The geometrical nature of optical resonances: from a sphere to fused dimer nanoparticles

Abstract

This version is available at https://strathprints.strath.ac.uk/42181/ Strathprints is designed to allow users to access the research output of the University of Strathclyde. Unless otherwise explicitly stated on the manuscript, Copyright © and Moral Rights for the papers on this site are retained by the individual authors and/or other copyright owners. Please check the manuscript for details of any other licences that may have been applied. You may not engage in further distribution of the material for any profitmaking activities or any commercial gain. You may freely distribute both the url (https://strathprints.strath.ac.uk/) and the content of this paper for research or private study, educational, or not-for-profit purposes without prior permission or charge.Any correspondence concerning this service should be sent to the AbstractWe study the electromagnetic response of smooth gold nanoparticles with shapes varying from a single sphere to two ellipsoids joined smoothly at their vertices. We show that the plasmonic resonance visible in the extinction and absorption cross sections shifts to longer wavelengths and eventually disappears as the mid-plane waist of the composite particle becomes narrower. This process corresponds to an increase of the numbers of internal and scattering modes that are mainly confined to the surface and coupled to the incident field. These modes strongly affect the near field, and therefore are of great importance in surface spectroscopy, but are almost undetectable in the far field.

Local optical responses of plasmon resonances visualised by near-field optical imaging

“…Thus, comparison of the image with theoretical simulation is indispensable to assign the feature to an oscillation mode of the disk. In this regard, we analysed the observed images based on a recently developed theoretical framework, [68][69][70][71][72] which is an extension of Mie scattering theory. The images simulated with this theory semi-quantitatively reproduced the observed images.…”

Nanoparticle shapes by using Wulff constructions and first-principles calculations

“…Therefore, the real challenge we are facing today is to be able to control the shapes of nanoparticles [3]. The shape of nanoparticles can have a big impact on their properties, not only in catalysis in which the number of active sites is clearly shape-dependent [4], but also in other applications such as optics [5–6]. …”

Plasmon modes in single gold nanodiscs

“…With numerical electromagnetic simulation approaches such as the finite difference time domain (FDTD) method [20] and the discrete dipole approximation (DDA) methods [21], the concept of modes cannot be introduced, although they can treat nanostructures of arbitrary shapes. We thus carried out assignments of the observed images based on the theoretical framework recently developed [22][23][24][25][26]. This approach enables us to give clear physical pictures of the spatial features of plasmon modes of metal nanoparticles observed in the experiments.…”