BOÎTES ET FILS DE GE SUR SI(001) ORDONNÉS À LONGUE DISTANCE PAR DES RÉSEAUX DE DISLOCATIONS DE FLEXION

The growth of ordered semiconductor nanostrucutres, with a controlled size and position, is an major technologic challenge. In this study, we propose an original method to grow by molecular beam epitaxy ordered germanium nanostructures on silicon (001). A periodic array of tilt dislocations is obtained by molecular bounding, and induces a periodic strain field at the surface of the substrate. The observed organization of germanium nanostructures is due to the strain field generated on the silicon surface by an interfacial tilt dislocation array.L'élaboration de nanostructures semi-conductrices ordonnées, contrôlées en taille et en position, est un enjeu technologique important pour satisfaire les besoins de miniaturisation des circuits actuels de la micro/nano-électronique. Dans cette thèse, une méthode originale d'organisation latérale de nanostructures a été explorée et appliquée au cas de nanostructures de germanium épitaxiées sur silicium (001). Cette technique utilise un réseau de dislocations de flexion proche de la surface libre du substrat, obtenu par collage moléculaire. Un champ de déformation élastique, périodique, se propageant de l'interface de collage jusqu'à la surface des échantillons, nous avons pu obtenir une croissance organisée de nanostructures de germanium

Seismic wave propagation in heterogeneous limestone samples

International audienceMimic near-surface seismic field measurements at a small scale, in the laboratory, under a well-controlled environment, may lead to a better understanding of wave propagation in complex media such as in geological materials. Laboratory experiments can help in particular to constrain and refine theoretical and numerical modelling of physical phenomena occurring during seismic propagation, in order to make a better use of the complete set of measurements recorded in the field. We have developed a laser Doppler vibrometer (laser interferometry) platform designed to measure non-contact seismic displacements (or velocities) of a surface. This technology enables to measure displacements as small as a tenth of a nanometer on a wide range of frequencies, from a few tenths to a few megahertz. Our experimental setup is particularly suited to provide high-density spatial and temporal records of displacements on the edge of any vibrating material (aluminum, limestone, ...). We will firstly present experiments in cuboid and cylinders of aluminum (homogeneous) in order to calibrate the seismic sources (radiation diagram, frequency content) and identify the wave arrivals (P, S, converted, surface waves). The measurements will be compared quantitatively to a direct 2D numerical elastodynamic simulation (finite elements, Interior Penalty Discontinuous Galerkin). We will then show wave measurements performed in cylindrical heterogeneous limestone cores of typical diameter size around 10 cm. Tomographic images of velocity (figure 2a) in 2D slices of the limestone cores will be derived based upon the time of first arrivals and implemented in the numerical model. By quantifying the difference between numerical and experimental results, the tomographic velocity model will be reciprocally improved and finally compared to a X − ray tomographic image of that slice. A brief overview of the studies Seismic sources We will explore piezo-electric sources of different frequencies (100 kHZ ∼ 5 M Hz) and test the new laser ablation source whose dominant frequency can reach 2 M Hz in aluminium. Avantages and drawbacks of each technology will be discussed in terms of source and wave propagation characterisation. Wave identification in an aluminium cube of side length 280 mm and seismic source at the center of one face We have identified experimentally P, S, head wave, PS, SP and surface waves measured on the cube surfaces. Meanwhile, direct numerical simulations have helped to quantitatively analyze the kinematics of wave fronts. For example, on the surface where the seismic source is excited, a P front, an S front and a PS head wave front are measured by the laser vibrometer right after the initial seismic impulse. These wavefronts can be understood by both the Huygens' Principle and the Snell-Descartes Law. In Figure 1, the seismic source excits simultaneously at time t = 0 a P wave and an S wave. As time evolves, waves propagate inside the volume and a P-wave propagates along the boundary as well: the latter one acts on the boundary as secondary sources which will emit both P and S waves, creating finally a new PS head wave front nicely measured in the experiments. The colours of magenta and green correspond to null amplitudes

Seismic imaging in laboratory trough laser Doppler vibrometry

International audienceMimic near-surface seismic field measurements at a small scale, in the laboratory, under a well-controlled environment , may lead to a better understanding of wave propagation in complex media such as in geological materials. Laboratory experiments can help in particular to constrain and refine theoretical and numerical modelling of physical phenomena occurring during seismic propagation, in order to make a better use of the complete set of measurements recorded in the field. We have developed a laser Doppler vibrometer (laser interferometry) platform designed to measure non-contact seismic displacements (or velocities) of a surface. This technology enables to measure displacements as small as a tenth of a nanometer on a wide range of frequencies, from a few tenths to a few megahertz. Our experimental setup is particularly suited to provide high-density spatial and temporal records of displacements on the edge of any vibrating material. We will show in particular a study of MHz wave propagation (excited by piezoelectric transducers) in cylindrical cores of typical diameter size around 10 cm. The laser vibrometer measurements will be first validated in homogeneous materials cylinders by comparing the measurements to a direct numerical simulation. Special attention will be given to the comparison of experimental versus numerical amplitudes of displacements. In a second step, we will conduct the same type of study through heterogeneous carbonate cores, possibly fractured. Tomographic images of velocity in 2D slices of the carbonate core will be derived based upon on the time of first arrival. Preliminary attempts of tomographic attenuation maps will also be presented based on the amplitudes of first arrivals. Experimental records will be confronted to direct numerical simulations and tomographic images will be compared to x-ray scanner imaging of the cylindrical cores

