Spectroscopy of AlN colored centers
The study of QD-like emission from deep emission centers in semiconductor has become an important topic in the general framework of quantum information processing and nanoscale sensing, the emblematic emission center being the N-V defect in diamonds. Recently, research has been conducted to evaluate the potential of other defects in various materials, for instance in GaN and BN. Oddly, not much is known on color centers in AlN, despite the many assets of this material : it can be epitaxially deposited, high quality bulk substrates are available, it can be processed as high quality factor microcavities.
We propose in this 12 months post-doc to explore the optical properties of deep luminescing centers in AlN. We will study by microphotoluminescence (either cw or time-resolved) various types of AlN : thin AlN grown on Si (possibly processed as membranes), thick AlN grown on sapphire, ensembles and single AlN nanowires.
Structural characterization, reactivity and physico-chemical properties of Pu(IV) colloidal suspensions
Pu(IV) is known to be highly prone to hydrolysis leading to the formation of extremely stable Pu(IV) colloidal suspensions (known as intrinsic colloids). The lack of knowledge concerning the speciation and reactivity of these Pu colloids hinders the development of reliable models allowing to predict their behavior in industrial and environmental systems. The behavior of these colloidal species towards dissolution, complexation, or aggregation has been very poorly described in the literature. It thus appears essential to study and characterize Pu(IV) colloids and in particular their surface charge properties which ensure their stability and their interactions with their environment. This pioneering project in the nuclear field aims to study and characterize colloidal Pu(IV) suspensions whose size, concentration and dispersion medium can be controlled by our approaches. It comprises: (i) the preparation of intrinsic Pu(IV) colloidal suspensions and the study of their chemical and sonochemical reactivity; (ii) the electrophoretic characterization of various colloidal suspensions and the study of their behavior under the influence of an electric field; (iii) the characterization of their multi-scale structural properties by small and large angle scattering (SAXS / WAXS) coupled with EXAFS / XANES measurements (MARS line, SOLEIL synchrotron).
Nano-silicon/graphene composites for high energy density lithium-ion batteries
This postdoctoral fellowship is part of the Graphene Flagship Core 2 H2020 european project (2018-2020) on the energy storage applications of graphene. In lithium-ion batteries, graphene associated to nanostructured silicon in a proper composite helps increase the energy capacity. Indeed graphene wraps silicon, reducing its reactivity with electrolyte and the formation of the SEI passivation layer. It also maintains a high electrical conductivity within the electrode.
The study will compare two technologies: graphene-silicon nanoparticles and graphene-silicon nanowires. The former composite, already explored in the above mentioned project, will be optimized in the present study. The latter is a new kind of composite, using a large scale silicon nanowire synthesis process recently patented in the lab. The postdoc will work within two laboratories: a technological research lab (LITEN) with expertise in batteries for transportation, and a fundamental research lab (INAC) with expertise in nanomaterial synthesis.
The postdoc will synthesize silicon nanowires for his/her composites at INAC. Following LITEN know-how, she/he will be in charge of composite formulation, battery fabrication and electrochemical cycling. He/she will systematically compare the electrochemical behavior of the nanoparticle and nanowire based silicon-graphene composites. Comparison will extend to the mechanism of capacity fading and SEI formation, thanks to the characterization means available at CEA Grenoble and in the European consortium: X-ray diffraction, electronic microscopy, XPS, FTIR, NMR spectroscopies. She/he will report her/his work within the international consortium (Cambride UK, Genova Italy, Graz Austria) meetings.
A 2-year post-doctoral position is open.
PhD in materials science is requested. Experience in nanocharacterization, nanochemistry and/or electrochemistry is welcome.
Applications are expected before May 31st, 2018.
Tunnel Junction for UV LEDs: characterization and optimization
Besides existing UV lamps, UV LEDs emitting in the UV-C region (around 265 nm) are considered as the next solutions for cost efficient water sterilization systems. But existing UV-C LEDs based on AlGaN wide band gap materials and related quantum well heterostructures still have low efficiencies which precludes their widespread use in industrial systems.
