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BOSCHI, Alex. « Studio dei meccanismi di trasporto di carica in film sottili a base di materiali correlati al grafene (GRM) ». Doctoral thesis, Università degli studi di Modena e Reggio Emilia, 2021. http://hdl.handle.net/11380/1244690.
Texte intégralRésumé :
L’avvento di tecniche economiche per produrre fogli di materiali con spessore mono-atomico, come il grafene [1], ha aperto la possibilità di progettare materiali nanostrutturati con proprietà chimico/fisiche pre-programmabili. I sistemi tecnologicamente rilevanti a base di materiali correlati al grafene (GRM) sono principalmente networks di microfogli bidimensionali distribuiti in modo casuale e altamente difettosi [2]. Sebbene il trasporto di carica sia stato ampiamente trattato per fogli bidimensionali isolati [3], uno studio esaustivo che correli le proprietà elettriche dei GRM networks con la complessità della struttura e della morfologia del materiale è ancora mancante in letteratura.
Lo scopo di questo lavoro è indagare il trasporto di carica (CT) in film sottili di GRM, con un certo grado di disordine strutturale. In particolare, abbiamo studiato i meccanismi di CT che si verificano all'interfaccia tra due fogli – spesso i meccanismi d’interfaccia sono considerati un fattore limitante – così come il ruolo della complessità geometrica del network nella conducibilità elettrica complessiva delle strutture di microfogli.
Abbiamo utilizzato fogli monoatomici di grafene ossido (GO) come materiale bidimensionale modello. Il GO consiste infatti in un reticolo di grafene conduttivo che include gruppo funzionali dell’ossigeno sia sul piano basale che ai bordi del foglio. I microfogli isolanti di GO vengono depositati su substrati di ossido di silicio e sono ridotti termicamente per ripristinare alcune delle proprietà del grafene, tra cui la conducibilità elettrica. Oltre al GO ridotto, abbiamo impiegato un GRM composto da fogli multistrato di grafene (parzialmente ossidato). Tale materiale è il GO esfoliato elettrochimicamente (eGO). Abbiamo quindi sfruttato diversi metodi di deposizione: i) spin-coating, ii) spray-coating e iii) filtrazione assistita da vuoto per fabbricare film sottili di fogli di GRM parzialmente impilati e con dimensioni laterali macroscopiche.
Le proprietà chimiche e morfologiche dei film sono state caratterizzate attraverso misurazioni di spettroscopia fotoelettronica a raggi X (XPS), microscopia a forza atomica (AFM) e diffrazione di raggi X (XRD). I meccanismi di trasporto sono stati studiati invece con misure di resistività elettrica (ρ) in funzione della temperatura, da valori ambientali fino a 5 K.
Possibili ambiguità sull'analisi quantitativa di ρ(T) sono state risolte utilizzando un metodo autoconsistente basato sull'energia di attivazione ridotta [5], ovvero la derivata logaritmica della resistività rispetto alla temperatura: W(T)=-(d lnρ)⁄(d lnT ). Questa trasformazione matematica ha permesso di analizzare il dataset ρ(T) con funzioni lineari. Abbiamo correlato i parametri caratteristici di trasporto con il grado di ordine dei nostri campioni e chiarito il ruolo dell'impacchettamento verticale dei fogli, ovvero dell'interazione π-π tra cluster aromatici sovrapposti, nel CT del film. Abbiamo inoltre evidenziato le differenze di CT tra i film basati su GO ridotto e quelli su eGO.
Il lavoro proposto pone le basi per lo sviluppo di nuovi modelli e protocolli riguardanti i meccanismi di CT in sistemi realistici di GRM, come inchiostri e compositi polimerici.
[1] Ferrari, A. C. et al. Nanoscale 7, 4598-4810, (2015).
[2] Palermo V., Chem. Comm. 49, 28, 2848-2857 (2013); Kelly A. et al, Science 356, 6333 (2017).
[3] Eda G. et al, J. Physics. Chem.C 113, 15768 (2009); Kaiser a. et al, Nano Letters 9, 1787 (2009); Joung D. and Khondaker S., Phys. Rev. B 86, 235423 (2012).
[4] Xia Z. et al, J. Physics. Chem.C 123, 15122 (2019).
[5] Zabrodskii A. G., Philos. Mag. B 81, 1131 (2001).The development of cheap techniques to produce large sheets of monoatomic thick materials, such as graphene [1], opened new avenues to design nanostructured materials with pre-programmed chemical and physical properties. Most of the technologically relevant graphene-related materials (GRMs) systems are networks composed of randomly distributed and highly defective 2D microsheets [2]. While the charge transport has been extensively studied in single nanosheets [3], a comprehensive study that correlates the electrical properties of networks composed of purely 2D graphene-based materials with the complexity of the material structure and morphology is still missing. The aim of this work is to investigate charge transport (CT) in GRMs films, going towards structures with increasing disorder. In particular we investigated the CT mechanisms occurring at the sheet-to-sheet interface – typically the interfacial mechanisms are considered as bottlenecks – as well as the role of the geometrical complexity of the network in the overall electrical conductivity of the nanosheets assemblies. As prototypical 2D material we used single monolayer sheets of graphene oxide (GO), which consists of a conductive graphene lattice including oxygen functionalities/ defects both on the basal plane and at the edges of the sheet. Electrical insulating GO sheets are deposited on silicon oxide substrates and thermally reduced restoring partially the conductive properties of the 2D sheets. In addition to reduced GO, we employed a GRM made of multiple staked sheets of (partially oxidised) graphene bilayers: electrochemical exfoliated GO (eGO) [4].We exploited different deposition methods: i) spin-coating, ii) spray-coating and iii) vacuum-assisted filtration to fabricate macroscopic GRMs thin films with sheets partially stacked. Chemical and morphological properties of the films were characterized by X-ray Photoelectron Spectroscopy (XPS), Atomic Force Microscopy (AFM) and X-ray Diffraction (XRD) measurements. We investigated transport mechanisms measuring the temperature-dependence of the electrical resistivity (ρ) from room temperature down to 5 K. Possible ambiguities on the quantitative analysis of ρ(T) were solved by using a robust self-consistent method based on the reduced activation energy [5], i.e. the logarithmic derivative of resistivity versus temperature: W(T)=-(d lnρ)⁄(d lnT ). This mathematical transformation allowed to analyse ρ(T) dataset with linear functions. We correlated the transport characteristic parameters with the degree of order of our samples and elucidate the role of the sheets vertical stacking, that is of the π-π interaction between overlapped aromatic clusters, in the CT in the film. We also highlighted the differences in CT between reduced GO based films and eGO ones. The presented work could pave the way to develop new models and protocols to access the CT mechanisms in realistic GRMs, such as inks and polymer composites. [1] Ferrari, A. C. et al. Nanoscale 7, 4598-4810, (2015). [2] Palermo V., Chem. Comm. 49, 28, 2848-2857 (2013); Kelly A. et al, Science 356, 6333 (2017). [3] Eda G. et al, J. Physics. Chem.C 113, 15768 (2009); Kaiser a. et al, Nano Letters 9, 1787 (2009); Joung D. and Khondaker S., Phys. Rev. B 86, 235423 (2012). [4] Xia Z. et al, J. Physics. Chem.C 123, 15122 (2019). [5] Zabrodskii A. G., Philos. Mag. B 81, 1131 (2001).
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FRANCESCHINI, PAOLO. « NOVEL SCHEMES FOR ULTRAFAST MANIPULATION OF QUANTUM MATERIALS ». Doctoral thesis, Università Cattolica del Sacro Cuore, 2022. http://hdl.handle.net/10280/111822.
Texte intégralRésumé :
La possibilità di controllare le proprietà elettroniche on-demand su una scala di tempo ultraveloce rappresenta una delle sfide più intriganti verso la realizzazione di dispositivi fotonici ed elettronici di nuova generazione. Stimolata da questo, negli ultimi decenni la ricerca scientifica ha concentrato la propria attenzione su diverse piattaforme a stato solido. Tra tutte, nanostrutture dielettriche (e metamateriali) e materiali correlati si presentano come i più promettenti candidati per la realizzazione di dispositivi dotati di nuove funzionalità. Al di là delle caratteristiche specifiche che rendono i dielettrici più adatti ad applicazioni in fotonica e i materiali correlati ai dispositivi elettronici, entrambe le categorie manifestano nuove funzionalità se soggetti ad uno stimolo esterno sotto forma di impulsi di luce con durata più breve della scala di tempo caratteristica del rilassamento dei gradi di libertà interni al sistema. Infatti, lo stato fuori equilibrio raggiunto a seguito di una foto-eccitazione presenta proprietà elettroniche ed ottiche di gran lunga differenti da quelle all'equilibrio. Pertanto, l'obiettivo di questo lavoro di tesi consiste nello sviluppo di nuovi metodi ed approcci sperimentali in grado di indurre, misurare e controllare nuove funzionalità in materiali complessi su una scala di tempo ultraveloce.The possibility to control the electronic properties on-demand on an ultrafast time scale represents one of the most exciting challenges towards the realization of new generation photonic and electronic devices. Triggered by this, in the last decades the research activity focused its attention to different solid-state platforms. Among all, dielectric nanostructures (and metamaterials) and correlated materials represent the most promising candidate for the implementation of devices endowed by new functionalities. Apart from the specific features making dielectrics more suitable for photonic applications and correlated materials for electronic devices, both categories exhibit new functionalities if subjected to an external stimulus in the form of excitation light pulses shorter than the relaxation timescale of the internal degrees of freedom of the system. Indeed, the out-of-equilibrium state achieved upon photoexcitation exhibits electronic and optical properties highly different from those at equilibrium. Therefore, the aim of this thesis work consists in the development of new methods and experimental approaches capable to induce, measure, and control new functionalities in complex materials on an ultrafast time scale.
