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Tesi sul tema "Electron microscopy"
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1
Jin, Liang. "Direct electron detection in transmission electron microscopy". Diss., [La Jolla, Calif.] : University of California, San Diego, 2009. http://wwwlib.umi.com/cr/ucsd/fullcit?p3344737.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--University of California, San Diego, 2009.Title from first page of PDF file (viewed April 3, 2009). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 148-151).
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Davies, D. G. "Scanning electron acoustic microscopy". Thesis, University of Cambridge, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.304042.
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Duncan, James Lyon. "Electron microscopy of photosystems". Thesis, Imperial College London, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.412477.
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4
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.
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5
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.
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Bruley, John. "Analytical electron microscopy of diamond". Thesis, University of Cambridge, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.237560.
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7
Briggs, John A. G. "Cryo-electron microscopy of retroviruses". Thesis, University of Oxford, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.408819.
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Sader, Kasim Stefan. "Aspects of biological electron microscopy". Thesis, University of Leeds, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.434150.
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9
Song, Se Ahn. "Electron microscopy of lanthanide diphthalocyanines". Thesis, University of Essex, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.328597.
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Cullen, Sarah Louise. "Electron microscopy of carbon nanotubes". Thesis, University of Cambridge, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.387605.
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Hytch, Martin J. "Quantitative high resolution electron microscopy". Thesis, University of Cambridge, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.317785.
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Clough, Robert N. "New detectors for electron microscopy". Thesis, University of Oxford, 2015. http://ora.ox.ac.uk/objects/uuid:6fe9b841-e55b-4e6f-b6a7-ed479be381b6.
Testo completoAbstract (sommario):
Detectors for Electron Microscopy have traditionally used a scintillator to generate photons from fast electrons, which are then detected by a sensor. However, in recent years direct detection has become an area of interest due to the potential improvements to detector performance. In this thesis various aspects of direct detection are presented. I will begin with simulations of direct detectors based on Joy’s model of straight trajectories between Rutherford scattering events, where signal is generated by inelastic scattering events. The effects of microscope operating voltage, detector thickness, a surface electrically dead layer and diode depth on detector performance are presented. A prototype detector was developed using the DUOS sensor, two thicknesses of the sensor were produced a 50μm thick detector and a 20μm thick detector. EBSD results are presented which show how the use of a reactive ion etch to reduce the dead layer thickness of a mechanically thinned sensor improve the detection efficiency of a sensor allowing EBSD work to be carried out at operating voltages as low as 5keV. The MTF and DQE of both thicknesses of DUOS sensor are measured at 80kV and 200kV, which show that there is little difference between the two thicknesses at 80kV, but at 200kV the thinner detector shows an improved MTF. The results are then and compared with the equivalent simulated detectors. I show how the high frame rate of a detector and rigid and non-rigid registration can be used to improve image quality, resolving the {331} lattice spacing which is not visible with a simple summation of frames. Detectors using gallium nitride rather than silicon as the base semiconductor are simulated. The MTF at the Nyquist frequency for a GaN detector is double that of a Si detector at an operating voltages of 80kV due to the smaller interaction volume of an electron in GaN. However, at higher voltages the improvement is much smaller as most electrons pass through the detector.
13
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.
Testo completoAbstract (sommario):
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 • 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.
14
Abedzadeh, Navid. "Diffractive electron mirror for use in quantum electron microscopy". Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/115627.
Testo completoAbstract (sommario):
Thesis: S.M., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2018.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
"February 2018." Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 66-70).
Periodic atomic structures in thin crystals and artificially fabricated periodic structures in transmission gratings have long been used to coherently split electrons by means of electron diffraction for applications such as interferometry, holography and imaging. Due to their reliance on transmission through matter, however, these methods are prone to electron scattering and absorption and are therefore lossy to some extent. This loss becomes a major issue for quantum electron microscopy (QEM), an interaction-free measurement scheme with electrons as probe particles. QEM relies on single electrons completing many round trips inside an electron resonant cavity, splitting and re-coupling during each round trip, effectively multiplying the probability of loss by the number of round trips. Thus, in one of the designs for QEM, the use of reflective diffraction gratings as lossless electron beam splitters is proposed. In this thesis, diffractive electron mirrors were fabricated by integrating one-dimensional diffraction gratings with tetrode electron mirrors. Optical interference lithography was used to fabricated silicon diffraction gratings with pitches varying from 200 nm to 500 nm. Furthermore, a proof-of-principle experiment to demonstrate their function as electron mirrors inside a scanning electron microscope was developed. It was demonstrated that the constructed tetrode electron mirrors satisfied the requirements of QEM for electron energies up to 3 keV. Finally, in a similar experiment, the fabricated diffractive electron mirrors were tested to demonstrate their function as lossless beam splitters. Preliminary results point to the evidence for electron diffraction, suggesting that diffractive electron mirrors could be used as as lossless electron beam splitters for QEM and other applications.
by Navid Abedzadeh.
