4D printing of thermo-magnetic composite materials using light-driven additive manufacturing techniques

This PhD research project explores the cutting-edge field of 4D printing, a field that integrates smart materials into additivemanufacturing processes. The aim is to create nanocomposite objects with multifunctional capabilities, enabling them to change shapeand properties in response to external stimuli.

In this PhD project, we will primarily focus on liquid crystal elastomers (LCEs) as the active matrix. LCEs are a versatile class ofprogrammable polymer materials that can undergo reversible deformation under various stimuli, such as light, heat, electric fields, andmagnetic fields, transitioning from disordered to oriented phases. Because of their actuation properties, LCEs are promising candidatesin applications like artificial muscles in medicine and soft robotics.

Consequently, the project's first objective is to devise a method for 3D printing LCE resins using light-driven printing processes, includingdigital light processing (DLP), direct ink writing (DIW), and two-photon polymerization. The project also explores the possibility of co-printing using two laser sources with different wavelengths. This will result in designed objects capable of programmed deformationsand reversibility. To further enhance the actuation capabilities of the LCE matrices, magnetic particles will be incorporated into thethermoresponsive LCE resin. Thus, the second objective of the project is to develop a strategy for self-assembling and spatiallyorienting embedded magnetic nanoparticles in LCE resins during light-driven printing processes (DLP, DIW, 2PP). Ultimately, the thirdobjective of this project is to combine these two strategies to create sophisticated multifunctional soft machines and devices suitable forcomplex environments. Experiments will follow an incremental trial-and-error research approach, with the aim of improving machinelearning models by designing purpose-built objects.

The envisioned research work can be summarized into the following macro-steps:
- Specification of target shape-changes depending on the multiple stimulation scenarios
- Selection of active particles, formulation of the LCE, and synthesis of the particles
- Development of hybrid additive manufacturing strategies with possible instrumentation
- Printing proofs-of concept and conducting mechanical and actuation tests
- Characterization of composite structures
- Development of simulation models
- Realization of a demonstrator (e.g., crawling robot, actuators for the automotive sector…)

Study of the production of martensitic stainless steel 13-4 by Laser Metal Deposition: influence of process parameters, powder characteristics and post-treatments on microstructure and mechanical properties at fracture

Additive manufacturing processes are now widely studied for numerous applications in the nuclear industry. The aim of the studies dedicated to optimising the Laser Metal Deposition (LMD) metal additive manufacturing process for the production and shaping of a 13-4 martensitic stainless steel is to obtain a material with mechanical properties at fracture, particularly in terms of impact strength, that comply with the specifications for use. This work explores the complex relationships between the microstructural characteristics (phase present, granular structure, texture, precipitation, etc.) induced by the process and the resulting mechanical performance.
Additive manufacturing, in particular the LMD process, offers multiple advantages in terms of design flexibility and customisation of metal components. However, obtaining mechanical properties at fracture that meet specifications is a major challenge, particularly for high-temperature applications in corrosive environments.
This thesis focuses on the optimisation of the LMD process to ensure that components manufactured from 13-4 martensitic stainless steel exhibit microstructural characteristics and mechanical performance appropriate to their intended applications, with particular emphasis on impact properties. Determining the optimum process parameters, including the characteristics of the powders and associated post-treatments, the analysis of the microstructure, and the correlation between the microstructure and the mechanical properties constitute a major challenge for the complete control of this process.

Multi-level functionality in ferroelectric, hafnia-based thin films for edge logic and memory

The numerical transition to a more attractive, agile and sustainable economy relies on research on future digital technologies.

Thanks to its non-volatility, CMOS compatibility, scaling and 3D integration potential, emerging memory and logic technology based on ferroelectric hafnia represents a revolution in terms of possible applications. For example, with respect to Flash, resistive or phase change memories, ferroelectric memories are intrinsically low power by several orders of magnitude.

The device at the heart of the project is the FeFET-2. It consists of a ferroelectric capacitor (FeCAP) wired to the gate of a standard CMOS transistor. These devices have excellent endurance, retention and power rating together with the plasticity required for neuromorphic applications in artificial intelligence.

The thesis will use advanced characterization techniques, in particular photoemission spectroscopy and microscopy to establish the links between material properties and the electrical performance of the FeCAPs.

Operando experiments as a function of number of cycles, pulse amplitude and duration will allow exploring correlations between the kinetics of the material properties and the electrical response of the devices.

The thesis work will be carried out in close collaboration with NaMLab (Dresden) and the CEA LETI (Grenoble).

Hybrid solid electrolytes for "all-solid" batteries: Formulation and multi-scale characterization of ionic transport

Lithium-ion batteries, widely present in our daily lives, have revolutionized portable applications and are now used in electric vehicles. The development of new generations of batteries for future applications in transport and storing electricity from renewable sources is therefore vital to mitigating climate change. Lithium-ion technology is generally considered as the preferred solution for applications requiring high energy density, while sodium-ion technology is particularly attractive for applications requiring power.

