University of Kentucky UKnowledge University of Kentucky Doctoral Dissertations Graduate School 2009 MICROSTRUCTURAL EVOLUTION AND PHYSICAL BEHAVIOR OF PALLADIUM AND OSMIUM-RUTHENIUM NOBLE METAL FILMS Wen-Chung Li University of Kentucky, [email protected] Right click to open a feedback form in a new tab to let us know how this document benefits ou.y Recommended Citation Li, Wen-Chung, "MICROSTRUCTURAL EVOLUTION AND PHYSICAL BEHAVIOR OF PALLADIUM AND OSMIUM-RUTHENIUM NOBLE METAL FILMS" (2009). University of Kentucky Doctoral Dissertations. 802. https://uknowledge.uky.edu/gradschool_diss/802 This Dissertation is brought to you for free and open access by the Graduate School at UKnowledge. It has been accepted for inclusion in University of Kentucky Doctoral Dissertations by an authorized administrator of UKnowledge. For more information, please contact [email protected]. ABSTRACT OF DISSERTATION Wen-Chung Li The Graduate School University of Kentucky 2009 MICROSTRUCTURAL EVOLUTION AND PHYSICAL BEHAVIOR OF PALLADIUM AND OSMIUM-RUTHENIUM NOBLE METAL FILMS ABSTRACT OF DISSERTATION A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the College of Engineering at the University of Kentucky By Wen-Chung Li Lexington, Kentucky Director: Dr. T. John Balk, Professor of Chemical and Materials Engineering Lexington, Kentucky 2009 Copyright © Wen-Chung Li 2009 ABSTRACT OF DISSERTATION MICROSTRUCTURAL EVOLUTION AND PHYSICAL BEHAVIOR OF PALLADIUM AND OSMIUM-RUTHENIUM NOBLE METAL FILMS Nanostructured noble metals exhibit novel physical, mechanical and chemical behavior, and hold promise for applications such as gas sensing and electron emission. A strong emphasis was placed on the processing and characterization of these materials, in the form of nanoporous or nanocrystalline thin films. Palladium-based and osmium-ruthenium alloys were investigated in this dissertation research and will be presented as follows: (1) Preparation and Characterization of Nanoporous Metal Thin Films (2) Characterization of Osmium-Ruthenium Coatings Nanoporous palladium (np-Pd) thin films were prepared by dealloying co-sputtered palladium-nickel precursor alloys. Nanoporous structures were created with 3-D interconnected ligaments and open pores. Size of ligaments and pores was ~5 nm, achieved with a novel processing method developed in this study. Hydrogen cycling tests performed with np-Pd films demonstrated a significant improvement in sensitivity to hydrogen and response time for sensing. Effects of alloying element (Ni), film thickness, local stress and pore/ligament size on hydrogen cycling behavior were investigated in detail. Additionally, nanoporous gold and gold-palladium thin films were studied to clarify the evolution of microstructure during dealloying, including the formation of nanoporous structure and effects of substrate curvature on dealloying behavior. The results from this project have yielded a new understanding of dealloying as well as an ideal coating material for hydrogen sensing. Nanocrystalline osmium-ruthenium (Os-Ru) thin films were deposited on porous tungsten substrates with varied sputtering parameters. These parameters were mapped to microstructure, film texture and film composition in samples that were comparable to commercial devices. Using this map, Os-Ru films can be produced with higher stability during annealing and/or high-temperature operation. These results should lead to Os-Ru top coatings that increase the lifetime and emission performance of dispenser cathodes. KEYWORDS: nanoporous, palladium, dealloying, osmium, ruthenium Wen-Chung Li Student’s Signature December 21, 2009 Date MICROSTRUCTURAL EVOLUTION AND PHYSICAL BEHAVIOR OF PALLADIUM AND OSMIUM-RUTHENIUM NOBLE METAL FILMS By Wen-Chung Li T. John Balk, Ph. D. Director of Dissertation Stephen E. Rankin, Ph. D. Director of Graduate Studies December 21, 2009 RULES FOR THE USE OF DISSERTATIONS Unpublished dissertations submitted for the Doctor's degree and deposited in the University of Kentucky Library are as a rule open for inspection, but are to be used only with due regard to the rights of the authors. Bibliographical references may be noted, but quotations or summaries of parts may be published only with the permission of the author, and with the usual scholarly acknowledgments. Extensive copying or publication of the dissertation in whole or in part also requires the consent of the Dean of the Graduate School of the University of Kentucky. A library that borrows this dissertation for use by its patrons is expected to secure the signature of each user. Name Date DISSERTATION Wen-Chung Li The Graduate School University of Kentucky 2009 MICROSTRUCTURAL EVOLUTION AND PHYSICAL BEHAVIOR OF PALLADIUM