S.M.
15
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.
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Malac, Marek. "Analytical electron microscopy of thin films". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ59627.pdf.
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Hetherington, Alan Veron. "Electron microscopy of CVD diamond films". Thesis, University of Cambridge, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.388429.
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Billyard, Paul D. "Controlled environment electron microscopy of catalysts". Thesis, University of Oxford, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.302914.
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Roberts, M. C. "Electron microscopy of VLSI MOS devices". Thesis, University of Oxford, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.370297.
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Toropova, Katerina. "Cryo-electron microscopy of bacteriophage MS2". Thesis, University of Leeds, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.503345.
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Jantou, Virginie. "Analytical electron microscopy of mineralised dentine". Thesis, Imperial College London, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.510760.
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Weller, Suzanne Catherine. "Electron microscopy of heterogeneous catalyst particles". Thesis, University of Birmingham, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.396431.
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Oke, Olusola Adetayo. "Electron Microscopy of myosin V molecules". Thesis, University of Leeds, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.405799.
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Worden, R. H. "Transmission electron microscopy of metamorphic reactions". Thesis, University of Manchester, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.234381.
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Rocca, F. J. "Ionization damage mechanisms in electron microscopy". Thesis, University of Cambridge, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.372301.
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Cockburn, John William. "Electron tunnelling microscopy at free surfaces". Thesis, University of Cambridge, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.304447.
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Snella, Michael T. "Drift correction for scanning-electron microscopy". Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/62605.
Testo completoAbstract (sommario):
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.
28
Sarigiannidou, Eirini. "Electron microscopy and III-nitride nanostructures". Université Joseph Fourier (Grenoble), 2004. http://www.theses.fr/2004GRE10245.
Testo completoAbstract (sommario):
Ce mémoire de thèse présente une étude structurale de puits et de boîtes quantiques GaN/AIN élaborés par épitaxie par jets moléculaires. La technique d'investigation est la microscopie électronique à transmission, utilisée en modes (i) haute résolution, (ii) imagerie filtrée,(iii) conventionnel et (iv) faisceau convergent. Un chapitre est consacré à l'analyse quantitative des images haute résolution par la méthode de projection et l'analyse de la phase géométrique. Ces méthodes sont analysées et optimisées (par exemple utilisation d'images "off-axis"). Dans les super-réseaux (SL) de puits quantiques GaN/AIN les polarités Ga et N sont analysées. Nous démontrons la supériorité de la qualité structurale des faces Ga: interfaces plus abruptes et uniformes, absence de domaines d'inversion et contraintes moins importantes. Nous analysons aussi l'évolution des nanostructures (puits ou boîtes) durant le processus d'encapsulation et nous prouvons que la croissance de l'AIN induit un amincissement des puits quantiques et une réduction isotrope de la taille des boîtes quantiques. Ce phénomène est attribué à un mécanisme d'échange entre les deux métaux et dépend de la relaxation des couches de GaN. Dans un SL de boîtes quantiques GaN/AIN nous examinons la distribution des contraintes et nous démontrons en combinant des analyses haute résolution, des calculs théoriques et de la diffraction X que l'alignement vertical des boîtes est du à une différence de l'état de contrainte de la couche d'AIN. Enfin, nous prouvons que le dopage au Mg à fortes concentrations d'une couche de GaN face N favorise la conversion de la structure de wurtzite à zinc-blendeIn this thesis we present the structural characterization of GaN/AIN quantum wells (QWs) and quantum dots (QDs) grown by plasma assisted molecular beam epitaxy. The technique we use is the transmission electron microscopy in (i) high resolution, (ii) energy filtered, (Hi) conventional and (iv) convergent beam modes. The quantitative analysis of our nanostructures is realized using a projection method and the geometric phase analysis. In order to obtain the most accurate results those methods are optimized and specific experimental conditions, like off-axis HRTEM images, are applied. A comparison study between a Ga-face and a N-face GaN/AIN superlattice (SL) is presented and the higher structural quality (the Ga-face SL is proven: abrupt and uniform interfaces, absence of inversion domain boundaries and partially strained QWs. We also analyze the effects of AIN overgrowth on the structural quality of GaN nanostructures. We show that the overgrowth process implies a thinning of the GaN QWs and an isotropic reduction of the GaN QDs size. The phenomenon is attributed to an exchange mechanism between AI atoms from the cap layer and Ga atoms in the nanostructures. We investigate the strain distribution in a GaN/AIN QD superlattice. Using HRTEM, theoretical calculations and X-ray diffraction experiments we demonstrate that the vertical alignment of the QDs is due to a modulation of the strain state of the AIN layers. Finally, we examine the polytype conversion of a GaN film from N-face wurtzite to zinc-blende structure due to Mg high doping
29
Parker, M. A. "The electron microscopy of polymer blends". Thesis, Brunel University, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.353861.
