Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1996. / Includes bibliographical references (leaves 75-78). / by Thomas D. Chen. / M.S.

Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1994. / Includes bibliographical references (p. 219-228). / by Richard Mlcak. / Sc.D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1997. / Vita. / Includes bibliographical references (leaves 52-54). / by Pradeep Sreekanthan. / M.S.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1994. / Includes bibliographical references (leaves 138-143). / by Hyoun-woo Kim. / Ph.D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2017. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 127-147). / The treatment of neurodegenerative and neurological conditions relies on better understanding the system that they afflict. However, the tools currently available to probe neural circuits are often limited to use in short-term studies primarily due to poor of biocompatibility. To address this challenge, flexible, minimally invasive neural probes were fabricated using a thermal drawing process, with polymers serving as their main structural constituent. Through the use of different polymers, probes containing arrays of tin electrodes as small as 5 [mu]m were fabricated, as were probes combining capabilities for electrical recording, optical stimulation, and drug delivery. A technique was developed to combine functionalities of these devices into a single probe to study the effect of optical stimulation with different waveforms on the brain activity. To break the longitudinal symmetry inherent to probes fabricated using the thermal drawing process, and to allow the incorporation of functionalities along the probe length, a method to combine thermal drawing with a method commonly used to fabricate neural probes, photolithography, was developed, along with the selection of the polymer that would allow consecutive processing using these two techniques. All of the fabricated probes were characterized and tested in vivo by implantation into mice and assessing their functionality. High signal-to-noise ratio (13±6) recordings were obtained using multielectrode arrays. Recordings of neural activity during simultaneous optical stimulation and drug delivery were performed with multifunctional probes. Hybrid probes combining metal electrodes with a polymer waveguide were used to study the response of large groups of neurons to different forms of optical stimuli. Most importantly, the biocompatibility of these probes was assessed over a 3 month period and compared favorably to that of steel microwires of similar size. / by Andrés Canales. / Ph. D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1997. / Includes bibliographical references (leaves 196-203). / by Pavel Bystrický. / Ph.D.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2007. / "June 2008." / Includes bibliographical references (leaf 28). / Multilayer rhombic magnetic rings are researched as a structure for the "pseudo spin valve" device that could possibly become useful in magnetic materials applications such as MRAM, digital logic, and sensors through the use of multiple resistance states exhibited within these devices. The magnetization reversal characteristics of these structures are explored in an effort to fully understand interactions occurring within the devices and their resulting effect on giant magnetoresistance (GMR). Contact configuration and angular dependence of applied field are also examined. Using submicron thickness rhombic rings with long axis dimension -1.5gjm, major loop magnetization sweeps were conducted, as well as minor loops in order to excite several resistance states within the devices. It was found from major loop applied field sweeps that rhombic multilayer rings exhibit five stable magnetoresistive states, with an additional state excited through execution of a minor loop field sweep. In addition, using the contact configurations known as "classical" and "wheatstone bridge" provide additional information on interactions that are occurring within the structures. It was found that both contact configurations were sensitive to similar changes in the devices, however, through different means of sensing. The major difference results in a larger GMR output in the wheatstone bridge configuration (-20%) versus the classical configuration (-1%). Preliminary work in angular dependence has shown the ability to alter resistance plateaus by changing the angle of applied field. Ultimately shown through this work is the amount of research that is still needed to truly understand these devices, as they contain more complex stable and metastable states of magnetization than generations and shapes before them. / by James N. Pacella. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references. / The blood clotting process is one of the human body's masterpieces in targeted molecular manipulation, as it requires the activation of the clotting cascade at a specific place and a specific time. Recent research in the biological sciences have discovered that one of the protein molecules involved in the initial stages of the clotting response, von Willebrand Factor (vWF), exhibits counterintuitive and technologically useful properties that are driven in part by the physical environment in the bloodstream at the site of a wound. In this thesis, we take inspiration from initial observations of the vWF in experiments, and aim to describe the behaviors observed in this process within the context of polymer physics. By understanding these physical principles, we hope to harness nature's ability to both direct molecules in both spatial and conformational coordinates. This thesis is presented in three complementary sections. After an initial introduction describing the systems of interest, we first describe the behavior of collapsed Lennard-Jones polymers in the presence of an infinite medium. It has been shown that simple bead-spring homopolymer models describe vWF quite well in vitro. We build upon this previous work to first describe the behavior of a collapsed homopolymer in an elongational fluid flow. Through a nucleation-protrusion mechanism, scaling relationships can be developed to provide a clear picture of a first-order globule-stretch transition and its ramifications in dilute-solution rheology. The implications of this behavior and its relation to the current literature provides qualitative explanations for the physiological process of vasoconstriction. In an effort to generalize these observations, we present an entire theory on the behavior of polymer globules under influence of any local fluid flow. Finally, we investigate the internal dynamics of these globules by probing their pulling response in an analogous fashion to force spectroscopy. We elucidate the presence of both a solid-liquid dynamic globule transition and a contour-based description of internal globule friction. It is possible to incrementally add levels of details to these Lennard-Jones polymer models to more accurately represent biological molecules. In the second section of this thesis, we investigate