Wireless biological sensor using 2D materials (Graphene , Molybdenium disulfide)
The main goal of the post-doctoral position is the fabrication of a biological sensor using 2D materials and that can be remotely addressed thanks to a RF antenna simultaneously fabricated alongside the biosensor.
The post-doctoral associate will be in charge of the fabrication and characterization of the prototype. Starting from well-designed modelling, he/she will first establish a design architecture for the sensor and RF antenna. Once designed and sized, the post-doctoral associate will adapt existing transfer protocol of 2D materials to develop an innovative fabrication process for the sensor. He/she will then fabricate the first prototypes of the sensors. Consecutively he/she will validate first the remote addressing of the sensor via the RF antenna. Secondly he/she will lead biodétection tests to assess the sensitivity of the fabricated sensors. Finally, he/she will try to integrate Transition Metal Di-chalcogenides 2D materials (such as MoS2) to graphene sensors inside a hybrid 2D materials biological sensor. The goal here will be to boost operational sensitivity.
Charge to spin conversion in HgTe topological insulators
The intrinsic spin-momentum locking of Dirac fermions at the surface or interface of topological insulators opens the path towards novel spintronic effects and applications.
Strained HgTe/CdTe is a model topological insulator and a very good candidate to design and demonstrate new spintronic devices exploiting the very large charge to spin conversion efficiency expected for such 2D systems. This postdoc position aims at realizing the first demonstration of the direct charge to spin conversion in topological HgTe nanostructures and use this demonstration as a building block for spin based logic elements.
Design of new extractant molecules for uranium and plutonium separation
The subject of this postoctoral position is related to the optimization of the process used to separate uranium and plutonium from spent nuclear fuels. In the so called PUREX process currently in operation at La Hague reprocessing plant in France, the TBP (tri-n-butylphosphate) is used as extractant in the solvent extraction system. This molecule shows high affinity for uranium and plutonium at oxidation states VI and IV and allows to reach high decontamination factors versus fission products. Nevertheless, the separation of U from Pu requires the use of reducing and anti-nitrous reagents to allow the back-extraction of Pu(III). In order to improve the process, researches are under way to design new extractant molecules which would allow to separate U and Pu without redox chemistry and with high selectivity versus fission products (Ru, Tc, Cs, lanthanides, etc) and other actinides (especially Np). The objective of the postdoctoral associate will be to select the molecules, to determine synthesis routes and to perform their synthesis using equipment available in the LCPE laboratory (micro-wave, flash chromatography, NMR, HPLC-MS, GC-HRMS) at the CEA Marcoule.
Modeling silicon-on-insulator quantum bits
Quantum information technologies on silicon have raised an increasing interest over the last five years. CEA is pushing forward its own original platform based on the “silicon-on-insulator” (SOI) technology. The information is stored in the spin of carrier(s) trapped in quantum dots, which are etched in a thin silicon film and are controlled by metal gates. SOI has many assets: the patterning of the thin film can produce smaller, hence more scalable qubits; also, the use of the silicon substrate beneath as a back gate provides extra control over the quantum bits (qubits).
Many aspects of the physics of silicon spin qubits are still poorly understood. It is, therefore, essential to complement the experimental activity with state-of-the-art modeling. For that purpose, CEA is actively developing the "TB_Sim" code. The aims of this 2-year post-doctoral position are to model spin manipulation and readout in SOI qubits, and to model decoherence and relaxation at the atomistic scale using TB_Sim. This modeling work will be strongly coupled to the experimental activity in Grenoble. The candidate will have access to experimental data on state-of-the-art devices.
Improvement of microfluidic tools for kinetic data measurement
The development and modeling chemical processes require the acquisition of many thermodynamic and kinetic data . Conventional methods for measuring these data generally involve significant amounts of reagents. In particular for the reactive crystallisation, where the stochastic nature of nucleation requires the realization of a large number of experiments . The subject is to continue the work already done on the development of a dedicated chip to measure rapid nucleation kinetics . Firstly , the validity of kinetic measurements obtained by microfluidics technique will be evaluated and optimized based on well known and non- radioactive chemical systems . The microfluidic tool will then be used to study the sensitivity of these reactions to various operating parameters ( supersaturation , impurities , additives, etc. . ), before considering its transposition to nuclear processes such as decontamination of radioactive effluents. Finally, a new chip design could be proposed for the measurement of kinetics of liquid-liquid extraction , in connection with the development of new hydrometallurgical processes.
Multiscale Modelling of Radiation Induced Segregation
Irradiation produces in materials excess vacancies and self-interstials that eliminate by mutual recombination or by annihilation at sinks (surfaces, grain boudaries, dislocations).
