Plasmon-enhanced Raman scattering in graphene: Quantum nature of the enhancement mechanism
2015
Plasmon-enhanced Raman scattering (PERS) describes the giant enhancement of the Raman cross section close to localized surface plasmons. It is used in surface-enhanced Raman spectroscopy (SERS) to detect single molecules and in tip-enhanced scattering (TERS) to increase the resolution of Raman imaging beyond the diffraction limit. Despite the wide-spread use of plasmon-enhanced Raman spectroscopy in imaging and materials characterization its fundamental principles remain strongly debated. Here we demonstrate the quantum nature of plasmon-enhanced Raman scattering and its striking consequences. We coupled graphene and carbon nanotubes to rationally designed plasmonic nanostructures.[1]
The
coupling
increased the
Raman
cross
section
by
105
when excited
under
resonance.
Raman
ima-‐ ging
and
wavelength-‐dependent
Ram-‐ an
measurements
show
that
the
en-‐ hancement
is
strongly
localized
in space
(10
nm)
and
frequency
(15 meV).
We
propose
a
quan-‐tum
theory of
plasmon-‐enhanced
Raman
scatter-‐ ing
based
on
perturbation
theory.[2]
It predicts
quantum
interferences
bet-‐ ween
scattering
pathways
that
result in
the
suppression
and
enhancement of
scattering
channels,
which
we demonstrate
experimentally.
We
also verify
other
surprising
consequences of
the
quantum
nature
of
PERS
such
as the
appearance
of
the
D-‐mode
in perfect
graphene. Left: Plasmonic gold nanodimer covered by graphene. Right: Imaging of the Raman intensity close to the dimer at its resonance energy. [1] S. Heeg et al., Nano Lett. 13, 301 (2013); S. Heeg et al., Nano Lett. 14, 1762 (2014). [2] P. Kusch et al., Quantum nature of plasmon-enhanced Raman scattering (submitted, 2015).
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