Understanding plasmon resonances of metal-coated colloidal crystal monolayers
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Metal films deposited over two-dimensional colloidal crystals (MFoCC) constitute a low-cost periodic structure with interesting photonic and plasmonic properties. It has previously been shown that this structure exhibits a behaviour similar to the well-known Extraordinary Optical Transmission (EOT) of metallic hole arrays in planar films. Here, we explore the transmission characteristics of AgFoCC by systematic comparison with that of the bare CC. Furthermore with additional reflectivity measurements we evaluate the AgFoCC overall plasmonic response, which, notably, exhibits a strong plasmon absorption band at wavelengths larger than those of the transmitted maximum. By corroborating these results with finite-difference time-domain electromagnetic simulations, we identify a hybrid metal-dielectric propagative mode in the transmission mechanism. On the contrary a strongly localized mode is responsible for the maximum light absorption by this structure. These results shed new light on the current understanding of this highly promising plasmonic structure, being useful for the design of surface-enhanced Raman scattering and enhanced fluorescence substrates.
KeywordsSERS Colloidal Crystal Plasmon Excitation Hole Array Propagative Mode
This work was supported by CNCSIS–UEFISCSU, project number PNII-ID_PCCE_129/2008. The author, M. Giloan, wish to thank for the financial support provided from programs co-financed by the Sectoral Operational Programme Human Resources Development, contract POSDRU 6/1.5/S/3—“Doctoral studies: through science towards society.”