Self-Assembled Monolayers of Ferrocenylazobenzenes on Au(111)/Mica Films: Surface-Enhanced Raman Scattering Response vs Surface Morphology

Surface-enhanced Raman scattering (SERS) and surface-enhanced resonance Raman scattering (SERRS) results are reported for self-assembled monolayers (SAMs) of 4-(4-mercaptobutyl)-4´-ferrocenylazobenzene, compound 1, on Au/mica and Pt/mica thin films. Two different Au/mica surfaces, designated Au(rough)/mica and Au(111)/mica, have been characterized by atomic force microscopy (AFM) to define their respective surface morphologies. Cyclic voltammetry of SAMs of 1 on Au(rough)/mica, Au(lll)/mica, and Pt/mica was used to directly measure the surface coverage of 1. A quantitative determination of the contributions to the measured surface Raman intensity from adsorbate-localized resonance Raman and substratederived electromagnetic enhancement effects is made. The surprising conclusion is that Au(lll)/mica surfaces of the type traditionally used for preparing and studying SAMs are “SERS-active” without the need for additional roughening or treatment with a “SERS-active” overlayer.