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Claveau, Yann. "Modeling of ballistic electron emission microscopy". Thesis, Rennes 1, 2014. http://www.theses.fr/2014REN1S074/document.
Testo completoAbstract (sommario):
Après la découverte de la magnéto-résistance géante (GMR) par Albert Fert et Peter Grünberg, l'électronique a connu une véritable avancée avec la naissance d'une nouvelle branche appelée spintronique. Cette discipline, encore jeune, consiste à exploiter le spin des électrons dans le but notamment de stocker de l'information numérique. La plupart des dispositifs exploitant cette propriété quantique des électrons consistent en une alternance de fines couches magnétiques et non magnétiques sur un substrat semi-conducteur. L'un des outils de choix pour la caractérisation de ces structures, inventé en 1988 par Kaiser et Bell, est le microscope à émission d'électrons balistiques (BEEM). A l'origine, ce microscope, dérivé du microscope à effet tunnel (STM), était dédié à l'imagerie d'objets (nanométriques) enterrés ainsi qu'à l'étude de la barrière de potentiel (barrière Schottky) qui se forme à l'interface d'un métal et d'un semi-conducteur lors de leur mise en contact. Avec l'essor de la spintronique, le BEEM est devenu une technique de spectroscopie essentielle mais encore fondamentalement incomprise. C'est en 1996 que le premier modèle réaliste, basé sur le formalisme hors équilibre de Keldysh, a été proposé pour décrire le transport des électrons dans cette microscopie. Il permettait notamment d'expliquer certains résultats expérimentaux jusqu'alors incompris. Cependant, malgré son succès, son usage a été limité à l'étude de structures semi-infinies via un méthode de calcul appelée décimation de fonctions de Green. Dans ce contexte, nous avons étendu ce modèle au cas des films minces et des hétéro-structures du type vanne de spin : partant du même postulat que les électrons suivent la structure de bandes du matériaux dans lesquels ils se propagent, nous avons établi une formule itérative permettant le calcul des fonctions de Green du système fini par la méthode des liaisons fortes. Ce calcul des fonctions de Green a été encodé dans un programme Fortran 90, BEEM v3, afin de calculer le courant BEEM ainsi que la densité d'états de surface. En parallèle, nous avons développé une autre méthode, plus simple, qui permet de s'affranchir du formalisme hors équilibre de Keldysh. En dépit de sa naïveté, nous avons montré que cette approche permettait l'interprétation et la prédiction de certains résultats expérimentaux de manière intuitive. Cependant, pour une étude plus fine, le recours à l'approche “hors équilibre” reste inévitable, notamment pour la mise en évidence d'effets d'épaisseur, lés aux interfaces inter-plans. Nous espérons que ces deux outils puissent se révéler utiles aux expérimentateurs, et notamment pour l'équipe Surfaces et Interfaces de notre départementAfter the discovery of Giant Magneto-Resistance (GMR) by Albert Fert and Peter Grünberg, electronics had a breakthrough with the birth of a new branch called spintronics. This discipline, while still young, exploit the spin of electrons, for instance to store digital information. Most quantum devices exploiting this property of electrons consist of alternating magnetic and nonmagnetic thin layers on a semiconductor substrate. One of the best tools used for characterizing these structures, invented in 1988 by Kaiser and Bell, is the so-called Ballistic Electron Emission Microscope (BEEM). Originally, this microscope, derived from the scanning tunneling microscope (STM), was dedicated to the imaging of buried (nanometer-scale) objects and to the study of the potential barrier (Schottky barrier) formed at the interface of a metal and a semiconductor when placed in contact. With the development of spintronics, the BEEM became an essential spectroscopy technique but still fundamentally misunderstood. It was in 1996 that the first realistic model, based on the non-equilibrium Keldysh formalism, was proposed to describe the transport of electrons during BEEM experiments. In particular, this model allowed to explain some experimental results previously misunderstood. However, despite its success, its use was limited to the study of semi-infinite structures through a calculation method called decimation of Green functions. In this context, we have extended this model to the case of thin films and hetero-structures like spin valves: starting from the same postulate that electrons follow the band structure of materials in which they propagate, we have established an iterative formula allowing calculation of the Green functions of the finite system by tight-binding method. This calculation of Green’s functions has been encoded in a FORTRAN 90 program, BEEM v3, in order to calculate the BEEM current and the surface density of states. In parallel, we have developed a simpler method which allows to avoid passing through the non-equilibrium Keldysh formalism. Despite its simplicity, we have shown that this intuitive approach gives some physical interpretation qualitatively similar to the non-equilibrium approach. However, for a more detailed study, the use of “non-equilibrium approach” is inevitable, especially for the detection of thickness effects linked to layer interfaces. We hope these both tools should be useful to experimentalists, especially for the Surfaces and Interfaces team of our department
31
Folea, Ioana Mihaela. "Electron microscopy of cyanobacterial membrane proteins". [S.l. : [Groningen : s.n.] ; University of Groningen] [Host], 2008. http://irs.ub.rug.nl/ppn/314679286.
