Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2018. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 111-129). / Recent trends in renewable energy made silicon based photovoltaics the undisputed leader. Therefore, technologies that enhance, instead of compete with, silicon based solar cells are desirable. One such technology is the use of organic semiconductors and noncrystalline semiconductors for photon up- and down-conversion. However, the understanding of energy transfer in these hybrid systems required to effectively engineer devices is missing. In this thesis, I explore and explain the mechanism of energy transfer between noncrystalline semiconductors and organic semiconductors. Using a combination of density functional calculations, molecular dynamics, and kinetic theory, I have explored the geometry, morphology, electronic structure, and coarse grained kinetics of these system. The result is improved understanding of the transfer mechanism, rate, and the device structure needed for efficient devices. I have also looked at machine learning inspired algorithm for acceleration of density functional theory methods. By training machine learning models on DFT data, a much improved initial guess can be made, greatly accelerating DFT optimizations. Generating and examining this data set also revealed a remarkable degree of structure, that perhaps can be further exploited in the future. / by Nadav Geva. / Ph. D.

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2006. / Includes bibliographical references (p. 104-105). / Lithium Ion (Li-ion) battery technology has the potential to compete with the more matured Nickel Metal Hydride (NiMH) battery technology in the Hybrid Electric Vehicle (HEV) energy storage market as it has higher specific energy and energy. However, in order to improve Li-ion battery technology to fulfill the' HEV energy storage requirements, a very high specific power characteristic is needed to boost its commercial attractiveness. The high specific power characteristic will in turn lead to better a vehicle performances, reduced fuel consumption and emissions. In this thesis, we quantify the fuel savings benefits from HEV, and the marginal value of each W/kg improvement in this battery technology. From the analysis, we conclude that the marginal value of regenerative braking, acceleration, social cost and fuel economy are $13.83, $22.64, $0.9959 and 0.0987 MPG per W/kg per each HEV lifespan respectively. Besides, a variety of start-up companies in various stages of commercialization of these technologies as well as the related intellectual property strategies are also discussed. Finally, suggestion of potential business strategies for licensing and commercializing Li-ion battery technology with respect to HEV energy storage market is presented. / by Seh Kiat Teo. / M.Eng.

Thesis (Ph. D.)--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. / Cataloged from student submitted PDF version of thesis. / Includes bibliographical references (p. 173-184). / Chemomechanical coupling in single eukaryotic animal cells is investigated in the con- text of the attached (substratum-adhered) and the suspended (free-floating) states. These dichotomous configurations determine behavioral differences and commonalities relevant to therapeutic reimplantation of stem cells and to our general under- standing of the cell as an animate material. Analytical, simulation, and experimental techniques are applied to key questions including: (1) How deep can mechanosensitive attached cells "feel" into the adjacent environment? (2) In what manner do suspended cells deform, absent the prominent actomyosin stress fibers that arise upon attachment to a rigid substratum? (3) What explains the remarkable mechanical heterogeney among single cells within a population? (4) Can we leverage putative mechanical markers of useful stem cells to sort them before reimplantation in tissue generation therapies? Attached cells are found to barely detect an underlying rigid base more than 10 micrometers below the surface of a compliant coating. This conclusion, based on ex- tensions to the Boussinesq problem of elasticity theory, is validated by observations of cell morphology on compliant polyacrylamide coatings in a range of thicknesses. Analytical equations are developed for estimating the effective stiffness sensed by a cell atop a compliant layer. We also identify and consider conceptualizations of a "critical thickness," representing the minimum suitable thickness for a specific application. This parameter depends on the cell behavior of interest; the particular case of stem cell culture for paracrine extraction is presented as a case study. Suspended cells are found to exhibit no single characteristic time scale during de- formation; rather, they behave as power-law (or "soft glassy") materials. Here, optical stretching is used as a non-contact technique to show that stress fibers and probe-cell contact are not critical in enabling power-law rheological behavior of cells. Further- more, suspended cell fluidity, as characterized by both the hysteresivity of complex modulus and the power-law exponent of creep compliance, is found to be unaffected by adenosine triphosphate (ATP) depletion, showing that ATP hydrolysis is not the origin of fluidity in cells during deformation. However, ATP