Surface-Enhanced Raman Spectroscopy Hot-Spots on Ostwald Ripened Silver Nanoparticles Prepared by Galvanic Displacement

Silver particles grown on silicon in a galvanic displacement process undergo Ostwald ripening in which small particles merge into bigger ones. In this process the particles are shown by scanning electron microscopy to become smoother. Even though the surface area of the nanoparticles is halved on ripening, the Raman enhancement provided by them is at least five times higher than of the particles that did not undergo the ripening. In several regions, transmission electron microscopy (TEM) images show that the ripened particles resemble agglomerated colloids. In these regions the signal due to surface-enhanced Raman scattering (SERS) is greatly enhanced, suggesting that they are the SERS hot spots. The importance of boundaries formed between silver particles to the increased Raman signal is suggested.