Unlike in bulk materials, energy transport in low-dimensional and nanoscale systems may be governed by a coherent ballistic behavior of lattice vibrations, the phonons. If dominant, such behavior would determine the mechanism for transport and relaxation in various energy-conversion applications. In order to study this coherent limit, both the spatial and temporal resolutions must be sufficient for the length-time scales involved. Here, we report observation of the lattice dynamics in nanoscale quantum dots of gallium arsenide using ultrafast electron diffraction. By varying the dot size from h = 11 to 46 nm, the length scale effect was examined, together with the temporal change. When the dot size is smaller than the inelastic phonon mean-free path, the energy remains localized in high-energy acoustic modes that travel coherently within the dot. As the dot size increases, an energy dissipation toward low-energy phonons takes place, and the transport becomes diffusive. Because ultrafast diffraction provides the atomic-scale resolution and a sufficiently high time resolution, other nanostructured materials can be studied similarly to elucidate the nature of dynamical energy localization.

Vanacore, G., Hu, J., Liang, W., Bietti, S., Sanguinetti, S., Zewail, A. (2014). Diffraction of Quantum Dots Reveals Nanoscale Ultrafast Energy Localization. NANO LETTERS, 14(11), 6148-6154 [10.1021/nl502293a].

Diffraction of Quantum Dots Reveals Nanoscale Ultrafast Energy Localization

Vanacore, G;Bietti, S;Sanguinetti, S;
2014

Abstract

Unlike in bulk materials, energy transport in low-dimensional and nanoscale systems may be governed by a coherent ballistic behavior of lattice vibrations, the phonons. If dominant, such behavior would determine the mechanism for transport and relaxation in various energy-conversion applications. In order to study this coherent limit, both the spatial and temporal resolutions must be sufficient for the length-time scales involved. Here, we report observation of the lattice dynamics in nanoscale quantum dots of gallium arsenide using ultrafast electron diffraction. By varying the dot size from h = 11 to 46 nm, the length scale effect was examined, together with the temporal change. When the dot size is smaller than the inelastic phonon mean-free path, the energy remains localized in high-energy acoustic modes that travel coherently within the dot. As the dot size increases, an energy dissipation toward low-energy phonons takes place, and the transport becomes diffusive. Because ultrafast diffraction provides the atomic-scale resolution and a sufficiently high time resolution, other nanostructured materials can be studied similarly to elucidate the nature of dynamical energy localization.
Articolo in rivista - Articolo scientifico
ballistic transport; energy localization; Femtosecond diffraction; quantum dots; Condensed Matter Physics; Bioengineering; Chemistry (all); Materials Science (all); Mechanical Engineering
English
2014
14
11
6148
6154
none
Vanacore, G., Hu, J., Liang, W., Bietti, S., Sanguinetti, S., Zewail, A. (2014). Diffraction of Quantum Dots Reveals Nanoscale Ultrafast Energy Localization. NANO LETTERS, 14(11), 6148-6154 [10.1021/nl502293a].
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10281/68279
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