Global ETD Search

251	WAVE PHENOMENA IN FLUID MEDIA FOR CHARACTERIZATION AND TRANSPORT OF NANOPARTICLES Andres Barrio-Zhang (20623424) 27 January 2025 (has links) <p dir="ltr">This doctoral thesis investigates how wave phenomena, including light and acoustic waves, can be harnessed to characterize and manipulate fluids, suspensions, and nanoparticles. It explores light-matter interactions and their role in material characterization, leveraging the complex refractive index as a material fingerprint. Additionally, it examines acoustic wave interactions to enhance particle separation and manipulation in fluid media.</p><p dir="ltr">The research introduces a portable Schlieren imaging system for real-time detection of refractive index gradients in pharmaceutical solutions, providing insights into heterogeneity and diffusion during thawing. A novel method based on Rayleigh-Sommerfeld diffraction theory is developed to size and determine the refractive index of sub-micron particles from holographic data, enabling precise particle characterization. Enhanced filtration performance in fiber filters is demonstrated using standing acoustic waves, with observed efficiency improvements through different fiber arrangements. Finally, the thesis presents Spectral Interferometric SCATtering (SiSCAT) microscopy, a label-free system that combines interferometry and wavelength-dependent scattering to achieve chemically dependent nanoparticle characterization. </p><p dir="ltr">These findings advance the fields of biophysics, materials science, and nanotechnology, offering innovative tools for material and particle analysis.</p> Microfluidics and nanofluidics Micro- and nanosystems Nanometrology Nanophotonics Nanoscale characterisation iSCAT Holography Acoustofluidics radiation force porous media filtration schlieren therapeutic heterogeneity nanoparticle characterization optics microscopy interferometry
252	Nanolithography on thin films using heated atomic force microscope cantilevers Saxena, Shubham 01 November 2006 (has links) Nanotechnology is expected to play a major role in many technology areas including electronics, materials, and defense. One of the most popular tools for nanoscale surface analysis is the atomic force microscope (AFM). AFM can be used for surface manipulation along with surface imaging. The primary motivation for this research is to demonstrate AFM-based lithography on thin films using cantilevers with integrated heaters. These thermal cantilevers can control the temperature at the end of the tip, and hence they can be used for local in-situ thermal analysis. This research directly addresses applications like nanoscale electrical circuit fabrication/repair and thermal analysis of thin-films. In this study, an investigation was performed on two thin-film materials. One of them is co-polycarbonate, a variant of a polymer named polycarbonate, and the other is an energetic material called pentaerythritol tetranitrate (PETN). Experimental methods involved in the lithography process are discussed, and the results of lithographic experiments performed on co-polycarbonate and PETN are reported. Effects of dominant parameters during lithography experiments like time, temperature, and force are investigated. Results of simulation of the interface temperature between thermal cantilever tip and thin film surface, at the beginning of the lithography process, are also reported. Characterization Deflection Setpoint Grain rearrangement Array Precise positioning Metrology Explosion Explosives Data storage Material Image processing Slow scan disabled Temperature Tip Local In-situ Nanoscale Electrical circuit fabrication Repair Co-polycarbonate Polymers Polycarbonates Energetic materials PETN Simulation Interface Nano-manufacturing Experiment Calibration Raman Frequency Deflagration Decomposition Detonation Build up Pile-up End capped End capping Cross linked Cross-linked Conductivity Microscale MEMS Microcantilever NEMS DPN tDPN Silicon Glass Peak InVOLS Manipulation AFM Atomic force microscope Defense Nanoscale Surface Stiffness Force Scan size Thermal cantilevers Imaging Lithography Nanolithography Thin films Cantilevers Heaters Technology Nanotechnology Scan velocity Scan rate Bake Anneal Pentaerythritol tetranitrate Thin films Thermal properties Atomic force microscopy Microlithography Nanotechnology Surfaces (Technology) Analysis
