Acousto-plasmonic Hot Spots in Metallic Nano-Objects

• Published in: Nano letters Vol. 9; no. 11; pp. 3732 - 3738
• Main Authors: Large, Nicolas, Saviot, Lucien, Margueritat, Jérémie, Gonzalo, José, Afonso, Carmen N, Arbouet, Arnaud, Langot, Pierre, Mlayah, Adnen, Aizpurua, Javier
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 11-11-2009
• Subjects: Collective excitations (including excitons, polarons, plasmons and other charge-density excitations); Condensed Matter; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Exact sciences and technology; Low-dimensional structures (superlattices, quantum well structures, multilayers): structure, and nonelectronic properties; Materials Science; Mechanical and acoustical properties of condensed matter; Mechanical properties of nanoscale materials; Physics; Surface and interface electron states; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Deformation; Nanocolumn; Mechanical properties; Nanostructures; Raman spectroscopy; Surface plasmons; Time resolved spectra; Transients; Vibrations; Silver; Time resolution; Raman scattering; Vibrational modes; Elasticity theory
• ISSN: 1530-6984; 1530-6992
• DOI: 10.1021/nl901918a

We investigate the acousto-plasmonic dynamics of metallic nano-objects by means of resonant Raman scattering and time-resolved femtosecond transient absorption. We observe an unexpectedly strong acoustic vibration band in the Raman scattering of silver nanocolumns, usually not found in isolated nano-objects. The frequency and the polarization of this unexpected Raman band allow us to assign it to breathing-like acoustic vibration modes. On the basis of full electromagnetic near-field calculations coupled to the elasticity theory, we introduce a new concept of “acousto-plasmonic hot spots” which arise here because of the indented shape of the nanocolumns. These hot spots combine both highly localized surface plasmons and strong shape deformation by the acoustic vibrations at specific sites of the nano-objects. We show that the coupling between breathing-like acoustic vibrations and surface plasmons at the “acousto-plasmonic hot spots” is strongly enhanced, turning almost silent vibration modes into efficient Raman scatterers.