Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1998. / Includes bibliographical references (p. 235-245). / by Benjamin M. Wu. / Ph.D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2016. / "September 2016." Cataloged from student-submitted PDF version of thesis. / Includes bibliographical references (pages 155-171). / Kinetic Monte Carlo (Kc) methods have the potential to extend the accessible timescales of off-lattice atomistic simulations beyond the limits of molecular dynamics by making use of transition state theory and parallelization. However, it is a challenge to identify a complete catalog of events accessible to an off-lattice system in order to accurately calculate the residence time for Kc. Possible approaches to some of the key steps needed to address this problem are developed in this thesis. After validating these methods in the study of vacancy diffusion, we implemented our off-lattice Kc method to study the kinetic behavior of the [Sigma]5 (210) grain boundary (GB) in copper. We found that the activation energy associated with intrinsic diffusion at this GB is between the activation energies of interstitial diffusion and vacancy diffusion. We have also measured GB mobility in this system and found the activation energy of GB migration to be similar to that of bulk diffusion. For comparison, we have performed a molecular dynamics study of this target GB and obtained diffusivity and mobility estimates that are sufficiently similar to our Kc results at high temperatures. At low temperatures, the molecular dynamics simulations did not yield meaningful predictions. The results of this case study indicate that the off-lattice Kc method developed herein may provide a means to study GB kinetic properties under conditions and timescales that were previously inaccessible. Towards the end of developing predictive relationships to describe GB kinetic properties, we have begun to assess whether the normalized ground state residence time of a GB is a good predictor of kinetic behavior by analyzing several low-CSL GBs. We see a clear relationship between normalized ground state residence time and kinetic properties for the GBs considered so far. A more thorough investigation will be required to establish whether or not these preliminary findings indicate a more general relationship. / by Kathleen Carmody Alexander. / Ph. D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2003. / Vita. / Includes bibliographical references. / Diblock copolymers incorporating liquid crystallinity via a lateral attachment of mesogenic species to a flexible backbone were studied for their microstructure-property relationships. Two families of materials were studied, distinguished primarily by the method of attachment of the mesogen to the polymer. In the first, azobenzene based mesogens were covalently tethered to the isoprene blocks of a poly(styrene)-block-poly(isoprene), P(S-b-ILC), series of diblock copolymers. In the second family of polymers, hydrogen bonding was used to complex bi-phenyl based mesogens to the acrylic acid units of a poly(styrene)-block-poly(acrylic acid), P(S-b-AA) diblock copolymer. The morphology of the P(S-b-ILC) system was characterized as a function of composition, and clear correlations between the microphase separated structure and the thermal properties of the liquid crystalline mesophase were observed and accounted for. Control of the hierarchical structure in these materials was pursued and achieved independently via surface epitaxy, oscillatory shear and, for the first time in this class of materials, via magnetic fields. It was found that the morphology adopted by the material under the external fields is strongly dependent on the orientation of the liquid crystalline mesophase with respect to the inter-material dividing surfaces present due to the microstructure. Oscillatory shear of a P(S-b-ILC) resulted in the first observation of a novel transverse cylindrical microdomain morphology in one case. The investigation of hydrogen-bonded side-group liquid crystalline block copolymers based on P(S-b-AA) followed a screening of several other candidate host diblock-mesogen pairs. The structure and thermal properties of a model P(S-b-AA) diblock and a homopolymer acrylic acid complexed with mesogens were studied and characterized as a function of composition. A high molecular weight analogue, based on poly(styrene)-block-poly(methacrylic acid), P(S-b-MAA), was successfully / (cont.) complexed with mesogens to produce a lamellae- forming liquid crystalline diblock copolymer with a very large repeat distance. The material exhibited a photonic band gap with a stop-band in the visible. It is the first example of a self-assembled coil block-LC block copolymer photonic crystal. The material was characterized optically and changes in temperature were used to reversibly manipulate the efficiency and location of the stop-band. The optical properties of the polymer as a function of temperature were correlated to changes in the order parameter of the liquid crystalline phase, observed as a function of temperature. / by Chinedum Osuji. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2005. / Includes bibliographical references (leaves 77-81). / Wafer-level, thermocompression bonding is a promising technique for microelectromechanical systems (MEMS) packaging. The process is a form of solid-state joining and requires the simultaneous application of temperature and pressure to wafers patterned with metallic thin films in order to bring the mating surfaces into atomic proximity. The quality of the resulting bond is critically dependent on the interaction between flatness deviations that range from wafer bow to surface roughness, the thin film properties and the process parameters and tooling used to achieve the bonds. Hitherto there has been limited modeling applied to understand the relative contributions of these effects. This thesis addresses the above issue through the development of a mechanics-based framework that allows the effect of flatness deviations to be assessed for typical geometries and process conditions. The strain energy release rate associated with the elastic deformation required to overcome wafer bow is calculated. A contact yield criterion is used to examine the pressure and temperature conditions required to flatten surface roughness asperities in order to achieve bonding over the full apparent area. The results are compared to experimental data of bond yield and toughness obtained from four-point bend delamination testing, microscopic observations and measurements on the fractured surfaces. Conclusions from the modeling and experiments indicate that wafer bow has negligible effect on determining the variability of bond quality and that the well-bonded area is increased with increasing bonding pressure. / (cont.) The enhanced understanding of the underlying deformation mechanisms allows for a better controlled trade-off between the bonding pressure and temperature. / by Konstantinos Stamoulis. / S.M.