Chemistry Reference
In-Depth Information
π
Table 3.1
Energy and line-width of the
plasmon in the long wavelength limit (small momenta)
for different systems
E
loss
(q
||
=
FHWM (q
||
=
0) in eV
0) in eV
Free-standing graphene
4.7 (Kramberger et al.
2008
; Liu
et al.
2001
)
0.45
∼
6 (Yuan et al.
2011
)
MLG/6H-SiC(0001), data taken
from Ref. (Lu et al.
2009
)
4.9
0.95
VA-SWCNT, data taken from
Ref. (Kramberger et al.
2008
)
3.1
1.00
Bilayer graphene on SiC(0001),
data taken from Ref. (Lu et al.
2009
)
3.3
1.10
Magnetically-aligned bundled
SWCNT, data taken from Ref.
(Liu et al.
2001
)
6.0
1.25
MLG/Pt(111) (our data)
6.2
1.40
3-4 layers graphene on
SiC(0001), data taken from Ref.
(Lu et al.
2009
)
6.3
1.70
Graphite, data taken from Ref.
(Diebold et al.
1988
)
6.5 (Diebold et al.
1988
;
Papageorgiou et al.
2000
)
2.90
7
(Büchner
1977
; Zeppenfeld
1969
)
∼
MLG/Ni(111), data taken from
Refs. (Generalov and Dedkov
2012; Rosei et al.
1984
)
6.7 (Generalov and Dedkov
2012
)
7.5 (Rosei et al.
1984
)
∼
3
A HREELS investigation on graphene grown on 6H-SiC(0001) showed the exis-
tence of a blue-shift of the
plasmon energy (Lu et al.
2009
) as a function of the
number of graphene layers. In fact, it shifted from 4.9 (MLG) to 4.3 eV for bilayer
graphene and to 6.2 eV for 3-4 layers of graphene.
The red-shift of the plasmon energy (at small momenta) when going from bulk
graphite to quasi-two-dimensional graphene is caused by a decrease of the screening
and of the interlayer coupling. This also influences the dispersion relation of the
plasmon frequency. A linear dispersion was found for both VA-SWCNT (Kramberger
et al.
2008
) and MLG on 6H-SiC(0001) (Lu et al.
2009
). On the other hand, a
quadratic dispersion has been recorded for bulk graphite (Papageorgiou et al.
2000
),
stage-1 ferric-chloride-intercalated graphite (Ritsko and Rice
1979
) and multilayer
graphene on 6H-SiC(0001) (Lu et al.
2009
). For the latter case, it is clear that the
realistic band structure of the system changes the dispersion of the
π
π
plasmon from
linear to quadratic as a function of the number of graphene layers.
The dispersion relations that we obtained for MLG on Pt(111) (Fig.
3.22
) indicate
a quadratic dispersion for the
plasmon. Even if a negligible hybridization between
Pt and graphene states has been observed by angle-resolved photoemission spec-
troscopy measurements (Sutter et al.
2009
), the dispersion relation of the
π
π
plasmon
