Thesis: S.B., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2001. / Cataloged from PDF version of thesis. / Includes bibliographical references (page 23). / The purpose of this work is to characterize the optical absorption in bismuth silicon oxide (Bi₁₂SiO₂₀) crystals grown using the Bridgman technique and to identify electronic transitions responsible for absorption. Optical measurements were taken in the range of 0.4 - 11 pm at 300 K and 77 K using a spectrometer. The results show that near the band edge, there is evidence of indirect transitions at 2.3 eV and excition transitions at 1.8 eV. Low temperature measurements revealed peaks of free carrier absorption in the visible light range at 1.7 eV and 2.1 eV. Illuminated samples at low temperature revealed empty donor levels in the visible range at 1.6-1.9 eV and 2.1 eV, indicating the presence of the photochromic effect and photorefractivity. / by Grace W. Lee. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2013. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 229-239). / The liquid metal battery has been shown to be a viable candidate for grid-scale energy storage, due to its fast kinetics and ability to be constructed from economically feasible materials. Various of the liquid metal couples that form high stable voltages, such as the calcium chemistries, are rate limited because they tend to form solid intermetallic compounds with high melting points. In order to understand and better engineer these batteries, the kinetic properties of these liquid alloys, in particular the chemical diffusivity, must be known accurately so that it can be used as input in computational simulations to avoid the nucleation of any solids. Unfortunately, the dominant experimental methods for measuring diffusion in liquid metals today are unreliable because the measurement timescales are on the order of days, require long capillaries susceptible to buoyancy-driven flow from temperature fluctuations, and composition analysis must be done ex-situ as a solid. To counter all these problems, a new and novel method for measuring the chemical diffusivity of metals in liquid alloys derived from electrochemical principles is presented in this thesis. This new method has the advantage of operating in shorter times scales of minutes rather than days, and requires the use of small capillaries which collectively minimize the effect of convectively-driven flow caused from temperature gadients. This new method was derived by solving the same boundary conditions required by the galvanostatic intermittent titration technique for solid-state electrodes. To verify the validity of the new theoretical derivation, the method was used to measure the chemical diffusivity of calcium in liquid bismuth within the temperature range of 550 - 700 'C using a three-electrode setup with a ternary molten salt electrolyte. Three compositions where studied (5% Ca-Bi, 10% Ca-Bi, and 15% Ca-Bi) for comparison. The chemical diffusion coefficient was found to range between (6.77 ± 0.21)x10- 5 cm 2/s - (10.9 ± 0.21)x10-5 cm 2/s at 5% Ca-Bi, (4.95 ± 0.65)x10- 5 cm2 /s - (7.93 ± 0.37)x10- 5 cm 2 /s at 10% Ca-Bi, and (6.22 ± 1.2)x10- 5 cm 2/s - (10.2 ± 0.26)x10- 5 cm 2 /s at 15% Ca-Bi which, to our knowledge, are the first successful measurements of calcium diffusivity in the liquid state. Arrhenius fits with good correlations revealed the activation energy for diffusion to be (21.4± 1.7) kJ/mol, (23.0± 2.4) kJ/mol, and (17.7 ±5.9) kJ/mol as the calcium concentration increased, which are in excellent agreement with literature published values and lie in the same range of 15-30 kJ/mol that is reported for most liquid metals. The chemical diffusivity value was then used as input in finite element simulations to model how convection affects the overall transport inside a 20-Ah liquid bismuth electrode under the influence of different thermal boundary conditions. Also, a phase field model was created to simulate the motion of the two interfaces inside a liquid metal battery during operation, which to our knowledge, is the first time phase field has been extended beyond two phases. Experimental kinetic values can then be used as input in these numerical models to help characterize and optimize the entire battery. / by Salvador A. Barriga. / Ph.D.

