Abstract
We present the results of an investigation of surface-enhanced Raman scattering (SERS) by optical phonons in colloidal CdSe nanocrystals (NCs) homogeneously deposited on both arrays of Au nanoclusters and Au dimers using the Langmuir–Blodgett technique. The coverage of the deposited NCs was less than one monolayer, as determined by transmission and scanning electron microscopy. SERS by optical phonons in CdSe nanocrystals showed a significant enhancement that depends resonantly on the Au nanocluster and dimer size, and thus on the localized surface plasmon resonance (LSPR) energy. The deposition of CdSe nanocrystals on the Au dimer nanocluster arrays enabled us to study the polarization dependence of SERS. The maximal SERS signal was observed for light polarization parallel to the dimer axis. The polarization ratio of the SERS signal parallel and perpendicular to the dimer axis was 20. The SERS signal intensity was also investigated as a function of the distance between nanoclusters in a dimer. Here the maximal SERS enhancement was observed for the minimal distance studied (about 10 nm), confirming the formation of SERS “hot spots”.
Highlights
Since its observation in 1974 [1], surface-enhanced Raman scattering (SERS) has become a powerful technique for detecting and studying ultra-low quantities of organic and biological substances [2,3,4,5,6,7] down to a single molecule [8,9]
The locally enhanced electromagnetic field induced by the localized surface plasmon resonance (LSPR) in the vicinity of metal surface is responsible for the Raman scattering intensity enhancement, which is proportional to the fourth power of the enhancement of the local field [3,4,5,6,7]
In this paper we report on the study of resonant SERS by CdSe NC coverage of less than one monolayer deposited onto regular arrays of Au nanoclusters, with a particular focus on Au dimer arrays
Summary
Since its observation in 1974 [1], surface-enhanced Raman scattering (SERS) has become a powerful technique for detecting and studying ultra-low quantities of organic and biological substances [2,3,4,5,6,7] down to a single molecule [8,9]. CdSe NCs are resistant against intense laser irradiation and have a direct band transition energy located in the same (red) spectral range as that for LSPR in Au nanoclusters and are considered as a model system for resonant SERS experiments.
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