Dissertations / Theses on the topic 'Nanostructured architectures'
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Jean, Joel Ph D. Massachusetts Institute of Technology. "Nanostructured architectures for colloidal quantum dot solar cells." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/82187.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2013.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (p. 73-79).
This thesis introduces a novel ordered bulk heterojunction architecture for colloidal quantum dot (QD) solar cells. Quantum dots are solution-processed nanocrystals whose tunable bandgap energies make them a promising active-layer candidate for next-generation optoelectronic devices, including solar cells and light-emitting diodes. Despite rapid advances in performance, however, modern QD solar cells remain limited by a fundamental trade-o between light absorption and photocarrier collection due to poor electronic transport. Vertically aligned arrays of ZnO nanowires can decouple absorption and collection: The nanowires penetrate into the QD film and serve as highly-conductive channels for extracting photogenerated electrons from deep within the film. After optimizing the nanowire growth and device fabrication processes, we nd that incorporating nanowires boosts the photocurrent and the eciency of planar QD photovoltaic devices by 50% and 35%, respectively. The demonstrated AM1.5G power conversion eciency of 4.9% is among the highest ever reported for a ZnO-based QD solar cell. We further show that graphene can serve as a viable alternative to tin-doped indium oxide (ITO) as a transparent conductive electrode for thin-film optoelectronics. We grow ZnO nanowires on graphene and fabricate prototype graphene-based ordered bulk heterojunction QD devices with photovoltaic performance approaching that of ITO-based solar cells. Our work shows that nanostructured architectures can substantially improve QD solar cell performance, and that a simple, low-temperature, bottom-up solution growth process can produce nanowire alignment and device performance matching that of top-down synthetic processes, with the added advantage of compatibility with a variety of rigid and flexible substrates. The 1-D nanostructure design principles we propose and apply here can be generalized to a broad range of optoelectronic device applications. This study of scalable bottom-up processing of ZnO nanowire-based QD solar cells suggests that 1-D nanostructures may be the key to enhancing the eciency and hence the economic viability of quantum dot photovoltaics.
by Joel Jean.
S.M.
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Bayle, Maxime. "Architectures plasmoniques enterrées : élaboration, propriétés optiques et applications." Toulouse 3, 2014. http://thesesups.ups-tlse.fr/2664/.
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Dans notre travail, nous présentons une étude d'architectures plasmoniques à base d'assemblées planes de nanoparticules (NPs) d'argent, enterrées à quelques nanomètres sous la surface d'une matrice diélectrique. L'analyse structurale des matériaux, notamment par microscopie électronique en transmission, a été menée pour déterminer le rôle des différents paramètres de la technique d'élaboration, l'implantation ionique à basse énergie, sur l'organisation à trois dimensions des NPs, dans des films de dioxyde ou de nitrure de silicium sur substrat de silicium. Afin de contrôler de manière systématique ces paramètres, nous avons étudié les réponses optiques élastique et inélastique des hétérostructures. La réponse optique élastique a été obtenue grâce à des mesures de réflectance optique, puis confrontée à des simulations numériques que nous avons développées afin de déterminer la taille moyenne des NPs et la quantité d'argent implantée. L'étude de la topographie du champ électrique a ainsi permis de tirer profit à la fois de la résonnance plasmonique et de l'amplification optique dans nos systèmes multicouches antireflet. La réponse inélastique a quant à elle été étudiée grâce à la spectrométrie Raman sur une large gamme de fréquence. Les modes collectifs de vibration (dits de Lamb) des NPs ont été analysés à basse fréquence, et à plus haute fréquence, nous avons extrait la densité d'états des modes de vibration (VDOS). Associée à des simulations atomistiques, celle-ci nous a donné des informations originales sur la dynamique vibrationnelle à l'échelle atomique et les propriétés thermodynamiques de NPs d'argent enterrées (mais également de NPs d'or déposées). Enfin, nous montrons plusieurs exemples d'applications des assemblées de NPs dans des dispositifs hybrides comme l'exploitation des couplages entre ces NPs et des dépôts (notamment de graphène) réalisés sur nos substrats. En particulier, ceux-ci peuvent être exploités pour la spectrométrie exaltée de surface (effet SERS). Puis nous avons conçu, grâce aux techniques de microélectronique, des dispositifs de plasmo-électronique exploitant les propriétés de photoconductance de ces assemblées de NPs, déposées ou enterréesIn our work, we present the study of plasmonic architectures made of a plane of nanoparticules (NPs) embedded at the vicinity of a dielectric matrix free surface, by low energy ion beam synthesis. Materials structural analysis, especially by transmission electron microscopy, have been carried out to determine the impact of the elaboration process parameters on the three dimensional organization of the NPs, in silicon dioxide or nitride layers grown on silicon substrates. To systematically check these parameters, we studied the elastic and inelastic optical responses of the heterostructures. The elastic response has been obtained by measuring the reflectance of the samples, and confronted to numerical modelling we developed, to determine the mean size of the NPs and the implanted silver amount. The study of the electric field topography allowed us to take benefit from both plasmonic resonance and optical amplification in antireflective layers. The inelastic response has been studied using Raman spectroscopy over a wide frequency range: vibrational collective modes (Lamb modes) of the NPs have been studied at low frequency, while at higher frequency, we have extracted the vibrational density of states (VDOS). Combined with atomistic simulations, the VDOS gave us original information on the vibrational dynamics and the thermodynamic properties of buried silver NPs (and deposited gold NPs). Finally, we present some applications of the assemblies of NPs in hybrid devices, such as the use of coupling between these NPs and deposited substances (e. G. Graphene) on our substrates. In particular, it can be used for surface enhanced Raman spectroscopy (SERS). Then using techniques from microelectronics, we designed plasmo-electronic devices exploiting photoconductance properties of these buried or deposited NPs assemblies
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Schulze, Carsten [Verfasser], Manfred [Akademischer Betreuer] Albrecht, Manfred [Gutachter] Albrecht, and Sibylle [Gutachter] Gemming. "Magnetization Reversal in Film-Nanostructure Architectures : Magnetization Reversal in Film-Nanostructure Architectures / Carsten Schulze ; Gutachter: Manfred Albrecht, Sibylle Gemming ; Betreuer: Manfred Albrecht." Chemnitz : Universitätsbibliothek Chemnitz, 2014. http://d-nb.info/1214302173/34.
