Chemistry Reference
In-Depth Information
Fig. 3.10
LEED pattern of
graphene on Pt(111),
recorded at E
p
=
74.7 eV and
for a sample temperature of
100 K
Such system is ideal for a study of phonon modes and elastic properties due to the
absence of corrugation of the graphene overlayer found on other substrates (Borca
et al.
2009
,
2010
) which has been demonstrated to be caused by the hybridization
with the substrate. The growing strength of hybridization is accompanied by a gradual
change in graphene morphology from nearly flat for MLG/Pt(111) to strongly corru-
gated in MLG on other substrates (Preobrajenski et al.
2008
). Thus, MLG on Pt(111)
behaves as nearly-flat free-standing graphene, as also confirmed by angle-resolved
photoemission spectroscopy experiments (Sutter et al.
2009
).
Graphene was obtained by dosing ethylene onto the clean Pt(111) substrate held
at 1150 K. At a certain temperature, the hydrocarbon is catalytically dissociated
and hydrogen desorbs, remaining carbon adsorbed species can then form graphene.
Moreover, the high temperature of the sample during depositions favours the in-
crease of the size of MLG islands (Zhang et al.
2009
) and allows maintaining the
substrate clean so as to avoid any contaminant-induced effect on graphene growth.
The completion of the first layer was reached upon an exposure of 3·10
−
8
mbar for
ten minutes (24 L, 1 L
1.33·10
−
6
mbar·s). After removing the C
2
H
4
gas from
the chamber the temperature was held at 1150 K for further 60 s.
The attained LEED pattern (shown in Figs.
3.10
,
3.11
) is essentially similar to
that one reported in Ref. (Gao et al.
2011
). The ring pattern indicates the existence
of different domains. Nonetheless, preferred orientations aligned with the substrate
(R
0
) are clearly distinguished. The presence of well-resolved spots in the LEED
pattern is a clear fingerprint of the order of the MLG over-structure, also evidenced
by the high electron reflectivity of the obtained surface (even higher with respect to
the bare Pt substrate). (Fig.
3.11
)
Despite the presence of other domains, the predominance of R
0
in the whole
sample has been clearly inferred by the analysis of phonon dispersion measurements
performed along the
¯
=
−
K and the
¯
−
M
directions (inset of Fig.
3.10
).
