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Reference : UMR5306-VALGIO-001
Workplace : VILLEURBANNE
Date of publication : Monday, May 25, 2020
Scientific Responsible name : Giordano
Type of Contract : PhD Student contract / Thesis offer
Contract Period : 36 months
Start date of the thesis : 1 October 2020
Proportion of work : Full time
Remuneration : 2 135,00 € gross monthly
Description of the thesis topic
This project deals with the study of novel materials for solving the thermal management issue in microelectronics and energy harvesting applications. One of the main challenges for our modern society consists in reducing the heat losses associated with energy consumption, amounting to about two thirds of the whole energy produced. In this context, nanostructuration has arisen as a promising approach, as the presence of interfaces and the inter-twining of different materials at the nanoscale has shown to effectively act on the quasi-particle responsible for heat transport – phonons – and possibly not on other functional properties.
We focus here on GeTe-based nanocomposites, made of nanometric crystalline grains of GeTe embedded in an amorphous matrix. GeTe is a so-called chalcogenide phase-change material (PCM) largely investigated for the novel technology of phase-change memory. PCM memories are non-volatile resistive memories where the information is coded through the amorphous to crystalline phase change of a PCM. The unique contrast of electronic properties between the two phases of the PCM is used to code the 1 or 0 bit in the memory cell. In PCM memory devices, the extremely rapid phase-change is assured through Joule heating of the material, which however requires high programming currents, leading to a very large local heating, which hinders any further miniaturization. Recently, nanostructuration has been found to greatly reduce the programming currents, indicating a drastic thermal conductivity reduction of the material. Such a reduction is expected to significantly enhance as well the ability of GeTe to convert heat into electric current (thermoelectric conversion), giving the perspective to use it to recycle the heat waste in the microelectronic devices.
In order to go beyond the proof of concept, it is necessary to understand how the nanostructuration will affect thermal and thermoelectric properties in GeTe nanocomposites, depending on a variety of parameters, such as the GeTe grain size, the film thickness, the amorphous phase properties.
This is the object of the nanoCHARME project founded by the Auvergne-Rhône-Alpes region, implying The Institute of Light and Matter, the Institut Néel, the CEA-LETI and the STMicroelectronic industrial company based in Crolles, Grenoble.
The objective of the project is to get a microscopic understanding of thermal transport properties in GeTe-based nanocomposites by investigating the thermal conductivity as a function of the different nanostructure parameter, and by studying the heat carriers in such material: electrons and atomic vibrations (phonons). The phonon spectrum will be measured by means of optical spectroscopies (Raman and Brillouin spectroscopy) as well as inelastic X-ray scattering at synchrotrons sources. The observation of the effect of the nanostructuration on the phonon spectrum will allow to understand the modifications in their contribution to thermal conductivity. The investigation of electronic transport properties (resistivity, charge carriers concentration) as well as of the seebeck coefficient will allow to understand the modifications in the electronic contribution to thermal transport, and assess the thermoelectric potential of the optimized nanocomposites.
The PhD student will be in charge of the thermal measurement by means of the 3w technique at the Néel Institut, and of phonon measurements at ILM and synchrotron sources.
He/She will also be in charge of the thermoelectric characterization of the nanocomposites at ILM.
At ILM the PhD student will work in the (Nano)materials for energy group (NME).
NME gathers experts in electric and thermal transport, and leads the Transport pole of ILMTech, gathering several experimental setups allowing for the electric/thermoelectric characterization spanning a large temperature range from 5 to 900 K. The originality of NME is its microscopic approach for the fundamental understanding of transport properties in materials for energy applications, relying on the expertise of S. Pailhes in electronic characterization with electron photoemission at laboratory and synchrotron sources and the expertise of both V. Giordano and S. Pailhès on optical phonon spectroscopy at laboratory and on inelastic scattering techniques at synchrotron and neutron sources.
At Néel Institute, the PhD student will work in the Thermodynamic of Small Systems group (TPS group). O. Bourgeois, in the TPS team, has developed since more than 15 years a renowned expertise in highly sensitive thermal measurements, especially on nano-objects and nanostructured thin films. This expertise has been widely used to study thermal properties of materials for energy applications and more generally heat management. The different experimental benches allow measurements from very low temperature (30 mK) up to above room temperature (400K).
The PhD project will take place in the context of the nanoCHARME consortium, allowing the student to be regularly in contact with the other partners of the project (CEA-LETI and STMicroelectronics) and exchange with experts in the chalcogenides synthesis and memory devices design and test, as well as with experts of the physics of chalcogenide phase-change materials. This will give him/her not only opportunities for educational growth but also contact with the industrial world, working in close collaboration with a CIFRE PhD student in charge of the samples synthesis.
This PhD thesis will be done in a very motivating scientific community structured around national organizations and meetings (GDR NAME Nanomaterials For Energy, C'Nano, SFP/JMC, GIS Thermoelectricity, International Thermoelectric Society) and international conferences (like E-MRS, Eurotherm, International Conference of Thermoelectricityetc…).
Profile and requested skills
The candidate must be graduated from an engineering school and/or with a Master 2 degree whose training focuses primarily on materials science and condensed matter physics. We are looking for a highly-motivated student with a strong interest in experimental physics and materials science. Interpersonal skills, dynamism, rigor and teamwork abilities will be appreciated. Candidates should be fluent in English and possibly with well-written English.
According to CNRS French regulations for a PhD
2135 €/month gross salary (1715.89€ net)
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