Air Force Institute of Technology AFIT Scholar Theses and Dissertations Student Graduate Works 12-17-2018 Electrical Characterization of Crystalline UO2, ThO2 AND U0.71Th0.29O2 Christina L. Dugan Follow this and additional works at: https://scholar.afit.edu/etd Part of the Engineering Physics Commons Recommended Citation Dugan, Christina L., "Electrical Characterization of Crystalline UO2, ThO2 AND U0.71Th0.29O2" (2018). Theses and Dissertations. 1944. https://scholar.afit.edu/etd/1944 This Dissertation is brought to you for free and open access by the Student Graduate Works at AFIT Scholar. It has been accepted for inclusion in Theses and Dissertations by an authorized administrator of AFIT Scholar. For more information, please contact [email protected]. ELECTRICAL CHARACTERIZATION OF CRYSTALLINE UO2, THO2 AND U0.71TH0.29O2 DISSERTATION Christina L. Dugan, Lieutenant Colonel, USA AFIT-ENP-DS-18-D-007 DEPARTMENT OF THE AIR FORCE AIR UNIVERSITY AIR FORCE INSTITUTE OF TECHNOLOGY Wright-Patterson Air Force Base, Ohio DISTRIBUTION STATEMENT A Approved For Public Release; Distribution Unlimited The views expressed in this thesis are those of the author and do not reflect the official policy or position of the United States Air Force, the Department of Defense, or the United States Government. AFIT-ENP-DS-18-D-007 ELECTRICAL CHARACTERIZATION OF CRYSTALLINE UO2, THO2 AND U0.71TH0.29O2 DISSERTATION Presented to the Faculty Department of Engineering Physics Graduate School of Engineering and Management Air Force Institute of Technology Air University Air Education and Training Command In Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy Christina L. Dugan, BS, MS Lieutenant Colonel, USA October 2018 DISTRIBUTION STATEMENT A Approved For Public Release; Distribution Unlimited . AFIT-ENP-DS-18-D-007 ELECTRICAL CHARACTERIZATION OF CRYSTALLINE UO2, THO2 AND U0.71TH0.29O2 Christina L. Dugan, BS, MS Lieutenant Colonel, USA Committee Membership: James C. Petrosky, PhD Chair John W. McClory, PhD Member Sheena L. Winder, Lt Col Member ADEDJI B. BADIRU, PhD Dean, Graduate School of Engineering and Management AFIT-ENP-DS-18-D-007 Abstract Hydrothermally grown structures of uranium dioxide (UO2), thorium dioxide (ThO2), and UxTh1-xO2 alloys were characterized for suitability in uranium-based neutron detectors and nuclear reactor fuels. ThO2 was studied for its potential in an envisioned UO2/ThO2 heterojunction. A U0.71Th0.29O2 alloy was studied because of its resistance to oxidation, and potential to stabilize the surface of UO2. The majority carrier mobility of the UO2 samples, as measured by Hall effect, was consistent with established literature values on samples requiring substantial surface preparation. Direct current I(V) measurements provided evidence that the Hall currents may penetrate below any surface oxidized region caused by ambient air exposure. The depth of this surface structure was further investigated using angular resolved x-ray photoemission spectroscopy (ARPES). The U0.71Th0.29O2 effective Debye temperature of 217± 24 K was measured using temperature-dependent x-ray photoemission spectroscopy (XPS). The specific heat capacity for the U0.71Th0.29O2 alloy was calculated from the Debye temperature in order to compare to the heat capacity obtained from the more traditional modulated- temperature differential scanning calorimetry (MDSC). The XPS derived Debye temperature specific heat capacity was lower than with MDSC, showing how surface oxidation and hydrolysis effect surface stability. 4+ The U 4f7/2 peak energy was observed using ARPES, providing evidence of U and U6+ oxidation states at the surface with an increased concentration of the U4+ oxidation states further from the surface. The U 5f peaks observed in ARPES provided iv evidence of U4+ at the surface but does not preclude the presence of U6+. Throughout the surface measurement, the electronic band-gap energy remained at 2.2 eV, confirming the dominance of UO2 in establishing the electronic structure. These surface characteristics also revealed a vacuum reduced UO2 surface and excess oxygen incorporated into the lattice to form a UO2+x selvedge region. v Acknowledgments First and foremost I would like to thank God, for with God nothing shall be impossible. God truly blessed me with a great advisor and dissertation committee, wonderful lab technicians, and loving parents. Without the assistance of the following personnel, none of this would have been possible. I would like to show my sincere gratitude to my faculty advisor, Dr. James Petrosky, for his guidance and support throughout the course of this dissertation effort. I would like to thank the other two members of my committee, Dr. John McClory and Lt Col Sheena Winder for their time, advisement, and knowledge of nuclear physics and material science. Their insight and experience was certainly appreciated. I want to acknowledge Air Force Research Laboratory for providing hydrothermally-grown, single-crystal actinide samples and assistance with modulated-temperature differential scanning calorimetry. I would like to thank the lab technician, Greg Smith for his constant support, patience, and time. The numerous hours he dedicated to repairing equipment, building new chambers, and troubleshooting are much appreciated. Last but not least, I would like to thank my parents, who support me throughout my life in all my endeavors. Christina L. Dugan vi Table of Contents Page Abstract .............................................................................................................................. iv Table of Contents .............................................................................................................. vii List of Figures ......................................................................................................................x List of Tables .....................................................................................................................xv I. Introduction ......................................................................................................................1 1.1 Motivation ..............................................................................................................1 1.2. Uranium Dioxide Atomic Structure ......................................................................4 1.2.1 Uranium Dioxide Detector Concepts ............................................................... 5 1.2.2 Uranium Dioxide As An Electronic Medium .................................................. 5 1.3 Crystal Quality and Electronic Performance ..........................................................7 1.4 UO2 Surface Morphology .......................................................................................8 1.5. Thorium Dioxide and U0.71Th0.29O2 Characteristics ..............................................9 1.6 Research Measurements and Methods .................................................................11 II. Theoretical Basis For Experimental Techniques ..........................................................19 2.1 Primary Experimental Techniques .......................................................................20 2.1.1 X-ray Photoemission Spectroscopy ............................................................... 20 2.1.2 Cathodoluminescence Spectroscopy .............................................................. 22 2.2 Supplementary Experimental Techniques ............................................................27 2.2.1 Hall Effect, I(V), and C(V) Characteristic Curves ........................................ 27 2.2.2 Ellipsometry Technique ................................................................................. 31 2.2.3 Differential Scanning Calorimetry ................................................................. 37 2.3 Reference ..............................................................................................................40 III. Electrical Characterization of UO2 – Improved Mobility in Single Crystal UO2 Based Electronics..........................................................................................................................42 Abstract.......................................................................................................................42 3.1 Research Innovation and Objective ......................................................................43 3.2 Impacts on Warfighter Mission ............................................................................43 3.3 Introduction ..........................................................................................................43 3.4 Method ..................................................................................................................45 3.4.1 Hydrothermal Growth .................................................................................... 45 3.4.2 Hall Measurements ........................................................................................ 45 3.4.3 Current-Voltage, I(V), Measurements ........................................................... 46 3.5 Results ..................................................................................................................47 3.5.1 Hall Measurement Results ............................................................................. 47 vii 3.5.2 Direct Current, Current Voltage Measurement Results ................................. 47 3.6 Discussion.............................................................................................................48