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In Situ TEM Observation of Metal-Graphene Interaction Emi In situ TEM Observation of Metal-Graphene Interaction Emi Kano February 2017 In situ TEM Observation of Metal-Graphene Interaction Emi Kano Doctoral Program in Materials Science and Engineering Submitted to the Graduate School of Pure and Applied Sciences in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Engineering at the University of Tsukuba Table of Contents Table of Contents ........................................................................................... i Abstract ......................................................................................................... iv Introduction ................................................................................. 1 1-1 Characterization of graphene by electron microscopy .......................................... 1 1-1-1 Background ................................................................................................ 1 1-1-2 Electron irradiation effects ........................................................................ 8 1-1-3 Objective of the research ......................................................................... 11 1-2 Previous studies on graphene .............................................................................. 12 1-2-1 Defects in graphene and their engineering .............................................. 12 1-2-2 Interactions between metals and graphene .............................................. 17 1-2-3 Originality of the thesis ........................................................................... 19 1-3 Thesis outline ...................................................................................................... 21 Basic principles and experimental methods ........................... 22 2-1 Electron microscopy ........................................................................................... 22 2-1-1 Aberration corrector and our equipment component ............................... 22 2-1-2 Imaging mode (TEM, DF-TEM, STEM) ................................................ 25 2-1-3 Electron energy-loss spectroscopy (EELS) ............................................. 33 2-2 Principles of electron irradiation effects ............................................................. 35 2-2-1 Elastic and inelastic scattering ................................................................. 35 2-2-2 Energy transfer and binding energy of metal-carbon bond ..................... 36 2-2-3 Scattering cross section ........................................................................... 38 2-3 Sample preparation ............................................................................................. 41 2-3-1 Chemical vapor deposition (CVD) .......................................................... 41 2-3-2 Transfer process ....................................................................................... 43 2-3-3 In situ heating effects ............................................................................... 49 i Cu atoms reknit graphene structure ....................................... 53 3-1 Introduction......................................................................................................... 53 3-2 Methods .............................................................................................................. 54 3-2-1 Sample preparations ................................................................................ 54 3-2-2 TEM imaging experiments ...................................................................... 56 3-2-3 First-principles calculations .................................................................... 57 3-3 Results and discussion ........................................................................................ 58 3-3-1 Cu sites in single-layer graphene............................................................. 58 3-3-2 Reconstruction of graphene ..................................................................... 60 3-3-3 Transformations promoted by Cu atoms ................................................. 64 3-3-4 Driving force of the transformations ....................................................... 69 3-3-5 Uniqueness of Cu compared with other transition metals ....................... 71 3-4 Summary ............................................................................................................. 73 Metal-mediated mending and etching of graphene edges .... 74 4-1 Introduction......................................................................................................... 74 4-2 Methods .............................................................................................................. 75 4-3 Results................................................................................................................. 76 4-4 Discussions ......................................................................................................... 79 4-4-1 Binding energy of metal-carbon bond ..................................................... 79 4-4-2 Effects of heating and irradiation ............................................................ 79 4-5 Summary ............................................................................................................. 80 Metal-terminated carbynes on graphene ............................... 81 5-1 Introduction......................................................................................................... 81 5-2 Methods .............................................................................................................. 82 5-3 Results and discussion ........................................................................................ 83 5-3-1 Formation and dynamics of carbyne ....................................................... 83 ii 5-3-2 Bending strength of carbyne .................................................................... 86 5-3-3 Role of Pt and Cu atoms .......................................................................... 87 5-4 Summary ............................................................................................................. 87 2D copper oxide on graphene .................................................. 88 6-1 Introduction ......................................................................................................... 88 6-2 Methods ............................................................................................................... 89 6-2-1 STEM-EELS experiments ................................................................... 89 6-2-2 First-principles calculations ..................................................................... 90 6-3 Results and discussion ........................................................................................ 91 6-3-1 STEM-EELS observations ...................................................................... 91 6-3-2 DFT calculations and image simulations ........................................... 95 6-3-3 Properties of 2D copper oxide ................................................................. 97 6-4 Summary ............................................................................................................. 98 Conclusions .................................................................................................. 99 Appendix .................................................................................................... 102 List of Figures and Tables ........................................................................ 111 List of Abbreviations................................................................................. 114 List of Publications ................................................................................... 115 References .................................................................................................. 118 Acknowledgements ................................................................................... 136 iii Abstract Graphene is a two-dimensional (2D) crystalline form of carbon with a honeycomb lattice structure. It is the fundamental structure of layered bulk graphite and some nanocarbon materials, such as carbon nanotubes. The successful isolation of graphene has greatly influenced the nanocarbon research and has opened a new field of layered 2D materials. Recently, interactions of graphene with metal atoms and clusters have been studied aiming to control the local properties of graphene for applications in electrocatalysts and nanoelectronic devices. Alternatively, placing metal clusters on graphene could lead to the formation of novel low-dimensional nanostructures. Using transmission electron microscopy (TEM), we can directly monitor metal-graphene interactions without the effects of bulk substrate. Atomic-resolution imaging of individual atoms in graphene lattice has become available, due to the recent development in graphene synthesis and spatial resolution improvement brought by correcting aberrations of electron microscope lens. This thesis investigates structure and interaction dynamics of metal atoms with graphene by atomic-resolution TEM. Previous studies reported that most metal atoms, which strongly interacted with graphene, promoted etching of graphene under electron irradiation. This phenomenon is generally detrimental for the fabrication of graphene-based nanoelectronic devices; on the other hand, it offers a promising method of graphene pattering and of producing graphene nanoribbons. Defects
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