Дисертації: "Scanning electron microscopy (MEB)"

1

Gaudenzi, de faria Marcelo. "Robust control for manipulation inside a scanning electron microscope." Thesis, Besançon, 2016. http://www.theses.fr/2016BESA2068/document.

Повний текст джерела

Анотація:

Cette thèse étudie le problème de nano-positionnement à l'intérieur d'un microscope électronique à balayage (MEB). Pour obtenir des informations de position avec rapidité et précision, une installation dédiée composée d’un vibromètre placé à l'intérieur du MEB a été mise en œuvre. Cette approche diffère de méthodes basées sur le traitement d'images, car elle permet de saisir des données en temps réel sur le comportement dynamique des structures étudiées. Dans une première étude, les perturbations mécaniques agissant à l'intérieur de la chambre à vide du microscope ont été caractérisées et leurs sources ont été identifiées. Cela a démontré comment les vibrations mécaniques externes et les bruits acoustiques peuvent influer largement sur les composants à l'intérieur du MEB par couplage mécanique, limitant ainsi la précision des manipulateurs. Dans un deuxième temps, une micro-pince du commerce a été étudiée. Une différence entre ses comportements dans l'air et dans le vide a été mise en évidence, ce qui a permis d'obtenir deux modèles dynamiques pour cet organe terminal, un pour chaque environnement. Deux lois de commande ont été proposées (commande H-infini et commande basée sur un observateur d'état étendu), afin d'obtenir en temps réel un positionnement précis dans le vide, et d'atténuer les effets des perturbations mécaniques externes. Les résultats ont été validés en simulation et expérimentalement
This work studies the nano-positioning problem inside the scanning electron microscope (SEM). To acquire fast and accurate positional information, a dedicated setup was implemented consisting of a vibrometer placed inside the SEM. This approach differs from methods based on image processing, as it allows to capture real-time data on the dynamic behavior of structures. In a first study, the mechanical disturbances acting inside the microscope’s vacuum chamber were characterized and its sources were identified. This demonstrated how external mechanical vibrations and acoustic noises can largely influence the components inside the SEM through mechanical coupling, limiting the effective positioning precision of manipulators. Next, a commercial micro-gripper was studied, both in air and in vacuum, and the differences between its response were highlighted. This allowed to obtain two dynamic models for this end-effector, one for each environment. Two control laws were proposed (H-infinity control and Extended State Observer based control) for the system, to obtain a real-time, precise positioning in the vacuum environment and to attenuate the effects of the external mechanical disturbances. Results were demonstrated through simulation and experimental validation

Стилі APA, Harvard, Vancouver, ISO та ін.

2

Comby, Dassonneville Solène. "Développement et application d'un nanoindenteur in situ MEB couplé à des mesures électriques." Thesis, Université Grenoble Alpes (ComUE), 2018. http://www.theses.fr/2018GREAI047/document.

Повний текст джерела

Анотація:

L’essor de la demande actuelle pour des matériaux architecturés, en microélectronique par exemple, ou pour des matériaux de structure, nécessite le développement d’outils de caractérisation toujours plus performants. Dans cette optique, un instrument de caractérisation multifonctionnel basé sur un couplage mécanique / électrique, a été développé au laboratoire SIMaP. Le cœur de ce dispositif est un nanoindenteur in situ FEG-SEM (Field Emission Gun Scanning Electron Microscope) couplé à des mesures électriques. Ce travail est porté par trois principales motivations: (1) L’étude du comportement mécanique d’objets petites échelles, (2) L’apport des données électriques à l’analyse quantitative du comportement mécanique pendant l’indentation, en particulier pour obtenir une meilleur estimation de l’aire de contact, (3) L’étude locale des propriétés électroniques d’empilements de films minces. L’intégration in situ SEM a été validée et permet un positionnement des indents avec une précision meilleure que 100 nm, autorisant ainsi l’étude des propriétés mécaniques à l’échelle submicrométrique. La rapidité des essais permet également des mesures statistiques. Des caractérisations mécaniques ont été menées aussi bien sur des échantillons composites massifs que sur des ilots d’or submicrométriques. Pour ce dernier cas, malgré la nature stochastique de leur comportement mécanique, une loi déterministe a pu être extraite des données mécaniques. Des mesures 3D-BCDI (Bragg Coherent Diffraction Imaging) au synchrotron ont été réalisées sur certains ilots avant et après chargement mécanique, révélant une germination de dislocations avant l’avalanche de grandes déformations plastiques. En parallèle de cette étude, des mesures électriques ont été réalisées pendant l’indentation de divers échantillons. Des mesures de nanoindentation résistive ont ainsi été effectuées sur des métaux nobles (Au) ou recouverts de leur oxyde natif (Cu, Al), soit à l’état de monocristal massif ou de film polycristallin. Les résultats quantitatifs soulignent l’importance de la présence d’une couche d’oxyde sur la réponse électrique. En présence d’un oxyde, l’interface pointe / échantillon semble être le lieu d’importantes réactions électrochimiques. En l’absence d’oxyde, la résistance mesurée peut être entièrement décrite par un modèle analytique. Dans ce cas, l’aire de contact électrique peut être prédite à partir des mesures de résistance. Enfin, des mesures capacitives ont été réalisées sur des structures MOS avec différentes épaisseurs d’oxyde. Les résultats expérimentaux sont parfaitement décrits par un modèle analytique, ce qui ouvre la voie à des mesures locales de permittivité diélectrique sous contrainte mécanique
The increasing demand for multifunctional materials has become a recurrent challenge for a wide panel of application fields such as microelectronics and structural applications. Within the frame of this project, a multifunctional characterisation set-up has been developed at SIMaP lab, mainly based on the electrical / mechanical coupling. The heart of this device is an in situ FEG-SEM (Field Emission Gun Scanning Electron Microscope) nanoindenter coupled with an electrical measurement apparatus. This work has threefold objectives: (1) The investigation of mechanical behavior of small scale systems, (2) The input of electrical data to the quantitative analysis of mechanical behavior during indentation, in particular to obtain a better estimation of the contact area (3) The local study of electronic properties of thin film stacks. SEM integration of the device has been validated and indent positioning with a precision better than 100 nm is successfully obtained. This performance allows the studies of mechanical properties at submicrometric length scale, with a high throughput allowing statistical measurements. Various bulk composite materials have been characterized as well as submicrometric gold islands on sapphire. In the latter case, despite the stochastic nature of their mechanical behavior, a deterministic law has been extracted. 3D-BCDI (Bragg Coherent Diffraction Imaging) experiments have been performed on a few islands at synchrotron facility to investigate the crystal state before and after mechanical loading. These experiments reveal initial dislocation nucleation prior to large deformation bursts. In parallel to this study, electrical measurements have been performed during indentation on various cases. Resistive-nanoindentations have been performed on noble metals (Au) and natively oxidized metals (Cu, Al), either as bulk single crystals or as polycrystalline thin films. Qualitative results emphasize the importance of the oxide layer on the electrical response. In the presence of an oxide layer, strong electrochemical reactions seem to occur at the tip-to-sample interface. When no oxide is involved, the measured resistance can be fully described by an analytical model and the computed electrical contact area is successfully validated with residual areas measurements. Finally, capacitive measurements have been performed on MOS structures with various oxide thicknesses. Experimental results have been well described by analytical modelling, which paves the way for quantitative local dielectric permittivity measurements under mechanical loading

Стилі APA, Harvard, Vancouver, ISO та ін.

3

Liu, Yang. "‘Tri-3D’ electron microscopy tomography by FIB, SEM and TEM : Application to polymer nanocomposites." Thesis, Lyon, INSA, 2013. http://www.theses.fr/2013ISAL0076/document.

Повний текст джерела

Анотація:

Ce travail a porté sur la caractérisation et la quantification en 3D de la répartition de charges de différents types (nanoparticules, nanotubes, etc.) dans des matrices polymères. Nous nous focalisons sur les techniques de tomographie en microscopie électronique. Une approche multiple en tomographie électronique a été réalisée : la tomographie en FIB/MEB (faisceau d’ions focalisé/microscope électronique à balayage), la tomographie en MEB et la tomographie en MET (microscope électronique en transmission). Les nanocomposites polymère sont généralement élaborés aux fins d’améliorer les propriétés physiques (mécanique, électrique, etc.) du matériau polymère constituant la matrice, grâce à une addition contrôlée de charges nanométriques. La caractérisation de tels matériaux, et l’établissement de corrélations précises entre la microstructure et les propriétés d’usage, requièrent une approche tri-dimensionnelle. En raison de la taille nanométrique des charges, la microscopie électronique est incontournable. Deux systèmes de nanocomposite polymère ont été étudiés par une approche multiple de tomographie électronique : P(BuA-stat-S)/MWNTs (copolymère statistique poly (styrène-co-acrylate de butyl) renforcé par des nanotubes de carbone multi-parois), et P(BuA-stat-MMA)/SiO2 (copolymère statistique poly(butyl acrylate-co-methyl methacrylate) renforcé par des nanoparticules de silice). Par combinaison de divers techniques, la caractérisation et la quantification des nanocharges ont été possibles. En particulier, la taille, la fraction volumique et la distribution des charges ont été mesurées. Cette étude a ainsi fourni des informations en 3D qui contribuent à mieux comprendre les propriétés des nanocomposites. Une attention particulière a été portée aux artefacts et causes d’erreur possibles durant l’étape de traitement 3D. Nous avons également essayé de comparer les différentes techniques utilisées du point de vue de leurs avantages et inconvénients respectifs, en dégageant des possibilités d’amélioration future
This work is focused on the characterization and quantification of the 3D distribution of different types of fillers (nanoparticles, nanotubes, etc.) in polymer matrices. We have essentially used tomography techniques in electron microscopy. Multiple approaches to electron tomography were performed: FIB-SEM (focused ion beam/scanning electron microscope) tomography, SEM tomography and TEM (transmission electron microscope) tomography. Polymer nanocomposites are basically synthesized in order to improve the physical properties (mechanical, electric, etc.) of the pure polymer constituting the matrix, by a controlled addition of fillers at the nanoscale. The characterization of such materials and the establishment of accurate correlations between the microstructure and the modified properties require a three-dimensional approach. According to the nanometric size of the fillers, electron microscopy techniques are needed. Two systems of polymer nanocomposites have been studied by multiple electron tomography approaches: P(BuA-stat-S)/MWNTs (statistical copolymer poly(styrene-co-butyl acrylate) reinforced by multi-walled carbon nanotubes) and P(BuA-stat-MMA)/SiO2 (statistical copolymer poly(butyl acrylate-co-methyl methacrylate) reinforced by silica nanoparticles). By combining various techniques, the characterization and the quantification of nanofillers were possible. In particular, statistics about size, distribution and volume fraction of the fillers were measured. This study has then provided 3D information, which contributes to a better understanding of properties of the nanocomposites. Attention has been paid to analyze carefully original data, and artifacts and causes of errors or inaccuracy were considered in the 3D treatments. We also attempted to compare benefits and drawbacks of all techniques employed in this study, and perspectives for future improvements have been proposed

Стилі APA, Harvard, Vancouver, ISO та ін.

4

Crouzier, Loïc. "Développement d'une nouvelle approche hybride combinant AFM et MEB pour la métrologie dimensionnelle des nanoparticules." Thesis, Poitiers, 2020. http://www.theses.fr/2020POIT2260.

Повний текст джерела

Анотація:

Afin de bénéficier des propriétés uniques des nanomatériaux liés à leur taille mais aussi d'évaluer leurs risques potentiels associés, les acteurs du secteur industriel ont besoin de s’appuyer sur des méthodes de mesure fiables, robustes et permettant d’obtenir l’ensemble des informations dimensionnelles requises. Cependant, il n’existe pas d’instrument capable de mesurer une nanoparticule dans les trois dimensions de l’espace avec une incertitude contrôlée. L’objectif de ces travaux est de combiner les mesures de diamètre par microscopie électronique à balayage (MEB) avec celles de hauteur par microscopie à force atomique (AFM). L’utilisation de particules de silice, supposée sphériques permet de valider cette approche hybride combinant AFM et MEB.Le bilan d’incertitudes associé à la mesure de nanoparticules par MEB a d’abord été établi. Nous avons mis en évidence que la principale contribution au bilan d’incertitudes est la taille du faisceau électronique, difficilement mesurable. Deux méthodes, fondées sur la modélisation Monte Carlo, ont été mises en place pour évaluer l’influence de ce paramètre sur la mesure MEB. La première est fondée sur la comparaison entre les signaux expérimentaux et simulés. La seconde repose sur la segmentation des images MEB en utilisant un point remarquable, non influencé par les dimensions du faisceau électronique. Ces deux méthodes ont permis de montrer que l’erreur liée à la taille du faisceau était largement surestimée en utilisant les outils de segmentation d’images classiques. À partir de ces résultats, une comparaison directe des mesures AFM et MEB a été réalisée sur les mêmes particules. Un écart systématique est observé entre les deux techniques pour les plus petites particules lié à leur non-sphéricité. L’utilisation d’une troisième technique, la microscopie électronique en transmission (MET) permet de confirmer ces observations. Enfin, l’approche de métrologie hybride a été mise en œuvre pour la mesure des trois dimensions caractéristiques de nanoparticules de formes complexes dont la morphologie était éloignée de celle de la sphère
In order to take advantages of remarkable properties of the nanomaterials related to their size but also assess their potential risks, industrial actors need to rely on robust measurement methods that provide all the required dimensional information. However, there is no instrument capable of measuring a nanoparticle in all three dimensions of space with controlled uncertainty. The aim of this work is to combine diameter measurements by scanning electron microscopy (SEM) with height measurements by atomic force microscopy (AFM). The use of silica particles, supposedly spherical, allows to validate this hybrid approach combining AFM and SEM. First, the uncertainty budget associated with the measurement of nanoparticles by SEM was established. We have demonstrated that the main contribution to the uncertainty budget is the size of the electron beam, which is difficult to measure. Two methods, based on Monte Carlo modelling, have been developed to evaluate the influence of this parameter on the SEM measurement. The first is based on the comparison between experimental and simulated signals. The second is based on the segmentation of the SEM images using a remarkable point, not influenced by the dimensions of the electron beam. These two methods have shown that the error related to the beam size is largely overestimated using conventional image segmentation tools. From these results, a direct comparison of AFM and SEM measurements was performed on the same particles. A systematic discrepancy was observed between the two techniques for the smallest particles related to their non-sphericity. The use of a third technique, transmission electron microscopy (TEM), confirms these observations. Finally, the hybrid approach has been implemented for measuring the three characteristic dimensions of the complex-shaped nano-objects with very non-spherical morphology

Стилі APA, Harvard, Vancouver, ISO та ін.

