Faits marquants 2018

Simulating Surface Resonant X-Ray Diffraction

The technique called Surface Resonant X-ray Diffraction is a powerful tool for characterizing an ultra-thin film on a surface or an electro-chemical interface. It probes the crystallographic structure of such surface systems by recording 2-Dimensional diffraction peaks at fixed X-Ray energy. Also, one can probe the electronic structure around selected atoms by recording the absorption of X-Rays as a function of their energy, especially at resonance with the binding energy of the atoms’ core electrons. However, the interpretation of the X-Ray data requires development of sophisticated ab initio theoretical methods that can create simulated spectra to be compared with the experimental spectra. Full text.

Dirac electrons’ spins get locked on a topological insulator’s surface

"Topological insulators" are a novel class of materials attracting great interest both theoretically and experimentally, because of the unique electronic and spin properties arising at their surfaces. Their defining characteristic is that they are insulating in their interior but they have conducting surface states. The surface electrons and hole states have a remarkable « Dirac-like » energy dispersion function, i.e. their kinetic energy is linear in their momentum, not quadratic. Also the surface electrons show the property of perpendicular "spin-momentum locking" : the orientation of the electron spins is locked perpendicular to the direction of the electron current flow, a feature potentially useful for spintronics and quantum technologies. Full text.

Scanning Hall-Probe Microscopy

At the Institut NEEL, we develop many highly sophisticated scanning probes to use for a large variety of experiments under extreme conditions of magnetic field, low temperature and vacuum, as well as microscopes sensitive to charge, to currents, to magnetic fields, forces, electrical potential, to name just a few. Here, we wish to highlight a microscope which does not operate under extreme conditions but has the advantage of being extremely versatile. This microscope is a "Scanning Hall-Probe Microscope" (SHPM) which allows us to do direct, quantitative measurements of the spatial variation of a a magnetic field, that is to "map" the field. Full text.

Sionludino : A fl exible control system for automation of experiments

Experiments are getting more and more complex, more and more precise, more and more greedy for measurement and control systems. Requirements for these systems also include high reliability and high repeatability. In this context, various options exist. Full text.

A tool for “smart“ projection-photolithography

The NEEL Institute’s research work has created a vital need for fabrication "in house" of highly specialized microelectronics devices. These include silicon devices such as diodes, p-n and field-effect transistors, etc, for use in a wide variety of experiments. These devices are fabricated on demand by depositing different materials (e.g. metal leads, contacts, electrodes, ...) on the silicon wafer and performing oxidations and other processes, often in very complex geometric patterns. Full text.

From nanomaterials to the bulk, one instrument to characterize them all

In materials science, characterizing the materials goes along with synthesizing them. One of the best and fastest characterization techniques is X-ray diffraction. This technique has mostly been restricted to well crystallized, homogeneous powders or bulk materials. However, research projects at the Institut NEEL are now focusing on more complex materials, such as nanomaterials, ultrathin films and layers, or striped alloys. These challenging cases, as well as increased demand from our researchers, have called for a dramatic evolution of our instrumentation. Full text.

High throughput characterisation of magnetic fi lms

The functional magnetic properties of magnetic films depend on their main constituent phase and their microstructure (grain size, grain orientation, secondary and grain-boundary phases…). These in turn depend on the film’s chemical composition as well as the deposition and annealing conditions applied during film preparation. "Combinatorial" thin film studies, based on the preparation and characterisation of films having a composition gradient across their width, are being used for the high-throughput screening and optimization of a range of functional materials. With the aim to apply the combinatorial approach to the study of high performance hard magnetic materials, we have developed a high field scanning Magneto-Optic Kerr effect (MOKE) magnetometer, for non-destructive high-throughput magnetic characterization. Full text.

Lithium-ion diffusion pathways within new battery-cathode materials

Li-ion batteries form a basic component on which our world of mobile electronics and communication is built. And they are increasingly used in high power applications such as electric vehicles and the storage of electricity from solar and other renewable power sources. In these batteries, the cathode is a lithium-containing compound. During a battery’s charging and discharging, Li+ ions are alternately extracted from and reinserted in the cathode as they move through the electrolyte to the anode and back. The cathode material must sustain wide variations of its Li+ ion content over many cycles. Full text.

New ceramics for domestic and cryogenic magnetic refrigeration

A continuously growing energy demand worldwide intensifies the need for development of new, high-performance energy conversion and storage technologies. A large part of energy consumption is due to cooling in the industrial sectors such as food conservation as well as air-conditioning for housing, buildings and vehicles. Hence, refrigeration appears as a major concern for the future involving both energy consumption and impact on the environment. To date, the energy for refrigeration comes primarily from fossil fuels which produce CO2, and it uses HFCs (hydrofluorocarbon type) gases for the classical gas-compression cycle. Both these gases pollute the environment. From this point of view, cooling based on using magnetocaloric ceramic oxides as the refrigerant material appears as a promising alternative. Full text.