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Pearson, David A. "Theory of ballistic electron emission microscopy /". Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC IP addresses, 1999. http://wwwlib.umi.com/cr/ucsd/fullcit?p9952664.
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Chan, Yu Fai. "Nanostructure characterization by transmission electron microscopy /". View Abstract or Full-Text, 2002. http://library.ust.hk/cgi/db/thesis.pl?PHYS%202002%20CHAN.
Testo completoAbstract (sommario):
Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2002.Includes bibliographical references (leaves 62-63). Also available in electronic version. Access restricted to campus users.
34
Holbrook, Owen. "Simulation of energy filtered electron microscopy". Thesis, University of Bath, 1998. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.266475.
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Kim, Doory. "Ultrastructural Studies by Correlative Stochastic Optical Reconstruction Microscopy and Electron Microscopy". Thesis, Harvard University, 2015. http://nrs.harvard.edu/urn-3:HUL.InstRepos:17463150.
Testo completoAbstract (sommario):
Fluorescence light microscopy (LM) and electron microscopy (EM) are two of the most widely used imaging modalities for probing cellular structures. In this dissertation I present our works in both developing methods of several correlative super-resolution fluorescence light microscopy (LM) and electron microscopy (EM) assays by combining stochastic optical reconstruction microscopy (STORM), a super-resolution imaging technique with several different EM imaging modalities and applying super-resolution microscopy to investigate the distributions and interactions of purine biosynthetic enzymes organization complex called purinosomes within the cell.
The first work contained in this dissertation is to develop Correlative fluorescence light microscopy and electron microscopy allows the imaging of spatial distributions of specific biomolecules in the context of cellular ultrastructure. Recent development of super-resolution fluorescence microscopy allows the location of molecules to be determined with nanometer-scale spatial resolution. However, correlative super-resolution fluorescence microscopy and electron microscopy (EM) still remains challenging because the optimal specimen preparation and imaging conditions for super-resolution fluorescence microscopy and EM are often not compatible. Here, we have developed several experiment protocols for correlative stochastic optical reconstruction microscopy (STORM) and EM methods, both for un-embedded samples by applying EM-specific sample preparations after STORM imaging and for embedded and sectioned samples by optimizing the fluorescence under EM fixation, staining and embedding conditions. We demonstrated these methods using a variety of cellular targets.
In the second part of this dissertation, I focus on the study of dynamic purine biosynthetic enzymes organization complex called purinosomes. Purine biosynthetic enzymes are assembled into dynamic multi-enzyme complex called purinosomes. However, spatial or temporal control of these structures remains unknown. Here, we explored the endogenous purinosomes in medically important HGPRT-deficient LND fibroblasts in order to understand the de novo purine biosynthesis. Using super-resolution microscopy we investigated the interaction of purinosomes and mitochondria or microtubules using photoactivatable fluorescent protein, mMaple3 and LND fibroblast as an ideal model system for the endogenous purinosomes formation in order to avoid possible protein aggregation problems. The STORM images with this ideal model system revealed a highly correlated spatial distribution of endogenous purinosomes with mitochondria or microtubules, suggesting direct physical associations between two structures. In addition to identifying endogenous purinosome association with other cellular components, we also demonstrated that mTOR directly influenced the purinosome association with mitochondria. Inhibition of mTOR decouples spatial correlation of purinosomes with mitochondria. These data provide strong evidences for physical and functional association of endogenous purinosomes with mitochondria and microtubules.Chemistry and Chemical Biology
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Yu, Enhua. "Crossed and uncrossed retinal fibres in normal and monocular hamsters : light and electron microscopic studies /". [Hong Kong : University of Hong Kong], 1990. http://sunzi.lib.hku.hk/hkuto/record.jsp?B13014316.