5

Foulon, Anthony. "Détermination de la signature acoustique de la corrosion des composites SVR (stratifiés verre résine)." Thesis, Compiègne, 2015. http://www.theses.fr/2015COMP2204/document.

Повний текст джерела

Анотація:

Depuis les années 80, Les matériaux composites stratifié verre résine (SVR) ont été utilisés pour la construction des tuyaux et des réservoirs dans l'industrie chimique, y compris pour le stockage d’acides. Ce matériau composite présente une résistance supérieure à la corrosion. Cependant, des auteurs ont observé des ruptures accidentelles de réservoirs (horizontaux et verticaux) contenant des acides (chlorhydrique et sulfurique). Ces ruptures sont attribuées au mécanisme de corrosion sous contrainte (CSC). La corrosion des fibres de verre dans une solution acide est moins connue mais reste très importante. Ce mécanisme de corrosion, appelée désalcalinisation de la fibre peut provoquer la fissuration de la fibre de verre.Des essais de corrosion avec de l’acide chlorhydrique (37%) ont été effectués sur éprouvette SVR. Ces essais de corrosion ont été suivis par émission acoustique. Les observations au microscope électroniques à balayage (MEB) et les analyses physico-chimiques confirment la corrosion de fibres de verre dans une solution de HCl. L’utilisation de la micro-tomographie nous montre que cette technique permet d’avoir une information sur la profondeur d’attaque du matériau.Une approche statistique est utilisée pour caractériser les paramètres de la salve d’émission acoustique afin de les séparer. Le Clustering est fait en utilisant la méthode des k-moyennes. Trois classes d’émission acoustique distinctes ont ainsi été identifiées. L’analyse croisée de l’émission acoustique et des observations ont permis de relier les classes observées aux conséquences de la corrosion du SVR
Since the 1980, Glass Reinforced Plastic (GRP) has been used for construction of pipes and tanks in the chemical industry, including the storage of mineral acids. This composite material offers superior and cost effective corrosion resistance. However, authors found accidental breakage of tanks (horizontal and vertical) containing mineral acids (hydrochloric and sulphuric). These failures are attributed to environmental stress-corrosion cracking (ESCC) mechanism. The corrosion of glass fibers in mineral acid solution is less known but very important. The mechanism of the corrosion, called leaching, is thought to induce tensile stresses in the surface of the glass. These stresses could be large enough to cause cracking of the fiber glass.Corrosion tests have been performed on GRP specimen. Aggressive environments used are hydrochloric acid (37%) This environment is known to react with E-glass. Corrosion tests have been monitored by acoustic emission.SEM observations and physicochemical analysis confirm the corrosion of glass fibers in HCl solution. The use of micro - tomography allows to have information on the depth of degradation of the material.Statistical approaches are used to characterize hit’s parameters. Clustering is made by using k-mean’s method. Three distinct acoustic emission classes are identified. Thanks to SEM observations and acoustic emission results, clusters can be assigned to the appearance of minor defects in the material

Стилі APA, Harvard, Vancouver, ISO та ін.

6

Frallonardo, Paola. "Ruolo dei cristalli di calcio nell'infiammazione. Studio del liquido sinoviale mediante Microscopia Elettronica a Scansione, in pazienti con artrosi del ginocchio." Doctoral thesis, Università degli studi di Padova, 2014. http://hdl.handle.net/11577/3423989.

Повний текст джерела

Анотація:

Background Osteoarthritis (OA) is a chronic joint disease characterized by a progressive loss of articular cartilage, osteophyte formation, thickening of the subchondral bone, along with frequent signs of intraarticular inflammation with moderate synovitis. The role of inflammation in the pathogenesis of OA is becoming increasingly evident especially in its early phases The pathogenesis is not yet clear. In the last years the role of calcium crystals in structural progression of OA was considered. Calcium pyrophosphate (CPP) and basic calcium phosphate (BCP) are the most common calcium crystals detected in OA. The role of calcium crystals in synovial inflammation and their significance in OA progression in this context continues to be debatable. Objective The aim of this study was to evaluate the presence of calcium crystals in synovial fluid using ultrasensitive analysis with scanning electron microscopy (SEM) at early and later stages of symptomatic and radiographic knee OA (KOA), to investigate the presence of CPP and BCP crystals in synovial fluid (SF) of patients with KOA and their relationship with main indices of clinical and synovial activities. Methods SF was collected from 120 patients affected with KOA, 84 females, mean age 68±10.7 yrs (range 50-93 yrs). All patients answered at three disease-specific questionnaires: WOMAC, Lequesne algofunctional index and VAS. SF calcium crystals analysis was performed by regular and polarized light microscopy. Alizarin red stain was performed in all speciments. As BCP crystals are more challenging to detect and are too small to be seen by light microscopy, SEM a highly specialized technique, has been used to define calcium-containing crystals. All patients underwent to knee ultrasound (US) with power Doppler. Everyone were undergoing knee X-ray and they were classified according to the radiological grade of Kellgren and Lawrence (KL). Results CC were detected by SEM in 62/120 (51.6%) of the patients. The patients with CC were older (p=0.036), had a greater difficulty in moving (p=0.0041); they had a higher PMN percentage in SF (0.0041) and a positive power Doppler statistically significant (p=<0.0001). CPP were positive in 37/120 patients (30%) by SEM. In patients with CPP, we found a significant difference with regard to age (p=0.0002), disease duration (p=0.041), pain (p=0.039), KL radiographic score (p=0.0334), US power Doppler (p=0.0001). BCP were detected by SEM in 33/120 pazienti (27.5%). In patients with BCP+ we found a significant difference with regard to WOMAC (p=0.0001), pain (p=0.0001), stiffness (p<0.0001), functional impairment (p<0.0001), Lequesne index (p<0.0001), Visual Analogic Scale (<0.0004), US power Doppler (p<0.0001). In the group of patients BCP+ we found a correlation between KL score and disease duration. On the basis of disease duration, the patients were subdivided into three groups I <1yr (49); II 1-5 yrs (27); III > 5 yrs (44). The main differences were found with regard to age, US power Doppler. The KL score were worse in III group. In the I group (early KOA) with CPP+ and BCP+ was found significant difference with regard to US Power Doppler (p=0.0039). In the III group we not found significant differences between CPP+ and CPP-. In the I group (early KOA) in patients with BCP+ we found a significant difference with regard to pain (p=0.0002), stiffness (p=0.045), functional impairment (p=0.0014), WOMAC (p=0.0002) US power Doppler (p=0.0009). Conclusion In us study we evaluated the presence of CC in LS of patients with KOA, using ultrasensitive method as the SEM. CC+ was found to be correlated with severe clinical status and worse imaging findings, and PD resulted positive in patients with CC+ by SEM. CC+ appeared to be an expression of worse evolution and aggressive KOA. Particularly intriguing BCP+in the early group. The presence of BCP is associated with a greater degree of inflammation.
Introduzione L'artrosi (OA) è una malattia articolare cronica, caratterizzata da lesioni degenerative e produttive a carico della cartilagine delle articolazioni diartrodiali. Tuttavia, grande interesse della comunità scientifica si è sviluppato attorno alla componente infiammatoria caratterizzata da una modesta sinovite. In questo ambito negli ultimi anni notevole interesse è stato rivolto al ruolo che possono svolgere i cristalli di calcio (CC) nella patogenesi dell'OA, ma se questi contribuiscano direttamente al danno cartilagineo o ne siano più semplicemente un epifenomeno è ancora argomento di dibattito. I CC più comuni nell'OA sono quelli di pirofosfato di calcio diidrato, dall'inglese calcium pyrophosphate (CPP) e quelli generalmente definiti di fosfato basico di calcio (BCP dall'inglese basic calcium phosphate) che comprendono idrossiapatite, octacalcio fosfato e tricalcio fosfato. Scopo dello studio Indagare con metodica ultrasensibile Microscopia Elettronica a Scansione (SEM) la presenza di cristalli di CPP e di BCP nel liquido sinoviale (LS) di pazienti con artrosi del ginocchio (GOA) e sui loro rapporti con i principali indici di attività e di gravità di malattia. Pazienti e metodi Sono stati sottoposti ad artrocentesi del ginocchio ed esame del LS 120 pazienti, 84 femmine, età media 68±10,7 anni (range 50-93). In ciascun paziente sono stati valutati i principali indici clinici di malattia attraverso i questionari WOMAC, Lequesne e VAS; su tutti è stato eseguito esame ultrasonografico (US) dell'articolazione colpita con tecnica power Doppler. Tutti i pazienti soddisfacevano i criteri dell'American College of Rheumatology per OA e avevano una diagnosi radiologica di GOA secondo i criteri di Kellgren e Lawrence (KL). Nel LS sono stati valutati la conta totale leucocitaria (GB), la percentuale di polimorfonucleati (PMN), e la presenza di eventuali CC. La ricerca di CC è stata condotta con microscopio a luce polarizzata, utilizzando anche il compensatore rosso di I ordine; veniva eseguita la colorazione aspecifica con rosso di Alizarina. La microscopia a scansione elettronica (SEM) è stata utilizzata come tecnica ultrasensibile per meglio identificare e caratterizzare i CC. Risultati Il nostro studio ci ha consentito con metodica ultrasensibile (SEM) di rilevare i CC nel LS in 62/120 pazienti (51,6%). Da una prima valutazione delle differenze tra le due popolazioni, i pazienti con CC rispetto a quelli senza erano più anziani (p=0,036), avevano una maggior difficoltà di movimento (p=0,0041); presentavano una % di PMN nel LS superiore (0,0041) e una presenza di power Doppler statisticamente significativa (p=<0,0001). I CPP sono stati evidenziati al SEM in 37/120 pazienti (30%). Nei pazienti con CPP+ abbiamo riscontrato una differenza significativa per età (p=0,0002), durata di malattia (p=0,041), dolore (p=0,039), grado KL (p=0,0334), power Doppler (p=0,0001). Nei pazienti con CPP+ abbiamo riscontrato una correlazione tra loro degli indici clinici: dolore, rigidità , difficoltà , WOMAC, Lequesne. Una correlazione inversa è stata rilevata tra il power Doppler e la conta totale di GB. I BCP sono stati evidenziati al SEM in 33/120 pazienti (27,5%). Nei pazienti con BCP+ abbiamo riscontrato una differenza significativa per WOMAC (p=0,0001), dolore (p=0,0001), rigidità (p<0,0001), difficoltà (p<0,0001), Lequesne (p<0,0001), VAS (<0,0004), power Doppler (p<0,0001); per l'età è stato riscontrato un trend positivo senza significatività statistica (p=0,046). Per quanto riguarda, inoltre, i pazienti con BCP+ abbiamo rilevato una correlazione tra KL e durata di malattia. Abbiamo inoltre suddiviso i pazienti in 3 gruppi in base alla durata di malattia: I gruppo (49) con durata di malattia < 1 anno; II gruppo (27) tra 1-5 anni; III gruppo (44) con durata di malattia > 5 anni. Le differenze principali fra i pazienti dei 3 gruppi sono state riscontrate per l'età , maggiore nel gruppo III, nella positività al power Doppler. La gravità del quadro radiografico erano peggiori nel III gruppo. Quando abbiamo suddiviso i tre gruppi per la presenza di CPP e BCP, nel I gruppo differenze significative si osservavano per il Power Doppler (p=0,0039); al limite della significatività il dolore. Nel III gruppo non abbiamo riscontrato differenze significative tra la presenza e assenza di CPP. Considerando i BCP nel I gruppo sono state riscontrate differenze significative nei BCP+ nei confronti dei BCP- per il dolore (p=0,0002), la rigidità (p=0,045), la difficoltà (p=0,0014), il WOMAC (p=0,0002) e per il power Doppler (p=0,0009). Conclusioni Questo è il primo studio che permette di valutare il significato della presenza di CC nel LS di pazienti affetti da GOA, utilizzando metodica ultrasensibile come il SEM in una popolazione piuttosto ampia di pazienti. Particolarmente intrigante risulta l'analisi di pazienti con BCP nel gruppo early. La presenza dei BCP è sicuramente associata a un grado maggiore di infiammazione e smentirebbe studi precedenti in cui veniva suggerito che i BCP fossero un epifenomeno e non influenzassero il tipo di malattia.

