Dirac Fermions in Graphene and Graphite—a view from angle ...

Figure 3.5. Intensity map at -1 eV as a function of k ‖ and k z .
Figure 3.6. Measured dispersions from single layer graphene to four layer graphene, from Ohta et al 48 .
This can also be achieved by measuring the dispersions along the out-of-plane direction k z . For a single layer
graphene, there is no dispersion along k z direction (see Fig. 3.5). For bilayer graphene or trilayer graphene,
the intensity oscillates periodically between the different π bands (see Fig. 3.6) 48 . When the number of
layers is larger than 10, the electronic structure is hardly distinguishable from that of graphite.
3.2.4 Low energy electron microscopy (LEEM)
LEEM is a powerful technique to study the surface topography and the dynamics of the growth process.
Fig. 3.7 shows the LEEM images in SiC before and after annealing at 900C under Si flux. After annealing,
the SiC surface shows less defects and a smoother surface. Further annealing without Si flux leads to growth
of the buffer layer 49,50 - a carbon layer with the same σ bands as graphene without the low energy π band
- and eventually the growth of graphene.
Fig. 3.8 shows the surface topography of the as-grown graphene. Clear color contrast between white,
gray to black (labeled by black, blue and red colors in Fig. 3.8) can be clearly observed. The temperature at
which these regions form increases from white, gray to black regions. Scans of the reflected electron intensity
as a function of electron energy in these three characteristic regions show that the gray and black regions
have one and two quantum oscillations, which correspond to single layer and bilayer graphene respectively.
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