Experimental investigation of photonic band gap influence on enhancement of Raman-scattering in metal-dielectric colloidal crystals

A simple chemical technique is implemented to fabricate a metal-dielectric colloidal crystal structure (MDCS) in order to enhance the otherwise weak Raman signals by combining the effects of localized surface plasmon resonance (LSPR) enhancement due to gold nanoparticles, precise field confinement of dielectric and air bands in the periodic dielectric structure and field enhancements at the photonic band gap (PBG) edges. The higher density of electromagnetic modes (DOS) near these band edges is explained as due to the reduced group velocity at the photonic band gap edges. Intense electric field strength due to the excitation of high DOS at the edges of PBG of MDCS and the LSPR excitation through field confinement in the dielectric medium of MDCS are employed to study the Raman-scattering signals of adsorbed benzenethiol (BT) molecule on the MDCS. Large enhancement for the Raman signal in MDCS in comparison to the Raman spectra observed for BT molecule dispersed on sputtered gold film shows the effectiveness of MDCS for the micro-level detection of the analyte.