A surfaced enhanced Raman spectroscopic investigation of the aggregation of silver nanoparticles formed via laser vaporization controlled condensation was undertaken. Using Rhodamine 6G as the adsorbate, nanoparticles with diameters in the range 5 to 50 nm were studied with the results from 8nm, 11nm and 15nm diameter particles reported to highlight the effects of particle size and halide ion concentration on particle aggregation. It was found that with 647.1 nm excitation maximum enhancement is observed using particles with 11nm diameters. Aggregates formed from particles of this size also exhibit significantly greater enhancements compared to aggregates formed from the other size particles. Upon addition of sodium halides, enhancement is proportional to the size of the anion for F-, Cl-, and Br-. Maximum enhancement was observed when the concentration of the anion was approximately equal to the concentration of the adsorbate. These observations are explained in terms of electromagnetic contributions to the enhancement.
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