Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1996. / Includes bibliographical references (leaves 158-162). / by Tony Ping-chen Chiang. / Ph.D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2013. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 117-122). / Integration of III-V compound semiconductors with silicon is an area that has generated a lot of interest because III-V materials and Si are best suited for different types of devices. Monolithic integration enables the best material to be chosen for each application, enabling new functionalities with the potential of additional miniaturization on a system level. Integration of GaAsP alloys on Si substrates would enable the creation of high efficiency dual-junction solar cells on low cost and light weight Si wafers and would also enable a path for yellow and green light emission devices on a Si platform. Our work focused on the materials integration problems for multiple pathways to integrate GaAsP alloys on Si substrates. We first addressed the direct integration of GaAsP alloys on Si substrates. Our results showed that despite the low lattice-mismatch conditions at the P-rich end of the GaAsP alloy spectrum, it was difficult to achieve thin films low defect density. We proceeded to focus on the integration of GaAsP alloys on Si via the use of SiGe compositionally graded layers. Through a combination of methods we addressed problems related to antiphase disorder and lattice mismatch between GaAsP and SiGe materials system. We demonstrated the epitaxial growth lattice-matched GaAsP on Si₀.₈₈Ge₀.₁₂, Si₀.₅Ge₀.₅, Si₀.₄Ge₀.₆ and Si₀.₃Ge₀.₇ virtual substrates with excellent interface properties. Our studies showed the effects of initiation conditions and intentional strain at the GaAsP/SiGe heterovalent interface. We have established strain-engineering methods at the GaAsP/SiGe heterovalent interface to prevent dislocation loop nucleation and expansion. We were able to attain GaAsP films on Si with a threading dislocation density as low as 1.2x10⁶/cm² . Our GaAsP/SiGe heterovalent interface research advanced the understanding of such structures. We developed methods to fabricate optimized GaAsP tunnel junction film, which would be necessary for any current-matched dual junction solar cell design. Prototype dual-junction GaAsP/Si solar cell test devices showed good preliminary performance characteristics and offer great promise for future devices integrated with the newly developed high quality GaAsP/Si virtual substrates. / by Prithu Sharma. / Ph. D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2018. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 119-136). / Electrochemical energy storage will play a pivotal role in our society's energy future, providing vital services to the transportation, grid, and residential markets. Depending on the power and duration requirements of a specific application, numerous electrochemical technologies exist. For the majority of the markets, lithium-ion (Li-ion) batteries are the state-of-the-art technology owing to their good cycle life and high energy density and efficiency. Their widespread penetration, however, is limited by high production cost and inherent safety concerns. Understanding the solid-electrolyte interphase (SEI) which governs the performance and lifetime of these batteries is critical to developing the next generation Li-ion batteries. As an alternative to Li-ion, redox flow batteries store energy in solutions of electroactive species, which are housed in external tanks and pumped to a power-converting electroreactor. This configuration decouples power and energy, improving the safety and flexibility of the system, however, flow battery energy density is inherently lower than Li-ion and expensive ion-selective membranes are required for efficient operation. As a contrast to Li-ion and redox flow batteries, convection batteries harnesses the key benefits of Li-ion batteries and redox flow batteries while overcoming their individual limitations. By incorporating thick electrodes into the cell, the energy density is increased and the cost of the system is reduced. To overcome the diffusive losses in the thick electrodes, electrolyte is pumped through the electrodes, enabling uniform ion transport throughout the porous structure. However, thick electrodes can lead to large ohmic losses in the cell resulting in lower energy efficiency. In this thesis, I discuss my work on understanding the SEI in Li-ion batteries, highlighting the thermodynamics of its origin, characterization of its structure, and strategies for future development. I then detail my work understanding redox active molecules from molecule characterization and mechanistic generation to redox flow cell level engineering. Finally, I highlight my work in the development of the convection battery technology explaining the synthesis of active materials, thick electrode design, and fabrication of the prototype convection cell architecture. Taken together, these projects highlight the theme of achieving low-cost electrochemical energy storage through various technical pathways. / by Thomas