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Memristors are continuously tunable resistors that emulate biological synapses. Conceptualized in the 1970s, they traditionally operate by voltage-induced displacements of matter, although the details of the mechanism remain under debate. Purely electronic memristors based on well-established physical phenomena with albeit modest resistance changes have also emerged. Here we demonstrate that voltage-controlled domain configurations in ferroelectric tunnel barriers yield memristive behaviour with resistance variations exceeding two orders of magnitude and a 10 ns operation speed. Using models of ferroelectric-domain nucleation and growth, we explain the quasi-continuous resistance variations and derive a simple analytical expression for the memristive effect. Our results suggest new opportunities for ferroelectrics as the hardware basis of future neuromorphic computational architectures.

The drive to improve digital memory through ever-shrinking electronic circuitry will ultimately face a bottleneck. Researchers propose exploiting the room 'inside' memory elements as a solution.

Ferroic-order parameters are useful as state variables in non-volatile information storage media because they show a hysteretic dependence on their electric or magnetic field. Coupling ferroics with quantum-mechanical tunnelling allows a simple and fast readout of the stored information through the influence of ferroic orders on the tunnel current. For example, data in magnetic random-access memories are stored in the relative alignment of two ferromagnetic electrodes separated by a non-magnetic tunnel barrier, and data readout is accomplished by a tunnel current measurement. However, such devices based on tunnel magnetoresistance typically exhibit OFF/ON ratios of less than 4, and require high powers for write operations (>1 × 10(6) A cm(-2)). Here, we report non-volatile memories with OFF/ON ratios as high as 100 and write powers as low as ∼1 × 10(4) A cm(-2) at room temperature by storing data in the electric polarization direction of a ferroelectric tunnel barrier. The junctions show large, stable, reproducible and reliable tunnel electroresistance, with resistance switching occurring at the coercive voltage of ferroelectric switching. These ferroelectric devices emerge as an alternative to other resistive memories, and have the advantage of not being based on voltage-induced migration of matter at the nanoscale, but on a purely electronic mechanism.

Auger sputter depth profiles of very thin (15 nm) plasma-nitrided SiO2 films thermally grown on silicon wafers have been measured before and after bombardment with energetic electrons (1, 3, or 5 keV). Electron irradiation of the film induced nitrogen depletion at the vacuum/dielectric interface and a nitrogen pile-up at the dielectric/silicon interface. Our results indicate that this phenomenon is maximum for the lowest primary electron energy. This behavior could be understood on the basis of an electron-stimulated Si-N bond decomposition and the creation of positive nitrogen ions. The released nitrogen ions could either escape into the vacuum or migrate through the dielectric layer and pile up at the dielectric/silicon interface due to the existence inside the layer of a non-uniform electric field, in agreement with recent theoretical predictions.

Low-energy (3–100 eV) electrons are shown to be efficient promoters of the superficial nitridation of thin SiO2 films grown on boron-doped Si(100) using low pure NH3 pressures (⩽2 × 10−4 mbar) at ambient temperature. The initial concentration (≈1015 at. cm−3) of ionized acceptors in silicon near the SiO2/Si interface is first lowered by the nitridation process and then restored by hydrogen annealing at 450°C. The ultrahigh vacuum experimental set-up permits us to uncouple two important effects from a thermally-assisted (700–950°C) r.f. NH3 plasma nitridation process: the role played by low-energy (3–5 eV) electrons and the temperature. It is found that the existence of charge particles near the sample surface must be taken into account in the plasma reaction process and that the main effect of thermal activation is to enhance the reaction and the diffusion of nitrogen species through the SiO2 layer up to the SiO2/Si interface.

Perovskite SnTiO3 has been predicted to be ferroelectric with properties comparable to BaTiO3. Here we report on the experimental discovery of a new SnTiO3 phase, in the form of thin films grown on various substrates by pulsed laser deposition. They exhibit an unexpected epitaxial relationship, different from the predicted perovskite structure. X-ray diffraction and transmission electron microscopy experiments show that the films grown have an ilmenite structure. The films are insulating but do not display any ferroelectricity at room temperature; however, some films contain a small second phase component consistent with the predicted perovskite phase.

Low energy (3–100 eV) electrons are shown to be efficient promoters of the superficial nitridation of thin SiO 2 films grown on boron-doped Si(100) using low pure NH 3 pressures ( -1 mbar) at ambient temperature. The initial active boron concentration in silicon (≌10 15 cm -3 ) is first lowered near the SiO 2 /Si interface by the nitridation process and then restored by a hydrogen annealing at 450°C. The ultra-high vacuum experimental set-up permits us to uncouple two important effects from a thermally-assisted RF NH 3 plasma nitridation process : the role played by low energy (3–5 eV) electrons and the temperature. It is found that the presence of electrons near the sample surface must be taken into account in the plasma reaction process and that the main effect of thermal activation is to enhance the reaction and the diffusion of nitrogen species through the SiO 2 /Si interface.

