The Pennsylvania State University The Graduate School The College of Earth and Mineral Sciences NOVEL APPROACHES TO THE SURFACE MODIFICATION OF GLASS BY THERMO-ELECTRIC POLING A Dissertation in Materials Science and Engineering by Nicholas J. Smith 2011 Nicholas J. Smith Submitted in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy August 2011 ii The dissertation of Nicholas J. Smith was reviewed and approved* by the following: Carlo G. Pantano Distinguished Professor of Materials Science and Engineering Dissertation Advisor Chair of Committee Michael T. Lanagan Professor of Engineering Science and Mechanics Venkatraman Gopalan Professor of Materials Science and Engineering Seong H. Kim Associate Professor of Chemical Engineering Gary L. Messing Distinguished Professor of Materials Science and Engineering Head of the Department of Materials Science and Engineering *Signatures are on file in the Graduate School iii ABSTRACT Many new and emerging applications of glass rely critically on surface properties, and have led to an ever-increasing demand for methods to controllably modify glass surfaces as a pathway to enhanced properties. The genesis of this thesis arose from such pursuits, wherein the thermo-electric poling of glass—encompassing treatment with high voltage and blocking electrodes at moderate temperatures—was found to provide a fertile research area. Versatile in its application to a variety of glasses, as well as the diversity of phenomena it produces, several novel approaches to the thermo-electric treatments of multicomponent glass are carried out in this work. This included (1) poling to produce normally-forbidden, second-order nonlinearity in high breakdown strength glasses as a potential avenue to greater nonlinear coefficients; (2) capitalizing on poling-induced modifications toward the novel end of manipulating the observed breakdown strength of glass; and (3) venturing outside the “typical” parameter space of poling treatments in order to realize even greater modifications to surface composition and structure by electrolyzing the glass network. The primary outcome for the first study indicates that, contrary to the usual assumption, the stored internal field from poling is limited to a substantial fraction of the intrinsic breakdown strength, and seemingly in a broad range of glass systems. This is most likely due to nonlinear conduction effects at the high poling temperatures. Meanwhile, the results of the second study indicate that the observed breakdown strength of glass is minimally influenced by the presence of a stored space charge field, and is likely attributable to the presence of the modified surface layer concentrating the applied voltage. The results of the last study provide the most intriguing possibilities for extensive and stable surface modification. Applied to a model alkali-free glass, a nanoscale layer is formed adjacent to the anodic surface composed of essentially only network-forming elements, and whose formation is attributed to the electrolytic migration of both cationic and anionic species within the glass network. This technique has significant potential for creating novel surface structures and compositions, anticipated applicability to a wide variety of glass compositions, and extensively modified transport and corrosion-resistance properties. iv TABLE OF CONTENTS LIST OF FIGURES ...................................................................................................... VI LIST OF TABLES ....................................................................................................... XIII ACKNOWLEDGEMENTS ......................................................................................... XV CHAPTER 1: INTRODUCTION AND STATEMENT OF OBJECTIVES .................................. 1 CHAPTER 2: BACKGROUND REVIEW .......................................................................... 5 2.1. INTRODUCTION ............................................................................................... 5 2.2. THERMO-ELECTRIC TREATMENT OF GLASS: A ROADMAP .............................. 8 2.2.1. ELECTRODE AND ATMOSPHERE CONSIDERATIONS ............................... 9 2.2.2. ION-MIGRATION PROCESSES IN GLASS WITH BLOCKING ELECTRODES ........................................................................................... 12 2.3. THERMAL POLING FOR SECOND-ORDER NONLINEARITY ................................ 16 2.4. STRUCTURAL MODIFICATION BY THERMO-ELECTRIC TREATMENT ................. 21 2.5. SUMMARY ....................................................................................................... 25 CHAPTER 3: THERMAL POLING OF ALKALI-FREE DISPLAY GLASSES WITH HIGH BREAKDOWN STRENGTH ....................................................................................... 