Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2018. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 121-128). / 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 possible to utilize this adverse fluid instability phenomenon to fabricate uniformly sized and uniformly structured spherical particles internal to the fibers. Judicial choice of the materials and control over the kinetics of this process allowed to integrate the spherical particles into an active fiber device. We have introduced additional ability to control the structure of the fiber by making this process selective, forming high density array of self-assembled spherical photodetectors, connected to continuous electrodes. This fiber structure shows enhanced photoconductivity and sensitivity to wavelength variation, due to spherical geometry of the photoresistive domains. Additionally, an alternative strategy for integrating active devices into fibers was demonstrated. Rather than addressing all the challenges of thermal drawing, we have developed a method to directly integrate commercial functional devices (light emitting diodes, photodetectors etc.) into fibers through thermal drawing. We package these devices internal to the fibers in high density and integrate them with conductive buses, during the thermal draw. This approach enables to combine the benefits of several technologies - high-efficiency devices integrated into kilometer long fibers, which could be weaved into highly functional fabrics. Endowing fibers with active devices will potentially establish a new generation of multifunctional fibers, with highly desired electronic properties. For example, flexible and resilient light emitting fibers could be integrated into textiles to enable covert, optical signal transmission from the soldier uniform to the external world, or high bandwidth photodetectors could be embedded into garments to allow high volume information reception via LiFi (WiFi through light). / by Michael Rein. / Ph. D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1983. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE / Includes bibliographical references. / by Michelle Wendy Gabriel. / M.S.

Thesis (Sc.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1983. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE / Vita. / Bibliography: leaves 235-242. / by Carol Anne Handwerker. / Sc.D.

Thesis: S.M., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2014. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 95-99). / Driven by rising environmental and geopolitical concerns, regulations have been put in place over the last decade to compel car makers to lower the CO2 emissions of their cars. Due to these increasingly stringent vehicle efficiency standards, considerable effort has been expended to reduce vehicle fuel consumption. Since the mass of the vehicle dominates all of these efforts, it can be argued that future emission requirements will be impossible to achieve with steel vehicle structures. A transition to lightweight, non-steel materials seems inevitable. However, non-steel materials in most cases require dedicated manufacturing systems due to specific manufacturing requirements. Thus, lightweight vehicle systems will require a distinct divergence between today's manufacturing environment and the potential future manufacturing system. While many studies have assessed greenfield production costs for conventional vehicles and the lightweight alternative, this research recognizes an important reality of the automobile marketplace: any future lightweight vehicle will be implemented out of a steel-based manufacturing environment. Carmakers will have to adapt existing plant infrastructure to the particular requirements of the non-ferrous material. This research develops a conceptual framework and a transition cost model to quantify change penalties of transition processes imposed on vehicle assembly systems. This transition model is applied to a case study provided by Ford Motor Company in order to better understand implications of different manufacturing strategies on the system's capability of switching materials. The research identifies three different manufacturing change penalties which have to be paid when switching the base material in vehicle assembly systems. Taking these penalties into account, case studies suggest when, to what extent, and how materials transitions can be realized most cost-effectively. Partial component-wise transitions are presented as an attractive alternative to full material transitions. Finally, strategies are proposed how to increase the material flexibility of automotive manufacturing systems. / by Christoph Wüstemeyer. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2008. / Includes bibliographical references. / Metal nanoparticles hold promise for many scientific and technological applications, such as chemical and biological sensors, vehicles for drug delivery, and subdiffraction limit waveguides. To fabricate such devices, a method to position particles in specific locations relative to each other is necessary. Nanoparticles tend to spontaneously aggregate into ordered two- and three-dimensional assemblies, but achieving one-dimensional structures is less straightforward. Because of their symmetry, nanoparticles lack the ability to bond along specific directions. Thus, the technological potential of nanoparticles would be greatly enhanced by the introduction of a method to break the interaction symmetry of nanoparticles, thus inducing valency and directional interparticle interactions. When a nanoparticle is coated with a mixture of two different ligands, the ligands have been shown to phase-separate into ordered domains