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Schulze, Carsten. "Magnetization Reversal in Film-Nanostructure Architectures ." Doctoral thesis, Universitätsbibliothek Chemnitz, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-142720.
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The concept of percolated perpendicular media (PPM) for magnetic data storage is expected to surpass the areal storage density of 1 Tbit in -², which is regarded as the fundamental limit of conventional granular CoCrPt:oxide based recording media. PPM consist of a continuous ferromagnetic thin film with densely distributed defects acting as pinning sites for magnetic domain walls.
In this study, practical realizations of PPM were fabricated by the deposition of [Co/Pt]8 multilayers with perpendicular magnetic anisotropy onto nanoperforated templates with various perforation diameters and periods. The structural defects given by the templates serve as pinning sites for the magnetic domain walls within the [Co/Pt]8 multilayers. Magnetometry at both the integral and the local level was employed to investigate the influence of the template on the magnetization reversal and the domain wall pinning.
It was found, that magnetic domains can be pinned at the ultimate limit, between three adjacent pinning sites. The coercivity and the depinning field, which both are a measure for the strength of the magnetic domain wall pinning, were found to increase with increasing perforation diameter. The size of magnetic domains within the magnetic film appeared not to depend solely on the diameter of the nanoperforations or on the period of the template, but on the ration between diameter and period. By means of micromagnetic simulations it was found, that the presence of ferromagnetic material within the pinning site given supports the pinning of magnetic domain walls, compared to a pinning site that is solely given by a hole in the magnetic thin film.
Investigation of the evolution of the magnetization in magnetic fields smaller than the coercive field revealed, that the energy barrier against thermally induced magnetization reversal is sufficiently large to provide long-term (> 10 years) stability of an arbitrary magnetization state. This could also be qualitatively supported by micromagnetic simulations.
Static read/write tests with conventional hard disk recording heads revealed the possibility of imprinting bit patterns into the PPM under study. The minimum bit pitch that could be read back thereby depended on the period of the nanoperforated template.
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Nguyen, Van Tang. "Nanostructured soft-hard magnetic materials with controlled architecture." Thesis, Le Mans, 2018. http://www.theses.fr/2018LEMA1007.
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Parmi les aimants sans terres raresactuellement étudiés, τ-MnAl ferromagnétique est uncandidat à haut potentiel, car il possède despropriétés magnétiques intrinsèques prometteuses.Dans cette thèse, Mn(Fe)AlC a été synthétisé parbroyage mécanique. Les effets du carbone sur lamicrostructure et les propriétés magnétiques ont étéétudiés. Les résultats montrent qu’une pureté élevéede τ-MnAl(C) pouvait être obtenue avec un dopage à2% en atomes de carbone, montrant clairement l’effetstabilisant du carbone. L’alliage Mn54.2Al43.8C2possède les meilleures propriétés magnétiques :aimantation à 2T M2T = 414 kAm-1, aimantationrémanente Mr = 237 kAm-1, coercivité HC = 229 kAm-1et |BH|max = 11,2 kJm-3. HC augmente inversementproportionnellement avec la taille des cristallites de laphase τ et proportionnellement à la teneur en C. Descalculs ab initio confirment l’effet stabilisant etindiquent les positions interstitielles préférentielles ducarbone dans la maille quadratique de la phase τ-MnAl.Les alliages Mn51-xFexAl47C2 (x = 0,25, 0,5, 1, 2, 4, 6)ont également été synthétisés par broyagemécanique, montrant une pureté élevée de la phaseτ jusqu'à un taux de substitution de 2% du Mn par duFe. L'ajout de Fe dans MnAl(C) réduit l'aimantationet TC, mais augmente légèrement la valeur de HC. Laspectrométrie 57Fe Mössbauer à 300K a été utiliséepour sonder l'environnement local dans ε-, τ-, β- etγ2-MnFeAl(C). γ2-, ε- et β-MnFeAl(C) présentent unestructure hyperfine quadripolaire alors que τ-Mn50.5Fe0.5Al47C2 montre une structutr hyperfinemagnétique assez complexe. Une expérience despectrométrie Mössbauer effectuée à bassetempérature (10K) et sous champ magnétique (8T)montre un ordre ferromagnétique local non colinéairedes moments magnétiques de Fer par rapport à ladirection du champ appliqué. Le champ hyperfin del’alliage MnFeAl calculé par Wien2k confirme lespropriétés magnétiques et les résultats despectrométrie MössbauerAmong currently investigated rare-earth-free magnets, ferromagnetic τ-MnAl is a highly potential candidate as having promising intrinsic magnetic properties. In my thesis, Mn(Fe)AlC was synthesized by mechanical alloying method. Effects of carbon on microstructure and magnetic properties were systematically investigated. It was found that high purity of τ-MnAl(C) could be obtained at 2 at.% C doping, showing clearly stabilizing effect of carbon. Mn54.2Al43.8C2 has the best magnetic properties: magnetization at 2T M2T = 414 kAm-1, remanent magnetization Mr = 237 kAm-1, coercivity HC = 229 kAm-1, and |BH|max = 11.2 kJm-3. HC increased inversely with the crystallite size of τ phase and proportionally with C content. Moreover, first principle calculation showed both stabilizing effect and preferable interstitial positions of carbon in tetragonal τ-MnAl. Mn51-xFexAl47C2 (x= 0.25, 0.5, 1, 2, 4, 6) alloys were also synthesized by mechanical alloying method, showing high purity of τ phase up to 2 at.% Fe doping. Adding of Fe on MnAl(C) reduced both magnetization and TC but likely increased slightly HC. 57Fe Mössbauer spectrometry at 300K was used to probe local enviroment in ε-, τ-, β-, and γ2-MnFeAl(C). In which, γ2-, ε-, and β-MnFeAl(C) exhibited a quadrupolar structure while τ -Mn50.5Fe0.5Al47C2 spectrum showed a rather complex magnetic hyperfine splitting. The interaction between Fe and Mn examined by in-field Mössbauer measurement at 10 K and 8 T showed a non-collinear magnetic structure between Fe and Mn with different canting angles at different sites. Hyperfine field of MnFeAl alloy calculated by Win2k supported both magetic properties and Mossbauer results
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Yip, Chi Kin. "A catalytic architecture composed of titanium silicalite-1 and nanostructured support for oxime synthesis /." View abstract or full-text, 2009. http://library.ust.hk/cgi/db/thesis.pl?CBME%202009%20YIP.