depletion does reduce the natural variation in hysteresivity values among cells. This finding, and the finding that changes in the power-law exponent and stiffness of single cells are correlated upon repeated loading, motivates study of how and why these parameters are coupled. To further explore this coupling, chemomechanical cues are applied to cell populations to elucidate the origin of the wide, right-skewed distribution of stiffness values that is consistently observed. The distribution and width are found to be not detectably dependent on cell-probe contact, cell lineage, cell cycle, mechanical perturbation, or fixation by chemical crosslinking. However, ATP depletion again reduces heterogeneity, now in the case of cell stiffness values. It is further found analytically that a postulated Gaussian distribution of power-law exponent values leads naturally to the log-normal distribution of cell stiffness values that is widely observed. Based on these connections, a framework is presented to improve our understanding of the appearance of mechanical heterogeneity in successively more complex assemblies of cell components. Two case studies are described to explore the implications of unavoidable intrinsic variation of cell stiffness in diagnostic and therapeutic applications. Finally, all the single-cell mechanical parameters studied so far (stiffness during creep and recovery, stiffness heterogeneity among cells, and power-law exponents in creep and recovery) are characterized in mesenchymal stem cells during twenty population doublings with the aim of developing a high-throughput sorting tool. How- ever, mechanical and structural changes that are observed in the attached state during this culture time are not observed after cell detachment from the substratum. The absence in the suspended state of these alterations indicates that they manifest themselves through stress fiber arrangement rather than cortical network arrangement. While optical stretching under the present approach does not detect mechanical markers of extended passaging that are correlated with decreased differentiation propensity, the technique is nevertheless found capable of investigating another structural transition: mechanical stiffening over tens of minutes after adherent cells are suspended. This previously unquantified transition is correlated with membrane resorption and reattachment to the cortex as the cell "remodels" after substratum detachment. Together, these quantitative studies and models of attached and suspended cells de- fine the extremes of the extracellular environment while probing mechanisms that con- tribute to cellular chemomechanical response. An integration of the results described above shows that no one existing model can describe cell chemomechanics. However, the cell can be usefully described as a material -- one in which animate mechanisms such as active contraction will generally, but not invariably, need to be considered as augmenting existing viscoelastic theories of inanimate matter. / by John Mapes Maloney. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2006. / Includes bibliographical references (p. 135-143). / Controlling the diameter and chirality of carbon nanotubes to fine tune their electronic band gap will no longer be enough to satisfy the growing list of characteristics that future carbon nanotube applications are starting to require. Controlling their band gap, wall reactivity and mechanical properties is imperative to make them functional. The solution to these challenges is likely to lie in smart defect engineering. Defects of every kind can induce significant changes on the intrinsic properties of carbon nanotubes. In this context, this thesis analyzes the effects of doping single and double walled carbon nanotubes with nitrogen and boron. We describe the synthesis of N-doped single-walled carbon nanotubes (N-SWNTs), that agglomerate in bundles and form long strands (<10cm), via the thermal decomposition of ferrocene/ethanol/benzylamine (FEB) solutions in an Ar atmosphere at 950°C. Using Raman spectroscopy, we noted that as the N content is increased in the starting FEB solution, the growth of large diameter tubes is inhibited. We observed that the relative electrical conductivity of the strands increases with increasing nitrogen concentration. Thermogravimetric analysis (TGA) showed novel features for highly doped tubes, that are related to chemical reactions on N sites. / (cont.) We also carried out resonance Raman studies of the coalescence process of double walled carbon nanotubes in conjunction with high resolution transmission electron microscope (HRTEM) experiments on the same samples, heat treated to a variety of temperatures and either undoped or Boron doped. As the heat treatment temperatures are increased (to 1300°C) a Raman mode related to carbon-carbon chains (w = 1855cm-1) is observed before DWNT coalescence occurs. These chains are expected to be 3-5 atoms long and they are established covalently between adjacent DWNTs. The sp carbon chains trigger nanotube coalescence via a zipper mechanism and the chains disappear once the tubes merge. Other features of the Raman spectra were analyzed as a function of heat treatment with special emphasis on the metallic or semiconducting nature of the layers constituting the DWNTs. DWNTs whose outer wall is metallic tend to interact more with the dopant and their outer tubes are the predominant contributors to the line shape of the G and G' bands. / (cont.) The metallic or semiconducting nature of the layers of the DWNTs does not affect their coalescence temperature. All the experiments and analysis presented in this thesis are the result of a collaborative effort between Professor Dresselhaus' group at MIT and its international collaborators, including Professor Endo's group at Shinshu University, Nagano, Japan, Professors Pimenta's and Jorio's group at the Federal University of Minas Gerais, Belo Horizonte, Brazil, and Professors M. and H. Terrones' group at IPICYT, San Luis Potosi, Mexico. / by Federico Villalpando Paéz. / S.M.