Spin into Control Spintronics—the use of the spin direction of subatomic particles to control on and off states, instead of electric charge—has the potential to create low-power electronics, because less energy is needed to flip spin states than to flip switches to create voltage barriers. Theoretical work hints that spin-polarized electrons from a ferromagnetic electrode can be controlled by a change in polarization created in a ferroelectric thin film. Garcia et al. (p. 1106 , published online 14 January) fabricated an iron-barium titanate junction on a lanthanum strontium manganate substrate that acts as a spin detector. Local control of spin polarization was observed in the ferroelectric layer, which retained its polarization without any applied power.

The persistency of ferroelectricity in ultrathin films allows their use as tunnel barriers. Ferroelectric tunnel junctions are used to explore the tunneling electroresistance effect-a change in the electrical resistance associated with polarization reversal in the ferroelectric barrier layer-resulting from the interplay between ferroelectricity and quantum-mechanical tunneling. Here, we use piezoresponse force microscopy and conductive-tip atomic force microscopy at room temperature to demonstrate the resistive readout of the polarization state through its influence on the tunnel current in PbTiO3 ultrathin ferroelectric films. The tunnel electroresistance reaches values of 50 000% through a 3.6 nm PbTiO3 film.

Mixtures of Gaussians are a crucial statistical modeling tool at the heart of many challenging applications in computer vision and machine learning. In this paper, we first describe a novel and efficient algorithm for simplifying Gaussian mixture models using a generalization of the celebrated k-means quantization algorithm tailored to relative entropy. Our method is shown to compare experimentally favourably well with the state-of-the-art both in terms of time and quality performances. Second, we propose a practical enhanced approach providing a hierarchical representation of the simplified GMM while automatically computing the optimal number of Gaussians in the simplified mixture. Application to clustering-based image segmentation is reported.

Using a low-temperature conductive-tip atomic force microscope in cross-section geometry we have characterized the local transport properties of the metallic electron gas that forms at the interface between ${\mathrm{LaAlO}}_{3}$ and ${\mathrm{SrTiO}}_{3}$. At low temperature, we find that the carriers do not spread away from the interface but are confined within $\ensuremath{\sim}10\text{ }\text{ }\mathrm{nm}$, just like at room temperature. Simulations taking into account both the large temperature and electric-field dependence of the permittivity of ${\mathrm{SrTiO}}_{3}$ predict a confinement over a few nm for sheet carrier densities larger than $\ensuremath{\sim}6\ifmmode\times\else\texttimes\fi{}{10}^{13}\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}2}$. We discuss the experimental and simulations results in terms of a multiband carrier system. Remarkably, the Fermi wavelength estimated from Hall measurements is $\ensuremath{\sim}16\text{ }\text{ }\mathrm{nm}$, indicating that the electron gas in on the verge of two dimensionality.

International audience; Ferroelectrics possess a polarization that is spontaneous, stable and electrically switchable, and submicrometre-thick ferroelectric films are currently used as non-volatile memory elements with destructive capacitive readout. Memories based on tunnel junctions with ultrathin ferroelectric barriers would enable non-destructive resistive readout. However, the achievement of room-temperature polarization stability and switching at very low thickness is challenging. Here we use piezoresponse force microscopy at room temperature to show robust ferroelectricity down to 1 nm in highly strained BaTiO3 films; we also use room-temperature conductive-tip atomic force microscopy to demonstrate resistive readout of the polarization state through its influence on the tunnel current. The resulting electroresistance effect scales exponentially with ferroelectric film thickness, reaching ∼75,000% at 3 nm. Our approach exploits the otherwise undesirable leakage current—dominated by tunnelling at these very low thicknesses—to read the polarization state without destroying it. We demonstrate scalability down to 70 nm, corresponding to potential densities of >16 Gbit inch-2. These results pave the way towards ferroelectric memories with simplified architectures, higher densities and faster operation, and should inspire further exploration of the interplay between quantum tunnelling and ferroelectricity at the nanoscale.

