Observation of propagating surface plasmon polaritons by using functionalized tip-enhanced Raman spectroscopy

Abstract

We report on surface plasmon polaritons (SPPs) observed by functionalized-tip/surface enhanced Raman scattering. In particular, a short-range SPPs was detected on a rough gold film with high spatial resolution. The SPPs are launched by large noble metal nanostructures. SPPs interferences patterns with a beating period of around 400 nm are observed. Manipulation of the optical enhancement has been carried out by tuning the tip-sample distance. An increase of Raman scattering due to the highly directional surface plasmon coupled emission is observed. A finite element simulation has been carried out in order to simulate the SPPs patterns and also the influence of the emission angle and the tip to sample distance on far field intensity. These simulations in particular confirm that the SPPs mode is resulting from the interference between the wave vector of the incident and scattered light and the wave vector of the scattered SPPs. The contribution of surface plasmon coupled emission in increasing the sensitivity of Raman intensity with a tip-enhanced Raman scattering configuration is observed.