Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1994. / Includes bibliographical references (leaves 148-151). / by Bethanie J. Hills Stadler. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, February 2005. / Includes bibliographical references (leaves 121-134). / Silicon oxynitride (SiON) is an ideal waveguide material because the SiON materials system provides substantial flexibility in composition and refractive index. SiON can be varied in index from that of silicon dioxide (n=1.46) to that of silicon-rich silicon nitride (n-2.3). This flexibility in refractive index allows for the optimization of device performance by allowing trade-offs between the advantages of low-index contrast systems (low scattering losses and easy fiber-to-waveguide coupling) and the benefits of high-index-contrast systems (small waveguide size and tight bending radii). This work presents sputter processing as an alternative to traditional CVD processing. Two room-temperature SiON sputter processes are explored. The first process is a co- sputtered deposition from a silicon oxide and a silicon nitride target. The second is a reactive sputtering process from a silicon nitride target in an oxygen ambient. Silicon nitride sputtered from a silicon nitride target is also investigated. Models are provided that predict the index and composition in both the reactive and co- sputtered depositions. The cosputtered deposition is shown to follow a mixture model, while the reactive sputter deposition is shown to be either Si-flux limited or O-flux limited, depending on the partial pressure of oxygen in the reaction chamber and the power applied to the silicon nitride target. A materials study is provided that shows sputtered SiON to be a homogeneous material that gives good control of refractive index. Reactively sputtered SiON is shown to be Si-rich. These sputtered materials investigated for use in waveguides and in Er-doped waveguide amplifiers. / (cont.) Low loss waveguides are demonstrated for both co-sputtered and reactively sputtered depositions. Losses below 1 dB/cm are shown for co-sputtered deposition (n=1.65). Photoluminescence of Er-doped material shows lifetimes comparable to commercial EDFA material for both co-sputtered SiON and sputtered silicon dioxide. / by Jessica Gene Sandland. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2006. / Includes bibliographical references (leaves 65-70). / The mechanical properties of compliant materials such as polymeric films and biological membranes that are of nanoscale in thickness are increasingly extracted from scanning probe microscope-enabled nanoindentation. These films are applied in various fields that require multiaxial loading conditions. The Hertzian contact models developed for linear elastic materials of semi-infinite thickness fail to accurately predict the elastic modulus E for these compliant materials. This makes it necessary to understand the evolution of stress and strain fields of these nanoscale structures. In this thesis we employ computational simulations that are based on experimental parameters for contact based analysis of compliant polymer thin films, to decouple the effect of thickness and angle of indentation on calculated mechanical properties. Traction applied by living cells to these compliant films are studied in detail. We thus identify the range of strains and material thickness for which contact models could be used to accurately predict the elastic stiffness of these polymeric films of nanoscale (<100 nm) thickness using scanning probe microscope-enabled experiments, and the volumes over which adhered cells deform these films. The key results of this thesis enable accurate experimental analysis of polymeric thin film elastic properties, and design of synthetic polymeric substrata that will dominate the mechanical environment of adhered cells. / by Binu K. Oommen. / S.M.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2018. / 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. / 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 chemistry, and mechanical variables, can have important consequences for devices operated in extreme environments, where unexpected stress may lead to fracture, or well-engineered strain may enhance device efficiency. Such effects are particularly important in thin film devices, where strain engineering is within reach, undesired fracture can devastate performance, and defect chemistry and related properties can differ from bulk systems. In this thesis, we present a concerted investigation of chemomechanical coupling, including interactions between material chemistry, environmental conditions, stress, strain, and mechanical properties, for films of the model material PrxCe1-xO2-[delta] (PCO) that is a fluorite-structured oxide relevant to SOFC applications. PCO is an excellent model system because of its well-established defect chemistry model and known thermal and chemical expansion coefficients. The thesis begins by first characterizing key chemomechanical effects in PCO, including electrochemically induced high temperature actuation and nonstoichiometry- dependent mechanical properties that are modulated by environmental conditions including temperature and oxygen partial pressure. We then explore the mechanisms and microstructural contributions to these effects via computational modeling and high temperature transmission electron microscopy, identifying ways in which chemomechanical effects in thin film non-stoichiometric oxides differ from those in bulk. Finally, we extend the experimental and computational methods developed in the thesis to characterizing similar effects in Li-storage materials, demonstrating the broad applicability of results across the classes of non-stoichiometric oxides. We first describe an experimental study in which we developed a novel method of detecting chemical expansion on short time scales in the model system PCO and characterized material deformation for a range of conditions of temperature and effective oxygen partial pressure (pO2). In this method, electrically-stimulated chemical expansion caused mechanical deflection of a substrate, an effect that for PCO was enhanced for elevated temperatures or reducing conditions ... / by Jessica G. Swallow. / Ph. D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2006. