Siga este enlace para ver otros tipos de publicaciones sobre el tema: In-situ TEM.
Tesis sobre el tema "In-situ TEM"
Crea una cita precisa en los estilos APA, MLA, Chicago, Harvard y otros
Consulte los 50 mejores tesis para su investigación sobre el tema "In-situ TEM".
Junto a cada fuente en la lista de referencias hay un botón "Agregar a la bibliografía". Pulsa este botón, y generaremos automáticamente la referencia bibliográfica para la obra elegida en el estilo de cita que necesites: APA, MLA, Harvard, Vancouver, Chicago, etc.
También puede descargar el texto completo de la publicación académica en formato pdf y leer en línea su resumen siempre que esté disponible en los metadatos.
Explore tesis sobre una amplia variedad de disciplinas y organice su bibliografía correctamente.
1
Hummelgård, Magnus. "In-situ TEM Probing of Nanomaterials". Doctoral thesis, Mittuniversitetet, Institutionen för naturvetenskap, teknik och matematik, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:miun:diva-8998.
Texto completoResumen
Nanomaterials because of their small size, may have special properties unlikely to be seen in ordinary types of materials. Nanomaterials like nanotubes,nanowires and nanoparticles are best studied at the nanoscale, vital but also problematic. In this thesis we use a transmission electron microscope (TEM)combined with a scanning tunneling microscope probe. This system allows TEM images to be captured and recorded into a movie together with recordedelectrical data for real time analysis. Using this method we found that the electrical conductivity of molybdenumbased nanowires Mo6S3I6 can be improved by current induced transformation. This might be a general method of improving nanowires which is of high valueif the wires are to be used in electrical circuits or field emission devices. The bending modulus for these nanowires were also determined, by an electromechanical resonance method, to 4.9 GPa. The sintering phase of silver nanoparticles, used in electrical conductive ink for printing electrical circuits, were studied by the in-situ TEM probing method. We observed that percolation path ways are formed and that the dispersive agent of the particles can be pyrolysed into a net of carbon with characteristics similar to graphite. We also developed a method for decorating nanowires and nanotubes with gold nanoparticles. Nanowire particle composites are often used in assembling more complex devices (electronic circuits) or for linking to organic molecules (biosensor applications) and existing particle decoration methods are either difficult or with low yield. By in situ TEM probing we found that carbon nanocages can be grown onto these gold nanoparticles. The size of the gold nanoparticles is controllable an thus the size of the nanocages. These nanocages may be used in medicine- or hydrogen storage-applications.Nanomaterial har givits stort intresse under det senaste årtiondet, detta på grund av deras unika egenskaper som gör att de i många hänseenden överträffar traditionella material. Egenskaperna beror till största del på storlek och därför är det nödvändigt att studera dessa material på nanonivå, något som är problematiskt. För sådana studier krävs ett instrument med tillräckligt hög upplösning på nanonivå samt ett system med en prob som möjligör selektion och karakterisering utav individuella byggstenar. I denna avhandling används ett transmissionselektronmikroskop (TEM) tillsammans med ett sveptunnelmikroskop (STM) där det senare används som prob. Systemet medger studier på nanonivå och karakterisering av enskilda byggstenar under realtids avbildning (in situ). Metoden medger en bättre överblick och hanterbarhet vid nanomanipulering än vad till exempel atomkraftmikroskopi medger. Piezodrivna probar kan även användas i svepelektronmikroskop men dessa medger inte samma upplösning som transmissionselektronmikroskopet. Nanotrådar av Mo6S3I6 är ett alternativt material till kolnanorör och överträffar dessa i form av löslighet i båda organiska såväl som polära lösningsmedel. De är enkla att syntetisera men deras elektriska konduktivitet är låg. Mo6S3I6 nanotrådar studerades med in situ TEM probing. Vi fann att genom att driva en tillräckligt hög elektrisk ström genom nanotråden så resulterade detta i en omvandling till en solid metallisk molybden nanotråd med en konduktivitet nära värdet för bulkmaterialet. Resultat är intressant då nanotrådar kan användas i t.ex. fältemission, men resultatet visar också på att det kan vara en generell metod för att förbättra nanotrådar överlag. På dessa nanotrådar har även en elektromekanisk resonans studie utförts där böjmodulen för materialet bestämdes till 4.9 GPa. Med in situ-TEM-probing metoden har även silvernanobläck studerats under en sintringsprocess. Studien visade att vid sintringen så bildas perkulativa vägar genom bläckets silvernanopartiklar samt att vid hög sinteringstemperatur förkolnades det lösningsmedel som silvernanopartiklarna är lösta i. Förkolningen av lösningsmedlet resulterade i ett kolnät med liknande egenskaper som för grafit. Förståelse utav sinteringsprocessen är nödvändig eftersom vid tryckning av elektriskt ledande banor på papper används sintring för att höja ledningsförmågan. Genom att växa nanopartiklar på nanotrådar förändras deras egenskaper och tillämpningar. Existerande metoder är endera komplicerade eller ger dåligt ut- byte. Ett enkelt recept för att växa guldnanopartiklar på kolnanorör och Mo6S3I6 nanotrådar har därför tagits fram. Dessa kolnanorör och nanotrådar har sedan studerats med in-situ-TEM-probing metoden som visade att utanpå dessa guldnanopartiklar kan burar av kol skapas. Eftersom partiklarnas storlek kan kontrolleras kan även kolnanoburarnas storlek kontrolleras. Burarna har användningsområden t.ex. inom medicin och vid lagring av vätgas.
The thesis covers six scientific papers
2
Hajduček, Jan. "Zobrazování metamagnetických tenkých vrstev pomocí TEM". Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2021. http://www.nusl.cz/ntk/nusl-443233.
Texto completoResumen
Komplexní magnetické materiály v nanoměřítku mají své nezastupitelné místo v moderních zařízeních, jako jsou digitální paměti nebo senzory. Moderní technologické procesy vyžadují porozumění a možnost kontroly moderních magnetických materiálů až na atomární úrovni. Jednou z možných cest je magnetická analýza za použití transmisní elektronové mikroskopie (TEM), která je unikátní díky možnosti zobrazování až v subatomárním měřítku. Tato práce popisuje možnosti zobrazování metamagnetických materiálů metodou TEM. Tyto materiály se vyznačují možností stabilizace více magnetických uspořádání najednou za daných vnějších podmínek. Modelovým systémem pro popis zobrazovacích možností metody TEM byly zvoleny tenké vrstvy metamagnetické slitiny FeRh. Tento materiál prochází při zahřívání fázovou přeměnou z antiferomagnetické do feromagnetické fáze. Podrobně jsou rozebrány procesy výroby vzorků, což je zásadní pro úspěšnou TEM analýzu. Pro magnetické zobrazování vzorků v TEMu je využita technika diferenciálního fázového kontrastu (DPC), umožňující přímé mapování rozložení magnetické indukce ve vzorku. Důsledně je diskutován vznik signálu v DPC, což je nezbytné pro porozumění a analýzu výsledných dat. FeRh vrstvy jsou podrobeny analýze struktury, chemického složení a především magnetických vlastností obou magnetických fází. Závěrem je představen proces přímého ohřevu metamagnetických vrstev v TEMu.
3
Jia, Xiaoting. "In-situ TEM study of carbon nanomaterials and thermoelectric nanomaterials". Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/69666.
Texto completoResumen
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2011.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 103-112).
Graphene nanoribbons (GNRs) are quasi one dimensional structures which have unique transport properties, and have a potential to open a bandgap at small ribbon widths. They have been extensively studied in recent years due to their high potential for future electronic and spintronic device applications. The edge structures - including the edge roughness and chirality - dramatically affect the transport, electronic, and magnetic properties of GNRs, and are of the critical importance. We have developed an efficient way of modifying the edges structures, to produce atomically smooth zigzag and armchair edges by using insitu TEM with a controlled bias. This work provides us with many opportunities for both fundamental studies and for future applications. I also report the use of either furnace heating or Joule heating to pacify the exposed graphene edges by loop formation in the graphitic nanoribbons. The edge energy minimization process involves the formation of loops between adjacent graphene layers. An estimation of the temperature during in-situ Joule heating is also reported based on the melting and evaporation of Pt nanoparticles. In this thesis work, I have also investigated the morphological and electronic properties of GNRs grown by chemical vapor deposition. Our results suggest that the GNRs have a surprisingly high crystallinity and a clean surface. Both folded and open edges are observed in GNRs. Atomic resolution scanning tunneling microscopy (STM) images were obtained on the folded layer and the bottom layer of the GNR, which enables clear identification of the chirality for both layers. We have also studied the electronic properties of the GNRs using low temperature scanning tunneling spectroscopy (STS). Our findings suggest that edges states exist at GNR edges which are dependent on the chiral angles of the GNRs.
by Xiaoting Jia.
Ph.D.
4
Issa, Inas. "In situ TEM nanocompression and mechanical analysis of ceramic nanoparticles". Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEI008/document.
Texto completoResumen
Dans cette étude, nous proposons d’utiliser la compression in situ dans le MET afin de caractériser les propriétés mécaniques de nanoparticules céramiques dont la taille caractéristique est de l’ordre de quelques dizaines de nanomètres. Nous appliquerons cette méthode à des nanocubes monocristallins de MgO, une céramique modèle dont la plasticité est bien connue dans le matériau massif. Les essais de nanocompression montrent que les nanocubes de MgO se déforment de façon homogène jusqu’à de grandes déformations (>50%) sans fissure apparente. L’analyse des résultats est assistée par des méthodes de corrélation d’images numériques et simulations de type dynamique moléculaire. Le mécanisme de déformation et l'effet de taille sur la limite élastique sont identifiés. Dans une deuxième partie de la thèse, nous présentons une étude sur des nanoparticules d’alumine de transition compactée en CED (Cellule à Enclumes en Diamant) à température ambiante, sous plusieurs pressions (5 GPa, 15 GPa et 20 GPa). Des lames minces préparées par FIB ont été étudiées en MET. Des images HRTEM montrent une texture cristallographique qui devient plus importante à des pressions plus élevées. Une orientation cristallographique préférentielle est observée, avec les plans {220} de la phase gamma de l’alumine la plupart du temps parallèles à la surface de contact avec une particule voisine. Ce comportement mécanique est cohérent avec un système de glissement, connu pour les structures spinelles. Une corrélation de ce comportement avec les tests in situ MET réalisés sur des nanoparticules similaires, par Emilie Calvié lors de sa thèse, est présentée. Enfin, des clichés de diffraction de type Debye Scherrer sont réalisés sur ces lames minces de nanoparticules d’alumine de transition compactées en CED à différentes pressions. L’analyse quantitative de ces clichés montre une transformation de phase de ces nanoparticules d’alumine de phase gamma en phase delta, de manière croissante avec la pressionIn this study, we propose an innovative mechanical observation protocol of ceramics nanoparticles in the 100nm size range. This Protocol consists of in situ TEM nanocompression tests of isolated nanoparticles. Load–real displacements curves, obtained by Digital Image Correlation, are analyzed and these analyses are correlated with Molecular Dynamics simulations. By this protocol a constitutive law with its mechanical parameters (Young modulus, Yield stress...) of the studied material at the nano-scale can be obtained. In situ TEM nano-compression tests on magnesium oxide nanocubes are performed. Magnesium oxide is a model material and its plasticity is very well known at bulk. The MgO nanocubes show large plastic deformation, more than 50% of plastic strain without any fracture. The TEM results are correlated to MD simulations and the deformation mechanism can be identified.The size effect and the electron beam effect on the yield strength are investigated. In a second part of the dissertation, we present a study on transition alumina nanoparticles compacted in a Diamond Anvil Cell at different uniaxial pressures. Thin Foils of these compacted nanoparticles are prepared by FIB for HRTEM Observations. Their analysis reveals the plastic deformation of the nanoparticles. The crystallographic texture observed inthese compacted nanoparticles in DAC shows a preferred orientation of the {110} lattice planes, orientated perpendicular to the compression direction. This is compatible with the slip system. This argument was reinforced with a preferred orientation of slip bands observed during in situ TEM nano-compression tests. Moreover, electron diffraction patterns (Debye Scherrer) analysis on these compacted transition alumina nanoparticles reveals the decrease of the presence of gamma-alumina and the increase of delta-alumina with increasing pressure. This reveals the phase transformation with increasing pressure from gamma to delta* alumina
5
Vineis, Christopher J. (Christopher Joseph) 1974. "Characterization of OMVPE-grown GaSb-based epilayers using in situ reflectance and ex situ TEM". Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/8452.
Texto completoResumen
Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2001.Includes bibliographical references (leaves 227-238).
