Influence of the light-scattering form factor on the Bragg diffraction patterns of arrays of metallic nanoparticles

Accurate models for the light-scattering form factors of nanoparticles are of crucial importance to characterize the optical properties of the particles and to develop new photonic devices. Analytical or semi-empirical models exist for particles of spherical and cylindrical shape. The angular spectrum of scattering for particles of more complex shape is very complex and can only be obtained by numerical simulations. Moreover, the light scattering of metallic particles depends on many parameters as size, shape, optical constants, substrate and polarization of light. Experimental verification of the differential scattering cross-sections obtained from different calculation methods is always necessary. Measurements done on single nanoparticles are very sensitive to their local properties and the signal-to-noise ratio may be very poor. Arrays of identical particles illuminated by a planes waves produce Bragg diffraction and the resultant patterns depend on the averaged values of the form factors of the particles. In order to test the validity of models for the scattering form factor, we present an experimental setup capable of measuring Bragg diffraction patterns of arrays of nanoparticles in the visible and near-infrared regions of the spectrum. The approach is similar to that of X-ray diffraction of crystals.