Dirac Fermions in Graphene and Graphiteâa view from angle ...

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transition 95 . Whether this universality is a general property of Dirac Fermions is certainly an interesting topic that needs to be further investigated. 5.5 Conclusions In summary, we have performed ARPES measurements of the electronic structure of epitaxial graphene with adsorbed NO 2 . Our data directly prove that NO 2 induces hole doping of graphene and provides a possibility of tuning the charge carriers from electrons to holes in a wide doping range. We show how the peculiar electronic structure of epitaxial bilayer and single layer graphene containing an excitation gap results in a metal to insulator transition upon hole doping. Our results suggest a way of achieving semiconducting graphene which is an important step in making it a practical component of electronics devices. This study also opens up an interesting route to studying the physics of the hole doping regime of the Dirac cone. 41
Chapter 6 Dirac fermions and effect of impurities in single crystalline graphite 6.1 Introduction In the previuos chapters we have seen that, as the number of graphene layers increases, the interlayer interaction is turned on and the electronic structure evolves from a pure two dimensional structure, characterized by massless quasiparticles, to a more three dimensional electronic structure. This results in a k z dependent band structure with coexistence of massless Dirac fermions at k z =0.5 c ∗ where c ∗ is the reciprocal lattice constant and massive quasiparticles at k z =0 64 . As in graphene, a variety of novel properties have been recently reported in graphite such as novel quantum Hall effect 86 , room temperature ferromagnetism 96 , metal-insulator-like transition 86 , and superconductivity 74 . The recent discovery of superconductivity with high critical temperature T c of 11.5K in C 6 Ca 97,98 has also attracted a lot of research interest in understanding the superconducting mechanism and searching for superconducting graphite intercalation compounds (GICs) with even higher T c . Although several transport experiments have shown results in agreement with the existence of Dirac fermions in graphite 99 , so far direct experimental evidence has been limited. This chapter presents a study of the electronic structure of single crystal graphite. The samples that we use here are natural graphite which is extracted from graphite mines and kish graphite which is the byproduct of steel making process. 6.2 Electronic structure of single crystal graphite Since graphite has three dimensional BZ, the dispersion also depends on k z and it is important to determine the k z values. Throughout this chapter the k z values are estimated using the standard freeelectron approximation of the ARPES final state 20,19,100 (see Chapter 2). The inner potential needed for extracting the k z value was determined from the periodicity of the detailed dispersion at the Brillouin zone center ΓA using a wide range of photon energies from 34 to 155 eV 101 . The consistency of the k z values is confirmed by the degeneracy of the π bands near H and a maximum splitting near K (Fig. 6.1), both in 42
Page 1 and 2: Dirac Fermions in Graphene and Grap
Page 3 and 4: Dirac Fermions in Graphene and Grap
Page 5 and 6: Contents Abstract 1 Contents Acknow
Page 7 and 8: 7.6 Conclusions and implication of
Page 9 and 10: Curriculum Vitæ Shuyun Zhou Educat
Page 11 and 12: • Selected as Science Highlight f
Page 13 and 14: The unit cell of graphene contains
Page 15 and 16: Projecting this equation into φ(r
Page 17 and 18: Figure 1.5. Schematic drawing of th
Page 19 and 20: Chapter 2 Experimental techniques 2
Page 21 and 22: dispersion E(k z ). Thus k z values
Page 23 and 24: where ɛ is infinitely small. Accor
Page 25 and 26: Langmuirs (1L=10 −6 torr·s) to c
Page 27 and 28: mean free path, E kin is the kineti
Page 29 and 30: a b c d e f graphite SiC f graphite
Page 31 and 32: Figure 3.3. XPS results showing dat
Page 33 and 34: Figure 3.5. Intensity map at -1 eV
Page 35 and 36: Chapter 4 Gap opening in epitaxial
Page 37 and 38: Figure 4.2. Observation of the gap
Page 39 and 40: the EDCs as well as the region of e
Page 41 and 42: Figure 4.7. Dispersions measured in
Page 43 and 44: Figure 4.9. (a-c) LEEM images taken
Page 45 and 46: Figure 4.10. Proposed mechanism for
Page 47 and 48: Chapter 5 Metal-insulator transitio
Page 49 and 50: Figure 5.2. (a) Dispersions through
Page 51: Figure 5.3. (a-f) Data taken throug
Page 55 and 56: Figure 6.2. Linear Λ-shaped disper
Page 57 and 58: Figure 6.4. Detailed low energy dis
Page 59 and 60: Figure 6.6. Detailed dispersion nea
Page 61 and 62: Chapter 7 ARPES study of partially
Page 63 and 64: Figure 7.2. (a) Fermi energy intens
Page 65 and 66: direction, i.e. perpendicular to gr
Page 67 and 68: Figure 7.5. ARPES intensity map mea
Page 69 and 70: Figure 7.7. (a) ARPES intensity map
Page 71 and 72: Figure 7.9. (a) ARPES intensity map
Page 73 and 74: 19. Hüfner, S. Photoelectron Spect
Page 75 and 76: 59. Jiang, Y. J., Yao, D.-Y., Carls
Page 77 and 78: 99. Luk’yanchuk, I. A. & Kopelevi
Page 79 and 80: List of Figures 1.1 (a) Sp 2 bondin
Page 81 and 82: 4.8 Thickness dependence of E D and
Page 83 and 84: 7.2 (a) Fermi energy intensity map.

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