• The Physics and Mechanics of Materials Department (PDP and SIMAC teams) at the Institut PPRIME is looking for a PhD on:

    Mechanical properties of nanotwinned gold thin films

    Scientific Context:

    A twin is a portion of a crystal with a particular orientation, for example obtained by a reflection, with respect to a matrix with the same crystalline structure. Twins may appear during plastic deformation, crystal growth or recrystallization. During the last years, nanotwinned materials have been the subject of great interest due to their remarkable mechanical properties: they present large mechanical resistance, ductility and work-hardening capacities. Moreover, they have the same electrical resistivity as coarse grain crystals.

    In this context, the “PtyMet” project aims at characterizing the stress field in nanotwinned thin films, and its impact on physical properties. We will combine experiments (X-ray diffraction and transmission electron microscopy) and simulations (molecular statics and dynamics) and focus on single-crystalline nanotwinned gold thin films. From a numerical point of view, atomistic scale simulations are particularly well adapted tools for these studies. They include key materials properties such as the stacking fault and twin boundary energies, allowing precise descriptions of the defect configurations (e.g. dislocations, grain boundaries, twins). Furthermore, atomic scale simulations and experiments are now working on converging spatial scales. From the experimental point of view, X-ray diffraction can be used to determine the twinned volume (via pole figures) or the stress state in the sample (via Bragg peaks displacement). Moreover, using a coherent X-ray beam allows the characterization of single crystalline defects such as dislocations or twins.

    PhD task:

    Optimization of the deposition conditions is mandatory in order to prepare homogeneous thin films, without other defects than the twins.The films’ microstructure before deformation will be precisely characterized.Simultaneously, atomic scale simulations will be used to establish the elastic strain field associated with different nanotwinned thin film microstructures. Equilibrium conditions will be determined using semi-empirical potentials, that are reliable for gold. The impact of the twins’ density and thickness will be studied.Finally,in-situ tensile tests at synchrotron radiation sources, using both classical and coherent X-ray diffraction,will be performed. This, together with atomic scale simulations,will allow a full characterization, from the atomic to the macro-scale, of the mechanical properties of nanotwinned gold thin films.

    Required skills/qualification:

    The applicant should hold a master degree in solid-state physics or materials science. He/she should show a shared interest in computer simulations and in experimental work. Skills in atomic scale simulations and / or X-ray diffraction will be an asset.

    Application:

    send a CV and a cover letter to the contacts below.

    Contact:

    Sandrine BROCHARD sandrine.brochard@univ-poitiers.fr

    Pierre GODARD pierre.godard@univ-poitiers.fr

    More information (and a french version) are available in the following document:  these_PhD_PtyMet_nanotwins.pdf »


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  • This post-doctoral position is to be held at FEMTO-ST (www.femto-st.fr), within the Dpt. Of Applied Mechanics. FEMTO-ST is a joint research unit which is affiliated with the French National Centre of Scientific Research (CNRS), the University of Franche-Comté (UFC), the National School of Mechanical Engineering and Microtechnology (ENSMM), and the Belfort-Montbéliard University of Technology (UTBM).

    Scientific context:

    This part of the CAVHYTATION project is intended to provide new insights in chemo-mechanical couplings at the microscale, in order to assess the potentialities of innovative micromechanical sensors. Micromechanical structures have been realized and a dedicated surface chemistry is under validation in order to provide a representative model system. As a post-doc in the PMMCM group, you will be in charge of two innovative experiments intended to probe the fine-scale deformation of the structures when their surface undergoes a chemical modification. One of these experiments is to be conducted together with a group operating at SOLEIL. These fine-scale displacements are crucial to elucidate the role of the material in the chemo-mechanical transduction.

    Required qualifications:

    The applicant is expected to have significant background and extensive experience as experimentalist. Experience in multidisciplinary environments would be greatly appreciated. Excellent communication skills as well as a team-oriented attitude are requested

    Further information may be obtained from Fabien Amiot (fabien.amiot@femto-st.fr).

    Information on duration and application are available in the following document: « profile_cavhytation.pdf »


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  • PhD Topic:

    Synthesis, mechanical properties and biodegradability of thin films metallic glasses

    Short description:

    The study of amorphous metal films (thin film metallic glasses, TFMGs) is receiving more and more attention due to the excellent mechanical properties: a tensile strength close to theoretical limit, high hardness and elastic deformation. Their disordered atomic structure is the source of unique physical properties that are different from their crystalline counterparts. However, studies on the synthesis and characterization of TFMGs are relatively recent, as efforts have focused on the bulk metallic glasses (BMGs). In this context, the main goal of the study is the TFMGs synthesis by magnetron sputtering on flexible polymer substrates with a structure totally or partially disordered at the nanometric scale. Structural-mechanical relationship will be identify trough the combination of x-ray diffraction, scanning electron microscope, nanoindentation, optoacoustic techniques and micro-tensile tests of films on flexible polymeric substrates. We aim to establish correlation between the elastic and plastic properties of TFMGs, and contribute to a better understanding of the microstructures and local atomic ordering influence on their mechanical properties. In addition, one application of these coatings in the biomedical field is considered, in partnership with the Laboratory for Translational Vascular Research (LVTS, INSERM U1148, Pr. F. Chaubet) who will perform specific biocompatibility tests (cells growth,…).

