Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2008. / Includes bibliographical references. / Patterned pseudo spin-valve rings show great promise for device applications due to their non-volatility and variety of stable magnetic states. However, the magnetic reversal of these elements under an applied field is complex due to the magnetostatic coupling between the two ferromagnetic layers. Elliptical rings are electrically probed using highly symmetric Wheatstone bridges in conjunction with traditional four-point electrical measurements and micromagnetic simulations. New insight into domain wall nucleation and propagation events are elucidated. The resulting behavior is found to yield large signals at very low fields, making these devices ideal for device applications in data storage and computer logic. 360° domain walls are found to be extremely stable until fields as high as 10000e, but are positionally uncontrollable in elliptical rings. Rhombic rings were investigated as a geometry that can nucleate, propagate and pin domain walls more easily. Measurements and simulations confirm that the same reversal mechanisms exist and domain walls are more systematically positioned. The control over 3600 domain walls is valuable since reversals can occur without nucleation by decoupling the wall into a reverse domain. As a result, rhombic rings are useful as devices that can perform device functions at extremely low fields. / by Bryan Ng. / M.Eng.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2001. / Includes bibliographical references (leaves 101-103). / In this thesis, the magnetic behavior of nanostructured ferromagnetic particle arrays are studied by experiments and numerical micromagnetics for ultra-high-density data storage applications. 1 00nm or 200nm period arrays of nanostructured nickel, cobalt, and cobalt phosphorus are fabricated by the techniques of interference lithography combined with evaporation and electrodeposition. The nanomagnet arrays are characterized by bulk magnetometry and magnetic force microscopy. The remanent states of evaporated conical particles and electrodeposited cylindrical particles are studied by micromagnetic simulations and compared with experimental measurements. For electrodeposited particles, the influence of size, aspect ratio and microstructure on switching field is also investigated. Finally, the effect of demagnetizing magnetostatic interactions and switching field spread on the squareness and the shape of hysteresis loops is studied with the help of an Ising-like interaction model. Based on these observations, a stability condition for patterned media is found and used for determining the optimum spacing between nanomagnets. / by Minha Hwang. / Ph.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1998. / In title on t.p., double-underscored characters appear as subscript. / Includes bibliographical references (p. 170-178). / by Mayank T. Bulsara. / 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 125-138). / This thesis introduces two chemical etching-based methods for the production of nanoporous silicon, improving on current state-of-the-art fabrication strategies in terms of scalability and simplicity. The developed processes also allow for new opportunities with respect to pore size, pore aspect ratio, and large-scale homogeneity. The first approach utilizes solution-casting of core-shell nanoparticle catalysts, where the shell is employed as a sacrificial spacer layer to maintain separation between etching-active catalyst cores. A second technique utilizing sputter-deposition of catalyst is developed with the goal of improving process scalability and homogeneity. With no intrinsic limitations on substrate size, this approach is used to produce nanoporous silicon over areas larger than 25 cm 2, pores less than 5 nm in diameter, and aspect ratios greater than 1000:1. Post-etch modification of the nanoporous silicon is performed by atomic layer deposition of alumina, titania, and tungsten nitride onto the surface and pore walls of the porous silicon, highlighting its morphological and chemical tunability. Utility of the material is demonstrated via its implementation in three industrially relevant use cases. As a nanofiltration membrane the material exhibits a size-cutoff as low as 2 nm, and tunable thickness-dependent permeability ranging over three orders of magnitude. Additionally, it demonstrates promise as an active material in a thermoelectric device, reducing thermal conductivity by approximately 70 fold with respect to bulk silicon, of which a factor of 20 can be attributed directly to the porosity in the film. Finally, applicability to the patterning of 2D materials is demonstrated using centimeter scale nanoporous silicon masks in the dry etching of molybdenum disulfide and tungsten disulfide, producing porous structures on the nanoscale. The broad impact of this work is the introduction of two new strategies for the manufacturing of nanoporous silicon at scale, and introduction of the relevant design metrics for control of pore size, pore aspect ratio, and homogeneity of the material. It is expected that this knowledge will be of use in applications which stand to benefit from the introduction of this unique form of nanoporous silicon. / by Brendan Derek Smith. / Ph. D.