253	Thermal Characterization of Heated Microcantilevers and a Study on Near-Field Radiation Park, Keunhan 05 April 2007 (has links) Recently, remarkable advances have been made in the understanding of micro/nanoscale energy transport, opening new opportunities in various areas such as thermal management, data storage, and energy conversion. This dissertation focuses on thermally-sensed nanotopography using a heated silicon microcantilever and near-field thermophotovoltaic (TPV) energy conversion system. A heated microcantilever is a functionalized atomic force microscope (AFM) cantilever that has a small resistive heater integrated at the free end. Besides its capability of increasing the heater temperature over 1,000 K, the resistance of a heated cantilever is a very sensitive function of temperature, suggesting that the heated cantilever can be used as a highly sensitive thermal metrology tool. The first part of the dissertation discusses the thermal characterization of the heated microcantilever for its usage as a thermal sensor in various conditions. Particularly, the use of heated cantilevers for tapping-mode topography imaging will be presented, along with the recent experimental results on the thermal interaction between the cantilever and substrate. In the second part of the dissertation, the so-called near-field TPV device is introduced. This new type of energy conversion system utilizes the significant enhancement of radiative energy transport due to photon tunneling and surface polaritons. Investigation of surface and bulk polaritons in a multilayered structure reveals that radiative properties are significantly affected by polariton excitations. The dissertation then addresses the rigorous performance analysis of the near-field TPV system and a novel design of a near-field TPV device. Atomic force microscopy Heated microcantilevers Steady heating Periodic heating Negative index metamaterial Bulk polariton Surface polariton Thermophotovoltaic energy conversion Near-field thermal radiation Heat transfer Nanoscale thermometer Cryogenic temperature Tapping mode Micromechanics Atomic force microscopy Energy conversion Heat Transmission Measurement Microelectronics
254	Imaging the bone cell network with nanoscale synchrotron computed tomography / Imagerie du réseau cellulaire osseux par nano-tomographie synchrotron Joita Pacureanu, Alexandra 19 January 2012 (has links) Les ostéocytes sont les plus nombreuses cellules du tissu osseux, enterrées dans la matrice osseuse. Elles sont interconnectées par des dendrites, situées dans des canaux appelés canalicules. Les lacunes ostéocytaires, les cavités dans lesquelles les cellules sont logées, avec les canalicules forment un réseau de communication à travers la matrice osseuse, permettant le transport des nutriments et des signaux. Ces cellules, considérées d’abord passives, ont révélé dernièrement leur rôle en tant que cellules mécanosensitives et orchestratrices du remodelage osseux. Malgré les progrès récents des techniques d'imagerie, aucune méthode disponible ne fournit une évaluation 3D adéquate du réseau lacuno-canaliculaire (LCN). Les objectifs de cette thèse ont porté sur l’imagerie 3D du LCN par tomographie synchrotron à rayons X (SR-CT), et le développement d’outils de détection et segmentation 3D de ce réseau cellulaire, afin de le quantifier et analyser. Nous démontrons la faisabilité de la SR-CT en géométrie parallèle pour imager le LCN dans le tissu osseux (voxel~300nm). Cette technique fournit des données 3D sur la morphologie du réseau cellulaire et aussi sur la composition de la matrice osseuse. Comparée aux méthodes d'imagerie 3D existantes, la SR-CT permet l'imagerie d’un volume de tissu beaucoup plus important, d'une manière plus simple et rapide. Cela rend possible l'étude de séries de spécimens afin d'obtenir des conclusions biomédicales. Nous proposons aussi l'utilisation de l’holotomographie divergente synchrotron, pour imager l'ultrastructure du tissu osseux (voxel~60nm). La reconstruction d'image fournit des cartes de phase, obtenues après application d'un algorithme d’inversion de phase adéquat. Cette