    PhD tasks :

    (i) coatings with thin films of metallic glasses on flat polymeric supports (Kapton or elastomer sheets) and curved structures of polymers obtained by 3D printing; 

    (ii) study of the structural and mechanical properties of hybrid materials, in particular at the polymermetal interface, 

    (iii) control of their degradation kinetics in simulated biological medium,

    (iv) in the context of a biomedical application, the evaluation of their mechanical properties in relation to the absorption of the materials constituting the hybrid,

    (v) evaluation of compatibility with human vascular cells (collaboration with the LVTS , Pr. F. Chaubet).

    Further information and application:

    Supervision: Prof. Philippe Djemia (LSPM, Université Sorbonne Paris Nord),

    Co-supervision: Dr. Fatiha Challali, Dr. Florent Tétard

    Financial support: MESR Grant (starting on September 1th 2020; 3 years duration).

    Start date: September 1st 2020

    More detail on the subject and information on application are available in the following document: « PhD offer-Thin film Metallic glass-LSPM-2020.pdf »


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  • Supervision: Dr. Antoine GUITTON (antoine.guitton[at]univ-lorraine.fr) Prof. Thierry GROSDIDIER
    Location: LEM3, Université de Metz, France

    Financial support: CNRS Grant (starting October 1th, 2020 ; 3 years duration).
    Keywords : Max Phases, MXenes, hydrogen storage, Microstructural analysis, Electron microscopy.

    Solid state storage of hydrogen in low pressure tanks (ground transportation purposes) can take advantage of the reversible transformation of metal into metastable metal-hydrides within an appropriate temperature range. Such storage systems using Mg hydrides is safe and lightweight but exhibit a low charge and discharge kinetic even at relatively high temperatures (>200°C). To overcome these limitations, new alloys and microstructural modifications are explored. Understanding the effects of structural defects and catalysts on the physical mechanisms involved in the hydride nucleation and growth reaction is however needed and difficult: hydrides are unstable under vacuum.

    Mn+1AXn phases (n = 1 to 3, M being a transition metal, A an A-group element and X = N or C) are nanolaminated ternary compounds–synthesized by powder metallurgy from cheap and widely available elements. Because of their anisotropic layered structure, the MAX-phases can theoretically store large amounts of hydrogen in solid solution. MAX phases are also precursors for MXenes, one of the largest families of two-dimensional materials. In the form of stacks, these materials have demonstrated remarkable performance as (co-) catalysts for key fuel cell reactions and are promising for hydrogen storage.

    In this thesis, we will explore the influence of microstructural defects (dislocations, grain boundaries, heterophasic interfaces) on the fundamental mechanisms of hydrogen storage in MAX phases, MXenes and their Mg-based nanocomposites. This thesis is part of a collaboration project between several laboratories – LEM3 (Metz, France), Institut Pprime (Poitiers, France), IC2MP (Poitiers, France), GPM (Rouen, France), Beijing Jiaotong University (China) and I2CNER (Japan) –

    More details HERE

     


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  • Supervision: Marc Legros (marc.legros[at]cemes.fr), Julio Cesar Brandelero (Mitsubishi Electric)

    Location: CEMES (Toulouse)

    Financial support: CIFRE Grant (starting on October 1th, 2020 ; 3 years duration).
    Keywords : Al microstructure, oxidation, grain boundaries, thermal & electrical cycling, electron &ion microscopy.

     

    Power devices, such as MOSFETs and IGBTs, are key components of the continuous growth of power electronics applications ranging from domotics to energy conversion. Their reliability becomes critical in transportation and off-shore applications. Anticipating or even preventing their failure is a key technical issue.

    In recent years, several weak spots have been identified in the structure of modern Si-based power devices, and some solutions (packaging) have already been found to increase their resistance to disruption. However, the aging of the top metal source and wire bondings, mainly made of Al or Al alloy has persisted as an intrinsic weak link, degrading the electrical performance of the device over time. This occurs through mechanisms that involve grain boundary diffusion, crack formation and surface/interface oxidation, also driven by stresses arising from thermal mismatch between the metal and the silicon. The goal of this thesis is to find methods (fresh devices processing, circuitry modification) favoring the self-healing or the non propagation of these cracks.

     

    More details HERE

     

    On the Mitsubishi Electric Research site


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