Carbon nanotubes grafting for positive electrodes of lithium/sulfur cells
In a view to develop electric vehicles, researches on lithium batteries are now focusing on sulfur active material. Indeed, this new system should allow to produce cheap and high energy batteries of about 600 Wh/kg. While being developed for more than 40 years, the limitations of such a system are still quite problematic: elemental sulfur is an electronic insulator, sulfur and intermediate lithium polysulfides are soluble in the electrolyte and final discharge product Li2S is non-soluble and insulating too.
This post-doctoral position will thus aim at improving the performances of the sulfur positive electrode, by combining :
- Carbon nanotubes that will allow to improve the electronic conductivity of the positive electrode, as well as to provide a substrate for sulfur grafting
- Disulfide functions that will be grafted on the nanotubes. Thanks to this chemical grafting of active material, the electrochemical reaction would occur without leading to sulfur and polysulfides dissolution, thus leading to higher capacity and cyclability along with lower self-discharge.
Crystalline materials for the selective extraction of monovalent metal cations: understanding the link between the crystalline structure and the selectivity
The selective extraction of monovalent metal cations from aqueous solutions have complex compositions is a key step in many energy-related fields. In this work, specific adsorbents for Cs, to decontaminate effluents produced by the nuclear industry, and for Li, to extract this strategic metal for the development of batteries, will be studied. Due to their modularity in terms of porosity and structure, crystalline oxides (as zeolites) are promising for the selective extraction of such cations. With a view to understand the role of their microstructure on their sorption/desorption performances and mechanisms, identify the selective sorption sites within these crystal structures is crucial.
For that purpose, the objective of this research work is, on the one hand, to synthesize crystal structures allowing the selective sorption of Cs or Li. Then, by using fine characterization techniques at the atomic scale as well as structures reconstruction effort, we will identify the location of selective sorption sites within these materials and, in this way, better understand their sorption mechanisms and properties.
For this post-doctoral position, we are looking for a PhD in material science with strong skills in synthesis and characterization of crystalline materials by X-ray diffraction. Experience in the study of crystalline oxides, such as zeolites, would be an advantage.
New electrode materials for Na-ion batteries
Na-ion battery is a challenging technology to replace Li-ion battery as it is cost competitve and may allow better cycle life. Sodium has also similar property to Lithium (light and electronegative element).
The eletrochemistry of the sodium is somewhat different of lithium with much less studies reported in the litterature.
The work will consist in the elaboration and characterization of promising electrode materials for Na-ion batteries.
Development of innovative metal contacts for 2D-material field-effect-transistors
Further scaling of Si-based devices below 10nm gate length is becoming challenging due to the control of thin channel thickness. For gate length smaller than 10nm, sub-5nm thick Si channel is required. However, the process-induced Si consumption and the reduction of carrier mobility in ultrathin Si layer can limit the channel thickness scaling. Today, the main contenders that allow the extension of the roadmap to ultra-scaled devices are 2D materials, particularly the semiconducting transition metal dichalcogenides (TMD). Due to their unique atomically layered structure, they offer improved immunity to short-channel-effects in comparison to usual Si-based field-effect-transistors (FETs). This makes them very attractive for the application of more-Moore electronics.
However, the scalability of MOSFET device and the introduction of new material make source and drain contact a major issue. If many efforts have been made, in the past years, to reduce Fermi level pinning and Schottky barrier height, for many, these approaches are not industrially scalable. The main objective of this work is then to propose an in-depth understanding of electrical contact characteristics (based on different material) to identify the lowest contact resistance. The processes involved, offering an optimal contact resistance, must be compatible with wafer-scale processing for an integration in our 200/300mm advanced CMOS platform. The post-doc will in-depth study mechanisms enabling the formation of small contact resistances (between MoS2 and metal). It will have to identify the most promising contact material and to develop the associated deposition processes (ALD/PVD). Finally, electrical characterization of contact will be performed to qualify both material and interfaces enabling optimal operation of future 2D FETs
3D sequential integration
3D integration is currently under great investigation because it offers a solution to keep increasing transistor density while relaxing the constraint on the transistor’s dimension and it eases the co integration of highly heterogeneous technologies compared to a planar scheme.
3D sequential integration offers the possibility of using the third-dimension potential: two stacked layers can be connected at the transistor scale. This contrasts with 3D parallel integration, which is limited to connecting blocks of a few thousand transistors. However, its implementation faces the challenge of being able to process a high performance top transistor at low temperature in order to preserve the bottom FET from any degradation, as the stacked FETs are fabricated sequentially.
Modelling of actinide electrorefining
Modelling of an actinide electrorefining process
In the frame of the SACSESS European project CEA, ITU and CNRS are studying jointly a pyrochemical process for the reprocessing of spent nuclear fuels by electrolysis in molten chloride salts.
