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Fabrication and Manipulation of Metallic Nanofeatures and CVD Graphene Through Nanopatterning and Templating

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Fabrication and Manipulation of Metallic Nanofeatures and CVD Graphene through Nanopatterning and Templating by Copyright 2014 Christina M. Edwards Submitted to the graduate degree program in Chemistry and the Graduate Faculty of the University of Kansas in partial fulfillment of the requirements for the degree of Doctor of Philosophy. Chairperson Cindy L. Berrie Michael A. Johnson Susan M. Lunte Timothy A. Jackson Prajna Dhar Date Defended: July 16, 2014 The Dissertation Committee for Christina M. Edwards certifies that this is the approved version of the following dissertation: Fabrication and Manipulation of Metallic Nanofeatures and CVD Graphene through Nanopatterning and Templating Chairperson Cindy L. Berrie Date Defended: July 16, 2014 ii Abstract Nanotechnology holds exciting potential to significantly advance research in many fields such as sensors, environmental sustainability and cleanup, energy harvesting and storage, as well as nanoelectronics. The resulting high demand for implementation into these areas has simultaneously created a large need for effective fabrication methods for nanostructured materials. It is important the fabrication methods are capable of significant control over size, orientation, and structural configuration of nanomaterials for effective function in these applications. Nanopatterning and templating are a promising means to achieve extreme selectivity over these parameters, and additionally be used as tools to control the growth and structure of large-scale materials through nanoscale manipulation. In this research, nanopatterning and templating are implemented to create metallic nanowire structures on surfaces of silicon substrates with highly selectivity over nanowire placement and design. Additionally, templating is incorporated in graphene growth on metallic substrates to influence the quality of graphene films,and further film patterning is used to improve the graphene electrical and optical properties. The first part of this work focuses on the fabrication of copper metallic nanowires through resist patterning coupled with electroless copper deposition. An atomic force microscope is used to selectively remove portions of a self-assembled monolayer resist on a silicon substrate, with patterns reaching down to widths of 20 nm. Electroless metal plating provides a facile way to deposit metal in selectively activated areas on surfaces with nanoscale dimensions. Here, it is employed to deposit copper selectively within these nanopatterned lines to create copper nanowire features. Through variation of the electroless metal solution conditions, the dimensions of the AFM-patterned line, and the iii doping of the underlying silicon substrate, the dimensions and uniformity of copper deposition within AFM-patterned lines can be influenced. Furthermore, this method provides a successful level of control to construct copper nanowire features between gold microelectrodes, which allows the electrical properties of these nanowires to be examined. The ability to selectively place nanowire features on a substrate surface with dimensions down to the tens of nanometers, as well as the capability to manipulate the nanowire size and uniformity, make this a promising method to construct metallic nanofeatures for complex nanodevices and circuitry. The second portion of this research investigates techniques to develop high quality graphene films produced by chemical vapor deposition (CVD) on copper substrates. Chemical vapor deposition shows great potential for developing graphene films of large area, but unfortunately CVD graphene oftentimes possesses low conductivity values due to an increased amount of misaligned grain boundaries and point defects, and oftentimes exhibits low optical transparency. The focus of this research is to better understand the role the copper substrate plays in CVD graphene formation, and to find ways to directly enhance CVD graphene quality through changes in the copper substrate template. The surface morphology, optical transmittance, and electrical properties of CVD graphene manufactured on two copper substrates with different surface structures were investigated. It was found that differences in the copper substrate grain alignment and crystal lattice could significantly influence the deposition and quality of graphene on copper substrates. Furthermore, the possibility of developing graphene films on nonmetallic substrates, as well as enhancing its properties through chemical doping, is demonstrated by nanopatterning and templating of graphene films. iv Acknowledgements I would first like to acknowledge my wonderful research advisor, Dr. Cindy Berrie. She has been a great inspiration as a teacher and mentor, and her smiling face has been a joy to be around for the past 5 and ½ years. Her optimism is exceptional, and I thank her for the many times she was much more optimistic about my research than me. I also greatly appreciate her patience, willingness to listen, and constant encouragement. She has made graduate school a very memorable experience. I also acknowledge my cohorts in the Cindy Berrie research group who have put up with me for the past several years. Jen, Brad, and Rodi have been great coworkers who I had the opportunity to share fun times with in lab. I would like to extend a special thanks to Greg Smith who answered my many, incessant questions and helped me immensely with any problem I faced with my research. He has been a remarkable resource for problem solving, interesting discussion, and lots of laughter. I want to also thank the many people in the Chemistry Department at the University of Kansas for their friendship and example. I would like to thank Roderick Black for allowing me to participate in the many outreach opportunities provided by the KU Chemistry Department, and encouraging me to get involved in spreading my enthusiasm for chemistry to others of all ages. Also to the many professors I had the opportunity to work with as a Graduate Teaching Assistant, I am grateful for your teaching examples. I would like to additionally acknowledge Dr. Judy Wu from the Physics Department at the University of Kansas, and all the members of her research group who I collaborated with on several research projects. Judy is involved in pretty much anything v she can get her hands on, so I appreciate all the time she has spent discussing science with me and allowing me to work with her and her group. Lastly, I would like to mention all the friends who have supported me throughout my journey through graduate school. A very special thanks goes to Dr. Stephen Egbert, for providing constant encouragement and having faith in my capabilities to finish my Ph.D., especially during the last few months of thesis writing. He was always there to be a shoulder to cry on, a listening ear, or great friend to provide some wonderful hugs! To my roommates Amy Murphy and Jessica Hall, I loved those dance parties to relieve the stress of graduate life! To my friend Anne Regel, I will miss our nights of boring everybody by only talking about our research and current experiments that were not working correctly. Lastly, I would like to thank Henry, my roommate’s cat, for always showing me love and being willing to provide company for me during those long nights of thesis writing. vi Table of Contents Abstract ................................................................................................................. iii Acknowledgements .................................................................................................v List of Figures and Tables ................................................................................... xiii Chapter 1: Introduction 1.1 Background .......................................................................................................1 1.2 Fabrication of Metallic Nanowire Features ......................................................8 1.2.1 ATP Synthase Nanobiodevice ..........................................................9 1.2.2 Nanofabrication Methods for Surface-Attached Metallic ................12 Nanowire Features 1.3 Controlled Growth and Manipulation of Graphene Films ..............................16 1.4 Overview .........................................................................................................18 1.5 References .......................................................................................................22 Chapter 2: General Methods and Instrumentation 2.1 Summary .........................................................................................................30 2.2 Self-Assembled Monolayers ...........................................................................31 2.3 Goniometry .....................................................................................................34 2.4 Ellipsometry ....................................................................................................37 2.5 Atomic Force Microscopy ..............................................................................39 2.5.1 General Overview ............................................................................39 2.5.2 Contact Mode ...................................................................................41 2.5.3 Tapping Mode ..................................................................................42 2.6 Implemenation ................................................................................................44 vii 2.7 References .......................................................................................................45
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