Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2013. / "June 2013." Cataloged from PDF version of thesis. / Includes bibliographical references (pages 129-138). / Nanocrystalline materials are inherently unstable due to their high material fraction of grain boundaries, preventing their improved properties from being used in application. To stabilize the nanoscale grain size against rampant growth, past literature has proposed lowering the grain boundary energy through solute segregation to the boundaries. This approach has seen varied experimental success, using a metric of segregation strength to select an alloying element. In those alloys were some measure of stabilization is gained through alloying, precipitation of a second phase disrupts the necessary segregation state and triggers grain growth. This work considers the total stability of a nanocrystalline alloy -- both stability against grain growth and stability against second phase precipitation -- by examining the changes in free energy associated with segregation and nanostructuring. It is discovered that the relationship of segregation and mixing enthalpies for a particular system dictates the nanocrystalline stability of the alloy. Nanocrystalline stability maps are constructed for several conditions that can be used to predict an alloy's ability to support a nanostructure. Also revealed by the generation of stability maps are new types of stable nanocrystalline phases - in addition to the expected nano-phase stabilized by solute decoration of the grain boundary, a solute-rich nanocrystalline phase is expected to be stable under some conditions, as is an amorphous phase. To connect material systems to the results predicted by this work, a new model for the enthalpy of segregation was derived. / by Heather A. Murdoch. / Ph. D.

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2008. / Includes bibliographical references (leaves 57-59). / Copper interconnects have shown its limit to meet the bandwidth demand even in the short reach applications due to its increase power consumption, RC delay, EMI, crosstalk and other effects which are aggravated as dimension shrinks. Despite efforts to increase the system performance, e.g. by multicore technology, migration to photonics is unavoidable, as it can give much superior performance. The major impediment to the wide-use of photonics is the cost. Three major components that contribute to the cost escalation are the absence of integrable light source, fast modulator, and effective fiber to waveguide coupler. The latest issue was addressed in this work. Coupling light efficiently from fiber to waveguide is challenging because of the size (6[mu]m core diameter for fiber, 500nm for waveguide), shape, and refractive index (~1.5 for fiber, 3.5 for waveguide) differences. Optical solder was proposed as the gap filler in between the fiber and waveguide to account for the fabrication uncertainties. Together with an inverse taper structure patterned in the waveguide end, the coupling loss was much reduced from 7.5dB (direct butt-coupling), to less than IdB. Besides, optical solder increases the reliability of device, as it prevents moisture and dust from impairing the optically active area of the die. Its fabrication is also integrable with the current CMOS technology. The configuration allows high density optical interconnect at the edges of the die; together with the electrical interconnect spreading across the area of the chip. All these make this system very good potential coupling method to solve one of the major impediments above, and thus enable the widespread use of electronic-photonic ICs. / by Fidelia Tjioe. / M.Eng.

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1998. / Includes bibliographical references (leaf 34). / by Edward C. Wu. / B.S.

Thesis: Sc. 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 student-submitted from PDF version of thesis. / Includes bibliographical references (pages 198-204). / The connection between charge and spin transport in solid state materials offers new techniques for generating and detecting spin currents and could potentially allow high-performance memory and logic devices. Simple multilayer thin films or "heterostructures" such as Pt/Co have broken inversion symmetry, so a charge current gives rise to net spin current. Electrical and optical measurements reveal the effect of spin current on the magnetization, including chiral spin textures such as domain walls (DWs) and skyrmions. The magnetic properties of an ultrathin magnetic film are strongly sensitive to interfacial effects such as interfacial anisotropy and the Dzyaloshinskii-Moriya Interaction (DMI), which stabilizes chiral spin textures. This thesis is motivated to systematically vary the layer structure of magnetic heterostructures to understand and quantify spin-orbit torques. I showed that switching efficiency is consistent with harmonic spin orbit torque measurements in Pt/Co/Ta. My automation software and improved electromagnet enabled a new experimental technique that highlights the role of DMI in spin-orbit torque switching. I showed that a gold spacer layer inserted between platinum and cobalt independently modulates the DMI and spin transport. I demonstrated SOT switching of a ferromagnetic insulator for the first time. I also developed a temperature-controlled, high-speed electrical and optical measuring system to observe record-breaking DW velocity in ferrimagnetic GdCo. This thesis focuses on building experimental apparatus and understanding spin-orbit torques. / by Maxwell Spencer Mann. / Sc. D.

