Plasmons – a metal cube is placed in an external electric field pointing to the right. Electrons accumulate on the left side, and positive ions on the right side. When the electric field is switched off, the electrons and positive ions oscillate back and forth at the plasma frequency. Light of frequency higher than the plasma frequency is transmitted, whereas light of frequency below the plasma frequency is reflected.
Plasmons are electronic oscillations in metal under the influence of an external electric field.
When the metal nanoparticle size decreases, the plasmonic wavelength decreases resulting in a blue shift.
Lycurgus cup – green color is from reflection. Red and purple colors are from transmitted light.
Stained glass – different colors come from the size variation of embedded gold nanoparticles.
Single nanoparticles appear blue, two nanoparticles appear green, and multiple particles appear orange.
Plasmon resonance can be used to measure nm scale distances, since the scattering light wavelength of two nanoparticles shifts as a function of the distance them.
Plasmons also can enhance the electro-magnetic field at a metal-dielectric interface.
Raman Scattering – light is scattered with a different frequency from the original frequency of the incident photons.
Surface Enhanced Raman Scattering (SERS) – surface sensitive technique that results in the enhancement of Raman scattering from molecules adsorbed on metal surfaces. The local electric field can be enhanced by 1014-1015. The technique can be sensitive enough to detect single molecules.
Raman- AFM system – uses a sharp metal tip and illuminating tip with a laser beam.
Surface Plasmonic wave – electromagnetic wave that propagates at the interface between a metal and a dielectric. Metals have dielectric constants that are negative. The wavelength of the plasmonic wave can be reduced significantly.