Description du sujet de thèse

The development of thermal switches to control heat flows would significantly improve the efficiency of solid-state refrigeration systems and could be used for novel computing strategies. Recently, an original mechanism based on the interaction between phonons and domain walls in ferroelectric materials has been proposed to develop compact and efficient thermal conductivity switches over a wide temperature range. First results on bulk materials [1] and thin films are promising [2], but reaching higher performances requires higher density of domain walls and no substrates that may short-circuit heat flows.

Freestanding membranes are ideal candidates. Modifying the thickness of the ferroelectric membrane and modifying mechanical boundary conditions should have a marked effect on the ferroelectric domain structure. Typically, we expect the ferroelectric domain size to decrease with decreasing thickness. For this PhD thesis, we will investigate freestanding membranes of perovskite oxides, e.g. BaTiO3, where we want to control the topology and size of ferroelectric domains. These materials will be studied as freestanding membranes of different thicknesses and compositions
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The student will participate in the material growth and the fabrication of the oxide membranes and their characterisation. They will learn how to characterise ferroelectric membranes using Raman spectroscopy, piezoresponse force microscopy and thermoreflectance, as function of temperature. They will acquire knowledge of sample preparation, optical and surface probe characterisation techniques, and statistical data analysis.

The candidate must have a master's degree in Physics, Chemistry or Materials Sciences. They must be motivated and dynamic with strong abilities for experimental work, a good command of the English language is required both written and oral (at least B2 level). Internship experience in a research laboratory will be appreciated. Experience in 2D materials and/or ferroelectric materials would be a plus.

[1] P. Limelette, … G. F. Nataf, Influence of ferroelastic domain walls on thermal conductivity, Phys. Rev. B 108, 144104 (2023). [2] L. Féger … G. F. Nataf, Lead-Free Room-Temperature Ferroelectric Thermal Conductivity Switch Using Anisotropies in Thermal Conductivities, Phys. Rev. Mater. 8, 094403 (2024).

Contexte de travail

The PhD student will work within the GREMAN laboratory (UMR CNRS 7347), which has strong expertise in ferroelectric oxides (from their growth to their integration into devices, including their complete characterization), in 2D materials, and on the measurement of thermal transport. They will work both in the cities of Tours and Blois. This project is part of the ERC Starting Grant “DYNAMHEAT”. In this context, the doctoral student will join a team of 3 PhD students and 1 postdoc.

Le poste se situe dans un secteur relevant de la protection du potentiel scientifique et technique (PPST), et nécessite donc, conformément à la réglementation, que votre arrivée soit autorisée par l'autorité compétente du MESR.