Jeudi 08 juillet
10:00

Jeudi 08 juillet

Ajout à votre liste de favoris
Suppression de votre liste de favoris
SC3
10:00 - 12:10

Symposium Commun 3
Nouvelles microscopies : Microscopies de phase, Champ proche et Sonde locale, Super résolution optique

Modérateurs : Damien JACOB (UMET, Lille), Elisabeth WERKMEISTER (Institut Pasteur, Lille)
Les dernières avancées technologiques concernant les microscopes et les détecteurs font de la microscopie de phase, la microscopie à sonde locale et la microscopie photonique super résolution, des outils en pleine évolution pour étudier à l’échelle atomique les matériaux et leurs propriétés ainsi que des échantillons biologiques à des résolutions allant jusqu’au nanomètre. En sciences de la vie, les techniques sont de plus en plus résolutives et rapides et sont adaptées à l’imagerie de compartiments subcellulaires. Ce symposium permettra de montrer l’évolution de ces différentes techniques et leur intérêt dans le domaine des sciences de la vie ou de la matière au travers de la présentation d’applications récentes.
10:00 - 10:30 3D nanoscale imaging using single-objective light-sheet microscopy. Jean-Baptiste SIBARITA (IINS, Bordeaux)
Assessing protein organization and dynamics in their native cellular context provides invaluable insights into their activities and functions. Fluorescence microscopy has drastically improved and diversified over the last 20 years, allowing major discoveries in cell biology, neuroscience and developmental biology. Single molecule localization microscopy (SMLM) allows monitoring the evolution of fluorescent markers with down to single molecule spatial resolution. However, it remains limited in its throughput, its capability to investigate 3D biological samples, and the quantifications that can be obtained.
In order to overcome these limits, we have developed a single objective Selective Plane Illumination Microscope (soSPIM) [1], as well as several popular point-cloud analysis methods dedicated to SMLM data [2, 3]. soSPIM is a light-sheet microscopy technique operating on a standard inverted microscope equipped with high NA objectives, compatible with single molecule imaging. It relies on dedicated microchips embedding arrays of microwells flanked with 45° micro-mirrors acting as light guides and culture vessels. In this talk, I will present our recent acquisition and analysis workflow to perform quantitative single cell 3D nanoscopy of membrane receptors, and discuss the challenges for its broad adoption by the scientific community.

[1] R. Galland, G. Grenci, A. Aravind, V. Viasnoff, V. Studer, J.B. Sibarita, 3D high- and super-resolution imaging using single-objective SPIM, Nat Methods, 12 (2015) 641-644.
[2] F. Levet, E. Hosy, A. Kechkar, C. Butler, A. Beghin, D. Choquet, J.B. Sibarita, SR-Tesseler: a method to segment and quantify localization-based super-resolution microscopy data, Nat Methods, 12 (2015) 1065-1071.
[3] F. Levet, G. Julien, R. Galland, C. Butler, A. Beghin, A. Chazeau, P. Hoess, J. Ries, G. Giannone, J.B. Sibarita, A tessellation-based colocalization analysis approach for single-molecule localization microscopy, Nature communications, 10 (2019) 2379.
10:30 - 10:40 Discussion.
10:40 - 11:10 En quête de sources brillantes : une source ponctuelle d'électrons isolant/conducteur. Evelyne SALENÇON (CINaM, Marseille)
Le développement de sources brillantes permet des ruptures technologiques, notamment dans le domaine de la microscopie. Cela passe par un contrôle et une compréhension très avancés des mécanismes d’émission.
Dans le cas de sources brillantes d’électrons, un microscope à projection fournit, à partir d'une pointe à émission de champ, une image interférentielle qui correspond à un enregistrement holographique. La reconstruction des images peut être effectuée numériquement pour former une image « réelle » de l’objet. Mais, l’obtention d’images interférentielles n’est possible qu’avec une source « ponctuelle, et, monochromatique » : souvent, une pointe ultrafine de tungstène dont le rayon de courbure est de l’ordre de 10nm.
La résolution ultime de ce type de microscope, mettant en œuvre une projection, ne dépend que de la taille de la source apparente (1). C’est pourquoi nous utilisons un microscope à projection pour caractériser une source dans son intégralité : l’analyse du contraste interférentiel permet d’estimer la taille de la source, par exemple.

Nous montrerons ensuite qu'il n'est pas indispensable de recourir à des pointes ultrafines en tungstène pour obtenir des sources brillantes. En appliquant des tensions induisant un champ électrique macroscopique faible (<1V/μm), nous avons en effet observé de l'émission de champ, intense à partir de cristaux isolants, microniques, déposés sur des conducteurs à fort rayon de courbure (>10μm)! De surcroît par l’analyse des hologrammes nous avons mesuré la taille de source et avons démontré que la brillance de ces nouveaux émetteurs égalait la brillance des sources à émission de champ classiques (2).

1. W. Stocker, H.W. Fink, and R. Morin. Low-energy electron and ion projection microscopy. Ultramicroscopy, 31 (379), 1989.
2. E. Salançon, Alain Degiovanni, Laurent Lapena, Mehdi Lagaize, and Roger Morin. Preparing a celadonite electron source and estimating its brightness. Journal of visualized experiments: JoVE, 153, 2019.
11:10 - 11:20 Discussion.
11:20 - 11:40 #26235 - Capacité Invasive de Cellules Gliales modulées par des Nanoparticules d'or-gadolinium.
Capacité Invasive de Cellules Gliales modulées par des Nanoparticules d'or-gadolinium.

Glioblastoma are characterized by an invasive phenotype, which is thought to be responsible for recurrences and the short overall survival of patients. In last decade, the promising potential of ultrasmall gadolinium chelatecoated gold nanoparticles (namely Au@DTDTPA(Gd)) was evidenced for image-guided radiotherapy in brain tumors. Considering the threat posed by invasiveness properties of glioma cells, we were interested to further investigate the biological effects of Au@DTDTPA(Gd) by examining their impact on GBM cell migration and invasion. In our work, exposure of U251 glioma cells to Au@DTDTPA(Gd) led into high accumulation of gold

nanoparticles, that were mainly diffusely distributed in the cytoplasm of the tumor cells. Experiments pointed out a significant decrease in glioma cells invasiveness when exposed to nanoparticles. As the proteolysis activities were not directly affected by the intracytoplasmic accumulation of Au@DTDTPA(Gd), the anti-invasive effect cannot be attributed to a matrix remodeling impairment. Rather, Au@DTDTPA(Gd) nanoparticles affected the intrinsic biomechanical properties of U251 glioma cells, such as cell stiffness, adhesion and generated traction forces, and significantly reduced the formation of protrusions, thus exerting an inhibitory effect on their migration capacities. These results highlight the interest of Au@DTDTPA(Gd) nanoparticles for the therapeutic management of astrocytic tumors, not only as radio-enhancing agent but also by reducing invasive potential of glioma cells.