The focus of this thesis was to investigate and characterize GaSb, GaInAsSb, and AlGaAsSb epilayers grown by organometallic vapor phase epitaxy (OMVPE). These epilayers were principally characterized using in situ spectral reflectance and ex situ transmission electron microscopy (TEM). An in situ spectral (380-1100 nm) reflectance monitoring system was designed and fitted to the OMVPE reactor. It was determined that longer wavelengths are more useful for quantitative growth rate analysis, while shorter wavelengths are more sensitive to the GaSb substrate oxide desorption process. It was also determined that the GaInAsSb and AlGaAsSb alloy compositions could be determined accurately using in situ reflectance ratios. Use of the in situ reflectance monitor to efficiently perform necessary reactor/growth calibrations was also demonstrated. Analytic functions were used to model the refractive indices of GaSb, AlGaAsSb, and GaInAsSb. Specifically, Adachi's Model Dielectric Function [1, 2] was curve-fit to data for GaSb between 400 and 1000 nm, and fourth-order polynomials were fit to data for GaSb and GaInAsSb between 1 and 3 gnm. A linear interpolation of binary functions was used to generate a refractive index model for AlGaAsSb between 1 and 3 m as a function of Al fraction. These models were helpful in interpreting in situ reflectance data, and also in designing distributed Bragg reflectors. Phase separation in GaInAsSb was studied using TEM. A wide range of microstructures was observed, from nearly homogeneous to strongly phase separated.
(cont.) It was seen that in phase separated samples, the composition modulations typically created and coupled to morphological perturbations in the surface. One interesting manifestation of the phase separation was the spontaneous formation of a natural superlattice (period typically 10-30 nm) throughout the epilayer. This superlattice had two variants: one parallel to the growth surface, and one tilted with respect to the growth surface. It was discovered that the tilted superlattice was coupled to surface to relieve surface strain associated with the superlattice ...
by Christopher J. Vineis.
Ph.D.
6
Qu, Weiguo. "In-situ TEM investigation of the phase transitions in perovskite ferroelectrics". [Ames, Iowa : Iowa State University], 2008.
Buscar texto completo
7
Wang, Lizhuo. "Nano Catalyst Design and Application in Sustainable Chemistry". Thesis, The University of Sydney, 2022. https://hdl.handle.net/2123/29570.
Texto completoResumen
Heterogenous catalytic process is a complex art of surface, the surface properties, especially the properties of active sites such as geometric structure and chemical environment would drastically influence the reaction performance. Traditionally, most studies for catalyst surface properties rely on the ex situ characterisation which examines catalysts out of reaction condition. However, considering most of the heterogenous catalytic reactions are carried out under a harsh condition, i.e. elevated temperatures and pressures, the surface dynamic change over catalyst under reaction condition is generally not negligible and dominating the reaction performance. Thus, for understanding the real catalyst surface behaviour, we must observe the catalyst during reaction condition. Three different catalytic systems were selected in this research and the combined in situ microscopy and spectroscopy techniques, including in situ TEM, in situ EELS spectroscopy and in situ DRIFTS spectroscopy, were implemented to investigate the catalyst behaviour during the reactions. The first reaction is the oxidative methane coupling reaction over Li/MgO. Then followed by the oxidative methane coupling over La/MgO and ammonia synthesis over Ru/MgO. The in situ TEM provides the information of surface geometric change while the in situ EELS and DRIFTS give the chemical information of catalyst surface as well as adsorbed intermediates. Combined with ex situ characterisation results, the more comprehensive pictures for the mechanism of the investigated reactions can be depicted. The outcome of this thesis bridged the gap between surface geometric-chemical change over catalysts active sites and the reaction performance over heterogenous catalyst, which might even be the guidance for heterogenous catalyst development in the similar systems.
8
Chang, Huai-Ning. "Electrostatic Feedback for Mems Sensor : Development of in situ TEM instrumentation". Thesis, Linköping University, The Department of Physics, Chemistry and Biology, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-11649.
Texto completoResumen
This thesis work is about further developing an existing capacitive MEMS sensor for in situ TEM nanoindentation developed by Nanofactory Instrument AB. Today, this sensor uses a parallel plate capacitor suspended by springs to measure the applied force. The forces are in the micro Newton range. One major issue using with this measurement technique is that the tip mounted on one of the sensor plates can move out of the TEM image when a force is applied. In order to improve the measurement technique electrostatic feedback has been investigated. The sensor’s electrostatic properties have been evaluated using Capacitance-Voltage measurements and a white light interferometer has been used to directly measure the displacement of the sensor with varying voltage. Investigation of the sensor is described with analytical models with detailed treatment of the capacitive response as function of electrostatic actuation. The model has been tested and refined by using experimental data. The model showed the existence of a serial capacitor in the sensor. Moreover, a feedback loop was tested, by using small beads as load and by manually adjusting the voltage. With the success of controlling the feedback loop manually, it is shown that the idea is feasible, but some modifications and improvements are needed to perform it more smoothly.
9
Boniface, Maxime. "Suivi à l'échelle nanométrique de l'évolution d'une électrode de silicium dans un accumulateur Li-ion par STEM-EELS". Thesis, Université Grenoble Alpes (ComUE), 2017. http://www.theses.fr/2017GREAY051/document.
Texto completoResumen
L’accroissement des performances des accumulateurs Li-ion sur les 25 dernières années découle principalement de l’optimisation de leurs composants inactifs. Aujourd’hui, l’urgence environnementale impose de développer de nouveaux matériaux actifs d’électrode pour proposer la prochaine génération d’accumulateur qui participera à la transition énergétique. A cet effet, le silicium pourrait avantageusement remplacer le graphite des électrodes négatives à moyen terme. Cependant la rétention de capacité des électrodes de silicium est mise à mal par l’expansion volumique que le matériau subit lors sa réaction d’alliage avec le lithium, qui mène à la déconnexion des particules de Si et à une réduction continue de l’électrolyte. Une compréhension de ces phénomènes de vieillissement à l’échelle de la nanoparticule est nécessaire à la conception d’électrodes de silicium viables. Pour ce faire, la technique STEM-EELS a été optimisée de manière à s’affranchir des problèmes d’irradiation qui empêchent l’analyse des matériaux légers d’électrode négative et de la Solid electrolyte interface (SEI), grâce à l’analyse des pertes faibles EELS. Un puissant outil de cartographie de phase est obtenu et utilisé pour mettre en lumière la lithiation cœur-coquille initiale des nanoparticules de silicium cristallin, la morphologie hétérogène et la composition de la SEI, ainsi que la dégradation du silicium à l’issue de cyclages prolongés. Enfin, un modèle de vieillissement original est proposé, en s’appuyant notamment sur un effort de quantification des mesures STEM-EELS sur un grand nombre de nanoparticulesOver the last 25 years, the performance increase of lithium-ion batteries has been largely driven by the optimization of inactive components. With today’s environmental concerns, the pressure for more cost-effective and energy-dense batteries is enormous and new active materials should be developed to meet those challenges. Silicon’s great theoretical capacity makes it a promising candidate to replace graphite in negative electrodes in the mid-term. So far, Si-based electrodes have however suffered from the colossal volume changes silicon undergoes through its alloying reaction with Li. Si particles will be disconnected from the electrode’s percolating network and the solid electrolyte interface (SEI) continuously grows, causing poor capacity retention. A thorough understanding of both these phenomena, down to the scale of a single silicon nanoparticle (SiNP), is critical to the rational engineering of efficient Si-based electrodes. To this effect, we have developed STEM-EELS into a powerful and versatile toolbox for the study of sensitive materials and heterogeneous systems. Using the low-loss part of the EEL spectrum allows us to overcome the classical limitations of the technique.This is put to use to elucidate the first lithiation mechanism of crystalline SiNPs, revealing Li1.5Si @ Si core-shells which greatly differs from that of microparticles, and propose a comprehensive model to explain this size effect. The implications of that model regarding the stress that develops in the crystalline core of SiNPs are then challenged via stress measurements at the particle scale (nanobeam precession electron diffraction) for the first time, and reveal enormous compressions in excess of 4±2 GPa. Regarding the SEI, the phase-mapping capabilities of STEM-EELS are leveraged to outline the morphology of inorganic and organic components. We show that the latter contracts during electrode discharge in what is referred to as SEI breathing. As electrodes age, disconnection causes a diminishing number of SiNPs to bear the full capacity of the electrode. Overlithiated particles will in turn suffer from larger volumes changes and cause further disconnection in a self-reinforcing detrimental effect. Under extreme conditions, we show that SiNPs even spontaneously turn into a network of thin silicon filaments. Thus an increased active surface will compound the reduction of the electrolyte and the accumulation of the SEI. This can be quantified by summing and averaging STEM-EELS data on 1104 particles. In half-cells, the SEI volume is shown to increase 4-fold after 100 cycles without significant changes in its composition, whereas in full cells the limited lithiation performance understandably leads to a mere 2-fold growth. In addition, as the operating potential of the silicon electrodes increases in full cells – potential slippage – organic products in the SEI switch from being carbonate-rich to oligomer-rich. Finally, we regroup these findings into an extensive aging model of our own, based on both local STEM-EELS analyses and the macro-scale gradients we derived from them as a whole
10
Berthier, Rémy. "Development of characterization methods for in situ annealing and biasing of semiconductor devices in the TEM". Thesis, Université Grenoble Alpes (ComUE), 2018. http://www.theses.fr/2018GREAY014/document.
Texto completoResumen
Dans cette thèse, nous abordons les défis rencontrés lors de la caractérisation des mémoires non volatiles par microscopie en transmission in situ. Les innovations récentes menées sur les porte-objets de TEM in situ basés sur l'utilisation de puces en silicium apportent de grands avantages comparée aux précédents modèles. Cependant, cette technique reste complexe et les expériences de MET in situ sont difficiles à mener à terme. Ce manuscrit tente d'apporter de nouvelles solutions pour permettre l'observation à l'échelle atomique pendant le recuit, ou la polarisation d'un échantillon dans le MET. Ce projet a été mené à travers plusieurs améliorations effectuées au cours des différentes étapes des expériences de MET in situ. Cette thèse se focalise plus particulièrement sur les problèmes rencontrés lors de la polarisation de dispositifs de mémoires résistives de taille nanométrique. Ces travaux furent conduits à travers une étude des instruments utilisés, le développement de nouvelles méthodes de préparation d'échantillons, et une analyse de l'impact de l'imagerie électronique sur le fonctionnement d'un dispositif dans le MET.Tout d’abord, une nouvelle méthode est développée spécifiquement pour les expériences de MET in situ en température. Grâce à ces développements, la cristallisation de mémoires à changement de phase en GeTe est observée en temps réel. Ces résultats ont notamment permis d'obtenir des informations utiles pour le développement de mémoires à changement de phase de type chalcogénure. Ensuite, de nouvelles puces en silicium dédiées à la polarisation in situ sont développées et produites. Une étude est ensuite menée sur la préparation d'échantillons par FIB afin d'améliorer la qualité des contacts électriques pour la polarisation in situ, ainsi que la technique de préparation elle-même. La qualité de cette méthode est ensuite démontrée à travers des mesures quantitatives obtenues pendant la polarisation in situ d'un échantillon de référence de type jonction PN. Ces développements sont ensuite appliqués afin d’observer des dispositifs de mémoires résistives de type CBRAM en fonctionnement dans le microscope électronique en transmission. Ces résultats ont permis d'apporter de nouvelles informations sur les mécanismes de fonctionnement des mémoires résistives, ainsi que sur la technique de polarisation in situIn this work, we address the current challenges encountered during in situ Transmission Electron Microscopy characterization of emerging non volatile data storage technologies. Recent innovation on in situ TEM holders based on silicon micro chips have led to great improvements compared to previous technologies. Still, in situ is a particularly complicated technique and experiments are extremely difficult to implement. This work provides new solutions to perform live observations at the atomic scale during both heating and biasing of a specimen inside the TEM. This was made possible through several improvements performed at different stages of the in situ TEM experiments. The main focus of this PhD concerned the issues faced during in situ biasing of a nanometer size resistive memory device. This was made possible through hardware investigation, sample preparation method developments, and in situ biasing TEM experiments.First, a new sample preparation method has been developed specifically to perform in situ heating experiments. Through this work, live crystallization of a GeTe phase change Memory Material is observed in the TEM. This allowed to obtain valuable information for the development of chalcogenide based Phase Change Resistive Memories. Then, new chips dedicated to in situ biasing experiments have been developed and manufactured. The FIB sample preparation is studied in order to improve electrical operation in the TEM. Quantitative TEM measurements are then performed on a reference PN junction to demonstrate the capabilities of this new in situ biasing experimental setup. By implementing these improvements performed on the TEM in situ biasing technique, results are obtained during live operation of a Conductive Bridge Resistive Memory device. This allowed to present new information on the resistive memories functioning mechanisms, as well as the in situ TEM characterization technique itself
11
Fawey, Mohammed [Verfasser], Horst [Akademischer Betreuer] Hahn y Hans-Joachim [Akademischer Betreuer] Kleebe. "In situ and Ex situ TEM Studies of Fluoride Ion Batteries / Mohammed Fawey ; Horst Hahn, Hans-Joachim Kleebe". Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2017. http://d-nb.info/114448426X/34.