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Cricchio, Francesco. « Multipoles in Correlated Electron Materials ». Doctoral thesis, Uppsala universitet, Materialteori, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-132068.
Texte intégralRésumé :
Electronic structure calculations constitute a valuable tool to predict the properties of materials. In this study we propose an efficient scheme to study correlated electron systems with essentially only one free parameter, the screening length of the Coulomb potential. A general reformulation of the exchange energy of the correlated electron shell is combined with this method in order to analyze the calculations. The results are interpreted in terms of different polarization channels, due to different multipoles. The method is applied to various actinide compounds, in order to increase the understanding of the complicate behaviour of 5f electrons in these systems. We studied the non-magnetic phase of δ-Pu, where the spin polarization is taken over by a spin-orbit-like term that does not break the time reversal symmetry. We also find that a non-trivial high multipole of the magnetization density, the triakontadipole, constitutes the ordering parameter in the mysterious hidden order phase of the heavy-fermion superconductor URu2Si2. This type of multipolar ordering is also found to play an essential role in the hexagonal-based superconductors UPd2Al3, UNi2Al3 and UPt3 and in the dioxide insulators UO2, NpO2 and PuO2. The triakontadipole moments are also present in all magnetic actinides we considered, except for Cm. These results led us to formulate a new set of rules for the ground state of a system, that are valid in presence of strong spin-orbit coupling interaction instead of those of Hund; the Katt's rules. Finally, we applied our method to a new class of high-Tc superconductors, the Fe-pnictides, where the Fe 3d electrons are moderately correlated. In these materials we obtain the stabilization of a low spin moment solution, in agreement with experiment, over a large moment solution, due to the gain in exchange energy in the formation of large multipoles of the spin magnetization density.Felaktigt tryckt som Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 705
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Zhou, You. « Correlated Oxides : Material Physics and Devices ». Thesis, Harvard University, 2015. http://nrs.harvard.edu/urn-3:HUL.InstRepos:17464472.
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In this work we study the metal-insulator transition in vanadium dioxide and samarium nickelate and the application of such transitions in electronic devices. Chapter 1 provides an introduction to the Mott metal-insulator transition mechanisms and an overview of the interplay between various degrees of freedom in correlated oxides. The phase transition in vanadium dioxide is presented as an example to emphasize the overarching electron-phonon and electron-electron interaction driven transition mechanisms. In Chapter 2, we describe the growth and structure-functionality relationship of thin film transition metal oxides. Chapter 3 goes on to examine the mechanism of voltage-triggered metal-insulator transition in vanadium dioxide two-terminal threshold switches through dynamic studies. Chapter 4 delves into the mechanism of conductance modulation in electrolyte-gated vanadium dioxide transistors, which reveals the importance of electrochemical effects versus electrostatic effects in these devices. Utilizing the idea of electrochemical doping, we designed and realized a strongly correlated insulating phase in samarium nickel oxide through electron doping with hydrogen and lithium interstitials in Chapter 5. Such techniques can be extended to other materials to achieve reversible and controllable carrier doping with high concentration to study the related physics.Engineering and Applied Sciences - Applied Physics
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Falk, Marcus. « Cultural Materiality : The correlation between material and cultural capital in the late eighteenth century Stockholm elite burgher home ». Thesis, Uppsala universitet, Historiska institutionen, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-360585.
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The eighteenth century saw the slow but steady rise of the middling classes to their nineteenth century social and cultural prominence, reinforced by a changing political landscape and the steadily increasing importance of the market. As the social and cultural power of the city burghers making up the majority of the middling classes grew, so did they start to consume in a manner to reflect to their new status in society. The question that arises then is more exactly how this group consumed, what types of objects that became important and what type of status that became the most paramount. Since status and social groups can differ greatly between both times and places, focus of this investigation is the burgher elite of Stockholm, the social, economical, and cultural centre of Sweden during the whole of the early modern era. By using a combination of Bourdieu's capital theories and Erving Goffman's theories on the presentation of self the inventories of fourteen elite burgher households has been analysed in order to investigate how these individuals constructed their home to present their own perceived social and cultural status. Through a thorough and theoretical investigation of these early modern front regions it can be revealed that the traditional representations of cultural capital, the main form of symbolic status capital, such as paintings and books, albeit important, constituted but a minor part of the capital presentation in the home. Instead it appears as if the most important status capital is presented through sociability, the ability to host social events or, if that option is unavailable, attend social events. Objects with the express function of sociability, such as tea- and dinner-ware, together with chairs, tables, and fashionable interior decoration suggests that sociability indeed stood at the forefront for the presentation of status for the late eighteenth century Stockholm burgher. At the same time, fashionability appears to have been extremely important, with almost all of the investigated households going to great lengths to stay up to date with the most recent trends in both furniture, colours, literature, and china. Much more research is however needed in order to really understand the structures of status and how it was expressed during the early modern times, and especially comparative studies between estate borders is needed in order to understand the status relations between social groups and how this affected status presentations.
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Thompson, Stephen. « Complex energy landscapes in strongly correlated materials ». Thesis, University of Cambridge, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.616204.
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Rösch, Oliver. « Electron phonon interaction in strongly correlated materials ». [S.l. : s.n.], 2005. http://nbn-resolving.de/urn:nbn:de:bsz:93-opus-24707.
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Radmanesh, Seyed Mohammad Ali. « Ultra-low Temperature Properties of Correlated Materials ». ScholarWorks@UNO, 2018. https://scholarworks.uno.edu/td/2511.
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Abstract
After the discovery of topological insulators (TIs), it has come to be widely recognized that topological states of matter can actually be widespread. In this sense, TIs have established a new paradigm about topological materials. Recent years have seen a surge of interest in topological semimetals, which embody two different ways of generalizing the effectively massless electrons to bulk materials. Dirac and, particularly, Weyl semimetals should support several transport and optical phenomena that are still being sought in experiments. A number of promising experimental results indicate superconductivity in members of half-Hesuler semimetals which realize the mixing singlet and triplet pairing symmetry. We now turn to results we got through the work on topological semimetals. This work presents quantum high field transports on Dirac and Weyl topological semimetals including Sr1-yMn1-zSb2 (y, z < 0.1), YbMnBi2 and TaP. In case of Sr1-yMn1-zSb2 (y, z < 0.1), massless relativistic fermion was reported with m* = 0.04-0.05m0. This material presented a ferromagnetic order for in 304 K < T < 565 K, but a canted antiferromagnetic order with a net ferromagnetic component for T < 304 K. These are considered striking features of Dirac fermions For YbMnBi2, we reported the unusual interlayer quantum transport behavior in magnetoresistivity, resulting from the zeroth LL mode observed in this time reversal symmetry breaking type II Weyl semimetal. Also, for Weyl semimetal TaP the measurements probed multiple Fermi pockets, from which nontrivial π Berry phase and Zeeman splitting were extracted. Our ultra-low penetration depth measurements on half-Heuslers YPdBi and TbPdBi revealed a power- law behavior with n= 2.76 ± 0.04 for YPdBi samples and n=2.6 ± 0.3 for TbPdBi sample. We may conclude the exponent n > 2 implies nodless superconducting gap in our samples. Also, we found that despite the increase in magnetic correlations from YPdBi to TbPdBi, superconductivity remains robust in both systems which indicates that AF fluctuations do not play a major role in superconducting mechanism.
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McConnell, Andrew W. « Reflectance study of two dimensional correlated electron materials ». Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape9/PQDD_0025/NQ51897.pdf.
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Tunnicliffe, Elizabeth Mary. « Experimental studies of superconductivity in correlated electron materials ». Thesis, University of Cambridge, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.611729.
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He, Yang. « Scanning Tunneling Microscopy Study on Strongly Correlated Materials ». Thesis, Harvard University, 2015. http://nrs.harvard.edu/urn-3:HUL.InstRepos:26718719.
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Strongly correlated electrons and spin-orbit interaction have been the two major research directions of condensed matter physics in recent years. The discovery of high temperature superconductors in 1986 not only brought excitement into the field but also challenged our theory on quantum materials. After almost three decades of extensive study, the underlying mechanism of high temperature superconductivity is still not fully understood, the reason for which is mainly a poor understanding of strongly correlated systems. The phase diagram of cuprate superconductors has become more complicated throughout the years as multiple novel electronic phases have been discovered, while few of them are fully understood. Topological insulators are a newly discovered family of materials bearing topological non-trivial quantum states as a result of spin-orbit coupling. The theoretically predicted topological Kondo insulators as strongly correlated systems with strong spin-orbital coupling make an ideal playground to test our theory of quantum materials.
Scanning tunneling microscopy (STM) is a powerful technique to explore new phenomena in materials with exotic electronic states due to its high spacial resolution and high sensitivity to low energy electronic structures. Moreover, as a surface-sensitive technique, STM is an ideal tool to investigate the electronic properties of topological and non-topological surface states. In this thesis, I will describe experiments we performed on high temperature superconductors and topological Kondo insulators using STM.
First, I will describe our experiments on a Bi-based high temperature superconductor $\mathrm{Bi_2Sr_2CuO_{6+\delta}}$. The quasiparticle interference technique uncovers a Fermi surface reconstruction. We also discovered the coexistence of Bogoliubov quasiparticle and pseudogap state at the antinodes. Afterwards, I will discuss our discovery of $d$-form factor density wave in the same material, showing the omnipresence of $d$ form factor density wave above and below the Fermi surface reconstruction. The relation between the $d$-form factor density wave and the pseudogap state is discussed.
