Thesis Manuscript

EPILOGUE
antenna loaded with a photoconductive semiconductor material has been introduced. The
nano-antenna optical response is dramatically shifted by short-circuiting the nano-antenna
with the free-carriers of the photoconductive material gap. This photoconductive switcher
can be used to control both far-field and near-field properties. Furthermore, shape and
size effects on plasmonic nano-resonators (i.e. nanoring-disks) have been investigated. I
have found that a rounded shape of the ring surfaces and edges is responsible for significant
red-shifts of the ring-like LSPR that can be very large with respect to the ideal
ring-disk exhibiting vertical side walls, flat surfaces and sharp edges. Good agreement
was found with the AFM and optical measurements. Shape effects are also important
for the understanding of Raman-Brillouin scattering properties. Indeed, I introduced the
concept of acousto-plasmonic hot-spots in metallic nanostructures. Well known plasmonics
hot-spots, modulated by low frequency acoustic vibrations, are responsible for the
activation of Raman-Brillouin acoustic modes in the scattering process of metallic nanoobjects.
The presence of defects (e.g. indentations in silver nanocolumns) or systems
with interacting nanoparticles (e.g. gold dimers) held such acousto-plasmonic hot-spots.
I have shown that, for the surface orientation mechanism, the breathing-like vibrations
which are almost silent for smooth cylindrical nanocolumns are strongly enhanced
in the case of indented nanocolumns. The indentations of the silver nanocolumns are responsible
for the strong localization of the surface plasmon near-field and its modulation
by breathing-like acoustic vibrations. Understanding the acousto-plasmonic dynamics of
metallic nano-objects is useful not only for the interpretation of Raman-Brillouin and
time-resolved pump-probe experiments but also for nanometrology, i.e. extracting information
on size and shape distributions from these optical measurements. The concepts,
the numerical and experimental approaches have been extended to other isolated nanoobjects
exhibiting strong field localization (dimers of nano-objects). It has been shown
that in the gap between the interacting nanoparticles, a strong field modulation by the
acoustic vibrations takes place. This modulation of controllable hot-spots may give rise
to Raman-Brillouin scattering by acoustic vibration modes that are normally forbidden in
isolated nanoparticles. The concept of acousto-plasmonic hot-spots opens up the way for
the vibrational transfer between interacting metallic nano-objects and can be extended
to clusters of nanoparticles or other interacting nanostructures.
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