Chemistry Reference
In-Depth Information
Fig. 3.23
Behaviour of the
FWHM of the
plasmon of
MLG/Pt(111) acquired for
two different scattering
conditions as a function of
a
the parallel momentum
transfer and
b
the plasmon
energy. Data for
MLG/6H-SiC(0001) are
shown for a comparison
π
spectrum. As a matter of fact, the FWHM increases by a factor 6 from free-standing
graphene to graphite.
Results for graphene on 6H-SiC(0001) showed that the
plasmon peak becomes
broader and blue-shifted as the thickness of the epitaxial graphene increases. In fact,
the
π
plasmon of 3-4 layer epitaxial graphene includes spectral contribution from
both the out-of-plane and in-plane excitations of graphitic origin. This may be due
to the three-dimensional band structure of graphite which allows interlayer coupling
and out-of-plane excitation.
Moreover, it is worth noticing that the
π
plasmon in MLG/Pt(111) (our data)
and MLG/Ni(111) (Generalov and Dedkov
2012
) has a shorter life-time (higher
FWHM) than in MLG/6H-SiC(0001) and free-standing graphene as a consequence
of enhanced screening by the metal substrate. This implies a broadening of the
plasmon peak due to Landau damping via the creation of electron-hole pairs.
π