the consequences of incorporating a Bell-model behavior into single homopolymer interactions to describe a "self-associating" polymer. We first demonstrate how this model is, in equilibrium, essentially the same as a Lennard-Jones polymer, however we demonstrate that the polymer dynamics are indeed both drastically different and tunable. This has ramifications under the presence of dynamic loads, and we investigate single-molecule response to both shear and pulling stimuli. In the former, we find novel and tunable giant non-monotonic stretching responses. In the latter, we use our observations to develop a complete and general theory of pulling these types of molecules that has ramifications in both the study of biological polymers and in the design of soft materials with tunable mechanical response. The final section introduces concepts related to the behavior of collapsed polymers in fluid flows near surfaces. During the blood clotting process, vWF undergoes a counterintuitive adsorption process and here we begin to develop the physical fundamentals required to understand this process. After a brief introduction to the relevant hydrodynamic treatment we use in simulations, we first describe the presence of a hydrodynamic lift force and the formalism we use as we include it in the context of our theory. We reveal the presence of a non-monotonic lift force, and subsequently utilize this theoretical formalism to describe the adsorption and desorption behavior of a collapsed polymer globule near an attractive surface. We investigate the limit of large flows and highly attractive surfaces by providing a description of the conformational and hydrodynamic behavior of a polymer tethered at a surface. We finally discuss the behaviors of a polymer that associates with a surface, and postulate the importance of such processes in vWF function. We finally include an addendum that describes an unrelated project that investigates the possibilities of using superparamagnetic beads as a tool for hydrodynamic propulsion by assembling these beads into "rotors" near a surface to create micro-walkers that have interesting applications in self-assembled microfluidic chips. / by Charles Edward Sing. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2003. / Includes bibliographical references (p. 191-201). / SiGe-on-insulator (SGOI) and strained-Si-on-insulator (SSOI) substrates combine both the benefits of a high-quality, monocrystalline SiGe or strained-Si surface layer with the advantages of an insulating substrate. In particular, many electronic and photonic devices are greatly enhanced by the use of such substrates. In this thesis, techniques were developed for the fabrication of SGOI and SSOI substrates for applications including strained-Si complementary metal-oxide-semiconductor (CMOS) field-effect transistors, and nanocrystalline-Ge waveguides and photonic devices. A versatile fabrication technique was pioneered for the fabrication of low defect density SGOI and SSOI substrates, allowing for the creation of ultra-thin SGOI and SSOI, combining both the benefits of high-mobility strained-Si and SOI. The method pioneered employed wafer bonding of polished, relaxed SiGe virtual substrates to oxidized handle wafers. Layer transfer onto insulating handle wafers was accomplished using grind-etchback or delamination via implantation. Both methods were found to produce a rough transferred layer, but chemical mechanical polishing (CMP) was found to be unacceptable due to non-uniform material removal across the wafer and the lack of precise control over the final layer thickness. To solve these problems, a strained-Si stop layer was incorporated into the bonding structure. After layer transfer, excess SiGe was removed using a selective etch process, stopping on the strained-Si. Within the context of ultra-thin SGOI and SSOI fabrication, this work describes recent improvements including metastable stop layers, low- temperature wafer bonding, and improved selective SiGe removal. Such ultra-thin SSOI substrates are ideal for fully-depleted CMOS, in comparison to some thicker SGOI substrates that were fabricated, which are required for partially-depleted CMOS. SGOI substrates can also be used as a platform for novel photonic devices. In this work, one such example is presented, whereby nanocrystalline-Ge waveguides were fabricated using SGOI substrates. These waveguides contained Ge nanocrystals embedded in an oxide matrix and isolated from the underlying Si substrate by a buried silicon dioxide layer. Fabrication challenges revolved around the instability of SiGe- oxide, which was required as an initial material for the nanocrystalline-Ge fabrication / (cont.) process. Nanocrystals were formed via the reduction of SiGe-oxide by annealing in a hydrogen ambient. Resulting nanocrystalline-Ge distributions were mapped as a function of hydrogen partial pressure, annealing temperature, and time. Based on these results, the process kinetics of the nanocrystal formation process was deduced, and a mathematical model was created based on the observations. Simulations generated predictions for nanocrystalline density as a function of temperature and hydrogen pressure which were consistent with experimental results. Based on the demonstrations in this thesis, SGOI and SSOI were shown to be enhanced platforms for microelectronic and photonic devices. With the advent and development of the general wafer bonding method presented in this work, these substrates may serve as platforms for a multitude of future novel applications. / b y Gianni Taraschi. / Ph.D.

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2003. / Includes bibliographical references (leaf 37). / Cellular bands A and B are in the 100s of :MHz frequency range. They are . discontinuous bands requiring sharp skirts - the specialty of superconducting filters. Superconducting filters are therefore ideal in the function of front-end filters on cell phone base stations, serving to reject any unnecessary signals, eliminating intermodulation distortion (IMD). Broader geographical coverage and higher calling capacity per tower are other effects of the superconducting filters compared to their dielectric counterparts. Were a business to sell these filters, the intended customer would be the cell phone company, rather than the base station manufacturer. The filters would have to be cryocooled. However this requirement is no longer a disadvantage, through an increase of cryocooler mean time between failure(MTBF) to more than 500,000 hours, and through a recently overturned patent on fail-safe operation in case of cooler failure. Comparable businesses have typical quarterly losses on the order of 10s of millions of dollars, but do sell products, so a new business should not expect to tum a profit immediately. However, the ability to learn from the experiences of predecessors would serve a new company well. In addition, the possibility of combining two devices onto one chip (filter and Josephson junction) could serve as a new area of growth for an emerging company. / by Abigail Kirschenbaum. / M.Eng.