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DSpace at MIT (104.280 recursos)

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Materials Science and Engineering - Ph.D. / Sc.D.

Mostrando recursos 1 - 20 de 981

  1. From self-assembly to communications via machine washable fibers

    Rein, Michael, Ph. D. Massachusetts Institute of Technology
    Fibers and fabrics are among the earliest forms of human expression, and yet they have not progressed much from a functional standpoint over the course of history. Recently, a new family of fibers composed of conductors, semiconductors and insulators has emerged. These fibers can achieve device attributes, yet are fabricated using scalable preform-based fiber-processing methods, yielding kilometers of functional fiber devices. Co-draw of different materials is possible for numerous material combinations and sizes, where one of the limiting factors to a continuous feature size in fibers is the Rayleigh-Plateau capillary instability. In my thesis I have shown that it is...

  2. Controlling properties of functional oxides by tuning oxygen defect chemistry

    Lu, Qiyang
    Oxygen defects are essential building blocks for properties and functionalities of oxides, including electrical conductivity, magnetism, ferroelectricity as well as catalytic and electrocatalytic activity. Therefore, fundamental understanding of how to tune the oxygen defect chemistry is essential for advancing applications based on these defect sensitive properties. This thesis investigated pathways to controlling the concentration and structure of oxygen defects on selected case studies with model oxide systems. Three novel effects were assessed and shown to be operative for obtaining a large impact on the oxygen defect chemistry equilibria. These are heterogeneous chemical doping of the surface for improving surface electrocatalytic...

  3. Designing dynamic mechanics in self-healing nanocomposite hydrogels

    Li, Qiaochu, Ph. D. Massachusetts Institute of Technology
    The functional versatility and endurable self-healing capacity of soft materials in nature is found to originate from the dynamic supramolecular scaffolds assembled via reversible interactions. To mimic this strategy, extensive efforts have been made to design polymer networks with transient crosslinks, which lays the foundation for synthetic self-healing hydrogels. Towards the development of stronger and faster self-healing hydrogels, understanding and controlling the gel network dynamics is of critical importance, since it provides design principles for key properties such as dynamic mechanics and self-healing performance. For this purpose, a universal strategy independent of exact crosslinking chemistry would be regulating the polymer...

  4. Simulating energy transfer between nanocrystals and organic semiconductors

    Geva, Nadav
    Recent trends in renewable energy made silicon based photovoltaics the undisputed leader. Therefore, technologies that enhance, instead of compete with, silicon based solar cells are desirable. One such technology is the use of organic semiconductors and noncrystalline semiconductors for photon up- and down-conversion. However, the understanding of energy transfer in these hybrid systems required to effectively engineer devices is missing. In this thesis, I explore and explain the mechanism of energy transfer between noncrystalline semiconductors and organic semiconductors. Using a combination of density functional calculations, molecular dynamics, and kinetic theory, I have explored the geometry, morphology, electronic structure, and coarse...

  5. Ground state determination, ground state preserving fit for cluster expansion and their integration for robust CE construction

    Huang, Wenxuan, Ph. D. Massachusetts Institute of Technology
    In this thesis, we propose strategies to solve the general ground state problem for arbitrary effective cluster interactions and construct ground state preserving cluster expansions. A full mathematical definition of our problem has been formalized to illustrate its generality and clarify our discussion. We review previous methods in material science community: Monte Carlo based method, configurational polytope method, and basic ray method. Further, we investigate the connection of the ground state problem with deeper mathematical results about computational complexity and NP-hard combinatorial optimization (MAX-SAT). We have proposed a general scheme, upper bound and lower bound calculation to approach this problem....

  6. Magnetic thin films For spintronic memory

    Agrawal, Parnika
    Domain walls are regions of spatially non-uniform magnetizations in magnetic materials. They form the boundaries between two or more uniformly magnetized regions called domains. Skyrmions are circular magnetic domains with chiral domain walls that are interesting due to their stability and potential for fast motion. These spin structures can be used to encode Os and Is in spintronic memory. Chiral domain walls and skyrmions have been seen in magnetic thin films sandwiched between non-identical non-magnetic materials which have high spin-orbit coupling and Dzyaloshinskii-Moriya interaction. An optimization of the different physical interactions involved in magnetic thin films can result in stripe...

