Designed nanoparticle–mesoporous multilayer nanocomposites as tunable plasmonic–photonic architectures for electromagnetic field enhancement
In this work we present the designed production of a highly tunable nanocomposite able to confine and enhance the electromagnetic field through the combined effects of photonic and plasmonic responses. Silver nanoparticles (NPs) were embedded within a Mesoporous Photonic Crystal (MPC) composed of a mesoporous multilayer presenting a TiO2–SiO2 unit cell. This nanosystem was synthesized by a combination of reproducible sol–gel thin film techniques with the selective production of NPs within the titania layers. The design of the MPC architecture was tuned so that each photonic band gap edge would match the plasmonic absorption peak of the Ag NP, in order to combine their confined plasmonic enhancement with that of the band gap edges due to the multilayer structure. We find that the MPC contributes to enhancing the Surface Enhanced Raman Scattering (SERS) signal of probe molecules trapped in the mesopores. This effect indicates the relevance of the unit cell interfaces for the local electromagnetic field enhancements, and opens the gate to performing plasmon-assisted SERS sensing. The resulting material results in a promising platform to study the interplay between photonic and plasmonic systems. These tuneable nano-architectures are highly robust, reproducible, and can lead to applications in sensing platforms, as well as in optoelectronics, enhanced photocatalysis, or artificial photosynthesis.