The problem of object tracking is a problem arising in domains such as computer vision (video surveillance for instance) and cinematographic post-production (special effects). There are two major classes of solution to this problem: region of interest tracking, which indicates a coarse tracking, and space-time segmentation, which corresponds to a precise tracking of the region of interest's contour. In both cases, the region of interest must be selected beforehand on the first, and possibly on the last image of the video sequence. In this thesis, we propose two tracking methods (one of each type). We propose also a fast implementation of an existing tracking method on Graphics Processing Unit (GPU). The first method is based on the analysis of temporal trajectories of salient points and provides a region of interest tracking. Salient points (typically of point of strong curvature of the isointensity lines) are detected in all the images of the sequence. The trajectories are built by matching salient points of consecutive images whose neighbourhoods are coherent. Our first contribution consists in the analysis of the trajectories on a group of pictures, which improves the motion estimation quality. Moreover, we use a space-time weighting for each trajectory which makes it possible to add a temporal constraint on the movement while taking into account the local geometrical deformations of the object ignored by a global motion model. The second method performs a space-time segmentation. The object contour motion is estimated using the information contained in an outer-layer centered on the object contour. Our first contribution is the use of this outer-layer which contains information about both the background and the object in a local context. Moreover, the matching using a statistical similarity measure (residual entropy) allows to improve the tracking while facilitating the choice of the optimal size of the crown. Finally, we propose a fast implementation of an existing tracking method of region of interest. This method relies on the use of a statistical similarity measure: the Kullback-Leibler divergence. This divergence can be estimated in a high dimension space using k-th nearest neighbor distance. These calculations being computationally very expensive, we propose a parallel implementation of the exhaustive search of the k-th nearest neighbors using GPU programming (via the programming interface NVIDIA CUDA). We show that this implementation speeds the tracking process up to a factor 15 compared to a classical implementation of this search using data structuring methods.; Le problème du suivi d'objets dans une vidéo se pose dans des domaines tels que la vision par ordinateur (vidéo-surveillance par exemple) et la post-production télévisuelle et cinématographique (effets spéciaux). Il se décline en deux variantes principales : le suivi d'une région d'intérêt, qui désigne un suivi grossier d'objet, et la segmentation spatio-temporelle, qui correspond à un suivi précis des contours de l'objet d'intérêt. Dans les deux cas, la région ou l'objet d'intérêt doivent avoir été préalablement détourés sur la première, et éventuellement la dernière, image de la séquence vidéo. Nous proposons dans cette thèse une méthode pour chacun de ces types de suivi ainsi qu'une implémentation rapide tirant partie du Graphics Processing Unit (GPU) d'une méthode de suivi de régions d'intérêt développée par ailleurs.La première méthode repose sur l'analyse de trajectoires temporelles de points saillants et réalise un suivi de régions d'intérêt. Des points saillants (typiquement des lieux de forte courbure des lignes isointensité) sont détectés dans toutes les images de la séquence. Les trajectoires sont construites en liant les points des images successives dont les voisinages sont cohérents. Notre contribution réside premièrement dans l'analyse des trajectoires sur un groupe d'images, ce qui améliore la qualité d'estimation du mouvement. De plus, nous utilisons une pondération spatio-temporelle pour chaque trajectoire qui permet d'ajouter une contrainte temporelle sur le mouvement tout en prenant en compte les déformations géométriques locales de l'objet ignorées par un modèle de mouvement global.La seconde méthode réalise une segmentation spatio-temporelle. Elle repose sur l'estimation du mouvement du contour de l'objet en s'appuyant sur l'information contenue dans une couronne qui s'étend de part et d'autre de ce contour. Cette couronne nous renseigne sur le contraste entre le fond et l'objet dans un contexte local. C'est là notre première contribution. De plus, la mise en correspondance par une mesure de similarité statistique, à savoir l'entropie du résiduel, d'une portion de la couronne et d'une zone de l'image suivante dans la séquence permet d'améliorer le suivi tout en facilitant le choix de la taille optimale de la couronne.Enfin, nous proposons une implémentation rapide d'une méthode de suivi de régions d'intérêt existante. Cette méthode repose sur l'utilisation d'une mesure de similarité statistique : la divergence de Kullback-Leibler. Cette divergence peut être estimée dans un espace de haute dimension à l'aide de multiples calculs de distances au k-ème plus proche voisin dans cet espace. Ces calculs étant très coûteux, nous proposons une implémentation parallèle sur GPU (grâce à l'interface logiciel CUDA de NVIDIA) de la recherche exhaustive des k plus proches voisins. Nous montrons que cette implémentation permet d'accélérer le suivi des objets, jusqu'à un facteur 15 par rapport à une implémentation de cette recherche nécessitant au préalable une structuration des données.

International audience; We have investigated transport properties of iron (Fe) nanoparticles embedded in zinc selenide (ZnSe) semiconducting epilayers prepared by molecular beam epitaxy. Both positive and negative tunneling magnetoresistances (TMRs) were measured depending on the applied voltage biases and on the temperature. A slow reduction of the TMR magnitude with temperature was detected and it could be explained in terms of a crossover between direct/resonant tunneling and variable range hopping. The temperature behavior of the magnetoresistance is a clear signature of tunneling and hopping mechanisms mediated by the ZnSe barrier localized states. (C) 2008 American Institute of Physics.

The recent improvements of graphics processing units (GPU) offer to the computer vision community a powerful processing platform. Indeed, a lot of highly-parallelizable computer vision problems can be significantly accelerated using GPU architecture. Among these algorithms, the k nearest neighbor search (KNN) is a well-known problem linked with many applications such as classification, estimation of statistical properties, etc. The main drawback of this task lies in its computation burden, as it grows polynomially with the data size. In this paper, we show that the use of the NVIDIA CUDA API accelerates the search for the KNN up to a factor of 120., Comment: 13 pages, 2figures, submitted to CVGPU 2008

International audience; The magnetic and structural properties of MnAs thin films grown on GaAs(111)B at different temperatures (160–280 °C) are investigated. A narrow optimum growth temperature window (200–240 °C) is found where the Curie temperature and the room temperature magnetization are maximized. High-resolution x-ray diffraction experiments are performed on the samples showing that the films are epitaxial for a minimum growth temperature of 200 °C. The room temperature fraction of the hexagonal phase is strongly dependent on the growth temperature in agreement with the magnetic properties.

