title: Electron Energy Loss Spectroscopy Investigation into Symmetry in Gold Trimer and Tetramer Plasmonic Nanoparticle Structures.
abstract: We present a combined scanning transmission electron microscopy-electron energy loss spectroscopy (STEM-EELS) investigation into the mode symmetries of plasmonic nanoparticle trimer and tetramer structures. We obtain nanometer-resolved energy loss spectra for both trimer and tetramer structures and compare these to boundary element method simulations. We show that EELS, in conjunction with eigenmode simulations, offers a complete characterization of the individual superstructures, and we trace the evolution of both optically dark and bright modes and identify multipolar mode contributions. We then apply this technique to tetramer structures that exhibit an expanded range of mode symmetries for two-dimensional and three-dimensional self-assembled geometries. These findings provide a comprehensive experimental account of the available photonic states in self-assembled nanoparticle clusters.
authors.affiliation: School of Chemistry and Bio21 Institute, University of Melbourne , Parkville, Victoria 3010, Australia.
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Barrow
authors.affiliation: Department of Materials Science and Metallurgy, University of Cambridge , 27 Charles Babbage Road, Cambridge CB3 0FS, United Kingdom.
authors.forename: Sean M
authors.initials: SM
authors.lastname: Collins
authors.affiliation: Materials Science and Engineering, McMaster University , Hamilton, Ontario L8S 4L8, Canada.
authors.forename: David
authors.initials: D
authors.lastname: Rossouw
authors.affiliation: Chemistry Department, Monash University , Clayton, Victoria 3800, Australia.
authors.forename: Alison M
authors.initials: AM
authors.lastname: Funston
authors.affiliation: Materials Science and Engineering, McMaster University , Hamilton, Ontario L8S 4L8, Canada.
authors.forename: Gianluigi A
authors.initials: GA
authors.lastname: Botton
authors.affiliation: Department of Materials Science and Metallurgy, University of Cambridge , 27 Charles Babbage Road, Cambridge CB3 0FS, United Kingdom.
authors.forename: Paul A
authors.initials: PA
authors.lastname: Midgley
authors.affiliation: School of Chemistry and Bio21 Institute, University of Melbourne , Parkville, Victoria 3010, Australia.
authors.forename: Paul
authors.initials: P
authors.lastname: Mulvaney
keywords: STEM−EELS; electron energy loss spectroscopy; nanoparticle assemblies; non-negative matrix factorization; surface plasmon