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Séminaire MCBT

mardi 30 septembre à 11h00,
Salle Louis Weil, E424,

Orateur : Yanqing Liu (Institut Néel)
"Thermal properties of a nanostructured Ge:Mn thin film for thermoelectricity"

Abstract :

Nanostructured materials have great potential for applications on energy harvesting,including thermoelectricity. Under the idea of “electron crystal-phonon glass”, the goal is to ensure a good electrical conductivity while decreasing the thermal conductivity. As the mean free path of electron (1nm at 300K) and phonon (100nm at 300K) differ importantly, nanoscaled (between 1 and 100 nm) barriers can possibly create more phonon scatterings without affecting the electron transport. Here we present a study on the characterization of thermal properties of a model "electron crystal - phonon glass " material. The material is an epitaxial Ge:Mn thin film elaborated at CEA/INAC. It is a doped Ge matrix containing randomly distributed nanoscale (5 - 50 nm) Ge3Mn5 inclusions, grown by MBE (Molecular Beam Epitaxy). As the Ge matrix is perfectly crystalline and highly doped, the material possesses a good Seebeck coefficient and electrical conductivity. Models based on the Maxwell-Boltzmann equation predict a small thermal conductivity for this material. To confirm these predictions, we have developed an advanced experimentaltechnique based on 3-omega method for precise measurements of thermal conductivity of thin films. The measurement results on Ge:Mn thin films have indeed revealed a remarkably reduced thermal conductivity, by a factor of at least 15 compared to the value for bulk Ge sample (60 W/mK at 300K). More measurements on different samples of Ge:Mn thin film (having different inclusion diameters and different distributions) would help us to achieve qualitatively and quantitatively a better understanding of the heat transport mechanism in nanostructured materials, and favor the development of material for heat management and thermoelectricity.

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