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Defect Studies in Metals, Alloys, and Oxides by Positron Annihilation Spectroscopy and Related Techniques

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Defect Studies in Metals, Alloys, and Oxides by Positron Annihilation Spectroscopy and Related Techniques DEFECT STUDIES IN METALS, ALLOYS, AND OXIDES BY POSITRON ANNIHILATION SPECTROSCOPY AND RELATED TECHNIQUES Sahil Agarwal A Dissertation Submitted to the Graduate College of Bowling Green State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY August 2021 Committee: Farida Selim, Advisor Abby Braden Graduate Faculty Representative Alexander Tarnovsky Marco Nardone © 2021 Sahil Agarwal All Rights Reserved iii ABSTRACT Farida Selim Advisor Positrons administer a unique non-destructive approach to probe materials with atomic- scale sensitivity and provide reliable information about the nature and size of defects. This study reflects on the powerful capabilities of positron annihilation spectroscopy (PAS) to characterize point defects at atomic-scale, which can be crucial in the development of relevant material for a wide range of applications like nuclear reactors, medical sciences, optoelectronic devices, nanotechnology, polymers etc. The work presented in this dissertation aims to gain a fundamental understanding of the defect structures in three unique material systems: Fe metal, Fe-Cr alloy, and Ce:YAG oxide by applying the methodology and concepts of PAS. A wide range of other complementary characterization techniques has also been employed to enhance the understanding. The depth-resolved PAS was used to identify vacancy clusters in ion irradiated Fe and measure their density as a function of depth. PAS measurements uncovered the structure of vacancy clusters and the change in their size and density with irradiation dose. Combining with TEM measurements led to discovering a novel mechanism for the interaction of cascade damage with voids in ion-irradiated materials. The effect of Cr alloying on the formation and evolution of atomic size clusters induced by ion irradiation in Fe-Cr alloys was also investigated using depth-resolved PAS measurements. Combining with atomic probe tomography (APT), a possible explanation for the long-standing question about the well-known resistance to radiation in Fe-Cr alloys was addressed. It was attributed to the stabilization of vacancy clusters around Cr atoms that act as indirect sinks for radiation-induced defects. iv The final part of this work focuses on studying the role of defects on the luminescence properties of an important photonic material, Ce:YAG. The work reports an interesting mechanism that modifies and completely reverses the photoluminescence (PL) temperature- dependent kinetics. Further, it is shown that PL temperature-dependent kinetics can be controlled by modifying microstructure and engineering defects. v To the greatest of sacrifices made by my beloved Mother and Father To the new beginnings with my lovely wife Hayley vi ACKNOWLEDGMENTS I want to express my deepest gratitude and thanks to my advisor Dr. Farida Selim as without her support and guidance I could not have made this far. She has been a great role model for me throughout this journey. Through her strong presence and kindness, she has touched my life and helped groom me into the researcher I am today. I also would like to extend my thanks and regards to Dr. Alexander Tarnovsky, Dr. Marco Nardone and Dr. Abby Braden for agreeing to be in my committee and giving their valuable time in reviewing my manuscripts and for their insightful suggestions. I am extremely grateful to my peers and lab mates, Dr. Pooneh Saadatkia, Dr. Petr Stepanov, Dr. David Winarski, Md. Minhazul Islam, Armando Hernandez, Noalick Aboa and Micah Haseman. They supported me at every step, helped me learn lab techniques and assisted me whenever I needed help. I am also thankful to all my collaborators and co-authors for being so supportive. I am forever indebted to my wife, Hayley, who stood by me in these final years and helped me see this through. Her love and support guided me through challenging times and kept me motivated. I want to dedicate this graduate journey to my parents, Rajni and Anil and to all the sacrifices they have made for me at every step of my life. They along with my sister, Surbhi, have been my greatest support system in every possible way. vii TABLE OF CONTENTS Page CHAPTER I. HISTORY AND OVERVIEW .......................................................................... 1 Introduction ............................................................................................................... 1 Application Of PAS ...................................................................................................... 3 References ............................................................................................................... 6 CHAPTER II. POSITRON ANNIHILATION SPECTROSCOPY FOR ATOMIC DEFECT STUDIES ............................................................................................................... 14 Introduction ............................................................................................................... 14 Positron Sources............................................................................................................ 15 Radioactive Decay ............................................................................................ 15 Pair Production.................................................................................................. 16 Positron Interactions With Matter.................................................................................. 17 Thermalization .................................................................................................. 17 Diffusion ........................................................................................................... 18 Trapping In Defects .......................................................................................... 18 Positron Wave Function, Momentum And Lifetime Distribution ................................ 20 Doppler Broadening Of Annihilation Radiation Spectroscopy (DBS) ............. 21 Positron Annihilation Lifetime Spectroscopy (PALS) ..................................... 24 Trapping Model And Interpretation Of PAS data............................................. 28 Variable Energy Positron Annihilation Spectroscopy (VEPAS) .................................. 29 Positron Implantation ........................................................................................ 30 Positron Moderation And Slow-Positron Beams .............................................. 31 Complementary Techniques To PAS Employed In This Work.................................... 32 viii X-Ray Diffraction (XRD) ................................................................................. 33 Scanning Electron Microscopy (SEM) ............................................................. 34 Transmission Electron Microscopy (TEM) ...................................................... 35 Atomic Probe Tomography (APT) ................................................................... 36 Photoluminescence (PL) Spectroscopy ............................................................ 36 Thermoluminescence (TL) Or Thermal Stimulated Luminescence (TSE) Spectroscopy ..................................................................................................... 38 References ............................................................................................................... 41 CHAPTER III. DEFECT STUDIES IN ION-IRRADIATED IRON ...................................... 45 Introduction ............................................................................................................... 45 Experimental Methods .................................................................................................. 46 Material Growth And Preparation .................................................................... 46 Ion Irradiation ................................................................................................... 46 Transmission Electron Microscopy (TEM) ...................................................... 47 Variable Energy Positron Annihilation Spectroscopy (VEPAS) ...................... 47 Results And Discussions ............................................................................................... 48 Radiation Damage And Positron Stopping Profiles.......................................... 48 DBS Measurements .......................................................................................... 49 Depth-resolved PALS Measurements ............................................................... 55 Defect Density Calculations ............................................................................. 59 TEM Measurements And Calculation Of Cavity And Void Density ........................... 63 Conclusions ............................................................................................................... 67 References ............................................................................................................... 68 ix CHAPTER IV. DEFECT STUDIES IN ION-IRRADIATED FE-CR ALLOY ..................... 72 Introduction ............................................................................................................... 72 Experimental Methods .................................................................................................. 74 Material Growth And Preparation .................................................................... 74 Ion Irradiation ................................................................................................... 74 Variable
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