encircling or spiraling around the core. Topological constraints inherent in assembling two-dimensional vectors (e.g., ligands) onto a sphere (the core of the nanoparticle) dictate the necessary formation of two diametrically opposed defect points within the ligand shell. The molecules at these points are not optimally stabilized by intermolecular interactions and thus these sites are highly reactive. By functionalizing the polar singularities with a third type of molecule, we generate divalent nanoparticles with "chemical handles" that can be used to direct the assembly of the particles into chains. For example, taking inspiration from the wellknown interfacial polymerization synthesis of nylon, we place carboxylic acid terminated molecules at the polar defect points and join the newly bifunctional nanoparticles into chains by reacting them with 1,6-diaminohexane through an interfacial reaction. / (cont.) Furthermore, we perform a full kinetic and thermodynamic characterization of the molecularly defined polar defect points. We demonstrate that the rate of place-exchange at these points is significantly faster than it is elsewhere in the ligand shell. We also determine the equilibrium constant and standard free energy of the place-exchange reaction at the polar defect sites and demonstrate that the reaction is strongly affected by the molecular environment, i.e. the composition of the ligand shell. / by Gretchen Anne DeVries. / Ph.D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2014. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / 127 / Cataloged from student-submitted PDF version of thesis. / Includes bibliographical references (pages 189-199). / With continuously growing energy demands, alternative, emission-free solar energy solutions become ever more attractive. However, to achieve sustainability, efficient conversion and storage of solar energy is imperative. Photoelectrolysis harnesses solar energy to evolve hydrogen and oxygen from water, thereby enabling energy storage via chemical means. Hematite or [alpha]-Fe₂O₃ has emerged as a highly promising photoanode candidate for photoelectrochemical cells. While significant improvements in its performance have recently been achieved, it remains unclear why the maximum photocurrents still remain well below their theoretical predictions. This study investigates the defect chemistry and conduction mechanism of hematite in order to understand and improve this material's shortcomings. A defect model for donor doped hematite was derived and its predictions conformed by the electrical conductivity of ilmenite hematite solid solution bulk samples as a function of temperature and oxygen partial pressure. The enthalpies of the Schottky defect formation and the reduction reaction for hematite were determined as 13.4 eV and 5.4 eV, respectively. In addition, a temperature independent value for the electron mobility of 0.10 cm2/Vs for 1% Ti donor doped hematite was derived. Furthermore, the electrical conductivity of nanometer scale, epitaxially grown thin films of the ilmenite hematite solid solution system was characterized by electrical impedance spectroscopy. This work reports a detailed correlation between the electrical conductivity of the undoped hematite, the 1 atom% Ti doped hematite and the thin films with higher ilmenite content and the conditions under which they were annealed (20° C=/< T =/< 800° c and 10-4 atm =/< po2 =/< atm). Hematite's room temperature conductivity can be increased from ~10-11 S/cm for undoped hematite films by as much as nine orders of magnitude by doping with the Ti donor. Furthermore, by controlling the non-stoichiometry of Ti-doped hematite, one can tune its conductivity by up to five orders of magnitude. Depending on processing conditions, donor dopants in hematite may be compensated largely by electrons or by ionic defects (Fe vacancies). The electron mobility of the film was determined to be temperature independent at 0.01 cm2/Vs for the < 0001 > epitaxial film containing a Ti donor density of 4.0 x 1020 cm-3. Finally, the photoelectrochemical performance of these materials was tested by cyclic voltammetry and measurements of their quantum efficiencies. The 1% Ti doped hematite thin film exhibited the highest photocurrent density of these dense, thin films at 0.9mA/cm2 with an applied bias of 1.5V vs. RHE. The IPCE of this sample reached 15% at wavelengths between 300nm and 350nm after an annealing treatment at 580° for 36 h. The solid solution containing 33% ilmenite preformed nearly as well as the doped hematite. The performance decreased with higher ilmenite concentrations in the solid solution. For all samples containing any ilmenite, the onset potential shifted to lower values by ~200mV after the annealing treatment. The increase in charge carrier density upon reduction of Ti doped hematite was conformed by a Mott-Schottky analysis of the hematite/electrolyte interface. In contrast, only minor changes in the carrier density were observed when reducing an undoped hematite photoanode. Changes in slope of the Mott-Schottky plots revealed the presence of deep trap states in the hematite films. In-situ UV-vis spectroscopy displayed a pronounced optical signature corresponding to the existence of such deep levels. These results highlight the importance of carefully controlling photoanode processing conditions, even when operating within the material's extrinsic dopant regime, and more generally, provide a model for the electronic properties of semiconducting metal oxide photoanodes. / by Johanna Engel. / Ph. D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1996. / Includes bibliographical references (p. 50-51). / by Sandra K. Joung. / M.S.