Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 157-171). / The structure of a material can be tuned reversibly or irreversibly by imposing elastic or inelastic strain, leading to change of properties. This defines the concept of strain engineering, which includes both elastic strain engineering (ESE) and inelastic strain engineering (ISE). In this thesis, we study ESE and ISE by deviatoric (nonhydrostatic) strain. For ESE, we model how imposition of slowly-varying inhomogeneous elastic strain can induce the electronic structure changes of semiconductor crystals. The strain-dependent shift of valence and conduction band energy levels leads to the formation of electronic and hole bound states in in-homogeneously strained crystals, whose energy levels can be dynamically tuned by the strain field. We developed a new envelope function method with strain-parametrized basis set that can solve the electronic structure of such inhomogeneously strained crystals by incorporating the local electronic structure information obtained from unit-cell level first-principles calculation of homogeneously strained crystals. For ISE, we study the deviatoric strain induced phase transformation and internal structure evolution in soft matter systems. Using largescale molecular dynamics simulation, we demonstrate that controlled sintering of the nanocrystals in self-assembled superlattices of alkanethiol-passivated gold nanoparticles can happen at room temperature through deviatoric stress-induced displacement of the organic ligands. We find that combining a hydrostatic pressure of order several hundred megapascal and a critical deviatoric stress along the nearest-neighbor direction of gold nanoparticle superlattices leads to ordered sintering of gold nanocrystals and the formation of gold nanowire arrays. Similar phenomena can happen in binary superlattices of gold and silver nanoparticles, and we predict the formation of gold-silver multijunction nanowire arrays through deviatoric-stress driven sintering of nanoparticles. We also simulate the plastic flow of two dimensional amorphous granular pillars subjected to athermal, uniaxial and quasistatic deformation. We find that for the athermal granular pillars under inhomogeneous load, the cumulative local deviatoric strains of particles with respect to their neighbors play the role of time in thermal systems, and drive the crossover of non-affine particle displacements from ballistic motion to diffusion. The result suggests that in disordered solids, deviatoric strain alone can drive particle diffusion even at zero vibrational temperature. / by Wenbin Li. / Ph. D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1996. / Includes bibliographical references (p. 138-144). / by Jaedeok Yoo. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1998. / Includes bibliographical references. / Three-dimensional printing (3DP) is a state-of-the-art manufacturing technology, One of its many important applications is to fabricate the metal tooling for plastic injection molding. In order to achieve a fully dense 3DP metal tool, the current 3DP process involves five steps: printing, debinding, sintering, liquid metal infiltration and heat treatment. Due to the infiltration requirement, all 3DP tools made to date are composed of a high-strength skeleton material and a low-strength infiltrant. The search for a hardenable/hard 3DP system is the mission of this dissertation. Five major accomplishments can be found in the dissertation: (1) development of the 420/bronze material system for 3DP tooling; (2) development and optimization of the post-processing of the system; (3) development of a computer model simulating the interaction of powder/liquid infiltrant; (4) computer-aided material system design and (5) methodology exploration of the material system development.The 420/bronze material system with a minimum reaction was developed experimentally, by screening 30 potential material systems. Compared to the initial 3DP and reactive system, the system strength was significantly improved. More than 50 3DP injection tools have been fabricated using this material system. A 3DP tool made of the 420/bronze system has been used to mold more than one hundred thousand plastic products without major repairing of the tool. It was the first time that an injection mold was made of 60 vol% 420 and 40 vol% bronze. The system was a milestone in the 3DP material system development. In addition, the post-processing of the system was well established and defined in terms of the procedures and parameters. Four problems associated with the processing were identified. The porosity, erosion, and reaction have been minimized. The dimensional accuracy has been substantially improved. The dimensional error is approaching to an average of ±0.1% in linear dimension. A 3DP tool made of the 420/bronze has achieved the second best in dimensional accuracy among many current rapid prototyping technologies. The procedures and parameters that have been developed serve as a good benchmark for future 3DP system. A thermodynamic database for steels, refractory metals and copper-based infiltrants for use with Thermo-Calc was developed with assessments of fifteen binary systems. / (cont.) Among the fifteen assessments, five were modified from published data; and ten were self-assessed. These data were combined with those in a commercial database to make a customized user database for 3DP materials system design/assessment. The user database has been successfully used for the simulation of a multi-component infiltration reaction. The computer predictions have excellent agreement with the experimental results. The model can be used for the development of a wide range of infiltrated composite materials. The most straightforward approach for materials... selection using this database is to search for a powder/infiltrant combination in which there is very limited tendency for interdiffusion of alloying elements between the powder and infiltrant alloys. Thermodynamic calculations that reveal solubilities of infiltrant elements in the powder alloy, and vice versa, provide an excellent predictive tool for minimizing powder/infiltrant reactions ... / by Honglin Guo. / Ph.