Scattering properties of dense clusters of colloidal nanoparticles

In this work, we present a new methodology to accurately calculate scattering properties of fractal clusters with arbitrary large fractal dimension, d(f) (up to 3), and arbitrary primary particle size and material optical properties. Our approach is based on a combination of Monte Carlo simulations to generate cluster structures and mean-field T-matrix theory for the calculation of scattering properties. We have used a conventional cluster-cluster aggregation algorithm to generate clusters with d(f) up to 2.1, a tunable cluster-cluster aggregation algorithm for clusters with d(f) up to 2.5 and a newly developed Voronoi tessellation-based densification algorithm for clusters with d(f) up to 3. The scattering properties of clusters have been computed by means of mean-field T-matrix code (proposed by Botet; et al. Appl. Opt. 1997, 36 , 8791 - 8797 ), which can account for intracluster multiple scattering at a very low computational cost, thus overcoming the major limitations of commonly used Rayleigh-Debye-Gans (RDG) theory. The results of the calculations show significant deviations of the scattering cross sections and zero-angle intensities as compared to RDG theory for large primary particle sizes and high d(f). Good accuracies of the method have been confirmed by comparisons with full T-matrix calculations. The proposed approach is an ideal compromise between accuracy and high computational efficiency, and is suitable for inversion of experimental scattering data.