Стилі APA, Harvard, Vancouver, ISO та ін.

7

Ait, Laasri Hicham. "Étude et élaboration de matériaux ferroélectriques sans plomb pour le stockage de l'énergie électrique." Thesis, Littoral, 2018. http://www.theses.fr/2018DUNK0528/document.

Повний текст джерела

Анотація:

Les matériaux ferroélectriques présentant une permittivité diélectrique élevée et de faibles pertes diélectriques présentent un grand intérêt pour la réalisation de condensateurs et le stockage de l'énergie électrique. Les propriétés structurales et diélectriques influencent les paramètres ferroélectriques tels que la polarisation maximale du matériau Pm et la polarisation rémanente Pr sous l'effet d'un champ électrique appliqué Em. Ce mémoire propose d'étudier les propriétés structurales, diélectriques et ferroélectriques des céramiques dérivées de BaTiO₃ (BT) et SrTiO₃ (ST) ainsi que des films épais PVDF pur et composites tels que PVDF/BT et PVDF/BZT. Les céramiques ont été synthétisées par la méthode de la réaction solide et le procédé sol-gel. La substitution dans les sites-A ou les sites-B du matériau BaTiO₃ avec des cations tels que Ca ²⁺, Sr²⁺ and Zr⁴⁺ réduit la densité d'énergie électrique stockée Wd et augmente l'efficacité de stockage énergétique η. La céramique BaZr₀.₅Ti₀.₅O₃ (BZT0.5) présente l'efficacité de stockage énergétique la plus élevée (η=75%). La substitution dans les sites-A du matériau SrTiO₃ avec 40% de cations Ca²⁺ diminue la permittivité diélectrique (ε'∽200), mais cette permittivité est cependant plus stable sur une large gamme de fréquence [100 Hz-1 GHz]. La céramique Sr₀.₆Ca₀.₄TiO₃ préparée par voie sol-gel présente la densité d'énergie électrique stockée la plus élevée (Wd=0.149 J/cm³) sous l'action d'un champ électrique maximal élevé (Em=105 kV/cm). Les films épais à base de polymère PVDF ont été synthétisés par Spin-Coating. La permittivité diélectrique des films épais PVDF pur augmente avec l'apaisseur du film. L'incorporation de particules BT et BZT0.15 dans la matrice polymère PVDF augmente la permittivité diélectrique des films composites PVDF/BT (ε'=32 pour 30% de particules BT) et PVDF/BZT0.15 (ε'=32 pour15% de particules BZT)
Ferroelectric materials with a high dielectric permittivity and low dielectric losses are very attractive for the realization of capacitors and for electrical energy storage. To improve the electrical energy density Wd, the structural and dielectric properties influence the ferroelectric parameters such as the maximum polarization Pm and the remanent polarization Pr under an applied electric field Em. This manuscript proposes to study the structural, dielectric and ferroelectric properties of ceramics derived from BaTiO₃ (BT) and SrTiO₃ (ST) as well as pure PVDF thick films and composites such as PVDF/BT and PVDF/BZT. The ceramics were synthesized by the solid state reaction reaction route and the sol-gel process. The subsitution in the A-sites or B-sites of the BaTiO₃ material with cations such Ca²⁺, Sr²⁺ and Zr⁴⁺ reduces the electrical energy density Wd and increases the energy storage efficiency η. The ceramic BaZr₀.₅Ti₀.₅O₃ (BZT0.5) has the highest energy storage efficiency (η=75%). The substitution in the A-sites of SrTiO₃ material with 40% of Ca²⁺ cations reduces the dielectric permittivity (ε'∽200), but is more stable over a wide frequency range [100 Hz -1 GHZ]. The Sr₀.₆Ca₀.₄TiO₃ ceramic prepared by sol-gel process has the highest electrical energy density (Wd = 0.149 J/cm³) under an electrical field Em = 105 kV/cm. The PVDF thick films were synthesized by Spin-Coating. The dielectric permittivity of pure PVDF thick films increases when increasing the thickness. The addition of BT and BTZ0.15 particles in the PVDF polymer matrix increases the dielectric permittivity of the composite PVDF/BT thick films (ε'=32 for 30% of BT particles) and PVDF/BZT0.15 ones (ε'=32 for 15% of BZT particles)

Стилі APA, Harvard, Vancouver, ISO та ін.

8

Davies, D. G. "Scanning electron acoustic microscopy." Thesis, University of Cambridge, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.304042.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

9

Zhao, Dan. "Study on the creep behavior of clay under complex triaxial loading in relation to the microstructure." Thesis, Université de Lorraine, 2017. http://www.theses.fr/2017LORR0372/document.

Повний текст джерела

Анотація:

Cette recherche vise à analyser et à identifier, par des essais, le comportement au fluage d'une argile de type kaolinite sous un état de contraintes triaxial. Une investigation fine de l’état microstructural, avant et après fluage, a par ailleurs été réalisée. Les résultats macroscopiques ont permis de constater que des phénomènes de dilatance et de contractante s’amplifient pendant le fluage. Les résultats montrent également que la position, sur le plan des contraintes (p'-q), du niveau de contrainte vis-à-vis des différents domaines volumétriques, contrôle le développement de la déformation au fluage et du taux de déformation. Les résultats de MEB ont montré que l'évolution microstructurale de l'argile, après le chargement mécanique, dépend fortement de l'histoire du chargement
The objective of this research is to analyze the creep behavior of a typical clay along triaxial tests, moreover, to analyze the microstructural mechanisms of creep. Analysis on the macroscopic results ascertained that both dilatancy and contractancy phenomena could occur during creep. The magnitude of the dilatancy/contractancy during creep was guided by the test conditions: stress level and the over consolidation ratio, which specifically governed the direction of the volumetric strain variations. The results of SEM indicated that the microstructural evolution of the clay after the mechanical loading depend on the stress history. Afterwards, the structural evolution in creep phase depends on the structural pattern developed in monotonic loading

Стилі APA, Harvard, Vancouver, ISO та ін.

10

Rima, Wael. "Apport de la microscopie electronique dans la compréhension des mécanismes d’interactions entre nanoparticules et cellules biologiques." Thesis, Lyon, INSA, 2012. http://www.theses.fr/2012ISAL0131/document.

Повний текст джерела

Анотація:

Parmi les nanoparticules aptes à accompagner la radiothérapie en clinique, les nanoparticules à base d’oxyde de gadolinium paraissent pertinentes, de part leur multimodalité en imagerie et leur effet radiosensibilisant prouvé in vitro et in vivo. Cet effet de radiosensibilisation est exceptionnel notamment sur des cellules cancéreuses radiorésistantes de la lignée SQ20B (carcinome squameux tête et cou) et uniquement pour des doses modérées de nanoparticules (aux alentours de 0.6 mM en Gd). Les clichés de microscopie électronique ont montré que ce maximum de radiosensibilisation est dû à une internalisation maximale des particules dans le cytoplasme, notamment par macropinocytose. Ce mécanisme d’internalisation est caractérisé par la formation de vésicules de grandes tailles, ou macropinosomes. Il se produit suivant deux étapes : la formation d’agglomérats de nanoparticules à proximité de la membrane cellulaire puis la récupération de ceux-ci par les lamellipodes de la cellule. La première étape est fortement dépendante des caractéristiques physicochimiques des particules, plus particulièrement leur potentiel zêta qui détermine la taille de l’agglomérat, et de la distance les séparant de la cellule. Dans des gammes de taille et de distance à la membrane optimales aux concentrations modérées, l’agglomérat peut être récupéré par les lamellipodes de la cellule. Il s’en suit une protubérance sur la membrane plasmique formant un macropinosome contenant les agglomérats de nanoparticules. Cet endosome précoce suivra ensuite le schéma d’endocytose classique dans le cytoplasme en fusionnant avec des corps multivésiculaires, uniquement visible en microscopie électronique à transmission, pouvant contenir des enzymes de dégradation détruisant leur contenu. Ces enzymes rendent le pH acide à l’intérieur de la vésicule. Plus les nanoparticules sont proches du noyau cellulaire plus leur effet radiosensibilisant sera efficace. Les espèces oxygénées réactives (ROS) et les électrons Auger et secondaires peuvent atteindre l’ADN du noyau plus facilement. A faibles doses (<0.4 mM) très peu de nanoparticules sont internalisées et un effet linéaire de la radiosensibilisation est observé jusqu'à 0.6 mM. A fortes doses (> 0.7 mM) les nanoparticules forment une couronne autour de la membrane cellulaire agissant comme écran, empêchant ainsi les ROS et les électrons générés de pouvoir atteindre l’ADN et induire des cassures, le noyau étant situé à quelques micromètres de la membrane cellulaire. Les résultats obtenus ouvrent la voie sur la nécessité de contrôler l'internalisation cellulaire des nanoparticules en contrôlant leur chimie, laissant envisager ainsi des opportunités prometteuses dans le domaine de la radiothérapie assistée par nanoparticules délivrant de faibles doses de radiation aux patients
Over the last few decades, nanoparticles have been studied in theranostic field with the objective of exhibiting a long circulation time through the body coupled to major accumulation in tumor tissues, rapid elimination, therapeutic potential and contrast properties. In this context, we developed sub-5 nm gadolinium-based nanoparticles that possess in vitro efficient radiosensitizing effects at moderate concentration when incubated with head and neck squamous cell carcinoma cells (SQ20B). Two main cellular internalization mechanisms were evidenced and quantified: passive diffusion and macro- pinocytosis. Whereas the amount of particles internalized by passive diffusion is not sufficient to induce in vitro a significant radiosensitizing effect, the cellular uptake by macropinocytosis leads to a successful radiotherapy in a limited range of particles incubation concentration. Macropinocytosis processes in two steps: formation of agglomerates at vicinity of the cell followed by their collect via the lamellipodia (i.e. the “arms”) of the cell. The first step is strongly dependent on the physicochemical characteristics of the particles, especially their zeta potential that determines the size of the agglomerates and their distance from the cell. These results should permit to control the quantity of particles internalized in the cell cytoplasm, promising ambitious opportunities towards a particle-assisted radiotherapy using lower radiation doses

Стилі APA, Harvard, Vancouver, ISO та ін.

11

Lafond, Clément. "Cartographie d’orientations cristallines à partir du contraste de canalisation en microscopie électronique à balayage." Thesis, Lyon, 2020. http://www.theses.fr/2020LYSEI031.

Повний текст джерела

Анотація:

Les cartographies d’orientations cristallines sont aujourd’hui un outil incontournable de la caractérisation des matériaux cristallins, notamment des métaux. Les cartographies d’orientations permettent entre autre de quantifier la nature et la taille de phases en présence, l’état de déformation ou la texture. Ce travail de thèse porte sur le développement d’une technique de cartographie des orientations basée sur l’analyse de contrastes du au phénomène de canalisation. Ces contrastes sont obtenus par imagerie aux électrons rétrodiffusés dans un Microscope Electronique à Balayage. La méthode se nomme eCHORD, pour electron CHanneling Orientation Determination. Dans un premier temps, la preuve de concept de la méthode est présentée sur un alliage d’aluminium et l’influence des paramètres d’acquisition est détaillée. Puis, deux problématiques particulières sont abordées : la cartographie d’échantillons de grandes tailles, ainsi que la cartographie à basse tension (1kV). La méthode eCHORD présente de grands intérêts pour l’analyse de matériaux peu conducteurs, habituellement très difficiles à cartographier avec les techniques actuelles, et ouvre de grandes perspectives pour l’étude de matériaux céramiques notamment
Crystalline orientation mapping is a key tool in material characterization, in particular for metals. For instance, orientation mapping allows to quantify the nature and size of phases in the presence, deformation state or texture. This thesis work focuses on the development of an orientation mapping approach based on the analysis of the electron channeling contrast. This contrast is obtained from electron back-scaterred imaging in a Scanning Electron Microscope. This method is called eCHORD for electron CHanneling Orientation Determination. First, the proof of concept of eCHORD is presented on an aluminum alloy and the influence of acquisition parameters is detailed. Then, two problematics are addressed: large scale orientation mapping and low voltage orientation mapping (1kV).eCHORD procedure present great interest concerning low conductivity materials on which orientation mapping are difficult to obtain and open wide perspective for ceramics studies

Стилі APA, Harvard, Vancouver, ISO та ін.

12

Alves, Luciana Mara Negrão. "Efeito da atmosfera de sinterização na resistência de união da porcelana com ligas de níquel-cromo e cobalto-cromo." Universidade de São Paulo, 2015. http://www.teses.usp.br/teses/disponiveis/58/58131/tde-19032015-085544/.