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 1996. / Vita. Cataloged from PDF version of thesis. / Includes bibliographical references (pages 144-153). / Components made of high-performance ceramics or superalloys are subject to strict requirements with regard to their geometric and dimensional accuracy. The surface finish and edge zone characteristics have a large effect on the component's performance. These requirements can not be met directly by the sintering process used in the manufacture of ceramic materials or traditional casting of superalloys. Grinding is both technically and economically the number one choice when one has to consider machining these materials. Metal Single Layer (MSL) grinding technology provides an alternative way to make use of the superabrasives, diamond and CBN, in grinding these materials. One of the primary challenges in MSL grinding technology is to develop suitable active braze alloy(s) which can bond the superabrasive grits. Ticusil (Ag-Cu eutectic+4.5 wt% Ti) and 70Cu-21Sn- 9Ti (wt%) are two of the currently used active braze alloys. The primary failure mode of these two MSL wheels in the grinding test is transverse fracture and debonding of the diamond grits. The high applied load is responsible for transverse fracture of the diamond grit, and the intermetallic phase existing at the interface between the diamond and the braze alloy is one of the causes of the debonding of the diamond grits. Also, a finite element analysis shows that most of the residual thermal stresses and the thermal mismatch strains are localized at the diamond/braze alloy interface. This results in potential weakness of this area. Moreover, the inherent defects, such as voids, and the brittle intermetallics in the interface can cause crack initiation and propagation. Both deteriorate the life of the grinding wheel. The failure of the braze alloy can be divided into two categories. If the grinding process is very abrasive, such as green concrete grinding, the wear resistance of the braze dominates the fracture of the braze alloy. On the other hand, failure of the braze alloy can also result from cracks at the interface. In such a case, the fatigue resistance of the braze alloy plays an important role in determining the wheel's life. The wear resistance of the braze alloy can be improved by introducing suitable hard particles. It was found that a braze alloy of 77Cu-23Sn-12.5Ti-7.5Zr-10TiC-0.2C (by weight) exhibits excellent performance in a wear test (a ten fold improvement), which is further confirmed in the grinding test (a two fold increase in life). The fatigue resistance of the active braze alloy can be modified by either reducing the volume fraction of the brittle intermetallic phase in the braze and/or enhancing the ductility of the braze alloy matrix. A ductile active braze alloy can be achieved by combining the two-layer structure and two step brazing process. To aid dissolution and diffusion of the Cu atoms into the Cu/Sn/Ti braze alloy, a lower volume fraction of the intermetallic phase and higher ductile matrix of the braze can be achieved. Both have beneficial effects in modifying the ductility of the active braze alloy, and make removal of the braze alloy from the substrate by acid etching easier. / by Ren-Kae Shiue. / Ph. D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1996. / Includes bibliographical references (p. 63-66). / by Shuba Balasubramanian. / M.S.

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2008. / Includes bibliographical references (leaves 51-55). / Hard drive industry is facing scaling challenge for areal density to be further increased. This is due to the triangular conflictions among thermal stability (superparamagnetic effect), single-to-noise ratio and writability of the recording media. One of the most promising methods to overcome this constraint is the patterned magnetic media technology. Although it is facing many challenges, the large potential gains in density offered by patterned media make it one of the possible milestones on the horizon for future of the disk drives industry. One of the biggest challenges for patterned media is to realize its mass fabrication provided reduced cost per bit. The basic fabrication approach is to use lithography to pattern the magnetic materials on the platter. However, patterned media requires well-ordered nanoarrays with dimensions less than 25 nm, which challenges the state-of-art lithography technologies. This M. Eng. project focuses on evaluations of the technologies and fabrication schemes potential for patterned media from various aspects like technical barriers, cost and intellectual properties. Technologies including E-beam lithography, nanoimprint lithography, templated diblock copolymer self-assembly and self-assembled magnetic nanoparticles are discussed. Cost modeling was done to prove the enormous gain in revenue for the proposed fabrication scheme. It is proposed that the fabrication scheme of templated diblock copolymer for making the master stamp for nanoimprint followed by nanoimprint lithography for mass production has the largest potential for patterned media. However, more R & D is needed for templated self-assembly of diblock copolymer before it is ready for this application. / (cont.) E-beam lithography which is a mature technology can also be a choice for making the stamp followed by mass production enabled by nanoimprint lithography, without a significant loss of gain in revenue for ultra-high-density media fabrications. Although the cost of a master stamp fabricated by E-beam is estimated to be 50 times more than for templated self-assembly of diblock copolymer lithography. / by Lei Du. / M.Eng.