Alexandre BERQUAND (Reims)
11:40 - 11:50 Discussion.
11:50 - 12:00 Axia ChemiSEM : new and fully integrated SEM EDS workflow - Thermo Fisher Scientific. Stefan SCHWARZMUELLER (Allemagne)
12:00 - 12:10 Discussion.
Room 1
12:10 Pause
13:10

Jeudi 08 juillet

Ajout à votre liste de favoris
Suppression de votre liste de favoris
SDV3
13:10 - 15:45

Symposium Sciences de la Vie 3
Imageries, spectroscopies en applications biomédicales
sdv3

Modérateurs : Emmanuel BEAUREPAIRE (Polytechnique, Paris), Ignacio IZEDDIN (Institut Langevin, ESPCI, Paris)
Ce symposium explorera le domaine très actif de la microscopie optique multidimensionnelle, des microscopies multiphotoniques, à super-résolution, à feuille de lumière, et d'autres nouvelles modalités, ainsi que leurs applications biologiques et médicales. Nous espérons que le large éventail de sujets pertinents présentés lors de cette conférence encouragera l'interaction entre les experts en instrumentation, en gestion et analyse d’images, et les chercheurs dans les différents domaines d'application.Nous vous invitons à présenter des contributions portant sur tous les domaines de développement et d'application des d’approches telles que :
- imagerie optique à super-résolution (PALM, STORM, STED, SIM, etc)
- l'imagerie à feuille de lumière de spécimens biologiques complexes ou de grande taille (SPIM et dérivées)
- microscopies multiphotoniques de tissus biologiques (2PEF, 3PEF, SHG, THG, CARS, SRS, etc)
- microscopies de phase ou de polarisation
- microspectroscopies
- Modalités FRET-FLIM et de fluorescence avancées
- développements instrumentaux
- applications à la biologie cellulaire, à la biologie du développement, aux neurosciences, aux modèles animaux
- applications cliniques
13:10 - 13:40 Enregistrement de l’activité neuronale à haute cadence chez la souris non-contrainte par imagerie confocale de fluorescence. Cathie VENTALON (ENS PSL, Paris)
Grâce au développement de l’optogénétique et en particulier de sondes calciques génétiquement encodées permettant la mesure de l’activité neuronale par imagerie de fluorescence, les méthodes optiques sont devenues des outils majeurs pour les études de neuroscience intégratives. Néanmoins, l'imagerie de l’activité neuronale chez la souris libre de se mouvoir est difficile en raison de contraintes de miniaturisation sévères. Ainsi, les méthodes utilisées actuellement présentent des limitations importantes : les microscopes large-champ conventionnels miniatures sont limités par un fort arrière-plan flou, et les microscopes à 2 photons miniatures souffrent de petits champs de vue ou de faibles cadences d’acquisition. Dans ce projet, nous avons mis au point un nouveau fibroscope permettant l’imagerie de l’activité neuronale par microscopie confocale de fluorescence à haute cadence (100 Hz), sur un champ de vue de 230 µm chez la souris non-contrainte.
Le dispositif est composé d'un microscope confocal couplé à l'animal avec un guide d’image et un micro-objectif. Le rapport signal sur bruit des enregistrements d’activité étant un paramètre critique, nous avons optimisé l’efficacité de détection de la fluorescence :
- Au sein du microscope, des lignes d’illumination sont créées par un DMD, tandis que les lignes (« pinholes ») de détection sont créées directement sur une caméra sCMOS fonctionnant en mode « feuille de lumière ». Ces deux lignes sont balayées simultanément.
- Nous avons développé de nouveaux micro-objectifs à haute ouverture numérique (0.7) permettant de gagner un facteur 2 à 3 sur le signal par rapport à des micro-objectifs à lentilles GRIN commerciaux
Nous avons appliqué le fibroscope à l’imagerie de l’activité neuronale dans l’hippocampe de souris non contraintes. L’hippocampe est l’une des régions du cerveau impliquées dans le codage de l’espace, et il contient en particulier des cellules de lieu, codant pour des positions précises de l’animal dans son environnement. Nous avons réalisé des sessions d’enregistrement de l’activité neuronale à 100Hz pendant 1.5h, en alternant des périodes de repos et de navigation sur une piste linéaire. Ces sessions sont reproduites chaque semaine, de façon à suivre l’évolution du codage spatial au cours du temps. Les premières analyses ont montré que le fibroscope permettait de suivre l’activité de 50 à 100 cellules de lieu dans chaque souris, et il devrait être donc un outil pertinent pour étudier le codage spatial à la fois sur des échelles de temps très courtes et très longues.
13:40 - 13:50 Discussion.
13:50 - 14:20 Multi-scale imaging using the soSPIM technology (single-objective Selective Plane Illumination Microscopy). Rémi GALLAND (IINS, Bordeaux)
Light microcopy offers to the cell biologists the capability to monitor living samples in conditions similar to their native environment. Combined with fluorescent probes, it opened the unique opportunity to image proteins of interest with a very high specificity and in a minimally invasive manner within 3D living samples. Since about fifteen years, 3D fluorescence microscopy for biology is undergoing an in-depth revolution with the advent of Light-Sheet Fluorescence Microscopy (LSFM or SPIM) technics which enable to tackle many limitations of standard 3D imaging technics in term of photo-toxicity, speed and sensitivity. Common LSFM implementation use at least two objective lenses positioned perpendicularly one from the other to create a thin sheet of light and collect the fluorescence signal respectively. However, this multi-objective architecture comes with some drawbacks. It prevents the possibility to use bulky high numeral aperture objective and limits the achievable imaging throughput due to complex sample mounting.
To overcome those limitations, we developed an alternative architecture, called soSPIM (single-objective Selective Plane Illumination Microscope), which uses a single objective to create both the excitation light-sheet and collect the fluorescent signal. It relies on the integration of 45° mirrors directly into the imaging devices in place of the excitation objective along with a laser beam steering unit. I will discuss the multiscale imaging capability of the soSPIM technology which allows to image the nanoscale organization of proteins within single cells up to the development of living 3D organoids by varying the size and design of the imaging devices. Especially, I will present the recently engineered multiwell devices, named JeWells, that enable to turn the soSPIM system into a high-content screening platform of living 3D cellular cultures (spheroids/organoids) greatly improving the imaging throughput of 3D imaging technics.
14:20 - 14:30 Discussion.
14:30 - 14:45 #26362 - Towards automation of mechanobiological measurements by atomic force microscopy (AFM).
Towards automation of mechanobiological measurements by atomic force microscopy (AFM).

Atomic force microscopy (AFM) has proven to be a powerful tool for performing biomechanical force measurements on living cells. However, this technology requires methodological improvements to be applied realistically to the medical field. To perform statistically relevant experiments, we need to automate AFM force measurements on living cells. A first strategy has been developed on C. albicans cells and we now want to be able to apply it to human cells. The strategy consists of two phases: patterning of cells in a defined network; measurement of mechanobiological properties by force spectroscopy.

To create the cells arrays, we pattern fibronectin by microcontact-printing (µCP) according to specific geometrical features and spacing. The master molds are designed and fabricated in LAAS-CNRS cleanroom facilities and µCP is performed automatically by Innostamp40TM (innovation of the joint lab between LAAS and Innopsys: BIOSOFT). Innostamp40TM prints fibronectin arrays by physical contact between a microstructured and inked PDMS stamp and a glass slide. Finally, the cells are seeded on the fibronectin array and organize themselves in the form of an ordered matrix (Fig. 1).