Texto completo
12
Fawey, Mohammed H. [Verfasser], Horst [Akademischer Betreuer] Hahn y Hans-Joachim [Akademischer Betreuer] Kleebe. "In situ and Ex situ TEM Studies of Fluoride Ion Batteries / Mohammed Fawey ; Horst Hahn, Hans-Joachim Kleebe". Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2017. http://nbn-resolving.de/urn:nbn:de:tuda-tuprints-69330.
Texto completo
13
Schilling, Sibylle. "Liquid in situ analytical TEM : technique development and applications to austenitic stainless steel". Thesis, University of Manchester, 2017. https://www.research.manchester.ac.uk/portal/en/theses/liquid-in-situ-analytical-tem-technique-development-and-applications-to-austenitic-stainless-steel(fd490551-7d7a-4b2e-9b1f-917b5f8165b3).html.
Texto completoResumen
Environmentally-assisted cracking (EAC) phenomena affect the in-service behaviour of austenitic stainless steels in nuclear power plants. EAC includes such degradation phenomena as Stress Corrosion Cracking (SCC) and Corrosion Fatigue (CF). Factors affecting EAC include the material type, microstructure, environment, and stress. This is an important degradation issue for both current and Gen III+ light water reactors, particularly as nuclear power plant lifetimes are extended ( > 60 years). Thus, it is important to understand the behaviour of the alloys used in light water reactors, and phenomena such as SCC to avoid failures. Although there is no agreement on the mechanism(s) of SCC, the importance of localized electrochemical reactions at the material surface is widely recognised. Considerable research has been performed on SCC and CF crack growth, but the initiation phenomena are not fully understood. In this project, novel in situ analytical TEM techniques have been developed and applied to explore localised reactions in Type 304 austenitic stainless steel. In situ transmission electron microscopy has become an increasingly important and dynamic research area in materials science with the advent of unique microscope platforms and a range of specialized in situ specimen holders. In metals research, the ability to image and perform X-ray energy dispersive spectroscopy (XED) analyses of metals in liquids are particularly important for detailed study of the metal-environment interactions with specific microstructural features. To further facilitate such studies a special hybrid specimen preparation technique involving electropolishing and FIB extraction has been developed in this thesis to enable metal specimens to be examined in the liquid cell TEM specimen holder using both distilled H2O and H2SO4 solutions. Furthermore, a novel electrode configuration has been designed to permit the localized electrochemical measurement of electron-transparent specimens in the TEM. These novel approaches have been benchmarked by extensive ex situ experiments, including both conventional electrochemical measurements and microcell measurements. The results are discussed in terms of validation of in situ test data as well as the role of the electron beam in the experiments. In situ liquid cell TEM experiments have also explored the localized dissolution of MnS inclusions in H2O, and correlated the behaviour with ex situ experiments. Based on the research performed in this thesis, in situ liquid cell and in situ electrochemical cell experiments can be used to study nanoscale reactions pertaining to corrosion and localized dissolution leading to "precursor" events for subsequent EAC phenomena.
14
Pawley, C. "The use of in-situ ion-irradiation/TEM techniques to study radiation damage in SiC". Thesis, University of Salford, 2014. http://usir.salford.ac.uk/32489/.
Texto completoResumen
SiC is a material currently under consideration to be used in future generations of fission and fusion reactors where it will be subjected to high temperatures and significant fluxes of energetic neutrons. The work reported in this thesis aims to answer some outstanding issues of the behaviour of SiC at high temperature during irradiation by high-energy neutrons in combination with a build-up of helium (from both transmutation reactions and by direct implantation). These processes have been simulated by in-situ ion-irradiation / TEM at the MIAMI and JANNuS facilities. This thesis contains the results of experiments which investigated the nucleation and growth of helium bubbles in SiC and the behaviour of these helium bubbles under high energy heavy ion-irradiation. Our conclusions are that helium bubbles in SiC are extremely stable at high temperatures and during high-energy ion-irradiation. However, we have discovered that there is a significant effect on the bubbles attributable to either electron beam irradiation alone or the synergistic effect of the electron beam and ionirradiation which causes helium bubbles to shrink.
15
Surrey, Alexander. "Preparation and Characterization of Nanoscopic Solid State Hydrogen Storage Materials". Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-217904.
Texto completoResumen
Die Speicherung von Wasserstoff in Form von Hydriden im festen Aggregatzustand hat den Vorteil einer hohen volumetrischen und gravimetrischen Wasserstoffspeicherdichte, die sowohl für die stationäre als auch die mobile Anwendung nötig ist. Um die Anforderungen dieser Anwendungen erfüllen zu können, müssen die Speichereigenschaften dieser Materialien weiter verbessert werden. Als zentrales Konzept dieser Dissertation wird die Nanostrukturierung verfolgt, die eine vielversprechende Strategie zur Modifizierung der thermodynamischen und kinetischen Eigenschaften von Hydriden darstellt. Die Transmissionselektronenmikroskopie (TEM) stellt dabei eine unverzichtbare Untersuchungsmethode solch nanoskopischer Materialien dar. Als problematisch erweist sich dabei die durch Radiolyse hervorgerufene Zersetzung der meisten Hydride bei der Beleuchtung mit dem abbildenden Elektronenstrahl. Im ersten Teil dieser Arbeit wird eine Methodik entwickelt um dieses Phänomen quantitativ mit Hilfe von Valenzelektronenenergieverlustspektroskopie zu untersuchen. Hierzu kommt kugelgemahlenes MgH2 als Modellsystem zum Einsatz. Die Dehydrierung kann quantitativ durch die inelastische Streuung der hochenergetischen Elektronen am MgH2-Plasmon erklärt werden. Eine Lösung dieses grundlegenden Problems wird theoretisch an Hand von Multislice TEM-Kontrastsimulationen untersucht. Hierbei wird ein TEM Experiment unter Wasserstoff bei Umgebungsdruck anstatt unter Vakuum simuliert, was mit Hilfe eines speziellen TEM Halters, in dem das Gas durch elektronentransparente Fenster eingeschlossen ist, realisiert werden kann. Im zweiten Teil wird der Einfluss des Nanoconfinements (Nanoeinschließung), einer speziellen Form der Nanostrukturierung, des komplexen Hydrids LiBH4 auf dessen Wasserstoffspeichereigenschaften untersucht, wofür eine neuartige nanoporöse aerogel-ähnliche Kohlenstoff-Gerüststruktur zum Einsatz kommt. Diese wird durch Salt Templating synthetisiert - einer simplen und nachhaltigen Methode zur Herstellung nanoporöser kohlenstoffbasierter Materialien mit großen Porenvolumina. Es wird gezeigt, dass durch das Nanoconfinement die Wasserstoffdesorptionstemperatur, die für makroskopisches LiBH4 bei über 400 °C liegt, auf 310 °C sinkt und die Desorption bereits bei 200 °C einsetzt. Eine teilweise Rehydrierung ist unter moderaten Bedingungen (100 bar und 300 °C) möglich, wobei die Reversibilität durch eine partielle Oxidation des amorphen Bor gehemmt ist. Im Gegensatz zu Beobachtungen einer aktuellen Veröffentlichung von in hoch geordnetem, nanoporösen Kohlenstoff eingebetteten LiBH4 deuten die in-situ TEM-Heizexperimente der vorliegenden Arbeit darauf hin, dass beide Reaktionsprodukte (B und LiH) in den Poren des aerogel-ähnlichen Kohlenstoffs verbleibenStoring hydrogen in solid hydrides has the advantage of high volumetric and gravimetric hydrogen densities, which are needed for both stationary and mobile applications. However, the hydrogen storage properties of these materials must be further improved in order to meet the requirements of these applications. Nanostructuring, which represents one of the central approaches of this thesis, is a promising strategy to tailor the thermodynamic and kinetic properties of hydrides. Transmission electron microscopy (TEM) is an indispensable tool for the structural characterization of such nanosized materials, however, most hydrides degrade fast upon irradiation with the imaging electron beam due to radiolysis. In the first part of this work, a methodology is developed to quantitatively investigate this phenomenon using valence electron energy loss spectroscopy on ball milled MgH2 as a model system. The dehydrogenation can be quantitatively explained by the inelastic scattering of the incident high energy electrons by the MgH2 plasmon. A solution to this fundamental problem is theoretically studied by virtue of multislice TEM contrast simulations of a windowed environmental TEM experiment, which allows for performing the TEM analysis in hydrogen at ambient pressure rather than vacuum. In the second part, the effect of the nanoconfinement of the complex hydride LiBH4 on its hydrogen storage properties is investigated. For this, a novel nanoporous aerogel-like carbon scaffold is used, which is synthesized by salt templating - a facile and sustainable technique for the production of nanoporous carbon-based materials with large pore volumes. It is shown that the hydrogen desorption temperature, which is above 400 °C for bulk LiBH4, is reduced to 310 °C upon this nanoconfinement with an onset temperature as low as 200 °C. Partial rehydrogenation can be achieved under moderate conditions (100 bar and 300 °C), whereby the reversibility is hindered by the partial oxidation of amorphous boron. In contrast to recent reports on LiBH4 nanoconfined in highly ordered nanoporous carbon, in-situ heating in the TEM indicates that both decomposition products (B and LiH) remain within the pores of the aerogel-like carbon
16
Stuckner, Joshua Andrew. "Investigating the origin of localized plastic deformation in nanoporous gold by in situ electron microscopy and automatic structure quantification". Diss., Virginia Tech, 2019. http://hdl.handle.net/10919/100733.
Texto completoResumen
Gold gains many useful properties when it is formed into a nanoporous structure, but it also becomes macroscopically brittle due to flow localization and may therefore be unreliable for many applications. The goal of this work was to establish processing/structure/property relationships of nanoporous gold, discover controllable structure features, and understand the role of structure on flow localization. The nanoporous gold structure, consisting of a 3D network of nanoscale gold ligaments, was quantified with an automatic software developed for this work called AQUAMI, which uses computer vision techniques to make statistically reliable numbers of repeatable and unbiased measurements per image. AQUAMI increased the efficiency and accuracy of characterization in this work, allowed for the conduction of more experiments, and provided better confidence in morphology and size distribution of the complex NPG microstructural features. Nanoporous gold was synthesized while varying numerous processing factors such as dealloying time, annealing time, and mechanical agitation. Through the expanded scope of synthesis experiments and detailed analysis, it was discovered that the curvature of the ligaments and the distribution width of ligament diameters could be controlled through processing. In situ tensile experiments in SEM and TEM revealed that large ligaments arrested crack propagation while curved ligaments increase ductility by straightening in the tensile direction and forming geometrically required defects, which inhibit dislocation activity. Through synthesis and microstructure characterization, two new controllable structure features were discovered experimentally. In situ mechanical testing revealed the role these structures play on the deformation behavior and flow localization of nanoporous gold.Doctor of Philosophy
17
Melinte, Georgian. "Advanced 3D and in-situ TEM approaches applied to carbon-based and zeolitic nanomaterials". Thesis, Strasbourg, 2015. http://www.theses.fr/2015STRAE009/document.
Texto completoResumen
Dans le cadre de cette thèse, des techniques avancées de Microscopie électronique à transmission (MET)ont été utilisées dans le but de caractériser et de fabriquer de nouveaux nanomatériaux pour des applications dans les domaines de la nanoélectronique et de la catalyse. Trois types de matériaux fonctionnalisés sont étudiés: le graphène multifeuillets (FLG– Few-Layer Graphene) avec des nanomotifs,des nanotubes de carbone (CNTs - Carbon Nanotubes en anglais) et des zéolithes mésoporeux. La formation de nanomotifs de tranchées et de tunnels sur des flocons de FLG à l’aide de nanoparticules(NPs) de fer est étudiée dans une approche qui combine la tomographie électronique et la MET environnementale. Le rôle des facettes de la nanoparticule et des paramètres topographiques de FLG a été déterminé du point de vue quantitatif, ce qui a mené à la mise en évidence du mécanisme de formation des nanomotifs de tranchées et de tunnels. Le transfert de nanoparticules à base de métal entre deux nanostructures de carbone a été également étudié, en temps réel, en employant un porte-échantillon MET couplé avec un dispositif STM (Scanning Tunneling Microscope en anglais). Le protocole de contrôle du transfert des nanoparticules, les transformations chimiques et structurales subies par celles-ci, le mécanisme de croissance de nouvelles nanoparticules et d’autres phénomènes liés à ces effets ont été étudiés avec attention. La dernière partie de la thèse est centrée sur l’étude de la tomographie électronique à faible dose de la porosité induite dans deux classes de zéolithes, ZSM-5 et zéolithe Y, en utilisant un traitement chimique novateur à base de fluorIn this thesis, advanced Transmission Electron Microscopy (TEM) techniques are used to characterize and fabricate new nanomaterials with applications in nanoelectronics and catalysis. Three types of functionalized materials are investigated: nanopatterned few-layer graphene (FLG), carbon nanotubes(CNTs) and mesoporous zeolites. The nanopatterning process of FLG flakes by iron nanoparticles (NPs) is studied using an approach combining electron tomography (ET) and environmental TEM. The role of the nanoparticle faceting and of the FLG topographic parameters has been quantitatively determined leading to the first determination of the operating mechanism of the patterning process. The mass transfer of metallic-based NPs between two carbon nanostructures was studied as well in real-time by using a TEMSTMholder. The protocol of controlling the mass transfer, the chemical and structural transformations of the NPs, the growth mechanism of the new NPs and other related phenomena were carefully investigated.The last part deals with the low-dose ET investigation of the porosity induced in two classes of zeolites,ZSM-5 and zeolite Y, by an innovative fluoride-based chemical treatment
18
Han, Ruixin. "SYNTHESIS, AND STRUCTURAL, ELECTROCHEMICAL, AND MAGNETIC PROPERTY CHARACTERIZATION OF PROMISING ELECTRODE MATERIALS FOR LITHIUM-ION BATTERIES AND SODIUM-ION BATTERIES". UKnowledge, 2018. https://uknowledge.uky.edu/chemistry_etds/90.
