Localized surface plasmon resonances (LSPR) occur in certain metals where electrons confined to the metal surface oscillate with similar frequency as the perturbation source, giving rise to localized electromagnetic fields. In this study we employ experimental and theoretical analyses to characterize LSPR in Alcore(Al2O3)shell nanoparticles with controlled morphologies. We perform simulations of LSPR using Boundary Element Methods, where the electron beam is passing at a 2.5 nm distance from the surface of an icosahedron-shaped Alcore(Al2O3)shell nanoparticles. The energy loss probability spectra show that for the mode located at an energy around 7 eV, the LSPR energy and intensity have lower values compared to other modes, when the impact factor is placed near a facet, edge and corner of the nanoparticle respectively. This agrees with our experiment, where we collected electron energy-loss spectroscopy-LSPR measurements near the surface of the nanoparticles using a monochromated 80 KeV electron source with 100 meV energy resolution. The experimental spectra appertaining to the edge and corner of the nanoparticle display an energy shift as a function of position of the electron beam with respect to the nanoparticle. By applying a Non-Negative Matrix Factorization algorithm, we de-coupled convoluted LSPR signals and attribute them to the geometry of the nanoparticle. This allowed us to map the coupling coefficient of the electron beam with the LSPR revealing the energy transfer path from the excitation source to the plasmonic nanoparticles. This study paves the way for a better understanding of the localization of LSPR in nanocatalysts with nano-engineered morphologies.

Date Published: 17 September 2018
PDF
Proc. SPIE 10725, Low-Dimensional Materials and Devices 2018, 107250H (17 September 2018); doi: 10.1117/12.2322948

Published in SPIE Proceedings Vol. 10725:
Low-Dimensional Materials and Devices 2018
Nobuhiko P. Kobayashi; A. Alec Talin; M. Saif Islam; Albert V. Davydov, Editor(s)