27 3.1. ABSTRACT ...................................................................................................... 27 3.2. INTRODUCTION ............................................................................................... 27 3.3. EXPERIMENTAL PROCEDURE ........................................................................... 29 3.4. RESULTS ......................................................................................................... 33 3.5. DISCUSSION .................................................................................................... 41 3.5.1. SECOND-ORDER NONLINEARITY AND EDC VERSUS BREAKDOWN .......... 41 3.5.2. CHARGE MIGRATION CONSIDERATIONS ............................................... 46 3.6. SUMMARY ....................................................................................................... 48 CHAPTER 4: DIELECTRIC BREAKDOWN STRENGTH OF ALKALI-FREE GLASS WITH SURFACE MODIFIED BY THERMAL POLING ............................................................ 50 4.1. ABSTRACT ...................................................................................................... 50 4.2. INTRODUCTION ............................................................................................... 50 4.3. EXPERIMENTAL PROCEDURE ........................................................................... 53 4.4. RESULTS ......................................................................................................... 58 4.4.1. BASELINE CHARACTERISTICS AND BREAKDOWN STRENGTH OF UNPOLED GLASS ..................................................................................... 58 4.4.2. THERMALLY POLED THIN GLASS AND BREAKDOWN STRENGTH .......... 70 4.5. DISCUSSION .................................................................................................... 75 4.6. SUMMARY ....................................................................................................... 79 v CHAPTER 5: STRUCTURAL AND COMPOSITIONAL MODIFICATION OF MULTICOMPONENT GLASS SURFACES BY THERMO-ELECTRIC POLING ................. 81 5.1. ABSTRACT ...................................................................................................... 81 5.2. INTRODUCTION ............................................................................................... 81 5.2.1. OPTIMIZING FOR SURFACE MODIFICATION ........................................... 84 5.2.2. APPLICATION TO A MODEL GLASS SYSTEM .......................................... 86 5.3. EXPERIMENTAL PROCEDURE ........................................................................... 88 5.3.1. SAMPLE AND THERMO-ELECTRIC TREATMENT PARAMETERS .............. 88 5.3.2. ANALYTICAL METHODS ....................................................................... 91 5.4. RESULTS ......................................................................................................... 97 5.4.1. SURFACE COMPOSITIONAL MODIFICATION CORRELATED TO ANODIC OXIDATION .............................................................................................. 97 5.4.1. STRUCTURE OF MODIFIED GLASS SURFACE LAYERS ............................ 112 5.5. DISCUSSION .................................................................................................... 132 5.5.1. OVERVIEW OF EVIDENCE FOR ELECTROLYSIS ....................................... 132 5.5.2. GLASS STRUCTURE CONSIDERATIONS .................................................. 135 5.6. SUMMARY ....................................................................................................... 140 CHAPTER 6: SUMMARY AND FUTURE WORK ............................................................. 141 APPENDIX A. SUMMARY OF ALKALI-FREE DISPLAY GLASS COMPOSITIONS ............. 143 APPENDIX B. VALIDATION OF INTERFEROMETRIC MEASUREMENT OF THIN GLASS USING INFRARED MICROSCOPY .............................................................................. 146 APPENDIX C. DECONVOLUTION OF BARIUM 4P AND BORON 1S PEAKS IN QUANTIFICATION OF XPS FOR MULTICOMPONENT GLASS .................................... 150 REFERENCES ............................................................................................................ 159 vi LIST OF FIGURES Figure 2-1: Schematic of thermo-electric treatment process. ..................................... 8 Figure 2-2: Concentration profiles of Na, Ca, and H for the anodic surfaces of poled soda-lime glass. (a) Profile with Al press contact electrodes and no effort to mitigate H+ injection; (b) evaporated Al/Cu bilayer electrodes, shown to effectively block H+ injection from the poling atmosphere; (c) a sample pre-etched with HF to remove hydrated surface layer prior to Al/Cu film deposition