Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2008. / Includes bibliographical references (p. [76]-80). / A novel SixGe₁-x, electro-absorption modulator design is experimentally demonstrated. The device is waveguide integrated, butt-coupled into high index contrast Si/SiO2 waveguides. 0.75% Silicon concentration in the alloy is optimized for 1550nm applications. With its 400nm height, 600nm width, and 50,pm length, the device has a footprint smaller than 30[mu]m². Low effective driving voltage, <2.5V, is needed to achieve an extinction ratio of 5.2dB in the broad 1510-1555nm wavelength operation range. At 1550nm, an extinction ratio of 6.5dB is achieved with an applied effective bias of -2.5V. High frequency measurements determine the device can reach a 3dB frequency of 1.2GHz. Electrical characterization of the device shows high series resistance (~15k[omega]) which is caused by fabrication over-etching during metal contact deposition. Series resistance reduction to ~100[omega] would allow the device to reach the predicted 3dB frequency of 100GHz with 10dB extinction ratio. A pseudo-linear relation is found between the achieved extinction ratio and the applied effective bias. The ratio between these two quantities, the modulation efficiency, can be considered as a new figure of merit of the device. The slope of this pseudo-linear relation measures 2.2dB/V for extinction ratio values ranging between 0 and 5.5dB. In terms of modulation depth it is equivalent to a slope of 40%/V in the range 0.5V-2V. Finally, an ultra-low power consumption per bit of 34fJ/bit is measured for a capacitance of 11fF and an effective applied reverse bias of 2.5V. / by Sarah Bernardis. / S.M.

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. / Cataloged from student-submitted PDF version of thesis. / Includes bibliographical references (pages 159-168). / Human intellectual desire inspires recent research to expand to interdisciplinary areas across biology, chemistry, and physics. Interdisciplinary research in unexplored areas is challenging, but holds great promise to elucidate what people did not see before. Scientific discoveries bring us not only intellectual pleasures, but also opportunities to contribute to the advancement of mankind. Photosynthesis is a representative interdisciplinary research field. Conducting research in photosynthesis requires a collaborative work of biology, photochemistry, and quantum physics. Nature has optimized photosystems in bacteria, algae, and plants over three billion years in an evolutionary fashion to utilize solar energy for their survival. The way nature has mastered such systems can provide insights into designing efficient solar energy conversion applications. This thesis explores artificial photosystems as proofs of nature's design concept using a biological scaffold of M13 bacteriophage. The main ideas in the thesis focus on maximizing transport phenomena in the systems, resulting in performance improvements. Genetic engineering of M13 bacteriophage enables nano-scale multi-component assemblies to create tunable, artificial photosystems for solar energy utilization. Artificial photosystems include light-harvesting antenna complexes and oxygen-evolving photocatalytic systems. In particular, a solid collaboration with Seth Lloyd's theory group inspires me to design a quantum light-harvesting antenna complex. The genetically engineered light-harvesting antenna complex creates a chromophore network interplaying between quantum and semi-classical mechanisms, thus maximizing exciton transport. / by Heechul Park. / Ph. D.

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2004. / Includes bibliographical references (leaves 65-66). / The feasibility of bringing a nascent technology for detection and quantification of local cytokine concentrations on cell surfaces to market is presented in this paper. Quantum dots or fluorochrome-loaded nanoparticles are conjugated with antibodies for target analytes and with proteins that allow nanoparticle attachment to the surface of T cells. A second labeled monoclonal antibody is introduced to detect the presence of any captured-cytokines using 3D fluorescent microscopy or flow cytometry. Microscopy of DO.ll cells labeled with cytokine-capture particles have shown successful detection of exogenous IL2. A comparison of existing patents with cytokine-capture technology revealed that although each aspect of the device is covered by prior IP, the capabilities of the technology exceed the claimed uses of the individual components. A preliminary market research for cytokine-capture technology applications resulted in dismissing the immunoassay industry as a target market. However, T cell monitoring was identified as a far more lucrative industry. / by Julee Y. Hong. / M.Eng.

Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 109-125). / The efficiency of many energy storage and conversion technologies, such as hydrogen fuel cells, rechargeable metal-air batteries, and hydrogen production from water splitting, is limited by the slow kinetics of the oxygen electrochemical reactions. Transition-metal oxides can exhibit high catalytic activity for oxygen electrochemical reactions, which can be used to improve efficiency and cost of these devices. Identifying a catalyst "design principle" that links material properties to the catalytic activity can accelerate the development of highly active, abundant transition metal oxide catalysts fore more efficient, cost-effective energy storage and conversion system. In this thesis, we demonstrate that the oxygen electrocatalytic activity for perovskite transition metal oxide catalysts primarily correlates to the a* orbital ("eg") occupation. We further find that the extent of B-site transition metal-oxygen covalency can serve as a secondary activity descriptor. We hypothesize that this correlation reflects the critical influences of the a* orbital and transition metal-oxygen covalency on the ability of the surface to displace and stabilize oxygen-species on surface transition metals. We further propose that this ability to stabilize oxygen-species reflect as the rate-limiting steps of the oxygen electrochemical reactions on the perovskite oxide surfaces, and thus highlight the importance of electronic structure in controlling the oxide catalytic activity. / by Jin Suntivich. / Sc.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2007. / Includes bibliographical references. / As dimensions shrink and current densities increase, the reliability of metal interconnects becomes a serious concern. In copper interconnects, the dominant diffusion path is along the interface between the copper and the top passivation layer (usually Si3N4). One of the predominant failure mechanisms in Cu has been open-circuit failure due to electromigration-induced void nucleation and growth near the cathode ends of interconnect segments. However, results from accelerated electromigration tests show that the simple failure analyses based on simple void nucleation and growth can not explain the wide range of times-to-failure that are observed, suggesting that other types of failure mechanisms are present. In this thesis, by devising and performing unique experiments through the development of an electromigration simulation tool, unexpected complex failure mechanisms have been identified that have significant effects on the reliability of copper interconnects. A simulation tool was developed by implementing the one-dimensional non-linear differential equation model first described by Korhonen et al. By applying an implicit method (Backward Euler method), the calculation time was significantly reduced, and stability increased, compared to previous tools based on explicit methods (Forward Euler method). / (cont.) The tool was crosschecked with experimental results by comparing void growth rates in simulations and experiments. Using this tool, one can simulate stress and atomic concentration states over the entire length of an interconnect segment or throughout a multi-segment interconnect tree, to identify analyze possible failure locations and mechanisms. Experiments were carried out on dotted-i structures, where two 25jim-lomg segments were connected by a via in the middle. Electrical currents were applied to the two segments independently, and lifetime effects of adjacent segments were determined. Using the simulation tool and calculations, it was shown that adjacent segments have a significant effect on a segment's stress state, even if the adjacent segment has no electrical current. This explains experimental observations. This also suggests that for reliability analyses to be accurate, the states of all adjacent segments must be considered, including the ones without electrical current. In a second set of experiments, the importance of pre-existing voids was investigated. Using in-situ scanning electron microscopy, voids away from the cathode were observed. These voids grew and drifted toward the cathode and the shape of the voids were found to be closely related to the texture and stress state of individual grains in the interconnect. / (cont.) The drift velocity of voids was shown to be directly proportional to surface diffusivity. Electromigration tests on unpassivated samples were performed under vacuum to obtain the surface diffusivity of copper and its dependence on texture orientations. Simulation results show that pre-existing voids cause void growth away from the cathode. Subsequent failure mechanisms differ depending on the location of the pre-existing void and the critical void volume for de-pinning from grain boundaries. If pre-existing voids are present, void-growth-limited failure is expected in interconnects at low current densities, due to growth of pre-existing void, and the lifetimes are expected to scale inversely with j. However, at higher current densities (typical for accelerated testing), failure can occur through nucleation of new voids at the cathode (so that lifetimes scale inversely with j2), or through a mixture of nucleation of new voids and growth of pre-existing voids. These effects must be taken into account to accurately project the reliability of interconnects under service conditions, based on experiments carried out under accelerated conditions. / by Zung-Sun Choi. / Ph.D.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2009. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 29). / This investigation seeks to investigate the relationship of kinematic fluid viscosity to the effective power transduction seen by a hydraulic motor. Applications of this research specifically relate to energy recovery from a vehicle suspension system through the shock absorbers. A regenerative, hydraulic-based, rotary shock absorber was designed and fabricated for the purposes of this investigation. The kinematic viscosities ranging from 100 cSt to 200 cSt were used in the fluid circuit and tested for maximal efficiency of the hydraulic system. Balance between shear-force losses in the fluid circuit, and effective transfer of momentum at the water-wheel type hydraulic motor demonstrates that optimized performance of the system is attained when a midpoint is reached in the kinematic viscosity of the fluid. / by Shakeel N. Avadhany. / S.B.