technique a permis l'évaluation du réseau cellulaire avec une précision plus élevée et de visualiser, pour la première fois en 3D, l'organisation des fibres de collagène. Afin d'obtenir des résultats quantitatifs sur la géométrie du réseau cellulaire, celui doit être segmenté. À cause des limitations de la résolution spatiale, les canalicules apparaissent comme de structures tubulaires très fines (diamètre 1-3 voxels). Ceci, combiné avec le bruit, le faible contraste et la grande taille des images (8Go), rendent la segmentation difficile. Nous proposons une méthode de filtrage non-linéaire 3D, basée sur le rehaussement des structures linéaires, combiné avec un filtrage bilatéral. Cela permet une amélioration de la détection des canalicules, la réduction du bruit de fond et de la préservation des lacunes cellulaires. Pour la segmentation d'images, nous avons développé une méthode basée sur la croissance de région variationnelle. Nous proposons deux expressions de fonctionnelles d'énergie à minimiser, afin de détecter la structure souhaitée. Des résultats quantitatifs préliminaires sont obtenus à partir d’une analyse en composantes connexes sur des échantillons humaines et des observations relatives au réseau ostéocytaire sont présentés. / The osteocytes are the most abundant and longest living bone cells, embedded in the bone matrix. They are interconnected with each other through dendrites, located in slender canals called canaliculi. The osteocyte lacunae, cavities in which the cells are located, together with the canaliculi form a communication network throughout the bone matrix, permitting transport of nutrients, waste and signals. These cells were firstly considered passive, but lately it has become increasingly clear their role as mechanosensory cells and orchestrators of bone remodeling. Despite recent advances in imaging techniques, none of the available methods can provide an adequate 3D assessment of the lacuno-canalicular network (LCN). The aims of this thesis were to achieve 3D imaging of the LCN with synchrotron radiation X-ray computed tomography (SR-CT) and to develop tools for 3D detection and segmentation of this cell network, leading towards automatic quantification of this structure. We demonstrate the feasibility of parallel beam SR-CT to image in 3D the LCN (voxel~300 nm). This technique can provide data on both the morphology of the cell network and the composition of the bone matrix. Compared to the other 3D imaging methods, this enables imaging of tissue covering a number of cell lacunae three orders of magnitude greater, in a simpler and faster way. This makes possible the study of sets of specimens in order to reach biomedical conclusions. Furthermore, we propose the use of divergent holotomography, to image the ultrastructure of bone tissue (voxel~60 nm). The image reconstruction provides phase maps, obtained after the application of a suitable phase retrieval algorithm. This technique permits assessment of the cell network with higher accuracy and it enables the 3D organization of collagen fibres organization in the bone matrix, to be visualized for the first time. In order to obtain quantitative parameters on the geometry of the cell network, this has to be segmented. Due to the limitations in spatial resolution, canaliculi appear as 3D tube-like structures measuring only 1-3 voxels in diameter. This, combined with the noise, the low contrast and the large size of each image (8 GB), makes the segmentation a difficult task. We propose an image enhancement method, based on a 3D line filter combined with bilateral filtering. This enables improvement in canaliculi detection, reduction of the background noise and cell lacunae preservation. For the image segmentation we developed a method based on variational region growing. We propose two expressions for energy functionals to minimize in order to detect the desired structure, based on the 3D line filter map and the original image. Preliminary quantitative results on human femoral samples are obtained based on connected components analysis and a few observations related to the bone cell network and its relation with the bone matrix are presented. Imagerie médicale Tomographie Tomographie par rayon X Echelle nanométrique Imagerie des os spongieux Microarchitecture osseuse Matrice osseuse Reconstruction d'Image Reconstruction tomographique Filtrage 3D Filtrage non linéaire Fémur Medical Imaging Tomography Tomography X Nanoscale Spongious Bone Imaging Bone MicroArchitecture Bone matrix Image Reconstruction 3D Filtering Non linear filtering Femoral bone 616.075 707 2
