Spectral Multipole Resonances of Super Elliptic Gold Nanoparticles in the Visible and Near-Infrared Spectral Ranges

The Local Surface Plasma Resonance (LSPR) of spherical metal particles is typically only observed within the visible spectrum. This inherent property renders modulation through alterations in radius or material challenging, significantly constraining its practical applications. In this work, we propose a super-elliptic gold nanoparticle model that allows for the continuous modulation of particle geometry from spherical to star-like shapes using a single roundness parameter (e). Unlike conventional nanorods or discrete nanostars, this geometry provides a unified framework to investigate the evolution of multipole resonances. The radiation characteristics of super elliptic gold nanoparticles in the range of 0.3~2.5 μm were calculated by using the Finite Difference Time Domain method. The present study investigates the effects of the particle roundness parameter and particle size on the LSPR response. The results demonstrated that an augmentation in the particle roundness parameter resulted in a substantial enhancement of the absorption efficiency of the particles. Concurrently, a discernible red shift in the LSPR peaks was observed within the visible light spectrum. A greater prevalence of LSPR peaks was observed in the visible and near infrared band for the super elliptical gold nanoparticles with large roundness parameter. Super-elliptical particles have been observed to exhibit multiple plasmonic absorption peaks, in contrast to the more typical behaviour of conventional noble metal particles, which typically exhibit only one or two such peaks. The effect of the roundness parameter on the local surface plasma resonance response of nanoparticles of varying sizes is consistent. The super elliptic gold nanoparticles have potential applications in the fields of solar heating, radiative cooling, biomedical and photocatalysis.