Повний текст джерела

Анотація:

O objetivo deste trabalho foi avaliar a influência de dois diferentes ambientes de sinterização (vácuo e argônio) sobre a resistência da união metaloceramica (RUMC) envolvendo diferentes ligas de metais básicos (Co-Cr e Ni-Cr) e uma porcelana odontológica, através do teste de flexão de três pontos, conforme preconizado pela ISO 9693:2012. As ligas estudadas foram Co-Cr: Remanium e Keragen e Ni-Cr: Verabond II e uma liga experimental “SR” . Foram obtidos 80 corpos de prova em forma tiras metálicas medindo 25 X 0,5 X 5 mm. Para esse ensaio, portanto, o número de corpos de prova foi o produto de 4 ligas x 2 condições de atmosfera de sinterização x 10 repetições. A parte metálica de todos os corpos de prova após a fundição foram usinados e jateados com óxido de alumínio (150μm) e a seguir tratados como preconizado pelo fabricante. O corpo cerâmico, com o auxílio de uma matriz, foi confeccionado na área central da tira, 8,0 X 3,0mm, apresentando 1,1mm de espessura, sendo 10 corpos de prova em cada ambiente de sinterização para cada tipo de liga. Os corpos de prova obtidos foram submetidos aos testes de flexão de três pontos na Máquina de Ensaios Mecânicos (EMIC) com velocidade de 1.0mm/min. para determinação da RUMC. Os valores da carga de ruptura obtidos em quilograma-força (Kgf) foram convertidos para Newton (N) e a partir disso foi calculado o valor da RUMC para cada corpo de prova, considerando o coeficiente de elasticidade de cada liga e a espessura exata de cada corpo de prova. Os dados obtidos (MPa) foram submetidos à análise estatística (ANOVA) e Bonferroni. A Análise de Variância indicou diferença estatisticamente significante para os fatores de variação ambiente (P=0,00), liga (P=0,009) e entre as interações ambiente de sinterização e liga (P=0,000). Na sinterização a vácuo as ligas Keragen, SR e Verabond II apresentaram maiores valores de RUMC do que o argônio. Para a liga Remanium, não houve diferença entre a sinterização em argônio e a sinterização a vácuo. Dentre os grupos sinterizados no argônio não houve diferença estatisticamente significante entre as ligas. Entretanto, no vácuo a liga Remanium apresentou menor valor de RUMC do que as demais ligas, que não apresentaram diferença entre si. Os corpos de prova, após os ensaios de flexão, foram submetidos a análise em microscopia optica, MEV e EDS para avaliar e registrar tipo de falha que sofreram. De acordo com a MO, houve predomínio de fraturas mistas. Os corpos de prova de Co-Cr (Remanium e Keragen), independende do ambiente de sinterização, apresentaram uma fina camada de óxido no corpo cerâmico, o que foi comprovado pelo EDS, com maior presença de íons Cr nessas regiões, já os grupos SR e Verabond II, apresentaram maior quantidade de opaco aderido em suas tiras metálicas. A MEV comprovou os achados da MO, onde foi possível encontrar grandes ilhas de material cerâmico nas ligas de Ni-Cr. A sinterização em argônio influenciou negativamente a RUMC dos pares metalocerâmicos confeccionados em Ni-Cr e na liga Keragem
The aim of this study was to evaluate the influence of two different firing atmosphere (vacuum and argon) on the metalceramic bond strength (MCBS) involving different base metal alloys (Co-Cr and Ni-Cr) and a dental porcelain through three-point bending test, as recommended by ISO 9693: 2012. Co-Cr alloys studied were: Remanium and Keragen and Ni-Cr: Verabond II and an experimental alloy \"SR\". 80 specimens were obtained in metallic form strips measuring 25X0.5 X 5.0 mm. For this test, therefore, the number of specimens was the product of 4 x 2 alloy sintering atmosphere conditions x 10 replicates. The metal portion of all specimens were machined after casting and sandblasted with aluminum oxide (100μm) and then treated as recommended by the manufacturer. By using a matrix, the ceramic body was made in the central area of the strip, 8.0 x 3.0 mm, it was made 1.1 mm thickness, 10 specimens in each sintering environment for each type of alloy. The specimens obtained were tested for three-point bending in a universal testing machine with a speed of 1.0mm / min. to determine MCBS. The values of the tensile strength obtained in kilogramforce (kgf) were converted into Newton (N) and from this the value of MCBS for each specimen was calculated, considering the coefficient of elasticity of each league and the exact thickness of each specimen. The data (MPa) were subjected to statistical analysis (ANOVA) and Bonferroni. The analysis of variance indicated statistically significant difference for the environment factors of firing atmosphere (P = 0.00) and alloy (P = 0.009). There was a statistically significant difference in the interaction factors for firing atmosphere x alloy (P = 0.000). In the vacuum Keragen, SR and Verabond II alloys showed higher MCBS than argon. To Remanium, there was no difference between the sintering in argon and vacuum. Among the groups sintered in argon there was no statistically significant difference between the alloys. However, the vacuum Remanium showed the lowest RUMC than other alloys, which showed no difference between them. The specimens after the bending tests, were subjected to analysis in optical microscopy, SEM and EDS to assess and record type of failure they suffered. According to the MO was predominantly mixed fractures. Specimens of Co-Cr (Remanium and Keragen) independende the atmosphere firing, showed a thin oxide layer on the ceramic body, which was confirmed by EDS, with greater presence of Cr in these regions, since the SR groups and Verabond II, presented more opaque stuck in their metal strips. SEM confirmed the findings of MO, where it was possible to find large islands of ceramic material in Ni-Cr alloys. The sintering in argon negatively influenced MCBS metalceramic of pairs made of Ni-Cr alloy and Keragem

Стилі APA, Harvard, Vancouver, ISO та ін.

13

Snella, Michael T. "Drift correction for scanning-electron microscopy." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/62605.

Повний текст джерела

Анотація:

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2010.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student submitted PDF version of thesis.
Includes bibliographical references (p. 91-92).
Scanning electron micrographs at high magnification (100,000x and up) are distorted by motion of the sample during image acquisition, a phenomenon called drift. We propose a method for correcting drift distortion in images obtained on scanning electron and other scanned-beam microscopes by registering a series of images to create a drift-free composite. We develop a drift-distortion model for linear drift and use it as a basis for an affine correction between images in the sequence. The performance of our correction method is evaluated with simulated datasets and real datasets taken on both scanning electron and scanning helium-ion microscopes; we compare performance against translation only correction. In simulation, we exhibit a 12.5 dB improvement in SNR of our drift-corrected composite compared to a non-aligned composite, and a 3 dB improvement over translation correction. A more modest 0.4 dB improvement is measured on the real image sets compared to translation correction alone.
by Michael T. Snella.
M.Eng.

Стилі APA, Harvard, Vancouver, ISO та ін.

14

McKeown, Karen. "Using scanning electron microscopy (SEM) and transmission electron nncroscopy." Thesis, Queen's University Belfast, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.492019.

Повний текст джерела

Анотація:

Electron impact excitation collisions are important processes for spectral line formation of plasmas. The work undertaken in this thesis focuses on such collisions involving Li-like ions, important in both astrophysical and magnetically confined plasmas. By having reliable atomic and collisional data, such as energy levels, radiative rates and excitation rate coefficients, it is possible to generate models to describe such plasmas. The atomic data were calculated using the General-Purpose Relativistic Structure Program (GRASP; Dyall et al 1989), for several Li-like ions, namely S XIV, Ar XVI, Ca XVIII, Ti XX, Cr XXII, Fe XXIV and Ni XXVI. Including relativistic effects in the calculations leads to the generation of 24 fine-structure energy levels when orbitals with 11,/ =:; 5 are considered. Oscillator strengths, were generated for all 276 transitions arising amongst these levels when maintaining a frozen core of Is2 Ã‚Â• Comparisons were made with both theoretical and experimental data available from the publications of Nahar & Pradhan (1999), Nahar (2002), Whiteford et al (2002) and Del Zanna (2006), along with NIST data. Collisional calculations were performed for Fe XXIV, an abundant ion in solar and fusion plasmas, which has the potential to be employed in photo-pumping schemes for X-ray lasers. The calculations were performed using the Dirac Atomic Relativistic Code (DARC; Ait-Tahar, Grant & Norrington 1996), which is a fully relativistic code based on R-matrix theory. In addition to carrying out these calculations, DARC was further developed to provide a solution to the problem of convergence which affects optically allowed transitions in the above threshold energy region. Comparison of these results was made with data already available in the literature, with discrepancies being highlighted and discussed. The work of Berrington & Tully (1997) did not include the n=5 orbital, and comparisons with the results presented here showed how important these are for low temperatures. Discrepancies between this work and that of Whiteford et al (2002) were also identified. Despite being given access to their unpublished data, the source of the identified discrepancies remains elusive. The problems identified require further investigation which lies beyond the scope and resources of the present work.

Стилі APA, Harvard, Vancouver, ISO та ін.

15

Findlay, Scott David. "Theoretical aspects of scanning transmission electron microscopy /." Connect to thesis, 2005. http://eprints.unimelb.edu.au/archive/00001057.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

16

Ciechonski, Rafal. "Growth and characterization of SiC and GaN." Doctoral thesis, Linköpings universitet, Materiefysik, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-10314.

Повний текст джерела

Анотація:

At present, focus of the SiC crystal growth development is on improving the crystalline quality without polytype inclusions, micropipes and the occurrence of extended defects. The purity of the grown material, as well as intentional doping must be well controlled and the processes understood. High-quality substrates will significantly improve device performance and yield. One of the aims of the thesis is further understanding of polytype inclusion formation as well as impurity control in SiC bulk crystals grown using PVT method also termed seeded sublimation method. Carbonization of the source was identified as a major reason behind the polytype inclusion occurrence during the growth. The aim of this work was further understanding of sublimation growth process of 4H-SiC bulk crystals in vacuum, in absence of an inert gas. For comparison growth in argon atmosphere (at 5 mbar) was performed. The effect of the ambient on the impurity incorporation was studied for different growth temperatures. For better control of the process in vacuum, tantalum as a carbon getter was utilized. The focus of the SiC part of the thesis was put on further understanding of the PVT epitaxy with an emphasis on the high growth rate and purity of grown layers. High resistivity 4H-SiC samples grown by sublimation with high growth rate were studied. The measurements show resistivity values up to high 104 cm. By correlation between the growth conditions and SIMS results, a model was applied in which it is proposed that an isolated carbon vacancy donor-like level is a possible candidate responsible for compensation of the shallow acceptors in p-type 4H-SiC. A relation between cathodoluminescence (CL) and DLTS data is taken into account to support the model. To meet the requirements for high voltage blocking devices such as high voltage Schottky diodes and MOSFETs, 4H-SiC epitaxial layers have to exhibit low doping concentration in order to block reverse voltages up to few keV and at the same time have a low on-state resistance (Ron). High Ron leads to enhanced power consumption in the operation mode of the devices. In growth of thick layers for high voltage blocking devices, the conditions to achieve good on-state characteristics become more challenging due to the low doping and pronounced thicknesses needed, preferably in short growth periods. In case of high-speed epitaxy such as the sublimation, the need to apply higher growth temperature to yield the high growth rate, results in an increased concentration of background impurities in the layers as well as an influence on the intrinsic defects. On-state resistance Ron estimated from current density-voltage characteristics of Schottky diodes on thick sublimation layers exhibits variations from tens of mΩ.cm2 to tens of Ω.cm2 for different doping levels. In order to understand the occurrence of high on-state resistance, Schottky barrier heights were first estimated for both forward and reverse bias with the application of thermionic emission theory and were in agreement with literature reported values. Decrease in mobility with increasing temperature was observed and its dependencies of T–1.3 and T–2.0 for moderately doped and low doped samples, respectively, were estimated. From deep level measurements by Minority Carrier Transient Spectroscopy (MCTS), an influence of shallow boron related levels and D-center on the on-state resistance was observed, being more pronounced in low doped samples. Similar tendency was observed in depth profiling of Ron. This suggests a major role of boron in a compensation mechanism. In the second part of the thesis growth and characterization of GaN is presented. Excellent electron transport properties with high electron saturate drift velocity make GaN an excellent candidate for electronic devices. Especially, AlGaN/GaN based high electron mobility transistors (HEMT) have received an increased attention in last years due to their attractive properties. The presence of strong spontaneous and piezoelectric polarization due to the lattice mismatch between AlGaN and GaN is responsible for high free electrons concentrations present in the vicinity of the interface. Due to the spatial separation of electrons and ionized donors or surface states, 2DEG electron gas formed near the interface of the heterostructure exhibits high sheet carrier density and high mobility of electrons. Al0.23Ga0.77N/GaN based HEMT structures with an AlN exclusion layer on 100 mm semiinsulating 4H-SiC substrates have been grown by hot-wall MOCVD. The electrical properties of the two-dimensional electron gas (2DEG) such as electron mobility, sheet carrier density and sheet resistance were obtained from Hall measurements, capacitance-voltage and contact-less eddy-current techniques. The effect of different scattering mechanisms on the mobility have been taken into account and compared to the experimental data. Hall measurements were performed in the range of 80 to 600 K. Hall electron mobility is equal to 17140 cm2(Vs)-1 at 80 K, 2310 cm2(Vs)-1 at room temperature, and as high as 800 cm2(Vs)-1 at 450 K, while the sheet carrier density is 1.04x1013 cm-2 at room temperature and does not vary very much with temperature. Estimation of different electron scattering mechanisms reveals that at temperatures higher than room temperature, experimental mobility data is mainly limited by optical phonon scattering. At relevant high power device temperature (450 K) there is still an increase of mobility due to the AlN exclusion layer. We have studied the behaviour of Ga-face GaN epilayers after in-situ thermal treatment in different gas mixtures in a hot-wall MOCVD reactor. Influence of N2, N2+NH3 and N2+NH3+H2 ambient on the morphology was investigated in this work. The most stable thermal treatment conditions were obtained in the case of N2+NH3 gas ambients. We have also studied the effect of the increased molar ratio of hydrogen in order to establish proper etching conditions for hot-wall MOCVD growth.

