Plasmon bands in metallic nanostructures

TL;DR

This paper investigates the photonic band structure of metallic nanostructures, revealing how sphere packing density influences plasmon modes and their optical absorption properties, explaining phenomena like colloidal silver's blackness.

Contribution

It provides a detailed calculation of plasmon bands in metallic nanostructures using an embedding technique, highlighting the effects of sphere filling factor on mode dispersion.

Findings

Maxwell-Garnett theory accurately describes dipole modes at low filling factors.

Multipole modes become dispersive at higher filling factors due to crystal field effects.

Touching spheres produce a broad continuum of plasmon modes causing strong light absorption.

Abstract

The photonic band structure of a three-dimensional lattice of metal spheres is calculated using an embedding technique, in the frequency range of the Mie plasmons. For a small filling factor of the spheres, Maxwell-Garnett theory gives an almost exact description of the dipole modes, and the multipole modes are fairly dispersionless. For a larger filling factor, crystal field effects modify the multipole frequencies, which show dispersion. These multipole bands are enclosed between the dipole modes. For touching spheres, there is a wide continuum of plasmon modes between zero frequency and the bulk metal plasmon frequency, which yield strong absorption of incident light. These plasmon modes are responsible for the blackness of colloidal silver.