  7. Electrochemically-induced phase transition in olivine type cathode materials

    Xiang, Kai, Ph. D. Massachusetts Institute of Technology
    Phase transitions are commonly observed in ion storage compounds when being used in rechargeable batteries and thus, the phase behavior of ion storage compounds as electrode active materials has significant impact on battery performance. This thesis aims to understand the interplay between materials structure, phase behavior and battery performance. The effects of operating conditions, especially overpotential and temperature, on phase behavior and battery performance are also investigated. Using olivine-type phosphates (i.e. phospho-olivines) with varying composition and particle size as model system, strain accommodation mechanism within single nanoparticles (Chapter 2 to 3) and mesoscale kinetics of nanoparticle aggregates (Chapter 4 to...

  8. On the electrolytic nature of molten aluminum and rare earth oxides

    Nakanishi, Bradley Rex
    The electrolytic cell method and its application for Gibbs energy measurement in high temperature, concentrated ionic melts was investigated. Previous challenges related primarily to signal interpretation during decomposition voltage measurement have hindered determination of Gibbs energy. An electrolytic cell method is proposed herein utilizing the sensitivity of large amplitude alternating current voltammetry, which enabled precise measurement of chemical potential during electrolytic decomposition. A novel, containerless approach for electrochemical study of high temperature, reactive electrolytes in a molten pendant droplet is described. For the first time, melts of pure alumina, lanthana and yttria were electrolytically decomposed to metal alloy and oxygen...

  9. Chemomechanics of non-stoichiometric oxide films for energy conversion

    Swallow, Jessica G
    Electrochemical energy conversion and storage devices including solid oxide fuel cells (SOFCs) and lithium ion batteries (LIBs) are enabled by materials known as "non-stoichiometric oxides" that contain large concentrations of point defects such as oxygen or lithium vacancies. While this non-stoichiometry provides the essential functional properties of ionic conductivity or reactivity that make these materials useful, it also tends to couple to material volume through the effect of chemical expansion. Chemical expansion, or volume coupled to defect concentration, is in turn tied to mechanical variables including stress, strain, and elastic constants. This electrochemomechanical coupling, or interaction between functional properties, defect...

  10. Development and validation of a computational approach to predicting the synthesis of inorganic materials

    Kitchaev, Daniil A
    The concept of computational materials design envisions the identification of chemistries and structures with desirable properties through first-principles calculations, and the downselection of these candidates to those experimentally accessible using available synthesis methods. While first-principles property screening has become routine, the present lack of a robust method for the identification of synthetically accessible materials is an obstacle to true materials design. In this thesis, I develop a general approach for evaluating synthesizeability, and where possible, identifying synthesis routes towards the realization of target materials. This approach is based on a quasi- thermodynamic analysis of synthesis methods, relying on the assumption...

  11. The system tantalum-rhenium

    Schwarzkopf, Peter
    by Peter Schwarzkopf.

  12. Fracture toughness enhancement and synthesis of ZrO2 bearing ceramic alloys

    Ketcham, Thomas Dale
    by Thomas Dale Ketcham.

  13. Integration of GaAsP alloys on Si for high-efficiency Ill-V/Si PV

    Milakovich, Timothy John
    Introduction: The motivation of this work is to create a platform that leverages the large area and low cost of Silicon wafers with the high performance of Ill-V materials. Ill-V semiconductor materials have enabled a host of electronic devices from record setting solar cells, high efficiency light emitting diodes, power amplifiers and high-mobility electron transistors. The last 60 years of research and development by the Si microelectronics industry has made the use of Si for microelectronics, power electronics and photovoltaics (PV) ubiquitous and low cost. The low cost of silicon technology is due to a mature and well developed supply...

  14. Creep behavior of binary solid solutions of nickel with molybdenum and tungsten

    Tiearney, Thomas Carson
    by Thomas Carson Tiearney, Jr.

