Strong shape-dependent intensity of inelastic light scattering by gold nanocrystals

We present a numerical approach to calculate inelastic light scattering spectra from gold nanocrystals, based on the finite element method. This approach is validated by comparison with previous analytic calculations for spherically symmetric scatterers. Superellipsoid nanocrystals are considered in order to smoothly vary the shape from octahedra to cubes via spheres, while preserving cubic symmetry. Spectra are calculated and discussed taking into account the irreducible representation of the involved vibration modes. A strong increase in the inelastically scattered light intensity is observed for small variations of the shape around the sphere. This increase is related to variations of the electric field inside the nanocrystals, which are very small for small nanospheres but increase quickly for nonspherical nanocrystals. This strong dependence with shape must be taken into account when interpreting experimental spectra acquired from inhomogeneous ensembles of nanocrystals whose shape dispersion are usually neglected. The overall changes in the spectra when varying the shape of the nanocrystals provide additional insight into previously published results. Preliminary calculations for chiral shapes further show a significant difference between spectra obtained with right or left circularly polarized light.