Second, I will describe our experiments on topological Kondo insulator $\mathrm{SmB_6}$ where spin-orbit coupling plays an important role in the strongly correlated electron system. I will present the spectroscopic evidence of Kondo hybridization based on a spectral decomposition technique. I will introduce a dimension reduction method in the fitting procedure to reduce the computation time by two order of magnitude. I will also discuss the possible quasiparticle interference patterns we discovered in $\mathrm{SmB_6}$.Physics
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Flesch, Andreas Robert [Verfasser]. « Electronic structure of strongly correlated materials / Andreas Robert Flesch ». Aachen : Hochschulbibliothek der Rheinisch-Westfälischen Technischen Hochschule Aachen, 2014. http://d-nb.info/1049350235/34.
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Zeigermann, Philipp, Dirk Mehlhorn, Jörg Kärger et Rustem Valiullin. « Correlating phase state and transport in hierarchical mesoporous materials ». Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-183277.
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Zeigermann, Philipp, Dirk Mehlhorn, Jörg Kärger et Rustem Valiullin. « Correlating phase state and transport in hierarchical mesoporous materials ». Diffusion fundamentals 20 (2013) 60, S. 1, 2013. https://ul.qucosa.de/id/qucosa%3A13637.
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Zhao, Yu. « Correlation between structure, doping and performance of thermoelectric materials ». Diss., Virginia Tech, 2014. http://hdl.handle.net/10919/64899.
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Thermoelectric materials can convert thermal energy into electrical energy and vice-versa. They are widely used in energy harvesters, thermal sensors, and cooling systems. However, the low efficiency and high cost of the known material compositions limit their widespread utilization in electricity generation applications. Therefore, there is a strong interest in identifying new thermoelectric materials with high figure of merit. In response to this need, this dissertation works on the synthesis, structure, doping mechanism, and thermoelectric properties of zinc oxide (ZnO) and lead tellurium (PbTe). The main focus is on ZnO based materials and in improving their performance. The influences of micro- or nano-structures on thermal conductivity, as well as the correlation between the electrical property and synthesis conditions, have been systematically investigated.
ZnO is a likely candidate for thermoelectric applications, because of its good Seebeck coefficient, high stability at high temperature, non-toxicity and abundance. Its main drawbacks are the high thermal conductivity (κ) and low electrical conductivity (σ). To decrease κ, two novel structures—namely, precipitate system and layered-and-correlated grain microstructure—have been proposed and synthesized in ZnO. The mechanisms iii governing the nature of thermal behavior in these structures have been explored and quantified. Due to strong phonon scattering, the nano-precipitates can reduce the thermal conductivity of ZnO by 73%. The ZnO with layered-and-correlated grains can further reduce κ by about 52%, which compares favorably with the dense ZnO with nanoprecipitates. The figure of merit of this ZnO based structure was 0.14×10⁻³ K⁻¹ at 573 K. In order to understand the electrical behavior in nanostructured ZnO, the impact of Al doping and chemical defects in ZnO under different synthesis conditions were studied. Under varying sintering temperatures, atmospheres and initial physical conditions, ZnO exhibited very distinct σ. High temperature, lack of oxygen, vacuum condition, and chemically synthesized powder can increase the carrier concentration and σ of ZnO. A promising alloy system, PbTe-PbS, undergoes natural phase separation by nucleation and growth, and spinodal decomposition depending on the thermal treatment. The correlation between the thermal treatment, structure, and the thermoelectric properties of Pb0.9S0.1Te has been studied. The nano-precipitates were incorporated in the annealed alloy resulting in a 40% decrease in κ. The PbS precipitation was shown to enhance the carrier concentration and improves the Seebeck coefficient. These concomitant effects result in a maximum ZT of 0.76 at 573 K.
Throughout the thesis, the emphasis was on understanding the impact of the microstructures on thermal conductivity and the effect of the synthesis condition on thermal and electrical properties. The process and control variables identified in this study provide practical ways to optimize the figure of merit of ZnO and PbTe materials for thermoelectric applications.Ph. D.
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Shanmugam, Janaki. « Correlation of optical anisotropy with structural changes in Ge2Sb2Te5 ». Thesis, University of Oxford, 2018. http://ora.ox.ac.uk/objects/uuid:8cee7355-0ff6-4939-a606-a406c7a9823d.
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Ge2Sb2Te5 (GST) is an established phase-change material that undergoes fast reversible transitions between amorphous and crystalline states with a high electro-optical contrast, enabling applications in non-volatile optical and electronic memories and optically-switchable structured metamaterials. This work demonstrates that optical anisotropy can be induced and recorded in pure and doped GST thin films using circularly polarised light (CPL), opening up the possibility of controlled induction of anisotropic phase transition in these and related materials for optoelectronic and photonic applications. While the amorphous-to-crystalline phase transition in GST has generally been understood to proceed via a thermal mechanism, significant optical anisotropy (measured by circular dichroism (CD) spectroscopy in this work) strongly suggests that there is an electronic athermal component of the phase change induced by the handedness of circularly polarised nanosecond laser pulses and implies the existence of chiral structures or motifs. Optically active and inactive regions in the films have also been studied using X-ray and electron diffraction and spectroscopic techniques in order to obtain a structural picture that can be correlated to the optical changes observed and the findings offer surprising evidence of the nature of the phase transition. Regions exhibiting higher CD signal intensities were found to be mostly amorphous with elemental phase separation observed within modified surface features. Several mechanisms are proposed for the observed phenomena, including the retention of chiral crystalline fragments in laser- irradiated and melt-quenched amorphous regions, which could explain the results of CD spectroscopy. This may be extended to other material systems and harnessed in potential metamaterials, plasmonics, photonics or chiroptical applications.
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Morales, Sánchez Alfredo. « Correlation between optical and electrical properties of materials containing nanoparticles ». Doctoral thesis, Universitat Autònoma de Barcelona, 2008. http://hdl.handle.net/10803/3409.
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En esta tesis, capas de óxido de silicio rico en silicio [SRO, (SiOx, x<2)] con diferentes excesos de silicio fueron depositadas por medio de la técnica de depósito químico en fase vapor a baja presión (LPCVD). Un segundo conjunto de muestras de SRO implantadas con silicio (SI-SRO) adicional fueron también fabricadas. Nanopartículas de silicio (Si-nps) en estas capas fueron creadas después de someter a las muestras a un tratamiento térmico en alta temperatura (1100 y 1250º C). La composición, microestructura y propiedades ópticas de estas capas de SRO y SI-SRO fueron analizadas en función de los diferentes parámetros tecnológicos, tales como exceso de silicio, implantación de silicio, así como de la temperatura de tratamiento térmico.Una vez conocido la microestructura, composición y propiedades ópticas de estos materiales, capas de SRO que exhibieron la mejor propiedad fotoluminiscente (FL más intensa) fueron escogidas para analizar sus propiedades eléctricas y electro-ópticas; estructuras Metal-Óxido-Semiconductor (MOS) fueron fabricadas usando las capas de SRO como material dieléctrico para tales estudios. Capas de SRO con exceso de silicio de ~4.0 and ~2.2 at.% y grosores de entre 24 y 80 nm fueron depositadas. El mecanismo de conducción en estas películas es analizado haciendo uso de modelos como tuneleo asistido por trampas (TAT) y tuneleo Fowler-Nordheim (FN) en bajos y altos campos eléctricos, respectivamente.
Las mediciones eléctricas mostraron importantes resultados tales como una reducción en la capacitancia y corriente durante el barrido de voltaje o después de estresar eléctricamente los dispositivos. Dichos efectos son relacionados con la aniquilación de caminos conductivos que son creados por nanoclusters de silicio (Si-cls) que se encuentran dispersados dentro de la película de SRO.
Además de lo anterior, algunos dispositivos exhibieron fluctuaciones en la corriente en la forma de picos y un comportamiento de escalera muy claro a temperatura ambiente. Dichos efectos son relacionados con los llamados efectos de bloqueo Coulómbico (CB) que se presentan en las nanopartículas de silicio que se encuentran dentro de las capas de SRO. A partir del ancho de cada escalón se pudo estimar el tamaño (cerca de 1 nm) de las nanopartículas.
Estudios de luminiscencia de efecto de campo en las capas de SRO son estudiados por excitar los dispositivos con pulsos de voltaje. Además de la electroluminiscencia (EL) pulsada, es mostrado que estos dispositivos también muestran EL en voltaje continuo, donde la emisión es observada como múltiples puntos brillantes de varios colores sobre la superficie de los dispositivos cuando estos son polarizados en inversa. El espectro de emisión en dichos dispositivos es amplio y va desde 400 hasta 900 nm.
Finalmente, una correlación entre las propiedades microestructurales, eléctricas y luminiscentes (FL y EL) es analizada y discutida.
In this thesis, silicon rich oxide [SRO, (SiOx, x<2)] films with different silicon excesses were deposited by low pressure chemical vapor deposition (LPVCD). Besides, Si implanted SRO (SI-SRO) films were also fabricated. Si-nps in these films were created after a thermal annealing at high temperature (1100 and 1250º C). The composition, microstructure and optical properties of these SRO and SI-SRO films were analyzed as a function of the different technological parameters, such as silicon excess, Si ion implantation dose, and thermal annealing temperature.
Once the microstructure, composition as well as the optical properties of these materials is known, SRO films which exhibited the best photoluminescent (strongest PL) properties were chosen in order to analyze their electrical and electro-optical properties.
Simple Metal-Oxide-Semiconductor (MOS) structures using the SRO films as the dielectric layer were fabricated for these studies. SRO films with Si-excess of ~4.0 and ~2.2 at.% and thickness ranging from 24 to 80 nm were deposited. The conduction mechanism in these films is analyzed by making use of trap assisted tunnelling (TAT) in low electric field as well as Fowler-Nordheim (FN) tunnelling in high electric fields.
