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Photonic crystals in SERS

The area of plasmonics offers the potential of inducing large local electromagnetic fields in the vicinity of metallic surfaces and has been exploited in areas such as Surface Plasmon Resonance (SPR).

The plasmonic properties of nanostructures have recently gained much attention, particularly for their use in surface enhanced spectroscopy.


 SEM micrograph of fabricated SERS active Plasmonic Photonic Crystal structure.

By metal-coating the patterned surfaces of the photonic crystals designed by Mesophotonics, it is possible to introduce plasmonic dispersion bands.  The complex interaction between the underlying diffraction bands and the surface and localised plasmons allows much greater control of the confinement of the strong electromagnetic fields.

Once a molecule or analyte is placed in proximity to the electromagnetic field of the designed broad long range plasmon, it is possible to form highly controlled and reproducible surface enhanced Raman scattering (SERS).

 Modelling of a localised plasmon residing in an air rod of a plasmonic Photonic Crystal.
Mesophotonics has developed rigorous numerical methods to allow the modelling and design of complex metallic photonic crystals allowing prediction of the location of the optically enhancing field as illustrated on the left. 

Additionally, the ability to optically characterise the complete plasmonic dispersion bands of the structures has provided a unique advantage in developing current and future SERS substrates.  Typical plots of the angular and wavelength dependence of the dispersion bands of a SERS substrates are shown below.

 Experimental angular resolved mapping of reflectivity for a photonic crystal structure (left) and a metal coated photonic crystal structure (right). The underlying dispersion bands of the photonic crystal (red construction lines) as well as the introduced surface plasmon modes (black lines) are clearly highlighted in each case.




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