Стилі APA, Harvard, Vancouver, ISO та ін.

17

Inácio, Estela Maris. "Impactos da deriva do herbicida 2,4-D em culturas sensíveis." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/11/11136/tde-30092016-105412/.

Повний текст джерела

Анотація:

O herbicida 2,4-D é utilizado principalmente para o controle de plantas daninhas em condições de pós-emergência em culturas em que o herbicida é seletivo, bem como no manejo da vegetação em pré-plantio; no entanto, devido a suas características físico-químicas, pode ocasionar danos às culturas vizinhas sensíveis, através dos fenômenos de deriva da molécula durante as pulverizações. Sendo assim, é de fundamental importância o conhecimento técnico dos impactos causados pela deriva do herbicida 2,4-D em culturas sensíveis. No entanto, as informações existentes na literatura para dar suporte às possíveis liberações futuras de culturas resistentes a este herbicida são escassas. Os experimentos foram conduzidos em casa-de-vegetação e laboratório da Escola Superior de Agricultura \"Luiz de Queiroz\" - Universidade de São Paulo - ESALQ/USP. Os objetivos da presente pesquisa foram: (i) avaliar a influência do herbicida 2,4-D no desenvolvimento das culturas do algodão e soja em, diferentes estádios fenológicos, (ii) avaliar os possíveis danos causados pela deriva do herbicida 2,4-D no crescimento e desenvolvimento das culturas de algodão e soja, em diferentes estádios fenológicos, e (iii) observar através da microscopia eletrônica de varredura possíveis alterações nas estruturas foliares das plantas de algodão e soja após o contato com o herbicida. Curvas de doseresposta foram obtidas a partir de experimentos conduzidos em casa-de-vegetação. Para isso, foram conduzidos dois ensaios, sendo os tratamentos com o herbicida aplicado quando as plantas atingiram os estágios fenológicos: V2 (segundo nó vegetativo); R1 (início da floração para a cultura de soja), F1 (início da floração da cultura de algodão); e R6 (vagens da soja com enchimento pleno e folhas verdes) e C1 (algodão no final do florescimento efetivo e frutificação plena). No primeiro experimento os tratamentos utilizados foram: 0D (testemunha), 0,25D, 0,5D, 1D, 2D e 4D, sendo D a dose recomendada do 2,4-D, e no segundo experimento as doses utilizadas foram: 0D, 1D, 0,1D, 0,01D, 0,001D, 0,0001D. Utilizando as mesmas plantas da primeira etapa da pesquisa foram feitas amostragens das folhas para a caracterização foliar através de microscopia eletrônica de varredura. O 2,4-D comprometeu significativamente o crescimento e desenvolvimento das plantas de soja em todos os estádios fenológicos, com fitotoxicidade superiores a 65%. Resultados semelhantes foram obtidos na cultura do algodão, onde o menor nível de dano foi de 42,5% relativa à aplicação do herbicida no estádio fenológico R6 na dose de 0,25D. Observando os tratamentos nas subdoses do herbicida, na soja, verificou se que a maior porcentagem de fitotoxicidade foi obtida na dose de 0,1D, em todos os estádios fenológicos, os níveis de dano foram superiores a 50% na última avaliação. Em relação à cultura do algodão resultados semelhantes foram obtidos, com exceção do estádio fenológico R6, quando todos os estádios apresentaram porcentagem de fitotoxicidade superior a 40%. Em relação às características foliares do algodão e soja após aplicações de 2,4-D através da análise das características foliares em microscópio eletrônico de varredura, após a aplicação do herbicida, observou-se que o produto promoveu alterações nas estruturas foliares de algodão e soja em todas as doses estudadas.
The herbicide 2,4-D is used to control weeds in post-emergence conditions in crops which it is selective, as well in pre-planting vegetation management, however, due to its physical-chemical characteristics it may cause damage to susceptible neighbor crops, by the drift of the molecule during the spray. Therefore, it is of fundamental importance the technical knowledge of the impacts caused by the drift of the molecule during the application. The experiments were conducted in greenhouse and in the laboratory of the College of Agriculture \"Luiz de Queiroz\". So the objectives of this study were (i) to evaluate the possible damage caused by 2,4-D in the initial development of cotton and soybean crops (ii) to evaluate the possible damage caused by 2,4-D drift in the initial development of cotton and soybean crops and (iii) to observe by electron microscopy scanning possible changes in leaf structure of plants cotton and soybeans after contact with the herbicide. Dose-response curves were obtained from experiments conducted in the greenhouse. For that, it was conducted two trials, being the treatments with the herbicide sprayed when the plants reached the following phenological stages: V2 (second vegetative node); R1 (beginning of flowering for soybeans) and F1 (beginning of flowering in cotton); and R6 (soybean pods with full filling and green leaves) and C1 (cotton at the end of effective flowering and fruiting full). In the first experiment the doses were related to the effect of doses (0D, 0.25D, 0.5D, 1D, 2D, 4D), where D is the recommended dose of the herbicide 2,4-D, and in the second experiment evaluated the effect of underdoses (0D, 1D, 0.1D, 0.01D, 0.001D and 0.0001D). Using the same plants of the first and second step of the research it was sampled leaves for the foliar characterization by scanning electron microscopy. The 2,4-D affected significantly the growth and development of the soybean plants in all phenological stages, with phytotoxicity superior to 65%. Similar results were obtained in cotton, where the lower level of damage was 42.5% on the application of the herbicide on growth stage R6 with the 0.25D dose. Regarding to the application of doses of the herbicide 2,4-D on soybeans, it was observed that the highest percentage of phytotoxicity to the crop was at the dose of 0.1D; in all growth stages the damage levels were above 50% in the last evaluation. Regarding to the cotton crop, similar results were obtained, except for the R6 growth stage, every stage showed higher percentage of phytotoxicity than 40%. Regarding to the characteristics of the cotton and soybean leaves following 2,4-D application, it was found that the product caused alterations in leaf structure of the plants in all doses.

Стилі APA, Harvard, Vancouver, ISO та ін.

18

Nellist, Peter David. "Image resolution improvement in scanning transmission electron microscopy." Thesis, University of Cambridge, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.361613.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

19

Stevens, Sam. "Understanding Porous Crystal Growth By Scanning Electron Microscopy." Thesis, University of Manchester, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.532223.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

20

Ramasse, Quentin Mathieu. "Diagnosis of aberrations in scanning transmission electron microscopy." Thesis, University of Cambridge, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.615070.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

21

Waller, Deborah. "Environmental scanning electron microscopy of freezing aqueous solutions." Thesis, University of Cambridge, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.613409.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

22

Harland, C. J. "Detector and electronic developments for scanning electron microscopy." Thesis, University of Sussex, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.370435.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

23

Ekwall, Hans. "Electron microscopy of cryopreserved boar spermatozoa : with special reference to cryo-scanning electron microscopy and immunocytochemistry /." Uppsala : Dept. of Clinical Sciences, Swedish University of Agricultural Sciences, 2007. http://epsilon.slu.se/2007123.pdf.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

24

Rocha, Milena Teixeira da. "Efeito do ambiente de sinterização na resistência de união de cerâmicas a ligas de níquel-cromo, cobalto-cromo e titânio comercialmente puro." Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/58/58131/tde-07122012-143258/.

Повний текст джерела

Анотація:

O objetivo deste trabalho foi avaliar o efeito do ambiente de sinterização vácuo e argônio na resistência de união (RUMC) de cerâmicas às ligas de Ni-Cr (Fit Cast SB), Co-Cr (Star Loy C) e titânio comercialmente puro (Tritan). A partir de uma matriz de teflon, foram obtidos 60 padrões de resina/cera em forma de cilindro, com 8 mm de comprimento e 5 mm de diâmetro. Os padrões foram incluídos e os anéis foram levados ao forno e submetidos a ciclos térmicos para a expansão do revestimento. Em seguida, os anéis para fundição em Ni-Cr e Co-Cr foram levados à máquina de fundição por indução eletrônica. Os anéis referentes ao titânio foram levados à máquina de fundição por arco voltaico. Após resfriamento dos anéis, as fundições foram desincluídas e jateadas com óxido de alumínio (100 μm). Depois de recortados dos canais de alimentação, os cilindros metálicos foram preparados para aplicação da cerâmica. Em seguida, foi realizada a aplicação e sinterização da cerâmica à vácuo ou em argônio. Para as ligas alternativas, foi utilizada a cerâmica IPS Classic V e para o titânio, a Triceram. Na sequência, os cilindros compostos pelo metal e disco cerâmico (5 mm de diâmetro e 2 mm de espessura) (n=10) foram submetidos aos ensaios de RUMC por cisalhamento na máquina de ensaios universais com célula de carga de 500 Kg e velocidade do travessão móvel de 0,5 mm/min. Após os ensaios, foram realizadas análises das fraturas por meio de microscopia óptica (MO) (15X) e microscopia eletrônica de varredura (MEV). Os dados de RUMC (MPa) obtidos foram analisados estatisticamente pelos testes ANOVA e Tukey (α=0,05). Os resultados demonstraram que a sinterização à vácuo propiciou obtenção de maiores valores (MPa) de RUMC (76,58) que a sinterização em argônio (51,31). Quanto às ligas avaliadas, as de Ni-Cr e Co-Cr apresentaram maiores valores de RUMC (71,32 e 71,28, respectivamente) que o titânio cp (49,23); sendo que entre elas não houve diferença estatística. Não houve interação entre os fatores avaliados. De acordo com a MO, houve predomínio de fraturas mistas. Segundo a MEV, os espécimes de Ni-Cr e titânio sinterizados a vácuo apresentaram maior rugosidade de superfície do que os sinterizados em argônio. Para a liga de Co-Cr não houve diferença na topografia de superfície. A sinterização em argônio influenciou negativamente a RUMC dos pares metalocerâmicos analisados.
The aim of this study was to evaluate the effect of firing atmospheres: vacuum and argon on the bond strength of ceramic to Ni-Cr (Fit Cast SB), Co-Cr (Star Loy C) and commercially pure titanium (Tritan) alloys. 60 wax/acrylic resin cylinder patterns (8 mm high and 5 mm in diameter) were prepared on a plastic custom mold for metalceramic bond strength (MCBS) test. The patterns were invested in phosphated investment and manipulated on vacuum. The rings were placed in a furnace to burn out patterns and thermally expand the molds. Then, the rings of Ni-Cr and Co-Cr were placed in an electronic machine to cast. The rings related to titanium were positioned in the casting machine with a voltaic arc. After the rings have cooled, the castings were divested manually and abraded with aluminum oxide particles (100 μm). Then, the cylinders were prepared for applying of the ceramic veneering disks. The ceramic was applied and fired in vacuum and argon atmospheres. IPS-Classic ceramic was used for alternative alloys and for titanium, Triceram ceramic. Then, the cylinders composed of metal and ceramic disk (5 mm diameter and 2 mm height) (n=10) were submitted to metal-ceramic bond strength (MCBS) shear tests on an universal testing machine with load cell of 500 Kg at a crosshead speed of 0.5 mm/min. After the tests, there were made fracture analysis by optic microscopy (OM) and scanning electron microscopy (SEM). The MCBS data (MPa) were statistically analyzed by the ANOVA and Tukey test (α=0.05). The results indicated that the vacuum firing (76.58) promoted higher MCBS values than argon firing (51.31). Among the metals, Ni-Cr and Co-Cr alloys presented higher MCBS (71.32 e 71.28, respectively) than titanium (49.23); between two base alloys there was no statistical difference. There was no interaction between the evaluated factors. According to MO analysis, there was predominance of mixed fractures. According SEM, the Ni-Cr and titanium specimens submitted to vacuum presented higher surface roughness than the specimens submitted to argon. For Co-Cr, there was no difference of surface topography. The argon firing influenced negatively the MCBS of metal-ceramic evaluated pairs.

Стилі APA, Harvard, Vancouver, ISO та ін.

25

Xiao, Juan. "Development of electron tomography on liquid suspensions using environmental scanning electron microscopy." Thesis, Lyon, 2017. http://www.theses.fr/2017LYSEI050/document.

