There is a strong need nowadays by confocal microscope end-users and manufacturers to access reliable and quantitative imaging in the extended red/infrared spectral range, as crucially demanded by the pharmaceutical industry (red fluorescence), for biology imaging needs of living tissues (near-IR at 0.9-1 µm) or for molecular sensing (mid-IR in the finger print spectral range). This means that there is an identified lack of industrial solutions in terms of optical standards to calibrate such microscopes in the red/infrared range. Therefore, there is a clear necessity to produce new integrated photonics solutions for optical standards based on high-contrast red/IR emitting structures distributed in 3D with sub-wavelength resolution. Concomitantly, 3D photonic architectures with rationally-engineered sub-wavelength periodicities have led this last decade to breakthrough concepts in photonics as well as in major achievements such as three-dimensional linear/nonlinear photonic crystals and metamaterials in optics. Despite remarkable achievements, it is still highly challenging to address such direct 3D fabrication by versatile all-optical laser-based means (not lithography, no clean room), in perennial materials (not polymers), with fully embedded architectures in a robust medium as glasses (not printing on a substrate, as in 3D printing) with technological transfer compatibility. In this context, the project ArchiFLUO ambitions firstly to develop innovative highly-photosensitive glasses under laser irradiation, to understand and improve fundamental mechanisms of glass modifications so as to create high-contrast red/IR emitting structures with sub-wavelength resolution. This will be investigated either by playing on the glass matrix behavior by introducing co-mobile alkali ions, by achieving resonant energy transfers from localized fluorescent silver clusters to IR emitters (rare earth or transition metal ions) or by the local precipitation of fluorescent dielectric / semiconductor nanocrystallites in fluoride / heavy metal oxide glasses. Secondly, ArchiFLUO ambitions to develop challenging all-optical laser-based approaches in inorganic glasses, to directly create multi-scale linear and/or nonlinear photonic crystal architectures for integrated applications such as light management or optical sensing. Thirdly, ArchiFLUO aims to succeed in technological transfer in glass science and laser irradiation processes to allow for the demonstration of new optical standard prototype as well as for the potential emergence of new industrial products so as to fill the gap of highly-demanded but still missing reliable optical standards with extended spectral range for fluorescence imaging calibration. ArchiFLUO is a collaborative multi-disciplinary PRCE ANR project with four partners with international visibility and recognized expertise in glass science, in material and mechanism characterization, and in femtosecond laser modification of materials, namely ICMCB, CELIA, LSI and the company ARGOLIGHT. ArchiFLUO targets thus to develop cutting-edge research in both glass elaboration and in laser manufacturing, compatible with international-grade progress, which will allow for an enlarged international scientific visibility to the partners as well as an international leadership in the targeted scientific topics. ArchiFLUO will also strengthen the pioneer position of ARGOLIGHT as an innovative optical standard manufacturer.

The aim of this project is to develop the theory and software for the ab initio predictive description, without adjustable parameters, of Resonant Inelastic X-ray Spectroscopy (RIXS). RIXS is an important experimental tool to probe elementary excitations in solids. It gives vital information about the (strong) electron correlation, thanks to the large variety of targeted excitations, including i) charge-transfer excitations (crucial to unravel the nature of an insulator, like charge transfer type or Mott-Hubbard); ii) crystal-field features such as dd excitations in strongly correlated materials. Other accessible and well studied excitations are excitons, plasmons, phonons, and magnons. Theory plays a crucial role in the interpretation and understanding of the experimental spectra, in particular to disentangle the many types of excitations in RIXS spectra. The physical picture of RIXS can be summarized as follows: i) an incoming photon promotes a core electron to an empty conduction state; ii) a different electron from the valence region fills the core hole. The net result is a final state with an electron-hole excitation, whose energy and momentum are defined by the conservation laws. Therefore, in RIXS one combines an excitation from a core level and a de-excitation to the same core level, the net result begin an excitation for the valence. So RIXS is not (only) a measure of core levels, but of valence states. In order to simulate RIXS spectra one has to describe the electron-hole interactions of the intermediate and final states. Therefore we will use the Bethe-Salpeter equation (BSE), an ab initio theory that explicitly takes into account electron-hole interactions in absorption spectra. The project has two main parts: 1) Extend both the theory and the implementation of the BSE to the calculation of RIXS spectra. This requires the description of high-energy photons and non-zero momentum transfer. It is important to note that we already have some preliminary results; we successfully generalized the BSE formalism to finite momentum transfer. In particular, the ab initio tool we will develop will describe the physics of the complex transition metal L and M edges, for which currently no ab initio approach exists. Moreover, the theory will be able to describe the so-called strongly correlated materials, for which a wealth of RIXS data have been collected. 2) Describe the electron correlation relevant to RIXS. In particular, RIXS is a powerful tool to study strong correlation. However, current approaches cannot accurately treat strong correlation without using adjustable parameters. To treat strongly correlated systems we will generalize an ab initio method developed by ourselves which has been successful in describing strong correlation. The starting point of our approach is the spectral representation of the Green function, whose imaginary part is linked to the photoemission spectrum, which we have expressed in a series of n-body density matrices. We have shown that simple approximations to this series gives accurate spectra for model systems, for both weak and strong correlation. We have also been able to correctly predict, without breaking the symmetry, that NiO in its paramagnetic phase is an insulator. Although we obtain qualitative good results, we have to improve the accuracy. This will be an important goal of the TRIXS project. Throughout the duration of the TRIXS project we will benchmark our results for semiconductors and correlated solids against high-resolution RIXS experimental spectra obtained by ourselves at the SEXTANTS beamline at SOLEIL. Finally, the ab initio numerical tool developed in the TRIXS project will be made available to the scientific community through a open source code.