We need to automate biomechanical AFM measurements on each spot of the array occupied by a cell. To reach this goal we are developing and adapting an algorithm based on a Jython script [1]. The script needs the centre coordinates of the first and last cell of the matrix and the number of cells between them, which allows calculating the distance between each cell. Then the AFM tip indents the first cell and then automatically moves to the next, recording force curves on each cell (Fig. 2). The aim of automation is to be able to analyse cell populations, instead of the usual few tens of cells. We applied this methodology to PC3 and RWPE-1 cells (grade IV prostate adenocarcinoma cell line derived from bone metastases and immortalized normal prostate cell line). The results obtained on the two cell lines will be compared by conventional analysis of cell stiffness and stress and by using supervised machine learning algorithms.

Reference:

[1] Severac et al. Automation of Bio-Atomic Force Microscope Measurements on Hundreds of C. albicans Cells. JOVE, (2020)


Ophélie THOMAS-CHEMIN (Toulouse)
14:45 - 14:55 Discussion.
14:55 - 15:10 #26363 - Individual characterization of drug nanocarriers for a comprehensive analysis of their degradation mechanisms.
Individual characterization of drug nanocarriers for a comprehensive analysis of their degradation mechanisms.

Over the last two decades, a plethora of drug nanocarriers have been developed to improve the therapeutic effect of their cargo. As “smart” vehicles, they enable the delivery of the intact drug across biological barriers such as cellular membranes. Recently, there has been an increasing interest for hybrid nanocarriers named nanoscale metal-organic frameworks (nanoMOFs). [1] Built by the self-assembly of metal clusters and organic linkers, these nanoparticles exhibit a highly porous structure allowing the incorporation of a wide variety of chemical species. Taking advantage of their versatile composition, their physicochemical properties can be customized with respect to the drug to be incorporated and to the biological target. Among nanoMOFs families, MIL-100(Fe) (MIL standing for Material of Institute Lavoisier) were among the most studied drug nanocarriers due to their biocompatibility, biodegradability and hydrophilic/hydrophobic inner microenvironment, which combined to their high surface area (~1700 m2/g), ensure elevated drug payloads, together with nearly 100% loading efficiency. [2] After injection, the drug release, enabled by the nanoMOFs structure degradation, is triggered by interactions with the biological environment. Recent studies have demonstrated the role of phosphate molecules, but the related mechanisms are still to be uncovered. [3,4]

To fully understand and control these interactions, spectromicroscopies constitute ideal tools for individual and label-free analysis at a nanoscale resolution. In this regard, STEM-EELS and AFM-IR appear to be remarkable and complementary high-resolution approaches. While STEM-EELS provides valuable chemical information on the inorganic part (Fig. 1), AFM-IR identifies the chemical signature of the organic part (Fig. 2). [5] Both were employed in our studies to characterize the physicochemical properties of individual nanoMOFs and to investigate their interactions with cellular media, their biodistribution and biomodification upon cellular incubation. In the future, we will aim to optimize the design of drug nanocarriers to target specific cells and organs to improve their therapeutic efficiency. 

References :

[1] Horcajada et al., Nat. Mater. 9 (2010), 2.

[2] Li et al., ChemMedChem 15 (2020), 274.

[3] Christodoulou et al., Nanomaterials 11 (2021), 3.

[4] Li et al., Sci. Rep. 7 (2017), 1.

[5] Pancani et al., Part. Part. Syst. Charact. 35 (2018), 1700457.


Maeva CHAUPARD (Paris-Saclay)
15:10 - 15:20 Discussion.
15:20 - 15:35 #26364 - 3D characterization of cardiac fibrosis in dystrophic rat : collagen SHG imaging on CUBIC cleared heart.
3D characterization of cardiac fibrosis in dystrophic rat : collagen SHG imaging on CUBIC cleared heart.

Duchenne muscular dystrophy (DMD) is a neuromuscular disease caused by mutations in the gene encoding dystrophin. It leads to progressive muscle weakness and premature death of patient. A dystrophic (DMDmdx) rat model has been described as reflecting the muscle lesions and functional abnormalities observed in patients [1]. These muscle impairments are coupled with increases of connective tissue defined as the excessive or dysregulated deposition of extracellular matrix components. This fibrosis, particularly collagen accumulation, is a crucial component in the DMD pathogenesis. Interfering with regeneration by altering muscle architecture and function, it could also play a role as potential obstacle to cell therapies. Thus, a better understanding of fibrosis development is essential. Three-dimensional (3D) collagen organization detected by second harmonic generation (SHG) microscopy was already described as highly informative to investigate fibrotic network in tissue [2].

Here, we combine for the first time tissue clearing with SHG microscopy to characterize in depth the 3D cardiac fibrosis network from DMDmdx rat model. Heart sections (1mm thickness) from one-year-old WT and DMDmdx rat were cleared using CUBIC protocol.

We identified a massive fibrosis network in all DMDmdx rat sections compared to WT ones. We observed a distinct pattern of SHG+-segmented objects in DMDmdx animals compared with WT ones, with a decrease of the elongative shape and increase of density. Based on the orientation of SHG+-collagen fibers, we identified two distinct profiles in DMDmdx rat sections that could correspond to the natural course of fibrosis development. A relative alignment of SHG+-collagen fibers was observed in WT rat in comparison to a profound disorganization observed in severe DMDmdx rats.

The current work highlights the interest to combine multiphoton microscopy and tissue clearing for 3D collagen network characterization in label free organ. It could be a relevant tool to characterize the natural course of the disease or to evaluate efficacy of therapeutic strategies in preclinical studies in DMD model or others fibrotic cardiomyopathies.

References :

[1] PLoS One. 2014 Oct 13;9(10)

[2] Sci Rep. 2016 Jul 20;6:29863.


Julien PICHON (Nantes)
15:35 - 15:45 Discussion.
Room 1

Jeudi 08 juillet

Ajout à votre liste de favoris
Suppression de votre liste de favoris
SDM2
13:10 - 15:45

