UNIVERSITY OF CINCINNATI Date:___________________ I, _________________________________________________________, hereby submit this work as part of the requirements for the degree of: in: It is entitled: This work and its defense approved by: Chair: _______________________________ _______________________________ _______________________________ _______________________________ _______________________________ Synthesis of Super-Long Carbon Nanotube Arrays by Chemical Vapor Deposition by Andrew J. Gorton A thesis submitted to the graduate faculty in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department: Mechanical Industrial and Nuclear Engineering Major: Mechanical Engineering Committee: Dr. Mark J.Schulz, Advisor, Mechanical Engineering Dr. Vesselin Shanov, Co-Advisor, Materials Engineering Dr. Jay Kim, Mechanical Engineering Dr. Randy Allemang, Mechanical Engineering University of Cincinnati Cincinnati, Ohio ABSTRACT Carbon nanotubes (CNT) that comprise large clusters referred to as carbon nanotube arrays were discovered in 1991 by Sumio Iijima. Carbon nanotubes are the strongest material known to exist and have amazing electrical and thermal properties. Chemical Vapor Deposition (CVD) is currently the best method for producing relatively pure super-long CNT arrays over large surface areas. The research presented here focuses primarily on new methods for improving the various aspects of the synthesis process with the intent of growing very long CNT arrays over large substrate surface areas. Experiments were conducted to optimize certain aspects of the substrate preparation and CVD processes. In addition, amazing advances in CNT growth were obtained by combining gadolinium with iron catalyst. Research was also conducted in two areas of carbon nano-composite materials. iii iv ACKNOWLEDGEMENT As I look back on my research work at the University Cincinnati, I begin to realize just how many people it took to complete this research. In a field as multi-disciplinary as nanotechnology, numerous people with very different skill sets are required to conduct this type of research. At this time I would like to thank all those who contributed to this body of work. I would first like to thank my advisor Dr. Mark Schulz and co-advisor Dr. Vesselin Shannov for their constant support and guidance. They were always willing to listen, and were instrumental in honing my ideas. They provided me with the opportunity to explore new research avenues, as well as participate in an array of research topics. Without this openness I would not have gained the breadth of knowledge that I did. My other professors that played a significant role in my education in the field of vibration and acoustics are Dr. Randy Allemang and Dr. Jay Kim. While they were not directly involved in the majority of my research, I learned much from them through their teaching as well as their willingness to entertain my endless questions in and out of class. I would also like to thank them, as well as Dr. Teik Lim for providing me with instrumentation and engineering assistance during the preliminary acoustics experiments discussed in the Chapter 7-Future Work. Thanks also to all my colleagues in the Smart Structures and Bio-Nanotechnology Lab for their support, inspiration and assistance during my thesis work- special thanks to Dr. v Yun Yeo-Heung and Dr. Goutham Kirikera for their friendship and willingness to help. I would also like to thank Dr. Robert Jones, for my AFM education and his willingness to answer my questions, Mr. Jeff Simkins for assisting with thin layer deposition as well as plasma oxidation and Mr. Ron Flenniken for his skill in depositing numerous thin films of catalyst metals and Mr. Dale Weber, the Instrumentation Specialist in the Chemical and Materials Engineering Department for his assistance with TGA analysis. The following research groups and individuals assisted in numerous parts of this thesis research: Dr. Jandro Abot and Yi Song (UC - Multiscale Material Characterization and Composite Structures Laboratory) for allowing me to participate in their novel composite material research - Dr. Joseph Caruso, Dr. Douglas Richardson and Mr. Kirk Lokits (UC) for their assistance with ICP Analysis - Dr. Punit Boolchand and Ping Chen (UC - Solid State Physics and Electronics Lab) for performing the raman analysis - Dr. Sergie Yarmolenko and Dr. Sudhere Nurella at North Carolina A&T University for providing combinatorial and layered substrates, not to mention their CNT synthesis expertise (Center for Advanced Materials and Smart Structures)- and Dr. Wentau Xu at the University of Kentucky for his expertise in high resolution TEM. Last but most certainly not least, I would like to thank my parents for their unending love, support