255	Propriétés physiques des cristaux liquides discotiques nanoconfinés / Physcal properties of discotic liquid crystals nanoconfined Ndao, Makha 14 October 2013 (has links) L'objectif de cette thèse est de mener une étude fondamentale et expérimentale des propriétés physiques des cristaux liquides discotiques colonnaires (CLDCs) confinés dans des matrices poreuses templates hautement ordonnées à l'échelle nanométrique. Les molécules des CLDCs de forme plane, composées de noyaux polyaromatiques rigides entourées de chaînes aliphatiques flexibles fonctionnalisables, sont susceptibles de s'auto-assembler dans des colonnes favorisant ainsi le recouvrement de leurs orbitales électroniques π. Ce qui fait de ces matériaux de véritables candidats pour des applications dans l'électronique moléculaire et la photovoltaïque grâce à la possibilité de migration des porteurs de charges le long de leurs colonnes. Cependant, ces applications nécessitent une bonne maîtrise des paramètres influant sur les mécanismes d'alignement dans les phases colonnaires, sur de grands monodomaines, et de préférence à température ambiante. Une méthode très prometteuse visant à optimiser les longueurs de diffusion des porteurs de charge a été récemment proposée, basée sur la formation de nanofils orientés de CLDCs par auto-assemblage dans des matrices dites « templates » (de moulage). Toutefois, les propriétés structurales, dynamiques et les effets de confinement sur ces technologies restent aujourd'hui mal connus et morcelés et pourraient constituer un véritable verrou scientifique pour leur réalisation. Notre étude s'est portée sur les CLDCs commerciaux (HPT) et le Py4CEH (moins connus) qui sont confinés dans des alumines poreuses (AAO) et du silicium poreux (Sip) de diamètres de pores de quelques dizaines de nm. Les diagrammes de phase ont été d'abord étudiés par DSC puis les effets structuraux ont été approfondis grâce à la diffusion de neutrons. Dans les géométries confinées, nous observons une dépression des températures de transition, un élargissement du domaine de stabilité de la phase colonnaire et l'ouverture d'une hystérèse amplifiée dans les pores de plus petite taille. Un ordre orientationnel très élevé a été trouvé dans les phases colonnaires bulk par la RMN du solide et la structure des systèmes confinés colonnaires, dominée par une distribution radiale avec un ancrage homéotrope a été déterminée. La dynamique moléculaire a été étudiée par diffusion quasiélastique de neutrons. Elle est affectée par le confinement : la dynamique de grande amplitude est fortement ralentie, tandis que la dynamique rapide locale devient régie par une distribution très large de temps caractéristiques. / The aim of this work is to conduct fundamental and experimental studies of the physical properties of columnar discotic liquid crystal (CDLCs) confined in highly ordered porous templates at the nanoscale. CDLC molecule of planar shape, consist in rigid polyaromatic nuclei surrounded by functionalizable flexible aliphatic chains, and are capable of self-assembly in columns, thereby promoting overlap of their π electron orbitals. This makes these materials real candidates for applications in molecular electronics and photovoltaics due to the possibility of migration of the charge carriers along their columns. However, these applications require a good control of the parameters affecting the alignment mechanisms in the columnar phases of large single domains, preferably at room temperature. A very promising approach to optimize the diffusion lengths of charge carriers has been recently proposed, based on the formation of oriented CDLC nanowires by self-assembly in so-called "templates". However, structural and dynamical proprieties and confinement effects are still scarce, and could be a real scientific lock to their implementation. Our study is focused on commercial CDLCs (HPT) and Py4CEH which are confined