Повний текст джерела

Анотація:

La Microscopie Electronique à Balayage Environnementale permet l'observation de liquides dans certaines conditions de pression et température. En travaillant en transmission, i.e. en mode STEM (Scanning Transmission Electron Microscopy), des nano-objets présents au sein du liquide peuvent même être analysés (mode « Wet-STEM»). Dans les solutions concentrées, l'arrangement du soluté peut changer être un paramètre microstructural important, qu’il est alors nécessaire de caractériser. Dans ce contexte, le but de ce travail est de développer la tomographie électronique sur des suspensions liquides en utilisant le mode STEM en ESEM, de manière à obtenir la structure 3D de nano-objets dispersés dans un liquide. Dans une première partie, le contraste entre des nanoparticules et le film d’eau est étudié en combinant des images expérimentales Wet-STEM (en 2D) et des simulations Monte Carlo. Deux types de nano-matériaux sont choisis : des nanoparticules d’or sphériques, de diamètre environ 40 nm, dispersées dans l’eau, ainsi qu’une suspension aqueuse de latex SBA-PMMA, contenant 3% de PMMA utilisé comme tensioactif stérique. La comparaison entre les résultats simulés et expérimentaux permet d’estimer comment le contraste entre l’eau et les nanomatériaux est affecté par l’épaisseur du film d’eau. Dans une deuxième partie, des expériences de tomographie sont réalisées à sec sur des films de polyuréthane contenant des nanotubes de carbone multiparois greffés ou non, en utilisant une platine développée précédemment au laboratoire. Le volume a pu être reconstruit correctement. Cependant, en effectuant une acquisition 3D sur des suspensions de latex SBA-PMMA, le contrôle de la température de l’échantillon s’est révélé insuffisant. Nous proposons une amélioration à la fois de la platine et des conditions d’observations permettant de mieux contrôler l’évaporation et la condensation de l’eau sur des échantillons liquides. La troisième partie est dévolue à une analyse approfondie d’une suspension de latex SBA-PMMA, de différentes concentrations (d’un état dilué à très concentré), les acquisitions étant effectuées avec les conditions optimisées. L’arrangement des particules de latex est comparé à des modèles issus de la littérature, et avec des résultats expérimentaux obtenus par cryo-SEM sur suspensions congelées. Nous présentons ensuite une étude du même latex en présence de tensioactif. La couche de tensioactif peut être mise en évidence dans les volumes reconstruits et segmentés. En conclusion, nous résumons les potentialités de la tomographie wet-STEM pour la caractérisation de nanomatériaux solides et liquides. Des perspectives sont proposées pour continuer dans l’exploration de ces potentialités et des limites de la technique
ESEM (Environmental Scanning Electron Microscopy) allows the observation of liquids under specific conditions of pressure and temperature. When working in the transmission mode, i.e. in STEM (Scanning Transmission Electron Microscopy), nano-objects can even be analyzed inside the liquid (“wet-STEM” mode). Moreover, in situ evaporation of water can be performed to study the materials evolution from the wet to the dry state. This work aims at developing electron tomography on liquid suspensions using STEM-in-ESEM, to obtain the 3D structure of nano-objects dispersed in a liquid. In a first part, Monte Carlo simulations and 2D wet-STEM experimental images are combined to study the contrast. Two kinds of liquid nano-materials are chosen as the sample: spherical gold particles (diameter around 40 nm) in suspension in water; latex SBA-PMMA suspension, a copolymer derived from styrene and metacrylic acid esters in aqueous solution, 3% PMMA shell included as steric surfactant. The comparison between simulated and experimental results helps to determine how water can affect the contrast of hydrated nano-materials. Tomography experiments are then performed on dry PU-carbon nanotubes nanocomposites using a previously developed home-made tomography device, and the volume is well reconstructed. When performing tomography on latex suspension, limitations are found on the temperature control of samples. We propose an optimization of the device with new observations conditions to better control water evaporation and condensation of liquid samples. Afterwards, a full 3D analysis on SBA-PMMA latex from dilute suspension to very concentrated one is performed, and a further study is presented in presence of a surfactant. The encouraging reconstruction results are used to model the particles arrangement. This shows the potentialities of wet-STEM tomography for the characterization of both solid and liquid nano-materials

Стилі APA, Harvard, Vancouver, ISO та ін.

26

Rakian, Audrey. "Scanning Electron Microscopy and Histological Evaluation of Flow Divertors." Scholarly Repository, 2007. http://scholarlyrepository.miami.edu/oa_theses/108.

Повний текст джерела

Анотація:

The purpose of this study is to evaluate the endothelialization, exclusion of the aneurysm from circulation and intra-aneurysmal thrombus formation induced by the implantation of endovascular flow divertors for the purpose of bridging aneurysms. The design of the flow divertors was based on previous in vitro hemodynamic experiments in aneurysm models. The significance of this work is manifested in the development of a minimally invasive technology that may be employed for aneurysm treatment. Divertors with two different filament sizes and three different porosities were implanted in the rabbit elastase-induced aneurysm model and their effectiveness evaluated both angiographically and histologically. Preliminary results demonstrated that it is possible to achieve substantial reduction in intraaneurysmal flow immediately after device deployment. Angiographically, the aneurysms were excluded from the circulation with the medium and low porosity devices. In addition, the device performed as expected: smooth deployment, no intralumenal clot formation, and exclusion of aneurysm from the circulation without occluding other arterial branches. Additional data is needed to make definitive conclusions regarding endothelialization and the formation of a neointima.

Стилі APA, Harvard, Vancouver, ISO та ін.

27

Wan, Quan. "Scanning electron microscopy investigation of bio-polymer composites morphology." Thesis, University of Sheffield, 2017. http://etheses.whiterose.ac.uk/19125/.

Повний текст джерела

Анотація:

The development of nano-composite materials puts higher demand on morphological analysis techniques. The bio-nano-composite material systems is among the most challenging nano-composite materials for morphology characterization due to its sensitivity to damage, complex molecular conformations and nano-structures. The aim of this project is to provide a nanometer resolution and convenient chemical mapping tool based on scanning electron microscope (SEM) and electron spectroscopy for complex bio-composite systems. This would combine the backscattered electron and secondary electron techniques based on the angle-selection and energy-filtering methods. Theoretical electron behavior in the SEM is calculated using Monte Carlo simulations for reference. This SEM technique is validated and applied on representative artificial and natural bio-composite systems. Poly(N-isopropylacrylamide) (PNIPAM) composite material is a family of widely applied temperature-responsive bio-materials. The phase separation and morphology in PNIPAM nano-composites can affect the bio-compatibility of material system. Silk fiber is a well known natural bio-material with exceptional properties as well as a model hierarchical material system. The organization of nano-repeating unit in silk is expected to be a key factor in the mechanical property formation. Direct chemical mapping of this organization was not available up to now in convenient methods. Our SEM techniques (secondary electron hyperspectral imaging, SEHI) were validated and applied for mapping of these bio-materials and provided high-resolution chemical characterization of their nano-structures. The application of SEM techniques were further extended to different silk fibers and artificial silk materials. Such experiment validated the complex fine structure of secondary electron spectra measured on silk materials. The comparison of the electron spectra in different silk materials suggested a possible reflection of protein conformation in secondary electron spectra and this may be exploited for characterization of such complex materials in future applications. In summary, SEM analysis technique using electron selective detection methods capable of nano-resolution chemical characterization were validated and applied on nano-bio-composite materials. These techniques show great potential for morphological analysis in complex and sensitive composite materials in the future.

Стилі APA, Harvard, Vancouver, ISO та ін.

28

Jian, Nan. "Scanning transmission electron microscopy of atomic structure of nanoparticle." Thesis, University of Birmingham, 2016. http://etheses.bham.ac.uk//id/eprint/7131/.

Повний текст джерела

Анотація:

This thesis presents the researches on the size and atomic structure of the nanoclusters including ligand protected monometallic clusters, ligand protected bimetallic clusters and biological metallic clusters, by using aberration corrected HAADF -STEM. The atom counting method with size selected clusters as mass balance was utilized to "fractionate" the relative broad distributed sample and make the structure study focus on the certain size range. The atomic structures of Auss Schmid clusters were investigated. Nearly half of these clusters were found to have a hybrid structure. A combination of geometric size analysis and atom counting method was performed to determine both the size and composition of the AuAg alloy clusters. We found that Ag-rich clusters tend to have an icosahedral structure while the Au-rich clusters prefer the fcc structure. For the biological nanoparticles, the ferritins' iron loadings were obtained. Different morphologies of the ferritin iron cores were observed as a function of iron loading, suggesting the iron core growth process in the protein shell. The HAADF -STEM was also successfully employed to characterize the ultra-small Au and Pd catalysts supported on the Ti02, which are helpful to understand the catalytic performance of these catalysts. A multilayer deposition method was developed to accommodate and process the large abundance of clusters from the new high-flux cluster source. With the similar experimental setup, size-selected colloidal clusters were produced by dissolving the multilayer cluster-PVP stacks. The colloidal clusters were observed by the STEM and their sizes were found to be conserved during the dissolving process.

Стилі APA, Harvard, Vancouver, ISO та ін.

29

Zheng, Tao. "Investigation of plant tissue by environmental scanning electron microscopy." Thesis, University of Cambridge, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.609068.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

30

Hrubanová, Kamila. "Scanning Electron Microscopy and its Applications for Sensitive Samples." Doctoral thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2019. http://www.nusl.cz/ntk/nusl-409082.

Повний текст джерела

Анотація:

Předložená dizertační práce s názvem “Rastrovací elektronová mikroskopie a její aplikace pro senzitivní vzorky” pojednává o problematice rastrovací elektronové mikroskopie v kontextu instrumentálního a metodologického vývoje vedoucího k inovativnímu řešení, které je dobře aplikovatelné zejména v mikrobiologickém výzkumu. Součástí práce je rozprava o historii a současném stavu elektronové mikroskopie (EM) jakožto vědecké zobrazovací a analytické techniky, tato část se nachází v úvodních kapitolách. Nepopiratelný přínos EM v biologických a lékařských oborech je dokazován mnoha citovanými vědeckými publikacemi. Předložená dizertační práce přináší novinky z oblasti přípravy preparátů a kryogenní rastrovací elektronové mikroskopie (cryo-SEM) vyvinuté na pracovišti Ústavu přístrojové techniky AV ČR, v.v.i. v Brně. Jedná se především o návrhy a výrobu speciálních držáků vzorků a vývoj nových metodik v oblasti přípravy mikrobiologických preparátů vedoucích k nalezení optimálních parametrů jednotlivých procesů. V experimentální části se nachází ověření metodologických postupů při studiu hydratovaných a na elektronový svazek senzitivních preparátů. Následné srovnání různých přístupů na definovaném biologickém systému z oblasti mikrobiologie přispívá k rozšíření interpretace doposud známých výsledků. Mezi zkoumanými mikrobiologickými kmeny byly biofilm-pozitivní bakterie Staphylococcus epidermidis a kvasinky jako Candida albicans a Candida parapsilosis, jež jsou považovány za klinicky významné, protože se podílejí na vzniku závažných infekcí zejména u imunokompromitovaných pacientů. Dále byl studován vliv růstu biofilmu bakterie Bacillus subtilis na biodeteriorizaci a biodegradaci poly--kaprolaktonových fólií. Vývoj v oblasti cryo-SEM byl aplikován ve výzkumu mikrobů s biotechnologickým potenciálem, jako jsou např. Cupriavidus necator a Sporobolomyces shibatanus.

Стилі APA, Harvard, Vancouver, ISO та ін.

31

Liu, Yangmingyue. "Scanning Electron Microscopy To Probe Working Nanowire Gas Sensors." OpenSIUC, 2013. https://opensiuc.lib.siu.edu/theses/1256.

Повний текст джерела

Анотація:

This study is dedicated to the implementing of Electron-Beam-Induced Current (EBIC) microscopy to study the behavior of metal oxide semiconducting (MOS) nanowire (NW) gas sensor in situ under exposure to different environment. First, we reported the development of a single nanowire gas sensor compatible with an environmental cell. The major component of the device we use in this study is a single SnO2 nanowire attached to an electron transparent SiN membrane (50-100 nm thick), which was used for mounting nanowire working electrodes and surface imaging of NW. First the NW's conductivity is investigated in different temperatures. Higher temperature is proved to cause higher conductivity of NW. We also found that often the Schottky barrier is formed at the nanowire's contacts with Au and Au/Cr electrodes. Then NW's responses to gas and electron beam (from SEM) are analyzed quantitatively by current measurement. Electron-Beam-Induced Current technique was introduced for the first time to characterize the conductivity behavior of the nanowire during the gas sensing process. Resistive contrast was observed in the EBIC image.

Стилі APA, Harvard, Vancouver, ISO та ін.

32

Behan, Gavin Joseph. "Optical sectioning in the aberration-corrected scanning transmission and scanning confocal electron microscope." Thesis, University of Oxford, 2009. http://ora.ox.ac.uk/objects/uuid:10c7151c-ff1f-4f88-a783-9ad5cf4831ec.

Повний текст джерела

Анотація:

This thesis concerns the experimental application of the technique of optical sectioning in the aberration-corrected scanning transmission electron microscope (STEM). Another aim was to perform optical sectioning experiments on the still relatively new scanning confocal electron microscope (SCEM). To test the feasibility of this technique, experiments were performed on a variety of samples to measure the achievable depth response. Deconvolution methods were explored in an attempt to further improve the depth response. Finally, some of the first optical sectioning experiments were performed in the SCEM using both elastic and inelastically scattered electrons. The results showed a clear need to investigate confocal electron microscopy due to the missing cone problem for incoherent imaging in the STEM. This is particularly evident when imaging objects of greater width than the STEM probe. Confocal electron microscopy using inelastic electrons appeared to be a promising imaging mode for the future with this thesis consisting of early work in the field.

Стилі APA, Harvard, Vancouver, ISO та ін.

33

Martín, Malpartida Gemma. "Combined Transmission Electron Microscopy and In-Situ Scanning Tunneling Microscopy Characterization of Nanomaterials." Doctoral thesis, Universitat de Barcelona, 2018. http://hdl.handle.net/10803/663184.

