GIANT GOLD CLUSTERS STABILIZED BY TRIPHENYLPHOSPHINE LIGANDS - CHARACTERIZATION BY SURFACE ENHANCED RAMAN AND REFLECTANCE SPECTROSCOPY

The binding of a new stabilizing ligand (monosulfonated triphenylphosphine) to the surface of large, monodisperse gold cluster particles is studied by surface enhanced Raman scattering (SERS). From a detailed assignment of the bands, partial information on the adsorption geometry of the ligand onto the colloid surface is obtained. The SERS enhancement is estimated from the experiment, and compared with the theoretical value calculated for the electromagnetic contribution due to local field enhancement. When a sample of the purple colloidal solution is placed on a glass substrate and the solvent is allowed to evaporate, the solid film takes on the appearance of metallic gold; this colour change is reversed upon re-dissolution of the solid. Reflectance spectra have been recorded to characterize the spectral changes occuring, and are interpreted in terms of the Maxwell-Garnett theory for a composite medium consisting of gold spheres in an aqueous host medium.