Chemistry Reference
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varies linearly with the surface area (see inset of Fig. 7(a)) [50].
Theoretical calculations show that SLG can accommodate up to 7.7 wt%
of hydrogen, while bi- and tri layer graphene can have an uptake of
~2.7%. The H
2
molecule sits on the graphene surface in end- on and side-
on fashion alternatively. CO
2
uptake of few-layer graphenes at 1 atm and
195 K is around 35 wt%. Theoretical calculations show SLG can have a
maximum uptake of 37.9 wt% of CO
2
(Fig. 7(b)). The CO
2
molecule sits
alternatively in a parallel fashion on the rings.
5. INTERACTION WITH ELECTRON DONOR AND ACCEPTOR MOLECULES
Raman bands of graphene are affected strongly by electron-phonon
interactions and hence by doping with holes and electrons. It has been
found recently that a top-gated single graphene layer transistor is able
to reach doping levels of up to 5 × 10
13
cm
-1
by in-situ Raman
measurements [51]. The G- and 2D- bands show changes on doping.
Electron-donor and -acceptor molecules have been found to affect the
Raman spectrum of few-layer graphene giving rise to rather large shifts
in the Raman bands positions and band widths. In particular, the changes
in the Raman spectrum caused by the interaction of tetrathiafulavalene
(TTF) and tetracyanoethylene (TCNE) with few-layer exfoliated graphene
are quite large [52], the shifts in the G-band going up to 25 cm
-1
. A
possible reason for such large changes in the Raman spectrum is
considered to be surface effects. We have, therefore, investigated the
effects of TTF and TCNE on the Raman bands with few-layer graphenes
prepared by three different methods and hence associated with
differences in the nature of the surface [53].
In Fig. 8, we show the Raman G-bands of the EG, DG and HG
samples and the changes brought about by interaction with TTF and
TCNE. The band on the right-side of G-band is due to the defect-related
G'-band (also referred to as D' band by some workers). The G'-band
is more prominent in HG than in DG and EG. The full-width at
half maximum (FWHM) of the G-band is lowest in HG and highest
in EG.
