Plasmonic Properties of Bimetal Nanoshell Cylinders and Spheres

Plasmonics is a new branch of the fascinating field of photonics and de- velops concepts to quench light beyond the diffraction limit and enhance electromag- netic fields. These enhancements occur in metals as localized surface plasmon polari- tons (LSP) a coupling of the the surface den- sity oscillations of the electron gas to the in- cident light. With three-dimensional nano- structures of coinage metals that are brought in intimate contact with analytes of inter- est such as molecules one can utilize the lo- cally enhanced electromagnetic field to ex- cite characteristic vibrational modes. This enhanced Raman effect (surface enhanced Raman scattering - SERS) gives the possi- bility to create spectroscopic vehicles which can act as highly sensitive molecular detec- tor using Raman signals as a fingerprint of the analyte. The effectivity of the metal nanostructures for local field enhancement strongly depends on the geometry of the nano-particle and its orientation with re- spect to the incident exciting laser light.