However, the intrinsic instability of liquid electrolytes results in safety issues. Faced with the requirements concerning the environment and safety, solid-state batteries based on solid electrolytes can provide an effective solution while meeting battery energy storage needs. The barriers to overcome allowing the development of all-solid-state battery technology consist mainly in the research of new chemically stable solid electrolytes with good electrical, electrochemical and mechanical performance. For this goal, this thesis project aims to develop “polymer/polymer” and “ceramic/polymer” composite solid electrolytes with high performance and enhanced safety. Characterizations by electrochemical impedance spectroscopy (EIS) will be carried out in order to understand the cation dynamics (by Li+ or Na+) at the macroscopic scale in composite electrolytes, while the local dynamics will be probed using advanced techniques of Solid-state NMR (23Na / 7Li relaxation, 2D NMR, in-situ NMR & operando). Other characterization techniques such as X-ray and neutron diffraction, XPS, chronoamperometry, GITT ... will be implemented for a perfect understanding of the structure of electrolytes as well as aging mechanisms at the electrolyte / electrolyte and electrolyte/electrode interfaces of the all-solid battery.

Key words: composite solid electrolyte, all-solid-state battery, interfaces, multiscale characterization, dynamics of Li + and Na + ions, electrochemical performance, solid-state NMR, X-ray / neutron diffraction.

Contribution of metal-semiconductor interfaces to the operation of the latest generation of infrared photodiodes

This thesis concerns the field of cooled infrared detectors used for astrophysical applications. In this field, the DPFT/SMTP (Infrared Laboratory) of CEA-LETI-MINATEC works closely with Lynred, a world leader in the production of high-performance infrared focal planes. In this context, the infrared laboratory is developing new generations of infrared detectors to meet the needs of future products.
One of the current development axes concerns the quality of the p-type semiconductor metal interface. These developments are driven by the increase in the operating temperature of the detectors, as well as by the very strong performance requirements for space applications.
The challenge of this thesis is to contribute to a better understanding of the chemical species present at the interface of interest as a function of different surface treatment types and to link them to the electrical properties of the contact made.
The candidate will join the infrared laboratory, which includes the entire detector production process. He/she will produce these samples using the technological means available in the LETI clean room, in collaboration with experts in the field. He/she will also have access to the necessary characterization tools (SIMS, XPS, AFM…) available on the nano-characterization platform (PFNC) or in the CEA clean room. Finally, he/she will be involved in the electro-optical characterization of the material, in collaboration with the Cooled Infrared Imaging Laboratory (LIR), which specializes in fine material characterization.

Stabilisation of Perovskite photovoltaic devices by passivation with Metal-Organic Frameworks type materials

MOFs are a type of porous organic-inorganic hybrid material with interesting properties in terms of the passivation of defects in the perovskite and its stability, particularly versus light. For example:
- Direct effect of MOF components as passivation agents: Metal ions and organic ligands can passivate defects at the MOF/PK interface.
- Downconversion of incident radiation: Certain metals (such as europium) or ligands (with aromatic groups) can absorb high-energy radiation (typically violet/near-UV), then re-emit this energy in the form of lower-energy radiation or transmit it directly in a non-radiative manner to the perovskite by Förster resonance (or FRET). This protects the perovskite from high-energy photons, and therefore a priori improves light stability, with little energy loss.
The thesis work will focus on
- integrating MOFs into the perovskite layer, either as a surface treatment or as a mixture of suspensions
- Materials studies (in particular advanced studies using XPS and UPS)
- Favrication of single-junction devices and then tandem devices with silicon sub-cells
- Study of lifetime under illumination (continuous, cycling) with associated characterisations (electrical measurements, photoluminescence, etc.).

Elucidation of the Correlation between the Electrochemical Activity of Oxygen Reduction and the Molecular Structure of the Platinum/Ionomer Interface in Proton Exchange Membrane Fuel Cells

This thesis focuses on the Proton Exchange Membrane Fuel Cell (PEMFC), used in the transportation sector to generate electricity and heat from hydrogen and oxygen. Although promising for reducing CO2 emissions through the use of green hydrogen, the PEMFC needs to enhance its performance and durability to compete with combustion engines and batteries. The electrode plays a crucial role, but the molecular complexity of the electrochemical interface between the platinum-based catalyst and the ionomer makes characterization challenging. Currently, the qualitative understanding of this interface is limited, impeding progress and model predictability. The thesis aims to establish a correlation between the molecular structure of the electrochemical interface and the electrochemical kinetics, focusing on platinum oxidation and ionomer adsorption. A unique device developed at CEA allows simultaneous electrochemical and spectroscopic characterizations. The novelty lies in using Atomic Force Microscopy (AFM) coupled with Raman spectroscopy and synchrotron-based micro-infrared spectroscopy as original techniques to obtain crucial information for PEMFC applications.

