Metallic nanostractures exhibit collective plasmon excitations with energies that can be tuned across the visible and near infrared parts of the optical spectrum by simply changing the geometrical shape or composition of the nanostructure.(1) Plasmon excitations are extremely efficient light capturers. When excited at resonance, the cross section of plasmonic nanostructures can be orders of magnitude larger than its physical cross sections. Because of this, a substrate does not to be completely covered by plasmonic nanostractures to benefit from plasmon-enhanced effects. Plasmons can efficiently capture incident light and focus it to nanometer sized hotspots, thus creating intense local electric fields, enabling nonlinear processes such as Raman Scattering, high harmonic generation, and field ionization of nearby structures .(2) Another important property of plasmons is that they can be efficient sources of hot electrons. Plasmons decay radiatively into photons or nonradiatively into electron-hole pairs. The ratio between nonradiative and radiative decay can be controlled by changing the geometrical structure and size of the nanostructure. For a small nanoparticle or for subradiant plasmon modes, the predominant plasmon decay mechanism is nonradiative.(2) The hot electrons created from nonradiative plasmon decay can transfer from the metallic nanoparticle into nearby structures and be used to control chemical reactions or in light harvesting applications.
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