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El, Barraj Ali. "Growth and electro-thermomigration on semiconductor surfaces by low energy electron microscopy". Thesis, Aix-Marseille, 2019. http://www.theses.fr/2019AIXM0393.
Testo completoAbstract (sommario):
Dans ce mémoire sont abordées quelques études sur la croissance, l'électromigration et la thermomigration de la surface des semiconducteurs tels que le Ge(111), le Si(100) et le Si(111). Sur le plan expérimental, la Microscopie à Electrons Lents (LEEM) nous a permis d'accéder à la dynamiques des phénomènes in situ et en temps réel. Nous étudions l'électromigration et la thermomigration sur la surface de Si(100) qui présente deux reconstructions de surfaces (2x1) et (1x2) selon l'orientation des dimères. Nous montrons que l'anisotropie de diffusion peut affecter le sens de mouvement des nanostructures (trous et îlots). Nous étudions aussi l'électromigration et la thermomigration sur la surface de Si(111). Nous montrons que les trous (1x1) dans la phase (7x7) bougent dans le sens opposé au courant électrique, et dans le même sens du gradient thermique. Nous avons obtenu la charge effective et le coefficient de Soret des atomes de Si en présence d'un courant électrique et d'un gradient thermique. Enfin est abordée l'étude de la nucléation, la croissance et la coalescence dynamique de gouttelettes d'Au sur la surface d'Au/Ge(111), ainsi que l'électromigration des domaines 2D d'Au/Ge(111)-(√3x√3) dans la phase (1x1)This thesis is focused on the study of the growth, electromigration and thermomigration of nanostructures on the surface of semiconductors such as Si(100), Si(111) and Ge(111). On an experimental viewpoint, Low Energy Electron Microscopy (LEEM) allows us to access to the dynamics of the phenomena in situ and in real time. We have studied under electromigration and thermomigration the motions of 2D monoatomic holes and islands on the Si (100) surface. We have shown that diffusion anisotropy due to (2x1) and (1x2) surface reconstructions can affect the direction of motion of nanostructures. We have also studied electromigration and thermomigration of Si (111) surface. We show that 2D-(1x1) holes in the (7x7) phase move in the direction opposite to the electric current, while in the direction of the thermal gradient. We have obtained the effective charge and the Soret coefficient of Si atoms in presence of an electric current and a thermal gradient. At last, the nucleation, growth and dynamic coalescence of Au droplets on Au/Ge(111) surface is studied, and the electromigration of 2D Au/Ge(111)-( √3x√3) domains on Au/Ge(111)-(1x1) surface
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Pach, Elzbieta. "Electron microscopy studies on functional carbon nanotubes". Doctoral thesis, Universitat Autònoma de Barcelona, 2017. http://hdl.handle.net/10803/456581.
Testo completoAbstract (sommario):
La presente tesis doctoral se centra en el estudio exhaustivo de nanotubos de carbono funcionales por medio de técnicas de microscopía electrónica. Los nanotubos de carbono (CNTs) funcionales están atrayendo una creciente atención debido a su potencial uso para aplicaciones biomédicas, incluyendo para la adquisición de imágenes in vivo, acumulación selectiva en tumores y sistemas de administración de fármacos. Una ventaja intrínseca de los nanotubos de carbono es que su cavidad interna puede llenarse con una carga útil de interés mientras que la superficie externa puede modificarse para mejorar su dispersabilidad y biocompatibilidad.
Debido a su potencial aplicación en el campo biomédico, es esencial una caracterización detallada de las muestras en todas las etapas de su proceso de preparación (purificación, acortamiento, llenado y funcionalidad externa). Para lograr este objetivo, en esta tesis doctoral hemos empleado tanto los análisis ya establecidos que incluye microscopía electrónica de transmisión de alta resolución para estudiar la estructura del material de relleno o espectroscopia de dispersión de energía de rayos X para evaluar su composición, pero también hemos explorado el uso de otras técnicas para ampliar las posibilidades de caracterización de las muestras.
En este sentido, hemos optimizado las condiciones para el estudio de las longitudes de CNTs monocapa purificados por microscopía electrónica de barrido de alta resolución (HRSEM) con sensibilidad superficial. Además, la microscopía electrónica de transmisión y barrido (STEM) a bajos voltajes se ha demostrado como una técnica eficiente y rápida para evaluar el rendimiento del rellenado y la pureza del material. De hecho, la combinación de alta resolución espacial y el trabajo a bajos voltajes de esta técnica la ha hecho particularmente adecuada para el estudio de la interacción de nanotubos de carbono funcionales con muestras biológicas, como por ejemplo células.