It sustains permanent fluxes of point defects towards those sinks. In case of preferential transport of one componant of an alloy, the chemical composition is modified in the vicinity of the sinks: a Radiation Induced Segregation (RIS). Its modelling requires a good description of the alloy properties: its driving forces (derived from the thermodynamics) and its kinetic coefficients (the Onsager matrix). The objectif on this project is to combine (i) atomic models (Kinetic Monte Carlo simulations and Self-Consistent Mean Field), fitted on ab initio calculations, that provide the Onsager coeffcients and the driving forces and (ii) a Phase-Field modelling that will give a description of the evolution of the alloy under irradiation at much larger time- and space-scales. The approach will be applied to Fe-Cr and Fe-Cu alloys, already modelled at the atomic scale. RIS will be first modelled near grain boundaries, then near dislocation loops. Special attention will be paid to the effect of elastic stresses on the RIS.
Development of methods for U quantification in cells after exposure to uranium
This project fits into the transverse Toxicology Program, led by CEA, whose purpose is to address by multidisciplinary approaches, the potential effects on living organisms of elements of strategic interest to the CEA. The objective is to provide some understanding on the mechanisms of uranium toxicity and behavior, in connection with its speciation in cells. Indeed, the radionuclides speciation governs their bioavailability, accumulation, biodistribution, toxicity, detoxification mechanisms and their interaction at the molecular level.
The post-doctoral project (12 months) consists in:
- Developing methods to quantify U accumulated in the cells as well as endogenous content of trace elements after exposure of cells to uranium.
- Developing methods to determine the precise isotopic composition of U in the cells after their exposure.
The candidate will be in charge of developing chemical purification and measurement methods for precise elemental and isotopic analyses. The analyses will be performed using inductively coupled plasma quadrupole mass spectrometer (ICP- MS Q) or inductively coupled plasma multi- collection mass spectrometer of the latest generation (ICP- MS MC), to achieve the lowest level of uncertainties.
Electric field and ab initio simulations, application to RRAM
Since several years, LETI/DCOS is engaged in a simulation effort of microscopic phenomena at the heart of oxide-based RRAM operation (made of HfO2, Ta2O5, Al2O3). The correct description of an external electric field applied to a MIM device (Metal-Insulator-Metal) is now possible thanks to two methods one by an orbital separation approach [1] the other by using the non equilibrium green function formalism [2]. In this work, we propose to develop and to handle these methods by combining already existing simulation approaches. The main goal is to study the degradation mechanisms of an oxide by following the oxygen atoms movements coupled directly to the applied external electric field. These mechanisms are not known and this study will support the optimization and characterization efforts already engaged at LETI on RRAM functional prototypes. The targeted simulations tools are SIESTA for the DFT part, and TB_SIM for the electronic transport part.
[1] S. Kasamatsu et al., « First principle calculation of charged capacitors under open-circuit using the orbital separation approach, PRB 92, 115124 (2015)
[2] M. Brandbyge et al., « Density functional method for nonequilibrium electron transport », PRB 65, 165401 (2002)
Synthesis of inorganic monoliths functionalized with nanoparticles
Since 2008, the "Institut de Chimie Separative de Marcoule" (ICSM) and specifically the "Laboratoire des Nanomateriaux pour l’Energie et le Recyclage" (LNER) has developped specific skills in synthesis routes and studies of porous materials (BET, TEM, SEM, SAXS).
This post-doctoral position is devoted to the synthesis of inorganic monoliths using high internal phase emulsion (HIPE) as soft template, and particularly to the functionalization of these materials with nanoparticles (NP).
The use of an emulsion in the procedure allows to consider innovative ways of functionalizing the material. For example, the oil-water interface in the emulsion may be the site of adsorption of nanoparticles of interest for a given application. In our case the goal is to prepare an emulsion with high internal phase (> 50% vol) stabilized by both surfactants (required for mesoporosity) and NP of interest to functionalize the macroporosity. NPs are chosen to cover liquid effluent decontamination (zeolite, nonatitanate, clathrate)
Evolution of the surface layers resulting from the physico-chemical interactions between low pH concrete and clays: experiments and modeling
The design of an industrial facility for storage of radioactive wastes in geological environment is an important issue taken into account in the French nuclear energy sector. In this context the cementitious materials are an important (packages, structures).
The main objective of the proposed study is to characterize alterations of the materials in the concrete-clay interfaces, caused by chemical exchanges. At the current stage, a comprehensive approach was initiated taking into account simultaneously the chemistry of the storage site and concrete considered for this application, based on commercial cements or innovative binders (low pH) formulated specifically. On these low pH materials in particular, questions remain as to their mineralogical and microstructural evolution. An experimental program (dedicated testing, microscopic characterization), supplemented by digital simulations, will increase the essential knowledge for use of these materials.
This project will involve both of the specialists of cementitious materials of the CEA, and researchers at the laboratory Hydrasa of the University of Poitiers.