PNNL

Abstract

We have conducted a study of laser excitation intensity-dependent nano-Raman spectral fluctuation dynamics using a AFM combined two-channel single-photon counting detection confocal microscopy. The dynamics of the fluctuations were highly inhomogeneous amongst individual nanoparticle clusters. Although the fluctuation above ~50 W/cm2 excitation was dominated by a photo-induced process, the spontaneous fluctuation could be measured at lower excitation intensity. The ratio of spontaneous and photo-induced fluctuation was nano-site dependent, presumably dependent on the local gradient field enhancement and the heterogeneous nano-geometry from cluster to cluster. The origins of the nano-SERS fluctuations could be due to the interactions of molecules with the local electromagnetic field, which in turn depend on the complexity of the substrate nano-metallic structure.