title: Optical Observation of Plasmonic Nonlocal Effects in a 2D Superlattice of Ultrasmall Gold Nanoparticles.
abstract: The advances in recent nanofabrication techniques have facilitated explorations of metal structures into nanometer scales, where the traditional local-response Drude model with hard-wall boundary conditions fails to accurately describe their optical responses. The emerging nonlocal effects in single ultrasmall silver nanoparticles have been experimentally observed in single-particle spectroscopy enabled by the unprecedented high spatial resolution of electron energy loss spectroscopy (EELS). However, the unambiguous optical observation of such new effects in gold nanoparticles has yet not been reported, due to the extremely weak scattering and the obscuring fingerprint of strong interband transitions. Here we present a nanosystem, a superlattice monolayer formed by sub-10 nm gold nanoparticles. Plasmon resonances are spectrally well-separated from interband transitions, while exhibiting clearly distinguishable blueshifts compared to predictions by the classical local-response model. Our far-field spectroscopy was performed by a standard optical transmission and reflection setup, and the results agreed excellently with the hydrodynamic nonlocal model, opening a simple and widely accessible way for addressing quantum effects in nanoplasmonic systems.
authors.affiliation: Department of Electrical and Computer Engineering, University of California, San Diego , 9500 Gilman Drive, La Jolla, California 92093-0407, United States.
authors.forename: Hao
authors.identifier: 0000-0002-0063-3153
authors.initials: H
authors.lastname: Shen
authors.affiliation: Department of Electrical and Computer Engineering, University of California, San Diego , 9500 Gilman Drive, La Jolla, California 92093-0407, United States.
authors.forename: Li
authors.initials: L
authors.lastname: Chen
authors.affiliation: Materials Science and Engineering, University of California, San Diego , 9500 Gilman Drive, La Jolla, California 92093-0418, United States.
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Ferrari
authors.affiliation: Department of Physics, National Tsing-Hua University , Hsinchu 30013, Taiwan.
authors.forename: Meng-Hsien
authors.initials: MH
authors.lastname: Lin
authors.affiliation: Department of Photonics Engineering, Technical University of Denmark , DK-2800 Kongens Lyngby, Denmark.
authors.forename: N Asger
authors.identifier: 0000-0001-7936-6264
authors.initials: NA
authors.lastname: Mortensen
authors.affiliation: Department of Physics, National Tsing-Hua University , Hsinchu 30013, Taiwan.
authors.forename: Shangjr
authors.initials: S
authors.lastname: Gwo
authors.affiliation: Department of Electrical and Computer Engineering, University of California, San Diego , 9500 Gilman Drive, La Jolla, California 92093-0407, United States.|Materials Science and Engineering, University of California, San Diego , 9500 Gilman Drive, La Jolla, California 92093-0418, United States.
authors.forename: Zhaowei
authors.initials: Z
authors.lastname: Liu
keywords: 2D superlattice; Surface plasmon resonances; hydrodynamic Drude−Lorentz model; nonlocal effect; ultrasmall AuNPs