At short length scales phonon transport is ballistic: the thermal resistance of semiconductors and insulators is quantized and length independent. At long length scales, on the other hand, transport is diffusive and resistance arises as a result of the scattering processes experienced by phonons. In many cases of interest, however, these two transport regimes coexist. Here we propose a first-principles approach to treat quasiballistic phonon transport where diffusive and ballistic phonons receive separate theoretical treatments.
Partitioning the overall phonon population for a given transport length is performed examining the mean free paths obtained from the solution of the Boltzmann transport equation and allowing only diffusive phonons to participate in anharmonic phonon-phonon scattering processes. We present results for Si and diamond, discussing the crossover from ballistic to diffusive transport as the length scale and/or the temperature increases and compute the relative contribution of ballistic and diffusive phonons to the thermal conductance in each transport condition.
Sustainable energy conversion & storage systems
Quasiballistic phonon transport from first principles
Pol Torres, Miquel Royo, Miquel López-Suárez, Junichiro Shiomi, and Riccardo Rurali
The development of high energy density battery technologies based on divalent metals as the negative electrode is very appealing. Ca and Mg are especially interesting choices due to their combination of low standard reduction potential and natural abundance.
Interfacial thermal transport plays a prominent role in the thermal management of nanoscale objects and is of fundamental importance for basic research and nanodevices. At metal/insulator interfaces, a configuration commonly found in electronic devices, heat transport strongly depends upon the effective energy transfer from thermalized electrons in the metal to the phonons in the insulator.
The global energy demand continues to grow both due to the increasing population and wealth. As one of the potential solutions, renewable energy resources can relieve the pressure on conventional energy sources. However, due to fluctuations in both supply and demand, they need to be complemented with load-leveling technologies.
We present a method to dissolve carbon nanotubes that simultaneously allows to prepare n-doped films. These films are composed of thinner bundles of longer tubes when compared to films prepared using surfactants and sonication.
Conspectus Over the past 30 years, the engineering of plasmonic resonances at the nanoscale has progressed dramatically, with important contributions in a variety of different fields, including chemistry, physics, biology, engineering, and medicine. However, heavy optical losses related to the use of noble metals for the fabrication of plasmonic structures hindered their application in various settings.