Patterning of silicon surfaces is essential for the design of opto and microelectronic devices. Creating microstructures like trenches, macropores or rods are essentials for the development of several component families in many research fields and commercial applications. Silicon etching is carried out either chemically or by using reactive-ion etching, usually involving one or more lithography steps. This is accompanied by some important constraints. The fabrication of complex structures involves a large number of technological steps that represent eventually a significant cost in the final device cost (and lithography/dry etching equipment also requires considerable investments). Moreover, one is often restricted in the design of perfectly suited surface structures because of limitations due for instance to the influence of the crystallography or to insufficiently high aspect ratios. In addition, in some industries (e.g. photovoltaic), lithography is incompatible with the cost issues and technical constraints of production lines, which strongly limit the surface structures that can be realized and therefore their effectiveness. Recently, a new method to etch silicon has emerged. It is based on the contact at the nanoscale of silicon with a noble metal in the presence of HF and an oxidizing agent (e.g. H2O2, anodic current). The metal acts as a catalyst allowing for a localized dissolution with a resolution of a few nm only. More recently, a Japanese group has shown that it is also possible with this method to use micrometer-sized electrodes made of Pt to etch large structures in silicon. Based on this principle, the PATTERN project aims at the development of a new silicon etching process using metal electrodes that perform "nano-imprints" by direct contact with silicon in a single electrochemical step. The goal is to be able to replicate a large variety of forms such as pores and trenches of high aspect ratio, inverted pyramids, micro-pillars, etc., cumulating high accuracy (~ 10 nm), multi-level etching profile and large surface area processing capabilities (> cm2). The biggest technological issue is the necessity to provide a nanostructured interface with a triple contact Silicon/Electrolyte/Metal. The innovative aspect is the development and use of volumetric nanoporous metal electrodes that can ensure this triple contact whatever the considered dimensions are, and be used several times in industrial processes. PATTERN is intended to provide the basis for this new contact etching process, including a demonstrator in the field of surface treatments for solar cells. PATTERN is divided into three tasks according to a multidisciplinary approach combining microelectronics, optics, powder metallurgy, electrochemistry of semiconductors and modeling of electronic interfaces: T1- Development of nanoporous metal electrodes with defined patterns (IEMN). Production of molds with basic and advanced periodic structures; Elaboration of nanoporous metal imprints by sintering metal powders in the molds. T2 - Contact etching of silicon (ICMPE). Study of the etching process and the transfer of the imprint electrodes surface pattern to the silicon substrate, with different oxidizing agents and metals; Optimization of the operating conditions. T3- 2D modeling of the Silicon/Electrolyte/Metal electronic interface (LGEP). Localization of the anodic currents around metal dots ~10x10 nm2 in size, as a function of the metal work function, the metal polarization, the inter-dot spacing. To conduct the project, three research teams specialized in microelectronics (IEMN), silicon (electro)chemical etching (ICMPE), and modeling of semiconductor electronic properties (LGEP) gathered together. They are acknowledged of a high level expertize in microelectronics, optoelectronics and photovoltaics applications, with several international patents taken in these fields.

The project aims to design an innovative magnetic component on board an electrical converter of a future aircraft. The magnetic core of this component will be made from a ceramic powder which microstructure will be optimized and implemented using the PIM (Injection Molding) process. The winding of this magnetic component will also integrate several magnetic functions that can operate efficiently at high frequency (a few hundred kilohertz). The whole will be integrated and tested in a operating converter to assess the improvements made. Thus, PIMCOMAP project will bring together all the actors necessary to develop a new material with an innovative process and test it in a technological evaluator with a TRL3 maturity level in a relatively short time.

While silicon-based solar cell technologies dominate the photovoltaic (PV) market today, their performance is limited. Indeed, the world record efficiency for Si-based PVs has been static at 25% for several years now. III-V multijunction PVs, on the other hand, have recently attained efficiencies > 40% and new record performances emerge regularly. Although tandem PV geometries have been developed combining crystalline and amorphous silicon, it has not been possible so far to form devices with efficiencies to rival III-V multijunctions. NOVAGAINS aims to benefit from combining the maturity of the Si technology with the potential efficiency gains associated with IIIV PV through the development of a novel tandem PV involving the integration of an InGaN based junction on a monocrystalline Si junction by means of a compliant ZnO interfacial template layer which doubles as a tunnel junction. Although the (In)GaN alloy has been used extensively in LEDs, its’ use in solar cell technology has drawn relatively little attention. Nevertheless, the InGaN materials system offers a huge potential to develop superior efficiency PV devices. The primary advantage of InGaN is the direct-band gap, which can be tuned to cover a range from 0.7 eV to 3.4 eV. As such, this is the only system which encompasses as much of the solar spectrum. Indeed, the fact that InGaN can provide such tunability of the bandgap means that PV conversion efficiencies greater than 50% can be anticipated. Unfortunately, it is very difficult to grow GaN based films of high materials quality directly on Si because they do not have a good crystallographic match. ZnO can be grown more readily on such substrates, however, because of its’ more compliant nature. Indeed, well-crystallized and highly-oriented ZnO can even be grown directly on the native amorphous SiO2 layer. Since ZnO shares the same wurtzite structure as GaN and there is less than 2% lattice mismatch it has been demonstrated that it is then possible to grow InGaN/GaN epitaxially on ZnO/Si using the specialized know-how offered by the consortium. Modeling indicates that when optimized, stacked InGaN and Si cells coupled by tunneling through a ZnO interlayer offer the perspective of tandem cells with overall solar conversion efficiencies in excess of 30%.