and guidance throughout all of my endeavors without them I would never have accomplished all that I have throughout my life including my long road to obtaining a masters degree in Mechanical Engineering. vi TABLE OF CONTENTS Chapter 1 - Introduction to Carbon Nanotubes and Their Properties 1.0 Introduction 2.0 Overview of Nanotechnology 3.0 Current Applications and Research Motivation 4.0 Overview of Carbon Nanotubes 4.1 Chirality 4.2 Mechanical Properties 4.3 Vibration 4.4 Electrical Properties 5.0 References Chapter 2 - Carbon Nanotube Array Synthesis 1.0 Introduction 2.0 CNT Synthesis Methods 2.1 CNT Synthesis Using Arc Discharge and Laser Ablation 2.2 CNT Synthesis Using Chemical Vapor Deposition 3.0 The Physics and Chemistry of CNT Growth 3.1 The Role of Carbon Feedstock Gases 3.2 CNT Growth Termination 3.3 Growth Mode Selection 4.0 The Effects of a Hydrogen Flow Prior to Carbon Precursor Gas Injection 4.1 Motivation for Hydrogen Pre-Deposition Phase vii 4.2 Hydrogen Pre-Deposition Experiments & Results 4.3 Discussion of Results from Hydrogen Pre-Deposition 5.0 Overview of Substrate Preparation Techniques 5.1 Typical Substrate Preparation Methodology 6.0 The Chemical Vapor Deposition (CVD) System 7.0 Summary of Conclusions regarding the CNT growth process and the Effects of Hydrogen on CNT growth 8.0 Future Literature Review and Work 9.0 References Chapter 3 - Overview of Experimental and Material Characterization Techniques 1.0 Material Characterization 1.1 Environmental Scanning Electron Microscope (ESEM) 1.2 Raman Spectroscopy 1.3 High Resolution Transmission Electron Microscope (HR-TEM) 1.4 Atomic Force Microscopy (AFM) 1.5 Thermo-Gravimetric Analysis (TGA) 1.6 Inductively Coupled Plasma Spectroscopy 2.0 Substrate Preparation Methods 2.1 Temescal Electron Beam Evaporation 2.2 March Plasma Oxidation System 2.3 Thermal Annealing 3.0 CVD Furnace Operation 3.1 Easy Tube 1000 User Guide viii 4.0 Method for Quickly Measuring CNT Array Height 5.0 References Chapter 4 - Carbon Nanotube Array Synthesis Using Iron Catalyst 1.0 Introduction 2.0 Motivation - How does Iron Function as a CNT Catalyst? 3.0 Substrate Preparation 4.0 Substrate Surface Characterization Using AFM 4.1 Characterization Process Using AFM 4.2 Results of Substrate Surface Characterization Study 4.3 Discussion of Substrate Study Results 5.0 Synthesis Using 100% Iron Catalyst Substrates 5.1 Results of Synthesis Study 5.2 Discussion of Synthesis Study Results 6.0 Fundamental Conclusions Regarding Substrate Preparation and CNT Array Synthesis 7.0 Future Work in Substrate Preparation and Synthesis 8.0 References ix Chapter 5 - Carbon Nanotube Array Synthesis Using Gadolinium as an Iron Catalyst Motivator 1.0 Introduction 2.0 Investigation Gadolinium as a Catalyst for CNT Growth 1.1 Motivation for Using 100% Gadolinium 1.2 Synthesis Experiments Using 100% Gadolinium 1.3 Findings of Synthesis Study Using 100% Gd Catalyst Film 2.0 Investigating Gadolinium as an Iron Catalyst Motivator 2.1 Motivation for Combining 2.2 Gd/Fe Substrate Preparation Using E-Beam Evaporation 2.3 Gd/Fe, E-Beam Substrate Surface Characterization Using AFM 2.3.1 Characterization Process Using AFM 2.3.2 Results of Gd/Fe Substrate Characterization 2.3.3 Discussion of Gd/Fe Substrate Study Results 2.4 Gd/Fe Substrates Produced Using Pulsed Laser Deposition (PLD) 2.5 Overview of Synthesis Using Gd/Fe, E-Beam Substrates 2.5.1 Synthesis Results Using Gd/Fe, E-Beam Substrates 2.5.2 Discussion of Synthesis Results Using Gd/Fe, E-Beam Substrates 2.6 Overview of Synthesis Using Gd/Fe, PLD Substrates 2.6.1 Synthesis Results Using PLD Substrates 2.6.2 Discussion of Synthesis Results Using PLD Substrates 2.7 Characterization of Gd/Fe, E-Beam Substrates 2.7.1 Overview of ESEM Study x 2.7.1.1 Results of ESEM 2.7.1.2 Discussion of ESEM Results 2.7.2 Overview of HR-TEM Study 2.7.2.1 Results of HR-TEM Study 2.7.2.2 Discussion of HR-TEM Results 2.7.3 Overview of Thermal Gravimetric Analysis 2.7.3.1 Results of Thermal Gravimetric Analysis 2.7.3.2 Discussion of Thermal Gravimetric Analysis Results 2.7.4 Overview of Raman Spectroscopy 2.7.4.1 Results of Raman Spectroscopy 2.7.4.2 Discussion of Raman Spectroscopy Results 2.7.5 Overview of ICP Analysis 2.7.5.1 Purpose of ICP Analysis 2.7.5.1.1 ICP Sample Preparation 2.7.5.2 Estimation of Elemental Mass on a Substrate 2.7.5.3 Results and Discussion of ICP Analysis 3.0 Explanation of Why Gadolinium Improves Synthesis with Iron Catalyst 4.0 Fundamental Conclusions Regarding the use of Gadolinium as an Iron Catalyst Motivator 5.0 Future Work in Gd/Fe Substrate Preparation and Synthesis 6.0 References xi Chapter 6 - Applications for CNT and CNF Particles 1.0 Overview of Carbon Nano-Composites 2.0 Improving Dispersion in Carbon Nanofiber Composites