Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, February 2003. / Includes bibliographical references. / The fundamental role of the layered-silicates in a styrene-butadiene-styrene triblock copolymer (SBS) as a function of layered-silicate dispersion during deformation was investigated. Predominantly immiscible composites of mixed morphology provided the initial proof that dramatic alteration of the SBS deformation behavior exists, but a clear understanding of the nature of reinforcement was precluded due to the fiber symmetric orientation of the SBS and the mixed clay morphologies. Following the theory of Vaia and Giannelis, use of a more hydrophobic organically modified clay resulted in an intercalated morphology with a near single crystalline texture of the SBS due to roll-casting. Significant heterogeneous deformation was observed at ambient conditions as well as at elevated temperature as verified through Cohen's affine deformation model in combination with Kratky's scattering pattern model. The intercalated morphology shows little or modest mechanical property enhancements at all temperatures studied. Exfoliated nanocomposite was produced by functionalization of the clay surfaces with polystyrene, altering the enthalpic interactions. Entropic interactions were also controlled by varying the molecular weight of the surfactant and the grafting density and shows remarkable agreement with the theory proposed by Balazs et al. Due to the increase surface volume ratio of the clay, a flipping transition of the block copolymer morphology was observed during roll-casting producing a near single crystalline parallel/parallel clay/BCP orientation. The modulus was relatively unaffected whereas the toughness increased significantly due to an earlier onset of strain hardening. / by Yung-Hoon Sam Ha. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1991. / Vita. / Includes bibliographical references (leaves 307-314). / by Marius Jacques Kloppers. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1994. / Includes bibliographical references (leaves 147-157) and index. / by Pratyush Kumar. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2007. / Includes bibliographical references (p. 185-188). / The silicon electronic-photonic integrated circuit (EPIC) has emerged as a promising technology to break through the interconnect bottlenecks in telecommunications and on-chip interconnects. High performance photonic modulators and photodetectors compatible with Si complimentary metal oxide semiconductor (CMOS) devices are indispensable to achieve this goal. A photonic modulator generates optical "1" and "0" signals by switching the light on and off, while a photodetector converts the optical signals to electrical ones so that they can be processed by a CMOS circuit. Due to its compatibility with Si CMOS processing and adequate optoelectric properties, epitaxial GeSi material has been considered as a promising candidate to achieve this goal. This thesis investigates epitaxial GeSi photodetectors and electro-absorption (EA) modulators integrated with high index contrast Si(core)/Si02(cladding) waveguides to form an EPIC circuit on a Si platform with CMOS compatibility. Tensile strain is introduced into the GeSi material to enhance its optoelectronic properties. The effect of tensile strain on the band structure of Ge is systematically studied, and the deformation potential constants of Ge are derived from the experimental results with relatively high accuracy. / (cont.) Methods to engineer the tensile strain in Ge are demonstrated. Tensile strain in small, selectively grown Ge mesas and stripes with at least one dimension <<10 jim is also investigated. The results are instructive to design selectively grown GeSi EA modulators and photodetectors integrated with Si/SiO2 waveguides. Free-space coupled Ge photodetectors on Si are fabricated with significantly improved performance in the L band (1561-1620nm) of telecommunications as a result of strain engineering. We have demonstrated a selectively grown Ge photodetector on a Si platform with a bandwidth of 8.5 GHz and a high responsivity over a broad wavelength range of 650-1605 nm. Full responsivity was achieved at 0 bias and full bandwidth was obtained at 1 V reverse bias, compatible with the requirement of Si ultra-large scale integrated circuits (ULSI). The GeSi EA modulator is based on Franz-Keldysh (FK) effect, where the electric field shifts the direct band edge of the GeSi material and significantly enhances its absorption coefficient in the weakly absorbing regime. Therefore, by modulating the electric field in the GeSi material, we can modulate the intensity of the light of a certain range of wavelength that passes through the GeSi material. A strain-enhanced FK effect in tensile strained epitaxial Ge material is demonstrated. / (cont.) A waveguide-integrated GeSi EA modulator with 4.8 dB insertion loss, 9.8 dB extinction ratio and a bandwidth >50 GHz has been designed with the material composition and device structure optimized for operations around 1550 nm. The same material and device structure can be also used for waveguide-integrated photodetectors with a responsivity of 1.1 A/W at 1550 nm and a bandwidth >35 GHz. A method to monolithically integrate GeSi modulators, photodetectors and Si/SiO2 waveguides is proposed and the expected performance is evaluated. Waveguide-integrated GeSi photodetectors and EA modulators are fabricated on a standard 180 nm CMOS production line based on the design. We demonstrate a waveguide-integrated GeSi photodetector with a responsivity of 1.0 A/W at 1518 nm and a bandwidth >4.5 GHz, as well as a GeSi EA modulator with an extinction ratio of -0.3 dB. While the device performance of the EA modulator is far from ideal due to fabrication issues, the preliminary results demonstrate the feasibility of the electronic-photonic integration on a Si platform with GeSi modulator and detector devices. The problems in this first device processing are identified, and solutions are proposed and partially tested. The device performance could be greatly enhanced with improved processing technique. / by Jifeng Liu. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1997. / Vita. / Includes bibliographical references (leaves 275-286). / by John Tsen-Tao Chen. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1995. / Includes bibliographical references (leaves 124-136). / by Jonq-Ren Lee. / Ph.D.

