Facile and rapid synthesis of highly luminescent nanoparticles via Pulsed Laser Ablation in Liquid

This paper demonstrates the usefulness of pulsed laser ablation in liquids as a fast screening synthesis method able to prepare even complex compositions at the nanoscale. Nanoparticles of Y2O3:Eu3+, Lu2O2S: Eu3+, Gd2SiO5:Ce3+ and Lu3TaO7:Gd3+,Tb3+ are successfully synthesized by pulsed laser ablation in liquids. The phase and stoichiometries of the original materials are preserved while the sizes are reduced down to 5-10 nm. The optical properties of the materials are also preserved but show some small variations and some additional structures which are attributed to the specificities of the nanoscale (internal pressure, inhomogeneous broadening, surface states...

Oriented Attachment of ZnO Nanocrystals

Self-organization of nanoparticles is a major issue to synthesize mesoscopic structures. Among the possible mechanisms leading to self-organization, the oriented attachment is efficient yet not completely understood. We investigate here the oriented attachment process of ZnO nanocrystals preformed in the gas phase. During the deposition in high vacuum, about 60% of the particles, which are uncapped, form larger crystals through oriented attachment. In the present conditions of deposition, no selective direction for the oriented attachment is noticed. To probe the driving force of the oriented attachment, and more specifically the possible influence of the dipolar interaction between particles, we have deposited the same nanocrystals in the presence of a constant electric field. The expected effect was to enhance the fraction of domains resulting from the oriented attachment due to the increased interaction of the particle dipoles with the electric field. The multiscale analytical and statistical analysis (TEM coupled to XRD) shows no significant influence of the electric field on the organization of the particles. We therefore conclude that the dipolar interaction between nanocrystals is not the prominent driving force in the process. Consequently, we argue, in accordance with recent theoretical and experimental investigations, that the surface reduction, possibly driven by Coulombic interaction, may be the major mechanism for the oriented attachment process

Deformation mechanism of cerium oxide nanocubes - an in situ transmission electron microscopy study

Cerium oxide nanoparticles are used in many industrial products, among which solid oxide fuel cell electrodes or catalysts. However, their mechanical properties are rarely taken into account and few studies dealt with the determination of their deformation mechanism [1, 2]. Please click Download on the upper right corner to see the full abstract

Oscilador LC monolítico comandado por tensão a 2,4GHz

Esta Comunicação tem como finalidade divulgar o projecto de um VCO monolítico a 2.4GHz para integrar uma Malha de Captura de Fase (PLL). O Oscilador projectado é baseado num par diferencial cruzado (parte activa). O circuito funciona com uma tensão de 2.8V e com uma tensão de comando entre 1.6V e 1.8V, produzindo uma variação de frequência entre 2.4GHz e 2.75GHz.info:eu-repo/semantics/publishedVersio

In situ nanocompression tests in an environmental TEM to study plasticity of cerium oxides

Cerium oxide plays an important role in several fields, among which catalysis, gas detection or fuel cells [1]. Cerium oxide nanoparticles are also used as superior abrasive particles in chemical mechanical planarization (CMP), which is a key process in semiconductor device fabrication [2]. Most of the current research focus on the synthesis of cerium oxide to optimize CMP, but analysing its deformation mechanisms is also a promising research direction [3]. Please click Additional Files below to see the full abstract

TEM observation and in situ compression tests of transition alumina prepared by high pressure compaction at room temperature

The behavior of ceramics at the nanometer scale strongly differs from the one of the corresponding bulk material. For instance, strong plastic deformation has recently been reported in isolated nanometer-sized alumina nanoparticles or MgO nanocubes, when tested in situ in a transmission electron microscope (TEM). This plastic behavior may also occur in a powder during the compaction process, even at room temperature. Controlling plastic deformation of nanoparticles during the ceramics processing might be a way to enhance their properties or to improve the processing route (compaction and sintering steps, for instance). We present here a comprehensive study of the mechanical behavior of transition alumina in the compacted powder. Please click Additional Files below to see the full abstract

Evidence for the formation of distorted nanodomains involved in the phase transformation of stabilized zirconia by coupling convergent beam electron diffraction and in situ TEM nanoindentation