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DeSantis, Christopher John. "Manipulating the architecture of bimetallic nanostructures and their plasmonic properties." Thesis, Indiana University, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=3665584.
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There has been much interest in colloidal noble metal nanoparticles due to their fascinating plasmonic and catalytic properties. These properties make noble metal nanoparticles potentially useful for applications such as targeted drug delivery agents and hydrogen storage devices. Historically, shape-controlled noble metal nanoparticles have been predominantly monometallic. Recent synthetic advances provide access to bimetallic noble metal nanoparticles wherein their inherent multifunctionality and ability to fine tune or expand their surface chemistry and light scattering properties of metal nanoparticles make them popular candidates for many applications. Even so, there are currently few synthetic strategies to rationally design shape-controlled bimetallic nanocrystals; for this reason, few architectures are accessible. For example, the "seed-mediated method" is a popular means of achieving monodisperse shape-controlled bimetallic nanocrystals. In this process, small metal seeds are used as platforms for additional metal addition, allowing for conformal core@shell nanostructures. However, this method has only been applied to single metal core/single metal shell structures; therefore, the surface compositions and architectures achievable are limited. This thesis expands upon the seed-mediated method by coupling it with co-reduction. In short, two metal precursors are simultaneously reduced to deposit metal onto pre-formed seeds in hopes that the interplay between two metal species facilitates bimetallic shell nanocrystals. Au/Pd was used as a test system due to favorable reduction potentials of metal precursors and good lattice match between Au and Pd. Alloyed shelled Au@Au/Pd nanocrystals were achieved using this "seed-mediated co-reduction" approach. Symmetric eight-branched Au/Pd nanocrystals (octopods) are also prepared using this method. This thesis investigates many synthetic parameters that determine the shape outcome in Au/Pd nanocrystals during seed-mediated co-reduction. Plasmonic, catalytic, and assembly properties are also investigated in relation to nanocrystal shape and architecture. This work provides a foundation for the rational design of architecturally defined bimetallic nanostructures.
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Wei, Diming. "The beauty of DNA architecture : the design and applications in DNA nanotechnology /." View abstract or full-text, 2009. http://library.ust.hk/cgi/db/thesis.pl?CBME%202009%20WEI.
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Belchi, Raphaëlle. "Architectures à base de nanostructures de carbone et TiO₂pour le photovoltaïque." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS329/document.
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Le photovoltaïque est une énergie renouvelable pouvant aider à lutter contre le réchauffement climatique et l’épuisement des ressources fossiles utilisées pour la production d’énergie. La filière émergente à base de matériaux pérovskites (photovoltaïque de 3ème génération) est très prometteuse car elle utilise des matériaux abondants et faciles à mettre en œuvre (technologie bas-coût) et a montré de plus des rendements record compétitifs en peu de temps. Il reste cependant des verrous technologiques à lever afin de pouvoir développer cette technologie à grande échelle. L’un deux consiste à améliorer la couche de TiO₂ qui transporte les électrons et dont les défauts limitent les performances et la durée de vie des cellules photovoltaïques pérovskites. Ce travail propose l’utilisation de matériaux à base de nanostructures de carbone et de TiO₂ pour améliorer le transport et la collecte des électrons au sein de ces cellules photovoltaïques et ainsi améliorer leur rendement. Pour cela, la pyrolyse laser, technique singulière de production continue de nanoparticules, a été adaptée pour l’élaboration de nanocomposites TiO₂/graphène aux propriétés contrôlées. Ces matériaux ont été caractérisés puis intégrés aux cellules photovoltaïques pérovskites qui ont démontré une meilleure efficacité en présence de graphène. Par ailleurs, ce travail présente une architecture innovante à base de nanotubes de carbone alignés verticalement, en vue d’une application pour la collecte des électrons photo-générés des cellules photovoltaïques pérovskites. Les matériaux carbonés présentent donc de fortes potentialités pour l’optoélectronique, et plus particulièrement pour le photovoltaïque de 3ème générationPhotovoltaic is a promising renewable energy to tackle global warming and the depletion of fossil resources. The emerging field of perovskite solar cells (3rd generation photovoltaic) is very attractive because it uses abundant and easy-processing materials (low-cost technology) and provides competitive efficiencies.Still, efforts remain to be performed to develop this technology, especially concerning the improvement of efficient and reliable charge transporting electrodes. Titanium dioxide layer, commonly used for electron extraction, presents defects that limit the performance and lifetime of the perovskite solar cells.This work proposes the use of materials based on TiO₂ and carbon nanostructures to improve the electron transport and collection within the solar cells, in order to enhance the power conversion efficiency. The singular technique of laser pyrolysis, which is a continuous process of nanoparticles synthesis, was adapted to produce TiO₂/graphene nanocomposites with well-controlled properties. These materials have been characterized and integrated into perovskite solar cells that demonstrate an improved efficiency in presence of graphene.Besides, this work presents an innovating architecture based on vertically aligned carbon nanotubes for the electron collection of a perovskite solar cell. We show then the strong potential of carbon materials for optoelectronic, especially 3rd generation photovoltaic
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Kong, David Sun 1979. "Nanostructure fabrication by electron and ion beam patterning of nanoparticles." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/28346.