Algunos de los compuestos con interés para aplicaciones biomédicas empleados en este trabajo tienen una estructura laminar. Se sabe que los materiales laminares forman monocapas que pueden tener propiedades mejoradas o nuevas debido a efectos de confinamiento. Los CNT pueden actuar como plantillas para guiar los materiales laminares a formar nanotubos monocapa. Este es el caso de los haluros de lutecio y el yoduro de plomo. En esta tesis de doctorado hemos conseguido la formación de nanotubos de haluros de lutecio de tamaño subnanométrico, y su naturaleza tubular se ha demostrado mediante STEM con corrector de aberraciones y simulaciones de imagen. Además, se ha logrado el crecimiento con alto rendimiento de nanotubos de PbI2 en el exterior de CNTs. La estructura de los híbridos se ha revelado mediante STEM con aberración corregida y tomografía electrónica. Cabe destacar que las propiedades ópticas de los híbridos difieren de las del PbI2 en masa. El desplazamiento azul observado por fotoluminiscencia se ha confirmado mediante análisis en híbridos PbI2-CNT individuales por catodoluminiscencia-STEM.
En conclusión, durante este proyecto de doctorado la gama de técnicas de microscopía electrónica utilizadas para el estudio de CNT funcionales se ha ampliado para obtener una caracterización exhaustiva de las muestras.The present PhD thesis focuses on the thorough study of functional carbon nanotubes by means of electron microscopy techniques. Functional carbon nanotubes (CNTs) are attracting an increased attention due to their potential use for biomedical applications, including in vivo imaging, tumour targeting and drug delivery systems. An intrinsic advantage of carbon nanotubes is that their inner cavity can be filled with a chosen payload whilst the outer surface can be modified to improve their dispersability and biocompatibility. Being the envisaged application in the biomedical field, a detailed characterization of the samples in all the steps of the preparation process (namely purification, shortening, filling and external functionalization) is mandatory. To achieve this goal, in this PhD thesis we have employed already established analysis including high resolution transmission electron microscopy to study the structure of the filling material, or energy dispersive X-ray spectroscopy to assess their composition, but also we have explored the use of other techniques to expand the possibilities of characterization of the samples. In this sense, we have optimized the conditions for the study of the lengths of as-purified single-walled CNTs by surface sensitive high resolution scanning electron microscopy (HRSEM). Besides, low voltage scanning transmission electron microscopy (STEM) has been demonstrated as a time-efficient technique for assessment of filling yield and purity. Indeed, the combination of high spatial resolution and low voltage operation of this technique has made it particularly suitable for the study of the interaction of functional carbon nanotubes with biological samples such as cells. Some of the employed compounds with interest for biomedical applications have a layered structure in their bulk form. Layered materials are known to form monolayers which may exert enhanced or novel properties due to the confinement effects. CNTs may act as templates to guide those layered materials to form single-layered nanotubes. This is the case of lutetium halides and lead iodide. In this PhD thesis we have succeeded in the formation of lutetium halide subnanometer-sized nanotubes, and proved their tubular nature by aberration corrected STEM and image simulations. Additionally, the high yield growth of PbI2 nanotubes on the exterior of CNTs has been achieved. Thanks to aberration corrected HAADF STEM and electron tomography, the structure of the hybrids has been revealed. Remarkably, the optical properties of the hybrids differ from those of the bulk PbI2. The blue shift observed by photoluminescence has been further confirmed by cathodoluminescence STEM analysis detected on individual PbI2-CNT hybrids. In conclusion, during this PhD project the range of electron microscopy techniques used for the study of functional CNTs has been expanded to get a thorough characterisation of the samples.
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Ndzane, Nolufefe Muriel. "Electron microscopy characterisation of polycrystalline silicon carbide". Thesis, Nelson Mandela Metropolitan University, 2014. http://hdl.handle.net/10948/d1020634.