The electrical measurements exhibited important results, such as a reduction in capacitance and current during the sweep or after applying a constant bias. These effects are ascribed to the annihilation of conduction paths created by silicon clusters (Si-cls) inside the SRO films.
A part from that, some devices exhibited current fluctuations in the form of spike-like peaks and a clear staircase at room temperature. These effects were related to Coulomb blockade (CB) effects in the silicon nanoparticles embedded in the SRO films. And from the current plateaus, the size of the Si-nps (about 1 nm) was calculated.
Field effect luminescence of these SRO films was studied by alternating negative (positive) to positive (negative) voltages (pulsed excitation). Moreover, it is demonstrated that these SRO films show EL emission in continuous current voltage, observed at naked eye. Multiple shining spots of several colours are seen on the MOS-like structure surface when reversely biased. These devices display a broad electroluminescent emission spectrum which goes from 400 nm up to 900 nm.
Finally, a correlation between the structural, electrical and luminescent (PL and EL) properties is discussed.
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Jürgens, Stefan [Verfasser], Björn [Gutachter] Trauzettel et Giorgio [Gutachter] Sangiovanni. « Correlated Topological Materials / Stefan Jürgens ; Gutachter : Björn Trauzettel, Giorgio Sangiovanni ». Würzburg : Universität Würzburg, 2017. http://d-nb.info/1137836067/34.
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Shenton-Taylor, Caroline. « Development of highfieldmagnetic Compton scattering andstudies of strongly correlated materials ». Thesis, University of Warwick, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.504860.
Texte intégralRésumé :
Magnetic Compton scattering (MCS) has been used to probe the spin momentum densities of ferromagnetic materials. A key focus of this work was the installation and commissioning of a new 9T cryomagnet, located at the European Synchrotron Radiation Facility in France. This generated a unique sample environment, allowing magnetic systems to be measured under applied fields ofup to 9T at temperatures from I.3K to 300K. This work reports on a series of materials studied using the new cryomagnet, alongside other interesting ferromagnetic systems measured at SPri~g-8 in Japan. A magnetic Compton profile (MCP) is produced by a difference measurement, obtained either by reversing the handedness of the incoming photon flux, or, reversal of an external magnetic field. As part ofthe cryomagnet installation tests, nickel MCPs were measured using both high and low magnetic field reversal and by using a helicity reversed approach. The helicity flipped approach was found to require large, relatively flat samples, for ease all the systems presented in this thesis were thereafter measured by magnetic field reversal. The hexaboride CeB6 was an ideal candidate for study using the new cryomagnet and allowed comparison with previous measurement. Approximately 10% of the spin moment was attributed to Ce 4felectrons with the remainder dominated by itinerant 5d and 2p contributions. Although difficult to distinguish between the 5d and 2p electrons, a boron contribution was essential in order to model the data at low momentum. The spin-dependent momentum density of the magnetocaloric material Gd7Pd3 was probed by magnetic Compton scattering using the cryomagnet facility at the ESRF. The total spin moment, at 2K, was determined as 50.8±0.7 JIB (f.u.rl . The Gd 4f contribution to the spin moment was determined K-as 43.4±l.8 JIB (f.u.r\ the Gd 5d moment as 4.4±0.7 JIB (f.u.rl and the Pd 4d spin moment contribution as 2.9±1.1 JIB (f.u.rl At 280K the total spin moment was 27.3±0.9 JIB (f.u.rl with individual contributions determined as: Gd 4fspin moment of 23.8±l.1 JIB (f.u·rl , Gd 5d contribution of2.2±O.5 JlB(f.u.rl and a Pd 5dspin moment of 1.2±0.6J1B(f.u.rl . MCPs measurements on single crystal CO(1-x1exS2 samples were measured at the SPring-8 synchrotron. The experimental measurements were compared to linear muffm tin orbital (LMTO) predictions which successfully modelled the profile shape down to l.a.u. By altering the small level of Fe doping a small ·change in the profile shape was observed. Through application of band structure calculations the density of states was calculated and applied to estimate the spin polarisation. Fe304MCPs were measured at SPring-8 on beam line BL08W. A single crystal sample was measured crossing the Verwey transition at 120K in the [100], [110] and [111] directions by reversal ofa 2.5T external field. For each direction, crossing the Verwey transition did not result in a change in profile shape. Previous research suggested that geometrical frustration in the spinel caused a large magnetic anomaly around the Verwey transition temperature. The Warwick results provided no evidence to support this suggestion. MCS measurements, at SPring-8, allowed investigation of the NiO nanoparticle spin moment. For a particle size of 6.4±l.5 om the unexpected result of an enhanced spin moment was observed of 0.078 ± 0.005 JIB f.u.- l This exceeded the total moment magnitude of 0.033 ± 0.002 JIB f.u: 1. This cannot be predicted by Ne6I's model of superparamagnetism. It suggests an appreciable orbital moment in an anti-parallel arrangement with the spin contribution. The magnitude ofthe spin moment was found to increase with decreasing particle size.
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Pike, Kevin John. « An NMR study of some low-dimensional magnetically correlated materials ». Thesis, University of Warwick, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.344004.
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Gardner, Dillon Richard. « X-Ray scattering investigations of subtle ordering in correlated materials ». Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/99312.
Texte intégralRésumé :
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2015.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 117-127).
The interaction of many particles can lead to spectacular new phases of matter whose properties and collective excitations bear little resemblance to the individual particles and interactions. Understanding how the macroscopic state transforms from one phase to another provides key insights into the underlying physics. In this thesis, we study two poorly understood states: the Hidden Order (HO) phase of URu2Si2 and the pseudogap of high Tc cuprates. In the case of URu2 Si2 , the HO phase causes a significant restructuring of the Fermi surface. Thermal conductivity and ultrasound measurements suggest that the lattice degrees of freedom couple strongly to this change. Additionally, torque magnetometry and x-ray diffraction suggest a breaking of C4 rotational symmetry. We directly study the lattice through x-ray scattering. We see no change of the acoustic phonon dispersions or of the phonon lifetimes from the HO transition. Calculations of phonon branch contributions to thermal transport suggest that magnetic excitations are responsible for the increase in thermal conductivity in the HO phase. For high Tc cuprates, the pseudogap state is not well understood. It is not even clear if it is a true phase transition or if it is a crossover regime. Recent reports of circular dichroism at the copper K-edge in double-layer BSCCO suggest breaking of inversion symmetry in the pseudogap. We perform copper K-edge dichroism measurements on carefully aligned BSCCO. Azimuthal rotations reveal the circular dichroic signal the result of linear bleed through. Polar rotations suggest that the previous reports were likely caused by misalignment.
by Dillon Richard Gardner.
Ph. D.
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Zhao, H. « Experimental and numerical modelling of gasket materials and property correlation ». Thesis, Liverpool John Moores University, 2015. http://researchonline.ljmu.ac.uk/4555/.
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In this work, a detailed combined numerical-experimental program has been developed to study the shore hardness testing of rubber materials principally used for gasket applications. The correlation between shore hardness and linear elastic and hyperelastic properties has been systematically investigated. A detailed FE model of the shore A hardness test has been developed with re-meshing functions in order to cope with the large deformation during simulation of shore hardness tests over a range of E values. The model is used in modelling shore A hardness on samples with standard thickness (over 6mm) and the result is validated against published experimental data. FE indentation models of thin samples are then developed and successfully used to predict the shore hardness of thinner samples over a property range relevant to gasket applications. A chart linking shore hardness, Young’s modulus and samples thickness is established and used to analyse shore hardness of three cases including silicone rubber made in the lab with different thicknesses, thin silicone rubber gasket and an EPDM (Ethylene Propylene Diene Monomer) gasket for plate heat exchangers. In all of the cases, the estimated E values based on shore hardness tests are able to predict the deformation of the material under different loading conditions including tensile and compression tests on samples of different shapes. In shore OO hardness modelling, the numerical results show a good agreement with analytical solution for spherical indenters. The shore hardness, thickness and E value chart predicted is used to evaluate the properties (Young’s modulus) of a soft silicone rubber and a latex rubber, in both cases, the E values predicted from hardness tests are able to predict the deformation of the material under tension and compression. In the case of latex rubber, the results also agree with hyperelastic properties from combined tensile and planar tests. Based on the FE model developed, extensive data over a larger spectrum of material properties are developed and used in developing an Artificial Neural Network (ANN) program for inverse estimation of material properties from shore hardness and direct prediction of shore hardness for the cases when the material properties are known. The results show that the E values can be predicted from shore hardness tests with accuracy within 10% for both shore A and shore OO hardness tests. In the direct analysis, the ANN is able to predict the shore hardness values accurately from the linear elastic properties and sample thickness or a combination of hyperelastic parameters and sample thickness. The effect of indenter shape, testing condition, and choice of linear or hyperelastic material models on shore hardness tests are established and discussed, which would provide a detailed understanding to further enhance the use of shore hardness tests as a quick and effective way to test rubber materials.
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Hu, Tao. « The Interplay Between Magnetism and Superconductivity in Strongly Correlated Materials ». Kent State University / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=kent1254297944.
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Ferlauto, Laura. « Correlation between structural and electrical properties of organic semiconducting materials ». Thesis, Strasbourg, 2015. http://www.theses.fr/2015STRAF009/document.
