Louisiana Tech University Louisiana Tech Digital Commons Master's Theses Graduate School Spring 5-2020 Local Oxidation Nanolithography of Highly Oriented Pyrolytic Graphite Zachary Swart Follow this and additional works at: https://digitalcommons.latech.edu/theses LOCAL OXIDATION NANOLITHOGRAPHY OF HIGHLY ORIENTED PYROLYTIC GRAPHITE by Zachary Swart, B.S. A Thesis Presented in Partial Fulfillment of the Requirements of the Degree Master of Science COLLEGE ENGINEERING AND SCIENCE LOUISIANA TECH UNIVERSITY May 2020 LOUISIANA TECH UNIVERSITY GRADUATE SCHOOL February 28, 2020 Date of thesis defense We hereby recommend that the thesis prepared by Zachary Swart, B.S. entitled Local Oxidation Nanolithography of Highly Oriented Pyrolytic Graphite be accepted in partial fulfillment of the requirements for the degree of Master of Science in Molecular Sciences and Nanotechnology Dr. Adarsh Radadia, Supervisor of Thesis Research Dr. Gergana Nestorova, Head of Molecular Sciences and Nanotechnology Members of the Thesis Committee: Dr. Sandra Zivanovic Dr. Arden Moore Approved: Approved: Hisham Hegab Ramu Ramachandran Dean of Engineering & Science Dean of the Graduate School GS Form 13 (1/19) ABSTRACT In this thesis, the physical and electrical alterations caused by local oxidation nanolithography (LON) on highly oriented pyrolytic graphite (HOPG) are characterized. The LON is an atomic force microscopy (AFM) based technique that applies a positive bias to the sample relative to the AFM tip, leading to an electrochemical oxidation of the sample surface. If these physical and electrical alterations due to LON are well understood, this could yield a higher degree of control over tailoring the surface to become conductive, semiconductive or insulative in nature. The advantages of LON include room temperature operation in a non-vacuum environment, less steps to fabricate nanoscale devices, reduced photoresist residues, and an ability to perform metrology in situ. First, we characterized patterns obtained through LON on HOPG as the write bias, write speed, and write force were varied. We organized patterns formed as either– bumps, cracked bumps, or trenches–which were characterized using four shape descriptors–pattern width, pattern height, cut width, and cut depth. This was the first reported attempt to characterize LON patterns on HOPG with shape descriptors. These findings help solve the mystery of why bumps were not reported at threshold voltages before 2008. Subsequently, the electrical nature of the LON patterns were characterized using Kelvin probe force microscopy (KPFM); only write force was varied during this study. The in situ KPFM after LON allowed mapping LON-induced changes in work function and capacitance gradient (dC/dz) of the surface, the latter being an indicator of a change in iii iv dielectric permittivity of the surface. This was the first attempt to characterize LON patterns using KPFM in-situ The findings of this thesis hold potential to make LON a more repeatable process. For future work on LON, it was also shown that the tip conditions need to be checked consistently using cantilever resonance frequency and scanning electron microscopy, and an environmental cell should be used to control the relative humidity around the tip. APPROVAL FOR SCHOLARLY DISSEMINATION The author grants to the Prescott Memorial Library of Louisiana Tech University the right to reproduce, by appropriate methods, upon request, any or all portions of this Thesis. It is understood that “proper request” consists of the agreement, on the part of the requesting party, that said reproduction is for his personal use and that subsequent reproduction will not occur without written approval of the author of this Thesis. Further, any portions of the Thesis used in books, papers, and other works must be appropriately referenced to this Thesis. Finally, the author of this Thesis reserves the right to publish freely, in the literature, at any time, any or all portions of this Thesis. Author _____________________________ Date _____________________________ GS Form 14 (8/10) DEDICATION I want to dedicate this thesis to my loving family, who have always believed and supported me through my academic pursuits. They always reminded me that anything was possible, so long as we set our mind to it and to pursue what is meaningful, not what is expedient. vi TABLE OF CONTENTS ABSTRACT ....................................................................................................................... iii APPROVAL FOR SCHOLARLY DISSEMINATION ..................................................... v DEDICATION ................................................................................................................... vi LIST OF FIGURES ............................................................................................................ x LIST OF TABLES ........................................................................................................... xiv ACKNOWLEDGMENTS ................................................................................................ xv CHAPTER 1 INTRODUCTION ........................................................................................ 1 Problem Statement .............................................................................................. 2 Research Objectives ............................................................................................ 2 Thesis Structure .................................................................................................. 3 CHAPTER 2 BACKGROUND .......................................................................................... 4 Brief History of Atomic Force Microscopy (AFM) ........................................... 4 Working Principle of AFM ................................................................................. 5 Components of AFM .......................................................................................... 7 2.3.1 AFM Cantilever Tip ........................................................................................ 7 2.3.2 Piezoelectric Scanner ...................................................................................... 8 Modes of AFM .................................................................................................... 8 2.4.1 Contact Mode .................................................................................................. 8 2.4.2 Non-Contact Mode.......................................................................................... 9 2.4.3 Tapping Mode ............................................................................................... 10 2.4.4 Kelvin Probe Force Microscopy ................................................................... 11 vii viii Local Oxidation Nanolithography .................................................................... 15 Related Research ............................................................................................... 17 CHAPTER 3 METHODS AND MATERIALS ............................................................... 22 Spring Constant Calculation ............................................................................. 24 3.1.1 Sader Method ................................................................................................ 24 3.1.2 Change in Tip Mass ...................................................................................... 26 3.1.3 AFM Force Spectroscopy ............................................................................. 29 Tip Radius Characterization ............................................................................. 31 Properties of HOPG .......................................................................................... 37 CHAPTER 4 LOCAL OXIDATION NANOLITHOGRAPHY OF HOPG..................... 39 Formation of Patterns ........................................................................................ 39 4.1.1 Variation of Sample Bias .............................................................................. 40 4.1.2 Variation of Write Speed .............................................................................. 42 4.1.3 Variation of Write Force ............................................................................... 45 CHAPTER 5 KELVIN PROBE FORCE MICROSCOPY OF HOPG ............................. 48 Change in Surface Chemistry ........................................................................... 48 5.1.1 Pattern Characteristics with Variation in Contact Force............................... 49 5.1.2 Change in Surface Potential .......................................................................... 51 5.1.3 Capacitance Gradient Imaging ...................................................................... 54 5.1.4 AFM Tip Condition Post Local Oxidation Nanolithography ....................... 57 CHAPTER 6 CONCLUSIONS AND FUTURE WORK ................................................. 62 Conclusion ........................................................................................................ 62 Future Work ...................................................................................................... 63 APPENDIX A ................................................................................................................... 66 A.1 Variation of Write Bias ..................................................................................... 66 ix A.2 Variation of Write Speed .................................................................................