Symposium Sciences de la Matière 2
Microscopies In-situ et in-operando
sdm2

Modérateurs : Damien ALLOYEAU (CNRS scientist) (LMPQ, Paris Diderot), Renaud PODOR (Group leader) (ICSM, Marcoule)
Compte tenu des liens étroits entre la structure atomique et les propriétés physico-chimiques de la matière, on ne peut pas développer des matériaux fonctionnels efficaces si on ne connait pas leur dynamique structurale dans leur milieu d’application. Pour répondre à ce challenge, les microscopes électroniques et champs proches ont été transformés en véritables nano-laboratoires afin d’étudier le comportement des (nano)matériaux dans des environnements liquides ou gazeux bien contrôlés et/ou en réponse à des excitations électriques, thermiques, mécaniques et optiques. Ces analyses in situ ou operando ont ouvert des champs d'investigation immenses aussi bien en chimie des matériaux (synthèse des nanomatériaux, électrochimie, catalyse, géosciences) qu’en physique des matériaux (électronique, optique, mécanique). Ce symposium vise à montrer des applications de plateformes in situ qui mettent en lumière les transformations structurales et chimiques des matériaux en fonctionnement, mais aussi des solutions innovantes pour minimiser les artéfacts expérimentaux et optimiser le traitement des données.
13:10 - 13:40 Microscopie électronique en transmission in situ appliquée à l’étude des nanomatériaux : état de l’art et perspectives. Ovidiu ERSEN (Professor) (IPCMS, Strasbourg)
L’étude à haute résolution spatiale des propriétés et de l’évolution structurale des matériaux nanostructurés à l’état d’équilibre ou dans des environnements représentatifs de leur formation ou de leur utilisation dans des applications est un enjeu majeur. Cette étude est indispensable pour comprendre les phénomènes physiques et chimiques qui gouvernent les propriétés d’intérêt, en permettant ainsi de résoudre des questions à fort impact sociétal telles que la catalyse du futur et les nouvelles formes de stockage ou de conversion de l’énergie. Grâce à sa résolution, la microscopie électronique est la technique de choix ; cependant, utilisée de manière classique par l’acquisition d’une image de l’échantillon qui se trouve dans le vide du microscope, elle est souvent insuffisante pour résoudre ses propriétés et sa dynamique structurale lorsqu’il est soumis à une contrainte environnementale spécifique. En utilisant des méthodologies d’analyse nouvelles et des conditions expérimentales s’éloignant du vide des microscopes, il est maintenant possible de se donner les moyens de se rapprocher de conditions de température et d’environnement dans lesquelles ces matériaux sont synthétisés, modifiés ou utilisés (mode operando). L’une de possibilités est l’utilisation des cellules environnementales fermées pour insérer les échantillons dans le microscope, ce qui permet de les étudier sous gaz et à haute température ou encore en milieu liquide. Il faut de plus pouvoir les exposer à des contraintes électrique, mécanique, chimique ou optique afin de récolter les informations nécessaires à la compréhension de leur comportement en conditions « réalistes ».
Cet exposé se propose de résumer les récents progrès dans le domaine de la microscopie électronique en transmission in situ et operando à travers quelques études types, allant de l’étude in-situ de la croissance des nanomatériaux, à leurs transformations structurales en fonction de la contrainte appliquée ou encore à leur évolution dans des conditions « operando ». Les domaines concernés sont nombreux, la synthèse des matériaux par voie chimique, la catalyse hétérogène, l’électrochimie, les processus de biominéralisation etc., et plus généralement tous les processus qui impliquent des réactions à l’interface « gaz-solide » ou « liquide-solide ». La quantification des résultats obtenus est aussi un aspect essentiel en microscopie environnementale, pour être capable d’extraire des paramètres physiques pertinents, tel que par exemple l’énergie d’activation de la diffusion d’une nanoparticule ou d’un atome individuel. Le concept d’étude de l’objet unique basé sur le couplage de la microscopie in-situ avec d’autres techniques appliquées au même objet est aussi important, sinon l’interprétation des résultats peut s’avérer compliquée en raison de la diversité en taille, en forme et en structure des nano-objets.
Dans la dernière partie de l’exposé, plusieurs nouveaux développements et perspectives d’évolution de la microscopie électronique in situ et operando seront présentés. Pour l’acquisition, au-delà du développement de nouveaux détecteurs plus sensibles et plus rapides, il s’agira de concevoir et utiliser des logiciels spécifiques permettant d’automatiser le protocole d’acquisition des données in-situ, d’enregistrer des données sous-échantillonnées pour diminuer la dose totale d’électrons sur l’échantillon et ainsi minimiser l’influence du rayonnement électronique dans le processus étudié, ou encore de développer de nouveaux porte-objets pour pouvoir appliquer une contrainte supplémentaire comme, par exemple, une excitation optique durant le suivi in-situ de l’objet. Du point de vue des traitements de données, plusieurs méthodologies sont en cours de développement pour permettre l’analyse des données acquises de manière corrélative ou encore l’utilisation des approches de type apprentissage profond qui sont essentielles pour extraire des paramètres statistiquement pertinents et qui seront sans doute indispensables dans les années à venir pour traiter la grande quantité des données générées par les microscopies in-situ.
13:40 - 13:50 Discussion.
13:50 - 14:20 Application of Liquid-Phase Electron Microscopy in materials science. Karine MASENELLI-VARLOT (Professeur) (MATEIS, Lyon)
Understanding and optimizing materials structures and properties implies the development of characterization techniques with which materials can be studied in conditions close to their native state, avoiding, therefore, possible artifacts due to sample preparation. Moreover, characterizing materials in situ during use, under conditions close to or mimicking real conditions, brings crucial information on the mechanisms involved. In this context, Liquid-Phase Electron Microscopy (LPEM) has become a key modality for the study of hydrated samples as well as liquid suspensions and mixtures.
Two different configurations are available: in closed cells or in dedicated environmental microscopes. Closed cells can be used in Scanning Electron Microscopes (SEMs) or Transmission Electron Microscopes (TEMs) operating under vacuum as the sample is protected by membranes. They can be used to study a large range of liquids, including corrosive ones. Specific set-ups in TEM include sample holders and external controllers. They allow tests at temperatures up to 100°C and quantitative electrochemistry experiments.
On the contrary, in dedicated environmental microscopes, the sample is preserved in the liquid state without any encapsulation. Actually, the sample temperature and the surrounding gas pressure are set in order to stay at the liquid-vapor equilibrium. Although several liquids can be studied this way, such solution is mainly used to study hydrated samples and aqueous suspensions. It is noteworthy that the gas pressure can be changed to induce in situ hydration- dehydration cycles. Up to now, the developments have mainly been carried out in ESEM, where a Peltier stage can be placed in the large sample chamber.
Within a brief introduction to the basic principles of LPEM, several examples using both configurations will be shown in order to illustrate its capabilities in materials science. Several detailed examples will be given using LPEM in ESEM. Fully hydrated materials and liquid suspensions will be used to discuss the choice of the configuration and the subsequent sample preparation, if needed, and the extracted data will show how the species evolve and interact in liquid. In situ water condensation will also be shown on dry samples. The latest developments of electron tomography in LPEM will finally be exposed.
14:20 - 14:30 Discussion.
14:30 - 14:45 #26430 - Exceptional reactivity of ultra-small gold nanoparticles under H2 at atmospheric pressure revealed by environmental TEM.
Exceptional reactivity of ultra-small gold nanoparticles under H2 at atmospheric pressure revealed by environmental TEM.

L'origine de l’activité catalytique remarquable des NPs Au demeure mal définie, en particulier celle des NPs inférieures à 5 nm [1]. Cette activité est généralement attribuée aux atomes sous-coordinés d’arêtes et de coins de nanoparticules de formes cristallines supposées statiques et parfaites dans les conditions de réaction. Dans cette contribution, en étudiant à l’échelle atomique la dynamique structurale sous H2 de NPs d’Au de taille inférieure à 7 nm par MET in situ, nous montrons que cette vision est erronée pour les NPs « ultrapetites » (~3 nm), avec la mise en évidence de la grande mobilité des atomes d'or à la fois en surface et en volume.

La figure 1 montre l’évolution structurale de deux NPs Au supportées sur anatase TiO2, l’une petite (~4,5 nm) et l’autre ultrapetite (~3 nm), initialement sous 40 Pa d’Argon à 400°C , puis pendant le refroidissement de 400 à 25 °C sous 105 Pa de H2. Les deux NPs ont une structure CFC et une morphologie de type octaèdre tronqué sous Ar (Fig 1.a et d). Sous H2, la petite NP d’Au conserve sa structure cristalline, sa morphologie et son orientation par rapport au support, même jusqu’à 25°C (Fig 1.b et c). A l’inverse, l’ultrapetite NP d’Au évolue vers une structure présentant un ordre icosaèdrique dès l’introduction de H2 à 400°C (Fig 1.e et f). La caractérisation MET ex situ des NPs Au traitées sous H2 dans un réacteur à lit fixe dans des conditions de pression et de température proches des observations in situ confirme la dépendance en taille de la réactivité des NPs Au sous H2 (Fig 2). Si les NPs de taille supérieure à 4 nm présentent très majoritairement une structure CFC (Fig 2.a et c), les structures des NPs de taille inférieure à 4 nm sont différentes de CFC et variables (principalement des structures icosaèdriques et déformées) (Fig 2.e-h). Les observations MET in situ et ex situ concordantes ont été corroborées par des études de dynamique moléculaire ab initio qui seront également présentées.

