DESIGN AND DEVELOPMENT OF SCANNING EDDY CURRENT FORCE MICROSCOPY FOR CHARACTERIZATION OF ELECTRICAL, MAGNETIC AND FERROELECTRIC PROPERTIES WITH NANOMETER RESOLUTION Dissertation Submitted to The School of Engineering of the UNIVERSITY OF DAYTON In Partial Fulfillment of the Requirements for The Degree Doctor of Philosophy in Mechanical Engineering By Vijayaraghava Nalladega, M.S. Dayton, Ohio August, 2009 DESIGN AND DEVELOPMENT OF SCANNING EDDY CURRENT FORCE MICROSCOPY FOR CHARACTERIZATION OF ELECTRICAL, MAGNETIC AND FERROELECTRIC PROPERTIES WITH NANOMETER RESOLUTION APPROVED BY: Shamachary Sathish, Ph.D. P.Terrence Murray, Ph.D. Advisory Committee Chairman Committee Member Professor, Materials Engineering Professor, Materials Engineering Department Department Donald Klosterman, Ph.D. Chakrapani Varanasi, Ph.D. Committee Member Committee Member Assistant Professor, Chemical and Sr. Research Engineer Materials Engineering Department University of Dayton Research Institute Mark P. Blodgett, Ph.D. Materials Research Engineer Wright-Patterson Air Force Base Dayton, Ohio Joseph E. Saliba, Ph.D., P.E. Malcolm W. Daniels, Ph.D. Dean, School of Engineering Interim Dean, School of Engineering ii © Copyright by Vijayaraghava Nalladega All rights reserved 2009 iii ABSTRACT DESIGN AND DEVELOPMENT OF SCANNING EDDY CURRENT FORCE MICROSCOPY FOR CHARACTERIZATION OF ELECTRICAL, MAGNETIC AND FERROELECTRIC PROPERTIES WITH NANOMETER RESOLUTION Name: Nalladega, Vijayaraghava University of Dayton Advisor: Dr. Shamachary Sathish This dissertation describes the design and development of a new high- resolution electrical conductivity imaging technique combining the basic principles of eddy currents and atomic force microscopy (AFM). An electromagnetic coil is used to generate eddy currents in an electrically conducting material. The eddy currents induced in the sample are detected and measured with a magnetic tip attached to the AFM cantilever. The interaction of eddy currents with the magnetic tip-cantilever is theoretically modeled. The model is then used to estimate the eddy current forces generated in a typical metallic material placed in induced current field. The magnitude of the eddy current force is directly proportional to the electrical conductivity of the sample. The theoretical eddy current forces are used to design a magnetic tip-cantilever system with appropriate magnetic field and spring constant to facilitate the iv development of a high-resolution, high sensitivity electrical conductivity imaging technique. The technique is used to experimentally measure eddy current forces in metals of different conductivities and compared with theoretical and finite element models. The experimental results show that the technique is capable of measuring pN range eddy current forces. The experimental eddy current forces are used to determine the electrical resistivity of a thin copper wire and the experimental value agrees with the bulk resistivity of copper reported in literature. The imaging capabilities of the new technique are demonstrated by imaging the electrical conductivity variations in a composite sample and a dual-phase titanium alloy in lift mode AFM. The results indicate that this technique can be used to detect very small variations in electrical conductivity. The spatial resolution of the technique is determined to be about 25 nm by imaging carbon nanofibers reinforced in polymer matrix. Since AFM is extensively used to characterize nanomaterials, the newly developed technique is used to characterize metallic nanoparticles. The results showed for the first time that it is possible to image helicons in nanometallic particles at low electromagnetic frequencies using an AFM. The theoretical analysis of the helicons in nanostructured materials is presented using the concept of effective mass of electrons. The primary objective of the research work reported in this dissertation is to develop a high-resolution electrical conductivity imaging system. However, the interaction of induced currents with different materials gives rise to different v interaction forces. If an appropriate probe and an imaging mode are used, different material properties can be characterized using the same experimental setup. Therefore, in this study, magneto-acoustic, magnetic and dielectric properties of materials placed in induced current fields are studied. The modifications necessary to image these properties are discussed in detail. The advantages, limitations and applications of the new methodology are discussed. vi Dedicated to my parents and my wife vii ACKNOWLEDGEMENTS This dissertation could not have been completed without the help and support of many people. Finishing my doctoral studies is definitely a high point in my career. Here, I would like to express