Exceptional enhancement of Raman scattering on silver chlorobromide nanocube photonic crystals: chemical and photonic contributions

Photonic crystals made from self-assembly of mono-dispersed AgClxBr1-x nanocubes, which are not plasmonically active, have been discovered to exceptionally enhance the Raman scattering of molecules chemically adsorbed on their surfaces. Comprehensive control measurements and X-ray absorption near-edge structure spectroscopy indicate that the Raman enhancement on AgClxBr1-x nanocube photonic crystals is primarily ascribed to the chemical enhancement mechanism associated with the chemical interactions between adsorbing molecules and the AgClxBr1-x surfaces. In addition, the ordering of AgClxBr1-x nanocubes in the photonic crystals can selectively reflect Raman scattering back to the detector at the bandgap position of the photonic crystals to provide additional enhancement, i.e., photonic mode enhancement. The thiophenol molecules adsorbed on AgCl0.44Br0.56 nanocube photonic crystals exhibit astonishingly strong Raman signals that are on the same order of magnitude as those recorded from the thiophenol molecules adsorbed on the assembled Ag nanocubes.