Charge-Transfer Induced Surface-Enhanced Raman Scattering in Silver Nanoparticle Assemblies

Molecular junctions of metal/molecule/metal were fabricated with silver nanoparticles and functional molecules through layer-by-layer self-assembly techniques. The Raman scattering of the interconnecting molecules between the silver nanoparticles can be greatly enhanced. For the silver/4-aminothiophenol/silver (Ag/PATP/Ag) assembly, in particular, the larger enhancement of the b 2 modes, relative to that of the a 1 modes, is ascribed to the charge transfer between the silver nanoparticles tunneling through the interconnecting PATP molecules. The molecular dipolar momentum and surface property of the silver nanoparticles have large effects on the enhancement of the Raman scattering of the interconnecting molecules.