Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1985. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Vita. / Bibliography: leaves 123-129. / by Barbara Poggiali. / M.S.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2009. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 202-211). / The rapid growing needs for high data transmission bandwidth challenge the metal interconnection technology in every area from chip-level interconnects to long distance communication. Silicon photonics is an ideal platform for the implementation of optical interconnection capable of high bandwidth and low power consumption by integrating electronic and photonic devices on silicon. Many optical components in silicon photonics have been extensively studied, among which a silicon-based laser is arguably the most challenging element. This thesis mainly focuses on using engineered germanium as the optically active material for silicon-based light emitters with many potential benefits: Si-CMOS compatibility (both material and processing), electrical injection capability, and direct gap emission at technologically important 1.55 pm telecommunication band. Tensile-strained n+ germanium is capable of behaving like a direct band gap material owing to the direct band gap shrinkage upon tensile strain and the state-filling in the indirect L valleys with extrinsic electrons from n-type dopants. Our theoretical calculation using a direct band-to-band transition model has shown great benefit of tensile strain and n-type doping on the direct gap optical gain characteristics. By considering free carrier absorption which dominates the optical loss we have proven net gain can be achieved in 0.25% tensile-strained Ge with n-type doping concentration in a range of 1019 to mid-1020 cm-3. The injection threshold of the net gain is about 1018 cm-3 which can readily be achieved with either optical pumping or electrical pumping. / (cont.) The net gain is in favor of the raise of temperature in a large injection range (threshold to mid-1019 cm-3) because of the increased number of high energy electrons in the direct F valley contributing to the direct band-to-band radiative recombination. We have successfully grown single crystalline germanium epitaxially on silicon with a two-step approach. Tensile strain between 0.2% and 0.25% is formed in germanium upon cooling from high growth temperature (or post-growth annealing temperature) to room temperature because of the larger thermal expansion coefficient of germanium compared to that of silicon. Phosphorus are in situ doped in germanium as n-type dopants during the epitaxial growth. By carefully adjusting the growth condition, we have obtained active doping concentration as high as 2 x 1019 cm-3. An in situ doping model built by considering the transportation processes and the reactions of phosphorus-containing species well explains the temperature dependence of the doping concentration. The deviation from the model while analyzing the influence of other growth parameters indicates possible compensation of the dopants. We used photoluminescence (PL) measurement to study to the optical properties of tensile-strained n+ germanium. Room temperature PL was observed from the epitaxial Geon-Si films near the direct gap wavelength of 1600nm. The direct gap PL spectrum exhibits Ge direct band-to-band optical transition properties. The direct gap PL intensity increases with n-type doping concentration as a result of the indirect valley state filling effect which increases the Fermi level leading to higher excited electron density in the direct F valley. / (cont.) The direct gap PL intensity also increases with temperature because of the increased number of high energy direct F valley electrons thermally activated from the indirect L valleys. This effect make germanium light emission robust to inevitable heating effects during operation in practice. The "unusual" n-type doping and temperature dependences of PL are unique properties of the direct gap emission from indirect bandgap Ge. There effects are predicted by our theory, and the observation of these effect in experiments is a strong evidence of validity of the theory. In order to study the electrical injection in Ge, we fabricated Si/Ge/Si heterojunction light emitting diodes (LEDs). Room temperature direct gap electroluminescence (EL) are observed from these diodes. It is the first observation of EL from Ge. The direct gap EL spectrum matches the PL spectrum underlying the same injection mechanism in both electrical pumping and optical pumping. The direct gap EL intensity increases superlinearly with injection current because of the raised quasi Fermi level leading to the increased fraction of the injected electrons in the direct F valley. The internal quantum efficiency of the LEDs is on the order of 10-3 consistent with the finite-element simulation results. This EL efficiency can be improved to 10-1 if doping germanium active region with n-type. The design of n+Ge based heterojunction diodes has been simulated, and an optimal design has been proposed based on the simulation. We used pump-probe spectroscopy to measure material gain of the tensile-strained n+ germanium. / (cont.) We have observed an optical bleaching effect, the reduction of absorption under pumping and the prelude of optical gain, above the direct band gap energy from the engineered Ge. The population inversion factor increases with the n-type doping concentration in Ge, as predicted by the theory. By increasing the injection level using a Ge micro-mesa structure carrier confinement, we have successfully demonstrated the net gain, i.e. population inversion. A peak gain of 50 ± 25 cm-1 at 1605 nm has been obtained from the experiment. It is the first report of observing net gain from germanium. / by Xiaochen Sun. / Ph.D.

