Most living cells exhibit a difference in electrical potential across their plasma membrane resulting from differences in ion concentration maintained by ion channels and pumps. The membrane of a neuron can be suddenly (≈1 ms) depolarised (its intracellular potential rising from -70 mV to +30 mV) by the synchronised opening of these channels, stimulated by other neurons, thus generating an 'action potential' that spreads to other cells to which that neuron is connected by synapses. Monitoring this depolarisation thus provides information on synaptic transmission, which is essential for cognitive and neuromotor processes. The classical approach consists of measuring electrophysiological activity using micropipettes on a few cells at a time ("patch-clamp"), or with a microelectrode array able to record the extracellular potentials of a group of neurons. In recent decades, optical measurement methods have been introduced to obtain the electrical activity of a large number of cells simultaneously with high resolution. Apart from a few works exploiting the modulation of electroplasmonic effects of gold nanoparticles or semiconductor nanocrystal charges, these methods present a certain number of drawbacks (photobleaching, toxicity...) or limitations regarding the measurement of an extracellular electrophysiological signal. The objective of our project is to develop and biologically validate a new photoluminescent probe of the extracellular potential based on a transduction mechanism never explored for this application and which should lead to a very high spatiotemporal resolution. These probes are ferroelectric nanocrystals (FENC) doped with rare-earth ions (RE3+) whose spectral modulation of photon up-conversion (UC) will be detected as a function of the surrounding electrical potential. The variations of this potential, under the effect of the opening of the ion channels, modify the surface density of the polarization charges P of the FENC, making P vary which in turn leads to a deformation of the FENC by inverse piezoelectric effect, inducing finally a change of intensity of certain emission lines of UC. This process is supported by our recent observation of such a UC modulation in an FNCE exposed to an electric field. First, we will synthesize BaTiO3 NCFEs of size≈200 nm doped with Er3+ and Yb3+ ions and also test other matrices with stronger piezoelectric response, and other dopants. Ab initio calculations will help us determine the most favourable crystallographic sites for ion incorporation. We will characterise the intensity of the CU and its lifetime. Next, we will image the ferro/piezoelectric domains of individual NCFEs by piezoelectric force microscopy (PFM) where an oscillating potential is applied to the tip. We will aim to produce bright single-domain FENCs. We will quantify the variation of the UC spectrum during PFM measurements, as well as under ion flux from a discharge tip. Finally, we will test the ability of FENCs to detect changes in charge density in solution, before using them, after biofunctionalization, as optical sensors of near-membrane potential changes during electroporation, and then to monitor nerve regeneration. This highly interdisciplinary project requires the complementary skills of five teams, in the synthesis and characterisation of FENCs, optical spectroscopy and near-field probe microscopy, bio-conjugation of nanoparticles and bioelectrochemistry. This project exploiting the polarisation charges of ferroelectric nanosystems will open up a new field of applications beyond the biomedical one.

With the advent of PetaWatt (PW) class lasers capable of achieving light intensities I=10^22W.cm-2 at which matter becomes plasma, Ultra-High Intensity (UHI) physics now aims at solving two major challenges: can we reach extreme light intensities approaching the Schwinger limit I=10^29W.cm-2, around which light self-focuses and produces electron-positron pairs in vacuum? Can we achieve high-charge compact particle accelerators with high-beam quality that will be essential to push forward the horizons of high energy science? Solving these major questions with the current generation of high-power lasers will require conceptual breakthroughs that I intend to develop in this project. In particular, I aim to show that so-called ‘relativistic plasma mirrors’, produced when a high-power laser hits a solid target, can provide simple and elegant paths to solve these two challenges. Upon reflection on a plasma mirror surface, lasers can produce high-charge relativistic electron bunches and bright short-wavelength attosecond harmonic beams. Could we use plasma mirrors to tightly focus harmonic beams and reach extreme light intensities, potentially approaching the Schwinger limit? Could we employ plasma mirrors as high-charge electron injectors in a PW laser field of 100TV.m-1, or in a laser wakefield accelerator, to build ultra-compact particle accelerators? In the PLASM-ON-CHIP project, I propose to answer these interrogations ‘on-chip’ using massively parallel simulations on the largest supercomputers, to help devise/validate novel and readily-applicable experimental solutions based on plasma mirrors. To this end, I will make use of our recent transformative developments in ‘first principles’ simulation of UHI laser-plasma interactions that enable the 3D modeling of plasma mirror sources with high-fidelity on current petascale and future exascale supercomputers.