Texto completoResumen
Iron oxides, have been widely studied as promising anode materials in lithium-ion batteries (LIBs) for their high capacity (≈ 1000 mA h g-1 for Fe2O3 and Fe3O4,), non-toxicity, and low cost. In this work, β-FeOOH has been evaluated within a LIB half-cell showing an excellent capacity of ≈ 1500 mA h g-1 , superior to Fe2O3 or Fe3O4. Reaction mechanism has been proposed with the assistance of X-ray photoelectron spectroscopy (XPS). Various magnetic properties have been suggested for β-FeOOH such as superparamagnetism, antiferromagnetism and complex magnetism, for which, size of the material is believed to play a critical role. Here, we present a size-controlled synthesis of β-FeOOH nanorods. Co-existing superparamagnetism and antiferromagnetism have been revealed in β-FeOOH by using a Physical Property Measurement System (PPMS).
Compared with the high price of lithium in LIBs, sodium-ion batteries (SIBs) have attracted increasing attentions for lower cost. Recent studies have reported Na0.44MnO2 to be a promising candidate for cathode material of SIBs. This thesis has approached a novel solid-state synthesis of Na0.44MnO2 whiskers and a nano-scaled open cell for in situ TEM study. Preliminary results show the first-stage fabrication of the cell on a biasing protochip.
19
Gonzalez, Martinez Ignacio Guillermo. "Novel thermal and electron-beam approaches for the fabrication of boron-rich nanowires". Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-218019.
Texto completoResumen
Pursuing the development and implementation of novel synthesis techniques to produce nanostructures with an interesting set of properties is a goal that advances the frontiers of nanotechnology. Also of fundamental importance is to revisit well-established synthesis techniques employing a new set of materials as precursors, substrates and catalysts. Fundamental breakthroughs in the field of nanotechnology can be achieved by developing new synthesis procedures as well as by adapting known procedures to new materials. This thesis focuses on both kinds of experiments.
A variant of chemical vapor deposition (CVD) has been used to produce Al5BO9 nanowires out of sapphire wafers without the need of a catalyst material. The novelty of the work relies on the formation mechanism of the Al5BO9 nanowires. Essentially, the process can be described as a large-scale topological transformation taking place on the substrate’s surface as its chemical composition changes due to the arrival of precursor molecules. Dense mats of Al5BO9 nanowires cover large areas of the substrate that were previously relatively flat. The process is enhanced by a high temperature and the presence of pre-existing superficial defects (cracks, terraces, etc.) on the substrates. Al5BO9 nanowires as well as B/BOX nanowires and BOX nanotubes were also produced via a novel in-situ electron beam-induced synthesis technique. The process was carried out at room temperature and inside a transmission electron microscope. Au nanoparticles were used as catalyst for the case of B/BOX nanowires and BOX nanotubes, while the Al5BO9 nanowires were synthesized without the need of a catalyst material. The formation and growth of the nanostructures is solely driven by the electron beam. The growth mechanism of the B/BOX nanowires and BOX nanotubes relies on interplay between electrostatic charging of the precursor material (to produce and transport feedstock material) and electron stimulated desorption of oxygen which is able to activate the catalytic properties of the Au nanoparticles. For the case Al5BO9 nanowires a nucleation process based on massive atomic rearrangement in the precursor is instigated by the e-beam, afterwards, the length of some of the nanowires can be extended by a mechanism analogous to that of the growth of the B/BOX nanowires.
20
Wang, Hao. "In-situ transmission electron microscopy investigation of deformation-induced microstructural evolution of a FeCoCrNiMn high-entropy alloy". Thesis, The University of Sydney, 2018. http://hdl.handle.net/2123/20068.
Texto completoResumen
High-entropy alloys (HEAs) are alloys with multiple (usually ≥5) principal elements. HEAs are attracting increasing interest because of their promising mechanical properties and phase stability, which can be used for various applications, such as high-speed cutting tools, anticorrosive high-strength parts in chemical plants and deep-sea exploration due to the excellent mechanical properties at cryogenic temperatures. Thorough understanding of the structural evolution during deformation of HEAs is a prerequisite for understanding and further improving their superior mechanical properties, which is critical for future production of high-entropy alloys with desirable properties. Many HEAs form a stable single solid-solution phase. However, phase transformation could occur in some HEAs under certain circumstances, including high stress. Because stress concentration usually occurs at crack tips during deformation, it is interesting to check if any deformation-induced phase transformation would occur at crack tips during the deformation processes of HEAs. This thesis aims at using various transmission electron microscopy techniques to investigate the structural evolution of HEAs at room temperature. Research results showed surprisingly crystalline to amorphous phase transformation at crack tips in a FeCoCrNiMn HEA with an ultrafine-grained structure. Details of the phase transformation process was video recorded. The mechanism responsible for the phase transformation is discussed based on the observed microstructural evolution. Toughening introduced by nanobridging and the phase transformation is also briefly discussed.
21
Ronge, Emanuel [Verfasser]. "In-Situ Environmental TEM Studies of Electro- and Photo-Electrochemical Systems for Water Splitting / Emanuel Ronge". Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2021. http://d-nb.info/1228364729/34.
Texto completo
22
Berlin, Katja. "In-situ transmission electron microscopy on high-temperature phase transitions of Ge-Sb-Te alloys". Doctoral thesis, Humboldt-Universität zu Berlin, 2018. http://dx.doi.org/10.18452/19219.
Texto completoResumen
Das Hochtemperaturverhalten beeinflusst viele verschiedene Prozesse von der Materialherstellung bis hin zur technologischen Anwendung. In-situ Transmissionselektronenmikroskopie (TEM) bietet die Möglichkeit, die atomaren Prozesse während struktureller Phasenübergänge direkt und in Realzeit zu beobachten. In dieser Arbeit wurde in-situ TEM angewendet, um die Reversibilität des Schmelz- und Kristallisationsprozesses, sowie das anisotropen Sublimationsverhaltens von Ge-Sb-Te (GST) Dünnschichten zu untersuchen. Die gezielte Probenpräparation für die erfolgreiche Beobachtung der Hochtemperatur-Phasenübergänge wird hervorgehoben. Die notwendige Einkapselung für die Beobachtung der Flüssigphase unter Vakuumbedingungen und die erforderliche sauberer Oberfläche für den Sublimationsprozess werden detailliert beschrieben. Außerdem wird die Elektronenenergieverlustspektroskopie eingesetzt um die lokale chemische Zusammensetzung vor und nach den Übergängen zu bestimmen. Die Untersuchung der Grenzflächenstruktur und Dynamik sowohl beim Phasenübergang fest-flüssig als auch flüssig-fest zeigt Unterschiede zwischen den beiden Vorgängen. Die trigonale Phase von GST weist beim Schmelzen eine teilweise geordnete Übergangszone an der fest-flüssig-Grenzfläche auf, während ein solcher Zwischenzustand bei der Erstarrung nicht entsteht. Außerdem läuft der Schmelzvorgang zeitlich linear ab, während die Kristallisation durch eine Wurzelabhängigkeit von der Zeit mit überlagerter Start-Stopp-Bewegung beschrieben werden kann. Der Einfluss der Substrat-Grenzfläche wird diskutiert und die Oberflächenenergie von GST bestimmt. Die anisotrope Dynamik führt beim Phasenübergang fest-gasförmig der kubischen Phase von GST zur Ausbildung stabiler {111} Facetten. Dies erfolgt über die Bildung von Kinken und Stufen auf stabilen Terrassen. Die Keimbildungsrate und die bevorzugten Keimbildungsorte der Kinken wurden identifiziert und stimmen mit den Voraussagen des Terrassen-Stufen-Kinken Modells überein.High-temperature behavior influence many different processes ranging from material processing to device applications. In-situ transmission electron microscopy (TEM) provides the means for direct observation of atomic processes during structural phase transitions in real time. In this thesis, in-situ TEM is applied to investigate the reversibility of the melting and solidification processes as well as the anisotropic sublimation behavior of Ge-Sb-Te (GST) thin films. The purposeful sample preparation for the successful observation of the high-temperature phase transitions is emphasized. The required encapsulation for the observation of the liquid phase inside the vacuum conditions and the necessary clean surface for sublimation process are discussed in detail. Additionally electron energy-loss spectroscopy in the TEM is used to determine the local chemical composition before and after the phase transitions. The analysis of the interface structure and dynamic during the solid-to-liquid as well as the liquid-to-solid phase transition shows differences between both processes. The trigonal phase of GST exhibits a partially ordered transition zone at the solid-liquid interface during melting while such an intermediate state does not form during solidification. Additionally the melting process proceeds with linear dependence on time, whereas crystallization can be described as having a square-root time-dependency featuring a superimposed start-stop motion. The influence of the interface is addressed and the surface energies of GST are determined. The anisotropic dynamic of the solid-to-gas phase transition of the cubic GST phase leads to the formation of stable {111} facets. This happens via kink and step nucleation on stable terraces. The nucleation rates and the preferred kink nucleation sites are identified and are in accordance with the predictions of terrace-step-kink model.
23
Vailhé, Christophe N. P. "Deformation mechanisms in B2 aluminides: shear faults and dislocation core structures in FeAl, NiAl, CoAl and FeNiAl". Diss., Virginia Tech, 1996. http://hdl.handle.net/10919/38075.
Texto completo
24
Serege, Matthieu. "Développement d'une nouvelle technique d'analyse pour les nanosctructures gravées par plasmas : (S)TEM EDX quasi in-situ". Thesis, Université Grenoble Alpes (ComUE), 2017. http://www.theses.fr/2017GREAT097/document.
Texto completoResumen
Avec la diminution perpétuelle des dimensions des circuits intégrés, la gravure de dispositifs à l’échelle nanométrique constitue un véritable défi pour les procédés plasma qui montrent des limites dans le cas d’empilement de couches minces notamment. L’anisotropie de gravure réside sur la formation de couches de passivations sur les flancs des motifs, qui agissent comme film protecteur bloquant la gravure latérale par les radicaux du plasma. Cependant, cette fine couche est responsable de l’apparition de pente dans les profils gravés et il est difficile de contrôler son épaisseur. De plus, une deuxième couche réactive est aussi formée en fond de motifs. Les produits de gravures sont formés au sein de cette couche permettant d’augmenter la vitesse de gravure du substrat. Il a récemment été admis que contrôler l’épaisseur de ces couches réactives constitue le paramètre clé pour obtenir une gravure à très haute sélectivité.Cependant, les couches réactives à analyser hautement réactives, en raison de leur forte concentration en halogènes, s’oxydent immédiatement lors de la remise à l’air.Cette étude se propose de développer une approche originale, simple et extrêmement puissante pour observer ces couches de passivation quasi in-situ (sans contact avec l’air ambiant) : Apres gravure, l’échantillon est transporté sous vide à l’intérieur d’une valise spécifique jusqu’à une enceinte de dépôt, où il est alors encapsulé par une couche métallique (PVD assisté par magnétron). L’échantillon ainsi encapsulé peut être observé ex-situ sans modification chimique grâce à des analyses STEM EDXAs the size of integrated circuit continues to shrink, plasma processes are more and more challenged and show limitations to etch nanometer size features in complex stacks of thin layers. The achievement of anisotropic etching relies on the formation of passivation layers on the sidewalls of the etched features, which act like a protective film that prevents lateral etching by the plasma radicals. However, this layer also generate a slope in the etch profile and it’s difficult to control its thickness. Another thin layer called “reactive layer” is also formed at the bottom of the features. Etch products are formed in this layer allowing a high etch rate of the substrate. It starts to be realized that controlling the thickness of this reactive layer is the key to achieve very high selective processes.However, the layers to be analyzed are chemically highly reactive because they contain large concentrations of halogens and they get immediately modified (oxidized) when exposed to ambient atmosphere.In this work we develop an original, simple and extremely powerful approach to observe passivation layers quasi in-situ (i.e. without air exposure): After plasma etching, the wafer is transported under vacuum inside an adapted suitcase to a deposition chamber where it is encapsulated by a metallic layer (magnetron sputtering PVD). Then, the encapsulated features can be observed ex situ without chemical / thickness modification thanks to (S)TEM-EDX analysis
25
Andersen, Ingrid Marie. "2D and 3D quantitative TEM mapping of CoNi nanowires". Thesis, Toulouse 3, 2020. http://www.theses.fr/2020TOU30205.
