title: Mode Coupling in Plasmonic Heterodimers Probed with Electron Energy Loss Spectroscopy.
abstract: While plasmonic antennas composed of building blocks made of the same material have been thoroughly studied, recent investigations have highlighted the unique opportunities enabled by making compositionally asymmetric plasmonic systems. So far, mainly heterostructures composed of nanospheres and nanodiscs have been investigated, revealing opportunities for the design of Fano resonant nanostructures, directional scattering, sensing and catalytic applications. In this article, an improved fabrication method is reported that enables precise tuning of the heterodimer geometry, with interparticle distances made down to a few nanometers between Au-Ag and Au-Al nanoparticles. A wide range of mode energy detuning and coupling conditions are observed by near field hyperspectral imaging performed with electron energy loss spectroscopy, supported by full wave analysis numerical simulations. These results provide direct insights into the mode hybridization of plasmonic heterodimers, pointing out the influence of each dimer constituent in the overall electromagnetic response. By relating the coupling of nondipolar modes and plasmon-interband interaction with the dimer geometry, this work facilitates the development of plasmonic heterostructures with tailored responses, beyond the possibilities offered by homodimers.
authors.affiliation: Microsystems Laboratory, Institute of Microtechnique, École Polytechnique Fédérale de Lausanne , 1015 Lausanne, Switzerland.
authors.forename: Valentin
authors.identifier: 0000-0002-1393-3198
authors.initials: V
authors.lastname: Flauraud
authors.affiliation: Nanophotonics and Metrology Laboratory, École Polytechnique Fédérale de Lausanne , 1015 Lausanne, Switzerland.
authors.forename: Gabriel D
authors.initials: GD
authors.lastname: Bernasconi
authors.affiliation: Nanophotonics and Metrology Laboratory, École Polytechnique Fédérale de Lausanne , 1015 Lausanne, Switzerland.
authors.forename: Jérémy
authors.identifier: 0000-0001-9598-9074
authors.initials: J
authors.lastname: Butet
authors.affiliation: Interdisciplinary Centre for Electron Microscopy (CIME), École Polytechnique Fédérale de Lausanne , 1015 Lausanne, Switzerland.
authors.forename: Duncan T L
authors.identifier: 0000-0003-4350-8587
authors.initials: DTL
authors.lastname: Alexander
authors.affiliation: Nanophotonics and Metrology Laboratory, École Polytechnique Fédérale de Lausanne , 1015 Lausanne, Switzerland.
authors.forename: Olivier J F
authors.initials: OJF
authors.lastname: Martin
authors.affiliation: Microsystems Laboratory, Institute of Microtechnique, École Polytechnique Fédérale de Lausanne , 1015 Lausanne, Switzerland.
authors.forename: Jürgen
authors.initials: J
authors.lastname: Brugger
keywords: bimetallic antennas; eigenmodes; electron beam lithography; electron energy loss spectroscopy; optical nanoantennas; plasmonic heterostructures