Institut des
NanoSciences de Paris
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Thesis Defense - Cyril Jean - Friday 23 june 2017 at 2 pm

Cyril Jean, team “Acoustics for nanosciences

Single nanowires as model systems to study acoustic confinement in nanostructures

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Abstract

Vibrational dynamics of individual nano-objects is studied experimentally using pump and probe time-resolved spectroscopy. First, suspended and individual nano-objects avoid the inhomogeneous broadening of the acoustic properties and increase the acoustics confinement inside the nano-object. Elastic properties of metallic, semiconducting, porous, alloys or core-shell nanowires are thus studied in this advantageous geometry. The increased acoustic confinement in the suspended geometry also lead us to the observation of gigahertz coherent guided acoustic phonons in single copper nanowires and gold nanobeams. We show that the observation of propagating acoustic waves in nanoscale waveguides provide additional elastic informations. Furthermore, it gives the opportunity to unambiguously discriminate which mode is excited and detected using pump and probe time-resolved spectroscopy. On the contrary, nanowires can be used as monochromatic acoustic sources of longitudinal waves when deposited on a substrate. As the acoustic source radiates longitudinal waves inside the substrate, the spatiotemporal imaging of the generated acoustic field is undergone and the nanowire’s orientation is detected in transmission thanks to the acoustic field’s anisotropy. Finally, as another step toward acoustic microscopy with nanoscale spatial resolutions, an atomic force microscopy tip is used as a waveguide and an acoustic transducer with nanometric spatial extension.

Jury

Natalia Del Fatti (ILM, Université Claude Bernard de Lyon) - Protractor
Michel Orrit (Leiden University) - Protractor
Yannick Guillet (I2M, Université de Bordeaux) - Examinator
Régis Marchiano (Institut d’Alembert, UPMC) - Examinator
Olivier Thomas (IM2NP, Université Aix Marseille) - Examinator
Laurent Belliard (INSP, UPMC) - Thesis Director

Figure : Artistic 3D view : pump-probe spectroscopy of propagating acoustic waves in a gold nanobeam suspended above a silicon substrate.