Non-Monochromatic Plasmonic Behavior of Metal Nanoparticle/Dielectric Nanorod Composite Material

The integration of plasmonic metal nanoparticles with dielectric materials has been extensively studied due to the enhanced photovoltaic and photocatalytic properties these composites can achieve [1]. However, most research has focused on their functionality rather than on a fundamental understanding of the plasmonic behavior that forms the basis of this functionality. A thorough investigation of the plasmonic resonance energy and spatial distribution of plasmonic fields in these systems is crucial for developing advanced materials with optimized performance.<br/>To address this, we utilized STEM-EELS, which has emerged as an unrivaled technique for exploring plasmonics at the nanoscale. Recent advancements in monochromator technology have enabled the exceptional spatial resolution of STEM-EELS to be applied in the visible spectrum, making it a highly active technique in plasmon research.<br/>Here, we present the non-monochromatic plasmonic behavior of metal nanoparticles on dielectric nanorods, highlighting the different field distributions of two distinct plasmons. Numerical simulations using the well-known MNPBEM toolkit for plasmons [2], along with STEM-EELS measurements of silver nanoparticles on zinc oxide nanorods, were conducted as a proof of concept. The plasmon peak of the metal nanoparticle was split into two different plasmons due to the incorporation of a dielectric nanorod. These two plasmons exhibited different spatial distributions: one with lower energy located on the opposite side of the nanoparticle adjacent to the dielectric nanorod, and the other with higher energy near the nanorod. This splitting is thought to arise from symmetry-breaking in the surrounding dielectric environment induced by the addition of the nanorod. This is supported by simulation results where the dielectric environment was artificially inverted by switching the dielectric function of the vacuum area and the nanorod area, resulting in lower energy plasmons appearing near the nanorod.<br/>This work demonstrates that the composite of metal nanoparticles and dielectric nanorods exhibits non-monochromatic plasmonic behavior due to the symmetry-breaking of the dielectric environment. It provides additional insights into the complex structure of metal/dielectric composite systems and offers hints for designing composites to enhance their functionality.<br/><br/>[1] Clavero, César. <i>Nature Photonics</i> 8.2 (2014): 95-103.<br/>[2] Hohenester, Ulrich. <i>Computer Physics Communications</i> 185.3 (2014): 1177-1187.