Morphology of silver and gold "SERS active" substrates from optical spectroscopy experiments and numerical simulations

In order to understand more deeply the surface enhanced Raman scattering (S ERS) effect, we develop different models allowing the determination (i) of the morphology of silver or gold clusters in colloidal sols from their ultr aviolet-visible extinction spectra and (ii) of the roughness features of si lver islands chemically deposited on various metals from differential refle ctivity measurements. For ultraviolet-visible absorption spectra, the model leads to calculated spectra of aggregated colloids in good agreement for b oth profiles and intensities with experimental ones and allows to approach the histogram of the clusters appearing in the aggregated colloid. This his togram reveals that the aggregated sols mainly consist of small spheres, re flecting unaggregated particles, and of elongated spheroids formed by the c oalescence of several spherical particles. In the last part of this paper, we present preliminary results showing how to obtain "SERS active substrate s" by chemically depositing silver islands onto various metals (Zn, Al, Cu) . The observed SERS spectra are qualitatively related to the differential r eflectivity spectra obtained on the same substrates.