The alpha-beta magneto-structural phase transition in MnAs/GaAs(111) epilayers is investigated by elastic neutron scattering. The in-plane parameter of MnAs remains almost constant with temperature from 100 K to 420 K, following the thermal evolution of the GaAs substrate. This induces a temperature dependent biaxial strain that is responsible for an alpha-beta phase coexistence and, more important, for the stabilization of the ferromagnetic alpha-phase at higher temperature than in bulk. We explain the premature appearance of the beta-phase at 275 K and the persistence of the ferromagnetic alpha-phase up to 350 K with thermodynamical arguments based on the MnAs phase diagram. It results that the biaxial strain in the hexagonal plane is the key parameter to extend the ferromagnetic phase well over room temperature., 4 pages, 3 figures, accepted for publication in Physical Review Letters

At the Frontiers of Condensed Matter III Workshop, Buenos Aires, ARGENTINA, DEC 11-15, 2006; International audience; In this contribution we present a study of the magnetic properties of MnAs thin films grown over GaAs(I 1 1) substrates, performed by ferromagnetic resonance experiments. We have calculated the magneto-crystalline anisotropy of the system analyzing the angular dependence of the resonance field with the applied field direction. The anisotropy measured for these films is much smaller than the calculated for MnAs bulk samples and MnAs/GaAs(I 0 0) thin films. We propose different microscopic mechanism for addressing the change in the anisotropy. (C) 2007 Elsevier B.V. All rights reserved.

The extraction of a video object contour, called "rotoscoping" in cinematographic post-production, is usually performed manually and frame by frame. Semi-automatic algorithms have been proposed to reduce the load of this task. However, they classically use region information and are usually based on a notion of homogeneity of the object. This homogeneity description might be difficult to establish and, consequently, the tracking may be not precise enough. The proposed method relies on the analysis of some temporal trajectories of salient points, or keypoints, called tracks. The main contribution of this paper is the local estimation, both spatially and temporally, of the contour motion from these tracks. The proposed method seems accurate, robust to outliers, and allows local deformation. Moreover, it can deal with partial occlusions.

This paper deals with region-of-interest (ROI) tracking for applications such as video surveillance or cinematographic post-production. An ROI is typically delineated by a bounding box or a basic shape such as an ellipse in the first frame of the video. The tracking problem consists in detecting the ROI throughout the video as it moves and deforms. This detection can be done based on the full content of the ROI. However, since the ROI is, by definition, an approximate segmentation of the actual object of interest, it includes some background. This can make the ROI detection less accurate and induce a drift. Instead, we propose to use keypoint extractors and local descriptors combined with robust motion estimation. The motion estimation relies on the analysis of the temporal trajectories, or tracks, of the keypoints in groups of pictures (GOP). Some results are presented on natural sequences. The proposed method seems accurate.

We explore the influence of the top electrode materials (W, Co, Ni, Ir) on the electronic band profile in ferroelectric tunnel junctions based on super-tetragonal BiFeO3. Large variations of the transport properties are observed at room temperature. In particular, the analysis of current vs. voltage curves by a direct tunneling model indicates that the metal/ferroelectric interfacial barrier height increases with the top-electrode work function. While larger metal work functions result in larger OFF/ON ratios, they also produce a large internal electric field which results in large and potentially destructive switching voltages.

We propose an analytical model of spin-dependent resonant tunneling through a 3D assembly of localized states (spread out in energy and in space) in a barrier. An inhomogeneous distribution of localized states leads to resonant tunneling magnetoresistance inversion and asymmetric bias dependence as evidenced with a set of experiments with MnAs/GaAs(7-10 nm)/MnAs tunnel junctions. One of the key parameters of our theory is a dimensionless critical exponent beta scaling the typical extension of the localized states over the characteristic length scale of the spatial distribution function. Furthermore, we demonstrate, through experiments with localized states introduced preferentially in the middle of the barrier, the influence of an homogeneous distribution on the spin-dependent transport properties.

International audience; The magnetic properties of MnAs epilayers have been investigated for two different substrate orientations GaAs(100) and GaAs(111). We have analyzed the magnetization reversal under magnetic field at low temperatures, determining the anisotropy of the films. The results, based on the shape of the magnetization loops, suggest a domain movement mechanism for both types of samples. The temperature dependence of the coercivity of the films has been also examined, displaying a generic anomalous reentrant behavior at T>200 K. This feature is independent of the substrate orientation and films thickness and may be associated to the appearance of pinning centers due to the nucleation of the beta phase at high temperatures.

The alpha-beta phase transition in MnAs thin (100 nm) films epitaxied on GaAs(001) is studied using optical spectroscopies. It is found that reflectance anisotropy spectra differ markedly for the two phases. Although no prominent feature appears in the spectrum related to the beta phase, the spectrum of the alpha phase exhibits two features centered at 2.9 and 5.0 eV. The origin of these spectral features has been further investigated using temperature-dependent differential reflectance. It is shown that the band centered at 2.9 eV can be assigned to interband transitions for light polarized along the c axis of alpha-MnAs. We show that reflectance anisotropy spectroscopy can be used to monitor the alpha-beta phase transition within the thin film. The observed spectral features and their evolution across the coexistence region are discussed in light of band-structure models in the literature. The data suggest that each phase retains its electronic structure in the coexistence region and that the transition between the alpha exchange-split band structure and the beta band structure is sharp.

