As part of the Carnot PIRLE project starting in early 2021, we are looking for a candidate for a post-doctoral position of 24 months (12 months renewable) with a specialty in material science. The project consists in developing a relaxed pseudo-substrate based on III-N materials for µLEDs applications, especially for emission in red wavelength. The work will focus on developing an InGaN-based epitaxy MOCVD growth process, on an innovative substrate based on electrochemically anodized and relaxed materials. He (She) will have characterize both the level of relaxation of the re-epitaxied layer and its crystalline quality. These two points will promote the epitaxial regrowth of an effective red LED. The candidate will be part of the team, working on the PIRLE project, will be associated to the work on red LED growth and its optical and electro-optical characterizations.
The Orano plant in Niger (Somaïr) precipitates its uranium concentrate in a fluidized bed reactor by adding sodium hydroxide. The concentrate obtained contains around 6% sodium which leads to converter penalties. Orano carried out tests at the end of 2019 on a fluidized bed in the laboratory to change the operating point of precipitation and preferentially form UO3 via a change in pH. To refine the management of the industrial unit, it is necessary to model the precipitation reactions of uranium. The candidate will have to propose and calibrate a competitive precipitation model for Na2U2O7 and UO3 based on the equilibrium constants and reaction kinetics, as a function of the pH within the reactor. In particular, the model should make it possible to understand the impact of pH on the distribution of the two main species identified in the concentrate: Na2U2O7 and UO3. This chemical model should serve as input to an existing physical model of the fluidized bed reactor. An extension of the model to other precipitation reagents, in particular magnesia, could also be studied.
In the frame of the collaborative project between the ICSM , CEA and Orano, a study is conducted in order to detect and identify minerals containing uranium (VI) by Time-Resolved Laser Fluorescence Spectroscopy (TRLFS). This technique showed its efficiency in order to identify the presence of uranyl in natural assemblies through the probing of the local environment of uranium. However, it requires the establishment of a database from synthetic and natural samples fully characterized. Therefore, in order to achieve this goal, we intend to synthesis, and thoroughly characterize a variety of compounds containing uranyl groups within the crystal structure. We can cite the families of oxi-hydroxide, sulfate, and silicates based compounds. Then, TRLFS spectra will be collected in order to complete the database and to evidence the impact of the local structure of uranyl cation on the intensity and the position of the emission bands. The obtained data will be also compared to a collection of natural samples.
State of the art: Understanding and modeling vertical leakage currents and trapping effects in GaN substrates on Si are among the crucial subjects of studies aimed at improving the properties of GaN power components : current collapse and Vth instabilities reductions, reduction of the leakage current in the OFF state.
Many universities [Longobardi et al. ISPSD 2017 / Uren et al. IEEE TED 2018 / Lu et al. IEEE TED 2018] and industrials [Moens et al. ISPSD 2017] are trying to model vertical leakages but until now, no clear mechanism has emerged from this work to model them correctly over the entire range of voltage and temperatures targeted. In addition, modeling the effects of traps in the epitaxy is necessary for the establishment of a a robust and predictive TCAD model of device.
For LETI, the strategic interest of such a work is twofold: 1) Understanding and reducing the effects of traps in the epitaxy impacting the functioning of GaN devices on Si (current collapse, Vth instabilities…) 2) Reaching the leakage specifications @ 650V necessary for industrial applications.
The candidate will have to take charge in parallel of the electrical characterizations and the development of TCAD models:
A) Advanced electrical characterizations (I (V), I (t), substrate ramping, C (V)) as a function of temperature and illumination on epitaxial substrates or directly on finite components (HEMT, Diodes, TLM )
B) Establishment of a robust TCAD model integrating the different layers of the epitaxy in order to understand the effects of device instabilities (dynamic Vth, dynamic Ron, BTI)
C) Modeling of vertical conduction in epitaxy with the aim of reducing leakage currents at 650V
Finally, the candidate must be proactive in improving the different parts of the substrate
The CEA LETI seeks to recruit a post-doctoral researcher to work on the development of advanced time of flight secondary ion mass spectrometry applications (TOF-SIMS). The candidate will work on a new TOF-SIMS instrument equipped with tandem MS spectrometry, in-situ FIB and Argon cluster sputtering. The research project will be focused around the following topics
• Developing methods to correlate TOF-SIMS with AFM, XPS and Auger
• Improving the sensitivity and efficiency of fragmention of the tandem MS spectrometer
• Developing 3D FIB-TOF-SIMS applications and improving the spatial resolution.