Texto completoResumen
Les nanofils magnétiques constituent un domaine de recherche en plein essor. De section cylindrique, ils permettent la propagation des parois de domaines magnétiques à très grandes vitesses et des interactions fortes avec les ondes de spin, ce qui les rend particulièrement intéressants pour le développement de futurs composants de la spintronique. L'objectif de ce travail de thèse est de fournir une analyse quantitative et qualitative complète de la configuration magnétique locale dans des nanofils magnétiques cylindriques d'alliage CoNi à anisotropie magnétocristalline perpendiculaire en utilisant les techniques d'imagerie magnétique avancées de la microscopie électronique à transmission (MET), principalement axées sur l'holographie électronique (HE). Une étude corrélative entre les propriétés structurales, les variations locales de composition et les configurations magnétiques de ces nanofils a été réalisée. De plus, les configurations tridimensionnelles (3D) complexes des domaines et des parois magnétiques ont été analysées par tomographie holographique de champ vectoriel (THCV) afin d'obtenir les trois composantes de l'induction magnétique. Enfin, un protocole a été développé pour étudier in situ par microscopie de Lorentz la configuration magnétique de ces nanofils lors de l'injection d'impulsions de courant. La première partie de ce travail est focalisée sur la corrélation des configurations magnétiques de nanofils individuels de CoNi avec les propriétés structurales et chimiques locales. L'orientation de la phase cristalline a été cartographiée en diffraction électronique par précession et combinée à des mesures de composition par spectroscopie de perte d'énergie des électrons. Les résultats révèlent une coexistence de grains de phase cfc et de phase hcp, cette dernière présente sa direction cristallographique c orientée presque perpendiculairement à l'axe du nanofil. Cette coexistence de phases cristallographiques est à l'origine de variations localisées et abruptes de la configuration magnétique. Deux nanofil configurations principales ont été observées : une chaîne d'états transversaux par rapport à l'axe du, de type vortex, et un état longitudinal. Nous avons observé que les états transversaux sont liés à la phase hcp possédant une forte anisotropie magnétocristalline perpendiculaire, ce que confirment les simulations micromagnétiques. Une autre partie de ce travail concerne l'étude de la structure magnétique 3D des domaines et des parois de domaines dans la phase hcp. Cette étude a été menée pour des états rémanents différents en fonction de l'application d'un champ de saturation perpendiculaire et parallèle à l'axe du nanofil. Les mesures ont été réalisées par la méthode THCV afin d'extraire les trois composantes de l'induction magnétique et reconstruire en 3D la configuration magnétique locale du nanofil. Les résultats montrent une stabilisation d'une chaîne de vortex dans le cas d'une saturation perpendiculaire, et des états d'enroulement longitudinaux séparés par des parois de domaine transversales après l'application d'un champ externe parallèle à l'axe du fils. La dernière partie du manuscrit présente les résultats obtenus en microscopie de Lorentz in situ démontrant la possibilité de manipuler les parois des domaines magnétiques d'un nanofil de CoNi par injection d'impulsions électriques. Cette preuve de concept est considérée comme le précurseur des observations in situ de la dynamique des parois de domaines en EH. Un protocole précis, axé sur les étapes cruciales de préparation des échantillons et les développements à poursuivre pour réaliser ces expériences délicates, est détailléCylindrical magnetic nanowires (NWs) are currently subjects of high interest due to fast domain wall velocities and interaction with spin-waves, which are considered interesting qualities for developing future spintronic devices. This thesis aims to provide a wholesome quantitative and qualitative analysis of the local magnetic configuration in cylindrical Co-rich CoNi NWs with perpendicular magnetocrystalline anisotropy using state-of-the-art transmission electron microscopy (TEM) magnetic imaging techniques, mainly focused on two-dimensional (2D) and three-dimensional (3D) electron holography (EH). A correlative study between the NW's texture, modulation in composition, and magnetic configuration has been conducted. Further, the complex 3D nature of the domain and domain wall configurations have been analyzed using holographic vector field electron tomography (VFET) to retrieve all three components of the magnetic induction. Finally, I have successfully manipulated the magnetic configuration observed by Lorentz microscopy in Fresnel mode by the in situ injection of a current pulse. A TEM study comparing the magnetic configuration to the local NW structure was performed on single NWs. The crystal phase analysis was done by precession electron diffraction assisted automated crystal orientation mapping in the TEM combined with compositional analysis by scanning-TEM (STEM) electron energy loss spectroscopy (EELS) for a detailed correlation with the sample's magnetic configuration. The results reveal a coexistence of fcc grains and hcp phase with its c-axis oriented close to perpendicular to the wire axis in the same NW, which is identified as the origin of drastic local changes in the magnetic configuration. Two main configurations are observed in the NW region: a chain of transversal vortex-like states and a longitudinal curling state. The chain or vortices are linked to the hcp grain with the perpendicular magnetocrystalline anisotropy, as confirmed by micromagnetic simulations. The 3D magnetic structure of the domains and domain walls observed in the hcp grain of the NWs has been studied for two different remnant states: after the application of a saturation field perpendicular (i) and parallel (ii) to the NW axis. The measurements were done using state-of-the-art holographic VFET to extract all three components of the magnetic induction in the sample, as well as a 3D reconstruction of the volume from the measured electric potentials, giving insight into the local morphology of the NW. The results show a stabilization of a vortex chain in the case of perpendicular saturation, but longitudinal curling states separated by transversal domain walls after applying a parallel external field. Finally, preliminary Lorentz microscopy results are presented, documenting the manipulation of magnetic domain walls by the in situ injection of electrical pulses on a single cylindrical CoNi nanowire contacted by focused ion beam induced deposition. This is believed to be the forerunner for quantitative electrical measurements and in situ observations of domain wall dynamics using EH at the CEMES. A detailed protocol focusing on the crucial steps and challenges ahead for such a delicate experiment is presented, together with suggestions for future work to continue the developments
26
Wuttke, Timo Verfasser], Cynthia A. [Akademischer Betreuer] [Volkert, Cynthia A. [Gutachter] Volkert y Michael [Gutachter] Seibt. "TEM in-situ Untersuchungen an Ti-Ni basierten Formgedächtnislegierungen / Timo Wuttke ; Gutachter: Cynthia Volkert, Michael Seibt ; Betreuer: Cynthia Volkert". Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2018. http://d-nb.info/1157094627/34.
Texto completo
27
Roos, Burkhard Verfasser], Cynthia A. [Akademischer Betreuer] [Volkert y Michael [Akademischer Betreuer] Seibt. "In-situ Zugversuche an einkristallinen Gold-Nanodrähten im TEM / Burkhard Roos. Gutachter: Cynthia Volkert ; Michael Seibt. Betreuer: Cynthia Volkert". Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2012. http://d-nb.info/1043609385/34.
Texto completo
28
Kraus, Ines Elise [Verfasser] y Matthias [Akademischer Betreuer] Hannig. "Untersuchung der In-situ-Pellikelbildung auf verschiedenen Substraten mittels AFM, TEM und Ellipsometrie / Ines Elise Kraus. Betreuer: Matthias Hannig". Saarbrücken : Saarländische Universitäts- und Landesbibliothek, 2012. http://d-nb.info/1052557414/34.
Texto completo
29
Edmondson, Philip D. "An in-situ TEM study of the formation and annealing of the damage resulting from single ion impacts in crystalline silicon". Thesis, University of Salford, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.490283.
Texto completoResumen
The work presented in this thesis describes both the thermal annealing of damage created in silicon due to low fluence ion implantation and the accumulation of that damage (to full amorphousness) at higher fluences. The technique utilised was in situ transmission electron microscopy (TEM).
30
Yu, Lei. "DECONVOLVING THE STEPS TO CONTROL MORPHOLOGY, COMPOSITION, AND STRUCTURE, IN THE SYNTHESIS OF HIGH-ASPECT-RATIO METAL OXIDE NANOMATERIALS". UKnowledge, 2017. http://uknowledge.uky.edu/chemistry_etds/82.
Texto completoResumen
Metal oxides are of interest not only because of their huge abundance but also for their many applications such as for electrocatalysts, gas sensors, diodes, solar cells and lithium ion batteries (LIBs). Nano-sized metal oxides are especially desirable since they have larger surface-to-volume ratios advantageous for catalytic properties, and can display size and shape confinement properties such as magnetism. Thus, it is very important to explore the synthetic methods for these materials. It is essential, therefore, to understand the reaction mechanisms to create these materials, both on the nanoscale, and in real-time, to have design control of materials with desired morphologies and functions.
This dissertation covers both the design of new syntheses for nanomaterials, as well as real-time methods to understand their synthetic reaction mechanisms. It will focus on two parts: first, the synthesis of 1-dimension (1-D) featured nanomaterials, including manganese-containing spinel nanowires, and tin dioxide and zinc oxide-based negative nanowire arrays; and second, a mechanistic study of the synthetic reactions of nanomaterials using in situ transmission electron microscopy (TEM). The work presented here demonstrates unique synthetic routes to single crystalline “positive” and “negative” metal oxide nanowires, and introduces a new mechanism for the formation of single-crystalline hollow nanorods.
31
Sun, Ye. "LINKING THE STRUCTURE AND MECHANICAL BEHAVIOR OF NANOPOROUS GOLD". UKnowledge, 2008. http://uknowledge.uky.edu/gradschool_diss/678.
Texto completoResumen
The structure of nanoporous gold (np-Au) provides a very limited volume for deformation to occur, and thus offers an opportunity to study the role of defects such as dislocations in nanoscale metal volumes. A practical goal is to understand mechanical properties of np-Au so that it can be can produced in stable form, for use in applications that require some mechanical integrity. Bulk and thin film np-Au have been fabricated and studied here.
Bulk np-Au was prepared by electrochemically dealloying Au-Ag alloys with 25 and 30 at.% Au. In the lower Au content material, cracks always formed during dealloying. When Au content increased to 30 at.% and a two-step electrochemical dealloying method was used (first using diluted electrolyte and then concentrated acid), bulk np-Au with no volume change and minimal cracking was successfully fabricated. Thermal and mechanical behavior of np-Au was studied by heat treatment and microindentation. During annealing in air, Ostwald ripening governed ligament coarsening, while annealing of ligaments in vacuum was more likely a sintering process.
Nanoporous Au thin films were produced by dealloying sputtered Au-Ag alloy films. Residual stresses in np-Au films were measured with wafer curvature. Similar to bulk materials, np-Au thin films made from 25 at.% Au alloy films exhibited extensive cracking during dealloying, whereas films from 30 at.% Au precursor alloys were completely crack-free. 25 at.% Au np-Au films carried almost no stress because of extensive cracking, whereas stress in 30 at.% Au np-Au films was up to ~230 MPa. Ligament coarsening followed a t1/8 time dependence for stress-free films, versus t1/4 in films under stress. It was proposed that bulk diffusion was responsible for formation of larger pits at grain centers during the incipient stages of dealloying.
In situ nanoindentation experiments inside the transmission electron microscope were performed to investigate deformation of np-Au films and dislocation motion within ligaments. Dislocations were generated easily and moved along ligament axes, after which they interacted with other dislocations in the nodes of the porous network. It was found that slower displacement rates caused load drops to occur at shorter distance intervals and longer time intervals.
32
Löffler, Markus. "Nanomanipulation and In-situ Transport Measurements on Carbon Nanotubes". Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-33242.