Thesis: S.B., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references (page 33). / In vitro liver models are a critical tool in pharmaceutical research, yet standard hepatocyte cultures fail to capture the complexity of in vivo tissue behavior. One of the most critical features of the in vivo liver is the extensive microvasculature which allows for the delivery of nutrients and metabolites without exposing hepatocytes to de-differentiating fluidic shear stresses. A new liver tissue scaffold design able to capture this histological organization may therefore improve the functional longevity of seeded hepatocytes. The additive manufacturing technique of projection micro-stereolithography (PuSL) proved capable of building non-cytotoxic and highly complex 3D structures with microvasculature on the order of 20 um inner diameter. While extensive biological testing remains to be carried out, the built structures reveal much promise in PuSL as a method of tissue scaffold fabrication in terms of in vivo mimicking architecture. / by Albert Keisuke Matsushita. / S.B.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1994. / Includes bibliographical references (leaf 65). / by Matthew Peter Galla. / M.S.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2005. / Includes bibliographical references (leaves 23-25). / The average operating temperature of RENÉ N5® high pressure turbine blades was evaluated via [gamma]/[gamma]' microstructure and coating/base metal interdiffusion methods. The [gamma]' volume fraction was measured by point counting and direct area measurement. The data, however, were found inadequate to accurately determine the operating temperature. The interdiffusion between the platinum aluminide coating and the base material was modeled with an error function solution to Fick's Second Law. This method provided an estimation of the operating temperature that varied from the reported operating temperature by only 1%. / by Wendy D. Ham. / S.M.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2013. / Cataloged from PDF version of thesis. / Includes bibliographical references. / When a gold nanoparticle is coated with two dislike ligands, the ligands selfassemble on the nanoparticle surface and the phase separation occurs based on the miscibility and the size mismatch of two ligands, and the sizes of nanoparticles. When the size of the gold core is approximately between 3-8 nm, the stripe-like ordered domains of two ligands are formed. The stripe-like structure is not favored when you consider only the enthalpy. However, the long ligands obtain extra free-volumes when they are surrounded by the short ligands due to the curvature of a nanoparticle, hence, the entropy increases when two ligands are mixed on the nanoparticle surface. The balance between enthalpy and entropy leads to the state where the stripe-like arrangement of two ligands is thermodynamically the most stable. When the size of the gold core becomes smaller, the entropy contribution becomes less and less relevant, since the gain of free-volume when two different ligands are closely placed is smaller due to the larger curvature of smaller nanoparticles. Under this condition, the final morphology is primarily determined by the enthalpy of separation. Therefore, for small particles, two ligands phase separate into two bulk phases, resulting the Janus nanoparticles. In the first part of this thesis, we demonstrate that gold nanoparticles with a core diameter smaller than 1.5 nm form Janus nanoparticles in many ligand combinations. We used four different nanoparticles and different techniques to confirm the presence of a majority of Janus particles. All of them show similar cut-off sizes for the Janus-to-stripe transition. In the second part of this thesis, we show nanoparticle hydrogels using the selfassembly of the stripe nanoparticles. One of unique surface properties of the stripe nanoparticle is divalency. A particle coated with stripe-like domains implies two defect points at the poles of NPs. These two polar defects can be selectively functionalized with molecules that in turn can act as handles for further assemblies. The network structure is formed only using ionic interaction between NPs, and it requires both divalent anionic nanoparticles and divalent cations. Gels are investigated to determine their properties using rheological characterization. / by Hyewon Kim. / Ph. D.