Thesis: S.B., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2010. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 45-46). / Metal-organic chemical vapor deposition (MOCVD) was used to grow InAsP graded layers and AlAs/GaAs superlattices for materials studies related to thermophotovoltaics and thermoelectrics respectively. High resolution x-ray diffraction (HRXRD) was used to determine the As concentration in each of the InAsP layers. Arsenic concentration was found to vary linearly with the percentage of AsH3 in the reactive gas flow up to 60 % deposited, and had an asymptotic relationship for higher incorporated concentrations. Higher growth temperatures reduced As incorporation. Transmission electron microscopy (TEM) images were used to determine layer thicknesses. The growth rate of InAsP layers was found to be independent of growth temperature and the percentage of As. Superlattice samples with 0 %, 5 %, 10 %, and 20 % variations in the superlattice period were grown via MOCVD and analyzed using HRXRD. The intensities of the satellite peaks were found to decrease and broaden with increasing variation in the period length and disappeared completely in samples with up to 10 % variation. Thermal conductivity measurements performed using an optical pump-probe technique showed lower thermal conductivities for samples with greater variation. The irregularity of the superlattice period is believed to enhance the structure's ability to impede phonon propagation. / by Brian K . Baum. / S.B.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 51-53). / Two classes of drugs, antiretrovirals and antibiotics, could benefit greatly from delivery through microneedles. Microneedles (MN) offer an increase in efficacy for these drugs by providing delivery to the lymphatic system through the skin, thus avoiding first pass metabolism and allowing more focused delivery to specific viral or bacterial reservoirs. Furthermore, microneedles present other advantages in the form of the ability to be self-administered, tunable controlled release, and painless administration. Saquinavir and Ciprofloxacin, an antiretroviral and an antibiotic respectively, were chosen for their optimal properties, including bioavailability, half-life, and dosage. Saquinavir was encapsulated in the organic phase of biodegradable poly(lactide-co-glycolide) microparticles (MP) synthesized through a double emulsion. Similarly, Ciprofloxacin was encapsulated in the aqueous phase of the microparticles. In addition, Ciprofloxacin microcrystals were synthesized. The microparticles and microcrystals were then loaded into molded polymer microneedles in a poly-acrylic acid (PAA) matrix. Standard curves were created for the two drugs from known concentrations and used to show the drug loading in the microparticles and microneedles. The Saquinavir microparticles showed a maximum loading of 1.35% the mass of particles and the Ciprofloxacin microparticles showed a maximum loading of 0.197%. The Saquinavir microparticle microneedles had a maximum loading of 11.95 [mu]g of Saquinavir per 1 cm² array and the Ciprofloxacin microparticle microneedles had a maximum loading of .41 [mu]g of Ciprofloxacin per 1 cm² array. The Ciprofloxacin microcrystal microneedlees had a maximum loading of 165 [mu]g per 1 cm² array. Analysis based on insulin delivery through microneedles showed these loadings to be too low to create the sufficient minimum drug concentration in plasma. However, there exist multiple strategies to increase the loading of the drugs in the microneedles. These results proved promising for the use of microneedles for the delivery of antiretroviral and antibiotic drugs. / by Zachary Jason Stauber. / S.B.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2001. / Includes bibliographical references (p. 76-79). / Mechanical stress in thin films is an important reliability issue in microelectronic devices and systems. The presence of large stresses can lead to the formation of defects that can cause device failure. The ability to control the magnitude of stress during film formation is, therefore, crucial to the fabrication of defect-free and reliable electronic devices and systems. However, the origin of stress in thin films is still a subject of intense debate. The development of a detailed understanding of the origin of stress hinges on our ability to make accurate stress measurements during and after film deposition. To this end, two novel MEMS structures were developed to measure the stress of thin films deposited using chemical vapor deposition (CVD). Buckled SOI membranes were designed and fabricated for the measurement of the stress in thin films deposited on them. A simple analytic model was developed and calibrated to assess the pre-deposition and post-deposition buckling of the structures. By measuring the changes in mechanical responses upon film deposition, it was successfully demonstrated that stress in thin films can be accurately measured. In particular, the stresses in evaporated chromium films measured using the SOI membranes and the curvature method were found to agree to within 5%. Stress pointers were designed and fabricated for in-situ stress measurements of CVD thin films. The design was based on mechanically amplified rotation and the novel concept of "footprinting". Stress is recorded during film formation in the form of beam rotation, which is also dependent on film thickness. As a result, stress can be measured as a function of film thickness in post-deposition analyses, without using real-time measurements during deposition. The fabricated structures were found to bend down and stick to the substrate. PECVD films were found to deposit non-uniformly underneath the beams, thereby complicating the mechanical responses of the stress pointers. A new and improved design is proposed. / by Yu-Hin F. Lau. / S.M.

Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1987. / Vita. / Bibliography: leaves 243-250. / by Dennis Michael Haezebrouck. / Sc.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2011. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 103-112). / Graphene nanoribbons (GNRs) are quasi one dimensional structures which have unique transport properties, and have a potential to open a bandgap at small ribbon widths. They have been extensively studied in recent years due to their high potential for future electronic and spintronic device applications. The edge structures - including the edge roughness and chirality - dramatically affect the transport, electronic, and magnetic properties of GNRs, and are of the critical importance. We have developed an efficient way of modifying the edges structures, to produce atomically smooth zigzag and armchair edges by using insitu TEM with a controlled bias. This work provides us with many opportunities for both fundamental studies and for future applications. I also report the use of either furnace heating or Joule heating to pacify the exposed graphene edges by loop formation in the graphitic nanoribbons. The edge energy minimization process involves the formation of loops between adjacent graphene layers. An estimation of the temperature during in-situ Joule heating is also reported based on the melting and evaporation of Pt nanoparticles. In this thesis work, I have also investigated the morphological and electronic properties of GNRs grown by chemical vapor deposition. Our results suggest that the GNRs have a surprisingly high crystallinity and a clean surface. Both folded and open edges are observed in GNRs. Atomic resolution scanning tunneling microscopy (STM) images were obtained on the folded layer and the bottom layer of the GNR, which enables clear identification of the chirality for both layers. We have also studied the electronic properties of the GNRs using low temperature scanning tunneling spectroscopy (STS). Our findings suggest that edges states exist at GNR edges which are dependent on the chiral angles of the GNRs. / by Xiaoting Jia. / Ph.D.

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, February 2011. / "February 2011." Cataloged from PDF version of thesis. / Includes bibliographical references (p. 69-80). / Enormous effort has been devoted to the development of a vaccine against human immunodeficiency virus (HIV). The purpose of this paper is to evaluate the technological and economical aspects of a potential vaccine designed by Professor Irvine's group. Lipid-enveloped virion-sized nano-particles with a biodegradable polymer core are used as synthetic pathogens to deliver HIV specific antigens and adjuvants. The nano-particles are designed to display multiple copies of the antigen on their surfaces and to elicit humoral immunity response. Topics such as patent ability, obtaining an FDA licensure, storage, cost of manufacturing, and supply of the vaccine are explored. A business model for commercialization of the vaccine is outlined, and some possible future business opportunities for the nano-particles are discussed. / by Pantea Khodami. / M.Eng.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2005. / Includes bibliographical references (p. 57-59). / This study explores the possibility of extending the Ph.D. work of Yan Xu on copper-tin alloys (University of Pennsylvania, 1999) to model stress accelerated grain boundary oxidation (SAGBO) in INCOLOY alloy 908. The steady state model involves the embrittlement along the grain boundary due to oxygen diffusion with the concentration gradient and the stress field ahead of the crack tip as the driving forces. As oxygen forms brittle phases with the segregates in the grain boundary, it reduces the cohesive strength of the grain boundary and causes intergranular cracking in the material. The extensions to the original model include (1) dependence of oxygen concentration at crack tips on oxygen partial pressure and (2) a new creep law specific to nickel-based superalloys. While the steady state model correctly indicates temperature as one of three leading factors in SAGBO, it fails to capture the effects of the two remaining factors: applied loading and oxygen partial pressure. / by Chaiyod Soontrapa. / S.M.

