Date of Award

8-2015

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Materials Science and Engineering

Major Professor

Yanwen Zhang

Committee Members

William J. Weber, Kurt E. Sickafus, Maik K. Lang

Abstract

The objective of this thesis work is to gain better understanding of ion-solid interaction in the energy regime where electronic and nuclear energy loss are comparable. Such responses of materials to ion irradiations are of fundamental importance for micro-electronics and nuclear applications. The ion irradiation induced modification for the crystal structure, the physical and chemical properties etc. may strongly affect the performance of functional materials that needs to be better understood.

Experimentally, ion irradiation induced damage accumulation and dynamic recovery in SiC [silicon carbide] and SrTiO3 [strontium titanate] were studied in this dissertation project. Five chapters are presented: Firstly, electronic stopping power for heavy ions in light targets was experimentally evaluated for SiC. Secondly, out-surface diffusion of Ag atoms through SiC coating layer was studied by ion implantation and thermal annealing. The result also suggested that a SiO2 [silicon dioxide] thin film might serve as a diffusion barrier. Thirdly, a thermally induced recovery was studied for single crystal SiC. Through well controlled isothermal and isochronal annealing processes, activation energies were estimated and attributed to certain defect migration/recombination mechanisms. The fourth chapter focuses on a competing effect on defect dynamics due to ionization-induced defect recovery in SiC. Recovery of the existing defects resulting from a thermal spike along the ion path was expected, and was experimentally confirmed by using energetic ions. The results suggest a low threshold of electronic stopping power for the ionization-induced recovery. In the last chapter, an example of how the target material responses differently to energy deposition are demonstrated for single crystal SrTiO3. Instead of the recovery that was observed in SiC, a synergy effect of the coupled electronic and nuclear stopping energy deposition leads to formation of amorphous ion tracks. Systematic studies towards the role of defect concentration and electronic stopping power in the synergy effect were performed.

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