Rotoscopy is a crucial processing for cinema post-production. It corresponds to the segmentation of an object of interest in a video in order to apply a local processing. In the industry, rotoscopy is usually performed manually, frame by frame. Semi-automatic algorithms have been proposed to reduce the load of this task. However, they classically use contour-based information and consequently lack robustness in case of occlusion. Here, we propose a region-based contour tracking algorithm relying on feature points which are temporally matched to build trajectories used to estimate a global or local deformation between a distant reference contour and the current frame. Then, we propose a rotoscopy algorithm based on a forward and a backward contour tracking. The use of region information and distant reference contours allows to avoid drift and greatly reduce the influence of occlusions. The rotoscopy algorithm was applied to CIF and SD sequences.

International audience; The properties of epitaxial MnAs/GaAs/MnAs epilayers grown on GaAs(111)B substrates are investigated. The different steps of the growth are detailed from the buffer layer to the top MnAs layer using scanning tunneling microscopy. Despite the high quality of the bottom MnAs surface, uncovered regions of MnAs are observed when the low-temperature-grown GaAs overlayer thickness is 3 nm, while a continuous barrier is formed for an overlayer thickness of 7 nm. The interfacial electronic properties of GaAs/MnAs and MnAs/GaAs are examined with x-ray and ultraviolet photoemission spectroscopy, indicating an absence of detectable reactivity between GaAs and MnAs. Two monolayers of MnAs over GaAs are metallic with a bulk-like valence band. In addition, an n-type barrier height of 0.7 eV is estimated for MnAs/GaAs/MnAs.

International audience; Soon afterwards the discovery of the giant magnetoresistance in metallic multilayers, researchers have attempted to integrate spintronic properties with semiconductor materials. They came up against several difficulties related to the structural and electronic properties of the ferromagnetic metal-semiconductor interface. We will report on the recent progress made in this field of spintronic with semiconductors. First of all we will explain the interfacial resistance conditions required to inject and detect efficient spin current in a semiconductor and in a second part we will show that efficient spin injection experiments have been now achieved thanks to the addition of a tunnel resistance at the interface. We will then report on the magnetoresistance experiment performed with diluted magnetic semiconductors as ferromagnetic material. This type of material can constitute an alternative road to achieving electrical control spintronic devices. Finally, we will finish by reporting on research for a highly spin-polarized source to inject spin-polarized current in a semiconductor. It will be mainly focused on tunnel magnetoresistance junctions with semiconductor barriers and hot electron transistor. To cite this article: J.-M. George et al., C R. Physique 6 (2005). (c) 2005 Academie des sciences. Published by Elsevier SAS. All rights reserved.

We have obtained bulk samples of the graphite intercalation compound, CaC6, by a novel method of synthesis from highly oriented pyrolytic graphite. The crystal structure has been completely determined showing that it is the only member of the MC6, metal-graphite compounds, which has rhombohedral symmetry. We have clearly shown the occurrence of superconductivity in the bulk sample at 11.5K, using magnetization measurements., 8 pages of text + 4 figures = 12 pages

International audience; This paper investigates the magnetoresistance of micron-sized MnAs/GaAs(AlAs)/MnAs magnetic tunnel junctions. We measure an asymmetric bias dependence of the magnetoresistance in which the negative contribution is attributed to resonant tunneling through a midgap defect band. Within this model we find a spin polarization of 60% for MnAs at the interface with GaAs. Moreover, we show that spin-dependent tunneling is a powerful technique for spectroscopic measurements of defects in a very thin layer.

We report on the use of the LaAlO3 (LAO) high-k dielectric as a tunnel barrier in magnetic tunnel junctions. From tunnel magnetoresistance (TMR) measurements on epitaxial La2/3Sr1/3MnO3/LAO/La2/3Sr1/3MnO3 junctions, we estimate a spin polarization of 77% at low temperature for the La2/3Sr1/3MnO3/LAO interface. Remarkably, the TMR of La2/3Sr1/3MnO3/LAO/Co junctions at low bias is negative, evidencing a negative spin polarization of Co at the interface with LAO, and its bias dependence is very similar to that of La2/3Sr1/3MnO3/STO/Co junctions. We discuss possible reasons for this behaviour., Comment: 14 pages, 3 figures

We have measured the tunneling magnetoresistance (TMR) of magnetic tunnel junctions based on ${\mathrm{La}}_{2/3}{\mathrm{Sr}}_{1/3}{\mathrm{MnO}}_{3}$ and various barrier materials $({\mathrm{SrTiO}}_{3},{\mathrm{TiO}}_{2},{\mathrm{LaAlO}}_{3}).$ The interfacial spin polarization of ${\mathrm{La}}_{2/3}{\mathrm{Sr}}_{1/3}{\mathrm{MnO}}_{3}$ is derived from the TMR and we find that its temperature dependence strongly resembles that of the bulk magnetization and hardly depends on the barrier material. However, the apparent Curie temperature is some 60 K lower. This dependence contrasts with that of the spin polarization of a free ${\mathrm{La}}_{2/3}{\mathrm{Sr}}_{1/3}{\mathrm{MnO}}_{3}$ surface, as probed by spin-polarized photoemission [J.-H. Park et al., Phys. Rev. Lett. 81, 1953 (1998)], thus evidencing that surfaces and interfaces have very different properties in manganites.