Texte intégralRésumé :
Cette thèse présents plusieurs techniques de caractérisation appliqués à diverses matières organiques dans le but de démêler leur structure-propriétés relation once encapsulés comme matériaux actifs dans les dispositifs de OFET. Un soin particulier est alors dédié aux méthodes de caractérisation structurale (2D-GIXRD, XRR et XRD) à la fois de source de laboratoire classique et de rayonnement de synchrotron. Divers matériaux polymères organiques, compris de p- et n-type de petites molécules et polymères en solution ou déposés par sublimation sous vide sont étudiées. En particulier, l'étude de OFET basée sur deux fonctionnalisés isomères péryléne ne différant que par la forme des alkyle côté chaînes démontre comment la nature ramifié et asymétrique des chaînes peut conduire à une amélioration de la performance électrique avec un simple traitement thermique post-dépôt, tandis que la fabrication de dispositifs ambipolaire polymères au moyen de la technique Langmuir-Schaefer souligne l'importance de la méthode de dépôt sur l'agencement de la matière sur la surface du substrat. Une approche inhabituelle, nommé enquête structurelle in_situ et en temps réel, est aussi présenté pour évaluer les modifications structurelles dans les films minces organiques subissent un processus particulier. Plus précisément, la réponse de la structure des films minces de pentacene à l’application de VSG et VSD au OFET et des films minces dérivés de TTF à la variation d’humidité ont été étudiésThis thesis presents multiple characterization techniques applied to various organic materials with the ultimate goal of unraveling their structure-properties relationship once encapsulated as active materials in OFETs devices. Particular care is then dedicated to the structural characterization methods (2D-GIXRD, XRR and XRD) both from classical laboratory source and from synchrotron radiation. Various organic materials, comprising p- and n-type small molecules and polymers deposited from solution or by vacuum sublimation are investigated. In particular, the study on OFETs based two functionalized perylene isomers differing only in the shape of the alkyl side-chians demonstrates how the branched and asymmetric nature of the chains can lead to an improvement of the electrical performance with a simple post-deposition thermal treatment, while the fabrication of ambipolar polymeric devices by means of Langmir-Schaefer technique highligts the importance of the deposition method on the arrangement of the material on the substrate surface. A more unusual approach, named in-situ and real-time structural investigation, is also presented to evaluate structural modifications in organic thin films undergoing a particular process. Specifically, the structural responce of pentacene thin films to the application of VSG and VSD to the OFET and of TTF derivatives thin films to the variation of humidty were investigated
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FERLAUTO, Laura. « CORRELATION BETWEEN STRUCTURAL AND ELECTRICAL PROPERTIES OF ORGANIC SEMICONDUCTING MATERIALS ». Doctoral thesis, Università degli studi di Ferrara, 2015. http://hdl.handle.net/11392/2389073.
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Åström, August, et Morgan Sten. « Macro segregation in continuous cast HSLA steels : With correlation to impact toughness ». Thesis, KTH, Materialvetenskap, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-254348.
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The report reviews macro segregations in continuous cast steels and possible correlations to impact toughness. The purpose of the thesis is to investigate centreline segregates and V-segregates to see which of them that affect impact toughness the most. Apart from a literature study, Charpy-V data was collected with permission from SSAB for two steel types, grade A and grade B, each with respective dominant segregation type. The collected data was yielded in three individual Charpy-V tests at different spots on the metal sheet, derived within a close area. The average value of these tests were used in statistical analysis to observe the spread of values in different heats of the two steels. Additionally, the specimens were etched and captured in cross-section. Results indicated that for the data of grade A, where centreline segregates were dominant, the spread of values was higher than for the data of grade B. The conclusion is that centreline segregations are worse in relation to impact toughness, since higher deviations translates to less predictable properties from a customers perspective.Denna rapport granskar makrosegringar i stränggjutet stål och eventuella kopplingar till slagseghet. Centrumsegringar och V-segringar undersöks för att undersöka vilken segringstyp som har störst effekt på slagseghet, vilket är syftet med denna avhandling. Förutom en litteraturstudie, hämtades Charpy-V data med SSAB’s medgivande från två olika stålsorter, kvalitet A och kvalitet B, med respektive dominant segringstyp. Datan som inhämtades erhölls från tre stycken Charpy-V tester för varje plåt, från ett närliggande område. Medelvärdet för dessa datapunkter användes i statistisk analysför att obeservera spridningen av datapunkter i olika charger av de två stålen. Dessutom, erhölls segringsbilder för respektive slab från SSAB. Resultaten visade att datapunkterna för kvalitet A, som hade centrumsegring som domiant segringstyp, var mer spridd än datan för kvalitet B. Således, är slutsatsen att centrumsegring är värre i relation till slagseghet eftersom en högre avvikelse leder till mindre förutsägbara egenskaper från en kunds perspektiv.
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Armengol, Monica. « Correlating material properties to matrix constitution on porcine tibial plateaux ». Thesis, University of Oxford, 2014. https://ora.ox.ac.uk/objects/uuid:5f5235b8-2517-4f78-b6c4-375e767e5e4a.
Texte intégralRésumé :
Osteoarthritis (OA) is one of the most common musculoskeletal diseases, mainly affecting people over the age of 60. This disease has multiple symptoms which include wear and loss of articular cartilage and debilitating pain. Its initiation and progression is not well understood and, at the moment, there is no cure. It is important that efforts are made to understand OA because as global life expectancy increases, diseases which affect the ageing population will become more predominant. However, before it is possible to understand what happens to cartilage in the diseased state, the interaction of cartilage structure, mechanical properties and external stimuli in healthy cartilage must be characterised first. The knee joint is commonly affected by OA. Knee OA is often unicompartmental (UKOA), occurring in either the medial or lateral compartment alone. The location of the lesions in UKOA has been observed to be very repeatable among patients. We believe that this could be explained by variations in cartilage properties over articular surfaces coupled with loading patterns. The distribution of material properties, glycosaminoglycans(GAG) concentration and cartilage thickness in healthy cartilage on six porcine tibial plateaux were examined. Approximately 1000 measurements were taken of in-situ mechanical properties of articular cartilage-on-bone through indentation using a novel mechanical testing machine on whole specimens. The Whole Articular Surface Indentation Machine (WASIM) possesses 5 degrees of freedom (DOF) and allows the interchange of several probes such as an indenter (hemisphercal with 1.35 mm radius), high resolution laser and ultrasound (US). The three dimensional geometry of articular surfaces were obtained by laser scanning. Routines were developed to analyse this topography, automatically calculate the surface normals and then rotate the specimen relative to the indenter; normal indentation was performed at every test point (displacement controlled, 10 percent per second (pps) strain rate). GAG concentrations in cartilage plugs (4 mm) were obtained using DMMB and an imaging method which combined a cationic contrast agent with fluoroscopy. Mechanical properties (elasticity modulus) were found to vary between 1 and 40 MPa depending on the spatial location of the test points on the articular surface. The differences in elasticity moduli between regions on the tibial plateaux correspond to the position of the meniscus and load-bearing areas. Central areas on each tibial compartment were found to have the highest stiffness, while peripheral areas, as well as areas uncovered by the meniscus were found to have a lower stiffness. Concentrations of GAG were found to be between 1 and 20 μg/mg depending on the location of test points. Overall, results showed heterogeneous distribution of elastic modulus, GAG concentration and cartilage thickness in terms of their spatial location over the tibial plateaux. Repeatable patterns were observed between all of the six tested specimens. These patterns were correlated to the position of the menisci, which lead to grouping parameters in regions. Region analysis showed inverse correlations ( r ) between GAG concentration and elastic modulus (-0.1<r <-0.6), and direct correlation between GAG concentration and cartilage thickness (0.1<r<0.6) across specimens. Finally, an analysis of the gradient changes in the mechanical properties over the tibial plateaux showed that steep gradients (i.e. relatively large changes in stiffness) occurred in locations that are associated with UKOA lesion locations in human joints. This work provides insight into the variation, distribution and correlation of mechanical properties, GAG concentration and cartilage thickness in healthy cartilage. Additionally, a testing device which can automatically scan and rotate uneven surfaces to allow normal indentation was introduced. This machine has the potential to measure mechanical properties and biological composition at the same test points in whole specimens, and therefore create distribution maps of different parameters. Further work needs to be carried out on healthy human articular cartilage to assess whether similar patterns are found. Also, implementation of these methods can be used to assess deterioration at different stages of disease.
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Fulcher, Jared T. « A DESIGN PATHFINDER WITH MATERIAL CORRELATION POINTS FOR INFLATABLE SYSTEMS ». UKnowledge, 2014. http://uknowledge.uky.edu/me_etds/39.
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The incorporation of inflatable structures into aerospace systems can produce significant advantages in stowed volume to mechanical effectiveness and overall weight. Many applications of these ultra-lightweight systems are designed to precisely control internal or external surfaces, or both, to achieve desired performance. The modeling of these structures becomes complex due to the material nonlinearities inherent to the majority of construction materials used in inflatable structures. Furthermore, accurately modeling the response and behavior of the interfacing boundaries that are common to many inflatable systems will lead to better understanding of the entire class of structures. The research presented involved using nonlinear finite element simulations correlated with photogrammetry testing to develop a procedure for defining material properties for commercially available polyurethane-coated woven nylon fabric, which is representative of coated materials that have been proven materials for use in many inflatable systems. Further, the new material model was used to design and develop an inflatable pathfinder system which employs only internal pressure to control an assembly of internal membranes. This canonical inflatable system will be used for exploration and development of general understanding of efficient design methodology and analysis of future systems. Canonical structures are incorporated into the design of the phased pathfinder system to allow for more universal insight. Nonlinear finite element simulations were performed to evaluate the effect of various boundary conditions, loading configurations, and material orientations on the geometric precision of geometries representing typical internal/external surfaces commonly incorporated into inflatable pathfinder system. The response of the inflatable system to possible damage was also studied using nonlinear finite element simulations. Development of a correlated material model for analysis of the inflatable pathfinder system has improved the efficiency of design and analysis techniques of future inflatable structures.
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Armengol, Monica. « Correlating material properties to matrix constitution in porcine articular cartilage ». Thesis, University of Oxford, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.711780.