International audienceThe transformation of zirconia from its tetragonal to its monoclinic phase is an important feature of the zirconia system. First found to be an advantage due to its important toughening effect, it can also be very detrimental when it occurs in the framework of low-temperature degradation, particularly in the case of biomaterial applications. One way to avoid or to control this phase transformation is to understand how it initiates and more particularly the stress states that can trigger it. A new technique available inside a transmission electron microscope seems to be particularly well suited for that type of study: convergent beam electron diffraction, a well-known technique to reveal stresses, was coupled to in situ transmission electron microscopy mechanical nanoindentation. The experiments reveal the presence of sheared nanoregions at grain boundaries. These could act as embryos for tetragonal-to-monoclinic phase transformations. This is an important first step in the understanding of the earliest stage of zirconia phase transformation

Apport de la microscopie électronique filtrée en énergie (TEM/EELS) à la caractérisation chimique des polymères

Because the chemical structure of polymers is increasingly complex, and polymeric composites have appeared, chemical characterization at high spatial resolutions has become compulsory, especially for interfaces. As most of the common techniques for polymer observation (XPS, IR, Raman, ToF-SIMS) are limited by their spatial resolution (about 1 µm²), I wanted to study the potentialities of electron energy-loss spectroscopy coupled with transmission electron microscopy (TEM/EELS). This technique has proved to be very powerfil as polymers can be characterised not only chemically (analysis of the chemical bondings) but also physically (dielectric function, density).A characteristic signature for each polymer was recorded even at high spatial resolution (2.4 nm), allowing very similar chemical structures like polyolefines to be differentiated. The fine structure was assigned in agreement with molecular orbital calculations (EHT).There is a major limitation to TEM/EELS, namely the degradation of polymers under electron beam, which is estimated to be about 1000 times greated with electrons than with synchrotron radiation (XAS). By studying the degradation, I was able to propose a degradation process for each polymer. The influence of experimental factors on degradation kinetics was also quantified in order to determine the optimum conditions for polymer observation. One point of interest, namely the use of a field emission gun (spectacularly low degradation) was noticed and discussed.Lastly, the results obtained on homopolymers have been exploited in energy-filtered TEM (image-spectrum method) in order to image the spatial distribution not only of mineral charges but also of chemical bondings (phase differentiation in a polymeric material). As irradiation damage can be considerable, this has to be taken into account when interpreting filtered images.La complexité grandissante de la structure chimique des polymères et l'apparition de composites polymériques imposent une caractérisation chimique à petite échelle, notamment au niveau des interfaces. La plupart des techniques usuelles d'observation des polymères (XPS, IR, Raman, ToF-SIMS) étant limitées par leur résolution spatiale, de l'ordre de 1 µm², l'objectif de ce travail est d'étudier les potentialités de la spectroscopie de pertes d'énergie des électrons couplée à la microscopie électronique en transmission (TEM/EELS). Cette technique est très puissante puisqu'il a été possible de caractériser les polymères à la fois chimiquement (étude des liaisons chimiques) et physiquement (fonction diélectrique, densité).Une signature caractéristique de chaque polymère a pu être enregistrée, y compris à haute résolution spatiale (2,4 nm), permettant ainsi de différencier des structures chimiques aussi voisines que celles des polyoléfines. L'indexation des liaisons chimiques a été faite en accord avec les calculs théoriques d'orbitales moléculaires (EHT).Cependant, l'utilisation de la technique TEM/EELS comporte un point particulièrement délicat : la dégradation des polymères sous faisceau électronique. Phénomène incontournable estimé environ 1000 fois plus important qu'avec le rayonnement synchrotron (XAS), les cinétiques de dégradation ont été étudiées et ont permis la proposition d'un processus de dégradation pour chaque polymère. De plus, l'influence des principaux facteurs expérimentaux sur la cinétique de dégradation a été quantifiée de manière à proposer des conditions optimales d'observation. En particulier, l'intérêt de l'analyse avec une source à émission de champ (dégradation spectaculairement moindre) a été remarqué et discuté.Enfin, les résultats sur les homopolymères ont été exploités en imagerie chimique (méthode images-spectres) afin de cartographier la répartition non seulement des charges minérales mais aussi des liaisons chimiques (différenciation des phases dans un composite polymérique). Les dégâts d'irradiation pouvant être considérables, les cartographies doivent être interprétées de manière raisonnable