Climate changes increase the severity and frequency of flooding thus spreading pollution and exposing water to contamination. Oil-shale is a source of fuel but it is also a source of mercury and other heavy-metal pollution. Water control agencies are at the front-line of monitoring groundwater quality and tracking pollution. Budget and manpower cuts make these tasks more difficult. Regulations push towards real-time, on-site or in situ analyses to improve the reliability of monitoring, the representatively of sampling and faster information requires fast, portable, low-cost, environmentally friendly, sensitive sensors that are able to quantify heavy metals in different types of water. The problem with conventional sampling is the collection of water, preservation, shipping and storing. Sampling changes the water: pH and oxygen content. This changes the concentration and oxidation state of metal ions and only gives a snap-shot of quality. Thus the trend in water monitoring is passive or in situ sampling. Passive sampling is done by placing cartridges into a body of water. The cartridges contain metal ion chelating polymers that selectively adsorb and pre-concentrate metal ions. After two weeks, the samplers are recovered and sent to a lab for extraction and analysis. The advantages of passive sampling are that the limits of detection (LODs) are very low, due to metal ion pre-concentration. Analysis results better represent the water, since passive samplers are at equilibrium with it. The problem with passive samplers is the long sampling times, the extraction and expensive analysis by atomic adsorption spectroscopy (AAS) or inductively coupled plasma mass spectroscopy (ICP-MS). Two particularly difficult toxic metal ions are mercury and chromium (VI). Allowed levels for mercury are sub µg/L (0.015 µg/L potable water and 0.5 µg/L residual waters - French water norms of 27 October 2011). Due to volatility, mercury is analysed separately from other metals. Mercury analysis is usually performed by AAS or ICP-MS with cold vapour trapping. AAS and ICP-MS are time consuming and require a centralised lab with trained personnel. Chromium (VI) can be analysed by colourimetry but lacks sensitivity. It can be analysed by LC-ICP-MS but this is rare in private labs. Chromium (VI) analysis requires fast analysis due to potential changes between sampling and analysis. Most of the current technology is not adequate to meet the demands of sensor manufacturers or end users. Electrochemical sensors are cheap with fast response times. The most sensitive are based on toxic mercury and the cheapest are disposable screen printed electrodes (SPE), that are portable and non-toxic but lack sub µg/L sensitivity. Moreover, mercury based electrochemical systems cannot detect mercury. For these reasons a consortium of two public research labs, LSI and BRGM, a private lab, SGS MULTILAB, and a small enterprise which devlopes prototypes and series, VALOTEC, have joined to validate the potential of a patented 3-D membrane sensor developed by the LSI, able to quantify heavy metals, notably mercury but also Chromium (VI), at trace levels, in situ, on-site and/or on-line, using passive sampling. The new sensitive 3-D membrane sensors passively pre-concentrate metal ions by a chelating polymer and obtain equilibrium with the environment. The adsorption time is 30 minutes to twenty four hours and the analysis is rapid and on-site thus bridging the gap between passive samplers and electrochemical sensors. This environmentally friendly sensor relies on ion-track etched nano-functionalized membranes made of bio-compatible polyvinylidene fluoride (PVDF). The sensors measures heavy metals well below the limitations imposed by existing norms making them competitive with electrodes containing toxic mercury. If proven reliable and cost effective, the sensor could be integrated into existing systems, or used standalone as portable devices.