Thesis (Sc D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1987. / Bibliography: leaves 168-174. / by Jon Michael Peltier. / Sc D.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2004. / "June 2004." / Includes bibliographical references (p. 159-163). / This thesis examines a small corpus of artifacts from Tal-i Iblis, Iran dating to the mid-6th millennium BCE. When excavated in the late 1960s, these artifacts were presumed to be evidence of an early copper smelting technology on the Iranian Plateau, and they were delivered to MIT for further analysis. In this thesis I briefly describe the origins of early metallurgical activity in the Old World focusing mainly on the Iranian Plateau. This will provide a basis for the significance of the thesis and of the early date associated with the metallurgical objects. I have studied six of the Tal-i Iblis artifacts curated at MIT through extensive qualitative and quantitative analytical methods. These methods are described in Chapter IV. The results and discussion are presented in Chapters V and VI. I have found that these Iblis sherds provide substantial evidence for the presence of a copper smelting technology during the early occupation levels at Tal-i Iblis, Iran. / by Lesley Frame. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1996. / Includes bibliographical references (leaves 199-204). / by Jean-Marc P. Genkin. / Ph.D.

Thesis (Ph. D.)--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. 261-282). / Biological materials have developed hierarchical and heterogeneous material nanostructures and microstructures to provide protection against various environmental threats that, in turn, provide bioinspired clues to man-made, protective material designs. In particular, designs of dermal fish armor are a tradeoff between protection and mobility. A comprehensive knowledge base of the materials and mechanical design principles of fish armor has broad applicability to the development of synthetic engineered protective/flexible materials. In this thesis, two fish armor model systems have been investigated by means of structure-property-function relationships, ultimately answering how the armor systems have been designed in response to their environmental threats. The first model system, Polypterus senegalus are descendants of ancient fish and their body is covered by a natural armor consisting of small bony scales. The quadlayered armor scales are composed of ganoine, dentin, isopedine and bone, to protect against predatory biting attacks. First of all, multilayer design principles of P. senegalus scales were understood with respect to penetration resistance by the multiscale experimental and computational study. The quad-layered scales exhibit mechanical gradient within and between material layers and have geometrically corrugated junctions with an undetectable gradation; all of which lead to effective penetration resistance including load-dependent effective material properties, circumferential surface cracking, plastic dissipation in the underlying dentin layer, stress redistribution around the interfaces with suppression of interfacial failure. Secondly, since the outmost ganoine is structurally anisotropic, the roles of anisotropy of ganoine in the entire system have been investigated by combining orientation-dependant indentation and mechanical modeling. The elastic-plastic anisotropy of the ganoine layer enhances the load-dependent penetration resistance of the multilayered armor compared with the isotropic ganoine layer mainly by (i) enhancing the transmission of stress and dissipation to the underlying dentin layer, (ii) lowering the ganoine/dentin interfacial stresses and hence reducing any propensity toward delamination, and (iii) providing discrete structural pathways for cracks to propagate normal to the surface for easy arrest by the underlying dentin layer. Inspired by P. senegalus scales, threat-protection interaction and structurefunction relationships among various layered armor systems have been investigated using parametric studies with finite element (FE) models. Geometry, microstructure and mechanical properties of a threat system significantly influence its ability to effectively penetrate into the armor system or to be defeated by the armor. Simultaneously, three structure parameters of multilayered armor designs are mainly considered: (i) the thickness of the outmost layer; (ii) the quad-layered vs. bilayer structure; and (iii) the sequence of the outer two layers. The role of the armor microstructure in defeating threats as well as providing avenues of energy dissipation to withstand biting attacks is identified. Microstructural length scale and material property matching between the threat and armor is clearly observed. Bilayered