Повний текст джерела

Анотація:

The main goal of this thesis has been to apply in-situ Transmission Electron Microscopy (TEM) electrical measurements using a Scanning Tunneling Microscopy (STM) tip, combined with TEM imaging and spectroscopic techniques, in order to address the characterization of relevant nanomaterials. This system has not only been used to measure electrical properties, but also to carry out in-situ experiments with Joule heating and to apply mechanical stresses. A review of the different in-situ TEM techniques, their development over the years and their impact in the scientific community has been presented. Moreover, the instrumental used in this thesis, in particular, the TEM-STM system, has been described. In addition, two techniques for the preparation of specific samples for in-situ TEM-STM experiments have been presented: for nanostructured samples (2D materials, nanowires, etc), and for localized samples (devices, thin layers, bulk samples, etc). A gridcase that allows the use of conventional TEM grids in the TEM-STM system has been designed and fabricated in the context of this thesis. The use of this homemade gridase has allowed us to improve the experiments, offering more reproducibility and versatility. Finally, the calibration of the electrical measurements of the system has been carried out. Using the TEM-STM system, different type of nanostructures have been characterized during the present thesis, from 2D nanostructures, as the elucidation of the effects of electrical current through a single graphene oxide sheet, to functional devices, as the study of the ferroelectric and piezoelectric behavior of structures based on La2WO6, the study of the anisotropic electrical conductivity of GaInP CuPtB type ordering layers used for multijunction solar cells or the study of the conductive filament (CF) formation mechanism in three different Resistive random-access memory (ReRAM) devices. In summary, in-situ microscopy expands the horizons of the characterization and study of materials and, in particular, in the context of this thesis, an in-situ TEM-STM system has been used to electrically characterize samples from nanomaterials to functional devices.
En aquesta Tesi, s'ha emprat una tècnica de Microscopia Electrònica de Transmissió (TEM, Transmission Electron Microscopy en anglès) in-situ que permet realitzar mesures elèctriques utilitzant una sonda de microscòpia d'efecte túnel (STM, Scanning Tunneling Microscopy en anglès), tot combinant-la amb imatge TEM i tècniques d'espectroscòpia. A més, aquest sistema no només s'ha utilitzat per a mesurar les propietats elèctriques, sinó també per a dur a terme experiments in-situ amb escalfament per efecte Joule o aplicant una tensió mecànica a la superfície de la mostra. D'aquesta manera s'han pogut caracteritzar nanomaterials, des de nanoestructures 2D, estudiant l’efecte del pas de corrent a través d'un sol full d'òxid de grafè, fins a dispositius completament funcionals, com la caracterització piezoelèctrica i ferroelèctrica de capes primes d'òxids funcionals lliures de plom, l'estudi de l’anisotropia en la conductivitat d’estructures ternàries III-V ordenades utilitzades en cèl·lules solars tàndem multicapa i l'estudi amb TEM de la formació de filaments conductors (CF) i del mecanisme de commutació resistiva en tres dispositius ReRAM diferents. En els diferents capítols d'aquesta tesi s'ha donat resposta a problemes de ciència de materials amb l'ajut d'una tècnica de TEM in-situ tot combinant-la amb altres tècniques d'espectroscòpia i difracció. El desenvolupament d'aquesta tècnica ha permès caracteritzar les propietats del materials a nivell nano.

Стилі APA, Harvard, Vancouver, ISO та ін.

34

Chen, Li. "Fabrication of electron sources for a miniature scanning electron microscope." Thesis, University of York, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.313904.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

35

Morgan, Scott Warwick. "Gaseous secondary electron detection and cascade amplification in the environmental scanning electron microscope /." Electronic version, 2005. http://adt.lib.uts.edu.au/public/adt-NTSM20060511.115302/index.html.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

36

Rifaai, Yasser. "Rhéologie des matrices hybrides composées de ciment et d’ajouts cimentaires activés." Thesis, CY Cergy Paris Université, 2020. http://www.theses.fr/2020CYUN1069.

Повний текст джерела

Анотація:

Face aux préoccupations environnementales liées à la production du ciment Portland, la recherche d’alternatives pour une construction plus durable s’avère une nécessité. En effet, la production du ciment est responsable de l’augmentation du potentiel de réchauffement global (PRG), ce qui remet en question sa grande utilisation de point de vue environnemental. Dans cette perspective, ce projet de doctorat s’inscrit dans l’optique de la réduction de l’impact environnemental des matériaux de construction, notamment les bétons fluides à rhéologie adaptée. Les géopolymères se présentent comme l’une des alternatives intéressantes pouvant réduire l’impact environnemental de la construction. Cependant, l’introduction de ces matériaux dans le secteur de construction confronte des difficultés de compréhension de leurs mécanismes de prise et de durcissement.Ainsi, l’objectif principal de cette thèse est d’étudier l’impact de l’activateur alcalin sur le comportement rhéologique et les mécanismes de prise des géopolymères à base de cendres volantes et de poudre de verre activées ainsi que des matrices hybrides composées de ciment et de géopolymères. Plus spécifiquement, cette étude vise à améliorer les performances rhéologiques et les caractéristiques viscoélastiques de ces matrices afin de les incorporer dans la matrice des bétons fluides, notamment le béton autoplaçant. Le couplage des mesures rhéologiques avec la spectroscopie infrarouge à transformée de Fourier et la microstructure permet de comprendre les différents mécanismes régissant le comportement à l’état frais des matrices étudiées. Les résultats obtenus ont permis d’identifier les concentrations optimales de l’activateur alcalin pour obtenir les meilleures performances rhéologiques, tout en prenant en considération les performances à l’état durci requises. La méthodologie utilisée dans cette étude a permis également de lier les performances rhéologiques au processus de géopolymérisation afin d’établir une meilleure compréhension de l’état frais de ces matériaux. Finalement, l’incorporation des pâtes optimisées dans la matrice d’un béton autoplaçant a été également évaluée. Le béton autoplaçant à base de matrice hybride a montré des performances rhéologiques et mécaniques prometteuses, ainsi qu’un potentiel de réchauffement global inférieur à celui du béton autoplaçant conventionnel. Ces résultats montrent que l’utilisation de ce nouveau type de béton autoplaçant propose une solution intéressante de point de vue environnemental, tout en maintenant les performances rhéologiques et mécaniques requises
With the increase of the environmental concerns related to the production of Portland cement, the search for alternatives to achieve sustainable and rational construction is becoming a necessity. Indeed, the production of cement is responsible for the increase in global warming potential (GWP), which questions its widespread use from an environmental point of view. In this perspective, this study aims at reducing the environmental impact of building materials, in particular self-consolidating concrete (SCC). Geopolymers are one of the interesting alternatives that can reduce the environmental impact of construction. However, the incorporation of these materials in the construction markets faces difficulties as long as the understanding of their setting and hardening mechanisms is still a hot topic.The main objective of this thesis is to evaluate the impact of alkaline activator on the setting mechanisms and rheological behaviour of geopolymers based on fly ash, alkali-activated glass powders, and hybrid matrices composed of cement and geopolymers. This study aims to assess the rheological properties and viscoelastic characteristics of these matrices and evaluate the feasibility of incorporating them to design SCC. Coupling the rheological properties with other measures, including Fourier-transform infrared spectroscopy and microstructure, makes it possible to define different mechanisms governing the fresh state of the investigated matrices. The obtained results allowed to identify the optimal concentrations of the alkaline activator to achieve the required rheological properties and mechanical performance. In addition, the methodology used in this study allowed to correlate the rheological properties to the geopolymerization process. This allowed better understanding of the fresh state of these materials. Finally, the incorporation of the optimized pastes into the matrix of SCC was also evaluated. Self-consolidating concrete based on hybrid matrix has shown promising rheological and mechanical performances, as well as a lower global warming potential than conventional SCC proportioned with cementitious materials. These results proved that the use of hybrid SCC offers an interesting solution from an environmental point of view, while achieving the required rheological and mechanical performances

Стилі APA, Harvard, Vancouver, ISO та ін.

37

Jenkins, L. "Development of environmental scanning electron microscopy for textile hydration studies." Thesis, University of Cambridge, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.605085.

Повний текст джерела

Анотація:

The possibility of supporting a saturated water vapour atmosphere together with the presence of liquid water in the Environmental Scanning Electron Microscope (ESEM) presents new opportunities for the observation of water-textile interactions. It is important to understand such interactions because they will affect many manufacturing and performance processes, including dyeing, finishing, comfort and washing behaviour. Control of temperature and pressure conditions surrounding the sample in the ESEM allows the performance of in situ hydration experiments at high magnification and resolution. Many organic materials are very susceptible to the effects of the beam in an electron microscope. Beam specimen interactions will change the nature and therefore behaviour of the sample. Experiments with cellulosic fibres showed that some of the visible signs of damage are identical to those indicating interaction with water. These signs include smoothing of the fibre surfaces, and loss of surface and edge detail. Experiments were performed to investigate the effect of various experimental parameters on the time of onset of damage. From the results of these experiments, conditions were found which delayed the onset of visible damage for 40-50 minutes. Using the damage-free conditions, mounting and hydration techniques were developed which allow the observation of cross-section area increase in fibres as they interact with liquid water. The results obtained for the lyocell fibres chosen for these experiments show good agreement with similar swelling experiments in the optical microscope performed to confirm the temperature independence of swelling at low temperature. The possibility of assessing the effect of packing density on swelling using the same hydration technique has also been investigated, but limitations of the mounting method prevent the acquisition of useful data for this purpose. A method has been developed for the observation of the wetting behaviour of various textile fabrics. It has been shown that the ESEM provides a quick and easy method of comparing the behaviours of sample materials. Ability to interpret the images produced in the microscope depends on a knowledge of wetting processes. Conditions have been found which allow the condensation of water droplets onto individual textile fibres. Initial assessment has been made to determine the suitability of the ESEM micrographs for the measurement of contact angles.

Стилі APA, Harvard, Vancouver, ISO та ін.

38

Fletcher, A. L. "Cryogenic developments and signal amplification in environmental scanning electron microscopy." Thesis, University of Cambridge, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.599080.

Повний текст джерела

Анотація:

This thesis describes the development of a cryogenic imaging system for an environmental scanning electron microscope (ESEM). The ESEM is an important new development in electron microscopy since it enables specimens to be viewed in a small pressure of gas - generally this gas is water vapour, although an alternative must be used for cryogenic applications. The presence of the gas also contributes to the imaging mechanism, a process whereby the signal electrons are amplified by the gaseous molecules prior to detection. The purpose of the cryogenic system was to image the complicated, four phase microstructure of ice cream. Although viewed routinely by conventional electron microscopy techniques, the harsh temperature and pressure regimes involved (around -120°C at 10^.6 torr) increase the likelihood of introducing artefacts. Therefore, a methodology was developed for imaging ice cream with ESEM in a small pressure of an alternative imaging gas at a much warmer temperature of -80°C. In order to stabilise the ice phase in the samples at a higher temperatures, a system was designed for mixing gases, so that a small amount of water vapour could be mixed into the imaging gas. This system lifted the temperature restrictions of ice cream imaging so it can, in principle, now be imaged at its storage temperature of -20°C. In the search for alternative imaging gases to water vapour, questions were raised about the fundamental way in which the signal electrons interact with the gas. In order to understand the electron amplification properties of the different gases, a Faraday cage was designed and the electron amplification was investigated. We suggest that the ratio of the peak amplification to the plateau amplification gives a semi-quantitative method of determining the imaging quality of the gas. Furthermore, by isolating experimentally the effects of different components of the signal, it was found that the low energy secondary electrons dominate the signal at low pressure, whereas the effect of backscattered electrons becomes more important as the pressure is raised. In addition, the performance of two ESEM detector designs were compared. The new gaseous secondary electron detector (GSED), which was designed to reduce the contribution of some sources of signal, was found to achieve its aim, but some of its overall contrast was sacrificed when compared to the original environmental secondary detector (ESD).

Стилі APA, Harvard, Vancouver, ISO та ін.

39

Kershaw, Matthew James. "Wettability and fluid absorption studies utilising environmental scanning electron microscopy." Thesis, University of Nottingham, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.423651.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

40

Jones, Lewys. "Applications of focal-series data in scanning-transmission electron microscopy." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:a6f2a4d5-e77a-47a5-b2d7-aab4b7069ce2.

Повний текст джерела

Анотація:

Since its development, the scanning transmission electron microscope has rapidly found uses right across the material sciences. Its use of a finely focussed electron probe rastered across samples offers the microscopist a variety of imaging and spectroscopy signals in parallel. These signals are individually intuitive to interpret, and collectively immensely powerful as a research tool. Unsurprisingly then, much attention is concentrated on the optical quality of the electron probes used. The introduction of multi-pole hardware to correct optical distortions has yielded a step-change in imaging performance; now with spherical and other remnant aberrations greatly reduced, larger probe forming apertures are suddenly available. Probes formed by such apertures exhibit a much improved and routinely sub-Angstrom diffraction-limited resolution, as well as a greatly increased probe current for spectroscopic work. The superb fineness of the electron beams and enormous magnifications now achievable make the STEM instrument one of the most sensitive scientific instruments developed by man, and this thesis will deal with two core issues that suddenly become important in this new aberration-corrected era. With this new found sensitivity comes the risk of imaging-distortion from outside influences such as acoustic or mechanical vibrations. These can corrupt the data in an unsatisfactory manner and counter the natural interpretability of the technique. Methods to identify and diagnose this distortion will be discussed, and a new technique developed to restore the corrupted data presented. Secondly, the subtleties of probe-shape in the multi-pole corrected STEM are extensively evaluated via simulation, with the contrast-transfer capabilities across defocus explored in detail. From this investigation a new technique of STEM focal-series reconstruction (FSR) is developed to compensate for the small remnant aberrations that still persist – recovering the sample object function free from any optical distortion. In both cases the methodologies were developed into automated computer codes and example restorations from the two techniques are shown (separately, although in principal the scan-corrected output is compatible with FSR). The performance of these results has been quantified with respect to several factors including; image resolution, signal-noise ratio, sample-drift, low frequency instability, and quantitative image intensity. The techniques developed are offered as practical tools for the microscopist wishing to push the performance of their instrument just that little bit further.