Seismic imaging in laboratory trough laser Doppler vibrometry

International audienceMimic near-surface seismic field measurements at a small scale, in the laboratory, under a well-controlled environment , may lead to a better understanding of wave propagation in complex media such as in geological materials. Laboratory experiments can help in particular to constrain and refine theoretical and numerical modelling of physical phenomena occurring during seismic propagation, in order to make a better use of the complete set of measurements recorded in the field. We have developed a laser Doppler vibrometer (laser interferometry) platform designed to measure non-contact seismic displacements (or velocities) of a surface. This technology enables to measure displacements as small as a tenth of a nanometer on a wide range of frequencies, from a few tenths to a few megahertz. Our experimental setup is particularly suited to provide high-density spatial and temporal records of displacements on the edge of any vibrating material. We will show in particular a study of MHz wave propagation (excited by piezoelectric transducers) in cylindrical cores of typical diameter size around 10 cm. The laser vibrometer measurements will be first validated in homogeneous materials cylinders by comparing the measurements to a direct numerical simulation. Special attention will be given to the comparison of experimental versus numerical amplitudes of displacements. In a second step, we will conduct the same type of study through heterogeneous carbonate cores, possibly fractured. Tomographic images of velocity in 2D slices of the carbonate core will be derived based upon on the time of first arrival. Preliminary attempts of tomographic attenuation maps will also be presented based on the amplitudes of first arrivals. Experimental records will be confronted to direct numerical simulations and tomographic images will be compared to x-ray scanner imaging of the cylindrical cores

BOÎTES ET FILS DE GE SUR SI(001) ORDONNÉS À LONGUE DISTANCE PAR DES RÉSEAUX DE DISLOCATIONS DE FLEXION

The growth of ordered semiconductor nanostrucutres, with a controlled size and position, is an major technologic challenge. In this study, we propose an original method to grow by molecular beam epitaxy ordered germanium nanostructures on silicon (001). A periodic array of tilt dislocations is obtained by molecular bounding, and induces a periodic strain field at the surface of the substrate. The observed organization of germanium nanostructures is due to the strain field generated on the silicon surface by an interfacial tilt dislocation array.L'élaboration de nanostructures semi-conductrices ordonnées, contrôlées en taille et en position, est un enjeu technologique important pour satisfaire les besoins de miniaturisation des circuits actuels de la micro/nano-électronique. Dans cette thèse, une méthode originale d'organisation latérale de nanostructures a été explorée et appliquée au cas de nanostructures de germanium épitaxiées sur silicium (001). Cette technique utilise un réseau de dislocations de flexion proche de la surface libre du substrat, obtenu par collage moléculaire. Un champ de déformation élastique, périodique, se propageant de l'interface de collage jusqu'à la surface des échantillons, nous avons pu obtenir une croissance organisée de nanostructures de germanium

Boîtes et fils de Ge sur Si(001) ordonnés à longue distance par des réseaux de dislocations de flexion

L'élaboration de nanostructures semi-conductrices ordonnées, contrôlées en taille et en position, est un enjeu technologique important pour satisfaire les besoins de miniaturisation des circuits actuels de la micro/nano-électronique. Dans cette thèse, une méthode originale d'organisation latérale de nanostructures a été explorée et appliquée au cas de nanostructures de germanium épitaxiées sur silicium (001). Cette technique utilise un réseau de dislocations de flexion proche de la surface libre du substrat, obtenu par collage moléculaire. Un champ de déformation élastique, périodique, se propageant de l'interface de collage jusqu'à la surface des échantillons, nous avons pu obtenir une croissance organisée de nanostructures de germanium.GRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF

Vibrométrie laser pour la caractérisation des roches réservoirs

International audienceLa reproduction en laboratoire d'expériences de géophysique représente un enjeu particulièrement important, permettant de faire le lien entre les modèles numériques et l'exploitation des données de terrain. Dans cet objectif, nous avons développé un banc de vibrométrie laser per-mettant d'acquérir des données sismiques sans contact, donc sans pro-blème de couplage. Basé sur le principe de l'interférométrie laser, cette technique nous permet d'accéder à des déplacements de surface aussi faibles que le dixième de nanomètre pour des fréquences allant de la centaine de kilohertz à quelques mégahertz. Un contrôle micrométrique du positionnement laser permet d'obtenir une grande densité de points de mesure. Lors de cette communication, nous présenterons le principe de cette technique novatrice et montrerons sa potentialité pour la ca-ractérisation haute résolution des hétérogénéités et éventuellement de l'anisotropie des carbonates