in porous alumina and porous silicon membranes with pore diameters of c.a. tens of nm. The phase diagram was first studied by DSC and more deeply characterized by neutron scattering. In confined geometries, we observe a depression of the phase transition temperatures, a broadening of the columnar phase stability domain and an opening of hysteresis loops amplified by smaller pore size. A high orientational order was found in the bulk columnar phases by solid-state NMR, and the structure of confined columnar systems, dominated by a radial distribution with homeotropic anchoring was observed. The molecular dynamics was studied by quasielastic neutron scattering. It is affected by confinement: large lengthscale motions are massively slowed down, whereas the rapid and local dynamics becomes submitted to large distributions of correlation times. Propriétés physiques Cristaux-liquides Discotiques Matrices- poreuses Modèles Moulage Confinement Nanométriques Interactions Surfaces, interfaces Transitions Phases Alignement Structure Ancrage Homéotrope Planaire Défaut Désordre Dynamique Locale Courte portée Longue portée Effets Taille Greffage Physical properties Liquid-crystal Discotic Porous matrices Template Casting Confinment Nanoscale Interactions Surfaces Interfaces Transitions Phases Alignment Structure Anchoring Homeotropic Planar Default Disorder Dynamic Local Short range Long range Effects Size Grafting
256	Thermo-Mechanische Charakterisierung von Grenzflächen zwischen Einwandigen Kohlenstoffnanoröhren und Metallen mittels Auszugsversuchen / Thermo-Mechanical Characterization of Interfaces between Single-WalledCarbon Nanotubes and Metals by Pull-Out Testing Hartmann, Steffen 04 February 2016 (has links) Vor dem Hintergrund zukünftiger Sensoren, basierend auf dem piezoresistiven Effekt von einwandigen Kohlenstoffnanoröhren (SWCNT), werden in dieser Arbeit umfangreiche Ergebnisse zum mechanischen Verhalten von Grenzflächen zwischen SWCNTs und edlen Metallen am Beispiel von Pd und Au präsentiert. Im Fokus steht dabei die Synergie von rechnerischen und experimentellen Methoden Molekulardynamik (MD), nanoskalige Tests und Analytik , um (1) mit guter Genauigkeit maximale Kräfte von gezogenen SWCNTs, welche in Metall eingebettet sind, vorauszuberechnen und (2) einen wertvollen Beitrag zum Verständnis der zu Grunde liegenden Fehlermechanismen zu liefern. Es wurde ein MDModell eines in eine einkristalline Matrix eingebetteten SWCNTs mit Randbedingen eines Auszugsversuchs entwickelt. Mit diesem Modell können Kraft-Weg-Beziehungen und Energieverläufe für einen quasistatischen verschiebungsgesteuerten Auszugsversuch errechnet werden. Das Modell liefert kritische Kräfte bei Versagen des Systems. Des Weiteren können mit diesem Modell der Einfluss des SWCNT-Typus, der Einbettungslänge, der Temperatur, von intrinsischen Defekten und Oberflächengruppen (SFGs) auf das Grenzflächenverhalten untersucht werden. Zum Vergleich wurden kritische Kräfte experimentell durch in situ Auszugsversuche in einem Rasterelektronenmikroskop bestimmt. Es wurde eine sehr gute Übereinstimmung von rechnerischen und experimentellen Daten festgestellt. Der vorherrschende Fehler im Experiment ist der SWCNT-Bruch, jedoch wurden auch einige SWCNT-Auszüge beobachtet. Mit Hilfe der MD-Simulationen wurde gefunden, dass die SFGs als kleine Anker in der umgebenden metallischen Matrix wirken und somit die maximalen Kräfte signifikant erhöhen. Diese Grenzflächenverstärkung kann Zugspannungen verursachen, die genügend hoch sind, so dass SWCNT-Bruch initiert wird. Im Gegensatz dazu zeigten Simulationen von Auszugstests mit idealen SWCNTs nur kleine Auszugskräfte, welche meistens unabhängig von der Einbettungslänge des SWCNTs sind. Dieses Verhalten wird mit einer inkommensurablen Konfiguration der Kristallstrukturen an der Grenzfläche von SWCNTs und der einbettenden Edelmetalle interpretiert. Zur Qualifizierung der Existenz von carboxylatischen Oberflächengruppen auf dem genutzten SWCNT-Material wurden analytische Untersuchungen mittels Fluoreszenzmarkierung von Oberflächengruppen durchgeführt. In Übereinstimmung mit Literaturstellen zum gesicherten Nachweis von SFGs, bedingt durch technologische Behandlungen, weisen diese Experimente stark auf das