Analysis of liquid suspensions using scanning electron microscopy in transmission: estimation of the water film thickness using Monte-Carlo simulations

International audienc

Contribution de la nanoindentation in situ en Microscopie Electronique en Transmission à l'étude des céramiques

La connaissance du comportement et des propriétés des matériaux est d une grande importance pour optimiser leur mise en forme et adapter leur utilisation. Pour étudier ces propriétés de nombreuses techniques sont couramment utilisées : les essais de traction, la microindentation, la nanoindentation instrumentée Aujourd hui, un intérêt particulier est porté sur les nanomatériaux et matériaux nanostructurés car ils présentent souvent des propriétés différentes et plus intéressantes. La nanoindentation instrumentée, notamment, permet de déterminer des paramètres matériaux de manière locale. Cependant, le comportement en temps réel ne peut être observé et l échantillon ne doit pas être de dimension trop faible (typiquement, l étude de nanoparticules n est pas envisageable). Le principal atout de la nanoindentation in situ en Microscopie Electronique en Transmission vis-à-vis des autres techniques existantes est la possibilité d étudier le comportement de nano-objets ou des comportements très locaux et en temps réel, tout en observant les transformations subies par le matériau. Dans cette étude, nous avons évalué les potentialités de cette nouvelle technique via l analyse de céramiques très étudiées au laboratoire notamment en tant que biomatériaux : la zircone stabilisée et l alumine. Dans le cas de la zircone (stabilisée à l yttrium ou au cérium), le but était de localiser à l échelle nanométrique les contraintes responsables ou inhérentes à la transformation de phase quadratique-monoclinique, phénomène ayant une très grande influence sur les propriétés du matériau massif. Pour ce faire, après avoir déterminé une technique de préparation adaptée, nous proposons une voie d étude pour la localisation des contraintes liées à la transformation de phase : le CBED (Convergent Beam Electron Diffraction) couplé à la nanoindentation in situ. Dans le cas de l alumine, l objectif était d étudier le matériau (commercial et non un matériau modèle) dans sa forme originelle à savoir sous forme de nanoparticules d alumine de transition. L idée était d étudier le comportement de ces nanoparticules sous compression. Nous avons notamment constaté que ces particules pouvaient subir une grande déformation plastique à température ambiante. Nous avons pu également, sur quelques particules, obtenir une série d images en cours de compression ainsi que la courbe de charge-déplacement correspondante. Ces résultats ont ensuite été soumis à une analyse des images couplée à une simulation de type Eléments Finis (réalisées par le LAMCOS).Knowledge of the behavior and properties of materials is of great importance to optimize their processing and adapt their use. To study these properties, many techniques are commonly used: tensile tests, microindentation, instrumented nanoindentation ... Today, particular interest is focused on nanomaterials and nanostructured materials because they often have different and more interesting properties. Instrumented nanoindentation allow to determine material parameters. However, the real-time behavior can not be observed and the study of nano-objects is difficult (nanoparticles for example). The main advantage of in situ TEM (Transmission Electron Microscopy) nanoindentation is the ability to study the behavior of nano-objects in real time. In this study, we evaluated the potential of this new technique by analyzing ceramics extensively studied in the laboratory such as biomaterials: stabilized zirconia and alumina. In the case of zirconia (stabilized with yttrium or cerium), the goal was to locate at the nanoscale, the constraints responsible for the tetragonal to monoclinic phase transformation. This phenomenon having a great influence on the bulk material properties. To do this, after having determined a suitable preparation method, we suggest a way to study the localization of constraints: the CBED (Convergent Beam Electron Diffraction) coupled with in situ TEM nanoindentation. In the case of alumina, the goal was to study the material in its original form (nano powder of transition alumina). The idea was to study the behavior of these nanoparticles under compression. We particularly observed that these particles could undergo large plastic deformation at room temperature. We have also obtained during compression on few particles, series of images and the corresponding load-displacement curve. These results were then analyzed by image analysis coupled with Finite Element simulations (performed in LAMCOS lab).VILLEURBANNE-DOC'INSA-Bib. elec. (692669901) / SudocSudocFranceF