http://hdl.handle.net/1721.1/7677 2013-05-21T12:24:47Z http://hdl.handle.net/1721.1/77665 Dispersions of barium titanate in organic liquids Parish, Mark V Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1982.; MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE.; Includes bibliographical references. 1982-01-01T05:00:00Z http://hdl.handle.net/1721.1/76146 Theoretical study on the band structure of Bi1̳-x̳Sbx̳ thin films Tang, Shuang, S.M. Massachusetts Institute of Technology The study on the electronic band structures of Bi1-xSbx thin films is a very interesting topic. Recall that in bulk Bi1-xSbx, the electronic band structure can be varied as a function of temperature T, pressure P and stoichiometry. The electronic band structure does not change with T significantly in the cryogenic temperature range under the atmospherical presure. The conduction band edge and the valence band edge are very close to each other at the three L points within the first Brillouin zone such that they are strongly coupled, and the energy band at the L points is non-parabolic dispersive. At certain conditions, the conduction band edge and the valence band edge will touch each other at the three L points, and the dispersion relation at the L points will become linear, which leads to the formation of three-dimensional Dirac points. By synthesizing Bi1-xSbx thin films, we have two more parameters to control the band structure, namely film thickness and growth orientation. We have developed the iterative-two-dimensional-two-band model to study the two- dimensional L-point non-parabolically dispersive electronic band structure of the Bi1-xSbx thin films system. The Lax model based on the k - p model describes the the L-point non- parabolic dispersion relations very well consistent with experimental results for bulk bis- muth. Because the band gap is narrow, the number of bands that are needed in the per- turbation is small. A satisfactory representation over a limited region of k-space has been archived in terms of the two coupled bands, which means that the Hamiltonian could be approximately diagonalized, and which gives a very simple form for the Lax model. In the thin films system, the anylysis is more different due to the non-parabolic quantum confinement effect. The L-point band gap is increased in a thin film compared to the L-point band gap in a bulk system. As the film thickness decreases, the L-point band gap increases. The L-point band gap and the L-point inverse-effective-mass tensor are coupled together and are different from the values for the bulk materials. Thus, iterative procedures are employed for getting the accurate values of the L-point band gap and its corresponding inverse-effective-mass tensor. The iterative-two-dimensional-two-band model can be gen- eralized to study other two-dimensional narrow-gap systems, for example lead telluride thin films and silicon-germanium alloys thin films. The model can also be modified to study one-dimensional narrow-gap systems such as Bi1-xSbx nanowires. The electronic band structure of Bi1-xSbx thin films for different growth orientations are studied. The results shows that by growing the Bi1-xSbx thin film normal to a low symmetry crystalline direction other than the trigonal axis, the three-fold symmetry of the three L points in the bulk Bi1-xSbx can be broken. Specifically, by growing the Bi1-xSbx thin film along the bisectrix axis, anisotropic single-Dirac-cone can be constructed at the L point associated with this bisectrix axis. In similar ways, by choosing proper antimony compositions, growth orientations and film thicknesses, a large variety of Dirac-cone materials can be constructed based on the Bi1-xSbx thin films system, including single-Dirac-cone materials with different aisotropies, bi-Dirac-cone materials, tri-Dirac-cone materials, quasi-Dirac-cone materials and semi- Dirac-cone materials. Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2012.; This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.; In title on title page, "1̳", "-x̳" and "x̳" in "Bi1̳-x̳Sbx̳" appear as subscript script. Cataloged from student submitted PDF version of thesis.; Includes bibliographical references (p. 56-61). 2012-01-01T05:00:00Z http://hdl.handle.net/1721.1/76133 Cost of quality tradeoffs in manufacturing process and inspection strategy selection Zaklouta, Hadi In today's highly competitive markets manufacturers must provide high quality products to survive. Manufacturers can achieve higher levels of quality by changing their manufacturing process and/or by product inspection where a multitude of different strategies are often available. Each option has its own cost implications that must also be taken into account. By reconciling the competing objectives of quality maximization and cost minimization, a cost of quality approach serves as a useful framework for comparing available manufacturing process and inspection alternatives. Still, any rigorous comparison requires both a metric as well as a profound understanding of cost of quality tradeoffs. The cost of