GGeeoorrggiiaa SSttaattee UUnniivveerrssiittyy SScchhoollaarrWWoorrkkss @@ GGeeoorrggiiaa SSttaattee UUnniivveerrssiittyy Physics and Astronomy Theses Department of Physics and Astronomy 12-18-2013 SSttuuddyy ooff tthhee SSuurrffaaccee MMoorrpphhoollooggyy ooff TThheerrmmaallllyy AAnnnneeaalleedd CCooppppeerr FFooiillss aanndd VVaarriioouuss TTrraannssffeerr MMeetthhooddss ffoorr GGrraapphheennee Olesya Sarajlic Follow this and additional works at: https://scholarworks.gsu.edu/phy_astr_theses RReeccoommmmeennddeedd CCiittaattiioonn Sarajlic, Olesya, "Study of the Surface Morphology of Thermally Annealed Copper Foils and Various Transfer Methods for Graphene." Thesis, Georgia State University, 2013. doi: https://doi.org/10.57709/4866188 This Thesis is brought to you for free and open access by the Department of Physics and Astronomy at ScholarWorks @ Georgia State University. It has been accepted for inclusion in Physics and Astronomy Theses by an authorized administrator of ScholarWorks @ Georgia State University. For more information, please contact [email protected]. STUDY OF THE SURFACE MORPHOLOGY OF THERMALLY ANNEALED COPPER FOILS AND VARIOUS TRANSFER METHODS FOR GRAPHENE by OLESYA SARAJLIC Under the Direction of Ramesh Mani ABSTRACT The surface morphology of thermally annealed copper foils utilized for graphene growth by chemical vapor deposition (CVD) has been studied by Optical microscopy, Scanning Electron Microscopy (SEM), and Scanning Tunneling Microscopy (STM) as a function of heat treatment. This study reports on the surface roughness and relative grain size before and after thermal annealing. The main results are that (a) the graphene covered foil exhibits reduced surface roughness, and (b) the graphene film preserves an imprint of the Cu grain structure. In the second part of the work, the transfer of CVD graphene is ex- perimentally investigated using Poly(methyl methacrylate) (PMMA), Polycarbonate (PC), and Polysty- rene (PS). Noticeable improvement to surface cleanness as well as electrical properties of graphene is observed after the ethanol treatment. Finally, Raman characterization showed apparent blue-shifts of the G and 2D bands suggesting that the graphene is heavily doped after the ethanol treatment. INDEX WORDS: Graphene, Chemical Vapor Deposition, Average roughness, Surface height variations, Graphene transfer, Thermoplastic polymers (PMMA, PC, PS), Ethanol STUDY OF THE SURFACE MORPHOLOGY OF THERMALLY ANNEALED COPPER FOILS AND VARIOUS TRANSFER METHODS FOR GRAPHENE by OLESYA SARAJLIC A Thesis Submitted in Partial Fulfillment of the Requirements for the Degree of Master of Science in the College of Arts and Sciences Georgia State University 2013 Copyright by Olesya Sarajlic 2013 STUDY OF THE SURFACE MORPHOLOGY OF THERMALLY ANNEALED COPPER FOILS AND VARIOUS TRANSFER METHODS FOR GRAPHENE by OLESYA SARAJLIC Committee Chair: Ramesh Mani Committee: Vadim Apalkov Douglas Gies Zhigang Jiang Unil Perera Electronic Version Approved: Office of Graduate Studies College of Arts and Sciences Georgia State University December 2013 v ACKNOWLEDGEMENTS I express my deep gratitude and appreciation to my thesis supervisor, Dr. Ramesh G. Mani for his influential guidance and support throughout this research. I have been extremely fortunate to have an advisor who gave me the freedom to explore on my own. His interesting ideas and constructive counsels have motivated me toward production of this thesis. I am also indebted to the members of the Nanoscience Laboratory, Tianyu Ye, Han-Chun Liu, and Zhuo Wang, with whom I have interacted during the course of my graduate studies. I wish to thank them for their generous support in the laboratory facility during the experiments and data accumulation stages. I would also like to thank my committee members, Vadim Apalkov, Douglas Gies, Zhigang Jiang, and Unil Perera for their instructive support and valued counsels. Most importantly, I would like to express my sincere gratitude to all of my family members, es- pecially to my mother and father for their constant support and inspiration throughout this research work toward Master Degree. And most of all, I would like to thank my loving, supportive, encouraging, and patient husband, Semir, whose faithful support throughout this graduate program is greatly appre- ciated. The support and care of my immediate family helped me overcome obstacles and stay focused on my graduate study. I would like to thank Rachana Singh and John Hankinson at Georgia Institute of Technology for their assistance with Raman measurements. I gratefully acknowledge the funding agencies that made my graduate work possible. The work for this thesis has been supported by the DOE-BES, MSE Division under DE-SC0001762, and the additional support was provided by the ARO under W911NF-07-01-0158. vi TABLE OF CONTENTS ACKNOWLEDGEMENTS .......................................................................................................... v