Surface-enhanced Raman scattering at well-defined single crystalline faces of platinum-group metals induced by gap-mode plasmon excitation

It is normally difficult to use surface enhanced Raman scattering (SERS) to study molecular adsorbates at well-defined planar metal surfaces or at Pt-group catalytic metal surfaces. In this paper, highly localized gap-mode plasmons are excited on atomically smooth metal surfaces by using a sphere-plane type plasmonic cavity. This method enables us to observe Raman scattering signals from molecular adsorbates on various single crystalline metal surfaces including non-SERS-active Pt and Pd. SERS spectra of self-assembled isocyanide monolayers on several metal substrates with (1 1 1) or (1 0 0) orientation reveal a significant orientation dependence of preferential adsorption sites, which information is hardly obtainable from conventional SERS spectra.