[1] Catalysis by Gold G.C. Bond, C.Louis, D.Thompson, Imperial College Press, 2006.


Abdallah NASSEREDDINE (MPQ, Paris)
14:45 - 14:55 Discussion.
14:55 - 15:10 #26434 - PLASMA-ENHANCED CVD IN A TEM?
PLASMA-ENHANCED CVD IN A TEM?

In plasma-enhanced chemical vapour deposition (PECVD), the radicals and atoms generated by the plasma have the effect, among others, of changing the surface energies of the growing materials, which allows one to prepare objects that would not stabilise in other conditions. This is the case of the Sn-Cu-catalysed Si nanowires (NWs) we present in this talk: without plasma, the liquid Sn, used by the vapour-liquid-solid mechanism [1], is so unstable that no growth is allowed, while in presence of the H atoms generated by the plasma,  the Sn droplet stabilises and growth can start [2]. Yet, this method is up to now the only way of growing 2H SiNWs (a metastable polytype with interesting optical properties [3]) (Fig. 1) [4]. The goal of our present in-situ study is to understand how this metastable phase can be preferred to the stable one (the 3C polytype).

However, no electric field is compatible with HRTEM, which forbids plasma under the beam. To circumvent this incompatibility, we implemented, on the H2 line of our in-situ TEM (“NanoMAX”, a modified Thermo Fisher Titan Environmental TEM), an electron-cyclotron-resonance plasma source (Aura-wave from SAIREM), to remotely generate the H atoms necessary for the growth. Thanks to this unique setting, we obtained Sn-Cu-catalysed SiNWs in-situ, with 2H regions (Fig. 2) [5]. 

The talk presents the effect on NW growth of switching the plasma on and off, and shows movies of the nucleation of the Si 2H metastable polytype recorded at atomic resolution.

Acknowledgements:

This work was funded by the ANR: TEMPOS-NanoMAX (ANR-10-EQPX-50); HexaNW (ANR-17-CE09-0011). We kindly thank P. Roca i Cabarrocas, M. Foldyna (LPICM), F. Glas, F. Panciera (C2N), for fruitful discussions, and also the CIMEX at École polytechnique.

References:

[1] R.S. Wagner, W.C. Ellis, Appl. Phys. Lett. 4 (1964), p. 89

[2] S. Misra, et al., J. Phys. D: Appl. Phys. 47 (2014), p. 393001

[3] M. Amato, et al., Nano Lett. 16 (2016), p. 5694

[4] W. Wang, PhD thesis, Institut Polytechnique de Paris, École polytechnique (2021)

[5] É. Ngo, PhD thesis, Institut Polytechnique de Paris, École polytechnique (2021)


Jean-Luc MAURICE (Palaiseau)
15:10 - 15:20 Discussion.
15:20 - 15:35 #26439 - In-situ biasing in 4D-STEM experiments to measure electric fields in p-n junction semiconducting nanowires.
In-situ biasing in 4D-STEM experiments to measure electric fields in p-n junction semiconducting nanowires.

The advance of fast pixelated detectors has allowed performing 4D-STEM, where by measuring the shift of the transmitted beam, the electric field distribution inside the sample can be accessed, as demonstrated for p-n junctions in lamella specimens prepared from bulk or thin-film semiconductor samples [1-3]. However, the detection of the transmitted beam can be affected by diffraction contrast. In thin semiconducting nanowires (NWs) a rotation of the crystal is often present and this change in orientation of the crystal across the NW modifies the diffraction condition, potentially affecting the algorithms used to detect the beam shift. 

Here, we present in-situ biasing 4D-STEM experiments to study the electrical properties of n-i-p/p+n+/n GaN NW photodetectors grown by MBE [4]. We show that artefacts due to crystal rotation in the NWs can be reduced or removed by a combination of in-situ biasing, different algorithms to detect the beam shift, and orienting the sample off-axis to reduce diffraction contrast. We were able to measure electric fields on the order of few MV/cm in a tunnel junction (p+/n+) with high spatial resolution, consistent with doping levels around 〖10〗^19 〖cm〗^(-3). The electric field profiles are compared to 3D finite element calculations and electron beam induced current (EBIC) maps, which also reflect the internal field distribution. We measure the current-voltage (IV) response of the NW at different stages of the experiment to better understand the effect of the electron beam exposure on the electrical properties.

This work illustrates the potential of 4D-STEM measurements combined with in-situ biasing to reveal the internal electric field quantitatively, which is linked with the electrically active doping concentrations and surface band bending. These properties are otherwise difficult to access in semiconductor NWs at nm length scales, and are crucial for development of new devices with carefully designed electrical properties.

Acknowledgements: ERC, CNRS, CEA

References:

[1] N. Shibata et. al., Scientific Reports 5 (2015), 10040.

[2] L. Bruas et. al., Journal of Applied Physics, 127 (2020), 205703.

[3] A. Beyer et. al., Nano Letters, 21 (2021), 2018-25.

[4] S. Cuesta et al. Nano Letters, 19 (2019), 5506-5514.


Bruno C. DA SILVA (Grenoble)
15:35 - 15:45 Discussion.
Room 2
15:40 Pause
16:00

Jeudi 08 juillet

Ajout à votre liste de favoris
Suppression de votre liste de favoris
SDV1
16:00 - 18:55

Symposium Sciences de la Vie 1
Cryométhodes : Particules isolées : applications et développements
sdv1