J. Carney. / Ph. D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2002. / Includes bibliographical references (v. 2, leaves 283-294). / To investigate stress evolution during film deposition, a novel electrical technique for in situ thin film stress measurements was developed utilizing piezoresistive silicon microcantilevers, or piezocantilevers. In addition to the thin film stress measurements of Cu made with the piezocantilevers, our collaborators at Sandia National Laboratories have studied thin film growth stresses for Al, Ag, and amorphous Ge (a-Ge) films measured using conventional laser deflectometery. A computer simulation of thin film formation by the Volmer-Weber mechanism was developed to model the nucleation and growth of individual islands that impinge and coalesce to form a continuous film. By including a size-dependent lattice contraction in pre-coalescence islands, the simulation can be used to qualitatively reproduce the measured compressive stress behavior of Al at low film thicknesses. In contrast to Al films that support stress from the very onset of deposition, Ag films exhibit no measurable stress until larger film thickness are achieved. This difference in behavior was attributed to shear occurring at the Ag-SiO2 interface, which is suppressed at the much stronger Al-SiO2 interface. Tensile stress generation resulting from island coalescence was modeled analytically and by finite element methods (FEM) as the energetic balance between interfacial energy reduction and strain energy generation resulting from grain boundary formation. The magnitude of the island-coalescence stress calculated using FEM was found to decrease dramatically with decreasing island-substrate contact angle. / (cont.) Using the contact-angle-dependent FEM calculations of island-coalescence stress, simulations closely matched the stress-thickness measurements of Al, by assuming perfect island-substrate traction, and of Ag, by assuming partial island-substrate sliding, over the range of thicknesses prior to film continuity. The compressive stress evolution during deposition of continuous films and the stress behavior during interrupts of film growth was modeled in terms of a non-equilibrium surface morphology that develops during deposition. For the resulting non-equilibrium grain shapes, the in-plane compressive stress resulting from excess surface stress was calculated using FEM. Model predictions are consistent with observed decreasing compressive stress-thickness with increasing film thickness observed experimentally for Cu and a-Ge, as well as the reversible tensile rise behavior observed during growth interrupts of Cu. / by Steven Craig Seel. / Ph.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2002. / Includes bibliographical references (leaves 153-160). / In this thesis, experimental, computational and analytical approaches are employed to examine systematically the mechanisms of deformation in crystalline materials. Such insight can be used to exploit and avoid contact in actuator and sensor applications, to derive mechanical properties for engineering of materials, and to investigate the fundamental role of defects. Here, localized mechanical contact of material surfaces is utilized to elucidate the effects of length scales on the transition from elastic (reversible) to plastic (irreversible) deformation. As the mechanical response of a material can be described by parameters which range from empirical constitutive (stress-strain) relations to fundamental descriptions of atomic interactions, the deformation response can be related to global mechanical properties such as yield strength, as well as to local phenomena such as dislocation nucleation. The concurrent design and implementation of experiments including micro- and nanoindentation and uniaxial compression, in situ experiments on a model, two-dimensional crystalline analogue, and computational modeling at the continuum (finite element) and atomistic (molecular dynamics) levels presented herein provide a unique opportunity to develop and validate hypotheses and analytical algorithms. Indeed, one of the major conclusions of this thesis is that the mechanical response observed for a specific volume of material under contact is a unique function of the deformation mechanisms described within that length scale regime. / Ultimately, the goal of this thesis is to provide a synergystic interpretation of deformation in crystalline materials by examining in detail the operative mechanisms under local, finite strain. This interpretation has been attained at the continuum level via development and experimental verification of a closed-form set of algorithms which convert an experimental indentation response into a set of elastic and plastic mechanical properties, and also predict the indentation response of a material via a corresponding set of mechanical properties. Modifications of this continuum interpretation under conditions of finite material thickness and residual stress profiles elucidate explicitly the effect of material length scales. At the atomistic level, this interpretation of deformation is framed in terms of an energetic elastic instability criterion which is validated experimentally and computationally for a particularly important instability: dislocation nucleation. Finally, the effects of material length scales such as grain size on the onset and development of dislocation-mediated deformation. / by Krystyn J. Van Vliet. / Ph.