ± 2.6 nm, respectively. In these etched crystals, ex-core radiation damage, so-called track halo, manifests itself by wide and aligned pyramidal etch pits that surround the track cores. Etch pit apertures - squares in LiF and triangles in CaF2 - possess the symmetries of the crystal faces. Thus, etching at the track halo is controlled both by point and extended ion-induced defects and by energies of crystal faces. Knowledge of the track structure and etching characteristics is a prerequisite in the developing field of ion-track engineering.