The candidate will also have access to the wide range of state of the art instruments present on the nanocharacterisation platform as well as bespoke samples coming from the advanced technology branches developed at the LETI. The candidate will also benefit from a collaboration with the instrument supplier.
To improve the battery management system, it is required to have a better knowledge of the physical and chemical phenomena inside the cells. The next generation of cells will integrate sensors for deepest monitoring of the cell to improve the performances, safety, reliability and lifetime of the battery packs. The main challenge is thus to measure relevant physico-chemical parameters in the heart of the cell to get a direct access to the real state of the cell and thus to optimize its management. To address this challenge, a research project will start at CEA at the beginning of 2020 to develop innovative optical sensors for Li-ion battery monitoring. He / She will participate, in a first step, to the development of optical probes and their integration on optical fibres. The work will focus on the synthesis of a photo-chemical probe (nanoparticle and/or molecule) as active part of the sensor. Then, theses probes will be put on the optical fibre surface to form the sensor. The candidate will also participate to the realization of an optical bench dedicated to the testing of the sensors. In a second step, he / she will work on integrating the sensors into the Li-ion cells and test them in different conditions. The objective is to demonstrate the proof of concept: validation of the sensors efficiency to capture the behaviour of the cell and correlate it to electrochemical measurements.
A post-doctoral position is open at the Interdisciplinary Research Institute of Grenoble (IRIG, formerly INAC) of the CEA Grenoble (France) on the theory and modeling of arrays of silicon-on-insulator quantum bits (SOI qubits). This position fits into an ERC Synergy project, quCube, aimed at developing two-dimensional arrays of such qubits. The selected candidate is expected to start between October and December 2019, for up to three years.
Many aspects of the physics of silicon qubits are still poorly understood, so that it is essential to support the experimental activity with state-of-the-art modeling. For that purpose, CEA is actively developing the “TB_Sim” code. TB_Sim relies on atomistic tight-binding and multi-bands k.p descriptions of the electronic structure of materials and includes, in particular, a time-dependent configuration interaction solver for the dynamics of interacting qubits.
The aims of this post-doctoral position are to improve our understanding of the physics of these devices and optimize their design, and, in particular,
- to model spin manipulation, readout, and coherence in one- and two-dimensional arrays of SOI qubits.
- to model exchange interactions in these arrays and assess the operation of multi-qubit gates.
The candidate will have the opportunity to interact with the experimental teams from CEA/IRIG, CEA/LETI and CNRS/Néel involved in quCube, and will have access to data on state-of-the-art devices.
A one year contract postdoctoral research position is open at the laboratory for light element studies (LEEL, CEA/DRF) and the Data Science for Decision Laboratory (LS2D, DRT/LIST) and focuses on data processing based on AI and machine learning, here in the scope of Ion Beam Analysis (IBA).
In the context of this project, the successful candidate will have to fulfill the following tasks:
1- Design of a multispectral dictionary.
2- Learning module development.
3- Main code programming.
4- Development of a module dedicated to multispectral mappings.
5- Benchmarking.
The postdoctoral research associate will be hosted and supervised within LEEL and LS2D.
For different applications, we are looking for materials having superior mechanical properties at high temperature (1000 ° C or higher) and that are resistant to oxidation. The family of ceramic matrix composite materials (CMC), especially C / SiC, seems the most relevant to our needs. However, it is necessary to conduct studies to determine the most efficient solutions among the wide variety of fibrous architectures and possible matrix microstructures, while taking into account the constraints related to available processes and targeted geometries. This work will be conducted in collaboration with other CEA laboratories.