Thesis (S. M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2009. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 106-111). / The effect of oxygen partial pressure on crack growth rates in Alloy 617 has been studied using both static and fatigue loading at 650°C. Tests were conducted at a constant stress intensity factor, K, for static loading conditions or constant AK for fatigue loading using a direct current potential drop measurement system to measure crack length. The oxygen concentration was measured on both the outlet of the test retort as well as in-situ with a probe located directly at the specimen surface. High purity argon gas was used to establish oxygen partial pressures at low as 10-22 atm while premixed oxygen/argon gases were used to vary the oxygen potential. For fatigue loading, the crack path was observed to be transgranular with increasing growth rates as the oxygen concentration was increased. A transition oxygen partial pressure of approximately 10-5 atm was found to exist, at which the fatigue crack growth rates started to increase with increases in oxygen concentration in the environment. Furthermore, fatigue at R = 0.5 also showed a slight increases in growth rates when the frequency was decreased from 2 Hz to 0.1 Hz. In contrast, the fracture surfaces resulting from static loading were found to be intergranular and exhibited two different environmental behaviors. At a stress intensity factor of 49.5 MPa'Im, decreasing the oxygen potential lead to an increase in crack growth rates. However, the static loading crack growth rates 33.0 MPadm exhibited negligible variation with oxygen potential. Detailed microstructural analysis of fracture surfaces and grain boundaries ahead of crack tips was performed using Auger spectroscopy. / (cont.) The results confirm the formation of chromium oxide in the wake of cracking and provide little or no indication of intergranular oxygen diffusion ahead of the crack. However, the resolution of the Auger spectroscopy results was insufficient for a definitive statement in this regard. The observations in this study most closely relate to dynamic embrittlement process involving short range intergranular oxygen absorption under the presence of stress. / by Julian K. Benz. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 57-62). / A screening metric for diffusion limitations in lithium ion battery cathodes is derived using transition state theory and common materials properties. The metric relies on net activation barrier for lithium diffusion. Several cathode materials are screened using this approach: [beta]'-LiFePO4, hexagonal LiMnBO3, monoclinic LiMnBO3, Li 3Mn(CO3)(PO4), and Li9V3 (P2O7)3(PO4) 2. The activation barriers for the materials are determined using a combined approach. First, an empirical potential model is used to identify the lithium diffusion topology. Second, density functional theory is used to determine migration barriers. The accuracy of the empirical potential diffusion topologies, the density functional theory migration barriers, and the overall screening metric are compared against experimental evidence to validate the methodology. The accuracy of the empirical potential model is also evaluated against the density functional theory migration barriers. / by Charles J. Moore. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1998. / Includes bibliographical references (leaves 110-113). / A forming process for creating MEMS and mesoscale ceramic parts with micron scale features has been developed. This micromolding process takes advantage of clean room compatible techniques to create silicon etchings, which are used to create a silicone transfer mold. The silicone molds are used to make numerous sacrificial mold into which ceramic slurry is cast. The wax molds are sacrificed leaving green ceramic parts which are fired to produce the final component. The process was found to reproduce features as small as 2 gm with a tolerance of ± 0.8 pm over about a 100 pm length scale. The production of several parts are examined, demonstrating the ability to make stand alone MEMS and mesoscale parts with complex geometries. A non-ceramic application involving precise particle arrangement is also discussed. Observations regarding part quality, defect formation, yield issues, and process enhancement are made, along with a characterization of the dimensional stability of the process. The costs associated with processing silicon molds are also compared to competing processing techniques. This technique has generated excellent results and has potential to become a major forming tool to fill the materials selection gap in MEMS and mesoscale component design. / by Matthew E. Rosenthal. / S.M.