Стилі APA, Harvard, Vancouver, ISO та ін.

41

Kauko, Hanne. "Quantitative scanning transmission electron microscopy studies on heterostructured GaAs nanowires." Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for fysikk, 2013. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-23864.

Повний текст джерела

Анотація:

This thesis presents a quantitative high-angle annular dark eld scanning transmission electron microscopy (HAADF STEM) study on heterostructured GaAs-based nanowires (NWs). Quantitative HAADF STEM was employed to investigate Sb concentration variations in axial GaAsSb inserts within GaAs NWs and in GaAsSb NWs, as well as Al concentration variations in the AlGaAs shell in GaAs/AlGaAs core-shell NWs. The NWs were grown with the vapor-liquid-solid (VLS) growth mechanism using Ga- and Au-assisted molecular beam epitaxy (MBE). Compositional characterisation by quantitative HAADF STEM was realized by comparing experimental image intensities normalized to the incident beam intensity with simulated intensities. The HAADF STEM image simulations were performed using the frozen-phonon multislice approach. For correct compositional analysis of GaAs1-ySby, static atomic displacements (SAD) had to be included in the simulations, however this was not the case with AlxGa1-xAs. GaAsSb inserts within GaAs NWs and GaAsSb NWs were studied with non-corrected STEM at a relatively low magnication using NWs in plane. In this case the known thickness prole of the hexagonal NWs could be exploited in the quantitative HAADF STEM analysis. In the GaAsSb inserts, concentration gradients axially along as well as radially across the insert were identied. The Sb concentration in the insert decreased axially towards the upper and lower interfaces with GaAs, and radially towards the outer surfaces. The axial concentration gradients were attributed to the reservoir eect related to the VLS growth process. The eects of the axial concentration gradients on the NWs optical properties were investigated. The radial concentration gradients in the GaAsSb inserts result from a combined eect of radial GaAs overgrowth and out-diusion of Sb during the post-insert axial GaAs growth, causing an increased surface depletion of Sb with increasing post-insert GaAs growth time. In GaAsSb NWs, increased surface depletion of Sb towards the bottom of the NW was observed, and this was attributed to out-diusion of Sb during the NW growth. GaAs/AlGaAs core-shell NWs were studied with aberration corrected STEM, using cross-sectional specimens prepared with ultramicrotomy. A method for mapping Al concentration in AlxGa1-x As at unit cell spatial resolution using the atomic resolution HAADF STEM images was developed. The method is independent of the eective source size and higher order lens aberrations. With the method, Al concentration variations in the AlGaAs shell could be quantied at unit cell spatial resolution.

Стилі APA, Harvard, Vancouver, ISO та ін.

42

Risnes, Ole Kristian. "Ex-situ and in-situ characterisation of polypropylene fibre morphology by scanning probe microscopy and environmental scanning electron microscopy." Thesis, Heriot-Watt University, 2003. http://hdl.handle.net/10399/419.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

43

Löfgren, André. "Detection of electron vortex beams : Using a scanning transmission electron microscope." Thesis, Uppsala universitet, Materialteori, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-255330.

Повний текст джерела

Анотація:

Electron vortex beams (EVBs) are electron beams with a doughnut-like intensity profile, carrying orbital angular momentum due to their helical phase shift distribution. When employed in an electron microscope, they are expected to be efficient for the detection of magnetic signals. In this report I have investigated high angle annular dark field (HAADF) images obtained using EVBs. This was done for 300 K and 5K. For 5 K, I also compared HAADF images from an ordinary electron beam with HAADF images from an electron vortex beam. What was found was that EVBs produced doughnuts around the atomic columns. However, when taking the size of the electron source into account, this phenomena could no longer be observed. When comparing images from EVBs with images from ordinary electron beams, I found that the intensity of scattered electrons around atomic columns was broader for EVBs. This was persistent even after taking the source size into account.
Elektronvirvelstrålar (EVS) är elektronstrålar med en munk-liknande intensitetsprofil. Dessa bär på rörelsemängdsmoment på grund av sin fasdistribution. När de används i ett elektronmikroskop förväntas de vara effektiva för detektering av magnetiska signaler. I denna uppsats har jag undersökt high angle annular dark field (HAADF) bilder som erhållits med hjälp av EVS. Detta gjordes för 300 K och 5K. För 5 K, jämförde jag även HAADF bilder från en vanlig elektronstråle med HAADF bilder från en elektronvirvelstråle. Vad jag fann var att EVS producerade en munkformad intensitetsfördelning runt atomerna. Men när hänsyn till storleken på elektronkällan togs i beaktande kunde inte detta fenomen observeras längre. När bilder från EVS jämfördes med bilder från vanliga elektronstrålar, fann jag att intensiteten av spridda elektroner runt atomkolumnerna var bredare för EVS. Detta kunde observeras även efter att jag tagit hänsyn till elektronkällans storlek.

Стилі APA, Harvard, Vancouver, ISO та ін.

44

Muellejans, Harald. "Secondary electron emission in coincidence with primary energy losses." Thesis, University of Cambridge, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240071.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

45

Schroeder-Reiter, Elizabeth. "High resolution analysis of mitotic metaphase chromosomes with scanning electron microscopy." Diss., lmu, 2004. http://nbn-resolving.de/urn:nbn:de:bvb:19-27942.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

46

Kola, B. O. "Development of an image processing workstation for scanning Auger electron microscopy." Thesis, University of York, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.374183.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

47

He, Dongsheng. "Quantitative scanning transmission electron microscopy characterisation of size-selected gold clusters." Thesis, University of Birmingham, 2014. http://etheses.bham.ac.uk//id/eprint/4743/.

Повний текст джерела

Анотація:

This thesis presents a systematic study on the three-dimensional atomic structures of the size-selected gold (Au) using aberration-corrected scanning transmission electron microscopy (STEM), fitted with a high angle annular dark field (HAADF) detector. The work involves experimental quantification of the microscope, HAADF-STEM image modeling and cluster structure identification. The study explores the cluster structure distribution as a function of experimental conditions and investigates their structural stability by electron beam irradiation. The Au clusters studied were produced by inert gas aggregation, size-selected by a lateral time-of-flight filter and soft-landed on thin amorphous carbon films. A quantitative image analysis methodology has been developed for rapid cluster structure identification, which involves direct comparison of atomic-resolved experimental images with simulated images. Applying the method to over two thousand individually imaged Au887 clusters (each containing nominal 887 gold atoms) revealed a distribution of structural isomers including icosahedron, decahedron and FCC structures. It was found that the isomer distribution depended critically on the cluster formation conditions. A quick condensation condition led clusters with icosahedral structure, while the slow condensation was favoured by clusters with FCC structure. In addition, the stability of Au887 clusters under the electron beam irradiation was investigated by following electron beam induced structural transformation in situ. The transformation sequence was found to be dominated by icosahedron to decahedron to FCC structure. The results provide insights to the understanding of cluster growth mechanism and dynamic behaviour at atomic scale, enabling the ability to control the three dimensional atomic structures of clusters.

Стилі APA, Harvard, Vancouver, ISO та ін.

48

Bera, Sagorika. "Analysis of Antibody-Induced Plasmodium falciparum Sporozoites Through Scanning Electron Microscopy." Scholar Commons, 2017. http://scholarcommons.usf.edu/etd/6679.

Повний текст джерела

Анотація:

Malaria is a devastating disease that continues to affect millions of people worldwide every year. Specifically, Plasmodium falciparum is the most common human malaria parasite, particularly in sub-Saharan Africa. P. falciparum causes the most malignant and debilitating symptoms with the highest mortality and complication rates. Even with the worldwide efforts of many researchers and organizations, the road to discovering a vaccine has been difficult and challenging. Due do to the improvements in in vitro liver stage assays as well as rodent models of mammalian malaria, pre-erythrocytic stages of malaria have become a more accessible target for experimental studies. These vaccine candidates target Plasmodium sporozoites in the liver and liver stages to prevent development to the blood-stage forms, which is responsible for the debilitating symptoms of the disease. Scanning electron microscopy has been used for decades to provide insight on the morphology and topography of specimens, which cannot be seen through a light microscope. The purpose of this study was to analyze the morphology of sporozoites with some target antibodies. Sporozoites have previously shown uncharacterized appearances and development in an immunofluorescent stain at different concentrations of particular antibodies. With this further understanding on the morphological impact few of the target antibodies have on sporozoites through scanning electron microscopy, further grasp can be acquired.

Стилі APA, Harvard, Vancouver, ISO та ін.

49

Krajnak, Matus. "Advanced detection in Lorentz microscopy : pixelated detection in differential phase contrast scanning transmission electron microscopy." Thesis, University of Glasgow, 2017. http://theses.gla.ac.uk/7906/.

Повний текст джерела

Анотація:

Modern devices require fundamental length scales to be analysed in a maximum detail to enable research of new types of phenomena and design new materials. In this thesis, an advancement in Lorentz microscopy will be presented where the focus was placed not only onto resolution in spatial space but also onto resolution in reciprocal space. This allows greater sensitivity to measurements of the integrated magnetic induction within thin samples. This was achieved by a novel approach to the data acquisition, where instead of a segmented (annular) detector, a pixelated detector was used to measure the deflection of the scanning transmission microscopy (STEM) probe due to the in-plane integrated magnetic induction. Computer vision algorithms were researched to find an efficient, noise-robust way to register the deflection of the STEM probe. This enabled a novel approach to data analysis, where a scatter of the 2D integrated induction (a bivariate histogram) is used to show the distribution of the magnetic induction vector. The experimental results are supported by simulations, where a model of a thin polycrystalline sample causes a shift of the simulated beam due to phase modulations. The results of the detection in both the simulation and experiment showed that cross-correlation based processing can efficiently separate the low spatial frequencies (from the in-plane magnetic induction), and high spatial frequencies (from the structure of the polycrystalline sample). This work will enable quantitative analysis of a greater number of thin magnetic samples, for which the current methods are hampered by the diffraction contrast. This will be particularly helpful for the study low moment, out of plane, magnetised thin films. Currently such systems are of great interest due to the tunability of their magnetic properties and the novel magnetic structures present within them. This work also provides an important step for computational methods in transmission electron microscopy, as this is one of the first examples of 4D data acquisition of processing in STEM (where two dimensions represent the spatial scanning dimensions and other two the reciprocal space). Imaging methods developed in this thesis were applied to the topic of skyrmions in a thin layer of a FeGe cubic helimagnet, where the very fine detail of the structure of their in-plane integrated magnetic induction was shown to contain a distorted modulations of its profile. This was compared to a simple three harmonic frequency model, which was altered to fit some characteristics of the imaged magnetic skyrmions. In this work, for the first time, a direct comparison of differential phase contrast and electron holography will be shown for a simple experiment in which the integrated electric field between two needles was measured in free space in the same microscope. Although it was concluded that both methods are equivalent, some small discrepancies of measured values were present due to a long range electric field in electron holography and/or drift of the beam in between scans in STEM.

Стилі APA, Harvard, Vancouver, ISO та ін.

50

Furnival, Thomas. "Single atom imaging with time-resolved electron microscopy." Thesis, University of Cambridge, 2017. https://www.repository.cam.ac.uk/handle/1810/270314.

Повний текст джерела

Анотація:

Developments in scanning transmission electron microscopy (STEM) have opened up new possibilities for time-resolved imaging at the atomic scale. However, rapid imaging of single atom dynamics brings with it a new set of challenges, particularly regarding noise and the interaction between the electron beam and the specimen. This thesis develops a set of analytical tools for capturing atomic motion and analyzing the dynamic behaviour of materials at the atomic scale. Machine learning is increasingly playing an important role in the analysis of electron microscopy data. In this light, new unsupervised learning tools are developed here for noise removal under low-dose imaging conditions and for identifying the motion of surface atoms. The scope for real-time processing and analysis is also explored, which is of rising importance as electron microscopy datasets grow in size and complexity. These advances in image processing and analysis are combined with computational modelling to uncover new chemical and physical insights into the motion of atoms adsorbed onto surfaces. Of particular interest are systems for heterogeneous catalysis, where the catalytic activity can depend intimately on the atomic environment. The study of Cu atoms on a graphene oxide support reveals that the atoms undergo anomalous diffusion as a result of spatial and energetic disorder present in the substrate. The investigation is extended to examine the structure and stability of small Cu clusters on graphene oxide, with atomistic modelling used to understand the significant role played by the substrate. Finally, the analytical methods are used to study the surface reconstruction of silicon alongside the electron beam-induced motion of adatoms on the surface. Taken together, these studies demonstrate the materials insights that can be obtained with time-resolved STEM imaging, and highlight the importance of combining state-ofthe- art imaging with computational analysis and atomistic modelling to quantitatively characterize the behaviour of materials with atomic resolution.

Стилі APA, Harvard, Vancouver, ISO та ін.

Дисертації з теми "Scanning electron microscopy (MEB)"

Оформте джерело за APA, MLA, Chicago, Harvard та іншими стилями