Modérateurs : Irina GUTSCHE (IBS, Grenoble), Célia PLISSON-CHASTANG (LBME, Toulouse)
La cryo-microscopie électronique a vécu une véritable révolution ces dernières années puisqu’elle permet maintenant couramment de déterminer la structure 3D de divers complexes biologiques à une résolution atomique. La taille des complexes macromoléculaires accessibles aux études par cryo-MET ne cesse de baisser, la flexibilité de ces objets devient un atout pour des analyses dynamiques plutôt qu’une entrave à la résolution, et l’hétérogénéité compositionnelle n’est plus une véritable contrainte puisque les images correspondant à chaque type objet peuvent être distinguées et traitées séparément. Au travers de cette session, il est proposé un éventail de ce qui se fait actuellement en cryo-MET, des développements récents de la cryo-MET 3D à l’apport de la cryo-MET à des problématiques biologiques diverses.
16:00 - 16:30 Novel algorithms for cryo-electron tomography. Dimitry TEGUNOV (MPIBPC, Göttingen, Allemagne)
While single-particle analysis of in vitro samples made major advances over the past decade to achieve atomic resolution, the analysis pipeline for tomographic in situ data has lagged behind. With the recent development of Warp and M, we were able to close the gap in processing, obtaining residue-level resolution for ribosomes images inside cells for the first time. In my talk, I will highlight our recent results and the underlying ideas, and discuss how new deep learning-based algorithms allow to further make sense of in situ data.
16:30 - 16:40 Discussion.
16:40 - 17:10 Phage revenge: allosteric inhibition of CRISPR-Cas9 by the anti-CRISPR protein AcrIIA6. Adeline GOULET (AFMB, Marseille)
Bacteriophages (phages) and their preys are engaged in an endless evolutionary arms race. Bacteria have evolved sophisticated defense mechanisms to thrive in virus-rich ecosystems, including the well-known CRISPR-Cas9 immune system. In parallel, phages have developed counter-attack strategies to overcome their host’s defenses, including anti-CRISPR proteins. The striking sequence diversity of anti-CRISPR proteins and the lack of homology with proteins of known function raise questions relating to their modes of action. Moreover, anti-CRISPR proteins, as natural CRISPR-Cas9 inhibitors, hold great promise as biotechnological tools to fine-tune CRISPR-Cas9-based gene edition, and as useful addition to phage therapy.
In this context, we embarked on the structural and functional characterization of the anti-CRISPR protein AcrIIA6, discovered in virulent phages infecting Streptococcus thermophilus, combining cryo-electron microscopy and single particle analysis, in vitro analyses of macromolecular interactions, and functional cellular assays. The AcrIIA6 molecular mechanism is unique: we showed that AcrIIA6 acts as an allosteric inhibitor and induces St1Cas9 dimerization. AcrIIA6 affects St1Cas9 conformational dynamics, which reduces St1Cas9 binding affinity for DNA and prevents St1Cas9 binding to its target within cells. Interestingly, these findings led us to identify a natural variant of St1Cas9 resistant to AcrIIA6, illustrating anti-CRISPR-driven mutational escape and molecular diversification of Cas9 proteins.
17:10 - 17:20 Discussion.
17:20 - 17:35 #26369 - How to get the maximum out of your cryo-EM data collection session.
How to get the maximum out of your cryo-EM data collection session.

Single-particle cryogenic transmission electron microscopy (cryo-EM) can be used to elucidate the 3D structure of macromolecular complexes. The sample is embedded in a thin layer of vitreous ice and maintained at liquid nitrogen temperature. It is then imaged directly in the microscope and a 3D reconstruction may be calculated from projections of individual macromolecular complexes by determining the orientations of the projections. For many years cryo-EM was limited to low-resolution, but driven by technological breakthroughs in electron microscope and electron detector developments coupled with improved image processing procedures,  cryo-EM is now a method of choice for the determination of high-resolution structures, termed as “The Resolution Revolution” [1].

These developments deeply modified the way of collecting cryo-EM data. Currently, after only a few hours of setup, data collection can run in a fully unattended and automated way for several days, producing high quality dataset of thousands of micrographs. These improvements led to new challenges in term of session setup, microscope alignments and acquisition parameters and new strategies were required to tackle these questions. This communication will present how high-end data collection is performed at the EMBL Heidelberg cryo-EM platform using SerialEM (Fig. 1) [3], insisting on some of the key steps of the workflow: Microscope alignments allowing a small electron beam and aberration-free beam shift/image shift [2]; pixel size choice for optimized data collection; alternative collection strategies for samples with very low concentration and uneven spreading on the grid [4]; ice thickness characterisation for optimal holes selection.

References :

[1] W Kühlbrandt, Science 343 (2014), p. 1443.

[2] F Weis and WJH Hagen, Acta Crystallogr D Struct Biol 76 (2020), p. 724.

[3] DN Mastronarde, J Struct Biol 152 (2005), p. 36.

[4] M Schorb et al, Nat Methods 16 (2019), p. 471.


Felix WEIS (Heidelberg, Allemagne)
17:35 - 17:45 Discussion.
17:45 - 18:00 #26370 - Structural characterization of a human Kir potassium channel and its involvement in Andersen syndrome.
Structural characterization of a human Kir potassium channel and its involvement in Andersen syndrome.

Inward rectifier potassium (Kir) channels belong to a family of integral membrane proteins that selectively control the K+ ions permeation at the cell membranes of various tissues and regulate the membrane electrical excitability [1]. The Kir channels gating is essentially modulated by phosphatidylinositol-4,5-bisphosphate (PIP2), although a full description of PIP2 role requires more details [1]. Genetically-inherited defects in Kir channels are responsible for several rare human diseases, including Andersen-Tawil syndrome (AS), a muscular disease that causes episodes of muscle weakness, arrhythmia, and developmental abnormalities, which the available treatments are inefficient [2]. Two-third of the mutations that causes this syndrome are situated on the PIP2 binding site [2]. 

Here, we present a 3.5 Å resolution cryo-EM map of the human Kir2.1 channel (Fig. 1). The data were collected on a Titan Krios TEM (FEI) operating at 300 kV equipped with a Gatan K2 Summit DED and Cs corrector. After micrographs selection based on visual quality inspection, it was obtained 7,188 images and 837,808 particles. All data was processed using Relion 3.0.

This is the first structural data of the whole human Kir2.1 channel, which can reveal useful insights about selectivity filter gate. The near-atomic resolution of the obtained cryo-EM map can provide a complete description of the PIP2 binding site in the Kir2.1 channel and the understanding of the clinically-relevant disease-causing mutations impact on the Kir channels function and dynamics. Molecular dynamis simulations performed with the final cryo-EM structure can provide the understanding of the full gating mechanism of human Kir2.1 channel and the PIP2 role on the dynamics of this channel.

References

[1] Suh et al. Curr. Opin.Neurobiol. v.15 (2005), p. 370-378.

[2] Andersen et al. Acta Paediatr. Scand. v.60 (1971), p. 559-564.

[3] Donaldson et al. Neurology v.60 (2003), p.1811-1816.

Figure 1: Structure of the human Kir2.1 channel. (A) Representative cryo-electron micrograph; (B) Representative 2D class averages of the particles; (C) Fourier Shell Correlation (FSC) curve indicating the map overall resolution; (D) Cryo-EM map obtained at 3.5 Å resolution highlighting the PIP2 binding site between cytoplasmic and transmembrane domains and including a map detailed view at the transmembrane domain. 


Carlos A. H. FERNANDES (Bioinformatique et BioPhysique (BIBIP))
18:00 - 18:10 Discussion.
18:10 - 18:25 #26372 - A hybrid approach to analyze continuous conformational variability of single particles based on deep learning.
A hybrid approach to analyze continuous conformational variability of single particles based on deep learning.

Cryo-electron microscopy (cryo-EM) allows high-resolution 3D reconstruction of biomolecular structures from highly noisy 2D parallel-beam projection images containing tens of thousands of copies of the same macromolecular complex but at different random orientations and positions. However, biomolecular complexes are not rigid but flexible entities that change their conformations gradually (continuous transition with many intermediate states) to accomplish biological functions (e.g., DNA replication, protein synthesis, etc.). The determination of the full distribution of conformations (conformational space or landscape) from cryo-EM images is challenging but could provide insights into working mechanisms of the complexes. In this presentation, we describe a method for conformational space determination, which uses deep learning in combination with cryo-EM image analysis and normal mode analysis [1,2] (Fig. 1), where the amplitudes of normal modes are the parameters of the elastic conformations of complexes. We show the performance of this new method

using synthetic cryo-EM data (Fig. 2). The conformational space predicted using the proposed method (Fig. 2(a)) allows obtaining molecular movies of the conformational transition (Fig. 2(b)).

