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ÉTUDE FEMTOSECONDE DE LA DYNAMIQUE ÉLECTRONIQUE ET VIBRATIONNELLE DANS DES NANOPARTICULES MÉTALLIQUES

Abstract : Electronic relaxation processes have been selectively studied in bulk and confined noble metals using high sensitivity femtosecond pump/probe techniques based on a home made titanium/sapphire laser, delivering 20 fs pulses tuneable in the 820 - 1080 nm range.
Using a probe energy at the threshold of the interband transitions, we have shown that internal thermalization of the electronic gas can be followed. This takes place on a 350 fs time scale in bulk silver (500 fs in gold). A large reduction of this interaction time has been observed for particles with a radius smaller than 5 nm. This has been ascribed to an increase of the electron-electron scattering rate due to the reduction of the screening effects close to the particle surface. Numerical simulations have also been performed by solving the Boltzmann equation and compared to the experimental data.
For probing out of resonance we have shown that the external thermalization dynamics (involving electron/phonons interactions) can be selectively studied. The characteristic electron-lattice energy exchange time is 850 fs in bulk silver (1 ps for gold). As for the internal thermalization, a strong reduction of this time has been observed for small sizes. This effect is independent of the environment, of the sample preparation technique and of the amplitude of the perturbation (in the low perturbation regime).
On a long time scale, (about 10 ps), we have observed a periodic modulation of the transmission around the surface plasmon resonance, due to in phase excitation of the fundamental radial vibration mode in all the excited particles. Using this time resolved technique we have analysed the damping rate of those oscillations as a function of the environment and particle/matrix interface quality. In particular, this has been modified using a high pressure technique.
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https://tel.archives-ouvertes.fr/tel-00175114
Contributor : Christophe Voisin <>
Submitted on : Friday, September 28, 2007 - 10:31:20 AM
Last modification on : Thursday, March 5, 2020 - 6:25:58 PM
Long-term archiving on: : Thursday, April 8, 2010 - 10:14:50 PM

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  • HAL Id : tel-00175114, version 1

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Christophe Voisin. ÉTUDE FEMTOSECONDE DE LA DYNAMIQUE ÉLECTRONIQUE ET VIBRATIONNELLE DANS DES NANOPARTICULES MÉTALLIQUES. Matière Condensée [cond-mat]. Université Paris Sud - Paris XI, 2001. Français. ⟨tel-00175114⟩

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