Diffraction of Quantum Dots Reveals Nanoscale Ultrafast Energy Localization
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- 作者：Giovanni M. Vanacore ; Jianbo Hu ; Wenxi Liang ; Sergio Bietti ; Stefano Sanguinetti ; Ahmed H. Zewail
- 刊名：Nano Letters
- 出版年：2014
- 出版时间：November 12, 2014
- 年：2014
- 卷：14
- 期：11
- 页码：6148-6154
- 全文大小：383K
- ISSN：1530-6992
文摘
Unlike in bulk materials, energy transport in low-dimensional and nanoscale systems may be governed by a coherent 鈥渂allistic鈥?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.