Effect of adsorbed molecules on surface-enhanced Raman scattering of metal/molecule/metal junctions

Abstract

Metal nanoparticles assembled with functional molecules to form advanced structures have proven to have wide applications in molecular electronics and sensors. The microenvironments of the assemblies may largely influence the properties of the advanced structures. Herein, silver/4-aminothiophenol/silver (Ag/PATP/Ag) structures are constructed to generate nanosized metal/molecule/metal junctions via a layer-by-layer assembly technique. The effect of the microenvironments, such as adsorption of molecules on the junctions, on the properties of the molecular junctions is investigated by surface-enhanced Raman scattering of the PATP molecules interconnected in Ag/PATP/Ag junctions. It is demonstrated that the modification of molecules such as n-octanethiol, 1,8-octanedithiol, thiophenol 1,4-benzendithiol, and 4-mercaptopyridine, shows negligible effects on the enhanced electromagnetic field arising from the plasmon coupling of neighboring silver nanoparticles. The contributions from photoinduced charge transfer (CT) between the silver nanoparticles through the interconnected PATP molecules could be altered by the modification of the molecules. The large influence from the aromatic thiols is ascribed to the delocalization of the free electrons in the metal nanoparticles to the conjugated structure of the modified molecules.