LIST OF TABLES ..................................................................................................................... vi LIST OF FIGURES .................................................................................................................... ix 1 INTRODUCTION ...............................................................................................................1 1.1 Carbon allotropes .....................................................................................................1 1.2 Methods of graphene synthesis ................................................................................2 2 THEORETICAL BACKGROUND ...........................................................................................6 2.1 Atomic structure of graphene ...................................................................................6 2.2 Electronic properties ................................................................................................7 2.3 Applications .............................................................................................................8 3 GRAPHENE SYNTHESIS, TRANSFER, AND FABRICATION .....................................................9 3.1 Exfoliated graphene .................................................................................................9 3.2 Epitaxial graphene on Silicon Carbide ..................................................................... 10 3.3 Chemical Vapor Deposition ..................................................................................... 11 3.3.1 Transfer methods ................................................................................................. 12 4 EXPERIMENTAL CHARACTERIZATIONS AND RESULTS ...................................................... 14 4.1 Copper foil annealing process ................................................................................. 14 4.2 Optical characterizations ........................................................................................ 15 4.2.1 Optical microscopy ............................................................................................... 15 4.2.2 Scanning Electron Microscopy ............................................................................... 18 4.2.3 Scanning Tunneling Microscopy ............................................................................ 21 4.3 Transfer process ...................................................................................................... 23 4.4 Raman Spectrum ..................................................................................................... 24 vii 5 EFFECTS ON COPPER SURFACE MORPHOLOGY: DISCUSSION ........................................... 26 6 POLYMER SUPPORT METHODS ....................................................................................... 28 6.1 Effect of Ethanol Treatment .................................................................................... 29 6.2 Raman Characterizations of Ethanol Treated Graphene ........................................... 31 6.3 Electrical Measurements as a Function of Polymer Support ..................................... 33 6.4 Graphene Surface Tears .......................................................................................... 35 7 SUMMARY AND FUTURE WORK ...................................................................................... 37 REFERENCES ........................................................................................................................ 39 APPENDICES ........................................................................................................................ 44 Appendix A: List of Abbreviations .................................................................................... 44 Appendix B: Methods ...................................................................................................... 45 Appendix B.1: Graphene Growth in Chapter 4 ............................................................... 45 Appendix B.2: Graphene Growth in Chapter 6 .............................................................. 45 Appendix B.3: Graphene Transfer in Chapter 4 .............................................................. 46 Appendix B.4: Graphene Transfer in Chapter 6 .............................................................. 46 Appendix B.5: Sample Fabrication Technique in Chapter 6............................................. 46 Appendix B.6: Optical Technology Classifications in Chapter 4 ....................................... 47 Appendix B.7: Optical Technology Classifications in Chapter 6 ....................................... 47 viii LIST OF TABLES Table 1.1 Latest reports of sample size and room temperature charge carrier mobility of mono-layer graphene synthesized by different methods ................................................................................. .