Surface-enhanced Raman direct deposition

Substrates for surface-enhanced Raman scattering (SERS) were prepared by vapor deposition of silver directly onto the surface of porous alumina. Silver nanostructures have been characterized by SEM and UV-Vis absorption. The SERS-activity of the substrates tested with water-soluble cationic Cu-porphyrin as a probe molecule, attained the maximum when Ag mass thickness vtas approximately 60 nm. 

Plasmon-assisted RS can operate in different modalities depicted in Eig. 3.17. The first modality is represented by bare Au NPs deposited as a film on a solid support and the molecules to be probed are in direct contact with the metal surface (Pig. 3.17a). This contact mode also applies to transition metal-coated NPs (Pig. 3.17b), which extend the SERS application to other wavelength regions and transition-metal catalyzed reactions. In contrast, tip-enhanced Raman scattering (TERS) operates in a noncontact mode the Au tip, acting as the Raman signal amplifier and the probed molecules on the surface are separated from each other (Pig. 3.17c). With this powerful approach of chemical imaging at the nanometre scale, any substrate can be probed without additional constraints on material composition and surface topography. 

---