Modelling the Optical Properties of Metal Nanoparticles: Analytical vs Finite Elements Simulation

Abstract

Metal nanoparticles are an important research field for their broad and various application. The modeling of their chemical and physical properties is essential for the correct design of innovative materials. In this study the analytical simulation, based on the bare Mie theory, is directly compared with the measured absorbance spectra of gold colloids, prepared through a seed-mediated process. The goodness in the prediction of the particles dimension gives an indication on the level of precision of the model to simulate the optical behavior of the sample. Then, a discrete simulation is performed, which implements finite element analysis; a good level of agreement with the analytical model is obtained for single isolated nanoparticles, and additional properties like electromagnetic behavior of the particles is modeled. At last the discrete simulation is used to explore complex particle structures, whose analytical simulation is not possible, like dimer, nanoparticles chain and planar distribution. For these configurations, the electric field is analyzed, with particular attention to the best configuration for the field enhancement, and the trend of the absorption spectrum is studied as a function of the relative distance among the particles. The results indicate that the plasmon resonance shifts to the red when array of particles are considered since 10 and 30nm shift has been observed for a chain of closely spaced nanoparticles and for a planar ordered nanoparticles, respectively.