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1997. / Includes bibliographical references (p. 41-42). / by Erin Baker Lavik. / M.S.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1998. / Includes bibliographical references (p. 92). / by Thomas Besson. / M.S.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 34-35). / Previous studies of nanoporous gold have found that, during the coarsening process, the genus per characteristic volume of nanoporous gold has remained constant. Using a rolling-ball type algorithm, in which a test probe rolls over the surface to identify atoms, several test structures and a small-scale nanoporous structure were meshed. The genus was then calculated for each of these meshed structures. It was found that an algorithm that accounts for periodic boundary conditions is required for an accurate genus calculation. / by Ryan Rosario. / S.B.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2013. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 31-32). / Nanogap devices have applications in single molecule sensing and single molecule transistors. Nanogap devices comprised of a gold nanowire with a nanoscale gap containing C₆₀ were fabricated using electromigration on a silicon substrate. Raman spectra were obtained for various features of this device in order to detect the presence of C6o and study its electronic properties. The 532 nm laser source showed Raman peaks at 300,522,930-980, 1570, 1900 and 2150 cm-¹ and the 632 nm laser source showed Raman peaks at 300, 522, 930-980, 1460, and 2124 cm-¹. The device feature (gold, C₆₀, silicon or combination thereof) responsible these peaks' presence in Raman spectra was determined. There was peak broadening present at long wavelengths for gold features in the Raman spectra taken using the 532 nm laser and for spectra using the 632 nm laser when C₆₀ is present in high concentrations. This is believed to be an effect of the creation of defects in the C60 lattice due to the presence of oxygen, resulting in Frenkel excitons becoming trapped. When the Frenkel excitons recombine, they emit light causing the photoluminescence at longer wavelengths. Peak broadening was also studied in devices comprised of a gold nanoparticle substrate with C60 spun cast onto the surface. Raman spectra of nanoparticle and nanogap devices shared similar features. / by Erin Perry. / 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 (pages 35-36). / As materials consumption increases globally, minimizing the end-of-life impact of solid waste has become a critical challenge. Cost-effective methods of quantifying and tracking municipal solid waste contents and disposal processes are necessary to drive and track increases in material recovery and recycling. This work presents an algorithm for estimating the average quantity and composition of municipal waste produced by individual locations. Mass fraction confidence intervals for different types of waste were calculated from data collected by sorting and weighing waste samples from municipal sites. This algorithm recognizes the compositional nature of mass fraction waste data. The algorithm developed in this work also evaluated the value of additional waste samples in refining mass fraction confidence intervals. Additionally, a greenhouse gas emissions model compared carbon dioxide emissions for different disposal methods of waste, in particular landfilling and recycling, based on the waste stream. This allowed for identification of recycling opportunities based on carbon dioxide emission savings from offsetting the need for primary materials extraction. Casework was conduced with this methodology using site-specific waste audit data from industry. The waste streams and carbon dioxide emissions of three categories of municipal waste producers, retail, commercial, and industrial, were compared. Paper and plastic products, whose mass fraction averages ranged from 40% to 52% and 26% to 29%, respectively, dominated the waste streams of these three industries. Average carbon dioxide emissions in each of these three industries ranged from 2.18 kg of CO₂ to 2.5 kg of CO₂ per kilogram of waste thrown away. On average, Americans throw away about 2 kilograms per person per day of solid waste. / by Jasper Z. Lienhard. / S.B.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2016. / 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 93-98). / Electrochemical energy storage and conversion devices are important for the application of sustainable clean energies in the next decades. However, the slow kinetics of oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) lead to great energy loss in many electrochemical energy devices, including polymer electrolyte membrane fuel cells (PEMFCs), water splitting electrolyzers, and rechargeable metal-air batteries, which hampers the development of new-energy applications such as electric vehicles. To increase the energy efficiency of ORR and OER processes, various catalysts have been studied for oxygen electrocatalysis, but they are still not active enough or not stable enough in developing commercial friendly electrochemical devices. In this work, systematic studies have been applied on two catalyst systems: Pt-metal (Pt-M) alloys for ORR and perovskite oxides for OER. The combination of electrochemical characterizations with transmission electron microscopy (TEM) techniques provides deeper insights on how the basic physical and chemical properties could influence the stability and activity of the catalysts. For Pt-M ORR catalysts, it is found that using transition metal with more positive dissolution potential or forming protective Pt-rich shell by mild acid treatment can improve their stability in acid electrolyte. While for perovskite oxide OER catalysts, it is found that a closer distance between O 2p-band and Fermi level leads to higher activity but lower stability at pH 7, due to the activation of lattice oxygen sites. Moreover, with the help of environmental TEM techniques, structural oscillations are observed on perovskite oxides in the presence of water and electron radiation, caused by the oxygen evolution after water uptake into the oxide lattice. Such structural oscillation is greatly suppressed if the formation and mobility of lattice oxygen vacancy is hampered. The various new activity and stability descriptors for oxygen electrocatalysis found in this work not only provided practical guidelines for designing new ORR or OER catalysts, but also improved our fundamental understandings of the interactions between catalysts and electrolyte. / by Binghong Han. / Ph. D.