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.

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.

Emerging communication technologies like 5G or Near Field Communication call for voltage tunable ferroelectric (FE) film capacitors to work at higher frequencies or lower voltage, thus requiring the reduction of the FE thickness. Unfortunately, two interface-related phenomena, the FE “dead layer” and leakage current, impede this evolution. Recent encouraging ab initio calculations showed the importance of the chemical bonding, polar discontinuity and distortion mismatch at electrode/FE perovskite interfaces for polarization stabilization and Schottky barrier height (SBH) adjustment. A systematic interface engineering using Combinatorial Pulsed Laser Deposition will chemically modulate electrode/(Ba,Sr)TiO3 interfaces of industrial capacitors. Advanced spectroscopy and microscopy methods coupled with first-principles calculations will help to understand the chemical, structural and electronic mechanisms controlling the SBH and FE polarization at the interface. TRL 6 industrial prototype varactors with the optimized interfaces will be tested against 5G and NFC specifications.

The goal of PHOTOMIC is to develop and integrate organic materials for all-photonic neuromorphic computing. Our approach is to develop photochromic materials as the active elements of all-optical synapses to be interfaced with semiconductor photonic neurons towards innovative machine learning schemes. More specifically, we will develop a hybrid semiconductor/molecular model elemental system to implement a machine learning algorithm. It will combine ultrafast micropillar semiconductor lasers as spiking neurons and optimized organic photochromic materials. Two types of photochromic effects will be considered: direct photoinduced refractive index modulation, and photoinduced surface relief formation. This highly interdisciplinary project thus combines semiconductor photonics, photophysics, molecular photonics and organic chemistry.

The goal of AdvTMR is to develop a new generation of spin electronics magnetic sensors based on the combination of state of the art magnetic tunnel junctions and a method for suppressing the low frequency noise large in these devices. The targeted performances are one order to two orders of magnitude better than existing magnetic sensors. The output of the project will be two sensors. The first one is a ultra low consumption 2D magnetometer with picotesla detectivity working up to 150°C and the second one is a nitrogen-cooled sensor with sub femtoTesla detectivity. The work is shared between a public research institute and a company for 3 years duration.Validation will be performed by three industrials partners involved in defense.