Testo completoAbstract (sommario):
This dissertation focuses on an electron microscopy investigation of the microstructure of SiC layers in TRISO coated particles deposited by chemical vapour deposition under different experimental conditions, which include temperature, concentration of gases and deposition time. The polycrystalline β-SiC was deposited from the decomposition of methyl trichlorosilane MTS in the presence of hydrogen (H2) as carrier gas. Scanning electron microscopy (SEM), using the backscattered electron (BSE) mode, was used to image the microstructure of and defects in the SiC layers of TRISO particles. Electron backscatter diffraction (EBSD) in the SEM was used to determine the SiC grain sizes and distribution thereof in TRISO particles deposited under different conditions. For samples with a poor EBSD indexing rate, transmission Kikuchi diffraction and transmission electron microscopy (TEM) investigations were also carried out. From the results, the effects of growth temperature on the SiC microstructure, specifically on the grain size and shape and the porosity were determined. The effects of cooling or non-cooling of the gas inlet nozzle on the SiC microstructure were also investigated. TEM and scanning TEM (STEM) analyses of the SiC layers in TRISO particles were performed to image the defects and reveal the crystallinity of SiC layers. The microstructure and composition of SiC tubes fabricated by reaction bonding (RB) was also investigated by using electron microscopy and Raman spectroscopy. SEM-BSE imaging of RBSiC samples allowed the identification of impurities and free silicon in the RBSiC. Finally, the penetration of the metallic fission product, palladium, in reaction bonded SiC at a temperature of a 1000ºC is determined. A brief comment on the suitability of RBSiC as candidate for fuel cladding in a PWR is made. A short discussion of the suitability of the characterisation techniques used is included at the end.
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Zhang, Yucheng. "Characterisation of GaN using transmission electron microscopy". Thesis, University of Cambridge, 2008. https://www.repository.cam.ac.uk/handle/1810/252119.
Testo completo
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Zhou, Yu. "Structural study of eIF2B by electron microscopy". Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/structural-study-of-eif2b-by-electron-microscopy(feacd470-3139-4648-9812-c152168c930d).html.
Testo completoAbstract (sommario):
In eukaryotic translation initiation, eIF2B, a 295 kDa multisubunit (from α to ε) complex,is the guanine nucleotide exchange factor (GEF) of eIF2, a GTP binding protein, and hasmultiple roles in regulating the level of active eIF2-GTP-Met-tRNAi ternary complexes inthe cytoplasm. Mutations in eIF2B subunits affect global protein synthesis and, in human,are responsible to cause a genetically inherited lethal childhood brain disease calledLeukoencephalopathy with Vanishing White Matter (VWM). Although the genetic aspectseIF2B have been widely studied over decades, detailed structural knowledge only becameavailable in recent years but is still limited. This study aims to gain structural insights intoyeast eIF2B by a range of electron microscopy techniques to improve our understandingtowards its GEF activity with eIF2 and regulatory response. By performing size-exclusion chromatography and multi-angle static light scattering (SECMALS), it was found that eIF2B is a stable dimer of pentamers (~600 kDa). Negativestaining (25.8 Å) and cryo-EM (12.1 Å) eIF2B decamer models that showed 2-foldrotational symmetry were generated by single particle reconstruction. Homology modelingof yeast eIF2B subunits revealed an eIF2B(αβδ)2 hexameric core and two separate arm-likeeIF2Bγε catalytic domains with potential flexibility. To constrain subunit position in thearm structure, Ni-NTA-Nanogold labeling against the multihistidine tag of eIF2Bγ wasperformed. In addition, genetic approaches were applied to eliminate synthesis of eIF2Bα(34 kDa) and eIF2B(βγδε)2 octamer complexes (532 kDa) were purified by SEC-MALSand analysed by negative staining single particle reconstruction. It was speculated thatdeletion of eIF2Bα might have triggered significant conformational rearrangement that ledto high uniformity in the 2D class averages. A hypothetical model was thus proposed forthe octamer where the two arm-like domains clamp together to form a compact structure.
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Findlay, Scott David. "Theoretical aspects of scanning transmission electron microscopy /". Connect to thesis, 2005. http://eprints.unimelb.edu.au/archive/00001057.
Testo completo
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Koda, Nobuko. "Transmission electron microscopy studies of fega alloys". College Park, Md. : University of Maryland, 2003. http://hdl.handle.net/1903/167.
Testo completoAbstract (sommario):
Thesis (M.S.) -- University of Maryland, College Park, 2003.Thesis research directed by: Dept. of Material, Science and Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Waterbury, Raymond. "The electron microscopy proteomic organellar preparation robot /". Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=102768.
Testo completoAbstract (sommario):
An Electron Microscopy Proteomic Organellar Preparation (EMPOP) robot was developed as a tool for high-throughput preparation of subcellular fraction samples for electron microscopic identification. It will provide a means for validation of subcellular sample purity and confirmation of protein localization needed for organellar proteomics.The device automates all chemical and mechanical manipulations required to prepare organelles for electron microscopic examination. It has a modular, integrated design that supports automated filtration, chemical processing, delivery and embedding of up to 96 subcellular fraction samples in parallel. Subcellular fraction specimens are extremely fragile. Consequently, the system was designed as a single unit to minimize mechanical stress on the samples by integrating a core mechanism, composed of four modular plates, and seven support subsystems for: (1) cooling, (2-3) fluid handling, (4-7) positioning. Furthermore, control software was developed specifically for the system to provide standardized, reproducible sample processing while maintaining flexibility for adjustment and recall of operational parameters.
