HDR

Jeudi 11 Janvier 2024 à 9h30.

The effect of nanoscale heterogeneities on phonon dynamics and thermal transport : a microscopic understanding

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Membres du jury / jury members :

P. Giura - Referee - Maître de conférence à Sorbonne-Université, IMPMC (Paris, France)
S. Volz - Referee - Research director at LIMMS (Tokyo, Japan)
I. Zardo - Referee - Associated Professor at University of Basel (Basel, Switzerland)
S. Dilhaire - Examiner - Professor at LOMA (Talence, France)
T. Niehaus - Examiner - Professor at University Claude Bernard Lyon 1
C. Sotomayor Torres - Examiner - Professor at ICN2 (Barcelona, Spain)

Résumé / Abstract :

With advances in nanoelectronics, and the need of novel and more efficient energy harvesting solutions, thermal management has arisen as one of the most urgent challenges. To reduce heat dissipation and improve the thermoelectric efficiency, the ultimate goal is a material with a glass-like thermal conductivity but still good electronic properties. One of the main strategies in the latter years has been to nanostructure the material, as interfaces at the nanoscale effectively scatter phonons, reducing their contribution to thermal transport. At this day, the microscopic mechanisms at play are not fully understood. A close look to phonon dynamics for wavelengths comparable to the nanostructure lengthscale is needed. This is the focus of my work.

Here I will specifically address two kinds of nanostructures: a nanocomposite made out of materials with a significant elastic contrast, and a nanophononic membrane, characterized by a periodic pattern of holes. In the former case I will show that phonon scattering from elastic nanoheterogeneities leads to phonon dynamics and thermal transport similar to glasses. In the latter case, I will evidence the presence of coherent phonon interference and its effect on phonon attenuation.

Finally, I will show that a glass-like thermal transport can also be found in some crystalline materials, where disorder is not alway important, arising from different microscopic mechanisms.

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