Development of new anode materials for potassium-ion batteries

Classic Li-ion batteries are composed of a graphite anode and a cathode containing a lithiated layered oxide (formula LiNixMnyCozO2). The development and the generalization of the electric automobile market will generate stress on certain chemical elements source, especially for lithium, nickel, cobalt and copper. In addition, the production method consumes a lot of energy (multiple calcinations) and several solvents/products used are not respectful of the environment (NMP, ammonia).
The thesis aims to develop a battery technology based on potassium without using any critical element in order to significantly decrease the ecological footprint.
The insertion of potassium ion inside the graphite structure has been reported as an advantage in front of Na-ion batteries. However, due to the potassium size, the graphite structure expands (60%) and can limit the batterie cycle life.
The final target of the PhD thesis is to solve this issu following two approches : 1/ Find the link beetween graphites specifications and the resulting electrochemical performances in order to select the best graphite grade 2/ Develop new anode materials for K-ion application.

Physics-based ageing model of Li-ion batteries

In recent years, Li-ion batteries have become the benchmark technology for the global battery market, supplanting the older Nickel-Cadmium and Alkaline technologies. Although slightly inferior to fossil fuels in terms of massic energy capacity, Li-ion batteries have a major advantage for the development of electric vehicles: their exceptional lifespan. It has recently been demonstrated that particular electric vehicle technologies can exceed one million km. Beyond the promising performance of ideal prototypes, the question of battery lifespan is linked to industrial, economic and environmental issues that are crucial to the ecological transition and energy sovereignty of our country.

One of the major challenges in developing these long-life batteries is to anticipate and control the various internal degradation phenomena that occur during actual use. Although most degradation phenomena have been identified in laboratory on common battery materials, the question of their kinetics in a battery pack in real use remains open, as does the prediction of the battery's state of health and end-of-life.

CEA's teams draw on a unique expertise combining experimental data and modeling to build a predictive physico-chemical model of Li-ion battery degradation. As part of this thesis, you will design and carry out basic characterization experiments on battery degradation mechanisms in the laboratory, using a wide range of advanced experimental techniques (electrochemical titration, impedance spectroscopy, operando gas measurements, DRX, etc.). Your work will also involve integrating your results into aging models, and studying the predictions and validation of these models.

Study of NMC electrode materials for lithium-ion batteries by experimental and theoretical soft and hard X-ray photoemission spectroscopy

The photoemission spectroscopy (X-ray, XPS, or ultraviolet, UPS) is one of the direct probes of the electronic structure of materials change during redox processes involved in lithium ions-batteries at the atomic scale. However, it is limited by the extreme surface sensitivity, with a typical photoelectron path length of a few nanometers to the energies usually available in the laboratory , . Moreover, the spectra interpretation requires the ability to accurately model the electronic structure, which is particularly delicate in the case of transition metal based electrode materials. Upon lithium insertion and de-insertion, the charge transfer toward cations and anions induces local electronic structure changes requiring an adapted model that takes in account the electronic correlations between atoms.
In this thesis, we propose to use these limitations to our advantage to explore the electronic surface structure including the solid electrolyte interphase (SEI), and the bulk of the active cathode particle.
Thanks to the lab-based hard X-ray photoemission spectrometer (HAXPES), the electronic structure of the bulk of the electrodes (LiCoO2 and LiNiO2) materials have been studied up to about 30 nanometers , . To widen our picture on the role of cation and anion from surface to bulk in the lamellar metal oxide electrode for lithium-ion battery, this thesis will focus on mixed lamellar metal oxide Li(Ni1-x-yMnxCoy)O2 (NMC).
The comparison between the Soft-XPS and HAXPES spectra, during battery operation (operando) and post-mortem, will allow decoupling of the surface and core spectra for different NMC compositions and at different stages of the battery life cycle. The interpretation of the photoemission spectra will be done by direct comparison with ab-initio calculations combining density functional theory (DFT) with dynamical mean field theory (DMFT) , . This coupled approach will allow to go beyond the usual techniques based on cluster models, which do not take into account long-range screening, and to validate the quality of theoretical predictions on the effects of electronic correlations (effective mass, potential transfer of spectral weight to Hubbard bands) .
The thesis will include an instrumental (in particular, calibration of Scofield factor on model systems) and theoretical (prediction of core photoemission spectra based on DFT+DMFT calculations) development. The performance of electrochemical systems based on different cathode materials (NMC with different compositions) in combination with liquid and solid electrolytes and a Li metal anode will be studied in the frame of combined experimental and theoretical soft and hard X-ray photoemission spectroscopy.
The candidate will be hosted at the PFNC in the Laboratory of Characterization for the Energy of CEA Grenoble under the direction of Dr. Anass BENAYAD (department of Material) and LMP (Department of Electricity and Hydrogen for Transport) under the supervision of Dr. Ambroise Van Roekeghem.
Contact : anass.benayad@cea.fr et ambroise.vanroekeghem@cea.fr