Objective The objective of the study was to determine whether transversus abdominis plane (TAP) block improves the early postoperative quality of recovery (QoR-40). The secondary objectives measured postoperative pain, length of stay, and narcotic use. Study Design This was a randomized, single-blinded trial of TAP block versus no block on women undergoing laparoscopic hysterectomy. TAP block patients received 20 mL of 0.5% ropivacaine with epinephrine 1:200,000 placed under ultrasound guidance on each side. The outcomes were measured using validated quality of recovery questionnaires (QoR-40), visual analog scales (VAS) for pain, and documented narcotic use in the electronic medical record. Results In 58 women, no differences in demographics were noted between groups. Comparisons of pain and recovery between the 2 groups showed no differences. There was no decrease in narcotic use or length of stay among those who received the TAP block. Conclusions TAP block does not improve postoperative QoR-40 scores or VAS pain scores following laparoscopic hysterectomy, nor does it decrease narcotic pain medication use.

Artificial multiferroic tunnel junctions combining a ferroelectric tunnel barrier of BaTiO(3) with magnetic electrodes display a tunnel magnetoresistance whose intensity can be controlled by the ferroelectric polarization of the barrier. This effect, called tunnel electromagnetoresistance (TEMR), and the corollary magnetoelectric coupling mechanisms at the BaTiO(3)/Fe interface were recently reported through macroscopic techniques. Here, we use advanced spectromicroscopy techniques by means of aberration-corrected scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy (EELS) to probe locally the nanoscale structural and electronic modifications at the ferroelectric/ferromagnetic interface. Atomically resolved real-space spectroscopic techniques reveal the presence of a single FeO layer between BaTiO(3) and Fe. Based on this accurate description of the studied interface, we propose an atomistic model of the ferroelectric/ferromagnetic interface further validated by comparing experimental and simulated STEM images with atomic resolution. Density functional theory calculations allow us to interpret the electronic and magnetic properties of these interfaces and to understand better their key role in the physics of multiferroics nanostructures.

We report on the appearance of magnetic stripes in MnAs/GaAs(100) epilayers at temperatures well below the ferromagnetic transition of the system. The study has been performed by ferromagnetic resonance experiments (FMR) on MnAs epilayers grown on (100) and (111) GaAs substrates. The FMR spectra of the MnAs/GaAs(100) samples at 180 K reveal the appearance of zones of different magnetic behavior with respect to the low-temperature homogeneous ferromagnetic phase. The angular and the temperature dependence of the spectra serve us to detect the inter-growth of the non-magnetic phase into the ferromagnetic phase at a very early stage of the process. The experimental data show that the new phase nucleates in a self-arranged array of stripes in MnAs/GaAs(100) thin films while it grows randomly in the same films grown on GaAs(111)., 8 pages, 5 figures

Entre les parents et l’enfant, la transmission psychique se revele structurante dans la mesure ou l’introjection de ce qui se transmet s’effectue de maniere fluide, c’est-a-dire si les projections parentales ne sont pas trop envahissantes, et si l’enfant n’est pas pris dans un champ de seduction ou de repression. L’auteur oppose la transmission a l’ingurgitation, la transmission ne pouvant se faire que par une appropriation par le sujet de ce qui lui vient (lui est propose) d’un autre affectivement investi. Une pensee transmise est une pensee recreee.

