Fabrication and Characterization of Macroscopic Graphene Layers on Metallic Substrates Víctor Manuel Freire Soler Aquesta tesi doctoral està subjecta a la llicència Reconeixement 3.0. Espanya de Creative Commons. Esta tesis doctoral está sujeta a la licencia Reconocimiento 3.0. España de Creative Commons. This doctoral thesis is licensed under the Creative Commons Attribution 3.0. Spain License. Departament de Física Aplicada i Òptica Universitat de Barcelona Fabrication and Characterization of Macroscopic Graphene Layers on Metallic Substrates Víctor Manuel Freire Soler Directores: Dr. Carles Corbella Roca (RUB) Prof. Enric Bertran Serra (UB) Programa de doctorado: Nanociencias, bienio 2010/2012 Memoria presentada para optar al grado de Doctor Barcelona, Julio de 2014 “Research is what I’m doing when I don’t know what I’m doing” Wernher von Braun Contents CONTENTS Agradecimientos v Resumen en castellano vii Preface xxi List of figures and tables xxv I. INTRODUCTION 1 1. Carbon materials retrospective 3 1.1. Graphite ................................................................................. 6 1.2. Diamond ................................................................................. 6 1.3. Diamond-like carbon (DLC) and amorphous carbon ............... 7 1.4. Fullerenes and nanotubes ...................................................... 8 1.5. References ............................................................................ 10 2. Graphene and 2D crystals 11 2.1. General ................................................................................. 12 2.1.1. Discovery ................................................................ 14 2.1.2. Properties ............................................................... 17 2.1.3. Potential applications ............................................. 22 2.1.4. Market expectations and regulations ..................... 25 2.2. Synthesis methods of graphene ........................................... 31 2.2.1. Mechanical exfoliation ............................................ 32 2.2.2. Chemical exfoliation ............................................... 32 2.2.3. Epitaxial growth ...................................................... 34 2.2.4. Chemical Vapor Deposition (CVD) ........................... 35 2.3. MoS2, h-BN, and Silicene ...................................................... 36 2.4. References ............................................................................ 40 i Fabrication and characterization of macroscopic graphene layers on metallic substrates II. EXPERIMENTAL SET 45 3. Synthesis methods and fabrication techniques 47 3.1. Mechanical exfoliation ......................................................... 48 3.2. Chemical Vapor Deposition (CVD) ........................................ 50 3.2.1. Basics ...................................................................... 50 3.2.2. CVD on copper ........................................................ 52 3.2.3. Monolayer formation time concept ........................ 55 3.3. Deposition reactor: GRAPHman ........................................... 58 3.3.1. New Pulsed-CVD system ......................................... 62 3.3.2. Magnetron Sputtering ............................................ 65 3.3.3. Residual Gas Analyzer (RGA) ................................... 69 3.3.4. Preliminary studies ................................................. 72 3.4. Transfer to polymers ............................................................ 74 3.5. References ............................................................................ 77 4. Characterization techniques 81 4.1. Structural and chemical ........................................................ 82 4.1.1. Raman spectroscopy ............................................... 82 4.1.2. Energy Dispersive X-ray Spectroscopy (EDS) ........... 89 4.2. Morphological ...................................................................... 94 4.2.1. Optical Microscopy ................................................. 94 4.2.2. Scanning Electron Microscopy (SEM) ...................... 96 4.2.3. Atomic Force Microscopy (AFM) ........................... 100 4.3. Electrical properties ............................................................ 103 4.3.1. Van der Pauw method .......................................... 103 4.4. References .......................................................................... 108 III. RESULTS 113 5. Mechanical exfoliation 115 5.1. Technique ........................................................................... 116 5.2. Samples .............................................................................. 117 5.2.1. Optical microscopy ............................................... 117 5.2.2. Raman spectroscopy ............................................. 119 ii Contents 5.2.3. AFM ...................................................................... 124 5.3. Summary and conclusions .................................................. 127 5.4. References .......................................................................... 128 6. CVD preliminary studies 129 6.1. Substrates and treatment ................................................... 130 6.2. Growth process .................................................................. 131 6.3. Samples .............................................................................. 133 6.3.1. SEM and EDS ......................................................... 133 6.3.2. Raman spectroscopy ............................................. 138 6.4. Summary and conclusions .................................................. 140 6.5. References .......................................................................... 142 7. Low Pressure Pulsed-CVD 145 7.1. Preparation of substrates ................................................... 146 7.2. Growth process .................................................................. 152 7.2.1. CVD pulses ............................................................ 155 7.2.2. Scaling parameters ............................................... 157 7.3. Samples .............................................................................. 158 7.3.1. Optical microscopy ............................................... 160 7.3.2. AFM ...................................................................... 161 7.3.3. EDS ....................................................................... 163 7.3.4. SEM ...................................................................... 165 7.3.5. Raman spectroscopy ............................................. 169 7.4. Transfer to silicon ............................................................... 175 7.5. Summary and conclusions .................................................. 178 7.6. References .......................................................................... 181 8. Study of the effect of Swift Heavy Ion (SHI) irradiation on 2D crystals 185 8.1. Introduction ....................................................................... 186 8.2. Experimental ...................................................................... 187 8.3. Results ................................................................................ 187 8.4. Summary and conclusions .................................................. 192 8.5. References .......................................................................... 194 iii Fabrication and characterization of macroscopic graphene layers on metallic substrates 9. Fabrication and characterization of a graphene transistor 197 9.1. Graphene-based FET .......................................................... 198 9.2. Summary and conclusions .................................................. 202 9.3. References .......................................................................... 203 IV. CONCLUSIONS 205 Publications and communications 213 Appendixes 221 A. CVD Review on chemical vapor deposition ........................... 221 B. Patent ................................................................................... 237 C. Sample list ............................................................................ 239 iv Agradecimientos Agradecimientos Voldria començar aquesta primera secció agraïnt en primer lloc al Prof. Enric Bertran (el meu tutor) la seva confiança amb mi i per haver-me fet un lloc al seu grup, FEMAN. La seva aportació científica i personal ha estat crucial en les diferents fases d’aquest treball. Els seus ànims i idees en moments on tot semblava perdut, sens dubte han marcat la diferència. Moltes gràcies! Inestimable també ha estat l’ajuda del Dr. Carles Corbella (director d’aquesta tesi doctoral) elevant el nivell d’aquest document. Apart de la quantitat ingent de coneixements que m’ha aportat, el seu sentit de l’humor i la seva motivació científica m’han fet donar un pas endavant des que vaig començar amb ell la fase de Master fins ara. Vull agraïr també la gran tasca realitzada pels Serveis Científico-Tècnics de la UB (CCTiUB), sense els quals no podria de cap manera haver desenvolupat la major part de la meva feina. En especial als tècnics de microscopia electrònica (SEM i EDS), i sobretot al Tariq i les meves mesures setmanals (sino diàries) d’espectroscòpia Raman. També al Taller Mecànic que ens ha proporcionat a mida totes les peces necessàries per poder dur a terme la construcció d’un reactor CVD i d’altres “invents”. No em puc anar tampoc sense comentar la gran professionalitat de les secretàries i el secretari del departament, sobretot