Acknowledgment:

We acknowledge the support of the French National Research Agency — ANR (ANR-19-CE11-0008-01 and ANR-20-CE11-0020-03 to SJ) and the access to the HPC resources of CINES and IDRIS granted by GENCI (2019-A0070710998, AP010712190, AD011012188 to S.J.).

References :

[1] Harastani M, Sorzano COS, Jonic S, Hybrid Electron Microscopy Normal Mode Analysis with Scipion. Protein Sci 29 (2020), p. 223-236.

[2] Jin Q, Sorzano CO, de la Rosa-Trevin JM, Bilbao-Castro JR, Nunez-Ramirez R, Llorca O, Tama F, Jonic S, Iterative Elastic 3D-to-2D Alignment Method Using Normal Modes for Studying Structural Dynamics of Large Macromolecular Complexes. Structure 22 (2014), p. 496-506.


Ilyes HAMITOUCHE (Paris)
18:25 - 18:35 Discussion.
18:35 - 18:45 CRYO TEM: Latest improvements on throughput & resolution - JEOL. Guillaume BRUNETTI (Responsable Marketing) (JEOL EUROPE)
18:45 - 18:55 Discussion.
Room 1

Jeudi 08 juillet

Ajout à votre liste de favoris
Suppression de votre liste de favoris
SDM1
16:00 - 19:05

Symposium Sciences de la Matière 1
Microscopies des matériaux/nanomatériaux et applications
sdm1

Modérateurs : Caroline ANDREAZZA (Professor) (ICMN, Orléans), Virgile ROUCHON (IFPEN, Lyon)
Les nanomatériaux sont au cœur de l’innovation technologique du XXIème siècle avec une grande variété d’applications, allant des domaines tels que l’énergie, les transports, l’environnement, le bâtiment à ceux de la santé ou de l’électronique. Cet essor des nano-objets est permis grâce à l’amélioration des méthodes de caractérisation qui permettent à la fois de décrire ces systèmes à l’échelle de l’atome et également d’analyser leurs propriétés fonctionnelles. La microscopie est un axe de développement central pour les nanomatériaux puisqu’elle permet de révéler à la plus fine échelle spatiale les informations bi- et tri- dimensionnelles nécessaires à l’optimisation de leur synthèse, leur fonctionnalisation, leur mise en forme et par voie de conséquence leurs comportements et performances.
Cette session interdisciplinaire vise à présenter les approches innovantes des techniques de microscopie à résolution nanométrique et sub-nanométrique, telles que la microscopie électronique à transmission ou à balayage ou encore la microscopie photonique hyper résolutive, pour l’étude de nanomatériaux (nanoparticules, nanofils, matériaux poreux et/ou nanostructurés, couches ultra-minces, …). Les développements techniques et méthodologiques, que ce soit d’un point de vue des performances instrumentales, des approches de microscopies corrélatives et multimodales (imagerie, spectroscopie, diffraction, …), ou du traitement de données seront mises en avant de façon à démontrer comment les informations obtenues contribuent au développement des nouveaux matériaux nanostructurés. Les domaines d’application des matériaux étudiés peuvent être très larges et englober des approches de développement durable (énergies renouvelables, conversion de l’énergie, dépollution, recyclabilité …) ou des questions de toxicité, de biosécurité ...
16:00 - 16:30 Highly doped Si nanostructures for infrared plasmonics. Caroline BONAFOS (CEMES, Toulouse)
The appearance of Localised Surface Plasmon Resonances (LSPR) in highly doped Si nanostructures opens a new field of applications, with Si-based plasmonic tunable over a wide infrared range [1]. However, doping low dimensional silicon remains a challenge due to self-purification mechanisms [2]. To circumvent this problem, we recently proposed a top down approach consisting at optimizing the doping of thin silicon layers, by means of P low energy ion implantation (LE-II) and further Laser Thermal Annealing (LTA), in which nanometer size disks are produced by electron beam lithography. The melting regimes and the regrowth processes as well as the redistribution of P in the top Si amorphized layer were studied as a function of the P content by coupling HRTEM and STEM-EDX. The results highlight the crucial role of the thin crystalline Si layer preserved after amorphization, which provides nucleation seeds for the liquid phase recrystallisation. FTIR measurements demonstrate that the Si overlayers can be massively doped over a wide range of active dopant concentrations. By processing these hyper-doped overlayers, we realized all-silicon-based plasmonic metasurfaces formed by submicrometer doped-Si nanodisks and demonstrated that such nanostructures support LSPR tunable between 2.5 and 5 µm via the free carrier density of the silicon [3].
In a second part of this talk, preliminary results on a bottom-up approach consisting of doping smal (3 nm) Si nanocrystals (SiNCs) synthesised by LE-II in a silica matrix will be presented. Atom Probe Tomography analysis clearly shows the dopant insertion in the SiNC volume. The decrease of the SiNC photoluminescence intensity after dopant insertion due to Auger quenching likely evidences its electrical activation. Finally, the first demonstration of LSPR from these small embedded P doped SiNCs has been obtained provided the passivation of surface defects.
This work was partly funded by ANR DONNA (ANR-18-CE09-0034).
References:
[1] D. J. Rowe et al. Nano Lett. 13 (2013), p. 1317
[2] J. P. Petropoulos, et al. Nanotechnology 22, (2011) p. 245704
[3] J. M. Poumirol, ACS photonics (2021) https://doi.org/10.1021/acsphotonics.1c00019
16:30 - 16:40 Discussion.
16:40 - 17:10 Contribution de la microscopie électronique au développement des électrodes de pile à combustible de type PEMFC et à la compréhension de leurs mécanismes de dégradation. Laure GUETAZ (LITEN, Grenoble)
Les piles à combustible de type PEMFC pour « proton exchange membrane fuel cell » permettent de générer de l’électricité à partir des deux réactions électrochimiques que sont l’oxydation de l’hydrogène et la réduction de l’oxygène. Elles sont principalement développées pour répondre au besoin de moyen de transport décarboné. Leurs performances actuelles sont suffisantes pour avoir permis la commercialisation des premiers véhicules à pile à combustible. Cependant leur coût et leur durabilité sont encore les deux verrous qui limitent l’extension de ce marché. Pour lever ces verrous, il est encore nécessaire d’optimiser les composants et la structure des électrodes et de mieux comprendre leurs mécanismes de dégradation.
Les électrodes sont un milieu poreux nano-composite composé de particules de carbone (30-50 nm) supportant des nanoparticules de Pt (2-5 nm) qui catalysent les réactions et entourées d’une fine (5-8 nm) couche de ionomère qui joue le rôle d’électrolyte mais aussi de liant. Pour analyser ces différents composants, la microscopie électronique et ses différentes techniques sont alors devenues des outils indispensables. Ainsi, le STEM/EDS ou STEM/EELS ont largement contribué au développement de nouveaux catalyseurs d’alliage de Pt plus performants et à la compréhension de leurs mécanismes de dégradation. Plus récemment la tomographie électronique a révélé que des carbones supports poreux pouvaient permettre de confiner les nanoparticules de Pt à l’intérieur des pores et ainsi limiter leur dégradation par le mécanisme de maturation électrochimique d'Ostwald. La répartition du ionomère au sein de l’électrode reste aujourd’hui encore mal connue et est pourtant un paramètre important à optimiser car d’elle dépend le taux d’utilisation des catalyseurs et la diffusion des gaz au sein de l’électrode. Ainsi, la visualisation en 3D du ionomère semble essentielle mais reste encore un défi. Des techniques de tomographie associant les signaux de plusieurs détecteurs pourraient être prometteuses.
17:10 - 17:20 Discussion.
17:20 - 17:35 #26352 - UNVEILING NANOSCALE OPTICAL PROPERTIES OF 2D SEMICONDUCTORS USING ELECTRON SPECTROSCOPY.
UNVEILING NANOSCALE OPTICAL PROPERTIES OF 2D SEMICONDUCTORS USING ELECTRON SPECTROSCOPY.