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Includes bibliographical references (p. 207-213). / The immersion precipitation process makes most commercial polymeric membranes, which enjoy widespread use in water filtration and purification. In this work, a ternary Cahn-Hilliard formulation incorporating a Flory-Huggins homogeneous free energy function is used to model both initial diffusion and the liquid-liquid demixing stage of the immersion precipitation process, which determines much of the final morphology of membranes. Simulations start with a simple non-solvent/solvent/polymer ternary system with periodic boundary conditions and uniform initial conditions with small random fluctuations in 2D. Results in 2D demonstrate the effects of mobilities (Mij) and gradient penalty coefficients (Kij) on phase separation behavior. A two-layer polymer-solvent/non-solvent initial condition is then used to simulate actual membrane fabrication conditions. 2D simulation results demonstrate an asymmetric structure of membrane morphology, which strongly agrees with the experimental observation. A mass transfer boundary condition is developed to model the interaction between the polymer solution and the coagulation bath more efficiently. Simulation results show an asymmetric membrane with connected top layer. / (cont.) Then a wide range of initial compositions are used in both the polymer solution and the coagulation bath, and the resulting morphology changes from isolated polymer droplets to bi-continuous pattern to continuous polymer with isolated pores. A nonuniform initial condition is proposed to model the evaporation of volatile solvent prior to immersion, which results in different time scale of the onset of spinodal decomposition and an asymmetric structure with different pore size in the membrane. Furthermore, a simple one-factor model is used to capture the concentration dependence of the polymer mobility in the low concentration range. Simulations with variable polymer mobility show faster coarsening kinetics. The membrane simulations are then extended to three dimensions. The 3D simulations show similar morphology as 2D results: an asymmetric structure with a dense layer on top of a porous bulk, but provide more information about the pore connectivity. The coarsening mechanism study confirmed the merge of the layers into the bulk membrane structure.. / (cont.) Finally, ternary Cahn-Hilliard equations are coupled with the Navier-Stokes equations to include fluid flow driven by the interface curvature change during spinodal decomposition in two dimensions. Different formulation of the Navier-Stokes equation are evaluated for computational efficiency. 2D simulation results show that fluid flow destabilizes the top layer of membrane. / by Bo Zhou. / Ph.D.

Thesis: S.B., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2014. / Cataloged from PDF version of thesis. / Includes bibliographical references (page 30). / Glial scarring is a major problem seen in brain electrode implants that can hinder electrode function. One major contributing factor is the mechanical mismatch between the stiff electrode and the soft brain tissue'. Hydrogel coatings are being investigated to determine their effectiveness in providing the necessary biocompatibility. Polyethylene glycol hydrogels of various formulations were fabricated and produced elastic moduli ranging from 13kPa to 687 kPa, which lie within two orders of magnitude of the elastic moduli of the brain (6kPa). Dehydration of the hydrogels provides the mechanical rigidity necessary for implantation into the brain. The surrounding aqueous environment allows the dried hydrogel to return to its swollen state. The swelling process in the brain phantom is slower than in unconstrained swelling. The equilibrium swollen hydrogel was also slightly smaller in the constrained state, implying the strain is being distributed between the hydrogel and the brain phantom. / by Di Judy Deng. / S.B.

Thesis: S.B., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2018. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 65-66). / Cobalt has become more and more popular in the realms of academia, industry, and media due to its integral role in many of the most commonly-used lithium-ion battery cathodes today. Many issues have been evaluated regarding the controversial labor and volatile sociopolitical environments associated with cobalt mining and concerns over the ability of cobalt supply to continue to meet demand, especially the increasing demand due to the electric vehicle revolution. Cobalt is a critical element in a variety of products outside of the battery industry, including: superalloys, hard-facing metals, cutting tools, magnets, chemical catalysts, and pigments. In this thesis, I assessed the criticality of cobalt demand in non-battery sectors with the intention of assessing whether demand of cobalt in its traditional, inelastic sectors will supply be a limiting factor of technological progress by 2030 and by 2050. In order to do so, data was collected on the past and present demands of cobalt in its four primary sectors, outside of batteries: superalloys, cutting tools and hard-facing metals, magnets, and chemical catalysts. Future demand projections were made based on the historic data as well as via a bottom-up approach from industry projections for future product demand and cobalt intensity of products. Substitutes for cobalt in these applications were also investigated and are discussed below. The prices at which substitutes become more favorable than cobalt were also evaluated. / by Alexandra A. Zele. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2003. / Includes bibliographical references (p. 151-162). / This thesis explores the photonic properties of block copolymer systems. One dimensionally periodic dielectric stacks are fabricated with symmetric, lamellar forming, copolymer systems: diblock copolymers, solvent swollen BCP materials, and homopolymer swollen BCP blends. Each system exhibits reflectivity in visible spectrum. These materials are also investigated for their phononic band properties by Brillouin scattering. A copolymer forming the three dimensional double gyroid at optically relevant length scales and its reflective properties are presented as well. Experimental results document the initial observation of photonic optical properties related to the microstructure of a block copolymer. One dimensionally periodic, lamellar polymer block copolymer systems of poly(styrene-b-isoprene) are used to fabricate multilayered optical structures with a range of lamellar dimensions. The lamellar repeat of the copolymer morphology is shown to be adjustable by blending symmetric amounts of like homopolymers of lower molecular weight with the copolymer. The composition of the blends remains symmetric and the morphology is shown to remain lamellar. An isopleth of composition is examined and photonic crystals containing up to 60 wt % homopolymer exhibit wavelength selective reflectivity from the ordered morphology. The wavelength of reflectivity is correlated with the lamellar repeat spacing and morphology. The optical properties of solvent swollen ultrahigh molecular weight block copolymers are examined. The wavelength selective reflectivity is shown to correlate with the expected behavior of the phase segregated morphology. Deformation sensitive ordered gels are fabricated by using a non-volatile, alkyl phthalate plasticizer. The optical properties are shown to respond to the material strain. A simple demonstration of the visualization of the strain field of a deforming system is presented. In addition these gels are shown to exhibit phononic band gap behavior. The system is studied by Brillouin scattering and resonant phonons arising from the morphology are predicted and observed. Three dimensionally periodic photonic crystals formed of a double gyroid styrene- isoprene diblock copolymer are also documented. The copolymer material is considered as formed and also after a series of processing steps. / (cont.) Etching of the isoprene matrix is demonstrated yielding a free standing air-styrene double gyroid. This material is then used to replicate the matrix geometry in titania by infiltration with a sol-gel precursor and subsequent pyrolysis. The structure of the double gyroid material is examined via x-ray scattering and electron microscopy. The photonic band properties of the double gyroid structure for multiple constituent materials with a broad range of refractive indices are examined. Features in optical measurements resulting from the double gyroid structure are observed consistent with the 250nm cubic lattice parameter. A block copolymer photonic crystal platform is outlined and presented. Acousto-optic, phononic crystal properties are noted in these materials and applications are discussed. Strategies for creating a block copolymer based material with an absolute band gap ... / by Augustine M. Urbas. / Ph.D.

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2006. / Includes bibliographical references (leaves 76-81). / The cost of manufacturing electronic displays currently limits the range of applications and markets into which it is currently economically feasible to adopt displays. Roll-to-roll manufacturing has been identified by the display industry as a new and fundamentally different manufacturing paradigm that has the potential to significantly reduce the manufacturing cost of a display relative to the conventional approaches used in the industry. This manufacturing cost reduction could have a profound impact on the display industry by not only transforming the display manufacturing infrastructure, but also by permitting electronic displays to penetrate new markets. The purpose of this thesis is to determine how roll-to-roll manufacturing technology could develop and to assess what impact the technology could have on the electronic display manufacturing industry. This work first identifies the material, patterning, and equipment technologies that need to come together in order for roll-to-roll manufacturing to be industrially feasible, and then determines how and if the technology will offer a cost reduction over conventional manufacturing techniques. / (cont.) Next, the markets for displays are segmented and analyzed to discern whether niche initial markets exist where roll-to-roll could have a distinctive advantage and gain traction. Competitive technologies such as LCD and modular LED are discussed and it is determined that roll-to-roll displays must compete with LCD technology on the basis of price in the markets in which LCD has incumbency in order to achieve widespread adoption. The display industry structure is analyzed by means of an assessment of the supply chain, intellectual property landscape, financing mechanisms, and business models to understand how partnerships and financial investment risk are salient aspects of the commercialization process. It is concluded that materials cost advantages over current manufacturing approaches and the timing of roll-to-roll technology integration developments relative to the incremental manufacturing cost decreases in competing technologies will ultimately dictate the success of roll-to-roll manufacturing. / by Michael Aaron Randolph. / M.Eng.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2011. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 55-65). / In this thesis, I consider two methods to improve organic photovoltaic efficiency: energy level cascades and promotion of triplet state excitons. The former relies on a thin layer of material placed between the active layers of a photovoltaic device to destabilize excitons. If the interfacial material is chosen properly, it can significantly improve device performance. The second method proposes to use quantum mechanical rules to reduce the rate of loss in organic photovoltaic devices. An electron in a triplet state cannot directly drop to the ground state by emitting a photon, so triplet excitons have longer lifetimes, and are thus more likely to diffuse to an interface to be dissociated. But this work suggests that, once they are at the interface, they are less likely to be dissociated than a singlet. / by Jason M. Sussman. / S.M.