Optical properties of two-dimensional and three-dimensional arrays of noble metal nanoparticles by the discrete dipole approximation method

Abstract

The optical aspects of plasmon coupling occurring through the near-field interactions among metallic spherical nanoparticles assembled in close proximity to each other in two-dimensional and three-dimensional arrays have been examined using the discrete dipole approximation (DDA). Calculations were performed for nano-sized close-packed spheres of silver, gold or copper, hexagonally arranged in a planar monolayer target and extended gradually to three-dimensional multilayer targets with a fastened interparticle spacing. Those targets were simulated under the incident ppolarized light with an energy range of 1.5 - 4.5 eV by executing an open-source code of the DDA. The optical response of three-dimensional targets was revealed in the absorption spectra calculated at various angles of the polarized incident light, showing a blue shift of the plasmon resonance (PR) peak for both gold and copper targets. The splitting of the surface plasmon resonance (SPR) observed in the response of the two-dimensional silver system eventually disappeared into one well-defined resonance peak as the system grew in the third dimension. Moreover, to shed light on the nature of the plasmon coupling among close-packed nanospheres of different metals, we simulated a target composed of mono-sized nanospheres of the three metals placed spatially in three consecutive layers. A combined optical behaviour was thus observed through the absorption spectrum, where the plasmon peaks attributed to the silver, gold and copper interacting nanospheres emerged at the original energy values as if it was applied in isolated planar hexagonal arrays.