and quadlayred models are mechanically comparable, but the quad-layer model achieves a weight reduction. Studies of predatorprey threat-protection interactions may lead to insights into tunability in mechanical functionality of each system in conjunction with adaptive phenotypic plasticity of the tooth and scale microstructure and geometry, "adaptive stalemates," and the so-called evolutionary "arms race." The second model system, Gasterosteus aculeatus, is well-known for light-weight and morphologically varied armor structure among different G. aculeatus populations. Marine and freshwater G. aculeatus armor structures have been assessed quantitatively by micro-computed tomography ([mu]CT) technique. The convolution of plate geometry in conjunction with plate-to-plate overlap allows a relatively constant armor thickness to be maintained throughout the assembly, promoting spatially homogeneous protection and thereby avoiding weakness at the armor unit interconnections. Plate-to-plate junctures act to register and join the plates while permitting compliance in sliding and rotation in selected directions. SEM and [mu]CT revealed a porous, sandwich-like cross-section of lateral plates beneficial for bending stiffness and strength at minimum weight. Moreover, the structural parameters of the pelvic assemblies were also quantified via pCT, which include the spatial dependence of the suture amplitude and frequency, the suture plate inclination angle, and the suture gap. Significant differences in these structural parameters were observed between the different G. aculeatus populations. Composite analytical and finite element computational models were developed and used in conjunction with the pCT data to simulate the mechanical behavior of the pelvic assembly, to predict the effective suture stiffness and to understand the conformational change of the pelvic assembly from the "rest" to "offensive" states. This study elucidates the structural and functional differences between different divergent populations of G. aculeatus and serves as a model for other systems of interest in evolutionary biology. / by Juha Song. / Ph.D.

Thesis. 1975. Sc.D.--Massachusetts Institute of Technology. Dept. of Materials Science and Engineering. / Vita. / Includes bibliographical references. / Sc.D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2017. / 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. / In an effort to make alternative energy competitive to fossil fuels, research in improving efficiencies of solar cells and fuel cells have grown rapidly over the last few decades. One prominent strategy to improving the efficiencies in these devices focuses on engineering materials with customized molecular structure for enhancements in specific properties. Herein, new organic materials are designed and synthesized to enhance selected properties for applications in fuel cells and solar cells. In chapter 1, triptycene poly(aryl ethers) are synthesized and characterized for enhancing ion conductivity of ion exchange membranes in fuel cells. Triptycene motif is incorporated to increase charge density and fractional free volume in the membranes. In Chapter 1.2, sulfonated triptycene poly(ether ether ketone) (S-tripPEEK) is synthesized and studied for proton exchange membranes (PEM). Increasing fractional free volume in the membrane results in high water uptake at relative humidity (RH) from 10 %RH to 90 %RH and higher proton mobility in the membranes. S-tripPEEK membranes show proton conductivities of 334 mS/cm at 85 °C at 90 %RH and 0.37 mS/cm at 85 °C at 20 %RH as compared to 18.9 mS/cm and 0.0014 mS/cm observed in commercially available Nafion117[superscript TM] membranes. In Chapter 1.3, methylimidazolium triptycene poly(ether sulfone)s (MeIm-tripPES) are made for alkaline anion exchange membranes (AAEM) and are found to have ion conductivities of 104 mS/cm at 80 °C in water. Controlled nanophase separation with increased domain size contributed by the triptycene moiety lead to the high observed conductivities. However, the methylimidazolium functional groups on the membranes are not stable to alkaline conditions in the operation of a fuel cell. In Chapter 2, dithiolodithiole (C₄S₄) heterocycle was synthesized and studied as a new building block for organic photovoltaic materials. As an electron-rich fused-ring motif, C₄S₄ is expected to be a more effective electron donor. Comparison with analogous thiophene derivatives shows that C4S4 moiety raises the highest occupied molecular orbital (HOMO) by 0.7 - 1.0 eV, suggesting a stronger electron donating character than thiophene. Furthermore, crystal structures of C4S4 molecules show planarity in the molecule which further reduces the bandgap. / by Lionel C. H. Moh. / Ph. D.