The diamond hexagonal (2H) phase does not appear in the pressure-temperature phase diagram of silicon. However, the partner Laboratoire de physique des interfaces et des couches minces (LPICM, CNRS, École polytechnique, Université Paris-Saclay) has demonstrated that silicon nanowires having the 2H phase can be produced by the vapour-liquid-solid (VLS) method in a plasma-enhanced chemical vapour deposition (PECVD) reactor. The goal of the HexaNW project is to understand what stabilises that phase during growth in order to establish a protocol to reliably reproduce it. In order to understand that mechanism, we will use the atomic-scale observation of the growth, in situ, in the NanoMAX environmental transmission electron microscope (ETEM), and its modelling by thermodynamic calculations using surface and interface energies that will be ab-initio calculated. NanoMAX is the environmental part of the “EquipeX” TEMPOS. The calculated band structure of 2H Si makes it a better absorber of the solar spectrum than standard diamond-cubic (3C) silicon (Amato, Nano Lett. 16, 5694, 2016) and its band gap would be direct in nanowires or under stress (Rödl, …, and Guillemoles, Phys. Rev. B 92, 045207, 2015). These electronic properties, together with the natural abundance of the element and its environmental innocuity, make it a wonderful candidate for future nano opto-electronic devices. LPICM develops solar cells based on radial junctions around crystalline nanowires grown by tin-catalysed PECVD. Quite remarkably, the amorphous silicon deposited around a 2H core in such devices would apply a stress that may possibly be used to tune the band gap of the 2H phase. Although 2H Si does not exist at equilibrium, it has been found in various systems under stress. It has also been obtained deliberately by epitaxy on wurtzite GaP nanowires. But, before our observations, it had never been demonstrated in as grown silicon nanowires without ambiguity. Our observations are uniquely performed in a zone axis of the type [110] (3C)/ [11-20] (2H), where the characterisation of the phase is direct (Tang, Maurice, et al., Nanoscale, 2017). The 2H nanowires we prepare differ from those usually studied by (i) their small size (5 nm), (ii) their low-temperature fabrication by plasma-enhanced VLS and (iii) their liquid tin catalyst. In addition to understanding the mechanisms of growth, the goal of HexaNW will also be to know the properties that will come out of such objects, as a function of their size and polytype. Its prospects are to develop opto-electronic devices or photovoltaic cells taking advantage of the unique band structure of 2H Si nanowires. The project will run over a period of 42 months. The programme is the following: growth will be optimised at LPICM in the reactor that already produces the phase. Developing this part will be the task of the PhD student hired by the project. It will be observed in the NanoMAX ETEM in real time and at atomic resolution. Given the risk of this task, the in situ study will also include molecular beam epitaxy of Ge NWs by partner C2N in conditions where the 2H structure would form. Major opto-electronic characterizations of the material will be performed at IRDEP on nanowires grown ex-situ with the help of two interns. Cathodoluminescence (LPICM-C2N) will bring information on the individual luminescence properties. Nucleation and growth will be modelled at C2N (CNRS, Université Paris-Sud, Université Paris-Saclay), with the help of a one-year postdoctoral fellow paid by the project, using surface and interface energies ab-initio calculated at LSI (CEA-CNRS-École polytechnique, Université Paris-Saclay), with the help of a second one-year postdoctoral fellow. The correlation of atomic-scale observations with this modelling will lead to a fine understanding of the ways the Si 2H phase stabilises itself.

In the last few years there has been an explosive development in material science. It began with the theoretical prediction of a new class of three dimensional (3D) topological insulators (TIs) which are fully gapped in the bulk, but with unusual gapless ‘protected’ 2D Dirac surface states. The protection arises from the linear energy-momentum dispersion, with the surface states near the Fermi surface residing on a single “massless” Dirac cone with locked spins. If realized, these systems could be the Holy Grail in the fields of spintronics and fault-tolerant quantum computing. However, access to this 2D quantum matter is a challenge, due to the difficulty of separating surface contribution from the non-zero conductivity of the bulk. In approaches taken thus far, such as nanostructured synthesis/growth, doping, compositional tuning, or band-gap engineering via device gating, complete suppression of the bulk conduction in TIs has not yet been realized. We propose a new approach, which consists of using controlled disorder to create stable charged point defects in the bulk of topological insulators by particle irradiation in order to compensate for the “intrinsic” charged defects and to achieve a fully insulating bulk. Using swift (<3 MeV range) electron or proton beams we will create simple, vacancy and interstitial type defects that will enable us to (a) tune the bulk carrier density, thereby tuning the Fermi level across the Dirac point, and (b) to reduce bulk conductivity by creating Anderson localization. The first objective will give rise to charge compensation in a bulk TI, while the second will enable us to test recent theoretical predictions of Quantized Anomalous Hall Effect (QAHE). Identification of bulk and surface contribution in irradiation-doped samples will be obtained by combination of electronic transport in high magnetic field by Shubnikov-de Haas oscillations (SdH) and Angular Resolved Photoemision Spectroscopy (ARPES). Definition of the route for fabrication of TIs with suppressed bulk conductivity is the primary goal of the project. The second goal is determination of the effect of disorder on the surface conducting states of TI’s. With the proper choice of irradiation dose, the bulk resistivity may be increased by many orders of magnitude when the chemical potential reaches the Dirac point. Using this technique we expect to further test a recent prediction of a Topological Anderson Insulator – a nontrivial quantum phase with quantized conductance obtained by introducing disorder in a metal with strong spin-orbit interaction. The third goal of the project is fabrication by proton implantation of p-n-p or n-p-n structures below the surface of TI’s. Such structures, if realized and properly contacted, are the prototype of a tunable spintronic device that may open a path for novel applications. This proposal is an international collaboration between two groups at Ecole Polytechnique in Palaiseau, and at Orsay University, France, with unique expertise in swift particle irradiation techniques and femtosecond ARPES with the consortium lead by condensed matter physics group of the City College of New York (CCNY) -CUNY. This collaboration combines the complementary technical strengths of material science with particle beam technology to control and tune key electronic properties of the newly discovered functional class of materials.