STABILIZATION OF SILVER COLLOIDS BY VARIOUS TYPES OF ANIONS AND THEIREFFECT ON THE SURFACE-ENHANCED RAMAN-SPECTRA OF ORGANIC-DYES

Using a recently published procedure, silver colloids with uniform par ticle size were prepared and stabilized by nine different anions. Alth ough the UV-visible extinction spectra of the colloids showed only sma ll variations with the nature of the stabilizing ions, dramatic differ ences were observed in the SERS spectra of seven dyes studied. It was demonstrated that each family of dyes experiences a large enhancement factor only with certain stabilizing ions. The adsorption geometry of oxazine dyes changes with the nature of the stabilizing anion and with the concentration of the dye. By comparison of observed and calculate d normal modes, conclusions about the adsorption geometry are drawn. T he results are discussed in the framework of the 'adatom model'.