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Graphene, Polycyclic Aromatic Hydrocarbons and Topological Insulators Graphene, Polycyclic Aromatic Hydrocarbons and Topological Insulators A scanning tunneling microscopy study Louis Nilsson Interdisciplinary Nanoscience Center (iNANO) and Department of Physics and Astronomy Aarhus University, Denmark PhD thesis July 2013 This thesis has been submitted to the Faculty of Science and Technology at Aarhus University in order to fulfil the requirements for obtaining a PhD degree. The work has been performed under supervision of Asso- ciate Professor Liv Hornekær and Professor Flemming Besenbacher in the Surface Dynamics Group at the Interdisciplinary Nanoscience Cen- ter (iNANO) and the Department of Physics and Astronomy, Aarhus University. I have not been involved in performing the density functional theory calculations presented in this thesis. The credit for most of these calcu- lations should be given to Mie Andersen in Professor Bjørk Hammer’s group. The sections about these calculations should therefore not be part of the evaluation of my work; however, they are presented here to- gether with the corresponding experimental results for the convenience of the reader. Contents List of publications i List of abbreviations iii 1 Introduction 1 1.1 Motivation . 2 1.2 Outline . 5 2 Techniques and experimental setups 7 2.1 Scanning tunneling microscopy . 8 2.1.1 Tersoff’s and Hamann’s theory for STM . 8 2.1.2 STM setups . 9 2.1.3 Scanning tunneling spectroscopy . 13 2.2 Temperature programmed desorption . 14 2.3 Angle-resolved photoemission spectroscopy . 16 2.4 Low-energy electron diffraction . 17 2.5 Density functional theory . 18 2.6 Experimental setups . 21 2.6.1 The green chamber . 21 2.6.2 The coal chamber . 21 2.6.3 The blue chamber . 22 3 Graphene 25 3.1 Introduction . 26 3.2 Production of graphene . 28 3.3 Graphene on metal surfaces . 29 3.3.1 Graphene on Ir(111) . 31 3.3.2 Graphene on Pt(100) . 32 3.4 Band gap opening in graphene . 41 3.4.1 Hydrogenation of graphene on Ir(111) . 45 3.4.2 Hydrogenation of graphene on Pt(100) . 51 3.4.3 Templating hydrogen on graphene . 53 3.5 Graphene Coatings . 59 3.5.1 Graphene coatings on Pt(100) . 59 4 Polycyclic aromatic hydrocarbons 83 4.1 Introduction . 84 4.2 Coronene . 85 4.2.1 Coronene on Cu(100) . 86 4.2.2 Hydrogenation of coronene on Cu(100) . 90 5 Topological insulators 93 5.1 Introduction . 94 5.2 Bismuth selenide (Bi2Se3)................... 97 5.2.1 Pristine Bi2Se3(111) . 98 5.2.2 Stability of the Bi2Se3(111) topological state . 103 6 Summary and Outlook 107 6.1 Graphene . 108 6.2 Polycyclic aromatic hydrocarbons . 110 6.3 Topological Insulators . 111 7 Dansk Resumé 113 7.1 Scanning tunnel mikroskopi . 114 7.2 Graphen . 116 7.3 Polyaromatiske kulbrinter . 119 7.4 Topologiske isolatorer . 121 Acknowledgements 123 List of publications • R. Balog, B. Jorgensen, L. Nilsson, M. Andersen, E. Rienks, M. Bianchi, M. Fanetti, E. Laegsgaard, A. Baraldi, S. Lizzit, Z. Sljivan- canin, F. Besenbacher, B. Hammer, T. G. Pedersen, P. Hofmann and L. Hornekaer. Bandgap opening in graphene induced by patterned hydrogen adsorption. Nature Materials, 9 (4): 315-319, 2010. • R. Hatch, M. Bianchi, D. Guan, S. Bao, J. Mi, B. Iversen, L. Nilsson, L. Hornekær and P. Hofmann. Stability of the Bi2Se3(111) topological state: Electron-phonon and electron-defect scattering. Physical Review B, 83 (24), 2011. • L. Nilsson, M. Andersen, J. Bjerre, R. Balog, B. Hammer, L. Hornekær and I. Stensgaard. Preservation of the Pt(100) surface reconstruction after growth of a continuous layer of graphene. Sur- face Science, 606 (3-4): 464-469, 2012. • L. Nilsson, M. Andersen, R. Balog, E. Lægsgaard, P. Hofmann, F. Besenbacher, B. Hammer, I. Stensgaard and L. Hornekær. Graphene Coatings: Probing the Limits of the One Atom Thick Protection Layer. ACS Nano, 6 (11): 10258-10266, 2012. • L. Nilsson, Z. Sljivancanin, R. Balog, W. Xu, T.R. Linderoth, E. Lægsgaard, I. Stensgaard, B. Hammer, F. Besenbacher and L. Hornekær. Linear hydrogen adsorbate structures on graphite and graphene induced by self-assembled molecular monolayers. Carbon, 50: 2052-2056, 2012. • L. Nilsson, M. Andersen, F. Besenbacher, B. Hammer, I. Stens- gaard and L. Hornekær. Graphene Coatings - An atomic investiga- tion of the coating breakdown by sequential exposure to O2 and H2S. Submitted. i • J. Thrower, E. Friis, A. Skov, L. Nilsson, M. Andersen, L. Ferrighi, B. Jørgensen, S. Baouche, R. Balog, B. Hammer and L. Hornekær. The Interaction between Coronene and Graphite from Temperature Programmed Desorption and DFT-vdW Calculations: Importance of Entropic Effects and Insights into Graphite Interlayer Binding. Accepted for publication in The Journal of Physical Chemistry. • C. Wang, X. Zhu, L. Nilsson, J. Wen, G. Wang, X. Shan, Q- Zhang, S. Zhang, J. Jia, Q. Xue. In-situ Raman spectroscopy of topologi- cal insulator Bi2Te3 films with thickness dependence. Accepted for publication in Nano Research. • S. Ulstrup, L. Nilsson, J. Miwa, R. Balog, M. Bianchi, P. Hof- mann and L. Hornekær. Electronic structure of graphene