ANALYSIS OF IRRADIATION INDUCED DEFECTS ON CARBON NANOSTRUCTURES AND THEIR INFLUENCES ON NANOMECHNANICAL AND MORPHOLOGICAL PROPERTIES USING MOLECULAR DYNAMICS SIMULATION By SHARON KAY PREGLER A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2008 1 © 2008 Sharon Kay Pregler 2 To my family and friends with love and gratitude 3 ACKNOWLEDGMENTS I would like to express my sincere gratitude to Prof. Susan Sinnott, for her encouragement and support during my graduate career. Her guidance and optimism has helped me accomplish my goals and tackle obstacles in academic research. I would also like to thank Prof. Simon Phillpot for guidance and valuable ideas on my research. Their care and enthusiasm for the members of the Computational Focus Group have truly made my last years at the University of Florida memorable and fulfilling. I would also like to acknowledge my supervisory committee, Prof. Jiangeng Xue, Prof. Wolfgang Sigmund, and Prof. Nam-Ho Kim, for their advice and support. I would also like to thank the members and graduated members of the computational focus group as well as fellow department colleagues, Abby Queale, Jillian Leifer, and Sean Bishop. Their encouragement and support especially during rough times have greatly impacted my time at UF. Especially, I show my deepest gratitude and appreciation to my parents, John and Norma Pregler, who have been compassionate and understanding throughout my collegiate studies. 4 TABLE OF CONTENTS page ACKNOWLEDGMENTS ...............................................................................................................4 LIST OF TABLES...........................................................................................................................7 LIST OF FIGURES .........................................................................................................................8 ABSTRACT...................................................................................................................................10 CHAPTER 1 INTRODUCTION ..................................................................................................................13 General Introduction...............................................................................................................13 Carbon Nanostructures ...........................................................................................................13 Graphene and Graphite....................................................................................................14 Fullerenes ........................................................................................................................16 Carbon Nanotubes ...........................................................................................................17 Structure and chirality .............................................................................................17 Mechanical properties and sword-in-sheath deformation.......................................19 Composites ......................................................................................................................20 Polymer as the composite matrix .............................................................................21 Carbon nanostructured based composites ...............................................................23 Interfacial Engineering of Nanocomposites ....................................................................24 Irradiation Effects in Carbon Systems and Composites .........................................................27 Graphite ...........................................................................................................................28 Fullerenes and Carbon Onions ........................................................................................29 Carbon Nanotubes ...........................................................................................................30 Composites ......................................................................................................................32 Photovoltaic Applications of Fullerenes and Hydrocarbons ..................................................34 2 COMPUTATIONAL METHODS..........................................................................................40 Classical Molecular Dynamics ...............................................................................................40 Reactive Bond Order Potential ...............................................................................................41 Lennard Jones Potential..........................................................................................................46 Adaptive Intermolecular Reactive Bond Order Potential.......................................................47 Periodic Boundary Conditions................................................................................................49 Predictor Corrector Algorithm................................................................................................50 Langevin Thermostats ............................................................................................................52 Primary Knock on Atoms .......................................................................................................53 3 ARGON IRRADIATION ON GRAPHITE AND EVOLUTION OF DEFECTS .................57 System Setup ..........................................................................................................................57 5 Experiment ......................................................................................................................57 Computation ....................................................................................................................58 Irradiation Results...................................................................................................................59 Defect Analysis.......................................................................................................................61 Conclusions.............................................................................................................................65 4 IRRADIATION AND AXIAL PULLOUT EFFECTS ON MWNTS....................................72 System Background................................................................................................................72 Results.....................................................................................................................................74 Irradiation ........................................................................................................................74 Pullout..............................................................................................................................76 Conclusions.............................................................................................................................79 5 ARGON BEAM MODIFICATION OF NANOTUBE BASED COMPOSITES ..................87 System Background................................................................................................................87 Results.....................................................................................................................................88 Effects on Irradiation.......................................................................................................88 Nanotube Pullout Analysis..............................................................................................92 Conclusions.............................................................................................................................94 6 MOLECULAR DYNAMICS AND MONTE CARLO STRUCTURE EVALUATION WITH ORGANIC SEMICONDUCTORS...........................................................................101 System Background..............................................................................................................101 Ordered Structures.........................................................................................................102 Random Structures ........................................................................................................103 Equilibration Using Molecular Dynamics.....................................................................105 Results...................................................................................................................................106 Phase Separation in Pentacene:C60 Mixtures ................................................................106 Controlling Film Morphology .......................................................................................109 Conclusions...........................................................................................................................111 7 GENERAL CONCLUSIONS...............................................................................................120 LIST OF REFERENCES.............................................................................................................123 BIOGRAPHICAL SKETCH .......................................................................................................132 6 LIST OF TABLES Table page 3-1 Defect formation energies of defects observed in graphite after Ar irradiation.....................66 4-1 The hybridization of the carbon