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2005. / In title on t.p., double-underscored "p" appears as subscript. / Includes bibliographical references (p. 17). / An amorphous Ni-W alloy matrix was incorporated with W particulate through two types of electrodeposition. The plating bath for the electrodeposition contained nickel sulfate, sodium tungstate, sodium citrate, ammonium chloride, and a variable amount of 1 gm tungsten particulate ranging in concentration from about 5g/L to 15g/L.The first method was electrodeposition with only moderate stirring of the plating bath. The second method had a forced flow of solution on the substrate via a pump. The results showed incorporation in both methods, but the flowed method resulted in more incorporation. The amount of incorporation increased with the amount of particulate in solution until a limit that lies somewhere between 10g/L and 15g/L of particle concentration. At this point, the incorporation became hindered by the excess amount of particulate in solution. It was also shown that an increase of particulate concentration caused more voids in the material, and the flowed method caused less voids than the normal method. A tapering in the amount of incorporation between the substrate side and the surface side of the deposit was observed; the area close to the substrate had a higher incorporation than the area near the surface. Hardness testing showed mechanical property differences through the thickness of the deposit with the area near the substrate being softer than the area near the surface. Compression testing showed an increase in the strain and a decrease in the stress before failure, suggesting an improvement in ductility. / by Donald R. Jenket, II. / S.B.

Thesis: Ph. D. in Electronic Materials, Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2016. / Cataloged from PDF version of thesis. "June 2016." / Includes bibliographical references (pages 163-189). / Germanium and silicon are ideal candidate materials for use as anodes in microbatteries since both are well established in microelectronics and reversibly store large amounts of lithium. However, implementation of either material has been limited by poor cyclability due to the large volumetric changes occurring during cycling. To better understand the mechanical stresses associated with these changes, in situ stress curvature measurements on thin film electrodes were conducted. The effect of the initial electrode structure on electrochemistry and mechanics was investigated by post-deposition annealing of hydrogenated silicon thin films. Compared to as-deposited films, annealed electrodes lithiated at lower potentials during the first cycle and could form Li₁₅Si₄ . Moreover, annealed electrodes underwent large structural changes in the first two cycles compared to as-deposited films, with polycrystalline silicon films showing the largest change. The changes in electrochemistry and mechanical behavior were attributed to the loss of hydrogen and densification of the film. In addition to silicon, stress evolution in lithium-germanium films was also investigated and stresses were found to be roughly one-third those of silicon. Rate testing revealed that germanium electrodes exhibit a smaller loss in capacity at high cycling rates than silicon. Cycling below 100mV resulted in crystalline Li₁₅Ge₄ formation which appeared as a tensile peak in the stress-capacity plots. Extended cycling of uncoated electrodes resulted in an irreversible reduction of stress but no loss in capacity, an outcome associated with the thin film fracturing while remaining adherent to the substrate. The reduced plastic flow stresses observed in lithium-germanium and their weak dependence on cycling rate may explain why germanium offers improved cyclability and reduced rate sensitivity compared to silicon. In addition to uncoated electrodes, lithium phosphorous oxynitride (LiPON) coated electrodes were also examined. By coating silicon and germanium thin films with LiPON, mechanical degradation (i.e. crack and island formation) and chemical degradation (i.e. reduction in solid electrolyte interphase formation) processes were strongly suppressed. The improvement in mechanical and electrochemical stability enabled more detailed studies of lithium-silicon and lithium-germanium alloying, including the kinetics of phase formation and dissolution (e.g. of Li₁₅Si₄ and Li₁₅Ge₄). / by Ahmed Al-Obeidi. / Ph. D. in Electronic Materials

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1994. / Includes bibliographical references (leaves 86-88). / by Rita Gupta. / M.S.

