Investigation into a surface plasmon related heating effect in surface enhanced Raman spectroscopy

The irreversible loss of surface enhanced Raman spectroscopy (SERS) intensity derived from electrostatically immobilized Au colloidal substrate is studied. The total intensity of the SERS scattering from crystal violet molecules adsorbed onto the substrate was monitored for up to 240 s under continuous laser irradiation. The rate of signal decay was found to depend upon the thickness of the liquid layer over the coated substrate. On the basis of this observation, we propose a plausible mechanism in which surface plasmon related heating induced a small but significant lateral particle diffusion in closely spaced Au particles. The result of the shifting is an increase in the average interparticle distance, which subsequently reduces the electromagnetic coupling between the Au nanoparticles, and in turn causes a reduction in the SERS activity. Finally, a three-state model is proposed and shown to satisfactorily describe the observed decays.