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

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Chapter 3 Growth and characterization of epitaxial graphene This chapter describes the growth and characterization of epitaxial graphene using various experimental techniques. The samples are grown by thermal decomposition of SiC. The surface topography is studied with scanning electron microscopy (SEM) and low energy electron microscopy (LEEM). The sample thickness is determined by XPS, ARPES and LEEM. 3.1 Growth of epitaxial graphene Graphene films were produced on the Si-terminated (0001) face of an n-type 6H-SiC single crystalline wafer purchased from Cree, Inc. The wafer was cut to pieces of a few mm in size by using a diamond saw, and cleaned with acetone and isopropyl alcohol in an ultrasonic bath. The clean wafers were then mounted with Ta-foil clips to a Mo sample holder and entered into an ultrahigh-vacuum preparation chamber (base pressure 1×10 −10 Torr). Before growing graphene layers, the wafer was cleaned in situ by annealing up to 850 ◦ C under silicon flux for 20 to 30 minutes. The silicon flux was produced by a silicon ingot heated by electron bombardment to approximately 1200 ◦ C and was calibrated with a quartz crystal monitor (deposition rate about 3 Å/min). This procedure removes native surface oxides by the formation of volatile SiO, which sublime at this temperature 36 . The growth process was monitored by LEED patterns, which were obtained at room temperature. The data reported below are mainly from three samples, henceforth referred to as samples A, B, and C. These samples are labeled in order of increasing thickness, a parameter controlled primarily by variation in the annealing temperature 37 . Fig. 3.1 shows selected LEED patterns obtained at different stages during the growth of sample A. After the initial cleaning procedure under Si flux, the LEED pattern (not shown) displayed a 3×3 reconstruction with respect to the SiC substrate, as has been well documented in the literature 36,38,39 . A subsequent 5 minute annealing at ≈ 1000 ◦ C in the absence of Si flux gives rise to the sharp pattern shown in panel (a), corresponding to the 1×1 spots of SiC. Further annealing for 5 min at ≈ 1100 ◦ C produces the ( √ 3× √ 3)R30 reconstruction shown in panel (b), attributed to a structural model comprised of 1/3 layer of Si adatoms in threefold symmetric sites on top of the outermost SiC bilayer 40,41 . Finally, annealing for 10 min at ≈ 1250 ◦ C 17
a b c d e f graphite SiC f graphite Figure 3.1. (a-d) LEED patterns with a primary energy of 180eV, obtained at four different stages during the growth of sample A. (a) 1×1 spots of SiC, after a 5 min anneal around 1000 ◦ C followed by the initial cleaning procedure under Si flux. (b) ( √ 3 × √ 3)R30 reconstruction, after 5 min around 1100 ◦ C. (c) (6 √ 3 × 6 √ 3)R30 reconstruction, after 10 min around 1200 ◦ C. (d) Sharper(6 √ 3 × 6 √ 3)R30 pattern, after 4 min around 1250 ◦ C. (e) and (f) LEED patterns with a primary energy of 130eV taken at the same stages as (c) and (d), respectively. In (f), the appearance of the 1×1 spots of graphite, located slightly farther out from the center relative to the spots observed at similar positions in (b, c, and e), indicates that a thin graphene overlayer has been formed in this last step. 18
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: mean free path, E kin is the kineti
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 and 52: Figure 5.3. (a-f) Data taken throug
Page 53 and 54: Chapter 6 Dirac fermions and effect
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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