toward understanding dynamic annealing processes in irradiated ceramics PDF
Preview toward understanding dynamic annealing processes in irradiated ceramics
LLNL-TH-611672 TOWARD UNDERSTANDING DYNAMIC ANNEALING PROCESSES IN IRRADIATED CERAMICS M. T. Myers January 18, 2013 Disclaimer This document was prepared as an account of work sponsored by an agency of the United States government. Neither the United States government nor Lawrence Livermore National Security, LLC, nor any of their employees makes any warranty, expressed or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States government or Lawrence Livermore National Security, LLC. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States government or Lawrence Livermore National Security, LLC, and shall not be used for advertising or product endorsement purposes. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. Rev. 1.2 TOWARD UNDERSTANDING DYNAMIC ANNEALING PROCESSES IN IRRADIATED CERAMICS A Dissertation by MICHAEL THOMAS MYERS Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Approved by: Chair of Committee, Lin Shao Committee Members, Sergei Kucheyev Sean McDeavitt Haiyan Wang Xinghang Zhang Department Head, Yassin Hassan May 2013 Major Subject: Nuclear Engineering Copyright 2013 Michael Thomas Myers Rev. 1.2 ABSTRACT High energy particle irradiation inevitably generates defects in solids. The bal- listic formation and thermalization of the defect creation process occur rapidly, and are believed to be reasonably well understood. However, knowledge of the evolution of defects after damage cascade thermalization, referred to as dynamic annealing, is quite limited. Unraveling the mechanisms associated with dynamic annealing is crucial since such processes play an important role in the formation of stable post- irradiation disorder in ion-beam-processing of semiconductors, and determines the “radiation tolerance” of many nuclear materials. The purpose of this dissertation is to further our understanding of the processes involved in dynamic annealing. In order to achieve this, two main tasks are undertaken. First, the effects of dynamic annealing are investigated in ZnO, a technologically relevant material that exhibits very high dynamic defect annealing at room temper- ature. Such high dynamic annealing lead to unusual defect accumulation in heavy ion bombarded ZnO. Through our work, the puzzling features that were observed more than a decade ago in ion-channeling spectra have finally been explained. We show that the presence of a polar surface substantially alters damage accumulation. Non-polar surface terminations of ZnO are shown to exhibit enhanced dynamic an- nealing compared to polar surface terminated ZnO. Additionally, we demonstrate one method to reduce radiation damage in polar surface terminated ZnO by means of a surface modification. These results should further our efforts in the long-sought- after goalofunderstanding complex radiationdamageprocesses innon-amorphizable oxides. Second, a pulsed ion beam method is developed and implement using Si as a ii Rev. 1.2 prototypical ceramic target. Such a method is shown to provide a novel experimen- tal method for direct extraction of dynamic annealing parameters. The relaxation times and effective diffusion lengths of mobile defects during the dynamic anneal- ing process play a vital role in damage accumulation. We demonstrate that these parameters dominate the formation of stable post-irradiation disorder. In Si, a de- fect lifetime of 6 ms and a characteristic defect dffiusion length of 30 nm are ∼ ∼ measured. These results should nucleate a number of future pulsed-beam studies of dynamic defect interaction processes in technologically relevant materials. In partic- ular, understanding the length and time scales of defect interactions are essential for extending laboratory findings to nuclear material lifetimes and to the time scales of geological storage of nuclear waste. The results of both, the pulsed beam method for measuring dynamic annealing parameters, as well as damage accumulation in various planes of ZnO bombarded by heavy ions, are discussed. The work presented in this dissertation should substan- tially further our understanding of dynamic annealing processes in ceramics. iii Rev. 1.2 DEDICATION To my wife and my parents, thank you for your endless encouragement. iv Rev. 1.2 ACKNOWLEDGEMENTS Iwouldliketoacknowledge Dr.Shaoforhisguidancesupportduringmytenureat Texas A&M University. I would like to thank my committee members, Dr. McDeav- itt, Dr. Wang, and Dr. Zhang for their support over the course of the present work. An additional debt of gratitude is owed to my Lawrence Livermore National Labora- torymentor, Dr.Kucheyev, whospent countless hourshelping megrowintoamature scientist. A sincere “thank you” to Dr. Charnvanichborikarn who spent many hours assisting with experimental design as well as performing the actual experiments at Lawrence Livermore National Laboratory. I would also like to thank my group mem- bers, colleagues, and collaborators, Dr. Aitkaliveya, Dr. Luo, Dr. Lee, M. S. Martin, D. Chen, M. Hollander, C. C. Wei, M. A. Myers, J. Wallace, and M. J. General for their help throughout the dissertation. Finally,IwouldliketoacknowledgetheLawrenceScholarProgramattheLawrence Livermore National Laboratory for funding the work performed in this dissertation. v Rev. 1.2 NOMENCLATURE A Ampere Al O Aluminum Oxide 2 3 AlO(OH) Aluminum Oxide Hydroxide BF Bright Field BP Bulk Defect Peak C Coulomb CdTe Cadmium Telluride CM Center of Mass DA Dynamic Annealing DF Dark Field DLTS Deep Level Transient Spectroscopy DPA Displacement Per Atom EDS Energy Dispersive X-ray Spectroscopy eV Electron Volt FIB Focused Ion Beam FZ Float Zone HAADF High Angle Annular Dark Field HEIS High Energy Ion Scattering IBA Ion Beam Analysis IBM Ion Beam Modification IED Ionization Enhanced Diffusion IP Intermediate Defect Peak vi Rev. 1.2 keV Kilo Electron Volt KP Kinchin-Pease L Diffusion Length d LED Light Emitting Diode LLNL Lawrence Livermore National Laboratory MeV Mega Electron Volt ME Molecular Effect MD Molecular Dynamics MgO Magnesium Oxide MgAl O Magnesium Aluminate Spinel 2 4 NEC National Electrostatics Corporation nm Nanometer NRT Norgett, Robinson and Torrens PKA Primary Knock-on Atom PL Photoluminescence RBS/C Rutherford Backscattering and Channeling Spectrometry RT Room Temperature Si Silicon SiC Silicon Carbide Si N Silicon Nitride 3 4 SP Surface Defect Peak SPER Solid Phase Epitaxial Recrystallization SRIM Stopping and Range of Ions in Matter SRP Spreading Resistance Profiling vii Rev. 1.2 STEM Scanning Transmission Electron Microscopy Tau (τ) Defect Lifetime TEM Transmission Electron Microscopy TFD Thomas-Fermi-Dirac TRIM Transport and Range of Ions in Matter UN Uranium Nitride UO Uranium Oxide 2 XTEM Cross Sectional Transmission Electron Microscopy ZnO Zinc Oxide viii
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