my thanks and gratitude to all those people who helped me throughout my research and contributed to the successful completion of this dissertation. First, I would like to thank my research advisor Dr. Sathish for his encouragement, help and support throughout the course of this research work. He has been a great mentor from my Master‟s research days and I have always learnt something new from our technical discussions. I am grateful for his guidance, insightful comments and his patience in answering my questions at all times. I truly value his advice in both personal and professional matters. I am lucky to have him as my teacher, friend and mentor. I would like to thank the members of doctoral advisory committee, Dr. Terry Murray, Dr. Don Klosterman, Dr. Mark Blodgett and Dr. Pani Varanasi for their willingness to serve on my thesis committee. I greatly appreciate their time, discussions and helpful suggestions throughout the research work and in preparation of the dissertation. viii I am exceptionally grateful to the financial support provided by Dayton Area Graduate Studies Institute (DAGSI), University of Dayton Research Institute, and Wright-Patterson Air Force Base for the successful completion of my doctoral research work. Samples used in this study came from different people. I would like to thank Dr. Terry Murray for providing the platinum nanoparticles sample, Dr. Klosterman for the carbon nanofiber composite sample, Dr. Blodgett for the titanium alloy sample. I am grateful to Dr. Michael Gigliotti and Dr. P. R. Subramanian, GE Global Research, for providing amorphous and nanocrystalline magnetic ribbon samples. I thank Dr. Dave Zelmon, Wright-Patterson Air Force Base for providing the ferroelectric KTP samples. I take this opportunity to personally thank Mr. Mike Bouchard, Division Head, Structural Integrity Division, UDRI, for providing me with an opportunity to work in the division and carry out my research. I am grateful for his constant support and encouragement throughout the research work. I am sincerely grateful to Dr. Allan Crasto, Associate Director, UDRI, for the encouragement and the financial support for my research. I would like to thank Dr. Kumar Jata, Wright-Patterson AFB for technical discussions. I would also like to express my sincere thanks to Mr. Brian Frock, UDRI, for his help, discussions, and encouragement over the last six years. He patiently taught me the basics of image processing which helped me to understand images and contrast in a better way for which I am always grateful to him. I would like to thank Tim Campbell for helping me with sample preparation whenever I needed and Ed ix Klosterman for his help in the lab. I would like to specially thank Richard Reibel for his extensive help with the instrumentation through out the project. I would like to thank Marla McCleskey, Administrative Assistant, Structural Integrity Division, for her gracious administrative assistance. I would like to thank all my friends who have directly or indirectly helped me throughout my graduate studies in University of Dayton. I am grateful for their support and encouragement. I truly cherish all the memories of last seven years spent at UD. I would like to thank, from the bottom of my heart, my parents and brothers for their love, support and encouragement. I am especially grateful to my father who taught me the importance of higher education and gaining knowledge. Finally, I thank my wife Pushyami for her constant encouragement, motivation, support and love throughout my research work. Without her patience and support, this work would not have been possible. x TABLE OF CONTENTS ABSTRACT...........................................................................................................iv DEDICATION.......................................................................................................vii ACKNOWLEDGEMENTS....................................................................................viii LIST OF ILLUSTRATIONS..................................................................................xvi LIST OF PRINCIPAL SYMBOLS.......................................................................xxii CHAPTER 1. INTRODUCTION..............................................................................................1 1.1. Motivation...................................................................................................1 1.2. Dissertation Overview...............................................................................13 2. MEASUREMENT OF ELECTRICAL AND MAGNETIC PROPERTIES AT MULTIPLE LENGTH SCALES...................................................................15 2.1. Introduction...............................................................................................15