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Thunström, Patrik. « Correlated Electronic Structure of Materials : Development and Application of Dynamical Mean Field Theory ». Doctoral thesis, Uppsala universitet, Materialteori, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-173300.
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This thesis is dedicated to the development, implementation and application of a combination of Density Functional Theory and Dynamical Mean Field Theory. The resulting program is shown through several examples to be a powerful and flexible tool for calculating the electronic structure of strongly correlated materials. The main part of this work is focused on the development and implementation of three methods for solving the effective impurity model arising in the Dynamical Mean Field Theory: Hubbard-I approximation (HIA), Exact Diagonalization (ED), and Spin-Polarized T-matrix Fluctuation-exchange (SPTF). The Hubbard-I approximation is limited to systems where the hybridization between the 4f-orbitals and the rest of the material can be completely neglected, and can therefore not capture any Kondo physics. It has been used to study the atomic-like multiplet spectrum of the strongly localized 4f-electrons in the Lanthanide compounds YbInCu4, YbB12, Yb2Pd2Sn, YbPd2Sn, SmB6, SmSn3, and SmCo5. The calculated spectral properties are shown to be in excellent agreement with experimental direct and inverse photoemission data, clearly affirming the applicability of the Hubbard-I approximation for this class of systems if we are not focusing on Kondo physics. Full self-consistence in both self-energy and electron density is shown to be of key importance in the extraction of the magnetic properties of the hard permanent magnet SmCo5. The Exact Diagonalization solver is implemented as an extension of the Hubbard-I approximation. It takes into account a significant part of the hybridization between the correlated atom and the host through the use of a few effective bath orbitals. This approach has been applied to the long-standing problem of the electronic structure of NiO, CoO, FeO, and MnO. The resulting spectral densities are favorably compared to photoemission spectroscopy. Apart from predicting the correct spectral properties, the Exact Diagonalization solver also provides full access to the many-body density operator. This feature is used to make an in-depth investigation of the correlations in the electronic structure, and two measures of the quantum entanglement of the many-body ground-states are presented. It is shown that CoO possesses the most intricate entanglement properties, due to a competition between crystal field effects and Coulomb interaction, and such a mechanism likely carries over to several classes of correlated electron systems. The Exact Diagonalization solver has also been applied to the prototypical dilute magnetic semiconductor Mn doped GaAs, a material of great importance in the study of future spintronics applications. The problem of Fe impurities in Cs has been used to study the dependence of the spectral properties on the local environment. Finally, the Spin-polarized T-matrix Fluctuation-exchange solver has been implemented and applied to more delocalized electron systems where the effective impurity problem can be solved as a perturbation with respect to the strength of the local Coulomb interaction. This approach has been used to study the magnetic and spectral properties of the late transition metals, Fe, Co and Ni, and NiS.
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Jenkins, Morgan Christen. « Fresh Mix Properties and Flexural Analysis with Digital Image Correlation of Additively Manufactured Cementitious Materials ». Thesis, Virginia Tech, 2020. http://hdl.handle.net/10919/96560.
Texte intégralRésumé :
Recently, additive manufacturing (AM), or "3D printing," is expanding into civil infrastructure applications, particularly cementitious materials. To ensure the safety, health, and welfare of the public, quality assurance and quality control (QA/QC) methods via standardized testing procedures are of the upmost importance. However, QA/QC methods for these applications have yet to be established. This thesis aims to implement existing ASTM standards to characterize additive manufactured cementitious composites and to gather better information on how to tackle the challenges that are inherent when printing with cementitious materials. In this work, fresh mix properties and hardened concrete properties were investigated using current ASTM standards as a starting point for applying or adapting them for AM applications.
Specifically, this project applied existing ASTM standards for fresh mix mortars to measure setting time, flow, and early compressive strength as qualitative indicators of printability, pumpability, and buildability. The fresh mix properties were investigated for 12 different mortar mixes to demonstrate the effect that moisture content, absorption, and sand type can have on these fresh mix properties. The results for setting time and compressive strength demonstrated that there was less variability in the properties when the moisture condition of the aggregate was measured and accounted. Flow was shown to be strongly influenced by the sand type.
Additively manufactured mortars were used to print a box in a layer-by-layer process. To evaluate the effect of layering on the flexural strength, three-point bending tests were implemented using four different loading orientations to explore the anisotropic mechanical properties. The observed anisotropic behavior was corroborated with stereo-digital image correlation data showing the stress-strain and load-deflection relationships. Two orientations (A and B) demonstrated brittle behavior while the other two orientations (C and D) experienced quasi-brittle behavior. In addition, setting a minimum unit weight of 132 pcf enabled an analysis of the effect that defects had on the mechanical performance: specimens greater than 132 pcf demonstrated greater and less variable strengths than the specimens less than 132 pcf. The discussion of how defects impacted performance of the different orientations can be valuable when determining how to effectively model, design, and inspect 3D printed structures in the future.
The findings of this thesis confirm that existing ASTM standards for mortars can be modified and applied to AM cementitious composites for QA/QC. It is recommended that mixtures used in 3D printing of cementitious composites should design and accommodate the moisture condition of the aggregate to optimize the predictability of the fresh and early-age properties. For the hardened properties, it is recommended that testing procedures such as flexural testing account for anisotropic behavior. Furthermore, for implementation of 3D printed concrete structures, it is highly recommended that design is a function of loading orientation due to the anisotropic properties of the composite.Master of Science
Recently, additive manufacturing (AM), or "3D printing," is expanding into civil infrastructure applications, specifically cementitious materials such as mortar and concrete. Understanding and predicting the behavior of the materials when using this new technique is vital for quality assurance and quality control (QA/QC). However, standard test methods have yet to be established for this new construction technique. This thesis aims to use existing testing standards to characterize AM cementitious composites and to gather better information on how to tackle the challenges of printing with these materials. In this work, properties before and after the materials hardened were studied by adapting current testing standards. Specifically, this project applied existing testing standards for fresh mix mortars to measure setting time, flow, and early compressive strength. These properties can serve as indicators of specific printing requirements. The fresh mix properties were studied for 12 different mortar mixes to show the effect of moisture content, absorption, and sand type. The results suggest that there was less variability in the properties when the moisture condition and type of the aggregate was accounted. The fresh mix materials were printed in a layer-by-layer process and then hardened in place. The effects of the layers were explored by performing flexure tests using four orientations with respect to how the load was applied to the layers. The observed difference in behavior for the different orientations was supported by digital image correlation data. In addition, an analysis of the effect defects had on the performance was included. Understanding how defects impacted performance can be valuable for effectively designing 3D printed structures in the future. The results of this thesis confirm that existing testing standards for mortars can be adapted and applied to AM cementitious materials for QA/QC. It is recommended that mixtures used in 3D printing of cementitious materials should account for the moisture condition of the aggregate to improve the predictability of the fresh and early-age properties. For the hardened properties, it is recommended that the design is a function of loading orientation due to the difference in behavior for the different orientations of the material.
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Hauber, Brett Kenneth. « Fatigue Crack Propagation in Functionally Graded Materials ». University of Dayton / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1259881312.
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Im, Soohyun. « Correlating Structural Heterogeneity to Properties of Metallic Glasses Using 4-D STEM ». The Ohio State University, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=osu1618865204994021.
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Toloui-Mantadakis, Daniil [Verfasser], et Philipp [Akademischer Betreuer] Hansmann. « Realistic calculations for correlated materials / Daniil Toloui-Mantadakis ; Betreuer : Philipp Hansmann ». Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2019. http://d-nb.info/1217253408/34.
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Allerbeck, Jonas [Verfasser]. « Ultrafast Multidimensional Spectroscopy of Semiconductors and Strongly Correlated Materials / Jonas Allerbeck ». Konstanz : KOPS Universität Konstanz, 2020. http://d-nb.info/1220635790/34.
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Mekky, Waleed Nicholson P. S. « Fracture toughness of the nickel-alumina laminates by digital image-correlation technique ». *McMaster only, 2005.
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Dellinger, Sarah Bonham. « Material properties of skin in a flying snake (Chrysopelea ornata) ». Thesis, Virginia Tech, 2011. http://hdl.handle.net/10919/42721.
Texte intégralRésumé :
The genus Chrysopelea encompasses the â flyingâ snakes. This taxon has the ability to glide via lateral aerial undulation and dorsoventral body flattening, a skill unique to this group, but in addition to other functions common to all colubrids. The skin must be extensible enough to allow this body shape alteration and undulation, and strong enough to withstand the forces seen during landing. For this reason, characterizing the mechanical properties of the skin may give insight to the functional capabilities of the skin during these gliding and landing behaviors. Dynamic and viscoelastic uniaxial tensile tests were combined with a modified particle image velocimetry technique to provide strength, extensibility, strain energy, and stiffness information about the skin with respect to orientation, region, and species, along with viscoelastic parameters. Results compared with two other species in this study and a broader range of species in prior studies indicate that while the skin of these unique snakes may not be specifically specialized to deal with larger forces, extensibility, or energy storage and release, the skin does have increased strength and energy storage associated with higher strain rates. The skin also has differing properties with respect to dorsoventral location, and regional differences in strength in the circumferential orientation. This may indicate that, although the properties of the skin may not be different, the rate at which the skin is strained in the different species may vary, thus altering the apparent properties of the skin during specific behaviors.Master of Science
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Siegel, Timothy C. « Correlation of mix characteristics with rutting in bituminous mixes ». Thesis, Georgia Institute of Technology, 1992. http://hdl.handle.net/1853/19552.
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Mingione, Carolyn J. B. A. « Correlates of Alcohol Use Trajectories following Bariatric Weight Loss Surgery ». University of Cincinnati / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1331296465.