Thesis: S.B., Massachusetts Institute of Technology, Department of Materials Science and Engineering, June 2010. / "May 2009." Page 47 blank. Cataloged from PDF version of thesis. / Includes bibliographical references (pages 28-29). / The present study investigates the naturally occurring interface between bone and tendon using scanning electron microscopy. The micrographs revealed a cartilaginous layer, 100 to 400 [mu]m thick apposing bone, that contained cells varying in size and shape as a function of their location in this cartilaginous layer. Further investigation is required to conclude whether these cells are undergoing further differentiation during development of this graded layer. This study found the interface between bone and the cartilaginous layer to be interdigitated, which may explain why injuries at the bone-tendon interface are comparatively rare. Also, the cartilaginous layer was revealed to be substantially mineralized. A somewhat higher concentration of calcium and phosphorus was observed near the interface with the apposing bone that gradually diminished into the cartilaginous layer. These findings support the four zone description of the bone-tendon interface established by others using histological methods. However, further research is suggested to resolve other questions about the observed sub-micrometer morphologies of the bone-tendon interface. / by Willie Mae Reese. / S.B.

Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1989. / Includes bibliographical references (leaves 222-227). / by Brian William Sheldon. / Sc.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2007. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Includes bibliographical references. / Organic optoelectronic devices are appealing for low-performance applications on very low cost and flexible substrates, due to their low-temperature processing. However, it still remains a challenge to develop suitable fabrication techniques to pattern organic thin films on low-cost, large-area substrates. The two techniques used commercially are inkjet printing of polymers, which limits the morphology and performance of devices, and shadow-masking of vacuum sublimation for small molecule materials, which is not scalable to large-area substrates. In this thesis, we investigate the use of MicroElectroMechanical Systems (MEMS) to provide new ways of patterning organic materials deposited by an evaporative process. We present the design, fabrication, modeling and characterization of two generations of micromachined printheads developed to expand the possibilities of printing of organic optoelectronics. The design and fabrication of a compact electrostatic actuator enabling the first generation of printhead is first presented. It is then used to actuate a microshutter, and modulate the flux of evaporated organic materials in a vacuum chamber. We prove the feasibility of evaporative printing of small molecular organic materials at resolutions of the order of 800 dpi with high-throughput on large areas. / (cont.) We demonstrate that MicroElectroMechanical Systems can be used to pattern organic thin films in a way that combines the advantages of ink-jet printing and thermal evaporation. We also present the design and fabrication of a microevaporator for molecular organics, and show its suitability for the ambient printing of devices on low-cost substrates, without the limitations of ink-jet printing due to the drying of solvent on the substrate. We demonstrate the feasibility of using an array of pores in a membrane to capture molecular organic materials delivered by a solvent and an integrated microheater to release them by evaporation onto a substrate. This second generation of printhead enables evaporative printing of organic materials at ambient pressure. This thesis also provides a study of the failure of thin film platinum heaters used in the second generation printheads. We study the effect of current level, temperature, presence of a membrane, anneal conditions, and adhesion layer thickness on the failure of the heaters. / by Valérie Leblanc. / Ph.D.