Effect of Substrate and Morphology on the Relaxation Dynamics of Carriers and Phonons in Graphene By Zeynab Jarrahi Dissertation Submitted to the Faculty of the Graduate School of Vanderbilt University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY in Physics August, 2016 Nashville, Tennessee Approved: Professor Norman Tolk Professor Jim Davidson Professor Richard Mu Professor Volker Oberacker Professor Kalman Varga Copyright © 2016 by Zeynab Jarrahi All Rights Reserved ii ACKNOWLEDGMENTS This Dissertation would not have been possible without the financial support from the Department of Energy (DOE), the Army Research Office (ARO), the National Science Foundation (NSF), as well as the resources and technical support provided by Vanderbilt Institute of Nanoscale Science and Engineering (VINSE). I am forever grateful to my parents for their never ending love and support and especially to my mom who raised me to believe I could do anything I set my mind to. I am thankful to Ted Cinker for his all-encompassing support and patience and for proof reading this dissertation despite it being long and boring. I am indebted to my advisor Dr. Norman Tolk for his guidance, trust and mentoring style which gave me the confidence to be an independent thinker and provided me with the freedom to shape my own path. I must acknowledge Dr. Jim Davidson for his help on all things diamond. I must also thank many others who were a part of this journey, VINSE staff: Anthony Hmelo, Bo Choi, Ben Schmidt and Vanderbilt administrative team: Don Pickert, Peggy McGowan, Jane Fall, Barbara Amann, Sheila Warf and Libby Johnson. iii TABLE OF CONTENTS ACKNOWLEDGMENTS .............................................................................................. III TABLE OF CONTENTS ............................................................................................... IV LIST OF FIGURES ...................................................................................................... VII FOREWORD..................................................................................................................... 1 1. GRAPHENE .............................................................................................................. 3 1.1. INTRODUCTION .......................................................................................................... 3 1.2. BAND STRUCTURE OF GRAPHENE ............................................................................... 4 1.3. OPTICAL PROPERTIES OF GRAPHENE ........................................................................... 9 1.3.1. Interband transitions and universal absorption of graphene ................... 10 1.3.2. Optical transmission in 2D graphene ...................................................... 12 1.3.3. Intraband transitions in graphene ............................................................ 14 1.3.4. Effect of doping on the transmission of graphene .................................. 15 1.3.5. Optical conductivity of graphene in the UV range ................................. 16 2. METHODS .............................................................................................................. 17 2.1. INTRODUCTION ........................................................................................................ 17 2.2. GRAPHENE SYNTHESIS ............................................................................................. 18 2.2.1. Mechanically exfoliated graphene .......................................................... 18 2.2.2. Epitaxial Graphene.................................................................................. 19 2.2.3. Chemical Vapor Deposition (CVD) Graphene ....................................... 19 2.3. CVD GRAPHENE GROWTH ........................................................................................ 20 2.3.1. CVD growth kinetics .............................................................................. 20 2.3.2. Copper foil contamination ...................................................................... 22 2.3.3. CVD growth recipe ................................................................................. 22 2.4. CVD GRAPHENE TRANSFER ..................................................................................... 23 2.4.1. Etching copper ........................................................................................ 24 2.4.2. PMMA removal ...................................................................................... 26 2.5. THE SUBSTRATE....................................................................................................... 28 2.5.1. Surface roughness ................................................................................... 29 2.5.2. Substrate cleaning ................................................................................... 32 2.5.3. Passivation of the diamond samples ....................................................... 34 2.6. CHARACTERIZATION ................................................................................................ 34 2.6.1. Visibility under optical microscopy ............................................................ 34 iv 2.6.2. Raman spectroscopy ................................................................................... 36 2.6.2.1. Phonons in graphene .................................................................... 38 2.6.2.2. Raman peaks of graphene ............................................................ 42 2.6.2.3. Nomenclature ............................................................................... 47 2.6.2.4. Raman spectroscopy and graphene layer number ........................ 49 2.6.2.5. Raman spectroscopy and layer stacking ...................................... 50 2.6.2.6. Raman spectroscopy and defects ................................................. 52 2.6.2.7. Raman spectroscopy and doping in graphene .............................. 53 2.7. CONCLUSION ............................................................................................................ 57 3. RELAXATION DYNAMICS OF GRAPHENE ON DIFFERENT SUBSTRATES ........................................................................................................................................... 58 3.1. INTRODUCTION ........................................................................................................ 58 3.2. ULTRAFAST PUMP PROBE SPECTROSCOPY OF GRAPHENE .......................................... 60 3.3. ULTRAFAST TRANSIENT TRANSMISSION RESPONSE OF GRAPHENE ON QUARTZ ......... 66 3.3.1. Experimental details................................................................................ 66 3.3.2. Fluence dependent dynamics of graphene on quartz .............................. 70 3.3.3. Excitation energy dependent dynamics of graphene on quartz .............. 73 3.4. SIMULATION AND FITTING PARAMETERS .................................................................. 75 3.5. EFFECT OF SUBSTRATE ON THE ULTRAFAST DYNAMICS OF GRAPHENE ..................... 79 3.6. SURFACE OPTICAL PHONON OF POLAR MATERIALS ................................................... 87 3.6.1. Fröhlich coupling and the role of the separation distance ...................... 89 3.6.2. Effect of doping and polarity of the substrate ......................................... 90 3.6.3. Intrinsic optical phonon vs. surface optical phonon scattering rate ........ 94 3.6.4. Effect of SP on IOP lifetimes of graphene.............................................. 99 3.7. TRANSIENT TRANSMISSION IN THE PRESENCE OF SURFACE OPTICAL PHONONS ....... 103 3.7.1. Effect of substrate on the band filling dynamics of graphene .............. 105 3.7.2. Effect of substrate on the induced carrier absorption of graphene ....... 106 3.7.3. Effect of substrate on the carrier relaxation times of graphene ............ 109 3.8. CONCLUSION .......................................................................................................... 112 4. PHOTO RESPONSE OF CURLED GRAPHENE RIBBONS ......................... 114 4.1. INTRODUCTION ...................................................................................................... 114 4.2. MORPHOLOGY OF GRAPHENE ................................................................................. 115 4.3. CURLED GRAPHENE RIBBON SYNTHESIS ................................................................. 119 4.4. MD SIMULATIONS .................................................................................................. 123 4.5. RAMAN SPECTROSCOPY ON CGR STRUCTURE ....................................................... 125 4.6. PHOTOCURRENT RESPONSE IN CGR ....................................................................... 126 v 4.6.1. Photocurrent setup ................................................................................ 129 4.6.2. Results and discussion .......................................................................... 131 4.6.3. Photocurrent generation mechanism in CGR ....................................... 131 4.7. CONCLUSION .......................................................................................................... 137 5.1.1. Materials of interest .............................................................................. 139 5.1.2. Ultrafast Pump Probe Spectroscopy (UPPS) ........................................ 139 5.1.3. Time Resolved Photo Luminescence spectroscopy (TRPL) ................ 140 5.1.4. Coherent Acoustic