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Kiesel, Maximilian Ludwig [Verfasser], et Werner [Akademischer Betreuer] Hanke. « Unconventional Superconductivity in Cuprates, Cobaltates and Graphene : What is Universal and what is Material-Dependent in strongly versus weakly Correlated Materials ? / Maximilian Ludwig Kiesel. Betreuer : Werner Hanke ». Würzburg : Universitätsbibliothek der Universität Würzburg, 2013. http://d-nb.info/1031630856/34.
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Grosu, Cristina. « Correlation between structure and electrochemistry of LiMO2 cathode materials (M = Ni, Co) ». Master's thesis, Alma Mater Studiorum - Università di Bologna, 2017. http://amslaurea.unibo.it/13355/.
Texte intégralRésumé :
Technical diversity and various knowledge is required for the understanding of undoubtedly complex system such as a Lithium-ion battery. The peculiarity is to combine different techniques that allow a complete investigation while the battery is working. Nowadays, research on Li-ion batteries (LIBs) is experiencing an exponential growth in the development of new cathode materials. Accordingly, Li-rich and Ni-rich NMCs, which have similar layered structure of LiMO2 oxides, have been recently proposed. Despite the promising performance on them, still a lot of issues have to be resolved and the materials need a more in depth characterisation for further commercial applications. In this study LiMO2 material, in particular M = Co and Ni, will be presented. We have focused on the synthesis of pure LiCoO2 and LiNiO2 at first, followed by the mixed LiNi0.5Co0.5O2. Different ways of synthesis were investigated for LCO but the sol-gel-water method showed the best performances. An accurate and systematic structural characterization followed by the appropriate electrochemical tests were done. Moreover, the in situ techniques (in-situ XRD and in situ OEMS) allowed a deep investigation in the structural change and gas evolution upon the electrochemically driven processes.
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Maalej, Sirine. « Micromecanical model : correlation between hydraulic and acoustic parameters of cement-based materials ». Phd thesis, Ecole Centrale de Lille, 2010. http://tel.archives-ouvertes.fr/tel-00590429.
Texte intégralRésumé :
L'objectif de cette thèse est la caractérisation de la porosité de la pâte de ciment partiellement saturée par des ondes ultrasonores. Les corrélations entre les vitesses ultrasonores et la porosité ont été étudiées en se basant à la fois sur les résultats expérimentaux et la modélisation micromécanique. Des mesures expérimentales de vitesses ultrasonores longitudinales et transversales en fonction du rapport eau/ciment et à différents états de saturation ont été réalisées sur la pâte de ciment avec et sans entraîneur d'air. En modélisation micromécanique, les effets de saturation ont été modélisés en supposant que la structure poreuse est formée d'inclusions ellipsoïdales de facteur de forme variable selon le rapport E/C. Afin d'estimer les modules homogénéisés élastique de la pâte de ciment et de pâte de ciment à entraîneur d'air différents modèles micromécaniques ont été étudiés. Les résultats de la modélisation micromécanique ainsi que les résultats expérimentaux ont montré que les vitesses des ondes longitudinales et transversales de la pâte de ciment à l'état sec sont inférieures à ceux de l'état saturé. Cet effet est tout aussi important pour l'ensemble des rapports E/C. Le modèle de Mori-Tanaka a donné la meilleure estimation des résultats expérimentaux mesurés sur la pâte de ciment. Alors que le modèle auto-cohérent a donné la meilleure estimation des propriétés mécaniques et ultrasonores de la pâte de ciment avec entraîneur d'air.Les résultats de ce travail devraient constituer le fondement d'un processus d'inversion et d'amélioration de la détermination de la porosité de la pâte de ciment par les ultrasons en tant que méthodes non destructives
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Mußhoff, Julian Verfasser], Eva [Akademischer Betreuer] [Pavarini et Stefan [Akademischer Betreuer] Weßel. « Susceptibility calculations for strongly correlated materials / Julian Mußhoff ; Eva Pavarini, Stefan Weßel ». Aachen : Universitätsbibliothek der RWTH Aachen, 2021. http://d-nb.info/1233600907/34.
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Lin, Tze-Chia. « Correlating molecular structure with linear and nonlinear optical properties in organic materials ». Thesis, University of Cambridge, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.648600.
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Locht, Inka L. M. « Theoretical methods for the electronic structure and magnetism of strongly correlated materials ». Doctoral thesis, Uppsala universitet, Materialteori, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-308699.
Texte intégralRésumé :
In this work we study the interesting physics of the rare earths, and the microscopic state after ultrafast magnetization dynamics in iron. Moreover, this work covers the development, examination and application of several methods used in solid state physics. The first and the last part are related to strongly correlated electrons. The second part is related to the field of ultrafast magnetization dynamics. In the first part we apply density functional theory plus dynamical mean field theory within the Hubbard I approximation to describe the interesting physics of the rare-earth metals. These elements are characterized by the localized nature of the 4f electrons and the itinerant character of the other valence electrons. We calculate a wide range of properties of the rare-earth metals and find a good correspondence with experimental data. We argue that this theory can be the basis of future investigations addressing rare-earth based materials in general. In the second part of this thesis we develop a model, based on statistical arguments, to predict the microscopic state after ultrafast magnetization dynamics in iron. We predict that the microscopic state after ultrafast demagnetization is qualitatively different from the state after ultrafast increase of magnetization. This prediction is supported by previously published spectra obtained in magneto-optical experiments. Our model makes it possible to compare the measured data to results that are calculated from microscopic properties. We also investigate the relation between the magnetic asymmetry and the magnetization. In the last part of this work we examine several methods of analytic continuation that are used in many-body physics to obtain physical quantities on real energies from either imaginary time or Matsubara frequency data. In particular, we improve the Padé approximant method of analytic continuation. We compare the reliability and performance of this and other methods for both one and two-particle Green's functions. We also investigate the advantages of implementing a method of analytic continuation based on stochastic sampling on a graphics processing unit (GPU).
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Zhao, He. « Probing the Strongly Correlated Quantum Materials with Advanced Scanning Tunneling Microscopy/Spectroscopy : ». Thesis, Boston College, 2020. http://hdl.handle.net/2345/bc-ir:108971.
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Thesis advisor: Ilija ZeljkovicWe used spectroscopic-imaging scanning tunneling microscopy (SI-STM) and spin-polarized STM (SP-STM) to unveil new electronic phenomena in several different quantum systems. We explored: (1) a potential topological superconductor heterostructure Bi₂Te₃/Fe(Te, Se), (2) high-Tc superconductors − Bi₂Sr₂CaCu₂O₈₊ₓ and Fe(Te, Se), and (3) doped spin-orbit Mott insulators Sr₂IrO₄ and Sr₃Ir₂O₇. In Bi₂Te₃/Fe(Te, Se), we observed superconductivity (SC) on the surface of Bi₂Te₃ thin film, induced by the iron-based superconductor substrate. By annealing the optimally-doped cuprate superconductor Bi₂Sr₂CaCu₂O₈₊ₓ, we drastically lowered the surface hole doping concentration to detect a unidirectional charge stripe order, the first reported charge order on an insulating (defined by the spectral gap with zero conductance spanning the Fermi level) cuprates surface. In the high-Tc SC Fe(Te, Se) single crystal, we found local regions of electronic nematicity, characterized by C₂ quasiparticle interference (QPI) induced by Fermi surface anisotropy and inequivalent spectral weight of dyz and dxz orbitals near Fermi level. Interestingly, the nematic order is locally strongly anti-correlated with superconductivity. Finally, utilizing SP-STM, we observed a short-range antiferromagnetic (AF) order near the insulator-metal transition (IMT) in spin-orbital Mott insulators Sr₂IrO₄ and Sr₃Ir₂O₇. The AF order inhomogeneity is found not to be strongly correlated with the charge gap. Interestingly, the AF order in the bi-layered Sr₃Ir₂O₇ shows residual memory behavior with temperature cycling. Overall, our work revealed new phenomena in a range of today’s most intriguing materials and set the stage for using SP-STM in other complex oxides
Thesis (PhD) — Boston College, 2020
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Physics
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Chen, Ying. « NMR Applications in Soft Materials Science : Correlation of Structure, Dynamics, and Transport ». Diss., Virginia Tech, 2015. http://hdl.handle.net/10919/75177.
Texte intégralRésumé :
This dissertation aims to investigate and correlate structure, dynamics and transport properties of several novel soft materials systems using multiple Nuclear Magnetic Resonance (NMR) methodologies, including solid-state NMR (SSNMR), diffusometry, and imaging, and with the help of X-ray scattering.
First, we report the investigation of structure and dynamics of three polymeric membranes: hydroxyalkyl-containing imidazolium homopolymers, poly(arylene ether sulfone) segmented copolymers, and disulfonated poly(arylene ether sulfone) random copolymers using a wide array of SSNMR techniques, including: 1) ¹³C cross-polarization magic angle spinning (CPMAS) with varying cross-polarization (CP) contact time, 2) ¹³C single-pulse magic angle spinning (MAS) with varying delay time, 3) ²³Na single-pulse MAS, 4) two dimensional phaseadjusted spinning sideband (2D PASS), 5) proton spin−lattice relaxation (T₁), 6) rotating frame spin−lattice relaxation (T₁ρ), and 7) center-band-only detection of exchange (CODEX). These various types of SSNMR spectroscopic methods provide a wealth of structural and dynamic information over a wide range of time scales from a few nanoseconds to seconds.
We further present a picture of rich structural and transport behaviors in supramolecular assemblies formed by amphiphilic wedge molecules using a combination of ²³Na solid-state NMR, ¹H/²H PFG NMR diffusion, relaxation and grazing-incidence small-angle X-ray scattering. Our results show that the liquid crystalline domains in these materials undergo a transition from columnar to bicontinuous cubic phases with a simple increase in humidity, while the amorphous domain boundaries consist of individual wedge molecules with a significant fraction (~ 10%) of total wedge molecules. Multiple-component diffusion of both wedges and water further confirms the structural and dynamic heterogeneity, with the bicontinous cubic phase being able to facilitate much faster water and ion transport than the columnar phase.