At the end of a rush lasting over half a century, in which CMOS technology has been experiencing a constant and breathtaking increase of device speed and density, Moore’s law is approaching the insurmountable barrier given by the ultimate atomic nature of matter. A major challenge for 21st century scientists is finding novel strategies, concepts and materials for replacing silicon-based CMOS semiconductor technologies and guaranteeing a continued and steady technological progress in next decades. Among the materials classes candidate to contribute to this momentous challenge, oxide films and heterostructures are a particularly appealing hunting ground. The vastity, intended in pure chemical terms, of this class of compounds, the complexity of their correlated behaviour, and the wealth of functional properties they display, has already made these systems the subject of choice, worldwide, of a strongly networked, dynamic and interdisciplinary research community. Oxide science and technology has been the target of a wide four-year project, named Towards Oxide-Based Electronics (TO-BE), that has been recently running in Europe and has involved as participants several hundred scientists from 29 EU countries. In this review and perspective paper, published as a final deliverable of the TO-BE Action, the opportunities of oxides as future electronic materials for Information and Communication Technologies ICT and Energy are discussed. The paper is organized as a set of contributions, all selected and ordered as individual building blocks of a wider general scheme. After a brief preface by the editors and an introductory contribution, two sections follow. The first is mainly devoted to providing a perspective on the latest theoretical and experimental methods that are employed to investigate oxides and to produce oxide-based films, heterostructures and devices. In the second, all contributions are dedicated to different specific fields of applications of oxide thin films and heterostructures, in sectors as data storage and computing, optics and plasmonics, magnonics, energy conversion and harvesting, and power electronics., The authors acknowledge financial support from the Netherlands Organization for Scientific Research (NWO). We acknowledge fruitful interactions with our many collaborators in the realm of artificial quantum materials, especially the groups of J.C. Séamus Davis, Craig J. Fennie, Eun-Ah Kim, Lena F. Kourkoutis, and David A. Muller. This work was supported by the National Science Foundation (Platform for the Accelerated Realization, Analysis, and Discovery of Interface Materials (PARADIM)) under Cooperative Agreement No. DMR-1539918. Financial support from the Spanish Ministry of Economy and Competitiveness (SEV-2015-0496, MAT2014-56063-C2-1-R, and MAT2017-85232-R), from Generalitat de Catalunya (2014 SGR 734), and from Slovenian Research Agency (P2-0091 and J2-6759) is acknowledged. The authors acknowledge funding from the EPSRC grant EP/ P027032/1. Prof. O. Nilsen is acknowledged for valuable discussions on the current status of ALD perovskites. Author thanks fruitful discussions with Dr. J. Santiso. Financial support from the Spanish Ministry of Economy and Competitiveness through the ''Severo Ochoa" Programme for Centres of Excellence in R&D (SEV-2015-0496), and projects MAT2015-71664-R and MAT2015- 67593-P is acknowledged. This work was supported by PARADIM, a National Science Foundation Materials Innovation Platform (Grant DMR-1539918), and by the Air Force Office of Scientific Research (Award number FA 9550-16-1-0305). Funding from the DFG (German Science Foundation) within the collaborative research center SFB 917 'Nanoswitches' and the W2/ W3 program of the Helmholtz association is gratefully acknowledged. We furthermore acknowledge funding by the ToBE CoST action (MP1308). We acknowledge financial support from the ERC Consolidator grant ‘‘MINT” (contract number n° 615759) and the ANR project ‘‘FERROMON”. This publication has received funding from the European Union’s Horizon 2020 research innovation programme under grant agreement 732642 (ULPEC project). This work is supported by a public grant overseen by the French National Research Agency (ANR) as part of the ‘‘Investissements d’Avenir” program (Labex NanoSaclay, reference: ANR-10-LABX-0035). This work was supported in part by the EFRE fund of the European Commission, by the Free State of Saxony (Germany), and by funding of the Deutsche Forschungsgemeinschaft (DFG project: Inferox). This work was supported in parts by the Deutsche Forschungsge-meinschaft (DFG) under Grant SFB 917 ''Nanoswitches" and the COST Action MP1308 ''TO-BE (Towards Oxide-Based Electronics)". This publication has received funding from the European Union’s Horizon 2020 research innovation programme under grant agree-ment 732642 (ULPEC project). We thank M. Belmoubarik and J. Uzuhashi for their technical assistance for Fig. 36. We acknowledge support from the ImPACT Program of Council for Science, Technology and Innovation, Japan. Gervasi Herranz acknowledges financial support from MAT2014-56063-C2-1-R and Severo Ochoa SEV-2015-0496 Projects, and the Generalitat de Catalunya (2014 SGR 734Project). Pablo Sanchis acknowledges financial support from TEC2016-76849 and FP7-ICT-2013-11-619456 SITOGA. We thank the financial support from the SNSF NRP70 ‘‘Energy Turnaround” and GRAPHENE project supported by the European Commission Seventh Framework Programme under contract 604391 is gratefully acknowledged. To the Spanish MINECO through the Severo Ochoa Centers of Excellence Program under Grant SEV-2013-0295; for the grant ENE2016-79282-C5-2-R and the OrgEnergy Excelence NetworkCTQ2016-81911-REDT. To the Agència de Gestió d’Ajuts Universitaris i de Recerca for the support to the consolidated Catalonia research group 2014SGR-1212 and the Xarxa de Referència en Materials Avançats per a l’Energia (Xarmae). To the CERCA Pro-gramme/Generalitat de Catalunya and to the European COST Action StableNextSol project MP1307. The authors would like to acknowledge the financial support from ACCIO-Generalitat de Catalunya and the European Union for the 3D-PHOTOXIDES ERA-NET MANUNET II and from IV Fondo de Emprendedores of Fundación Repsol for the SOLAR OXIDES project. The authors would also thank Mr. Andrés Gómez from Institut de Ciència de Materials de Barcelona (ICMAB) for the pc-AFM measure-ments and Mr. Alex Hernández from Institut de Recerca en Energia de Catalunya (IREC) for the sputtering and valuable guidance. We would like to acknowledge the financial support granted by the Spanish Government [Projects MAT2014-56063-C2-1-R, MAT2015-73839-JIN, MAT2014-51778-C2-1-R and MAT2014-57960-C3-1-R, and associated FEDER], I.F. acknowledges Ramon y Cajal contract RYC-2017-22531, the Generalitat de Catalunya (2014-SGR-734). ICMAB-CSIC authors acknowledge financial support from the Spanish Ministry of Economy and Competitiveness, through the ‘‘Severo Ochoa” Program for Centers of Excellence in R&D (SEV-2015-0496). C.P. and B.D. acknowledge a public grant overseen by the French National Research Agency (ANR) as part of the ‘‘Investissements d’Avenir” program (Grant No. ANR-10-LABX-0035, Labex NanoSaclay). The authors would like to acknowledge L. Pereira and P. Bar-quinha for fruitful discussions during the manuscript preparation. We acknowledge the funding from Portuguese Foundation for Science and Technology, Reference UID/CTM/50025/2013 and FEDER funds through the COMPETE 2020 Programme under the project number POCI-01-0145-FEDER-007688. Part of this work is partially financed from European Community H2020 program under grant agreements No. 665046 (project Symbiotic) and No. 644631 (project Roll-Out). Several of the recent advances in electrochromic and ther-mochromic materials, reported above, were reached with financial support received from the European Research Council under the European Community’s Seventh Framework Program (FP2007– 2013)/ERC Grant Agreement No. 267234 (‘‘GRINDOOR”).