Texto completoResumen
With the advent of microelectronics and micromechanical systems, the benefits of miniaturized technology became evident. With the discovery of carbon nanotubes by Iijima in 1991, a material has been found that offers superior porperties such as high tensile strength, excellent electrical and heat conductivity while being lightweight, flexible and tunable by the specific atomic arrangement in its structure. The first part of this thesis deals with a new synthesis approach, which combines the known routes of chemical vapour deposition and laser ablation. The results concerning diameter and yield fit well within an established model for the nucleation and growth of carbon nanotubes and extend it by considering a larger parameter space. Furthermore, conventional laser ablation has been used to synthesize C-13 augmented carbon nanotubes, whose diameters depend among the usual synthesis parameters also on the C-13 content, an influence which is in line with the changed thermal conductivities of isotope mixtures. Manipulation of carbon nanotubes inside a transmission electron microscope forms the second part of this thesis. With the help of an in-situ nanomanipulator, several experiments involving the mechanical and electrical properties of carbon nanotubes have been performed. Two-probe resistances of individual nanotubes have been measured and the observation of individual shell failures allowed for the determination of current limits per carbon shell. With the help of electrical current, a nanotube was modified in its electrical characteristics by reshaping its structure. By application of DC-currents or square current pulses, the filling of iron- or cementite-filled multi-wall carbon nanotubes has been found to move in a polarity-defined direction guided by the nanotube walls. Depending on the current, nanotube shape, and composition of the filling different regimes of material transport have been identified, including the reworking of the inner nanotube shells. The application of a high driving current leads to a complete reworking of the host nanotube and the current-induced growth of carbonaceous nanostructures of changed morphology. Utilizing the obtained results, a transport mechanism involving momentum transfer from the electron wind to the filling atoms and a solid filling core during transport is developed and discussed. Finally, measurements of mechanical properties using electrically induced resonant or non-resonant vibrations inside the transmission electron microscope have been observed and important mechanical parameters have been determined with the help of a modified Euler-Bernoulli-beam approachMit dem Aufkommen von Mikroelektronik und mikromechanischen Systemen wurden die Vorteile miniaturisierter Geräte augenscheinlich. Mit der Entdeckung von Kohlenstoff-Nanoröhren durch Iijima 1991 wurde ein Material gefunden, welches überlegene Eigenschaften wie hohe Festigkeit, exzellente elektrische und Wärmeleitfähigkeit zeigt, während es zeitgleich leicht und flexibel ist. Diese Eigentschaften können durch eine Änderung der spezifischen atomaren Anordnung in der Nanoröhrenhülle beeinflusst werden. Der erste Teil dieser Dissertationsschrift behandelt einen neuartigen Syntheseansatz, welche die bekannten Syntheserouten der chemischen Gasphasenabscheidung und Laserablation kombiniert. Die Ergebnisse bezüglich des Durchmessers und der Ausbeute lassen sich gut mit einem etablierten Modell der Nukleation und des Wachstums von Kohlenstoff-Nanoröhren beschreiben - sie erweitern es, indem sie einen größeren Parameterraum berücksichtigen. Des Weiteren wurde konventionelle Laserablation benutzt, um C-13 angereicherte Kohlenstoff-Nanoröhren herzustellen, deren Durchmesser nicht nur von den üblichen Parametern, sondern auch vom C-13 Anteil abhängt. Diese Abhängigkeit geht mit der veränderten thermischen Leitfähigkeit von Isotopenmischungen einher. Die Manipulation von Kohlenstoff-Nanoröhren in einem Transmission-Elektronenmikroskop formt den zweiten Teil der Dissertationschrift. Mit Hilfe eines in-situ Manipulators wurden vielfältige Experimente durchgeführt, um die mechanischen und elektrischen Eigenschaften der Kohlenstoff-Nanoröhren zu bestimmen. Zweipunktmessungen des Widerstands einzelner Nanoröhren und die Beobachtung des Versagens einzelner Kohlenstoffschichten erlaubte die Bestimmung der Stromtragfähigkeit einzelner Hüllen. Mit Hilfe eines elektrischen Stromes konnte eine Nanoröhre durch die veränderung der Struktur in ihren elektrischen Eigenschaften verändert werden. Unter Verwendung dauerhaften oder gepulsten Gleichstroms konnte die Eisen- oder Zementit-Füllung der Kohlenstoff-Nanoröhren in eine polaritätsabhängige Richtung bewegt werden. Die Füllung wurde dabei durch die Wände der Nanoröhre geführt. Abhängig von Strom, Form der Nanoröhre und Zusammensetzung der Füllung ließen sich verschiedene Bereiche des Materialtransports identifizieren, u.a. das Umarbeiten einiger innerer Kohlenstoffschichten. Ein hoher Strom hingegen bewirkt eine Umarbeitung der kompletten Nanoröhre und strominduziertes Wachstum von Kohlenstoff-Nanostrukturen mit veränderter Morphologie. Mit Hilfe der gewonnenen Resultate wurde ein Transportmodell entwickelt, welches den Impulstransfer von Elektronen an Füllungsatome sowie einen festen Füllungskern während des Transports diskutiert. Messungen der mechanischen Eigenschaften, welche mit Hilfe von resonanter oder nicht-resonanter elektrischer Anregung von Schwingungen im Transmissions-Elektronenmikroskop durchgeführt wurden bilden den Abschluss der Arbeit. Durch die Beobachtungen konnten mit einem modifizierten Euler-Bernoulli-Balkenmodell wichtige mechanische Eigenschaften bestimmt werden
33
Subedi, Samikshya. "Evaluation of Microstructural and Mechanical Properties of Multilayered Materials". Research Showcase @ CMU, 2017. http://repository.cmu.edu/dissertations/802.
Texto completoResumen
Microstructure controls many physical properties of a material such as strength, ductility, 1density, conductivity, which, in turn, determine the application of these materials. This thesis work focuses on studying microstructural features (such as grain size, shape, defects, orientation gradients) and mechanical properties (such as hardness and yield strength) of multilayered materials that have undergone different loading and/or operating conditions. Two materials that are studied in detail are 18 nm Cu-Nb nanolaminates and 3D printed Inconel 718. Copper-Niobium (Cu-Nb) nanolaminate is a highly stable, high strength, nuclear irradiation resistant composite, which is destabilized with application of high pressure torsion (HPT). This work focuses on understanding the deformation and failure behavior of Cu-Nb using a novel orientation mapping technique in transmission electron microscopy in (TEM) called Automated Crystal Orientation Mapping (ACOM) and Digistar (ASTARTM) or Precession Electron Diffraction (PED). A new theory is postulated to explain strengthening mechanisms at the nanoscale using a data analytics approach. In-situ TEM compression and tensile testing is performed to image dislocation movement with the application of strain. This experiment was performed by Dr. Lakshmi Narayan Ramasubramanian at Xi’an Jiaotong University in China. Another major aspect of this research focuses on the design, fabrication, and microstructural characterization of 3D printed Inconel 718 heat exchangers. Various heat exchanger designs, machine resolution, printing techniques such as build orientation, power, and velocity of the laser beam are explored. Microstructural and mechanical properties of printed parts (before and after heat treatment) are then analyzed to check consistency in grain size, shape, porosity, hardness in relation to build height, scan parameters, and design. Various tools have been utilized such as scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), x-ray computed microtomography (at Advanced Photon Source at Argonne National Lab), hardness and micro-pillar compression testing for this study.
34
Chethala, Neelakandhan Shyam Kumar [Verfasser], Ralph [Akademischer Betreuer] Krupke y Christian [Akademischer Betreuer] Kübel. "In situ TEM studies on the graphitization and growth of nanocrystalline graphene from polymers / Shyam Kumar Chethala Neelakandhan ; Ralph Krupke, Christian Kübel". Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2019. http://d-nb.info/1201086515/34.
Texto completo
35
De, Clercq Astrid. "In-situ study of the growth, structure and reactivity of Pt-Pd nanoalloys". Thesis, Aix-Marseille, 2015. http://www.theses.fr/2015AIXM4077/document.
Texto completoResumen
Les propriétés catalytiques des nanoparticules métalliques peuvent être améliorées par effet d’alliages. La synthèse en solution par voie colloïdale permet de préparer des nanoalliages homogènes en taille, en forme et en composition chimique, de structure ordonnée, désordonnée ou cœur-coquille. La nucléation et la croissance des nanoalliages de Pt-Pd sont étudiées ici par microscopie électronique en transmission, en condition standard, puis in situ dans une cellule liquide formée par des feuilles d’oxyde de graphène. La cinétique de croissance des nanoalliages de Pt-Pd correspond à l’incorporation directe des monomères en solution, compatible avec un processus limité par la réaction de surface, sans phénomène de coalescence, contrairement à la croissance du Pt pur. La structure théorique à l’équilibre des nanoalliages de Pt-Pd est déterminée par des simulations Monte Carlo. La structure la plus probable correspond à une surface riche en Pd et à une sous couche atomique riche en Pt, stable à des températures élevées. L’effet de l’adsorption de gaz oxydants ou réducteurs sur la forme des nanoparticules, est étudié in situ par microscopie environnementale sous pression de quelques mbar, dans un porte objet environnemental. On observe des changements de formes sous oxygène, dus au développement de facettes d’indices plus élevés. La réactivité des nanocubes de Pd@Pt est étudiée pour l’oxydation du CO en fonction du recouvrement de Pt à la surface. La réactivité maximale pour un faible recouvrement est interprétée par une baisse de l’énergie d’adsorption du CO liée au désaccord paramétrique entre le Pt et le Pd et à la modification de la structure électronique du Pt lié au PdThe catalytic properties of metal nanoparticles can be improved by the alloying effect. Nanoalloys homogeneous in size, shape and chemical composition can be prepared with the colloidal synthesis method, with an ordered, random or core-shell chemical structure. Nucleation and growth of colloidal Pt-Pd nanoalloys were studied by transmission electron microscopy (TEM), in standard conditions and in situ with the aid of a graphene oxide liquid cell. The growth kinetics of homogeneous Pt-Pd nanoalloys corresponds to the direct incorporation of the monomers in solution. It was compatible with a process limited by the surface reaction, without coalescence (Lifshitz-Slyozov-Wagner mechanism). On the contrary, coalescence occurs during the growth of pure Pt nanoparticles. The theoretical structure of Pt-Pd nanoalloys is determined by Monte Carlo simulations. The most stable structure corresponds to a Pd surface and Pt subsurface layer, which is stable up to high temperatures. The effect of adsorption of oxidizing or reducing gasses on the shape of pure Pd nanocubes and core-shell Pd@Pt nanocubes is studied in situ by TEM with an environmental cell. The observed changes in a few mbar of oxygen are due to the development of higher index facets. The CO oxidation reaction is used to compare the reactivity of homogeneous Pt-Pd nanoalloys and core-shell Pd@Pt nanocubes with increasing coverage of Pt at the surface. A maximal reactivity is attained for a low coverage. The effect is interpreted by a decrease in adsorption energy of CO, due to electronic effects originating from the lattice mismatch between Pt and Pd and the mixed Pt-Pd bonds
36
Arai, Shigeo, Shunsuke Muto, Takayoshi Tanji, Katuhiro Sasaki, Yahachi Saito, Michiko Kusunoki, Jiro Usukura y Nobuo Tanaka. "Development of an environmental high-voltage electron microscope for reaction science". Oxford University Press, 2013. http://hdl.handle.net/2237/20833.
Texto completo
37
Calvié, Emilie. "Contribution de la nanoindentation in situ en Microscopie Electronique en Transmission à l'étude des céramiques". Thesis, Lyon, INSA, 2012. http://www.theses.fr/2012ISAL0098.
Texto completoResumen
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)
38
Jackman, Henrik. "Mechanical behaviour of carbon nanostructures". Doctoral thesis, Karlstads universitet, Institutionen för ingenjörsvetenskap och fysik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-32041.
Texto completoResumen
Abstract Carbon nanotubes (CNTs) have extraordinary mechanical and electrical properties. Together with their small dimensions and low density, they are attractive candidates for building blocks in future nanoelectromechanical systems and for many other applications. The extraordinary properties are however only attained by perfectly crystalline CNTs and quickly deteriorate when defects are introduced to the structure. The growth technique affects the crystallinity where in general CNTs grown by arc-discharge are close to perfectly crystalline, while CVD-grown CNTs have large defect densities. Mechanical deformation also affects these properties, even without introducing defects. When CNTs are bent they behave similarly to drinking straws, i.e. they buckle or ripple and their bending stiffness drops abruptly. In this thesis, the mechanical behaviour of individual CNTs and vertically aligned carbon nanofibers (VACNFs) has been studied by performing force measurements inside electron microscopes. Cantilevered CNTs, and VACNFs, were bent using a force sensor, yielding force-deflection curves while their structure was imaged simultaneously. We have found that CNTs grown by arc-discharge have a high enough crystallinity to possess a Young’s modulus close to the ideal value of 1 TPa. CVD-grown CNTs possess a Young’s modulus that is about one order of magnitude smaller, due to their large defect density. The VACNFs are yet another order of magnitude softer as a result of their cup-stacked internal structure. We also found that a high defect density will increase the critical strain for the rippling onset and the relative post-rippling stiffness. Multi-walled CNTs with a small inner diameter are less prone to ripple and have a larger relative post-rippling stiffness. Our findings show large variations in the onset of rippling and the bending stiffness before and after rippling. These variations open up possibilities of tailoring the mechanical properties for specific applications.Baksidetext Carbon nanotubes (CNTs) have extraordinary mechanical and electrical properties. Together with their small dimensions and low density, they are attractive candidates for building blocks in nanoelectromechanical systems (NEMS), and many other applications. In this thesis the mechanical behaviour of individual CNTs and vertically aligned carbon nanofibers has been studied by performing force measurements inside electron microscopes. We have found that the mechanical behaviour is very sensitive to the defect density and the internal structure of the CNTs. The extraordinary properties are only attained by defect free CNTs and quickly deteriorate if defects are introduced to the structure. Mechanical deformations also alter these properties. Single-walled CNTs behave similarly to drinking straws when bent, i.e. they buckle, while the inner tubes of multi-walled CNTs prevent buckling. Instead a more distributed rippling pattern is created for multi-walled CNTs. Both these deformation behaviours will cause an abrupt drop in the bending stiffness, which is detrimental for many applications. The findings in this work will have implications for the design of future NEMS.