Analysing the reasons of the low efficiencies of present UV-C LEDs led us to propose a solution based on the use of a Tunnel Junction (TJ) inserted within the AlGaN heterostructure diode. p+/ n+ tunnel junctions are smart solutions to cope with doping related problems in the wide band gap AlGaN materials but give rise to extra tunneling resistances that need to be coped with. The post-doctoral work is dedicated to understanding the physics of tunneling processes in the TJ itself for a better control of the tunneling current.
The post-doctoral work will be carried out at the “Plate-Forme de Nanocaractérization” in CEA/ Grenoble, using different optical, structural and electrical measurements on stand-alone TJs or on TJs inserted within LEDs. The candidate will have to interact strongly with the team in CNRS/CRHEA in Sophia Antipolis where epitaxial growth of the diodes will be undertaken. The work is part of a collaborative project named "DUVET" financed by the Agence Nationale de la Recherche (ANR).
In situ synchrotron X-ray monitoring of the growth of defect-free two-dimensional materials by liquid-metal catalytic routes
The postdoctoral research project is part of a four-year European FET-Open project called LMCat (http://lmcat.eu/) bringing together five European labs, including the ESRF and the CEA-INAC, to develop the growth of defect-free two-dimensional materials by liquid-metal catalytic routes. A central lab will be established at the ESRF to develop an instrumentation/methodology capable of studying the ongoing chemical reactions on the molten catalyst. The growth by chemical vapor deposition at high pressure and temperatures will be characterized in situ, by means of two main techniques: Raman and X-ray scattering (Grazing Incidence X-Ray Scattering and Reflectivity). It will be complemented by theoretical calculations performed in Munich. The successful candidate will be in charge; together with a PhD student, of the in situ synchrotron X-ray scattering measurements, using the ESRF ID10 liquid scattering beamline (http://www.esrf.eu/UsersAndScience/Experiments/CBS/ID10) and the P08 beamline of PETRA-III (photon-science.desy.de/facilities/petra_iii/beamlines/p08_highres_diffraction/index_eng.html), in Desy.
You should hold a PhD in physics, chemistry or material science or closely related science. Previous experience of complex instrumental environment, MBE or CVD growth methods and / or with synchrotron X-ray scattering / diffraction / reflectivity, especially on liquids, will be an advantage. You should be motivated to work with an international team of young researchers with an experimental setup at the forefront of instrumental development, and ready to travel in Germany (Hambourg) for extended periods to perform some of the experiments. A good practice of English is mandatory. You should also have:
This is a full time, 3 year contract.
Please submit a 1 page cover letter stating the motivation, research experience and goals, ; a curriculum vitae, and contact information for 3 references.
Simulation of semimetal nanowires
The candidate’s mission will be:
• Simulation using ab-initio tools of the structure of bismuth nanowire bands of different diameters (from 1 nm to 10 nm).
• Extraction of parameters as effective masses, density of states, band offsets for these nanowires.
• Implementation of these parameters in a NEGF simulator to simulate bismuth nanowire transistors with variable diameter.
• Ab-initio simulation of the bismuth-dielectric nanowire interface and study of various elements of chemical passivation.
• This work will be done in collaboration with LETI / DCOS / SCME / LSIM (Philippe Blaise)
• The candidate will interact with an experimental team that will produce the simulated devices and will help to supervise one or more doctoral students, in collaboration with IMEP.
• The candidate will interact with the LTM to help predict the properties of the grid bismuth-insulator interface and implement the IMEP results in the simulator.
Physisorption of chemical species on sensitive surfaces during transfer in controlled mini-environment in microelectronics industry
A characterization platform based on the connection concept between process and characterization tools through the use of a transfer box under vacuum was implemented allowing a quasi in-situ characterization of substrates (wafers) of the microelectronics. Currently, this transfer concept based simply on static vacuum inside a carrier box is satisfactory regarding the residual O or C on the surface of especially sensitive materials (Ge, Ta, Sb, Ti…) and the MOCVD layers growth on GST or III/V surfaces. Its optimization for more stringent applications (molecular bonding, epitaxy…) in terms of contamination surface prevention requires studies the understanding of the physico-chemical evolution of the surfaces.