An electrical power plug that connects by magnetism

Connecting and disconnecting electrical-power plugs, to and from their sockets, has become a routine action for everyone, especially with the increasing numbers of electrical, electronic and computing devices. The Institut NEEL is a partner in the project PRIMA ("PRIse MAgnétique") which is developing a novel, quick-action magnetic connector. This connector exploits a strong magnetic field to guide the plug to its socket and to attach it firmly while, at the same time, providing complete security for both the user and the power or signal. In certain applications, it will also provide a "smart" connection with inbuilt intelligence for supervision and management of the electrical power transmission. The Institut NEEL’s role is to provide its expertise in magnetic materials for the development of the powerful magnets to be integrated in these connectors. Full text.

Grapheal : Therapeutics and diagnostics of chronic wounds

Grapheal is a spin-off project of the Institut NEEL. This startup company, currently in the creation phase, aims to develop innovative solutions for treating people with chronic wounds. Typically, chronic wounds are deep skin injuries that do not heal after 4-6 weeks. Large populations are at risk, including diabetics (whose numbers are rapidly rising around the world) as well as the elderly. The recent epidemic of chronic wounds is a major concern, as they are the leading source of necrosis, which can unfortunately lead to amputations. Such wounds are the cause of more than half a million amputations each year worldwide. Full text.

Diamond Epitaxy for future power electronics : DiamFab

DiamFab is a future company currently in the incubation step before its full creation in 2019. The original idea came from a small group of NEEL Institute researchers who are participating in DiamFab. A large volume of research work done at the Institut NEEL over the last 20 years is enabling the company to acquire skills and know-how related to the homoepitaxial growth of diamond layers on synthetic diamond substrates. During the pre-incubation phase, the Linksium SATT (Société d’Accélération du Transfert de Technologies) for the Grenoble-Alps area is helping the inventors to construct their project and prepare the establishment of the company. DiamFab’s business model is focused on the epitaxial growth of diamond layers and development of diamond electronics device components for high power applications. Full text.

Thermal energy harvesting on a chip : toward autonomous sensors

The measurement of very tiny quantities of heat is essential for a deep understanding of thermal transfer in nanostructures. Fundamental research on "nanothermal" physics, carried out over ten years at the Institut Néel has now given rise to a disruptive technology for harvesting thermal energy at the nanometre scale. Full text.

Nano-Neuroelectronics : sensing the activity of neurons

The brain is one of the most important systems of the body, activating and controlling its every function. However, it is still barely understood, in health nor in disease. The coding processes and the connections of the nervous system, are highly complex as is their relation to behaviour. It is still not attainable to follow the electrical activity of such dense and intricate networks (billions of connected neurons) without damaging them. Novel approaches and technologies are required to examine neurons and neural circuits by various means and at different scales. Full text.

Deep depletion transistor : a new concept for diamond power-electronics

Silicon is the ubiquitous semiconductor for most digital and analog electronics. And silicon has been extremely useful even for the power-electronics industry. However, the performance of silicon-based devices is near their maximum capability for certain high current and high voltage applications. Full text.

Heat transport in the quantum regime has its own limits !

At extremely low temperature, the transport of matter, charge or energy through a very narrow "quasi one-dimensional" channel can be quantized. This has been demonstrated for a long time, for example for a current of electrical charges. Indeed, electrical conductance across a quantum dot takes values that are an integer multiple of the quantum of electrical conductance 2e2 /h, where e is the charge of the electron and h is the Planck constant. We expect to observe the same quantization phenomenon for heat currents, a regime that would no longer follow Fourier’s law, the classical law of heat conduction. As this quantization has been shown clearly for electrons and photons, it remains a mystery for phonons, the quanta of vibration of the crystal lattice. Full text.

Ultrasensitive and universal vectorial force-field sensor

Due to their ultralow mass, nanometre-scale mechanical oscillators can be used to convert a very weak force into a measurable displacement. By measuring the vibrations of a long, cylindrical, nanowire oscillator, and recording their modifications as the nanowire is scanned through a force field (e.g. an electrostatic field), one can measure and map the variations of the magnitude and direction of the force field with attonewton (10-18 N) precision. Lateral force-field gradients couple the nanowire’s two transverse eigenmodes, i.e. the transverse modes of oscillation in two perpendicular directions, causing frequency shifts and rotation of the eigenmode basis. Full text.

A Single-Electron Transistor breaks the law of thermal conductivity

Good conductors of heat are usually also good conductors of electricity. The celebrated Wiedemann-Franz law states that, at a given temperature, the thermal conductivity of a metal is proportional to its electrical conductivity. Yet, a joint group of researchers of the Institut NEEL and Aalto University (Finland) has led an experiment revealing that this law is violated in a specific quantum electronic device, a single-electron transistor. Full text.

Running a nano-engine just by looking at it

In quantum physics, measuring a quantum system can strongly perturb its state, which also affects the system’s energy. We have recently proposed a new kind of engine that, in theory, can extract work from such energetic fluctuations of purely quantum nature, induced by the measurement. This « nano-engine » adapts James Clerk Maxwell’s thought experiment (the "Maxwell’s daemon") to the quantum domain. Full text.

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