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Thesis (S.M.)--Massachusetts Institute of Technology, School of Architecture and Planning, Program in Media Arts and Sciences, 2004.Includes bibliographical references (leaves 82-83).
Two modes of energetic beam-mediated fabrication have been investigated, namely focused ion beam (FIB) direct-writing of nanoparticles, and a technique for electrostatically patterning ionized inorganic nanoparticles, termed nanoxerography. A FIB has been used to directly pattern thin films of organometallic Ag-precursors down to a resolution of 100 nm. The sensitivity of the resist to 30 keV Ga+ ions was measured to be approximately 5 C/cm2. Using this technique arbitrary structures were fabricated in two and three dimensions with resistivity on the order of 1x10 4 Q-cm and 1x1 0-5 Q-cm for single- and multi-layer structures, respectively. A new unit of merit for characterizing direct-write processes, termed resistivity-dose (Q-jC/cm), has been introduced. A Nanocluster Source capable of generating a beam of charged, inorganic nanoparticles has been characterized. The relationship between power supplied to the magnetron of the source and the size of deposited clusters has been plotted. Techniques for utilizing such clusters to develop latent electrified images patterned by an electron beam (EB) have been proposed. The charge-storing characteristics of a variety of substrates such as mylar and polyimide were studied by developing EB-patterned charge images with toner particles.
David Sun Kong.
S.M.
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Yuen, Mai-yan, and 袁美恩. "Semiconducting and electroluminescent cyclometalated platinum (II) complexes: from molecular functionalmaterials to supramolecular architecture and self-assemblednanomaterials." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2010. http://hub.hku.hk/bib/B44758121.
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Liang, Qizhen. "Preparation and properties of thermally/electrically conductive material architecture based on graphene and other nanomaterials." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/44846.
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With excellent electrical, thermal and mechanical properties as well as large specific surface area, graphene has been applied in next-generation nano-electronics, gas sensors, transparent electrical conductors, thermally conductive materials, and superior energy capacitors etc. Convenient and productive preparation of graphene is thereby especially important and strongly desired for its manifold applications.
Chemically developed functionalized graphene from graphene oxide (GO) has significantly high productivity and low cost, however, toxic chemical reduction agents (e.g. hydrazine hydrate) and raised temperature (400-1100°C) are usually necessary in GO reduction yet not preferred in current technologies. Here, microwaves (MW) are applied to reduce the amount of graphene oxide (GO) at a relatively low temperature (~165°C). Experimental results indicate that resurgence of interconnected graphene-like domains contributes to a low sheet resistance with a high optical transparency after MW reduction, indicating the very high efficiency of MW in GO's reduction.
Moreover, graphene is usually recumbent on solid substrates, while vertically aligned graphene architecture on solid substrate is rarely available and less studied. For TIMs, electrodes of ultracapacitors, etc, efficient heat dissipation and electrical conductance in normal direction of solid surfaces is strongly desired. In addition, large-volume heat dissipation requires a joint contribution of a large number of graphene sheets. Graphene sheets must be aligned in a large scale array in order to meet the requirements for TIM application. Here, thermally conductive fuctionalized multilayer graphene sheets (fMGs) are efficiently aligned in a large scale by vacuum filtration method at room temperature, as evidenced by SEM images and polarized Raman spectroscopy. A remarkably strong anisotropy in properties of aligned fMGs is observed. Moreover, VA-fMG TIMs are prepared by constructing a three-dimensional vertically aligned functionalized multilayer graphene architecture between contact Silicon/Silicon surfaces with pure Indium as a metallic medium. Compared with their counterpart from recumbent A-fMGs, VA-fMG TIMs have significantly higher equivalent thermal conductivity and lower contact thermal resistance.
Electrical and thermal conductivities of polymer composite are also greatly interested here. Previous researches indicated that filler loading, morphology of fillers, and chemical bonding across filler/polymer interfaces have significant influence on electrical/thermal conductivity of polymer composite. Therefore, the research also pays substantial attention to these issues. First, electrical resistivity of CPCs is highly sensitive on volume or weight ratio (filler loading) of conductive fillers in polymer matrix, especially when filler loading is close to percolation threshold (pc). Thermal oxidation aging usually can cause a significant weight loss of polymer matrix in a CPC system, resulting in a filler loading change which can be exhibited by a prompt alteration in electrical resistivity of CPCs. Here, the phenomena are applied as approach for in-situ monitoring thermal oxidation status of polymeric materials is developed based on an electrical sensors based on conductive polymeric composites (CPCs). The study developed a model for electrical resistivity of sensors from the CPCs as a function of aging time at constant aging temperature, which is in a good agreement with a Boltzmann-Sigmoidal equation. Based on the finding, the sensors show their capability of in-situ in-situ monitor and estimate aging status of polymeric components by a fast and convenient electrical resistance measurement.
Second, interfacial issues related to these thermal conductive fillers are systemically studied. On the one hand, the study focuses on relationship between morphology of h-BN particles and thermal conductivity of their epoxy composites. It is found that spherical-agglomeration of h-BN particles can significantly enhance thermal conductivity of epoxy resin, compared with dispersed h-BN plates, by substantially reducing specific interfacial area between h-BN and epoxy resin. On the other hand, surface of high thermal conductive fillers such as SiC particles and MWNTs are successfully functionalized, which makes their surface reactive with bisphenol A diglycidyl ether and able to form chemical bonding between fillers and epoxy resin. By this means, thermal conductivity of polymer composites is found to be significantly enhanced compared with control samples, indicating the interfacial chemical bonding across interface between thermal conductive fillers and polymer matrix can promote heat dissipation in polymeric composites. The finding can benefit a development of high thermal conductive polymer composites by interfacial chemical bonding enhancement to meet the demanding requirements in current fine pitch and Cu/low k technology.