Artikel 2 Image formation mechanisms tidigare som manuskript, nu publicerad: urn:nbn:se:kau:diva-16425 (MÅ 150924)
39
Mierwaldt, Daniel Joachim [Verfasser], Christian [Akademischer Betreuer] Jooß, Christian [Gutachter] Jooß y Simone [Gutachter] Techert. "In Situ X-ray Spectroscopy and Environmental TEM Study on Manganite Water Oxidation Catalysts / Daniel Joachim Mierwaldt ; Gutachter: Christian Jooß, Simone Techert ; Betreuer: Christian Jooß". Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2017. http://d-nb.info/1149959045/34.
Texto completo
40
Ben, Haj Slama Meriem. "Étude multi-échelle et in situ des évolutions microstructurales en conditions isothermes d’aciers bainitiques en lattes". Thesis, Université de Lorraine, 2018. http://www.theses.fr/2018LORR0042/document.
Texto completoResumen
Les aciers bainitiques sont utilisés industriellement pour leur bon compromis entre résistance, ductilité et ténacité. Cependant, après obtention de sa microstructure d'emploi, l’acier peut subir des maintiens additionnels en température (soit en fin de fabrication et/ou lors de son utilisation), susceptibles de dégrader ses propriétés. Ces travaux de thèse cherchent à comprendre les origines microstructurales de cette dégradation. Pour ce faire, des traitements thermiques contrôlés ont été appliqués à des aciers de nuances modèles FeNiC et FeNiMnC. Une première série de traitements a permis de fabriquer des microstructures bainitiques supérieure, inférieure, martensitique et mixtes. Ces produits de transformation bruts ont été caractérisés et analysés en détail, en particulier par EBSD en résolution angulaire améliorée. Les données ont été exploitées pour reconstruire les ex-grains austénitiques et distinguer les différents produits de transformation par l'organisation spatiale de leurs variants cristallographiques. Une deuxième série de traitements a consisté à soumettre ces microstructures à des maintiens isothermes prolongés. Nous avons montré que ces microstructures bainitiques en lattes ne sont pas stables dans certaines conditions ultérieures de maintien isotherme. Dans les cas les plus sévères, nous avons observé un processus de « granularisation » de la microstructure en lattes avec disparition des variants fortement désorientés et une maturation des carbures. Ces phénomènes sont observés sur nos alliages modèles y compris sur des temps courts (<1h) à basses températures (300°C). Ces évolutions ainsi que leurs cinétiques ont été investiguées à différentes échelles en couplant des observations en MEB, EBSD, MET et aussi in situ par DRX Haute Energie sur grands instruments. La composition chimique et la microstructure initiale affectent sensiblement les cinétiques. Mais nous avons surtout pointé le rôle majeur de la présence (même résiduelle) de bainite dite supérieure dans la microstructure initiale pour amorcer le processus de granularisation, indépendamment de la température de dénaturation. L’ensemble des résultats permet de discuter les possibles mécanismes sous-jacents et leurs forces motrices et ouvre une discussion plus large sur la classification des bainitesBainitic steels are widely used in industry thanks to their good combinations of strength, toughness and ductility. Meanwhile, after obtaining the targeted microstructure, the steel can undergo additional isothermal holdings (either during manufacturing and/or during usage) prone to degrade its properties. The thesis work aims at understanding the microstructural origins of this degradation. To achieve this, we applied controlled heat treatments on model FeNiC and FeNiMnC steel grades. A first set of heat treatments allowed us to obtain different microstructures; upper and lower bainites, martensite and mixed concepts. These transformation products were characterized and analyzed in detail, particularly by EBSD with improved angular resolution. Data was operated to reconstruct prior austenitic grains and to distinguish the different transformation products according to their crystallographic variant spatial organization. A second set of heat treatments consisted in aging these microstructures by extended isothermal holdings. We show that lath-like bainitic microstructures are not stable under certain isothermal conditions. In the most advanced cases, we observed a « granularization » process of the lath microstructure, associated with high misoriented variant disappearance and carbides ripening. These phenomena were observed for the studied model alloys, even within short holding times (<1h) and at low temperatures (300°C). These highlighted evolutions as well as their kinetics were investigated at different scales, coupling SEM observations, EBSD, TEM and in situ XRD High Energy on large instruments. The initial microstructure and the steel chemical composition affect significantly the « granularization » kinetics. But we have above all put the light on the major role of the presence of an upper bainite fraction (even a residual one) in the initial microstructure, to start the granularization phenomenon, independently of aging temperature. All of these results allow discussing possible mechanisms with their respective driving forces and opening larger discussion about bainite classification
41
Masliuk, Liudmyla [Verfasser], Robert [Akademischer Betreuer] Schlögl, Reinhard [Akademischer Betreuer] Schomäcker, Robert [Gutachter] Schlögl, Malte [Gutachter] Behrens y Michael [Gutachter] Lehmann. "Exploring the local differences of M1-type mixed oxides by quasi in-situ (S)TEM / Liudmyla Masliuk ; Gutachter: Robert Schlögl, Malte Behrens, Michael Lehmann ; Robert Schlögl, Reinhard Schomäcker". Berlin : Technische Universität Berlin, 2018. http://d-nb.info/1171306237/34.
Texto completo
42
Stricker, Elizabeth Ann. "Cuprous Bromide Electrochemistry and its Application in a Flow Battery". Case Western Reserve University School of Graduate Studies / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=case1546604124529032.
Texto completo
43
Liu, Qiong. "Mechanical properties of Ti-o based ceramic nanowires". Thesis, Queensland University of Technology, 2020. https://eprints.qut.edu.au/201954/1/Qiong_Liu_Thesis.pdf.
Texto completoResumen
This thesis thoroughly investigated the mechanical properties of Ti-O based ceramic nanowires. It revealed that elastic bending properties including elastic strain and elastic moduli of different kinds of Ti-O based ceramic nanowires were related to their crystalline structures, defects in the structures, and defect activities during bending deformation. These findings help to provide more opportunities for strain engineering on Ti-O NWs and promote potential applications of Ti-O NW-based devices.
44
Guitton, Antoine. "Mécanismes de déformation des phases MAX : une approche expérimentale multi-échelle". Thesis, Poitiers, 2013. http://www.theses.fr/2013POIT2280/document.
Texto completoResumen
Il est couramment admis que la déformation plastique des phases MAX est dueau glissement de dislocations dans les plans de base s'organisant en empilements et murs. Cesderniers peuvent former des zones de désorientation locale appelées kink bands. Cependant, lesmécanismes élémentaires et le rôle exact des défauts microstructuraux sont encore mal connus. Cemanuscrit présente une étude expérimentale multi-échelle des mécanismes de déformation de laphase MAX Ti2AlN. A l'échelle macroscopique, deux types d'expériences ont été menés. Des essaisde compression in-situ à température et pression ambiantes couplés à la diffraction neutroniqueont permis de mieux comprendre le comportement des différentes familles de grains dans le Ti2AlNpolycristallin. Des essais de compression sous pression de confinement ont également été réalisés dela température ambiante jusqu'à 900 °C. À l'échelle mésoscopique, les microstructures des surfacesdéformées ont été observées par MEB et AFM. Ces observations complétées par des essais denanoindentation ont montré que la forme des grains et leur orientation par rapport à la directionde sollicitation gouvernent l'apparition de déformations intra- et inter-granulaires ainsi que lalocalisation de la plasticité. Finalement à l'échelle microscopique, une étude détaillée par METdes échantillons déformés sous pression de confinement a révélé la présence de configurations dedislocations inédites dans les phases MAX, telles que des réactions entre dislocations, des dipôleset des dislocations hors plan de base. À la vue de ces résultats nouveaux, les propriétés mécaniquesdes phases MAX sont rediscutéesIt is commonly believed that plastic deformation mechanisms of MAX phases consistin basal dislocation glide, thus forming pile-ups and walls. The latter can form local disorientationareas, known as kink bands. Nevertheless, the elementary mechanisms and the exact role ofmicrostructural defects are not fully understood yet. This thesis report presents a multi-scale experimentalstudy of deformation mechanisms of the Ti2AlN MAX phase. At the macroscopic scale,two kinds of experiments were performed. In-situ compression tests at room temperature coupledwith neutron diffraction brought new insight into the deformation behavior of the different grainfamilies in the polycrystalline Ti2AlN. Compression tests from the room temperature to 900 °Cunder confining pressure were also performed. At the mesoscopic scale, deformed surface microstructureswere observed by SEM and AFM. These observations associated with nanoindentationtests showed that grain shape and orientation relative to the stress direction control formationof intra- and inter- granular strains and plasticity localization. Finally, at the microscopic scale,a detailed dislocation study of samples deformed under confining pressure revealed the presenceof dislocation configurations never observed before in MAX phases, such as dislocation reactions,dislocation dipoles and out-of-basal plane dislocations. In the light of these new results, mechanicalproperties of MAX phases are discussed
45
Lahouij, Imène. "Mécanismes de lubrification des nanoparticules à structure Fullerène : approche multi-échelle". Phd thesis, Ecole Centrale de Lyon, 2012. http://tel.archives-ouvertes.fr/tel-00790813.
Texto completoResumen
Les fullerènes de bisulfure métallique de type ( M eS2 , où Me= Mo et W) rencontrent un intérêt croissant du fait de leurs pouvoirs anti usure et réducteur de frottement en régime de lubrification limite. Les propriétés tribologiques de ces nanoparticules, dépendent à la fois de leurs caractéristiques intrinsèques (structure, morphologie, taille, ... ), des conditions de sollicitations (nature des surfaces, pression, température, ... ) ainsi que du cocktail d'additifs présent dans une formulation d'huile moteur. La compréhension de l'origine de ces propriétés passe obligatoirement par une parfaite connaissance du mode d'action des nanoparticules. L'objectif de ce travail de thèse est d'identifier les paramètres pouvant avoir une influence sur le comportement des nanoparticules à l'échelle nanométrique et de faire le lien entre ce comportement, les mécanismes de lubrification des nanoparticules, et leurs propriétés tribologiques. Afin de répondre à cet objectif nous avons adopté une approche multi échelle qui consiste dans un premier temps à étudier le comportement de fullerènes individuels (IF - M eS2 , ou Me= Mo et W) en cours de sollicitation. Ainsi grâce à une méthodologie expérimentale originale couplant la technique de nano indentation à une observation in situ dans un microscope électronique à transmission haute résolution (HRMET), nous avons visualisé pour la toute première fois et en temps réelle comportement de nanoparticules individuelles d'if- M eS2 (Me= Mo et W) sollicitées en compression et/ou en cisaillement dans un contact dynamique. Cette étude a permis d'identifier l'influence des caractéristiques intrinsèques des fullerènes sur leur réponse à l'échelle nanométrique et d'estimer des pressions de contact pour lesquelles le fullerène s'exfolie, roule ou glisse dans le contact. Nous nous sommes ensuite intéressés aux mécanismes de lubrification des fullerènes en dispersion dans une base lubrifiante, en condition de lubrification limite. En se basant sur des analyses XPS et des observations MEB et MET des tribofilms et des débris d'usure générés à l'issu d'essais de frottement réalisés dans trois contacts de nature différente (acier, alumine et DLC), nous avons clairement montré que les propriétés lubrifiantes des nanoparticules d'IF - M eS2 (Me= Mo et W) dépendaient à la fois de leurs caractéristiques intrinsèques et de la nature des surfaces frottantes. Ainsi un lien a été établi entre le comportement des fullerènes à l'échelle nanométrique et leur mode d'action dans un contact tribologique. Enfin, l'influence de la mise en dispersion des nanoparticules sur leurs propriétés tribologiques a été étudiée. Les propriétés tribologiques des nanoparticules dans une huile moteur ont été également évaluées. Deux approches expérimentales de type 'Bottom up' et 'Top dawn'ont été adoptées afin d'évaluer les interactions entre les nanoparticules et l'ensemble des additifs présents dans une huile complétement formulée. L'influence de la température sur les propriétés tribologiques des nanoparticules a été également abordée.
46
Sylvain, Wilgens. "Étude de la plasticité du monocristal de phase MAX par déformation aux petites échelles". Thesis, Poitiers, 2016. http://www.theses.fr/2016POIT2307/document.