Vorhandensein von carboxylatischen Oberflächengruppen auf dem genutzten SWCNT-Material hin. Demnach kann der dominante SWCNT-Bruch Fehler durch die Grenzflächenverstärkung auf Grund von SFGs erklärt werden. / In the light of future sensors, that are based upon the piezoresistive effect of singlewalled carbon nanotubes (SWCNTs), this work presents comprehensive results of studies on the mechanical behavior of interfaces between SWCNTs and noble metals using the examples of Pd and Au. With this contribution, the focus is on a synergy between computational and experimental approaches involving molecular dynamics (MD) simulations, nanoscale testing, and analytics (1) to predict to a good degree of accuracy maximum forces of pulled SWCNTs embedded in a noble metal matrix and (2) to provide valuable input to understand the underlying mechanisms of failure. A MD model of a SWCNT embedded in a single crystalline matrix with pull-out test boundary conditions was developed. With this model, force-displacement relations and energy evolutions for a quasi-static displacement controlled test can be computed. The model provides critical forces for failure of the system. Furthermore, the influence of SWCNT type, embedding length, temperature, intrinsic defects and surface functional groups (SFGs) on the interface behavior can be studied using this model. For comparison, critical forces were experimentally determined by conducting pull-out tests in situ, inside a scanning electron microscope. A very good agreement of computational and experimental values was discovered. The dominant failure mode in the experiment was a SWCNT rupture, although several pull-out failures were also observed. From MD simulations, it was found that SFGs act as small anchors in the metal matrix and significantly enhance the maximum forces. This interface reinforcement can lead to tensile stresses sufficiently high to initiate SWCNT rupture. In contrast, pull-out test simulations of ideal SWCNTs show only small pull-out forces, which are mostly independent on SWCNT embedding length. This behavior is interpreted with an incommensurate configuration of crystal structures at the interface between SWCNTs and embedding noble metals. To qualify the existence of carboxylic SFGs on the used SWCNT material, an analytical investigation by means of fluorescence labeling of surface species was performed. In agreement with literature reports on the secured verification of SFGs due to necessary technological treatments, these experiments strongly indicate the presence of carboxylic SFGs on the used SWCNT material. Thus, the dominant SWCNT rupture failure is explained with an interface reinforcement by SFGs. info:eu-repo/classification/ddc/629 ddc:629 Kohlenstoff-Nanoröhre; Grenzfläche
257	Nanoscale resistive switching memory devices: a review Slesazeck, Stefan, Mikolajick, Thomas 10 November 2022 (has links) In this review the different concepts of nanoscale resistive switching memory devices are described and classified according to their I–V behaviour and the underlying physical switching mechanisms. By means of the most important representative devices, the current state of electrical performance characteristics is illuminated in-depth. Moreover, the ability of resistive switching devices to be integrated into state-of-the-art CMOS circuits under the additional consideration with a suitable selector device for memory array operation is assessed. From this analysis, and by factoring in the maturity of the different concepts, a ranking methodology for application of the nanoscale resistive switching memory devices in the memory landscape is derived. Finally, the suitability of the different device concepts for beyond pure memory applications, such as brain inspired and neuromorphic computational or logic in memory applications that strive to overcome the vanNeumann bottleneck, is discussed. info:eu-repo/classification/ddc/530 ddc:530
258	Biocompatible Electrospun Vehicles To Enhance the Effectiveness Of Anti-Fertility Strategies And Their Biomimetic Properties As Blood Vessel Scaffolds Chaparro, Francisco Javier 01 June 2018 (has links) No description available. Biomechanics Biomedical Research Chemical Engineering Engineering Materials Science Polymers Polymer Chemistry Plastics Organic Chemistry Nanotechnology Nanoscience Medicine Design
