title: Mechanical Coupling in Gold Nanoparticles Supermolecules Revealed by Plasmon-Enhanced Ultralow Frequency Raman Spectroscopy.
abstract: Acoustic vibrations of assemblies of gold nanoparticles were investigated using ultralow frequency micro-Raman scattering and finite element simulations. When exciting the assemblies resonantly with the surface plasmon resonance of electromagnetically coupled nanoparticles, Raman spectra present an ultralow frequency band whose frequency lies below the lowest Raman active Lamb mode of single nanoparticles that was observed. This feature was ascribed to a Raman vibration mode of gold nanoparticle "supermolecules", that is, nanoparticles mechanically coupled by surrounding polymer molecules. Its measured frequency is inversely proportional to the nanoparticle diameter and sensitive to the elastic properties of the interstitial polymer. The latter dependence as well as finite element simulations suggest that this mode corresponds to the out-of-phase semirigid translation (l = 1 Lamb mode) of each nanoparticle of a dimer inside the matrix, activated by the mechanical coupling between the nanoparticles. These observations were permitted only thanks to the resonant excitation with the coupling plasmon excitation, leading to an enhancement up to 10(4) of the scattering by these vibrations. This enhanced ultralow frequency Raman scattering thus opens a new route to probe the local elastic properties of the surrounding medium.
authors.affiliation: Institut Lumière Matière, Université de Lyon, Université Claude Bernard Lyon 1, UMR CNRS 5306 , 69622 Villeurbanne, France.
authors.forename: A
authors.initials: A
authors.lastname: Girard
authors.affiliation: Institut Lumière Matière, Université de Lyon, Université Claude Bernard Lyon 1, UMR CNRS 5306 , 69622 Villeurbanne, France.
authors.forename: H
authors.initials: H
authors.lastname: Gehan
authors.affiliation: Institut Lumière Matière, Université de Lyon, Université Claude Bernard Lyon 1, UMR CNRS 5306 , 69622 Villeurbanne, France.
authors.forename: A
authors.initials: A
authors.lastname: Crut
authors.affiliation: Institut Lumière Matière, Université de Lyon, Université Claude Bernard Lyon 1, UMR CNRS 5306 , 69622 Villeurbanne, France.
authors.forename: A
authors.initials: A
authors.lastname: Mermet
authors.affiliation: Laboratoire Interdisciplinaire Carnot de Bourgogne, UMR 6303 CNRS-Université de Bourgogne Franche Comté , 9 Avenue A. Savary, BP 47 870, F-21078 Dijon Cedex, France.
authors.forename: L
authors.initials: L
authors.lastname: Saviot
authors.affiliation: Institut Lumière Matière, Université de Lyon, Université Claude Bernard Lyon 1, UMR CNRS 5306 , 69622 Villeurbanne, France.
authors.forename: J
authors.initials: J
authors.lastname: Margueritat
keywords: Brillouin; Lamb; Raman; Vibration; gold NPs dimer; mechanical properties