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1998. / Includes bibliographical references (leaf 40). / by Shawn Patrick Doherty. / B.S.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2016. / Cataloged from PDF version of thesis. / Includes bibliographical references. / With the emerging need for advanced sensing and imaging capabilities in personalized healthcare, there has been motivation to develop new classes of nanomaterials; with performance vastly superior to existing technologies. In this work, we explore the one- and two-dimensional forms of carbon nanomaterials, namely, single-walled carbon nanotubes (SWNTs), and graphene derivatives (graphene oxide, or GO), for their remarkable potential in biomedical imaging and sensing. This thesis presents three functional applications, along with the necessary processing at the interface of nanotechnology and biomaterials required to achieve the desired set of properties enabling these applications. First, we attempt to address the rise in antibiotic-resistant bacterial infections by developing a nano-probe for targeted sensing, with potential for early, non-invasive diagnosis of infectious diseases through optical imaging. Using genetically engineered M13 bacteriophage, we synthesize biologically-functionalized, aqueous-dispersed SWNTs, for actively-targeted, modularly-tunable, high-contrast, highly-specific detection of deep-tissue pathogenic infections, at an order-of-magnitude lower dosage compared to other probes reported in literature. Second, we investigate the role of guided surgery in enhancing the survival lifespan of patients with gynecological cancers. We deploy a combination of targeted SWNT probes, along with a custom-designed real-time intraoperative imaging system, which offers sub-millimeter resolution at a sensitivity over 93%. Using image-guided surgery in a mouse model of ovarian cancer, compared to the control group receiving non-guided surgery we report improvement in the median survival by 40%, with large societal benefit expected upon clinical translation. Third, we develop a scalable, one-step mild thermal annealing treatment for enhancing the properties of graphene derivatives, with no chemical treatments involved, while preserving the rich oxygen framework in GO unlike current protocols used in literature. This treatment provides a handle to control the spatial distribution of oxygen functional groups on the graphene basal plane. Using nano-bodies decorated on our treated GO substrate, we report 38% increase in the efficiency of cell capture from whole blood, compared to conventional sensors using as-synthesized GO. Finally, we discuss challenges in moving the field forward, and provide a brief glimpse into the next-generation imaging technologies currently under development, which are generally applicable to a much broader class of materials. / by Neelkanth Manoj Bardhan. / Ph. D.

Thesis: S.B., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2001. / Cataloged from PDF version of thesis. "June 2001." / Includes bibliographical references (pages 47-48). / GaN:Er is an attractive material for room temperature 1.54 pm luminescence enhancement devices for use in telecommunications because it does not experience thermal quenching at room temperature like Si:Er and can be electronically pumped. GaN:Er layers grown by molecular beam epitaxy (MBE) on single crystal substrates have shown excellent room temperature 1.54 [mu]m luminescence, but to integrate GaN:Er into microresonator devices it is necessary to grow a good quality GaN:Er film on an amorphous substrate. This thesis examines the optical properties and morphology of GaN:Er layers grown on Si₃N₄ and SiO₂ substrates, and evaluates two microresonator devices with incorporated GaN:Er layers. GaN:Er layers grown by MBE on SiO₂ and Si₃N₄ substrates were shown to give room temperature luminescence comparable to that of GaN:Er grown on (11 1)Si. GaN:Er layers grown on a buffered oxide etched Si₃N₄ substrate showed the best luminescence. The ability to grow good quality layers on amorphous substrates allows GaN:Er to be used in waveguide devices, the first of which studied was the microring resonator. Microring resonators were made by depositing a blanket GaN:Er layer on patterned Si₃N₄ microring structures. These structures were damaged, and transmission measurements were not possible. When looking at surface roughness measurements it appears that channel waveguide structures are unsuitable for GaN:Er grown on amorphous substrates, and so a ridge waveguide structure is proposed to lower this surface roughness scattering loss. A microcavity with a GaN:Er defect layer and a-Si/a-SiO₂ stacks was fabricated and tested for luminescence enhancement. The refractive index of GaN:Er was determined by reflectance measurements to be 2.1. The layer was not of uniform thickness which led to a broad resonance peak, but a distortion of the spectrum including a lower luminescence at the 1517 nm peak and a higher luminescence at the 1557 nm peak were observed, which suggests enhancement by the microcavity. / by David M. Gibbons. / S.B.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2006. / Includes bibliographical references (leaves 63-66). / Introduction: Research on the metallurgy of archaeological artifacts has focused primarily on the examination of objects to reveal their design, their composition, the properties of the material people selected to achieve the design, and the fabrication processes used in managing the metal to produce the end product. Recently that focus has begun to broaden, and archaeologists are taking a step back to investigate the earliest stages of prehistoric metal processing that precede object manufacture, namely ore mining and extractive metallurgy. However, little archaeological work on mining and extraction has been accomplished to date, in part because so few metal processing sites have been identified. These sites are very difficult to find because of the lack of standing architecture, particularly smelting installations. Prehistoric smelting furnaces tend to be small and are either excavated beneath the ground surface or are above ground but made of impermanent materials. / by Antonella I. Alunni. / S.B.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1999. / Includes bibliographical references (leaves 88-90). / by Tilghman L. Rittenhouse. / S.M.