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1999. / Includes bibliographical references. / Block copolymers containing pendant charge transport groups were synthesized for use in optoelectronic devices. The polymers were synthesized by the living ring-opening metathesis polymerization (ROMP) of functionalized norbomene derivatives, using a well-defined ruthenium carbene complex, RuC]z(=CHPh)(PCy3) 2, as the initiator. A monomer with pendant carbazole groups, 2-([methyldi(N-carbazolyl)]silyl)norbomene, was used as the hole-transporting species. A monomer with pendant dinitrobenzene groups, 2-[(3',5'-dinitrobenzoyl)methyl]norbomene, was used as the electrontransporting species. Both homopolymers and diblock copolymers were synthesized. Spincoated films of the diblock copolymer were prepared, which exhibited eithe; microphase separated or nonmicrophase separated morphologies depending on the choice of casting solvent. Charge transfer complex formation was observed in the diblocks, and the extent of complex formation was found to be greater in the nonmicrophase separated samples. Block copolymers containing the charge transport groups and different types of coordinating ligands were also prepared. Microphase separated diblock copolymers that contained a carbazole block and an alcohol block were synthesized. Cadmium sulfide nanoclusters were selectively synthesized within the spherical alcohol-functionalized microdomains, by treating the films with dimethylcadmium and hydrogen sulfide gas. The clusters were extremely small (less than 2 nm in diameter) and exhibited interesting optoelectronic properties, including a highly blue-shifted absorption edge and a broad, red-shifted photoluminescence peak indicative of poor surface passivation. Triblock copolymers containing a dinitrobenzene block, a carbazole block, and a phosphine block were synthesized, and the phosphine groups were used to load the polymer with monodisperse solution-synthesized cadmium selenide nanoclusters that were better passivated. Photovoltaic devices were fabricated from the CdSe-loaded triblocks. Microphase separated samples that possessed a morphology of cylinders oriented perpendicular to the substrate developed a larger open circuit voltage than did nonmicrophase separated samples, when the clusters were photoexcited. The improved performance is attributed to a decreased carrier recombination rate, which results from the rapid separation of the oppositely charged carriers into separate domains or channels. The effect of morphology on device performance, using samples of the exact same chemical composition, is thus clearly demonstrated for the first time. / by Jason Adam Gratt. / Ph.D.

Massachusetts Institute of Technology. Dept. of Metallurgy and Materials Science. Thesis. 1971. M.S. / Includes bibliographical references. / M.S.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1995. / Includes bibliographical references (leaves 134-137). / by Heather Elizabeth Inglefield. / Ph.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2001. / Includes bibliographical references (p. 237-241). / Three Dimensional Printing 3DPTM is a novel solid freeform fabrication technology that has been applied to the fabrication of complex pharmaceutical drug devices. Limitations of the technology as relating to pharmaceuticals have been addressed and prototype dosage forms have been fabricated. The resolution of the 3DP tablets was found to depend on particle size and liquid migration during printing and drying. The surface finish of 3DP tablets was enhanced by uniaxial pressing. Migration inhibiting additives were effective in limiting transport. Both aqueous and ethanol-based solutions showed a decrease in migration on the order of 20% when appropriate powder bed additives were introduced. Migration was also decreased by pre-printing barriers to confine secondary printed drug solutions. Low dosage forms were fabricated with as little as 2.3 nanograms. Lower dosages are expected upon dilution of the initial drug solution. Printing forms with high dosage is limited by powder void volume, filling efficiency, and drug solubility limits. Multiple print passes increased the dosage per tablet volume, 6, at the expense of process time. The use of drug suspensions to overcome solubility limits and uniaxial compression to reduce tablet volume was shown to significantly increase 6. The highest 8 achieved was 427 mg/cc for pressed suspension-printed tablets, representing 74% of the theoretical limit. Complex oral dosage forms were fabricated with 3DP to show lagged-release, extended-release, double-release, and zero-order-release. Release properties, such as lag time and release rate, were manipulated by varying the printing parameters. / (cont.) Dual-release and zero-order-release forms were fabricated using a surface degradation/erosion system based on HPMC, lactose, and Eudragitʾ L100. Erosion rate constants were used to model release from tablets with non-uniform drug distributions. Diclofenac and chlorpheniramine dual-release tablets were designed with 3 drug regions, and dissolution of the tablets followed the model closely, exhibiting 2 onsets. Two types of zero-order tablets were invented and fabricated by 3DP. These contained drug concentration gradients designed to complement the volumetric nonuniformity of eroding shells. Three formulations showed constant release of diclofenac sodium over 1-7 hours (9.6mg/hr), 1-15 hours (6.8mg/hr), and 1-36 hours (2.5mg/hr). / by Wendy E. Katstra. / Ph.D.

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.