Development of the automated process progressed from initial validation experiments and process screening to define operational parameters for preservation of sample integrity and establish a basic starting point for successful sample preparation. A series of successive modifications to seal the local environment of the samples and minimize the effect of fluidic perturbations further increased process performance. Subsequent testing of the robot's full sample preparation capacity used these refinements to generate 96 samples in approximately 16 hours; reducing the time and labor requirement of equivalent manual preparation by up to 1,000 fold.
These results provide a basis for a structured approach toward process optimization and subsequent utilization the device for massive, parallel preparation of subcellular fraction samples for electron microscopic screening and quantitative analysis of subcellular and protein targets necessary for high-throughput proteomics.
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Plamann, Tobias. "Dynamical scattering in super-resolution electron microscopy". Thesis, University of Cambridge, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.396094.
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Chau, Ka Lok. "Automated control in high resolution electron microscopy". Thesis, University of Cambridge, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.283920.
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Hetherington, C. "Transmission electron microscopy of GaAs/AlGaAs multilayers". Thesis, University of Oxford, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.379967.
Testo completo
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Yu, Chak Chung Andrew. "Electron microscopy studies of magnetic tunnel junctions". Thesis, University of Oxford, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.302402.
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Haydon, S. K. "Structure determination using electron diffraction and microscopy". Thesis, University of Cambridge, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.603876.
Testo completoAbstract (sommario):
This thesis presents a program of work initiated to implement, assess and test a difference potential methodology of structure refinement using quantitative electron diffraction. The results of a parallel synthetic and structural study of the pentagonal tunnel (PT) structure, tetragonal lead tungsten bronze (lead-TTB), and the unexplored quaternary Pb-Nb-W-O system are also presented. Quaternary Pb-Nb-W-O phases are synthesised via fully oxidised and reduced reaction mechanisms. The phases observed in both experiment types are similar and based on superstructures of basic TTB, formed by the ordering of pentagonal columns (PCs) within the host framework. The formation of a fully oxidised quaternary analogue of lead-TTB is discussed. Reduced phase preparations prove it is possible to incorporate lead into PC structures whilst maintaining the parent framework PC distribution. In other experiments an alternative PT/PC ordering scheme is found. A model for this phase and its hidden supercell is presented and discussed. A new TTB related phase is also observed possessing a tetragonal cell repeat five times the (210)TTB plane spacing. A possible model for this phase is proposed. Methods of extracting experimental intensities for the difference potential calculation from an exposure series of diffraction patterns are discussed. A software package (EDIM) for performing the intensity extraction automatically is presented. Tests performed to investigate the characteristics of the difference potential are described, and the results of a limited refinement of lead-TTB using EDIM generated experimental electron diffracted intensities are presented. These calculations confirm that the electron difference potential is a viable means of determining light atom positions in structures containing heavy atom components.
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Dwyer, C. "Scattering theory for advanced transmission electron microscopy". Thesis, University of Cambridge, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.598710.
Testo completoAbstract (sommario):
Aspects of a theoretical and computational basis for the simulation of fast electron scattering in a solid due to elastic, electron-phonon and atomic ionisation events are developed. The primary motivation for this work arises from the need for detailed simulations of fast electron scattering to assist in the quantitative interpretation of experimental data acquired using high-spatial-resolution analytical techniques in the scanning transmission electron microscope. The scattering behaviour of Å-scale electron probes in simple atomic structures is examined with specific reference to the origin of core energy-loss signals and the spatial resolution of annular dark-field images generated by such probes. A multiscale theory of the dynamical elastic and inelastic scattering of fast electrons is then developed. This theory is applicable to many forms of inelastic scattering, and is developed in the form of a multi-dimensional extension of the well-known multislice theory of dynamical elastic scattering of fast electrons. Methods for obtaining the key quantities required for the application of this theory to the inelastic scattering of fast electrons due to atomic ionisation are presented. One of these methods is extended to enable the inclusion of relativistic effects in the ionisation process. A preliminary test of the multislice theory is made by comparing calculated and experimental characteristic-loss electron diffraction patterns acquired from silicon. The treatment of incoherent electron waves using Monte Carlo integration, which in certain circumstances can reduce computation time dramatically, is also demonstrated. Finally, the predictions of the theory are compared with those of approximate methods for calculating the origin of the core energy-loss signal in the scanning transmission electron microscope.