Electric field enhancement and concomitant Raman spectral effects at the edges of a nanometre-thin gold mesotriangle†

The local electric field enhancement at various regions of an individual nanometre-thin gold mesotriangle has been demonstrated both numerically and experimentally. This work provides, for the first time, direct experimental evidence of localized enhancement of Raman signals at three edges of nanometre-thin gold mesotriangles at single particle level, using Raman microscopy. Raman images were collected from mesotriangles of 11 mm edge length and 30 nm thickness, using adsorbed crystal violet as the probe molecule. Spatial distribution and the extent of electric field enhancement around a single mesotriangle are investigated theoretically by finite-difference time-domain (FDTD) simulations. Confocal Raman studies provided direct proof for the substantial electrical field enhancement at the edges and corners compared to the face of the mesotriangle. The simulated electric field enhancement was in the order, corner > edge > surface, which is in complete agreement with the experimental results.