Thesis: S.M., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2013. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 37-39). / Limitations in the currently available technology for neural probes impede our progress towards a comprehensive brain activity map. The lack of understanding the brain function leads to limited options for the treatment of neurological disorders. In this thesis, I employed a two-step thermal drawing process (TDP), widely used in fabrication of optical fibers, to create arrays of metal microelectrodes embedded in a polymer cladding. The pitch and size of the electrodes were determined on the macroscale and preserved during the TDP. I have applied these fiber-inspired probes to record spontaneous and stimulated neural activity in vivo. / by Andrés Canales. / S.M.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2016. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 93-97). / The emergence of multimaterial fibers that combine a multiplicity of solid materials with disparate electrical, optical, and mechanical properties into a single fiber presents new opportunities for extending fiber applications. Different functional fiber devices have been fabricated with a thermal co-draw approach. In order to make the thermal co-draw feasible, only materials with similar viscosity at the draw temperature are used, which excludes a wide range of metal and semiconductors that have good electrical property but not compatible viscosity profile. From the fiber structure point of view, the nature of the fiber drawing process makes fabricating a large quantity of fiber with identical inner structures feasible. The scalability of thermal drawing approach offers access to large quantities of devices however constrains the devices to be translational symmetric. Lifting this symmetry to create discrete devices in fibers will increase the utility of fiber devices. Also, the surface of the fiber is rarely studied though complex inner structure have been fabricated for different functionalities. Functionalize the fiber surface would give fiber the ability to better interact with the outer environment. This thesis seeks to address the abovementioned considerations, i.e. to expand materials selection for the fiber co-draw process and to explore variance of the fiber structure including breaking the inner structure translational symmetry and functionalize the outer surface. On the material side, a chemical reaction phenomenon is observed and studied in two different fiber drawing situations. In both cases, new composition is formed during the draw and play an important role in the formed fiber devices. On the structure side, relying on the principle of Plateau-Rayleigh instability, the fiber inner structure is designed to form a series of discrete semiconductor spheres contacting two metal buses after a thermal selective breakup process. This gives rise to photodecting devices in a silica-cladding fiber which shows a large working bandwidth. The fiber surface is also studied and successfully patterned with micron-scale features during the draw process. The formed patterned fiber surface shows potential in structural coloration and directional wetting. / by Chong Hou. / Ph. D.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2013. / MIT Institute Archives copy: incomplete; ends at page 7. / Includes bibliographical references (leaf 16 ). / by Sean Morton. / S.B.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2017. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 119-127). / Solid-state electrolytes have the potential to dramatically improve the safety and longevity of state-of-the-art battery technology by replacing the flammable organic electrolytes currently employed in Li-ion batteries. Recent advances in the development of new thiophosphate electrolytes have reenergized the field by achieving room temperature conductivities exceeding those liquid electrolytes, but a number of practical challenges to their widespread adoption still exist. This thesis applies ab initio computational methods based on density functional theory to investigate the structural origins of high conductivity in ionic conductor materials and provides a thermodynamic explanation of why the integration of these newly developed thiophosphates into high-rate cells has proven difficult in practice, often resulting in high interfacial resistance. As a result of these computational investigations, we report the prediction and synthesis of a new high performance sodium-ion conducting material: NaioSnP 2S 12, with room temperature ionic conductivity of 0.4 mS cm-1, which rivals the conductivity of the best sodium sulfide solid electrolytes to date. We computationally investigate the variants of this compound where Sn is substituted by Ge or Si and find that the latter may achieve even higher conductivity. We then investigate the relationship between anion packing and ionic transport in fast Li-ion conductors, finding that a bcc-like anion framework is desirable for achieving high ionic conductivity, and that this anion arrangement is present in a disproportionately high number of known Li-conducting materials, including Na10SnP2S12 and its structural analog Li10GeP2S2 . Using this bcc anion lattice as a screening criterion, we show that the I4 