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2000. / "February 2000." / Includes bibliographical references (p. 126-129). / Two novel and practical methods for controlling the propagation of light are presented: First. a design criterion that permits truly omnidirectional reflectivity for all polarizations of incident light over a wide selectable range of frequencies is derived and used in fabricating an all dielectric omnidirectional reflector consisting of multilayer films. Because the omnidirectionality criterion is general, it can be used to design omnidirectional reflectors in many frequency ranges of interest. Potential uses depend on the geometry of the system. For example, coating of an enclosure will result in an optical cavity. A hollow tube will produce a low-loss, broadband waveguide, planar film could be used as an efficient radiative heat barrier or collector in thermoelectric devices. A comprehensive framework2 for creating one, two and three dimensional photonic crystals out of self-assembling block copolymers has been formulated. In order to form useful band gaps in the visible regime, periodic dielectric structures made of typical block copolymers need to be modified to obtain appropriate characteristic distances and dielectric constants. Moreover, the absorption and defect concentration must also be ~ontrolled. This affords the opportunity to tap into the large structural repertoire, the flexibility and intrinsic tunability that these self-assembled block copolymer systems offer. A block copolymer was used to achieve a self assembled photonic band gap in the visible regime. By swelling the diblock copolymer with lower molecular weight constituents control over the location of the stop band across the visible regime is achieved, One and three-dimensional crystals have been formed by changing the volume fraction of the swelling media. Methods for incorporating defects of prescribed dimensions into the self-assembled structures have been explored leading to the construction of a self assembled microcavity light-emitting device. / by Yoel Fink. / Ph.D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1996. / Includes bibliographical references (leaves 113-119). / by George Kristian Schwenke. / M.S.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2013. / 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 (p. 29-30). / by Amanda Olender. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1997. / Includes bibliographical references (p. 175-180). / by Yingchun Liu. / Ph.D.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, February 2008. / "December 18, 2007." / Includes bibliographical references (leaves 47-48). / The benefits of recycling have long been understood and the conspicuous energy savings of secondary aluminum production have caused aluminum recycling to increase. Obsolete aircraft are a valuable source of aluminum scrap and recent efforts to fortify the aerospace aluminum recycling infrastructure have drawn attention to the potential of sophisticated sorting methods to maximize the economic gain of using aerospace scrap in secondary production. The aim of this research was to use linear optimization to assess the economic viability of sorting technologies for enabling wrought products in general and aerospace alloys in particular to be recycled back to high value applications. A chance-constrained model was used to select the alloys that consumed the largest quantity of aerospace alloys in their production, thereby establishing a strategic portfolio of finished goods. Ten of the fifteen alloys in the portfolio were of the 2xxx and 7xxx alloy series that are standard in the production of aerospace components. An aerospace end-of-life case study was performed in which cases varied by their input scrap streams, each having a compositional uncertainty associated with the different degrees of sorting that methods currently in use and technologies in development can achieve. The chance-constrained model calculated the production cost for each case and determined that when aerospace components were identified to the precision of individual alloys, the production cost was 20.87% lower than the cost for primary production. Using automatically sorted scrap input yielded a production cost that was 5.34% lower than the cost of primary production. / (cont.) Before concluding that the development of sorting technology should only be pursued with a budget of $0.0743/kT, a break-even point calculated by the model, it is necessary to take into account the fact that dismantled scrap is more expensive than sorted. In addition to performing sensitivity analysis on the scrap prices, future work should test the production of different portfolios of finished goods and take varying demand for each alloy into consideration. / by Emily Chen. / S.B.