The main objective of the proposed post-doctoral work concerns the modelling of electrorefining runs onto aluminium cathodes using U-Pu-Zr-Am-Gd-Nd-Ce-Y metallic alloy. The modelling aims to evaluate the efficiency of this electrolytic process in terms of separation factors and to optimize the process flow sheets for a safe nuclear materials management.
Development and application of TERS/TEPL technique for advanced characterization of materials
TERS/TEPL (Tip-Enhanced Raman Spectroscopy and Tip-Enhanced Photoluminescence) are powerful analytical techniques developed for nanoscale material characterization. The recent acquisition of a unique and versatile TERS/TEPL equipment at PFNC (Nano-characterization Platform) of CEA LETI opens up new horizons for materials characterization. This tool combines Raman spectroscopy, photoluminescence, and scanning probe microscopy. It features multi-wavelength capabilities (from UV to NIR), allowing a wide range of applications and providing unparalleled insights into the composition, structure, and mechanical/electrical properties of materials at nanoscale resolution. The current project aims to develop and accelerate the implementation of the TERS/TEPL techniques at PFNC to fully exploit its potential in diverse ongoing projects at CEA-Grenoble (LETI/LITEN/IRIG) and with its partners.
Immunotargeting of based-organic nanoparticles for clinical applications
The project aims to tailor-make based-organic nanocarrier enabling to target antibodies to increase the efficacy of therapy (more particularly mantle cell lymphoma) for clinical applications. Our group has developed a unique delivery system based on lipid nanoparticles for imaging and therapeutic purposes since the last 6 years. Based on this technology, the candidate will:
- optimize the targeting of specific ligands into organic nanoparticles (bioconjugate chemistry)
- optimize the encapsulation of drugs in the immunotargeted nanoparticles
- assess the physico-chemical characterization of all nanoparticles
- evaluate the binding affinity of doped and targeted nanoparticles
Modelling of interstitial cluster evolution in bcc metals after helium implantation
Under irradiation, structural materials inside nuclear reactors undergo changes in mechanical properties, which result from the formation of point defect clusters, such as cavities (clusters of vacancies) and interstitial dislocation loops (clusters of self-interstitial atoms). Understanding the formation processes of such clusters is thus of prime importance. Recently, three-dimensional interstitial clusters, known as C15 clusters, have been shown theoretically to be highly stable in iron [1]. In order to detect such clusters experimentally, an idea is to make them grow, as shown for dislocation loops after helium implantation [2].
This approach will be carried out experimentally in various bcc metals in the framework of the ANR project EPigRAPH, in collaboration with Chimie ParisTech, GEMaC and LPS.
In this project, the following modelling tasks will be performed by the postdoc:
- DFT calculations will be done to obtain the energetic properties of point defects and point defect clusters in the bcc metals envisaged in the project.
- These data will then be used to parameterize a kinetic model based on cluster dynamics [3]. This formalism is particularly well adapted to simulate the evolution of point defect clusters over long physical times.
The modelling work will be performed in close collaboration with another postdoc working on the experimental part.
[1] M. C. Marinica, F. Willaime, J.-P. Crocombette, Phys. Rev. Lett. 108 (2012) 025501
[2] S. Moll, T. Jourdan, H. Lefaix-Jeuland, Phys. Rev. Lett. 111 (2013) 015503
[3] T. Jourdan, G. Bencteux, G. Adjanor, J. Nucl. Mater. 444 (2014) 298
Predictive design of heat management structures
Heat management is a paramount challenge in many cutting edge technologies, including new GaN electronic technology, turbine thermal coatings, resistive memories, or thermoelectrics. Further progress requires the help of accurate modeling tools that can predict the performance of new complex materials integrated in these increasingly demanding novel devices. However, there is currently no general predictive approach to tackle the complex multiscale modeling of heat flow through such nano and micro-structured systems. The state of the art, our predictive approach “ShengBTE.org”, currently covers the electronic and atomistic scales, going directly from them to predict the macroscopic thermal conductivity of homogeneous bulk materials, but it does not tackle a mesoscopic structure. This project will extend this predictive approach into the mesoscale, enabling it to fully describe thermal transport from the electronic ab initio level, through the atomistic one, all the way into the mesoscopic structure level, within a single model. The project is a 6 partner effort with complementary fields of expertise, 3 academic and 3 from industry. The widened approach will be validated against an extensive range of test case scenarios, including carefully designed experimental measurements taken during the project. The project will deliver a professional multiscale software permitting, for the first time, the prediction of heat flux through complex structured materials
of industrial interest. The performance of the modeling tool will be then demonstrated in an industrial setting, to design a new generation of substrates for power electronics based on innovating layered materials. This project is expected to have large impacts in a wide range of industrial applications, particularly in the rapidly evolving field of GaN based power electronics, and in all new technologies where thermal transport is a key issue.