In this contribution, we will present results on the optical and the structural properties of a monolayer of semiconducting transition metal dichalcogenide (TMD) encapsulated with hexagonal boron-nitride (h-BN), at the tens of nanometers scale. In this work we the correlate optical spectra at the nanoscale with structural and chemical maps. In this way, we connect the information usually available separately from optical diffraction-limited techniques, such as photoluminescence (PL) [1], and from high-resolution techniques, such as electron microscopy [2] or scanning tunneling microscopy [3].

To achieve this, we used combined high spatial and spectral resolution techniques in a scanning transmission electron microscope (STEM), such as illustrated in Fig. 1. Electron energy loss spectroscopy (EELS) was used to obtain optical absorption (low-loss range) and chemical analysis (core-loss range). Cathodoluminescence (CL), a nanoscale coun-terpart of PL [4], was used to measure light emission at the tens of nanometers scale. The two types of spectral data were acquired in the same regions. This gave access to, for example, the local Stokes shift (SS), which is the difference between absorption and emission energies. This quantity gives information about the physical mechanism in-volved in the absorption and emission processes [1]. In addition to these spectral meas-urements, spatial structural information was gathered using either atomically-resolved imaging or diffraction mapping for local strain measurements. Moreover, chemical maps were measured using core-loss EELS.

Using these combined techniques, we detected spatially localized emission from excitonic complexes in WS2 monolayers maintained at 150 K, with bright spots as small as few tens of nanometers (Fig. 2). The presence of such bright spots was linked to the chemi-cal environment, displaying small patches of contaminants (such as C, O, N, or Si), prob-ably coming from sample preparation [5].

References
[1] Kolesnichenko et al. 2D Mater. 7 025008 (2020)
[2] Chang et al. Appl. Miscosc. 49, 10 (2019)
[3] Schuler et al. Sci. Adv., 6, eabb5988 (2020)
[4] Kociak and Zagonel, Ultramicroscopy, 176, 112-131 (2017)
[5] Bonnet et al. arXiv :2102.06140 [cond-mat.mes-hall]


Noémie BONNET (LPS - STEM, Paris)
17:35 - 17:45 Discussion.
17:45 - 18:00 #26354 - Mapping Built-in electric field in nanowires and in-situ biasing by 4D scanning electron transmission microscopy.
Mapping Built-in electric field in nanowires and in-situ biasing by 4D scanning electron transmission microscopy.

Today's progress in semiconductor technology and electronic device miniaturization, necessitate the exact estimation of electrostatic properties like local electric field and electronstatic potential to enhance the performance and functionality of nano-devices. Though, the direct observation and precise measurements of local electric fields are still quite challenging, 4D scanning transmission electron microscopy (4D STEM) technique is known as a sensitive detection tool to map the internal electric fields arising from nanoscale features like p-n junctions [1-4]. Moreover, the development of fast pixelated detectors based on direct electron detection technology, has improved the feasibility of 4D STEM through their higher acquisition speed, high dynamical range and fast readout. 

In this work, we aim to map the internal electric field of highly doped (1019 atom/cm3) Ge p-n junction nanowires prepared by gold catalyzed chemical vapour deposition (CVD). 4D-STEM measurements with careful tuning of the parameters, with/without precession and in different crystal orientation, are applied to get the maximum spatial resolution, necessary for the built-in electric field detection in the junction. Also, for the first time, in-situ electrical measurements are exploited to monitor the I-V characteristics of the nanowires during different steps of the 4D STEM experiments to verify if the system is electrically modified during 4DSTEM data acquisition. Moreover, reverse and forward biased data are acquired to separate the contribution of electrical characteristics and the ones due to artifacts in the reconstructed data. MerlinEM fast pixelated detector is used for STEM data acquisition. Post-acquisition data analysis is performed by Python and MATLAB based scripts to reconstruct the STEM images from the data sets and investigate the effect of experimental parameters. Moreover, scanning electron microscopy (SEM) based Electron beam Induced current (EBIC) is also used to verify the position of the junction and compared with the STEM data. Also, the data from EBIC can be exploited to acquire higher resolution data by 4D STEM, focusing on the small region of the nanowire containing the field. Different methods for data analysis, including Center of Mass (CoM) and template matching (TM) is applied on the data and pros and cons of each method will be investigated.


Zahra SADRE MOMTAZ (Grenoble)
18:00 - 18:10 Discussion.
18:10 - 18:25 #27017 - Individual magnetic moments in assemblies of magnetic nanoparticles in a ferrofluid.
Individual magnetic moments in assemblies of magnetic nanoparticles in a ferrofluid.

Ferrofluids, which are suspensions of magnetic nanoparticles in a liquid, have many current and potential applications in the biomedical field (e.g. improved MRI agents, magnetic hyperthermia) and in the technological industry (e.g. permanent magnets, magnetic memory). When the nanoparticles have a large enough magnetic moments, magnetic dipole interactions give rise to different assemblies of nanoparticles. Indeed, theoretical simulations [1] have predicted the existence of nanoparticles assembled in chains, rings, or a combination of both. These assemblies modify the macroscopic properties of the ferrofluid significantly. Thus, in order to achieve a better understanding of these materials, we aim to study the correlation between the magnetic properties and the self-organisation. To that goal, we have used Cryogenic Transmission Electron Microscopy (Cryo-TEM) and Electron Holography to study a suspension composed of nanoflowers of cobalt ferrite with 25nm diameter, which are known to present a large magnetic anisotropy and their ferrofluidic solution in water have shown efficient magnetic hyperthermia [2]. 

Cryo-TEM allows visualising the self-organisation of the ferrofluid. By rapidly plunge-freezing a drop of the sample in liquid ethane, we show the theoretically predicted assemblies (fig. 1) and establish the statistical occurrence of each shape. Several assemblies were further investigated by Electron Holography, a TEM-based technique, that allows retrieving the magnetic induction at the nanoscale by interfering the transmitted electron beam with a reference beam and measuring the phase shift. We quantitatively mapped the in-plane magnetic induction within several assemblies and deduced the magnetization orientation of each particle (fig 2.). While dipolar magnetic interactions are expected to align dipolar moments top to tail within a chain, we show that the relative orientation of particle magnetization varies from parallel to anti-parallel configuration, suggesting a significant contribution of the particle’s magnetic anisotropy. This contribution cannot, therefore, be neglected when performing Monte-Carlo simulations of magnetic properties for ferrofluids presenting such a large magnetic anisotropy.


Malika KHELFALLAH (IMPMC)
18:25 - 18:35 Discussion.
18:35 - 18:55 Distinguer les phases à l'aide de l'EBSD - Oxford Instruments. Brooke JABLON (Applications and Field Service Engineer FRANCE)
18:55 - 19:05 Discussion.
Room 2