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Zhao, Teng. "Development of new cathodic interlayers with nano-architectures for lithium-sulfur batteries." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/275684.
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Issues with the dissolution and diffusion of polysulfides in liquid organic electrolytes hinder the advance of lithium–sulfur (Li-S) batteries for next generation energy storage. To trap and re-utilize the polysulfides, brush-like, zinc oxide (ZnO) nanowires based interlayers were prepared ex-situ using a wet chemistry method and were coupled with a sulfur/multi-walled carbon nanotube (S/MWCNT) composite cathode. The cell with this configuration showed a good cycle life at a high current rate ascribed to (a) a strong interaction between the polysulfides and ZnO nanowires grown on conductive substrates; (b) fast electron transfer and (c) an optimized ion diffusion path from a well-organized nanoarchitecture. A praline-like flexible interlayer consisting of titanium oxide (TiO2) nanoparticles and carbon (C) nanofiber was further prepared in-situ using an electrospinning method, which allows the chemical adsorption of polysulfides throughout a robust conductive film. A significant enhancement in cycle stability and rate capability was achieved by incorporating this interlayer with a composite cathode of S/MWCNT. These results herald a new approach to building functional interlayers by integrating metal oxides with conductive frameworks. The derivatives of the TiO2/C interlayer was synthesized by changing the precursor concentration and carbonization temperature. Finally, a dual-interlayer was fabricated by simply coating titanium nitride (TiN) nanoparticles onto an electro-spun carbon nanofiber mat, which was then sandwiched with a sulfur/assembled Ketjen Black (KB) composite cathode with an ultra-high sulfur loading. The conductive polar TiN nanoparticles not only have a strong chemical affinity to polysulfides through a specific sulfur-nitrogen bond but also improve the reaction kinetics of the cell by catalyzing the conversion of the long-chain polysulfides to lithium sulfide. Besides, carbon nanofiber mat ensures mechanical robustness to TiN layer and acts as a physical barrier to block polysulfides diffusion. The incorporation of dual interlayers with sulfur cathodes offers a commercially feasible approach to improving the performance of Li-S batteries.
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Ludlow, James M. III. "Design and Synthesis of Terpyridine based Metallo-Supramolecular Architectures." University of Akron / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=akron1444989836.
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Benamira, Messaoud. "Conducteurs mixtes nanostructurés pour les piles à combustible à oxyde solide (SOFC) : élaboration et performances de nouvelles architectures." Phd thesis, Paris 6, 2008. http://pastel.archives-ouvertes.fr/pastel-00004896.
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La réduction de la température de fonctionnement des piles à combustible à oxyde solide, de 1000°C à moins de 700°C, est la meilleure solution pour en diminuer les coûts de fabrication et augmenter la durée de vie. Néanmoins, l'abaissement de la température de fonctionnement s'accompagne d'une chute ohmique au sein de l'électrolyte et une augmentation des surtensions aux électrodes entraînant une diminution des performances de la pile. Dans cette optique, notre étude est centrée sur la recherche de nouveaux matériaux et de nouvelles architectures pour les piles SOFC. Des demi-cellules cathode/électrolyte avec des couches minces interfaciales de YSZ, LSM et La2NiO4 ont été élaborées sur des substrats denses de YSZ par différentes techniques (ALD, PVD et sol-gel). Ces demi-cellules ont été caractérisées par plusieurs techniques physico-chimiques (microscopie électronique à balayage, diffraction des rayons X) ; leurs propriétés électriques ont été étudiées par spectroscopie d'impédance. Une deuxième étude a été menée sur l'élaboration par ALD et les caractérisations physico-chimiques et électriques de couche minces d'oxyde zirconium dopé à l'oxyde d'indium (IDZ) présentant un gradient de composition, permettant de passer d'une conduction ionique à une conduction électronique. La dernière partie de ce travail a été dédiée à un nouveau matériau composite d'électrolyte, GDC-carbonates, dont l'étude des propriétés électriques et de vieillissement a montré des résultats encourageants.
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Gu, Tang. "Modélisation multi-échelles du comportement électrique et élasto-plastique de fils composites Cu-Nb nanostructurés et architecturés." Thesis, Paris, ENSAM, 2017. http://www.theses.fr/2017ENAM0017/document.
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Les fils composites nanostructurés et architecturés cuivre-niobium sont de candidats excellents pour la génération de champs magnétiques intenses (>90T); en effet, ces fils allient une limite élastique élevée et une excellente conductivité électrique. Les fils Cu-Nb multi-échelles sont fabriqués par étirage et empaquetage cumulatif (une technique de déformation plastique sévère), conduisant à une microstructure multi-échelle, architecturée et nanostructurée présentant une texture cristallographique de fibres forte et des formes de grains allongées le long de l'axe du fil. Cette thèse présente une étude compréhensive du comportement électrique et élasto-plastique de ce matériau composite, elle est divisée en trois parties: modélisation multi-échelle électrique, élastique et élasto-plastique. Afin d'étudier le lien entre le comportement effective et la microstructure du fil, plusieurs méthodes d'homogénéisation sont appliquées, qui peuvent être séparées en deux types principaux: la méthode en champs moyens et en champs complets. Comme les spécimens présentent plusieurs échelles caractéristiques, plusieurs étapes de transition d'échelle sont effectuées itérativement de l'échelle de grain à la macro-échelle. L'accord général parmi les réponses de modèle permet de suggérer la meilleure stratégie pour estimer de manière fiable le comportement électrique et élasto-plastique des fils Cu-Nb et économiser le temps de calcul. Enfin, les modèles électriques prouvent bien prédire les données expérimentales anisotopique. De plus, les modèles mécaniques sont aussi validés par les données expérimentales ex-situ et in-situ de diffraction des rayons X/neutrons avec un bon accordNanostructured and architectured copper niobium composite wires are excellent candidates for the generation of intense pulsed magnetic fields (>90T) as they combine both high strength and high electrical conductivity. Multi-scaled Cu-Nb wires are fabricated by accumulative drawing and bundling (a severe plastic deformation technique), leading to a multiscale, architectured and nanostructured microstructure exhibiting a strong fiber crystallographic texture and elongated grain shapes along the wire axis. This thesis presents a comprehensive study of the effective electrical and elasto-plastic behavior of this composite material. It is divided into three parts: electrical, elastic and elasto-plastic multiscale modeling. In order to investigate the link between the effective material behavior and the wire microstructure, several homogenization methods are applied which can be separated into two main types: mean-field and full-field theories. As the specimens exhibit many characteristic scales, several scale transition steps are carried out iteratively from the grain scale to the macro-scale. The general agreement among the model responses allows suggesting the best strategy to estimate reliably the effective electrical and elasto-plastic behavior of Cu-Nb wires and save computational time. The electrical models are demonstrated to predict accurately the anisotropic experimental data. Moreover, the mechanical models are also validated by the available ex-situ and in-situ X-ray/neutron diffraction experimental data with a good agreement
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Niu, Jianbing. "Growth Mechanisms, and Mechanical and Thermal Properties of Junctions in 3D Carbon Nanotube-Graphene Nano-Architectures." Thesis, University of North Texas, 2014. https://digital.library.unt.edu/ark:/67531/metadc700065/.