259	<b>Two-dimensional Transition Metal Carbides as Precursor Materials for Applications in Ultra-high Temperature Ceramics</b> Srinivasa Kartik Nemani (20135232) 19 November 2024 (has links) <p dir="ltr">In this dissertation, we investigate the potential of two-dimensional (2D) transition metal carbides, known as MXenes, as precursor materials for the development of ultra-high temperature ceramics (UHTCs), with a focus on Ti<sub>3</sub>C<sub>2</sub>T<sub><em>x</em></sub> MXene. MXenes are distinguished by their unique combination of 2D structure, high surface area, and chemically active basal planes, making them ideal candidates for a wide range of high-performance applications. This study focuses on the phase transformation, grain growth, surface texturing, and electrocatalytic behavior of Ti<sub>3</sub>C<sub>2</sub>T<sub><em>x</em></sub> MXene films when subjected to high-temperature annealing, along with their role as sintering aids in UHTCs.</p><p dir="ltr">We present the transformation of 2D Ti<sub>3</sub>C<sub>2</sub>T<sub><em>x</em></sub> flakes into ordered vacancy carbides of three-dimensional (3D) TiC<sub>y</sub> phases at temperatures above 1000°C. Using X-ray diffraction and ex-situ annealing (up to 2000°C in a tube furnace and spark plasma sintering), we investigate the resulting nano-lamellar and micron-sized cubic grain morphologies. Single-flake Ti<sub>3</sub>C<sub>2</sub>T<sub><em>x</em></sub> films retain a lamellar morphology after annealing, while multi-layer clay-like MXene transforms into irregular cubic grains.</p><p dir="ltr">In addition to investigating the structural evolution, we examine the influence of cationic intercalation on grain growth and texture. Specifically, Ca²⁺ ions lead to highly templated growth along the (111) crystal plane, significantly altering carbon diffusion and metal atom migration during annealing. We show that this preferential growth influences properties with hydrogen evolution reactions (HER) as an example functionality. We observe that with Ca²⁺-intercalated Ti<sub>3</sub>C<sub>2</sub>T<sub><em>x</em></sub> films, exhibit an overpotential of 594 mV and a current density of -13 mA/cm² due to increased surface area and dominant texturing.</p><p dir="ltr">Additionally, we investigate the use of MXenes in self-assembly with ceramic materials such as ZrB<sub>2</sub>, facilitated by optimizing zeta potentials. MXenes, with their functionalized hydrophilic surfaces and negative zeta potentials, serve as sintering aids and reinforcements in UHTC composites. The introduction of Ti<sub>3</sub>C<sub>2</sub>T<sub><em>x</em></sub> to ZrB<sub>2</sub> enables improved sinterability, achieving 96% relative density compared to 89% for pure ZrB<sub>2</sub>. Furthermore, the addition of MXenes leads to a core-shell microstructure with (Zr,Ti)B<sub>2</sub> solid-solution interfaces, enhanced mechanical properties such as a 36% increase in hardness, and reductions in oxygen content. These findings establish MXenes as promising materials for the development of advanced UHTCs, suitable for extreme environments.</p><p dir="ltr">Through a combination of experimental techniques, and theoretical estimations, and advanced characterizations, this dissertation provides critical insights into the role of MXenes in both phase transformation and mechanical reinforcement, thereby laying the foundation for future studies and opening new avenues for applications of MXene derived carbides and the design of high-performance UHTCs.</p> Aerospace materials Composite and hybrid materials Functional materials Nanomaterials Nanoscale characterisation MXenes MAX phases Ultra high temperature self-assembly aerospace materials mechanical properties microstructure solid-solution strengthening Composites High temperature stabi
