Reference : UMR5295-JERMAI-001
Workplace : TALENCE
Date of publication : Wednesday, August 3, 2022
Scientific Responsible name : Jérémie Maire
Type of Contract : PhD Student contract / Thesis offer
Contract Period : 36 months
Start date of the thesis : 1 January 2023
Proportion of work : Full time
Remuneration : 2 135,00 € gross monthly
Description of the thesis topic
Context: To devise efficient thermal management solutions, especially at small scales, it is critical to understand thermal transfer mechanisms, and therefore measure heat transfer and thermal properties. Numerous such studies have been performed on specially designed samples, whereas it remains challenging to characterize functioning devices. Indeed, despite techniques to access temperature information in a material from surface measurements, it is of great scientific and technological interest to map temperature and thermal properties in three dimensions within a working device.
This is particularly true in the current context of a smart society that rely increasingly heavily on autonomous devices and sensors with multiple components integrated on-chip. Supercapacitors are a promising energy storage solution for applications requiring higher charge/discharge rates and better cyclability than batteries (up to 1000x that of Li-ion batteries). The performances and characteristics of these devices are strongly impacted by external temperatures and heat dissipation during the charge/discharge cycles, especially via the Joule effect.  On-chip micro-supercapacitors (MSCs) in particular are gaining traction but few studies focus on their thermal properties. Measurements will provide invaluable benefits to future designs but remain challenging.
MSCs are inherently multiscale devices, whether in size, from nanoscale to millimeter scale, in time, from sub-millisecond to hours. They are also heterogeneous, as the electrodes, the substrate and the electrolyte are made of different materials. Therefore, it is necessary to develop a technique catered to multiscale and heterogeneous devices that account for multiphysical phenomena, including conduction, radiation and potentially convection at multiple spatio-temporal scales. Optical techniques are ideal to access the combined timescales and dimensions. Infrared wavelengths have the advantage over the visible range that they can be used to access information in the depth of materials, as many common materials such as silicon are semi-transparent in the mid-IR range. Inversion methods are then instrumental in retrieving the properties of the materials and eventually reconstructing heat sources within devices. [2,3]
Objectives: This PhD has two main objectives. The first goal will be to develop an experimental system capable of reconstructing the 3D time-dependent temperature field in a heterogeneous microstructure using contactless optical techniques. Practically, the candidate will start from a thermo-transmittance characterization setup currently in development and further improve it to obtain time-resolved information in three dimensions.
The second goal will be to apply this new technique to the complete thermal characterization of MSCs in operation. From the measurements, we will retrieve the temporal thermal behavior of the different materials, including T(x,y,z,t) and the thermal properties as detailed above. We will then provide thermal design guidelines based on the data obtained with different MSC designs, especially thermal interface resistances.
Approach: The candidate will develop a confocal time-resolved thermo-transmittance system to access the temperature information within the devices. A supercontinuum laser accordable in wavelength from visible to the mid-IR will be used to avoid the issue of the opacity of solid materials. The broad range of wavelengths has two additional advantages. First it can be adjusted to fit the optical properties of many materials, providing versatility to the system. In a second step, it will enable confocal spectroscopic measurements, which will provide additional information about the local chemistry of the materials, such as the electrolyte. Combined with confocal microscopy, this will enable the 3D mapping of the thermophysical properties of the device. The candidate will then post-process the obtained data. The first point is to improve the resolution beyond the diffraction limit. This will be done by combining displacements of the samples with steps of 100 nm, with an algorithm that has been recently developed in the team. Obtaining the thermal properties of the materials and reconstructing the spatio-temporal profile of the heat sources will be done with inversion methods, which also constitute one of the core know-hows of the host team. The quadrupole method, among other analytical and numerical models, will be applied to 3D temperature fields to extract thermal interface resistances. To achieve the second objective, namely the characterization of MSCs, the candidate will also be expected to fabricate some samples in clean room that involve lithography and metal evaporation steps. These samples will be used to test the performances and the limits of the optical setup. By collaborating with scientific teams specialized in the investigation of micro-energy devices, we will have access to state-of-the-art devices to propose design and integration guidelines for their MSCs.
1. Xiong G., Kundu A., Fisher T. S. Thermal Effects in Supercapacitors; SpringerBriefs in Applied Sciences and Technology; Springer International Publishing: Cham, 2015.
2. Groz M.-M., Abisset-Chavanne E., Meziane A., Sommier A., Pradère C. "Bayesian Inference for 3D Volumetric Heat Sources Reconstruction from Surfacic IR Imaging". Appl. Sci. 10 (5), 1607, (2020).
3. Pailhes J., Pradere C., Battaglia J.-L., Toutain J., Kusiak A., Aregba A.W., Batsale J.-C. "Thermal Quadrupole Method with Internal Heat Sources". Int. J. Therm. Sci. 53, 49–55, (2012).
The candidate will be hosted in the Thermal Imaging Field Characterization group in I2M which has a strong expertise in experimental heat transfer characterization (IR thermo-spectroscopy, tomography, photothermal measurements and the flying spot technique to cite the main ones) with numerical inverse methods that have been successfully used for super-resolution imaging and reconstructing embedded 3D heat sources.
I2M is a research institute located on the campus of the University of Bordeaux. You will work alongside other PhD students and several permanent researchers with proven expertise in the field. The campus is 15 minutes away from the center of the city of Bordeaux which is listed as a “Word Heritage Site” by UNESCO. You will be under a CNRS work contract with competitive salary and included health insurance.
Academic background: Master degree or equivalent in physics, engineering, optics or related fields
Required knowledge and skills: Optics and optical systems, Spectroscopy, Heat transfer. Additional required skills:
- Practical experience with softwares such as Matlab and Labview.
- Business level English required.
- Hands-on laboratory experience in optics.
What we expect: The candidate should be active and rigorous, curious and eager to perform experimental work. He should also have good communication skills and enjoy working in a collaborative environment. He will attend regular group meetings and is expected to disseminate his results in conferences as well as through written publications.
This PhD offer is a highly experimental work combining experimental development, micro-fabrication and optics within the ANR project TTIMSCAP. The candidate will be supervised and helped by people with extensive experience in these fields (Jérémie Maire (Researcher), Stéphane Chevalier (Associate Professor) et Jean-Luc Battaglia (Professor)) but is expected to contribute and take a leading role in the main aspects of the project.
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