Utah State University DigitalCommons@USU All Graduate Theses and Dissertations Graduate Studies 5-2005 Measurements of the Secondary Electron Emission Properties of Insulators Clint D. Thomson Utah State University Follow this and additional works at: https://digitalcommons.usu.edu/etd Part of the Physics Commons Recommended Citation Thomson, Clint D., "Measurements of the Secondary Electron Emission Properties of Insulators" (2005). All Graduate Theses and Dissertations. 2093. https://digitalcommons.usu.edu/etd/2093 This Dissertation is brought to you for free and open access by the Graduate Studies at DigitalCommons@USU. It has been accepted for inclusion in All Graduate Theses and Dissertations by an authorized administrator of DigitalCommons@USU. For more information, please contact [email protected]. MEASUREMENTS OF THE SECONDARY ELECTRON EMISSION PROPERTIES OF INSULATORS by Clint D. Thomson A dissertation submitted in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY in Physics Approved: Dr. John R. Dennison Dr. W. John Raitt Major Professor Committee Member Dr. D. Mark Riffe Dr. Jan J. Sojka Committee Member Committee Member Dr. Charles Swenson Dr. Laurens H. Smith, Jr. Committee Member Interim Dean of Graduate Studies UTAH STATE UNIVERSITY Logan, Utah 2005 ii Copyright © Clint D. Thomson 2005 All Rights Reserved iii ABSTRACT Measurements of the Secondary Electron Emission Properties of Insulators by Clint D. Thomson, Doctor of Philosophy Utah State University, 2005 Major Professor: Dr. John Robert Dennison Department: Physics Measurements of the electron-induced electron emission properties of insulators are important to many applications including spacecraft charging, scanning electron microscopy, electron sources, and particle detection technology. However, these measurements are difficult to make since insulators can charge either negatively or positively under charge particle bombardment that in turn alters insulator emissions. In addition, incident electron bombardment can modify the conductivity, internal charge distribution, surface potential, and material structure in ways that are not well understood. A primary goal of this dissertation work has been to make consistent and accurate measurements of the uncharged electron yields for insulator materials using innovative instrumentation and techniques. Furthermore, this dissertation reports on the experimental work undertaken by our group to explore insulator charging rates as a function of incident electron energy and fluence. Specifically, these charging studies include: (i) the study of the effectiveness of charge-neutralization techniques such as low-energy electron flooding and UV light irradiation to dissipate both positive and negative surface potentials induced by incident electron irradiation, (ii) the exploration of several noncontacting methods used to determine insulator surface potentials and the insulator iv first and second crossover energies that are important in determining both the polarity and magnitude of spacecraft material potentials, (iii) the dynamical evolution of electron emissions and sample displacement current as a function of incident charge fluence and energy with ties to evolving surface potentials as an insulator reaches its current steady state condition, and (iv) the slow evolution of electron yields with continuous incident electron bombardment. These charging data are explained in the context of available insulator charging models. Specific insulator materials tested included chromic acid anodized aluminum, RTV- silicone solar array adhesives, and KaptonTM on aluminum. (357 pages) v ACKNOWLEDGMENTS I am grateful to NASA Marshall Space Flight Center for providing me with the funding to pursue a PhD in physics. I am especially thankful for my advisor, J.R. Dennison, for his continual counsel, encouragement, and optimism. I am indebted to Rob Davies, Neal Nickles, and Albert Chang for leaving to me a great lab, and for showing me the ropes. Vladimir Zavyalov was also a great teacher. He imparted to me many great lessons, and without his data acquisition electronics, I would have been in the lab for several more years. My fellow graduate students have made life more enjoyable over the last few years. I am thankful to Jason Kite, Alec Sim, and Prasanna Swaminathan for many stimulating conversations that broke up the occasional monotony of lab work and dissertation writing. Also, Jodie Corbridge was a fun lab partner, and because of her scrutinizing glares, I probably broke less equipment than I would have if I had been on my own. I am grateful to Ralph Carruth and his group at Marshall Space Flight Center for their collaboration and hospitality. I was also grateful to have interacted with other members of the spacecraft charging community, including Rob Frederickson, Leon Levy, Jodie Minor, and Dale Ferguson. These people imparted to me both their resources and invaluable experience. I am thankful for the Physics Department staff, Deborah Reece, Karalee Ransom, Marilyn Griggs, and Sharon Pappas for helping me with all of my administrative needs, and for providing a small haven where I could catch up on the latest gossip. I want to thank Lee Pearson and Tim Doyle at Thiokol for providing me with an internship that has, in the end, led to a career away from Utah State. I am deeply appreciative of Gwena Couillard for her time, wisdom, and kindness. I want to thank members of my family including my mom and dad for their support, Tige for our fall hunting excursions, and my girls, Kensi, Jaidyn, and Ady, for patiently vi enduring a graduate student’s lifestyle of poverty. Finally, I want to thank Julie for sticking with me through some tough times. I have finally finished, and easier times lie ahead. Clint D. Thomson vii CONTENTS Page ABSTRACT.............................................................................................................................iii ACKNOWLEDGMENTS......................................................................................................... v LIST OF TABLES ................................................................................................................... ix LIST OF FIGURES................................................................................................................. xii NOMENCLATURE.............................................................................................................. xvii CHAPTER 1. INTRODUCTION .............................................................................................................. 1 2. BACKGROUND ................................................................................................................ 7 2.1 Secondary and Backscattered Electron Emission ..................................................... 7 2.2 Electron Emission Measurements on Insulators ..................................................... 14 2.3 Physical Models for Insulator Electron Emissions ................................................. 22 2.3.1 Overview of the Three-Stage Model............................................................. 23 2.3.2 Traditional Semiempirical Models................................................................ 25 2.3.3 Production Mechanism for Uncharged Insulators......................................... 35 2.3.4 Transport Mechanism for Uncharged Insulators........................................... 36 2.3.5 Escape Mechanism for Uncharged Insulators............................................... 44 2.3.6 Relationships between Evolving Surface Potentials and Electron Emissions ............................................................................... 48 2.3.7 Electron Radiation Induced Charge Distributions in Insulators.................... 66 2.3.8 Models for Internal and Surface Charge Distributions, Electric Fields, and Potentials ..................................................................... 76 2.3.9 Evolving Electron Yields, Sample Currents, and Surface Potentials by a Pulsed Incident Electron Source ........................................................ 82 3. INSTRUMENTATION .................................................................................................... 92 3.1 General Experimental Setup ................................................................................... 92 3.2 DC-Yield Measurement Setup................................................................................ 97 3.3 Pulsed-Yield Measurement Setup......................................................................... 101 3.4 Electron Gun Operation and Characterization ...................................................... 114 3.5 Charge Neutralization Sources.............................................................................. 124 4. PULSED-YIELD MEASUREMENTS .......................................................................... 134 4.1 General Pulsed-Yield Measurement Procedure .................................................... 134 viii 4.2 Electron Yield and Spectral Analysis ................................................................... 139 4.3 Absolute Electron Yields: Measurement Correction Factors................................ 152 4.4 Validation of Pulsed Measurements with DC Measurements............................... 164 4.5 Monitoring of Sample Charging ........................................................................... 171 4.6 Other Methods for Determining Yield Crossover Energies.................................