Dissertation

First-Principles Studies of Defect Dynamics in Crystalline Solids

Yoshimura, Anthony

2020

Overview

Any crystalline material inevitably contains interruptions in its crystal structure, which are called defects. While sometimes detrimental to the material’s performance, these defects drastically expand the space of properties accessible to the crystal, often introducing variations in electronic, vibrational, and optical attributes. It follows that the control and prediction of these defects can vastly extend the range of applications for materials in modern devices. In this work, we use first-principles density functional theory (DFT) to simulate the time evolution of these defects in several crystalline materials and suggest means by which they can be controlled and manipulated. To this end, two classes of defect dynamics are considered. The first is passive dynamics, in which the evolution of defects is probabilistic, and its rate is dictated only by the environmental conditions in which the material exists. For this, thermally induced defect creation and migration in various materials are modeled by employing the nudged elastic band method to determine the energy barriers for these processes, from which the Arrhenius equation is used to relate those barriers to rates of occurrence. The second class is active defect dynamics, in which defects are intentionally produced, guided, and precisely manipulated under properly tuned electron beam irradiation. Here, we lay out how DFT can be combined with quantum electrodynamics to reveal how phononic and electronic excitations affect the atomic displacement rates in response to the incident beam electron collisions. In doing so, we provide theoretical support for the use of the electron beam as a reliable high-precision instrument for atomic-scale defect engineering in various materials. We hope that such an understanding of defect dynamics can grant materials en- gineers the ability to tune and control the properties of novel materials for the purpose of targeted functionality.

• Publisher: ProQuest Dissertations & Theses
• Subject: Computational physics / Condensed matter physics / Materials science
• ISBN: 9798662575967