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University of Alberta Spectroscopic and Electronic Characterization of Microfabricated Solid State Molecular Electronic Junctions by Amr Mohamed Mahmoud Mohamed A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Doctor of Philosophy Department of Chemistry © Amr Mohamed Mahmoud Mohamed Fall 2012 Edmonton, Alberta Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission. Dedication To my mother, Fatma, who gave me my life & to my wife, Fatma, who gave me her life. Abstract The objective of the research described in this thesis is structural characterization of molecular electronic devices and investigation of their compatibility with widely use conventional microelectronics. Back-side spectroscopy was performed to probe organic molecular later integrity at buried interfaces, during and after fabrication. Modifications of optically transparent substrates with organic molecules were achieved using ultrathin Ti as a primer, which then spontaneously reduced aromatic diazonium ions in solution to form free radicals. The free radicals then bond covalently to the substrate. Then, a second conducting contact was deposited by direct physical vapor deposition onto the molecular layer. The molecular layer integrity was probed by “back-side” Raman and infrared spectroscopy. The results demonstrated that metal deposition had minimal influence on molecular layer structure. The compatibility of carbon based molecular junctions with various microfabrication processes such as elevated temperatures, photolithographic processing and metal deposition was investigated. Flat carbon surfaces were modified electrochemically by reduction of aromatic diazonium ions. The aromatic molecules bond covalently to the electrode though strong C-C bonds. Then the top metal contact was deposited to form a complete junction. Molecular layer integrity after deposition of various metals was inspected by “back-side” spectroscopy. Both Ti and Pt metals caused significant damage to the molecular layer, while Au and Cu had no observable effect on the molecular layer. The modified samples were thermally stable up to 400 oC and the complete junctions were stable up to 250 oC under vacuum. Carbon based molecular junctions were compatible with a photolithographic process and different solvents used during the process. The charge transport mechanism through silicon based molecular junctions was investigated by replacing carbon of previous investigations by a Si electrode. Heavily doped n- and p-Si (111) substrates were modified electrochemically with aromatic molecular layers and Cu contact was deposited, resulting in reproducible junctions with high yield. The junctions were characterized spectroscopically and electrically. Junctions made with n-Si exhibited significantly higher conductivity than those made with either p-Si or carbon substrates. This difference in conductivity was attributed to difference in the barrier height for tunneling as estimated from ultraviolet photoemission spectroscopy measurements. Acknowledgement First and foremost, I would like to thank God “Allah” for bestowing me with the grace of science and knowledge. I hope that this grace would be useful for others. Second, I would like to express my deep gratitude and thankful for my supervisor Prof. Dr. Richard L. McCreery, for accepting me in his group and offering me such a great opportunity. Furthermore, I would like to thank him for his support, advice, patient and guidance all the way during my PhD research from my first day in the laboratory to thesis writing. I would like also to thank him for his group meetings that were the first step to learn how to conduct scientific research. I have earned a lot from his discussions, interpretations, corrections, suggestions and knowledge. Last but not least, I would like to thank him for his social gather of the group members and thank his wife Jane. Third, I would like to thank the present and past group members in Prof. McCreery group, I was fortunate to work in such a collaborative environment. In particular, I would like to express my gratitude to Dr. Adam Johan Bergren for his help, time, advice and effort that helped me a lot to accomplish my thesis. In addition, I would like to thank Dr. Haijun Yan, Dr. Andrew Bonifas, Jie Ru, Dr. Jing Wu, Dr. Lian Shoute, Dr. Kenneth Harris, Dr. Fengjun Deng, Dr. Nikola Pekas, Dr. Rajesh Kumar and Dr. Rajesh Pillai for their helpful scientific discussions and support. In addition, I would like to thank Bryan Szeto, for his friendship and support in training me a lot of microfabrication skills and his technical help. Furthermore, I would like to thank Dr. Sayed Nagy for his friendly and scientific support and help. Fourth, I would like to thank people who directly support me to perform my experimental work: National Institute for Nanotechnology staff, University of Alberta NanoFab staff, University of Alberta ACSES staff especially, Dr. Dimitre Karpuzov, machine and glass shop staff. The department of chemistry graduate coordinators and the complete team. Finally, I would like to thank my mother, my father, my two brothers, my sister, and latest member in my small family, my wife. I would like to thank my unforgotten friends here in Canada and Egypt for their unusual and special support that was essential during my PhD. I thank the Egyptian Student Association, the members of the department of analytical chemistry at faculty of pharmacy in Cairo University. Thanks all Table of Contents DEDICATION ABSTRACT ACKNOWLEDGEMENT TABLE OF CONTENTS LIST OF TABLES LIST OF FIGURES LIST OF ABBREVIATIONS CHAPTER 1 ............................................................................................................................. 1 INTRODUCTION .................................................................................................................... 1 1.1 MOLECULAR ELECTRONICS ............................................................................................... 1 1.2 CONTACTING THE MOLECULES TO ELECTRODE SURFACE .................................................... 5 1.2.1 LANGMUIR-BLODGETT (LB) FILMS ................................................................................. 5 1.2.2 SELF-ASSEMBLED MONOLAYERS (SAMS) ........................................................................ 6 1.2.3 ELECTROCHEMICAL MODIFICATION ................................................................................ 9 1.2.3.1 Aromatic Diazonium Salt Chemistry ....................................................................... 9 1.2.4 ADDITIONAL METHODS FOR SI SURFACE MODIFICATION ............................................... 10 1.3 PLATFORMS TO STUDY MOLECULAR LAYER ELECTRICAL PROPERTIES .............................. 13 1.3.1 “SINGLE” MOLECULAR ELECTRONIC JUNCTIONS ........................................................... 13 1.3.1.1 Scanning Tunneling Microscopy ........................................................................... 14 1.3.1.2 Conducting Probe Atomic Force Microscopy [CP-AFM] ...................................... 15 1.3.1.3 Mechanically controllable break junctions ............................................................ 19 1.3.1.4 Electromigration break junctions .......................................................................... 20 1.3.1.5 Crossed-wire tunnel junctions............................................................................... 21 1.3.1.6 Surface diffusion mediated deposition ................................................................... 21 1.3.2 “ENSEMBLE” MOLECULAR ELECTRONIC JUNCTIONS ....................................................... 21 1.4 TOP CONTACT FORMATION AND MOLECULAR LAYER INTEGRITY...................................... 24 1.4.1. DIRECT METAL TOP CONTACT DEPOSITION .................................................................. 24 1.4.2 INDIRECT, OR “SOFT” DEPOSITION TECHNIQUES ............................................................. 28 1.4.2.1 Soft Liquid Contact............................................................................................... 28 1.4.2.2 Indirect Physical Vapor Deposition ...................................................................... 28 1.4.2.3 Nanotransfer Printing (nTP) ................................................................................. 29 1.4.2.4 Spin Coating of conductive polymers .................................................................... 29 1.4.2.5 Lift-Off Float-On (LOFO) .................................................................................... 30 1.4.2.6 Soft Deposition through Metal Diffusion ............................................................... 31 1.4.2.7 Electrodeposition ................................................................................................. 31 1.5 CARBON BASED MOLECULAR ELECTRONIC JUNCTIONS ...................................................

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