material LiZnPS4 also contains such a framework and has the potential for very high ionic conductivity. While the stoichiometric material has poor ionic conductivity, engineering of its composition to introduce interstitial lithium defects is able to exploit the low migration barrier of the bcc anion structure. Thermodynamic calculations predict a solid-solution regime in this system that extends to x = 0.5 in Li1+2xZn-xPS 4 , thus it may yield a new ionic conductor with exceptionally high lithium-ion conductivity, potentially exceeding 50 mS cm- 1 at room temperature. Finally, we develop a computational methodology to examine the thermodynamics of formation of resistive interfacial phases through mixing of the electrode and electrolyte. The results of the thermodynamic model of interfacial phase formation are well correlated with experimental observations and battery performance, and predict that thiophosphate electrolytes have especially high reactivity with high voltage oxide cathodes and a narrow electrochemical stability window. We also find that a number of known electrolytes are not inherently stable, but react in situ with the electrode to form passivating but ionically conducting barrier layers. / by William D. Richards. / Ph. D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 39-40). / The Taylor method is a proven way to produce Cu-based shape memory microwires that aren't plagued by problems typical in polycrystalline copper SMAs produced by other methods. Here we set out to expand and refine this processing method to take the first critical steps toward large-scale continuous production. Using a semi-automated processing route, we draw continuous, uniform fibers up to 5 meters in length with diameters in the range 10 - 35 microns. Particular attention is paid to microwires made from a Cu-Sn shape memory alloy. In addition, because the properties of shape memory microwires depend on their diameter, processing parameters were varied to understand their impact on the diameters of the resulting wires. / by Eric Szablinski. / S.M.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2015. / Cataloged from student-submitted PDF version of thesis. / Includes bibliographical references (pages 97-105). / Bombardier beetles possess one of the most remarkable defense mechanisms in nature, using explosions inside their bodies to synthesize and eject a hot, noxious spray at attackers. The chemical reactions that enable this process are well understood, but many aspects of the beetles' two-chambered defensive glands, which house the explosions and produce the defensive spray, remain unexplored. In this Thesis, I describe our recent progress in understanding the operation, structure, and materials composition of the defensive glands-topics which have to date received little treatment in the literature-of the best-known bombardier beetles, the brachinines (Carabidae: Brachininae: Brachinini). Chapter 2 deals with the pulsed-jet character of brachinines' sprays, which is in contrast to all other types of bombardier beetles that emit their sprays as continuous streams. Brachinine sprays comprise a number of spray pulses emitted in a rapid sequence, each pulse formed in a discrete explosion event inside the reaction chamber of the defensive gland, with the frequency of pulsation ranging from 300 to 1000 Hz. Using a combination of high-speed synchrotron x-ray phase-contrast imaging of live beetles, anatomical studies of the excised defensive glands, and mathematical analyses, we determined that spray pulsation arises due to explosion-induced displacement of the inlet structures to the reaction chamber periodically cutting o the ow of reactant solution into the reaction chamber. In Chapter 3, the interior cuticular microsculpture of the reaction chamber is studied using scanning electron microscopy and synchrotron x-ray phase-contrast microtomography. The microscupture is found to be highly complex, with a number of distinct spiny microtextures localized to specific regions of the reaction chamber. Quantitative details of the spine lengths and spacings are reported, and on the basis of the similarity of some of the features to the beetles' external abdominal microscupture and the micro-textural transitions observed inside the reaction chamber, we hypothesize that the reaction chamber microsculpture is homologous with the exterior microsculpture, consistent with the fact that the defensive glands are invaginations of the abdomen. Chapter 4 reports our preliminary investigations of the materials composition of the defensive glands. We use scanning electron microscopy to examine the fibrous composite structure of the gland cuticle and employ various light microscopy techniques to understand spatial variations in the cuticle sclerotization and chemical composition. The reaction chamber is found to exhibit dramatic spatial variation in sclerotization, including several lightly sclerotized regions, and possible functions of these regions are proposed. Additionally, the inter-chamber valve is found to contain the rubber-like protein resilin, likely as an adaptation to allow the valve to consistently make and hold a tight seal during each explosion, in analogy to rubber gaskets used in technological valve applications. / by Eric Michael Arndt. / Ph. D.