Surface-Enhanced Raman Spectroscopy of Dye and Thiol Molecules Adsorbed on Triangular Silver Nanostructures: A Study of Near-Field Enhancement, Localization of Hot-Spots, and Passivation of Adsorbed Carbonaceous Species

Figure 1

(a) Fabrication steps of metal templates by nanosphere lithography. (A) Colloidal crystals formed by crystallization of PS spheres during solvent evaporation. (B) Metal coating. (C) Molecules in solution adsorbed (physisorbed or chemisorbed) at the metal nanoparticles obtained after spheres lift-off. (D) Polymer cast used to protect the sample and to change refractive index of the medium close to the metal nanoparticles. Using transparent substrates, the illumination of the sample can be done from both sides. (b) AFM topography image of a Ag pattern with 50 nm film thickness. (c) SEM micrographs of a 50 nm thick silver pattern, fabricated using PS spheres of 3 diameter. Small clusters (30 to 50 nm) are found close to the triangular particles. The smaller clusters between the triangles are formed by sputtering of a gold-palladium target, used for the coating required for the scanning electron microscope. This coating has a thickness of 4 nm.