  15. Block copolymer self-assembly : lithography, magnetic fabrication, and optimization

    Tu, Kun-Hua
    Block copolymer (BCP) self-assembly is attractive because it provides nanoscale long-range ordered structures in a massive quantity. The capability of generating features with size as low as 5 nm is of particular interest in semiconductor fabrication since current photolithography has reached its resolution limitation and the other competing technologies are either too slow such as e-beam lithography or too expensive such as EUV system. In this thesis, BCP lithography is utilized to fabricate magnetic nanostructure and the corresponding magnetic properties are explored. The polystyrene- b-polydimethylsiloxane (PS-b-PDMS) diblock copolymer with different molecule weight is used to generate various sizes of robust...

  16. In search of Mg battery cathode materials - a migration energy high-throughput screening machinery

    Rong, Ziqin
    In this thesis, we demonstrate the results and progress of developing a high-throughput migration energy calculation machinery and applying it in search for Mg battery cathode materials. We discuss the key challenge of developing functional Mg battery cathode, and propose to use NEB algorithm in high-throughput calculations to screen for materials with good Mg" diffusivity. However, though NEB algorithm performs quite well on individual systems, due to its very long run-time, it is difficult to be scaled up in high-throughput applications. Therefore, new algorithms are developed and implanted, and 17 potential Mg cathode materials are selected by the new high-throughput...

  17. Accounting for temperature and local structure in atomistic calculations of interface free energies in metals

    Navale, Sanket Sunil
    Interfaces are ubiquitous in crystalline materials and they predominantly govern the properties of metals at nanoscale. Free energy is the most significant characteristic of an interface that determines its behavior and other properties. However, interfaces have an internal structure with nanoscale features that gives the interface free energy, a location dependent variation. The interface free energy is also expected to depend on temperature, especially for entropy stabilized phases such as liquids. I present methods for calculating location-dependent energies for solid-state interfaces and temperature-dependent free energies for solid/liquid interfaces using atomistic models. I demonstrate these methods on CuNbHe and AlGa models...

  18. Properties of thin film III-V/IV semiconductor alloys and nanostructures

    Jia, Roger (Roger Qingfeng)
    A large amount of research and development has been devoted to engineering materials for the next generation of semiconductor devices with high performance, energy efficiency, and economic viability. To this end, significant efforts have been made to grow semiconductor thin films with the desired properties onto lattice constants with viable, cost effective substrates. Comparatively less effort has been made to explore III-V/IV heterovalent nanostructures and alloys, which may exhibit properties not available in existing materials. The investigation of these structures, grown using MOCVD, is the goal of this thesis and is motivated by two factors: one, that III-V/IV nanostructures should...

  19. GaAsP/InGaP heterojunction bipolar transistors for III-V on Si microelectronics

    Heidelberger, Christopher
    GaAs-based transistors are capable of operating at high frequency with low noise, and are produced in large volumes for a wide range of applications including microwave frequency ICs for input/output in mobile devices. However, Si CMOS still holds an advantage for digital logic due to wide market penetration resulting in decades of development and lower cost. Monolithic integration of III-V analog circuity and Si CMOS gives circuit designers the best of both materials. In addition, by substituting GaAsxP₁-x (0.8 < x < 1) for GaAs as an active material, we can take advantage of its higher breakdown voltage and reduced...

  20. Directed self-assembly of block copolymers with functional materials : a study of nanocomposite thin film fabrication on graphoepitaxial templates

    Ding, Yi, Ph.D. Massachusetts Institute of Technology. Department of Materials Science and Engineering
    Block copolymers (BCPs) are a class of soft materials consisting of two (or more) different chains joint together by covalent bond. This special chemical structure leads to microphase separation and consequently a variety of highly controllable self-assembly patterns. Directed self-assembly (DSA) of BCPs has therefore emerged as one of the most promising technologies to fabricate functional nanostructures and is able to produce patterns with ultra-small resolution (sub-10 nm) while maintaining high throughput and order. However, existing DSA methods depend mostly on carbon or silicon-based BCPs, thus lack functionality for sophisticated applications. This work aims at expanding the capability of DSA...

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