The proposed work will be focused on physico chemical studies of the evolution and molecular contamination of surfaces during transfers and will take place in clean room. XPS, TD-GCMS and MS coupled to the carrier itself (to be implemented) will be used to address the sources (wall, seals, gaseous environment…) of the adsorbed chemical species implied and to determine the physisorption mechanisms on the substrates. The studied surfaces will be sensitive to the contaminants in such a way than the box environment impact will be extracted and studied parameters will be the nature of polymer seal used, the carrier box thermal conditioning, the vacuum level, the use of low pressure gaseous environment in the carrier (gas nature, pressure level…).
Simulation of thermal exchange between fluid and structure in turbulent channels
There is presently a huge effort in Europe for the Development of high power (PW range), high repetition rate (1-10 Hz) lasers: the ELI project in three countries of Eastern Europe , the Apollon program in France have the objective to install multipetawatt high repetition rate lasers for scientific research and applications in various fields of physics. These large projects result in – and demand – an increased mastering of most challenging issues in laser technology; at high repetition rate one of the greatest issues consists in the cooling of the laser amplifiers for the highest repetition rates. In order to master this technology, CEA (Grenoble and Saclay, with a collaboration with Grenoble/LEGI) has decided to start an R&D program, with the following tasks to perform: (i) simulation of the cooling of amplifiers; (ii) validation of the calculations; (iii) design of an appropriate cooling system dedicated to future high power high repetition rate lasers: for this, cryogenic helium gas is a very interesting fluid, as working at low temperature for laser amplification allows a better thermal conductivity of the amplifiers (consequently a better uniformity of their temperature), and an increased efficiency of the laser amplification.
This postdoc position is associated with the first (simulation) task.
Bio-compatible, bio-resorbable microbatteries for medical applications
In the framework of its activities dedicated to embedded micro-batteries, LETI initiates prospective research in the field of micro-batteries for medical applications, and in particular as energy power sources for implantable micro-devices. In this context, a collaborative project, including LETI labs and an academic Partner (ICMCB, Bordeaux), is aiming at designing, manufacturing and studying prototypes of bio-resorbable primary microbatteries.
The main tasks will include (i) a contribution to the design of the thin film electrochemical cell by the selection of adequate biocompatible materials (able to generate the targeted electrical power, corrodible and able to solubilize in the body), (ii) the manufacture of the cell constituents (electrodes, electrolyte, substrate) as thin films (sputtering, electrochemical plating, doctor blade coating) and their characterization,(iii) the achievement of full prototype cells and the study of their in vitro behaviour.
The work will be carried out at ICMCB (Bordeaux) in a joint CEA/ICMCB team, in collaboration with LETI labs in Grenoble.
Atomic sensors based on metastable 4He
Detection of weak magnetic fields opens the way to new techniques of medical imaging, geophysics and chemistry. Optically pumped magnetometers are currently the most accurate and precise sensors for magnetic fields [1]. Our lab works on optically-pumped magnetometers based on a thermal gas of helium-4 metastables, a spin-one electronic species. Our main achievement in last years has been the design and space qualification of the most recent generation of magnetometers available for spatial exploration, which were launched by ESA Swarm mission [2].
We are now starting a new project in order to explore further applications of magneto-optical effects of metastable helium. Indeed, dichroism and birefringence have been observed on 4He from the very first times of optical pumping [3] but, in strong contrast with alkali [4], the nonlinear regimes which can be reached from the introduction of 1083 nm lasers have been hardly studied. These regimes open new possibilities for realizing not only magnetometers but also other kind of useful sensors which address a broader range of industrial applications.
We are looking for a motivated postdoc candidate willing to work towards a better understanding of these effects but also towards harnessing them for building ultra-precise sensors. The applicant should have a PhD in physics, ideally with a good background in experimental atomic physics and/or laser physics. Our lab is well equipped and staff engineers will be available to assist the post doc on technical aspects related to optics, design of electronics and magnetic materials. The results will be divulgated in form both of journal publications and of patents.
[1] Kominis et al., Nature 422 (2003)
[2] http://smsc.cnes.fr/SWARM
[3] Laloë, Leduc, Minguzzi, Journal de Physique, 30 (1969)
S. Pancharatnam, J. Phys. B: At. Mol. Phys. 1 (1968).
[4] Budker et al., Rev. Mod. Phys. 74 (2002)