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Junctions are the key component for 3D carbon nanotube (CNT)-graphene seamless hybrid nanostructures. Growth mechanism of junctions of vertical CNTs growing from graphene in the presence of iron catalysts was simulated via quantum mechanical molecular dynamics (QM/MD) methods. CNTs growth from graphene with iron catalysts is based on a ‘‘base-growth’’ mechanism, and the junctions were the mixture of C-C and Fe-C covalent bonds. Pure C-C bonded junctions could be obtained by moving the catalyst during CNT growth or etching and annealing after growth. The growth process of 3D CNT-graphene junctions on copper templates with nanoholes was simulated with molecular dynamic (MD) simulation. There are two mechanisms of junction formation: (i) CNT growth over the holes that are smaller than 3 nm, and (ii) CNT growth inside the holes that are larger than 3 nm. The growth process of multi-layer filleted CNT-graphene junctions on the Al2O3 template was also simulated with MD simulation. A simple analytical model is developed to explain that the fillet takes the particular angle (135°). MD calculations show that 135° filleted junction has the largest fracture strength and thermal conductivity at room temperature compared to junctions with 90°,120°, 150°, and 180° fillets. The tensile strengths of the as-grown C–C junctions, as well as the junctions embedded with metal nanoparticles (catalysts), were determined by a QM/MD method. Metal catalysts remaining in the junctions significantly reduce the fracture strength and fracture energy. Moreover, the thermal conductivities of the junctions were also calculated by MD method. Metal catalysts remaining in the junctions considerably lower the thermal conductivity of the 3D junctions.
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Montana, garcia Juan. "Architecture multi-échelle de matériaux polymères : de l’auto-assemblage à l’assemblage forcé." Thesis, Paris, ENSAM, 2017. http://www.theses.fr/2017ENAM0060/document.
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Les copolymères à blocs (BCP) sont des macromolécules capables de s’auto-assembler produisant des morphologies bien définies à l’échelle nanométrique. Un certain nombre de leurs propriétés macroscopiques peuvent être largement modifiées par des effets de confinement à l’échelle moléculaire, mais aussi par des effets de cisaillement (l’orientation des structures et donc un comportement mécanique fortement anisotrope). L’une des technologies permettant d’étudier ces effets sur la structuration des BCP est la coextrusion multinanocouches, qui permet de produire à grande échelle des matériaux sous forme de films possédant deux ou plusieurs constituants organisées en milliers de couches alternées ayant chacune une épaisseur nanométrique. À l’aide de ce procédé, des films constitués du tribloc poly(méthacrylate de méthyle-b-butyle acrylate-b-méthacrylate de méthyle) et des homopolymères polyméthacrylate de méthyle, polystyrène et polycarbonate (ayant donc différentes interfaces) ont été fabriqués en variant la composition du mélange et les conditions de coextrusion afin d’obtenir différentes épaisseurs du film (et donc différentes épaisseurs de couche). Une caractérisation multi-échelle a été effectuée en couplant différentes techniques, notamment AFM, MET (après une étape préalable de marquage) et SAXS. Elle a permis d’identifier les structures locales au sein des couches et de mieux comprendre la relation procédé-structure-propriétés suite à des essais en traction uni-axiale montrant de meilleures propriétés dans le cas de structures multicouches. Une faible stabilité thermique, à de temps comparables à ceux du procédé, a montré une influence sur la structuration de ce type de BCP. Nous avons mis en évidence un changement dans la morphologie du tribloc à partir d’une structure lamellaire, lorsque le matériau se trouve dans un état proche de l’équilibre thermodynamique, vers une structure cylindrique au sein du système multicouche et maintenue, quelle que soit l’épaisseur de couche, à grande distance. La maitrîse des procédés de transformation de matériaux à base de polymère à l’échelle micro ou nanométrique prend ainsi toute son importance afin de mieux contrôler, dans le cas des BCP, la structuration lors d’une production à grande échelle de matériaux hiérarchisés constitués de ces matériaux, ce qui influence fortement leurs propriétés macroscopiquesBlock copolymers (BCP) have proven to be of great interest, especially for their ability to spontaneously self-assemble in ordered and well-defined nanostructures. Some of their macroscopic properties can be altered by physical effects such as confinement (constraining domains at molecular scale) or shear (predominant orientation of domains with anisotropic mechanical response). Here, the study of these effects over the BCP structuration is achieved by using an industrially scalable technique, nanolayer coextrusion, which allows fabrication of macroscopic films made of thousands of alternating layers with individual thickness tuned down to a few tens of nanometers. Films are then coextruded using the triblock : poly(methyl methacrylate-b-butyl acrylate-b-methyl methacrylate) and the polymers : polymethyl methacrylate, polystyrene and polycarbonate (having different interfaces) by varying weight proportions and process parameters to target different layer thicknesses. A multi-scale characterization by coupling different technics as AFM, TEM (after samples staining) and SAXS allowed the local identification of nano-domains and the better understanding of process-structures-properties relation as a result of tensile tests showing improved mechanical behavior for these films. A low thermic stability for comparable process times showed a clear influence over structuration of this kind of BCP. We have observed a change in the triblock morphology from lamellar structures, when it is a close to thermodynamic equilibrium state, to cylindrical structures within the multilayer system which is maintained over long distances indistinct of layer thickness. The well understanding of the forming process parameters to create polymer-based materials at micro- or nanoscale scale is therefore an important factor in order to control nano-structures during a large-scale production of hierarchized materials consisting of BCP, which could strongly influence their macroscopic properties
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Schmitt, Thomas. "Mécanismes de dégradation de revêtements base CrN élaborés par arc-PVD : Intérêt d'une nano-architecture." Phd thesis, Ecole Centrale de Lyon, 2010. http://tel.archives-ouvertes.fr/tel-00633784.