quality tradeoffs in manufacturing process and inspection strategy selection are examined through a probabilistic cost of quality model explored analytically using a sample set of fundamental inspection strategies (reinspect rejects, reinspect accepts and single inspection) and applied to the case of electric vehicle battery pack assembly. From an expected value point of view a series of parametric sensitivity analyses reveal that complex tradeoffs between manufacturing process, inspection, internal and external failure costs determine the optimal manufacturing process and inspection strategy combination. In general, reinspect rejects minimizes internal failure costs, reinspect accepts minimizes external failure costs and single inspection lies in between while minimizing inspection costs. This thesis illustrates the fact that results are scenario specific and depend on product cost-, manufacturing process and available inspection method attributes. It is also observed that manufacturing process improvement often coincides with a need to change inspection strategy choice, thereby indicating that manufacturing process and inspection strategy selection should not be performed independently of each other. This thesis demonstrates that the traditional expected value approach for evaluating cost of quality implications of manufacturing and inspection is often misleading. Decision tree formulations and discrete event simulations indicate that cost of quality distributions are asymmetric. High internal- and external failure costs, manufacturing process non-conformance rates and inspection method error rates are contributing factors. The alternative metric of expected utility captures decision makers risk aversion to high cost outliers and changes the criteria for optimality and favors inspection strategies and manufacturing processes that minimize external failure events with increasing risk intolerance. In the examined case of electric vehicle battery pack assembly both material- and external failure costs are very high. Analytical and discrete event simulation results indicate that for the given welding process the inspection strategy that minimizes external failure costs is optimal from an expected cost point of view as well as at high degrees of risk aversion. This result is shown to be sensitive to parameters driving the cost and probability of external failure events. Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2011.; Cataloged from PDF version of thesis.; Includes bibliographical references (p. 106-108). 2011-01-01T05:00:00Z http://hdl.handle.net/1721.1/76132 Morphologies of PDMS-containing diblock polymers Stewart-Sloan, Charlotte (Charlotte Roberta) The morphologies of polydimethylsiloxane (PDMS)-containing diblock polymers are investigated as a function of volume fraction, segregation, processing procedure, and temperature. Strongly segregated polyisoprene-PDMS and polystyrene-PDMS diblocks are prepared according to standard procedures in the literature by anionic synthesis in the laboratory of Professor Apostolos Avgeropoulos at the University of Ioannina in Ioannina, Greece and their morphologies are investigated using small angle x-ray scattering and transmission electron microscopy. Good agreement is found between this work and other work on the structures of diblocks containing PDMS with a variety of complementary blocks and between this work and theoretical predictions for the morphologies of diblock polymers. Different processing treatments including casting from solvents with a range of preference for each block and a week-long anneal are tested to determine whether processing has a strong effect on final morphology; it is found that in most cases the morphology displayed after processing is consistent independent of the processing treatment, indicating that the morphologies are in equilibrium and fairly robust to preparation procedure. Finally, selected weakly segregated diblocks were studied at varying temperatures using synchrotron small angle x-ray scattering. The diblock samples appeared to be affected by the prior x-ray dose that the materials had received. With limited prior dose, the materials studied were ordered with little dramatic change in morphology throughout the temperatures investigated; under continual irradiation by a 1.371Å (9.1 keV) beam for half an hour, the samples were damaged. The thesis concludes with a summary and suggestions for future work, including a discussion of experimental and theoretical work on the ways that equilibrium morphologies of block copolymers are perturbed when they are spatially confined to dimensions on the order of several times their repeat period. The small domain sizes achievable with and technological relevance of PDMS-containing diblocks make them ideal for use in microelectronics and information storage which provides a motivation for exploring this topic further. Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2012.; Cataloged from PDF version of thesis.; Includes bibliographical references (p. 117-123). 2012-01-01T05:00:00Z