Texto completoResumen
L'objectif de cette thèse est l'étude de la déformation, à l'échelle microscopique, de la phase MAX Ti2AlN, synthétisée par métallurgie des poudres. Ce travail se divise en trois parties : une première dans laquelle l'accent a été mis sur l'hystérèse mécanique des phases MAX via des essais cyclés, en nanoindentation sphérique et compression ex-situ de micro-piliers, sur des grains d'orientations différentes déterminées par l'EBSD. Dans la deuxième nous nous sommes intéressés à la déformation de micropiliers via des essais de compression cyclés in-situ couplés à la micro-diffraction Laue. L'objectif a été d'analyser les taches diffraction au cours de la déformation du pilier afin de mettre en évidence les mécanismes de déformation élémentaires mis en jeu et d'observer les structures finales via des images MEB post-mortem des piliers. Enfin, une dernière dans laquelle l'objectif a été l'étude des mécanismes de déformation en température à l'échelle microscopique via des essais de nano-indentation allant jusqu'à 800°C. La caractérisation des lignes de glissement en surface et des configurations microstructurales sous l'empreinte a été réalisée par AFM et MET respectivement. Toutes les données recueillies par ces divers essais aux petites échelles, ont permis d'affiner notre compréhension des mécanismes de déformation du monocristal de phase MAX, notamment vis à vis des modèles usuellement proposés dans la littératureThe thesis's goal is to study the deformation, at microscopic scale, of the MAX phase Ti2AlN synthesized by powder metallurgy. This work is divided into three parts: in the first part, the interest has been put on the hysteretic behavior of the MAX phases via cyclic mechanical solicitations, during spherical indentation tests and ex-situ compression of micro-pillars, on differently orientated grains beforehand determined by EBSD. In the second part, we were interested into the micro-pillar's deformation via insitu cyclic compression tests coupled with Laue micro-diffraction. The goal was to analyse the evolution diffraction lines during the pillar's deformation in order to highlight the elementary deformation mechanisms and to observe the finale structures via the post-mortem SEM imaging of the pillars. Finally, a last part was devoted to study the deformation mechanisms in temperature at microscopic scale via nano-indentation tests up to 800°C. The characterization of the slip lines on the surface has been revealed by AFM and that of t he microstructural configurations (dislocations) under the indent has been done by TEM. All data collected by these various tests at the small scales have refined our understanding of the deformation mechanisms of crystal MAX phase, particularly with respect to the models usually proposed in the literature
47
Nie, Chunyang. "Etude de nanocristaux unidimensionnels confinés dans des nanotubes de carbone". Thesis, Toulouse 3, 2016. http://www.theses.fr/2016TOU30214/document.
Texto completoResumen
Le remplissage des nanotubes de carbone (NTC) est considéré comme une approche relativement simple permettant de synthétiser des nanocristaux du fait de l'effet de confinement 1D imposé par la cavité centrale des NTC, qui peut être seulement de l'ordre du nanomètre ou moins, notamment dans le cas des NTC monoparoi et en particulier des NTC biparois (DWCNT) sur lesquels nous avons concentré nos efforts. De tels nanocristaux devraient avoir des propriétés physiques (électriques, magnétiques) différentes de celles de leurs équivalents à l'état massif du fait de la modification de la coordinence des atomes ou des ions les composant. Parmi les différentes méthodes existantes pour le remplissage des NTC, (in situ pendant la synthèse, a posteriori à partir de solutions), la méthode faisant intervenir des matériaux fondus est la plus populaire pour le remplissage par des matériaux inorganiques. Elle permet en effet d'atteindre des taux de remplissage raisonnablement élevés et demeure assez simple à mettre en œuvre. Cependant, elle fait preuve d'un certain nombre de limitations (techniques) qui posent problème dans le cas de matériaux à haut point de fusion (typiquement > 1000°C), dont la réactivité avec le carbone à haute température pourrait être gênante (carboréduction des oxydes par exemples), ou encore dont la faible mouillabilité vis-à-vis du carbone à l'état fondu est rédhibitoire (métaux par exemple). Il est possible de palier à cette difficulté en procédant par étapes successives et en remplissant d'abord les NTC avec un précurseur puis d'utiliser la cavité interne des NTC comme des nanoréacteurs afin de procéder dans un second temps à une transformation in situ. Dans ces travaux, nous avons étudié (1) le remplissage de DWCNT avec de l'iode ainsi qu'avec différents iodures métalliques en mettant en œuvre essentiellement la méthode des sels fondus. Nous avons étudié en détails l'influence des paramètres physico-chimiques du matériau de remplissage (réactivité chimique sous la forme en particulier du potentiel rédox du couple iodure métallique / métal, mais aussi viscosité, tension de surface, pression de vapeur saturante en milieu fondu) mais aussi du NTC (texture cylindrique ou "en arrêtes de poisson", diamètre, nombre de parois) sur le taux de remplissage. (2) Nous avons étudié en détail un certain nombre de structures inhabituelles de nanomatériaux confinés dans les DWCNT, en faisant appel à la modélisation structurale et à la simulation d'images de microscopie électronique sur la base de ces modèles pour guider notre analyse. (3) Nous avons enfin étudié différentes réactions in situ dans les DWCNT telles que la sulfuration, la réduction sous hydrogène ou encore la fluoration afin de synthétiser des nanocristaux originaux et de les caractériser en détails à l'aide d'outils tels que par exemple le MET Haute Résolution et la spectroscopie de perte d'énergie des électrons (EELS)Filling carbon nanotubes (CNTs) has been considered as an easy approach to synthesize various nanocrystals since the inserted materials are forced to adopt a nearly one-dimensional morphology arising from their very high aspect ratio, especially in the case of single-walled CNTs (SWCNTs) or double-walled CNTs (DWCNTs). Nanocrystals/nanowires of transition metals, especially those with very narrow diameters, are predicted to exhibit peculiar magnetic property differing from the bulk metals. Filling CNTs provides a possible way for the synthesis of such metal nanocrystals/nanowires. There are several methods for filling CNTs including the in situ method, gas phase method, molten phase method, solution method, etc. Among them, molten phase has been very popular for filling various types of nanotubes due to the possibility to reach high filling rates, simplicity and versatility. However, for materials with high melting point such as metals, it is difficult to insert them into CNTs directly. To solve this problem, we also took advantage of the inner cavity of CNTs which not only templates the growth but also acts as a nanoreactor in order to perform chemical reactions. The insertion of materials with high melting point is typically achieved by first filling CNTs with a precursor, and then transforming the precursor into the desired 1D nanostructure by post-treatments. In this thesis, (i) filling DWCNTs with iodine and various halides via the molten phase method was performed and the influence of the relevant physical and chemical properties of the halides on the filling rate was investigated. The role of the redox potential as a main parameter driving the filling efficiency is pointed out, and explained; (ii) peculiar structures of the nanocrystals confined within DWCNTs were imaged by transmission electron microscopy (TEM) and corresponding modeling of the observed crystal nanostructures and related TEM images were proposed; (iii) different in situ transformations on the iodide-filled DWCNTs were attempted and the chemical composition of the encapsulated 1D nanocrystals before and after post-filling treatments was systematically identified by means of electron energy loss spectroscopy (EELS)
48
Carlier, Thomas. "Croissance de couches minces et de nanostructures piézoélectriques A2WO6 (A=lanthanide) par ablation laser et caractérisation nanométrique par microscopie à force atomique". Thesis, Artois, 2016. http://www.theses.fr/2016ARTO0407/document.
Texto completoResumen
Afin de répondre à l’essor des nanotechnologies dans le domaine des capteurs et du stockage de l’information, la recherche de nouveaux matériaux éco-acceptables, sous forme de films minces et possédant de hautes performances s’inscrit dans une politique environnementale toujours plus présente.Le but de ce travail est donc double : (i) synthétiser des films minces d’oxydes de A2WO6 (A = lanthanide) et d’en démontrer le caractère piézo-/ferroélectrique à l’échelle locale ; (ii) nanostructurer ce type de matériau par une approche « bottom-up ».Cette thèse a débuté par l’étude de ces oxydes sous forme massive et notamment de leur comportement en température. À la suite de cette étude, des films minces de La2WO6 ont été synthétisés par ablation laser pulsé sur des substrats de SrTiO3 et de LaAlO3 orientés (100). La caractérisation structurale par diffraction de rayons X haute résolution et par microscopie électronique en transmission a permis de déterminer les paramètres de maille ainsi que les relations d’épitaxie de ces films. Par la suite, le caractère piézo-/ferroélectrique des films de α-La2WO6 haute température a été confirmé à l’échelle locale par microscopie à force piézoélectrique ainsi que par TEM-STM in situ. Le composé Nd2WO6 présente également toutes les caractéristiques d’un matériau piézoélectrique. Enfin, la nanostructuration via un masque en nitrure de silicium et l’ablation laser pulsé a permis la fabrication d’îlots piézoélectriques de La2WO6 de diamètres de 1,2 μm et 450 nm. Ces résultats prometteurs font des oxydes A2WO6 des candidats de choix pour la conception de nano-dispositifs piézo-/ferroélectriquesWith the development of nanotechnology in the field of sensors and information storage, the research for new eco-friendly materials in the form of thin films with high performances is part of an ever present environmental policy. The purpose of this work is twofold. It is (i) to synthesize oxide thin films of A2WO6 (A = lanthanide) and to demonstrate the local piezo / ferroelectric behavior; (ii) to nanostructure this type of material by using a "bottom-up" approach. Thus this thesis has began by studying the behavior of these oxides in bulk form, considering particularly the temperature and pressure effects. As a result, La2WO6 thin films were grown by pulsed laser deposition on (100)-oriented SrTiO3 and LaAlO3 substrates. The structural characterization by X-ray diffraction high resolution and transmission electron microscopy was used to determine the lattice parameters and the epitaxial relationships of these films. Thereafter, the piezo / ferroelectric behavior of high temperature α-La2WO6 film was locally confirmed by piezoelectric force microscopy and transmission electronic microscopy combined with the scanning tunneling microscopy. The Nd2WO6 compound has also the characteristics of a piezoelectric material. Finally, the nanostructuration by combining a silicon nitride mask and the pulsed laser deposition technique has enabled the fabrication of La2WO6 piezoelectric islands with diameters of 1.2 μm and 450 nm. These promising results make A2WO6 oxides ideal candidates for the design of piezo / ferroelectric nanodevices
49
Zhang, Wei. "Initiation and Propagation of Localized Corrosion of Mild Steel in Marginally Sour Environments". Ohio University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1605039352183903.
Texto completo
50
Abbes, Omar. "Etude de la diffusion réactive entre Mn et Ge à l'échelle nanométrique pour des applications en spintronique". Thesis, Aix-Marseille, 2013. http://www.theses.fr/2013AIXM4325.
Texto completoResumen
Le couplage des propriétés ferromagnétiques et semiconductrices représente une perspective prometteuse, afin de réaliser des technologies qui exploitent le spin des électrons. Ceci permettra de stocker et traiter des bits informatiques de façon instantanée dans le même dispositif, plutôt que dans des dispositifs séparés (mémoire et processeur). La Spintronique pourrait alors révolutionner la technologie de l'information. Un candidat potentiel pour la fabrication d'hétérostructures métal ferromagnétique/semiconducteur pour des applications en Spintronique, est le système Mn-Ge. Ce système qui est compatible avec la technologie CMOS, présente une phase intéressante pour la Spintronique qui est Mn5Ge3, avec une possibilité d'épitaxie sur le Ge(111). Afin d'intégrer cette phase dans des procédés de fabrication, nous étudions la diffusion réactive à l'état solide entre un film de Mn et un substrat de Ge (comme dans le cas de la formation des siliciures dans la technologie CMOS). L'accent a été mis sur la séquence de formation de phases lors de la réaction entre un film nanométrique de Mn et le Ge, l'influence de l'interface sur cette réaction, et sur la diffusion du Mn dans le Ge. L'incorporation du carbone dans des films minces de Mn5Ge3 a montré une augmentation notable de la température de Curie : nous présentons alors l'effet du carbone sur la réaction Mn-Ge, et sa redistribution dans les couches minces MnxGeyCoupling ferromagnetic and semi-conducting properties represents a pathway toward producing technologies that exploit the spin of electrons. That would allow store and process computer bits instantly in a same device, rather than separate devices (memory and CPU). The Spintronics could then revolutionize the information technology. A potential candidate for the fabrication of heterostructures ferromagnetic metal / semiconductor for Spintronics applications is the Mn-Ge system. This system is compatible with CMOS technology, and presents an interesting phase for Spintronics which is Mn5Ge3 phase, which is able to be grown epitaxially on Ge(111). To integrate this phase in the manufacturing process, we study the solid state reactive diffusion between a thin Mn film and Ge substrate, to form a germanide upon the Ge substrate (as in the case of the formation of silicides in CMOS technology). Emphasis was placed on the sequence of phase formation during the reaction between a 50 nm thick Mn film and Ge, the influence of the interface on the reaction, and the diffusion of Mn in Ge. Incorporation of carbon in thin Mn5Ge3 films showed a significant increase in the Curie temperature, we then present the effect of carbon on the reaction Mn-Ge and its redistribution in thin MnxGey films