Artificial neural networks (ANN) are well known for performing Recognition, Data mining and Synthesis (RMS) tasks. However, the most famous ANNs are software implemented on computers that never take into account the power consumption management. Chip designers are aiming at low-power consumption by developing the neuromorphic engineering field. The goal is to design and produce neuralinspired architectures allowing energy-efficient computation systems. One decade ago, neuromorphic engineering had a renewal of interest, in particular due to the unveiled memristive devices. Indeed, memristors own all the features necessary in order to play the role of plastic synapses in ANNs. Among all memristive technologies, ferroelectric devices present an important advantage for low power systems: their high resistance which implies low current. In this paper, we will present a Verilog-A model of ferroelectric memristors. This model is based on measurements and therefore takes into account the variability of devices in terms of RON, ROFF and switching characteristics. This realistic model will be helpful for designing neuromorphic systems based on these devices. Finally, we will present some Cadence simulations of learning in small neural networks composed of CMOS neurons and memristive synapses.

My research is dedicated to the electronic properties of functional oxides. My activity specifically focuses on ferroelectric tunnel junctions in which an ultrathin layer of ferroelectric material is intercalated between two metallic electrodes. In these devices, polarization reversal induces large modifications of the tunnel resistance, leading to a non-destructive readout of the information. After a demonstration of the concept with scanning probe microscopy techniques, I have been exploring the properties of ferroelectric tunnel junctions with various ferroelectric materials (BaTiO3, BiFeO3, and PVDF). I showed that these devices possess attractive properties for applications as non-volatile binary memories. In addition, exploring the fact that polarization usually reverses by the nucleation and propagation of domains, I demonstrated a memristive behavior in the junctions associated to non-uniform configurations of ferroelectric domains. Such ferroelectric memristors can be used as artificial synapses in neuromorphic architectures. Coupled to magnetic electrodes, the resulting multiferroic tunnel junctions enable a non-volatile control of magnetism at the ferroelectric/electrode interface and of the spin-polarized current associated. Besides this main activity on tunnel devices, I explored the influence of ferroelectricity on magnetic orders and on the properties of functional oxides., This is my Habilitation Thesis (HDR), defended July 13th 2017, in front of the jury composed of: Philippe Lecoeur (C2N, Paris-Saclay), Agnes Barthelemy (CNRS-Thales, Paris-Saclay), Brahim Dkhil (CentraleSupelec), Josep Fontcuberta (ICMAB), Alexei Gruverman (Univ. Nebraska), Jacobo Santamaria (Univ. Complutense Madrid)

International audience; Topological states are currently gathering intensive investigation in condensed matter physics due to their potential as configurable electronic devices for the future era coined "topotronics". Beyond numerous breakthroughs in magnetism over the last decade, a new paradigm is emerging with the proposal of topologically-protected objects in ferroelectric materials. Recently, ferroelectric skyrmions and vortices were observed in PbTiO3/SrTiO3 superlattices, opening the path towards ultra-small topological objects with low-power electric-field control. Here we report the observation of chiral polar windings in a single epitaxial thin film, triggered by its self-organized stripe domain pattern arrangement. Combining resonant elastic X-ray scattering and scanning transmission electron microscopy, we show signatures of polar chirality in epitaxial BiFeO3 thin films corroborated with a complex ferroelectric domain wall structure. The net chirality suggests that domain walls induce a polar rotation through a small path alternating with an unexpected long path at every second domain wall. In addition, scanning probe microscopy reveals singularities associated to this peculiar domain wall structure. These results bring new insights into the unexpected complexity of standard striped-domain BiFeO3 thin films and open questions as for the driving force of this polar chirality.

In ferroelectric memory devices, information is stored within the polarization direction whose reversal usually occurs by the nucleation and propagation of domains. In ultrathin ferroelectrics, ultrafast dynamics may be achieved by nucleation-limited switching, avoiding the inherently speed-limited propagation of domain walls. Here, we investigate polarization reversal dynamics in ultrathin ferroelectric films by transient current measurements. Thanks to the tunnel electroresistance, the start of polarization reversal induces sharp variations of the transmitted current under voltage pulses. These single-shot measurements show extremely fast switching with durations down to 3 ns that is only limited by the current device geometry. While the OFF-to-ON switching shows finite nucleation times that scale with the pulse amplitude, the ON-to-OFF switching speed cannot be detected under such rectangular pulses. Resorting to triangular pulse excitations allows us to detect the dynamics of this switching direction. Both cases can be interpreted by nucleation switching models following Merz's law.