Nano-Raman Spectroscopy: Surface Plasmon Emission, Field Gradients, and Fundamentally Near Field Propagation Effects

Abstract

Nano-Raman spectra differ from far-field Raman spectra. The differences result from a strong electric field gradient near the metal tip, propagation, and polarization, but the dependence upon probe-sample distance can only be explained by the inclusion of surface plasmons and the near-field, non-propagating terms of the dipole emission. A simple model based upon these components accurately describes distance-dependent data measured with a near-field scanning optical microscope. Our essentially near-field model will apply generally to Raman spectroscopy near a nanoscale conductor.