on a re- constructed Pt(100) surface: Hydrogen adsorption, doping and band gaps. Submitted. Proceedings • J.D. Thrower, L. Nilsson, B. Jørgensen, S. Baouche, R. Balog, A.C. Luntz, I. Stensgaard, E. Rauls, and L. Hornekær. Superhydro- genated PAHs: catalytic formation of H2: EAS publications series: PAHs and the Universe, 46: 453-460, 2011. Public outreach • L. Nilsson, B. Jørgensen, R. Balog and L. Hornekær. A new age of carbon electronics. iNano annual report: 24-25, 2010. • L. Nilsson, B. Jørgensen and L. Hornekær. En ny generation af elektriske kredsløb. (Title in English: A new generation of electronic circuits). Aktuel Naturvidenskab 4:18-20, 2010 ii List of abbreviations ARPES Angle-resolved photoemission spectroscopy ASTRID Aarhus storage ring in Denmark CVD Chemical vapour deposition CyA Cyanuric acid DFT Density functional theory DOS Density of states GPAW Grid-based projector-augmented wave HOPG Highly oriented pyrolytic graphite ISM Interstellar medium LDA Local-density approximation LDOS Local density of states LEED Low-energy electron diffraction PAH Polycyclic aromatic hydrocarbon PBE Perdew-Burke-Ernzerhof QMS Quadrupole mass spectrometer RT Room temperature STM Scanning tunneling microscopy/microscope STS Scanning tunneling spectroscopy SW Stone-Wales TPD Temperature programmed desorption TPG Temperature programmed growth UHV Ultra high vacuum UV Ultraviolet VASP Vienna ab-initio simulation package iii Chapter 1 Introduction This chapter gives a short motivation and an outline for the work presented in this thesis. Because of the variety of different subjects treated; graphene, polycyclic aromatic hydrocarbons and topological insulators, a more thorough introduction with a literature review for each subject will be presented in the respective chapters. The motivation in this chapter will instead provide a broader view of the subjects and the link between them in a more general way. 1 2 Chapter 1. Introduction 1.1 Motivation The importance of carbon is accentuated by the fact that it is the fourth most abundant element in the universe and the second most abundant element, by weight, in the human body. Indeed, all known life is strongly dependent on carbon, not only as a vital element in all living organisms but also in our way of living: The majority of our energy consumption comes from carbon-based compounds; Carbon is expected to play a vital role as a catalyst in the formation of the most abundant molecule in the universe, H2; Plastic, wool, silk etc. are all polymeric forms of carbon; Diamond is used for jewellery but also for drilling and cutting tools owing to its extreme hardness, however, graphite is used as a lubricant due to its softness; Activated carbon is used for water purification, in medicine to extract toxins etc.; Carbon is used for alloying e.g. carbon steel as well as in batteries and even for printing this thesis. However, at present most of our electronic world is based on the next element in the 14th group of the periodic table, silicon. An enormous development in carbon-based electronics has occurred since the experimental realization of graphene, a single layer of sp2 hy- bridized carbon atoms in a honey-comb structure, in 2004 [1]. A search for the topic “graphene” on Web of Knowledge returns ca. 50.000 hits, which emphasizes the extreme interest graphene has attracted in the sci- entific community. Unlike many other scientific breakthroughs that of- ten that often spend decades maturing in the scientific community before industrial companies engage in the research, graphene already attracted companies from a variety of industries. IBM had for instance already fab- ricated a graphene-based 100 GHz transistor in 2010 [2]. Samsung likewise contributed to the production of a 30" graphene sheet in 2010 [3] and these and other companies have played a central role in the development of gra- phene based transistors and fabrication of large sheets of graphene since. The industrial interest in graphene so shortly after its discovery indicates that carbon might have the potential to complement silicon in electronic device fabrication in the future. The reasons for the great expectations for graphene are many. To mention a few: it is the material known today with highest electronic con- ductivity at room temperature; despite the fact that graphene is only one atomic layer thick and almost transparent, it is extremely strong and at the same time flexible; it is chemically very inert and impermeable to most gases. Graphene, however, as a semimetal, has a poor on/off ratio when used in transistors. Silicon, on the other hand, is a semiconductor and the 1.1. MOTIVATION 3 majority of the electronics industry today is based on semiconductors. As a consequence, preliminary approaches to induce a band gap in graphene and thereby make it a semiconductor have already been published, how- ever, further investigation is presently being carried out worldwide, which will be addressed in further detail later in this thesis together with our contribution to the field.
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