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2005. / Includes bibliographical references (leaves 46-47). / Photovoltaic cells based on organic semiconducting materials have the potential to compete with the more mature crystalline and thin film based photovoltaic technologies in the future primarily due to the expectation of significantly reduced manufacturing costs. Stabilized power conversion efficiencies of organic photovoltaics are still well below those of crystalline Si photovoltaics, however a continuous, high throughput, roll-to-roll manufacturing process involving low temperature deposition or printing techniques is expected to partially account for their reduced efficiency and boost their commercial attractiveness. In addition, organic photovoltaics are flexible, light weight, and not fragile which makes them particularly suitable for transportation and portable electronics applications. Four organic photovoltaic technologies as well as the advantages and setbacks of each are described including Graetzel (wet) cells, blended photovoltaics, asymmetric tandem cells with hybrid planar-mixed molecular heterojunctions, and external antenna photovoltaics. A variety of start-up companies in various stages of commercialization of these technologies as well as the intellectual property related to these technologies is also discussed. / (cont.) A simplified cost model is presented to quantitatively estimate the possible cost reductions that continuous roll-to-roll production could entail for three different scenarios. Finally, a discussion of potential business strategies for licensing and commercializing organic photovoltaics is presented. / by Jonathan Barr. / M.Eng.

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 110-121). / Nature provides many examples of flexible armor systems which may serve as a source of inspiration for materials scientists and engineers. This thesis explores multiscale material and morphological design principles of the shells of chitons (Mollusca: Polyplacophora). The chiton shell consists of eight plates encircled by a structure known as a girdle, which is often covered by scales. The shell provides protection while permitting the flexibility needed to conform to rough substrata, as well as to roll defensively into ball-like conformation to cover its soft ventral side. In typical flat conformations, X-ray micro-computed tomography revealed that the shape and imbrication of the plates results in an overall continuous curvature and constant armor thickness. However, in defensive postures, vulnerable regions exist between the plates due to decreases in plate overlap. In the peripheral scale armor, gradients in the size and overlap of the scales control local levels of flexibility and protection. Scale armor prototypes inspired by the girdle scales were fabricated via multi-material 3D printing. Bending tests demonstrated that the stiffness of the bio-inspired scale armor is highly anisotropic. Remarkably, in certain species, a visual system is integrated within the shell plates. The system contains hundreds of lens eyes, which were found to be capable to forming images. Ray-trace simulations of individual eyes determined that they have a resolution of ~9°, which is consistent with prior behavioral experiments. Unlike the protein-based lenses of most animal eyes, the lenses of chitons, like their shells, are principally composed of aragonite. Chitons are able to tailor the local shape, crystallography, and interfaces of aragonite to achieve a multifunctional armor. However, the integration of lens eyes was found to locally decrease penetration resistance, suggesting a materials-level trade-off between protection and sensation. / by Matthew James Connors. / Ph. D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2007. / Includes bibliographical references (p. 193-199). / Computational methods, including density functional theory and the cluster expansion formalism, are used to study materials for hydrogen storage. The storage of molecular hydrogen in the metal-organic framework with formula unit Zn40(02C-C6H6-COD3 is considered. It is predicted that hydrogen adsorbs at five sites near the metal-oxide cluster, in good agreement with recent experimental data. It is also shown that the metal-oxide cluster affects the electronic structure of the organic linker, qualitatively affecting the way in which hydrogen binds to the linker. Lithium imide (Li2NH), a material present in several systems being considered for atomic hydrogen storage, is extensively investigated. A variation of the cluster expansion formalism that accounts for continuous bond orientations is developed to search for the ground state structure of this material, and a structure with a calculated energy lower than any known is found. Two additional discrete cluster expansions are used to predict that the experimentally observed phase of lithium imide is metastable at temperatures below approximately 200 K and stabilized primarily by vibrational entropy at higher temperatures. A new structure for this low-temperature phase that agrees well with experimental data is proposed. A method to improve the predictive power of cluster expansions through the application of statistical learning theory is developed, as are related algorithms. The Bayesian approach to regularization is used to show that by taking advantage of the prior expectation that cluster expansions are local, the convergence and prediction properties of cluster expansions can be significantly improved. / (cont.) A variety of methods to generate cluster expansions are evaluated on three different binary systems. It is suggested that a good method to generate cluster expansions is to use a prior distribution that penalizes the ECI for larger clusters more and has few parameters. It is shown that the generalized cross-validation score can be an efficient and effective substitute for the leave-one-out cross-validation score when searching for a good set of parameters for the prior distribution. Finally it is shown that the Bayesian approach can also be used to improve the convergence and prediction properties of cluster expansions for surfaces, nanowires, nanoparticles, and certain defects. / by Timothy K. Mueller. / Ph.D.