Abstract #69036 From Bedding To Cleavage: The Evolution Of Clay Fabric Near A Thrust

International audienceText: In foothills, the propagation of faults within incompetent bed is potentially accompanied by the development of oblique cleavage. This is particularly demonstrated in the Southern Pyrenees where the out-of-sequence propagation of a flat thrust imposed the development of oblique cleavage within the flat-lying Pamplona marls. Over hundreds of meters, it is possible to trace step by step the cleavage development. The horizontal bedding is gradually superimposed by oblique cleavage (dip ~60°N). At the end of the studied outcrop, a pervasive ~mm spaced cleavage is observed. The anisotropy of magnetic susceptibility (AMS) is a classic tool for study the deformation in shales. In the Pamplona marls, AMS is essentially controlled by clays fabric. AMS shows that the degree of anisotropy Pjis not the best parameter to highlight the degree of deformation of marls. This parameter is positively correlated to the bulk magnetic susceptibility Km (~10-4 SI). On the contrary, the shape parameter T is more consistent with the degree of deformation: higher is the degree of deformation observed in outcrop (occurrence of pervasive cleavage), lower is the T parameter. As m-spaced cleavage starts to develop, the shape parameter T decreases linearly from ~0.8 to ~0.2, reflecting a gradual disorganization of clay particles. Despite the development of mm-spaced cleavage, the magnetic fabric remains oblate and is still dominated by the sedimentary fabric. This means that the bulk fabric of clay particles remains parallel to the bedding plane. Our study demonstrates that AMS is a powerful tool to trace the deformation of clay rocks and that the study of the shape parameter T is a robust and fast gauge of clays fabric.

On the use of a laser ablation as a laboratory seismic source

International audienceMimic near-surface seismic imaging conducted in well-controlled laboratory conditions is potentially a powerful tool to study large scale wave propagations in geological media by means of upscaling. Laboratory measurements are indeed particularly suited for tests of theoretical modellings and comparisons with numerical approaches. We have developed an automated Laser Doppler Vibrometer (LDV) platform, which is able to detect and register broadband nano-scale displacements on the surface of various materials. This laboratory equipment has already been validated in experiments where piezoelectric transducers were used as seismic sources. We are currently exploring a new seismic source in our experiments, a laser ablation, in order to compensate some drawbacks encountered with piezoelectric sources. The laser ablation source is considered to be an interesting ultrasound wave generator since the 1960s. It was believed to have numerous potential applications such as the Non-Destructive Testing (NDT) and the measurements of velocities and attenuations in solid samples. We aim at adapting and developing this technique into geophysical experimental investigations and produce and explore complete micro-seismic data sets in the laboratory. We will first present the laser characteristics including its mechanism, stability, reproducibility, and will evaluate in particular the directivity patterns of such a seismic source. We have started by applying the laser ablation source on the surfaces of multi-scale homogeneous aluminum samples and are now testing it on heterogeneous and fractured limestone cores. Some other results of data processing will also be shown, especially the 2D-slice V P and V S tomographic images obtained in limestone samples. Apart from the experimental records, numerical simulations will be carried out for both the laser source modelling and the wave propagation in different media. First attempts will be done to compare quantitatively the experimental data with simulations. Meanwhile, CT-scan X-ray images of these limestone cores will be used to check the relative pertinences of velocity tomography images produced by this newly developed laser ablation seismic source

High-Curie-temperature ferromagnetism in self-organized GeMn nanocolumns

International audienceThe emerging field of spintronics would be dramatically boosted if room-temperature ferromagnetism could be added to semiconductor nanostructures that are compatible with silicon technology. Here, we report a high-TC (>400 K) ferromagnetic phase of (Ge,Mn) epitaxial layer. The manganese content is 6%, and careful structural and chemical analyses show that the Mn distribution is strongly inhomogeneous: we observe eutectoid growth of well-defined Mn-rich nanocolumns surrounded by a Mn-poor matrix. The average diameter of these nanocolumns is 3 nm and their spacing is 10nm. Their composition is close to Ge2Mn, which corresponds to an unknown germanium-rich phase, and they have a uniaxially elongated diamond structure. Their Curie temperature is higher than 400 K. Magnetotransport reveals a pronounced anomalous Hall effect up to room temperature. A giant positive magnetoresistance is measured from 7,000% at 30K to 200% at 300K and 9 T, with no evidence of saturation