We then develop a quantitative approach to probe the migration of two novel “theranostic” polymeric agents (combining “therapeutic” and “diagnostic” functions) into bulk hydrogels using two distinct time-resolved magnetic resonance imaging (MRI) methods. To the best of our knowledge, this is the first work that combines time-resolved MRI experiments to reliably quantify diffusivity of paramagnetic and superparamagnetic nanoparticles in bulk biological media. Our results agree closely with those obtained from fluorescence techniques, yet the capability of our approach allows the analysis of actual nanoparticles diffusion through biogels on mm to cm scales during a range of time periods.
Finally, we employ a combination of NMR techniques to obtain a comprehensive understanding of ion clustering and transport behaviors of ionic liquids inside the benchmark ionic polymer Nafion. Spin relaxation shows that anion relaxation is more influenced by the fixed sulfonate groups than cation relaxation. 2D ¹H-¹⁹F heteronuclear Overhauser effect spectroscopy (HOESY) and 1D ¹⁹F¹⁹F selective nuclear Overhauser effect (NOE) spectroscopy confirm our assumption of the formation of ion clusters at low water content in the ionomer. While we observe non-restricted diffusion behavior for cations, anion diffusion is strongly restricted both between domain boundaries and within domains in the absence of water. The restricted anion diffusion can serve as a reliable probe for detailed multiscale structures of the ionomer.Ph. D.
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Tariq, Farid. « Correlative tomography : three dimensional multiscale imaging and modelling of hierarchical porous materials ». Thesis, Imperial College London, 2011. http://hdl.handle.net/10044/1/6345.
Texte intégralRésumé :
Heterogeneous catalyst based pellets typify a material where functionality is dependant on hierarchical pore structures spanning many orders of magnitude from nanometers up to tens of microns. The total activity, selectivity and lifetime of catalyst based pellets depends on the ability of molecules to flow through a large pellet bed (m), into the pellets (mm) and their pore structure (μm-nm) to/from the active sites. Three dimensional imaging techniques such as tomography allow for the direct characterisation and quantification of pore structures. However, the field of view in tomography decreases as resolution increases. This work circumvents this issue with multiscale tomography (MT) combining x-ray microtomography (XMT), dual beam focused ion beam tomography (DB-FIB) and electron tomography (ET) to probe porous pellet based catalysts. The results show MT as a viable method that offers new insights into the quantification and behaviour of pellet based catalysts across large length scales, all in three dimensions (3D), that no single tomographic technique can adequately capture. MT was successfully used in the characterising of pore sizes, distributions, structures and spatial relationships and this was compared to existing multiscale characterisation techniques to illustrate the new insights that can be obtained. The pore structures were meshed and modeled using MT data to provide results for understanding the transport properties scaled up from the nanometre length scale to the packed bed, through pellet based catalysts produced under different manufacturing conditions. The results show the very strong dependence on the calcining temperature which is important for designing better catalysts in future. The tomography data was also used to determine thermal/mechanical stresses at both a pellet and pellet bed level. Although many stresses are compressive; the packing of the pellets creates local tensile stresses and a potential cause for pellet failure through internal flaws at relatively low loads. In summary, multiscale tomography was demonstrated to be a viable method for obtaining new insights for the development of pellet based catalysts by both improved quantification and allows for the first time direct 3D multiscale simulation of transport and mechanical properties across multiple scales from nanometers to metres to catalyst pellets in beds.
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Batista, Ito Leonardo. « The correlation between thermal conductivity and wear rate of composite friction materials ». OpenSIUC, 2010. https://opensiuc.lib.siu.edu/theses/346.
Texte intégralRésumé :
During the engagement of a dry clutch system heat is generated at the friction surfaces and the temperature rise caused by this heat depends on the thermal properties of the clutch facings. Usually these facings are made of polymer matrix composite friction materials and they have a low thermal conductivity. Any increase in the thermal conductivity of these materials is expected to reduce the contact surface temperature and improve their tribological performance. The thermal conductivity of six polymer matrix composite friction materials was measured at room temperature, 100ºC, 200ºC, and 300ºC using the laser flash diffusivity technique with density corrections for these temperatures. The wear rate of the materials was measured in the low energy test, medium energy test, and high energy test according to standard norms for clutch facings testing. The correlation analysis between thermal conductivity and wear rate for the materials and conditions studied did not confirm the expected relation between high thermal conductivity and low wear rate. Wear is a system property and it can not be considered as a material property. Obviously there are other variables which were not studied on this work with a more significant impact on the wear behavior of the materials.
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Winograd, Emilio. « Orbital-selectivity in strongly correlated fermionic systems. From materials to cold-atoms ». Thesis, Paris 11, 2013. http://www.theses.fr/2013PA112031.
Texte intégralRésumé :
Cette thèse se concentre sur des aspects multiorbitales des systèmes fermioniques fortement corrélés. En particulier, sur l'existence d'une différentiation orbitale dans laquelle la coexistence de caractère itinérant et localisé peut être associée à différentes orbitales. Cette problématique est examinée dans le contexte des atomes froids et des matériaux, offrant un pont entre les deux communautés.Dans la première partie de la thèse, nous donnons un aperçu du problème des corrélations fortes dans les matériaux, et nous introduisons le concept de 'transition de Mott sélective en orbitales'. Nous fournissons également les principaux outils pour comprendre comment les matériaux peuvent être simulés avec des atomes froids, et nous présentons des résultats importants liés à la transition métal-isolant de Mott. Les aspects techniques, basées sur la théorie du champ moyen dynamique sont également discutés, et la solution de deux principaux modèles de systèmes fermioniques fortement corrélés, à savoir le modèle d'Hubbard (HM) et le modèle de Falicov-Kimball (FKM), sont passés en revue.Ensuite, nous étudions en détail la physique de deux espèces fermioniques en interaction forte avec des masses différentes dans un réseau optique. Nous établissons les différentes phases (avec et sans ordre à longue portée) en termes de la force des interactions (U), du rapport des masses et de la température (T), et aussi nous discutons les variables thermodynamiques, qui sont pertinentes pour les expériences d'atomes froids. Nous montrons que dans la phase métallique (U inférieure à une valeur critique) et avec un certain degré de différence de masses, un 'crossover' apparaît entre un état métallique du type de liquide de Fermi à basse T, et un état avec différentiation orbital à haute T, où les fermions lourds se localisent tandis que les fermions légers restent itinérant. Par conséquent, nous proposons ce modèle minimal pour étudier la physique des systèmes qui présentent une différentiation orbitale avec des expériences d'atomes froids.Basé sur les propriétés du modèle étudié, nous proposons la 'chromatographie entropique' comme une nouvelle méthode pour refroidir des atomes fermioniques dans les réseaux optiques. Nous discutons son efficacité et ses limites, et fournissons quelques idées afin de les surmonter.Dans la dernière partie de la thèse, nous généralisons le modèle précédent aux matériaux corrélés à plusieurs bandes qui permet d'afficher la différentiation orbitale. Nous montrons que l'état de Mott sélectif en orbital peut être stable sous les distorsions du réseau, modélisées par une hybridation locale entre les orbitales. Cependant, l'état de Mott est caractérisé par un pseudo-gap, où les fluctuations de charge sont brusquement réduites, mais l'état reste compressible. En relation au modèle précédent, nous discutons le 'crossover' entre l'état métallique et l'état sélectif induit par des effets température, nous comparons nos résultats avec les expériences de photoémission, et nous prédisons ce qui se passerait dans les matériaux qui présentent une hybridation locale entre les bandesThis thesis focuses on multiorbital aspects of strongly correlated fermionic systems. In particular, it focuses on the existence of orbital differentiation in which coexistence of itinerant and localized character can be associated to different orbitals. This subject is discussed in the context of cold atoms and materials, providing a bridge between both communities.In the first part of the thesis, we give an insight into the problem of strong correlations in materials, and we introduce the concept of 'orbital-selective Mott transition'. We also provide the main tools to understand how materials can be simulated with cold atoms experiments, and we present important related results in the context of the metal-Mott insulator transition. The technical aspects, based on dynamical mean-field theory are also discussed, and the solution of two key models of strongly correlated fermionic systems, i.e., the Hubbard model (HM) and the Falicov-Kimball model (FKM), are reviewed.Then we study in detail the physics of two interacting fermionic species with different masses in an optical lattice. We establish the different phases (with and without long-range order) in terms of the interactions strength (U), mass ratio and temperature (T), and also discuss the thermodynamic variables, which are relevant in cold atoms experiments. We show that in the metallic phase (U below a critical value) and for some degree of mass imbalance, a crossover appears between a Fermi-liquid metallic state at low T, and an 'orbital-selective' state at higher T, where the heavy fermions effectively localize while the light species remain itinerant. Hence, we propose this minimal model for addressing orbital-selective physics with cold atoms experiments.Based on the properties of the studied model, we propose the 'entropic chromatography' as a new method for cooling fermionic atoms in optical lattices. We discuss its efficiency and limitations, and provide some ideas in order to overcome them.In the last part of the thesis we generalize the previous model to a model relevant for multiband correlated materials that can display orbital differentiation. We show that the orbital-selective Mott state can be stable under lattice distortions modeled by local hybridization between the orbitals. However, the Mott state is characterized by a pseudogap, where charge fluctuations abruptly reduce, but the state remains compressible. In connection with the previous model, we discuss the temperature-induced orbital-selective crossover in this problem, we compare our results with photoemission experiments, and predict what would happen in materials that display local hybridization between the bands