The electrification of transport implies a strong increase in power and voltage in on-board networks (particularly in aeronautics). The risk of damages due to arcing faults is thus increased. The arc fault is unavoidable, so it must be detected. The arc detection involves a minimum delay during which the damages generated by the arc must be minimized. The objective of the DESMARC project is to propose a passive protection of embedded systems, based on polymer materials, which would mitigate the consequences of the arc on its environment. This protection consists in a layer of materials deposited on the usual cables whose degradation products by the arc would modify the characteristics of the arc and reduce the consequences. For that, the project focuses on the defects at the level of cables. Several challenges are identified. It is necessary to identify the key parameters between the nature of the polymers that are stable at cable operating temperatures, the nature of their degradation products and the behavior of the arc in their presence. To reach these objectives we propose to model the arc-material interaction and to develop an approach (test/selection criteria) to ensure the beneficial effects of the proposed material. It will be necessary to define a validation process and success/failure criteria based on existing materials and standards and the expertise of the partners. In this project, two laboratories (GeePs and UMET) and two industrial companies (Protavic and Safran) have complementary roles in interaction. UMET and Protavic are developing and characterizing functionalized polymeric materials resistant to extreme conditions. GeePS and UMET characterize the materials during and after the arc in terms of arc resistance. Safran, GeePS and UMET are modeling the arc/material interaction and degradation modes (validation will be done by experiment) to propose material design options.

The ETAE project suggests significant advancements about the emergence and control of hydrodynamic instabilities in closed recirculating flows with a free surface. This generic flow configuration is present in numerous industrial contexts. The present aim is, from well-designed excitations by electro-active actuators, to manipulate the flow, and thus to identify the mechanisms promoting large-scale vortical instabilities arising in the presence of external mechanical noise. Bringing together the experimental/numerical skills on rotating flows at LIMSI, and the experience of GEEPS about modelling and conception of active actuators, will address important issues about the effect of parasitic noise on closed fluid systems. The exploratory side about actuators opens wide perspectives on the application of new measurement and control techniques in a fluid set-up, in close interaction with the development of new active materials expected to contribute in the future to fluid control strategies. The study of instabilities in closed rotating flows, triggered by rotating disks, has been one of the key topics for which LIMSI is internationally recognised. Such flows have now become classical topics due to their genericity and their importance in geophysical or industrial contexts. Using an experimental device consisting of a rotating vessel partially filled with liquid and a free surface, the team at LIMSI has shown evidence for instability modes due to the free surface. The flow before the instability is axisymmetric, and this axisymmetry is broken by instability modes above a given threshold (for the angular velocity of the disk). Two cases can be identified: weak deformations of the free surface where the instability manifests itself as a array of large-scale vortices, versus strong deformations where the free surface itself has broken its axisymmetry. From an experimental point of view, measurements of the free surface height in real time demands novel techniques. Besides, the strong deformation case remains even today a true challenge for numerical simulation. However, even in the weal deformation case, threshold measurements have revealed significant departures between experimental results and numerical predictions. Sensibility methods, developed only recently in the context of open flows, appear as relevant tools to understand the effect of generic external unsteadiness (of weak amplitude and mechanical origin) on the fluid system. Moreover, adding a perfectly controlled vibration to a given flow should explain, and more importantly reduce the mismatch between observed thresholds. Devising such actuators, the associated measurement methods, and integrating them into an efficient feedback loop represent as for today important technological challenges. This project is at the junction between active control of rotating flows at LIMSI and modelling of active-material-based actuators at GEEPS. Bringing together such skills is expected to lead to both fundamental and practical progress about the sensibility of confined flows to unavoidable parasitic vibrations. The exploratory side about actuators in the large deformation regime opens new important perspectives on the development of fluid-structure simulation codes as well as on the characterisation of electro-active materials.