Thesis: S.B., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2018. / 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 30-31). / Molecular self-assembly has been an area of recent interest due to its application in a variety of important contexts including drug delivery, regenerative medicine, energy applications, and others. Simultaneously, host-guest chemistry provides a robust and powerful mechanism for inducing switching on the molecular level. In this research, we demonstrate a new platform that combines molecular self-assembly of an amphiphilic chromophore guest molecule with its host molecule counterpart, CB[8] in water. We find that upon addition of CB[8] to a solution of the amphiphilic guest molecule, host-guest complexation occurs and a transition in the morphology of the observed self-assembled nanostructures occurs. Here we present the synthetic route to our amphiphilic guest molecule, in addition to the nanostructural characterization of the supramolecular nanostructures and the host-guest nanostructure by TEM, UV-Vis, and fluorescence spectra. / by Cynthia Tsien Lo. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2006. / Includes bibliographical references (p. 127-137). / The investigation of ordering and phase stability in the ZrO2-Y203 system involves two sets of calculations. The first set of calculations uses the cluster expansion method. A guide to the practical implementation of the cluster expansion outlines methods for defining a goal and choosing structures and clusters that best model the system of interest. The cluster expansion of the yttria stabilized zirconia system considers 447 configurations across the ZrO2-Y203 composition range. The effective cluster interaction for pair clusters show electrostatic repulsion between anions and little interaction between cations. Triplet anion terms largely modify the energy contributions of the pair terms. Separate cluster expansions using structures at single compositions show that cation clusters become more important at high yttria composition. The cluster expansion led to the discovery of three previously unidentified ordered ground state structures at 25, 29, and 33 % Y on the cubic fluorite lattice. The ground state with 33 % Y is stable with respect to the calculated energies of monoclinic ZrO2 and the Y4Zr3012 ground state. The ground states have the common ordering feature of yttrium and vacancies in [1 1 2] chains, and Monte Carlo simulations show that vacancy ordering upon cooling is contingent on cation ordering. / (cont.) The second set of calculations consider three driving forces for order: ionic relaxation, vacancy arrangements, and differences in Zr and cation dopant radii. Bond valence sums of fully relaxed and anion relaxed structures are nearly equal at all compositions. In supercells of ZrO2, the vacancy arrangement of the ground state with 25 % Y is more stable than arrangements maximizing the distance between vacancies or aligning vacancies in [1 1 1]. Comparing the YSZ ground state with structures of the same configuration with scandium replacing yttrium shows different stable phases on the convex hull between cubic ZrO2 and the dopant M203 phase. The change in the stability of the configurations may be a result of cation radius sizes. The factors suggest that the driving forces of phase stability depend on composition. / by Ashley P. Predith. / Ph.D.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2008. / Includes bibliographical references (p. 35). / Polyelectrolyte multilayer thin films are polymer films assembled through a layer-by-layer sequential addition of oppositely charged polymers. The layer-by-layer film assembly technique allows for properties such as film thickness, chemical functionality, and elastic moduli to be easily altered by changing the pH in solution, or the number of bilayers added. This thesis examined the use of polyelectrolyte multilayer films, assembled with poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA), to alter substrata mechanical stiffness, which was used to explore the response of biofilm forming staphylococci epidermidis. The formation of biofilms on medical device surfaces is currently responsible for a significant amount of infections acquired in hospitals. Currently mechanisms responsible for the initial adhesion of bacteria are not completely understood. Previous work completed in the Rubner and Van Vliet labs at MIT suggests a mechanoselective adhesion mechanism in prokaryotes. The existence of a positive correlation between mechanical stiffness and bacterial adhesion, independent of surface roughness or charge density, has already been shown in a non-biofilm forming strain of bacteria. This thesis focused on exploring the role mechanical stiffness substrata has on biofilm forming bacterial adhesion by conducting bacterial assay experiments on polyelectrolyte multilayer films. The results showed no positive correlation between mechanical stiffness and cell adhesion with biofilm forming staphylococcus epidermidis. Also, even under an applied shear force the amount of bacteria adhered on the surface was not affected. In all cases tested, the biofilm forming strain of bacteria was able to adhere and grow successfully. / by Maricela Delgadillo. / S.B.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2008. / Includes bibliographical references (p. 93-96). / A series of case studies on raw materials inventory strategy for both wrought and cast aluminum alloy productions were conducted under recourse-based modeling framework with the explicit considerations of the demand uncertainty compared to the traditional strategy based on point forecast of future demand. The result shows significant economic and environmental benefits by pre-purchasing excess amount of cheaper but dirtier secondary raw materials to hedge the riskier higher-than-expected demand scenario. Further observations demonstrate that factors such as salvage value of residual scraps, cost advantage of secondary materials over primary materials, the degree of the demand uncertainty, etc. all have direct impacts on the hedging behavior. An analytical study on a simplified case scenario suggested a close form expression to well explain the hedging behavior and the impacts of various factors observed in case studies. The thesis then explored the effects of commonality shared by secondary materials in their application in multiple final products. Four propositions were reached. / by Yaoqi Li. / S.M.