SURFACE-ENHANCED RAMAN-SCATTERING FROM FUNCTIONALIZED SELF-ASSEMBLED MONOLAYERS .1. DISTANCE DEPENDENCE OF ENHANCED RAMAN-SCATTERING FROM A TERMINAL PHENYL GROUP

The enhancement factor for surface-enhanced Raman scattering (SERS) is measured as a function of distance using a self-assembled monolayer as the spacer and a terminal phenyl group as the Raman label. The Raman label is covalently linked to the spacer layer by an amide bond. The measured enhancement factor decays approximately exponentially as a function of distance. The decay rate, expressed as the distance at which the enhancement factor decreases to half of its initial value, is about 0.35 nm. Analysis of the decay curve by two similar theories of electromagnetic enhancement shows that roughness dimensions on the order of 10 nm are responsible for the observed SERS signals under the 647.1 nm laser excitation.