……………2 Table 4.1 Description of the protocols applied to the unetched bare foil (BF) and the etched foil (EF) of copper .......................................................................................................................................... .……………15 Table 6.1 Molecular characteristics of thermoplastic polymers (PMMA, PC, and PS) and ethanol (ethyl alcohol). Molecular formula defines corresponding molecular structure. The geometry of PC and PS shows the existence of benzene rings that are attached to the carbon atom on the backbone of their chemical structures unlike the one of PMMA. Molecular characteristics of ethanol demonstrate the presence of hydroxyl group (-C H ) that is able to dissolve many ionic and polar compounds and ethyl 2 5 group (-OH) that attracts non-polar substances. ......................................................................... .……………28 ix LIST OF FIGURES Figure 1.1 Multi-dimensional sp2-bonded carbon: (a) 0D buckyball structure, (b) 1D single-walled carbon nanotubes, (c) 2D graphene, (d) 3D graphite .............................................................................................. 1 Figure 2.1 (a) AFM topography of graphene deposited on SiO substrate. (b) Large area STM image of 2 mechanically exfoliated graphene sheet on SiO substrate. (c) STM images of atomic-scale resolution of 2 mechanically exfoliated graphene film on SiO wafer ................................................................................. 6 2 Figure 2.2 Schematic of the band structure of graphene, where two in-equivalent points, K and Kʹ, at the vertex of the Brillouin zone display no energy gap between two sublattices .............................................. 7 Figure 2.3 Potential graphene applications in industry and research .......................................................... 8 Figure 3.1 Exfoliated graphene: (a) process of mechanical exfoliation of graphene from bulk graphite using scotch tape, (b) single layer graphene transferred on SiO wafer ..................................................... 9 2 Figure 3.2 Epitaxial graphene on Silicon Carbide: (a) schematics of epitaxial graphene on silicon carbide showing buffer layer and Si- and C-termination, (b) atomic force microscope (AFM) image of gra- phene/SiC terraces ...................................................................................................................................... 10 Figure 3.3 Graphene synthesized by CVD. (a) CVD growth process, where hydrogen atoms support the reaction between methane and catalytic substrate during which process carbon atoms are chemically adsorbed on the metal surface. (b) SEM image of CVD graphene on copper substrate with copper stria- tions and grain boundaries are clearly visible. (c) CVD graphene transferred onto SiO substrate after 2 copper has been chemically removed ....................................................................................................... .12 Figure 3.4 Schematic illustration of wet transfer process of CVD grown graphene on copper foil onto SiO 2 substrate ..................................................................................................................................................... 13 Figure 3.5 (a) Optical micrograph of CVD graphene on SiO substrate, (b) Raman spectroscopy of the 2 transferred graphene on SiO substrate in image (a) illustrating the presence of single-layer (brown 2 curve), bilayer (blue curve), and few-layer graphene (black curve) with identified D, G, and 2D peaks .. 13 Figure 4.1 (a) Schematics of the CVD system. (b) Photo of the experimental set-up of CVD growth fur- nace ............................................................................................................................................................ 14 Figure 4.2 Optical images of 25 μm Cu foil at 400 magnification. The label at the top right of the images indicates the protocol to which the specimen was subjected, see also Table 4.1. BF indicates bare foil, EF indicates etched foil. (a) This panel shows that bare foil includes striations resulting from rolling copper at high pressure. (b) Bare foil subjected to a Fe(NO ) etch produces a nonuniform surface with microm- 3 3 eter sized pores ........................................................................................................................................... 16 Figure 4.3 Optical images of 25 μm Cu foil at 400 magnification. The label at the top right of the images indicates the protocol to which the specimen was subjected, see also Table 4.1. BF indicates bare foil, EF indicates etched foil, H N indicates heat treatment in forming gas at 1025 °C for 30 min. (a) Bare Cu foil 2 2 heat treated in H N at 1025 °C for 30 min displays a 250 μm wide copper grain along with traces of stri- 2 2