AND OSMIUM-RUTHENIUM NOBLE METAL FILMS DISSERTATION A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the College of Engineering at the University of Kentucky By Wen-Chung Li Lexington, Kentucky Director: Dr. T. John Balk, Professor of Chemical and Materials Engineering Lexington, Kentucky 2009 Copyright © Wen-Chung Li 2009 ACKNOWLEDGMENTS I had a dream that I want to be a great scientist when I was a child, and I think I am a lucky guy who is still possible to fulfill his childhood dream when he has grown up. Completing the PhD study is a critical step for making the dream to come true. There are many people whom I want to thank because they help and support me a lot for the important step because my PhD study could not be done without their help. Dr. T. John Balk, a young gentleman, is the most important person who supports me as not only an academic advisor but also a good friend every moment in my life at the University of Kentucky. Dr. Balk knows how to give me a hand very well when I lost my way in the materials world although he is a young professor. His talent, knowledge, patience and positive attitude have guided me to be a great scientist. I also want to thank Dr. Balk’s family, especially to his parents (Thomas and Michele) and his wife (Ilka), because they always take care of me as their family member. It is not easy that a foreign student wants to adapt his new life in a different environment. However, Dr. Balk and his family let me feel that I am not alone when I faced challenges. I also deeply appreciate all members of my committee: Dr. Kimberly W. Anderson, Dr. Alan T. Male, Dr. Bruce Hinds, Dr. Fu-Qian Yang and Dr. J. Todd Hastings for their helpful suggestions. I thank them for agreeing with being my committee members and their time spending on my study. Especially, I thank Dr. Yang for his encouragement and concern about helping me in adapting my study life at the UK. I want to thank Dr. Ye Sun who was my colleague during the first three years in Dr. Balk’s group and is my best friend forever. He is always the person whom I can discuss experiments with and share my feeling with. I also thank my other colleagues for their help in my study: Simone C. Schendel, Thomas König, Elizabeth Fadde and Phillip D. Swartzentruber. In addition, I would like to send my thankfulness to my classmates who accompanied me when I needed someone’s help: Ashley Brinegar, Bin-Hui Wang, Xue-Bei Shi, Bing Hu, and all people who have ever helped me out. I thank Dr. Shun-Tian Lin who is the advisor of my M.S. study and pushed me toward my dream. I also deeply appreciate Mr. Pat Chiao and Dr. Herng-Der Chiou for their kind support and long-term encouragement. iii I want to send my best gratitude to my family, especially to my parents. Without their support, I could not come to the US and take four and half years for fulfilling my childhood dream. There is no doubt that my wife, Shu-Ping (Aikey) Lin, is the person whom I want to send my greatest gratitude. To her, this is not only acknowledgement but also the firmest love and promise of all my life. Finally, I thank the God for giving me the best gift – Ashley L. Li, my dear princess, in the year of my graduation. She has been the most important force driving me to a more successful future. Thank all the people who have ever helped me out and supported me!! iv TABLE OF CONTENTS ACKNOWLEDGMENTS ................................................................................................. iii LIST OF TABLES ........................................................................................................... viii LIST OF FIGURES ........................................................................................................... ix LIST OF FILES ............................................................................................................... xvi Chapter 1 Introduction ........................................................................................................ 1 1.1 Introduction of Np-Pd Films…………………………..……………………………1 1.2 Introduction of Nanocrystalline Os-Ru Films………………………………………3 1.3 Hypotheses………………………………….………………………………………5 Chapter 2 Background ........................................................................................................ 6 2.1 Applications of Pd-based Alloy Thin Films ………………………………………..7 2.1.1 Electrode Material of Fuel Cells…………………………………………….....7 2.1.2 H 2 Sensors…………………………………………………………………...8 2.2 Dealloying…………………………………………………………………………..9 2.2.1 Selection of Precursor Alloys and Etchant Solutions ........................................ 9 2.2.2 Mechanisms of Dealloying .............................................................................