260	<b>Probabilistic Computing Through Integrated Spintronic Nanodevices</b> John Arnesh Divakaruni Daniel (20360574) 10 January 2025 (has links) <p dir="ltr">Probabilistic computing is a novel computing scheme that offers a more efficient approach than conventional complimentary metal-oxide-semiconductor (CMOS)-based logic in a variety of applications ranging from Bayesian inference to combinatorial optimization, and invertible Boolean logic. These applications, which have found use in the rapidly growing fields of machine learning and artificial intelligence, are traditionally computationally-intensive and so make the push for novel computing schemes that are intrinsically low-power and scalable all the more urgent.</p><p dir="ltr">The probabilistic bit (or p-bit, the base unit of probabilistic computing) is a naturally fluctuating entity that requires <i>tunable </i>stochasticity; low-barrier nanomagnets, in which the magnetic moment fluctuates randomly and continuously due to the presence of thermal energy, are a natural vehicle for providing the core functionality required. This dissertation describes the work done in mining the rich field of spintronics to produce devices that can act as natural hardware accelerators for probabilistic computing algorithms.</p><p dir="ltr">First, experiments exploring Fe<sub>3</sub>O<sub>4</sub> nanoparticles as naturally stochastic systems are presented. Using NV center measurements on an array of such nanoparticles, it is shown that they fluctuate intrinsically at GHz frequencies at room temperature; these fluctuations could be harnessed to act as a stochastic noise source, and would, in principle, enable fast computation.</p><p dir="ltr">The focus then shifts to the development of a platform that allows for easier <i>electrical</i> readout: the low-barrier magnetic tunnel junction (MTJ). We show the work done in the development and characterization of these devices, how they respond to non-ideal environments, such as elevated temperatures and exposure to high-energy electromagnetic radiation, how their intrinsic stochasticity might be tuned with electrical currents and external magnetic fields, and then how these might be integrated with a simple transistor circuit to produce a compact low-energy implementation of a p-bit.</p><p dir="ltr">Next, by integrating our stochastic MTJs with 2D-MoS<sub>2</sub><sup> </sup>field-effect transistors (FETs), the first <i>on-chip </i>realization of a key p-bit building block, displaying voltage-controllable stochasticity, is demonstrated. This is followed by another key demonstration through the fabrication of stochastic MTJs directly on top of an integrated circuit platform, where the transistor circuitry is provided by 180nm-node CMOS technology.</p><p dir="ltr">In addition, supported by circuit simulations, this work provides a careful device-level analysis of the three transistor-one magnetic tunnel junction (3T-1MTJ) p-bit design, evaluating how the characteristics of each component can influence the overall p-bit’s output. In particular, we show that – against common wisdom – a large tunnel magnetoresistance (TMR) is not the best choice for p-bits; bimodal telegraphic fluctuations are highly undesirable and are a sign of a slow device; and an ideal inverter with a large gain is unsuitable for p-bit applications due to the higher likelihood of unwanted plateaus in the resulting p-bit’s output.</p><p dir="ltr">This analysis is extended to consider the impact of such non-ideal p-bits when used to construct probabilistic circuits, with the focus on the emulation of the Boolean logic AND gate through a three p-bit correlated system. It is found that a probabilistic circuit made with ideal p-bits can accurately emulate the function of an AND gate, while the non-ideal p-circuits suffer from an increased error rate in emulating the AND gate’s truth table.</p><p dir="ltr">The understanding gained at the individual device level, in what makes a good or bad MTJ, to how the different components of the 3T-1MTJ p-bit can affect its output, and subsequently how non-ideal p-bits can impact circuit performance, can be important for the future realization of scaled on-chip p-bit networks.</p> Nanoelectronics Nanomaterials Nanoscale characterisation Nanotechnology not elsewhere classified Probabilistic Computing Spintronics Magnetic Tunnel Junctions Stochastic MTJs Low-barrier nanomagnets Magnetic Materials Electrical and Magnetic Characterization Probabilistic Bit p-bit True Random Number Generator (TRNG) Nanofabrication Process Development Magnetic Fluctuations

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