Lubricating oils are being increasingly used across several industrial applications and the demand for these materials is on the rise and is expected to grow further in order to reduce machinery energy consumption and wear. Within this framework, the development of high performance lubricants is the key for the expansion of important industries and markets. Recently ionic liquids (ILs) have been shown to be promising candidates for novel high performances lubricants thanks to their various physico-chemical properties and their ability to lower significantly the friction between two surfaces. Such promising properties of ILs were found to be highly related to their capacity to nanostructure in bulk and at interfaces. However, the range of viscosities available in most IL classes is rather narrow compared to macromolecular lubricants. Poly(ionic liquid)s (PILs) are thus promising candidates to translate the frictional and chemical properties of both polymers and ILs to innovative and highly tuneable macromolecular lubricants. The addition of local interactions inherited from ILs to macromolecules results in a complex and rich panel of chemical and physical properties opening new opportunities to design polymeric materials with targeted functions which are highly related to both structural and dynamical properties of PILs. The POILLU project aims to take advantage of the lubrication properties of ILs and strong slippage ability of polymer melts to develop PILs with enhanced lubrication properties. Supported by the synthesis of a new class of tailored PILs specifically designed to meet the stringent criteria and ambitious objectives of this the project, this multidisciplinary consortium will perform a detailed molecular description of the bulk and interfacial stress transmission mechanisms involved in PILs using complementary state-of-the-art experimental techniques mastered by skilled soft matter physicists. The coupling of extensive bulk rheological characterization and advanced scattering techniques (SANS, WAXS) will enable us to determine the multi-scale structure/dynamic relationship occurring in PILs. The enhanced interfacial nano-structuration of PILs and its impact on surface chains dynamics will be studied thanks to Grazing Incident X-ray Scattering and Surface Force Apparatus nano-rheological measurements. Finally, the lubrication properties of PILs will be characterized using photobleaching based velocimetry technique. This interdisciplinary approach gathering internationally renowned skills in polymer chemistry, physical chemistry and physics that will highlight the exotic properties of PILs both in bulk and at interfaces opening appealing scientific perspectives in the field of complex polymeric materials targeting specific function through a multiscale molecular design.

The progresses in photonic technologies require the independent control of the phase propagation and the energy of light. This is possible using hyperbolic metamaterials, an ultimate case of birefringence with ordinary and extraordinary dielectric constants of opposite sign. Self-organized molecular and/or macromolecular systems offer a route to the realization of such media since they can embed various pi-conjugated mesogens amenable to form a large variety of structures with record-breaking optical anisotropy. Our objective is to develop an innovative self-organized (macro)molecular system incorporating fluorescent moieties in order to combine hyperbolic dispersion with light emission or optical gain. Beyond the compensation of the intrinsic losses of metamaterials, we target the realization of innovative light-emiting devices by embedding the source in the bulk of the metamaterial, whereas most current realizations involve complex nanoscale combinations of different emissive and birefringent media.

The present project aims at developing a new model of the experimental spin resolved electron density common to experimental techniques as different as Polarised Neutron Diffraction (PND), high resolution X-Ray Diffraction (XRD), X-ray Magnetic Diffraction (XMD) and Magnetic Inelastic Compton Scattering (M-ICS). Thanks to methodological developments to which some of us participated, XRD and PND are now routinely used to determine the charge or spin densities in position space. XMD technique is an interesting alternative which complement polarised neutron diffraction; it is a powerful method for separating the orbital and the spin contributions to the magnetic diffraction. The Magnetic Compton scattering data give access to the spin resolved momentum density. In a previous ANR contract (CEDA, 2007-2011) we showed that the spin resolved electron density can be obtained by a joint refinement of polarised neutrons and high resolution X-ray diffraction data, by adapting the electron density multipole model. This allows for the very first time the experimental distinction between ? (spin up) and ? (spin down) electrons (Deustch et al, accepted to IUCrJ 2014). For atoms having spin and orbital moments, PND cannot distinguish between the two contributions, the orbital contribution being usually estimated from theoretical considerations. In order to have an experimental only spin density model, we want to bypass this theoretical estimation by including XMD. These three diffraction techniques give access to a more precise and accurate spin resolved distribution of localised electrons in position space. To complete the density model, the delocalised electrons can be more precisely determined using Compton scattering experiments (electron density in momentum space). Since these experiments can all be conducted on the same system, which means we are looking at the same object from different angles, our main objective is to construct a unique common physical model that exploits the richness of these scattering techniques. The common denominator for all these experiments is the 1 electron reduced density matrix (1RDM). Hence the aim of the project is to determine experimentally the elements (in a given basis set of atomic functions) of this matrix through a joint refinement against XRD, XMD, PND and ICS. The main problem of the joint refinement is to find a unique parameterisation common to all these techniques and to find a way to handle the variety and the precisions of the experimental data. In particular, this requires finding a proper weighting scheme and the refinement strategy, without losing any information coming from each experiment. The strategy will be defined using YTiO3 crystals, an interesting perovskite which shows orbital ordering not fully understood. As soon as the method is validated, it will be applied to suitable materials and the resulting software will be improved to be users friendly in order to distribute it to crystallographers, physicists and chemists.