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Les enjeux environnementaux liés à l'utilisation des fluides de coupe lors des étapes d'usinage, nécessitent le développementde nouveaux matériaux résistant à une utilisation en lubrification réduite, voire à sec. Le domaine des revêtements en couchesminces et plus particulièrement des dépôts physiques en phase vapeur (PVD) permet de synthétiser des surfaces adaptées à cetype d'utilisation sévère. Le nitrure de titane (TiN), largement utilisé dans l'industrie, montre toute l'efficacité de cesrevêtements. Ses performances sont cependant limitées à des températures modérées. Au contraire, le caractère réfractairemarqué du nitrure de chrome (CrN) en fait un candidat de choix pour des applications à hautes températures. Les propriétésmécaniques de ces nitrures sont certes moindres, mais le développement récent de microstructures nanométriques laisseaugurer des performances intéressantes que nous nous proposons d'étudier. L'objectif de ce travail est de déterminer l'influenced'une microstructure contrôlée à l'échelle nanométrique sur la durabilité de films minces base CrN, synthétisés par évaporationpar arc cathodique. Les différentes microstructures sont obtenues par modification chimique (addition d'aluminium et desilicium) ou par alternance des couches.L'ajout d'aluminium à CrN aboutit à la formation d'une solution solide et améliore les propriétés mécaniques du revêtement.La résistance à l'oxydation est augmentée par la présence de liaisons fortes Al-N, qui permettent de limiter le départ d'azote etainsi de retarder le phénomène d'oxydation. De plus, la démixtion de la phase initiale CrAlN en deux phases distinctes, CrN etAlN, tend à isoler les grains de CrN et ainsi à améliorer leur stabilité thermique. La même transformation est observée aprèsles essais de frottement et semble à l'origine des performances accrues du dépôt vis-à-vis de l'usure. L'addition de silicium setraduit par la synthèse d'un revêtement nanocomposite pour une teneur minimale d'environ 2 % at. Cette structure est forméede grains nanométriques enrobés dans une matrice amorphe. Le changement de structure s'accompagne d'une meilleurerésistance à l'oxydation, en raison des propriétés de barrière diffusionnelle de la matrice qui protège les nano-grains de CrN.En revanche, une fraction volumique trop importante de la phase amorphe apparaît préjudiciable au comportementtribologique. Le revêtement présente dans ce cas un comportement fragile, favorisant la formation et la propagation defissures. L'emploi de ces mêmes films (CrN et CrSiN) en architecture nanostratifiée inhibe néanmoins ce comportement. Desessais de micro-traction montrent que l'alternance des couches permet de limiter la formation de fissures, si bien quel'architecture multicouche semble prometteuse dans le cas de sollicitations sévères. De même, la stratification de CrN etCrAlN donne des revêtements extrêmement durables, malgré des propriétés mécaniques intermédiaires régies par une loi desmélanges.L'originalité de ce travail réside dans la détermination des mécanismes de dégradation des différentes microstructures, d'unepart en établissant le lien entre microstructure et propriétés d'usage, et d'autre part en considérant ces dégradation selon uneapproche in situ locale.
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Arndt, Grégory. "Architecture système et conception électronique de réseaux de capteurs de masse à partir de micro et nanorésonateurs." Phd thesis, Université Paris Sud - Paris XI, 2011. http://tel.archives-ouvertes.fr/tel-00658843.
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Le sujet de thèse porte sur des micro/nanorésonateurs ainsi que leurs électroniques de lecture. Les composants mécaniques sont utilisés pour mesurer des masses inférieures à l'attogramme (10-18 g) ou de très faibles concentrations de gaz. Ces composants peuvent ensuite être mis en réseau afin de réaliser des spectromètres de masse ou des détecteurs de gaz. Afin d'atteindre les résolutions nécessaires, il a été choisi d'utiliser une détection harmonique de résonance détectant les variations de la fréquence de résonance d'une nanostructure mécanique. Les dimensions du résonateur sont réduites afin d'augmenter sensibilité en masse, cependant le niveau du signal électrique en sortie du composant est également réduit. Ce faible signal nécessite donc de concevoir de nouvelles transductions électromécaniques ainsi que des architectures électroniques qui minimisent le bruit, les couplages parasites et qui peuvent être mise en réseau.
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Charles, Cédric. "Etude théorique et expérimentale des relations architecture - propriétés optiques de films minces d'oxyde de tungstène pulvérisés par GAD." Phd thesis, Université de Franche-Comté, 2013. http://tel.archives-ouvertes.fr/tel-01063023.
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Cette thèse participe à l'étude générale et à la compréhension des relations structure- propriétés optiques de couches minces d'oxyde de tungstène, nanostructurées lors de leur dépôt par la technique Glancing Angle Déposition. Cette technique repose sur le contrôle de l'orientation relative du substrat vis à vis de la source de vapeur.[...]
