Raman scattering of aryl isocyanide monolayers on atomically flat Au(1 1 1) single crystal surfaces enhanced by gap-mode plasmon excitation

Raman scattering spectra of aryl isocyanide monolayers on atomically ‘flat’ Au(1 1 1) single crystal surfaces, on which conventional SERS is not expected, were observed by means of gap-mode plasmon excitation. The gap-mode resonance nano-structures were introduced to the monolayer/Au(1 1 1) system by topping Au–nanoparticles and thus Raman scattering efficiency was substantially enhanced. By comparison with a conventional SERS on a rough Au–polycrystalline substrate, it was confirmed that molecular packing was affected by geometric and electronic states of Au surfaces. This novel spectroscopic technique can be used for studies of intrinsic metal–molecular interfaces without influence of surface morphology.