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Ovalle, Robles Raquel. "Physical process in OLED architectures with transparent carbon nanotube sheets as electrodes /." 2008. http://proquest.umi.com/pqdweb?did=1663060241&sid=8&Fmt=2&clientId=10361&RQT=309&VName=PQD.
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Rreza, Iva. "Designing Quantum Dot Architectures and Surfaces for Light Emitting Diodes." Thesis, 2019. https://doi.org/10.7916/d8-hd0j-as89.
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Quantum Dots (QD) have become a commercial reality for tunable displays and light-emitting diodes. The Department of Energy believes further improvements in efficacy and stability will allow for widespread adoption of solid-state lighting in the United States. QD geometric and compositional architecture, crystal phase and surface chemistry are arguably some of the important aspects governing QD performance in these applications.
Chapter I outlines the efforts of QD design, encapsulation and performance for phosphor converted, “on-chip” LEDs. Cadmium chalcogenide QDs with a quantum well geometry and ZnS encapsulation (CdS/CdSxSe1-x/CdS/ZnS) resist photoluminescence bleaching on chip under harsh accelerated ageing tests. Trends in device performance are linked primarily to success of ZnS passivation.
Chapter II presents findings regarding crystal structure control (Zinc Blende vs Wurtzite) for CdX (X = S, Se) systems by focusing on crystal phase conversion. The ZB to W transition for CdX is shown to be size, material and surfactant dependent.
Chapter III focuses on expanding the precursor compound library for CdSe with aryl substituted cyclic selenones (imidazole and pyrimidine-based compounds). These molecules are shown to react sluggishly at ZB synthetic conditions and that the rate is heavily influenced by compound sterics.
Chapter IV presents the findings of a metal carboxylate displacement study on PbS NCs with various L-type ligands. Upon displacement and purification with N,N,N′,N′-tetramethylethylene-1,2-diamine, tri-n-butylamine, and n-octylamine, oriented attachment occurs along the 100 plane and with bis(dimethylphosphino)ethane and tri-n-butylphosphine, attachment is suppressed. This difference allows for the study of ligand density dependent optical properties without the confounding attachment of nanocrystals in solution. A decreasing trend of time resolved photoluminescence lifetime values as a function of ligand density is observed.
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Sampaio, Maria José Fernandes. "Nanostructured Architectures Based on Metal Oxides With Direct Wide Band-Gap for the Engineering of Photocatalytic Reactions." Doctoral thesis, 2016. https://hdl.handle.net/10216/100177.
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Sampaio, Maria José Fernandes. "Nanostructured Architectures Based on Metal Oxides With Direct Wide Band-Gap for the Engineering of Photocatalytic Reactions." Tese, 2016. https://hdl.handle.net/10216/100177.
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Schulze, Carsten. "Magnetization Reversal in Film-Nanostructure Architectures : Magnetization Reversal in Film-Nanostructure Architectures." Doctoral thesis, 2013. https://monarch.qucosa.de/id/qucosa%3A20055.
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The concept of percolated perpendicular media (PPM) for magnetic data storage is expected to surpass the areal storage density of 1 Tbit in -², which is regarded as the fundamental limit of conventional granular CoCrPt:oxide based recording media. PPM consist of a continuous ferromagnetic thin film with densely distributed defects acting as pinning sites for magnetic domain walls.
In this study, practical realizations of PPM were fabricated by the deposition of [Co/Pt]8 multilayers with perpendicular magnetic anisotropy onto nanoperforated templates with various perforation diameters and periods. The structural defects given by the templates serve as pinning sites for the magnetic domain walls within the [Co/Pt]8 multilayers. Magnetometry at both the integral and the local level was employed to investigate the influence of the template on the magnetization reversal and the domain wall pinning.
It was found, that magnetic domains can be pinned at the ultimate limit, between three adjacent pinning sites. The coercivity and the depinning field, which both are a measure for the strength of the magnetic domain wall pinning, were found to increase with increasing perforation diameter. The size of magnetic domains within the magnetic film appeared not to depend solely on the diameter of the nanoperforations or on the period of the template, but on the ration between diameter and period. By means of micromagnetic simulations it was found, that the presence of ferromagnetic material within the pinning site given supports the pinning of magnetic domain walls, compared to a pinning site that is solely given by a hole in the magnetic thin film.
Investigation of the evolution of the magnetization in magnetic fields smaller than the coercive field revealed, that the energy barrier against thermally induced magnetization reversal is sufficiently large to provide long-term (> 10 years) stability of an arbitrary magnetization state. This could also be qualitatively supported by micromagnetic simulations.
Static read/write tests with conventional hard disk recording heads revealed the possibility of imprinting bit patterns into the PPM under study. The minimum bit pitch that could be read back thereby depended on the period of the nanoperforated template.
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Lu, Po Wei, and 呂柏緯. "Effect of nanostructured architecture on the enhanced optical absorption in silicon thin-film solar cells." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/59964676233803441611.
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碩士國立臺灣師範大學
光電科技研究所
100
We apply the finite difference time domain method to numerically calculate the enhanced optical absorption of three nanostructures (i.e., nanorod, nanocone, and nanolens arrays) that were decorated on the surface of 2 µm thick crystal silicon thin films. Compared with the nanorod and nanocone arrays, the nanolens array exhibits the highest power conversion efficiency. This result is mainly attributed to the natural capability of the nanolens array to optically couple incident light into in-plane guided modes, which increases the optical path of the incident photons in the long-wavelength regime. The power conversion efficiencies of the optimized nanorod, nanocone, and nanolens arrays are =17.4%, 18.8%, and 22.0%, respectively. These efficiencies correspond to enhancements of 26.1%, 36.2%, and 59.4% for the nanorod, nanocone, and nanolens arrays, respectively, compared with a planar Si thin-film with a standard quarter-wavelength antireflection layer. These findings show promises for the nanostructured design of silicon thin-film solar cells that exhibit enhanced optical absorption.