Thesis: S.B., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2011. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 59-60). / In nature, aquatic birds can interact with water without their feathers being easily wetted; some species dive tens of meters and emerge to spread their wings to dry. In past studies attempting to connect such ecological behavior and feather structure, the typical approach of microscopy has demonstrated the difficulty in characterizing specimens as delicate and complex as feathers by visual techniques alone. In this work, the question was addressed of how various species balance the wettability problem with the need to dive to various depths or to remain on or near the water surface as dictated by their feeding habits. Texture of wing feathers from six different species of aquatic birds was characterized by measuring contact angles and applying the previously developed framework of the effective spacing ratio, D*, and robustness factor, A*, according to the Cassie-Baxter relation for composite interfaces. This "effective microscopy" technique was successfully employed to assess the wettability and robustness of bird feather textures. The observable water-related behaviors of diving, wing-spreading, shallow foraging, and dabbling for the species studied were explained as partly determined by feather structure, exhibiting effective- D* analysis as an adequate technique for characterizing complex, textured surfaces, fabricated or natural. / by Jesus O. Guardado. / S.B.

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2009. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 79-81). / Flash memory, the current leading technology for non-volatile memory (NVM), is projected by many to run obsolete in the face of future miniaturization trend in the semiconductor devices due to some of its technical limitations. Several different technologies have been developed in attempt for replacing Flash memory as the most dominant NVM technology; none of which seems to indicate significant success at the moment. Among these technologies is RRAM (Resistive Random Access Memory), a novel type of memory technology which has only recently emerged to join the race. The underlying principle of an RRAM device is based on the colossal electroresistance (CER) effect, i.e. the resistance switching behavior upon application of voltage of varying polarity and/or magnitude. This thesis aims to investigate the CER effect and how it can be designed to be a non-volatile memory as well as other novel application, e.g. memristor. The various technical aspects pertaining to this phenomenon, including the materials and the physical basis, are explored and analyzed. As a complementary to that, the market potential of the RRAM technology is also assessed. This includes the market study of memory industry, the current intellectual property (IP) landscape and some of the relevant business strategies. The production strategy (i.e. the production cost, initial investment, and pricing strategy) is then derived from the technical and market analysis evaluated earlier and with using some reasonable assumptions. / by Aulia Tegar Wicaksono. / M.Eng.

Thesis: S.M., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2015. / 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. Page 61 blank. / Includes bibliographical references (pages 59-60). / Currently, the synthesis of semiconducting or metal microspheres has occurred via top-down approaches, such as through ball milling or e-beam lithography, or via bottom-up approaches, such as colloidal chemistry. Top-down approaches often generate a wide particle size distribution, while bottom up approaches often involve toxic and sometimes rather expensive precursors to generate the particles. By utilizing a phenomenon known as axial thermal capillary instability, highly homogeneous semiconducting and metal microspheres are able to be generated inside of a silica fiber in a simple, inexpensive, and non-toxic top-down approach. Further applications of these in-fiber microspheres, such as the band gap shift due to localized pressure on Germanium microspheres, and terahertz plasmonic resonances on Silver microspheres, were also studied. / by Tara Sarathi. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1997. / Includes bibliographical references (leaves 226-232). / by Rizwan Mahmood Gul. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1985. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Vita. / Bibliography: leaves 150-154. / by Eric Peter Kvam. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2009. / Includes bibliographical references (p. 185-192). / The Lifshitz formulation is a quantum electrodynamic, first principals formulation used to determine van der Waals - London dispersion interactions in the continuum limit. It has many advantages over crude, pairwise potential models. Most notably, it can solve for complex interactions (e.g. repulsive and multi-body effects) and determine the vdW-Ld interaction magnitude and sign a priori from the optical properties rather than by parameterization. Single wall carbon nanotubes (SWCNTs) represent an ideal class of materials to study vdW-Ld interactions because very small changes in their geometrical construction, via the chirality vector [n,m], can result in vastly different electronic and optical properties. These chirality-dependent optical properties ultimately lead to experimentally exploitable vdW-Ld interactions, which already exist in the literature.Proper use of the Lifshitz formulation requires 1) An analytical extension for the geometry being studied 2) The optical properties of all materials present and 3) A method to incorporate spatially varying properties. This infrastructure needed to be developed to study the vdW-Ld interactions of SWCNTs systems because they were unavailable at the onset. The biggest shortfall was the lack of the E" optical properties out to 30+ eV. / (cont.) This was solved by using an ab initio method to obtain this data for 63 SWCNTs and a few MWCNTs. The results showed a clear chirality AND direction dependence that is unique to each [n,m]. Lifshitz and spectral mixing formulations were then derived and introduced respectively for obtaining accurate Hamaker coefficients and vdW-Ld total energies for these optically anisotropic SWCNTs at both the near and far-limits. With the infrastructure in place, it was now possible to study the trends and breakdowns over a large population as a function of SWCNT class and chirality. A thorough analysis of all these properties at all levels of abstraction yielded a new classification system specific to the vdW-Ld properties of SWCNTs. Additionally, the use of this data and an understanding of the qualitative trends makes it straightforward to design experiments that target, trap, and/or separate specific SWCNTs as a function of SWCNT class, radius, etc. / by Richard F. Rajter. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2009. / Cataloged from PDF version of thesis. / Includes bibliographical references. / The main goal of this thesis is to study the coupled interactions between chemically and mechanically characterized materials and cells that are relevant to microvascular physiology and pathology. In particular, the mechanical characterization of cell surface structure and force generation are realized via various atomic force microscopy (AFM) imaging techniques including AFM cell force spectroscopy and functionalized force imaging. In these approaches, the recognition of mechanical responses of cells or mapping of cell surface receptors is mediated by chemomechanically characterized AFM cantilevers. The high spatial and force resolution of AFM imaging techniques and force spectroscopy enabled investigation of mechanical interaction at the cell-cell or cell-material interfaces. This interaction was studied via the mapping of specific receptors on endothelial cell surfaces and the detection of pN-scale force transmission through ligand-receptor pairs on the plasma membrane with biophysical interpretation of cellular force generation. This thesis consists of four major chapters: the recognition of vascular endothelial growth factor receptors and of anti-angiogenic oligopeptide receptors on endothelial cell surfaces, mechanical interaction between endothelial cells and pericytes that encompass capillary blood vessels; cell-matrix contact via focal complexes; and leukemia cells rolling on endothelial cell surfaces and P-selectin-conjugated glass substrata. / (cont.) This thesis also includes appendices that detail the effect of force transducer stiffness on the measurement of unbinding force, nerve cell imaging to I observe the connection between axons and dendrites, and chemomechanical characterization of polyelectrolyte multilayers, biodegradable hydrogels, and biological glues. In Chapter 2, transmembrane receptors on endothelial cell surfaces are mapped and associated binding kinetics/thermodynamics of ligand-receptor pairs are quantified via AFM functionalized force imaging or single-molecule recognition imaging. Functionalized force imaging is then used to identify unknown receptors, receptors for an oligopeptide isolated from tissue inhibitor of metalloproteinase-2, called Loop 6. In Chapter 3, mechanical stress by pericytes that envelop capillary blood vessels is quantified, demonstrating that pericytes exert significant mechanical strain on the extracellular environment. In Chapter 4, picoNewton-scale force dynamics at fibroblasts' focal complexes, measured in real-time through cell force spectroscopy, demonstrates that cells exert mechanical force that can speed the rupture of ligand-receptor pairs in focal complexes during migration and adhesion to underlying substrata. The last part of this thesis, Chapter 5, discusses the role of actin-mediated force in leukemia cell rolling on endothelial cell surfaces. The measurement of picoNewton-scale force dynamics using cell force spectroscopy suggests that, in addition to drag force exerted by blood flow, cytoskeletal force dynamics contribute to the cell rolling process. / (cont.) Together, these studies from the single-molecule to whole-cell level detail the strong coupling between mechanical force and ligand-receptor reaction kinetics. / by Sunyoung Lee. / Ph.D.

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2008. / 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. 67-73). / The price of oil has continued to rise, from a high of US$100 per barrel at the beginning 2008 to a new record of above US$140 in the recent weeks (of July). Coupled with increasing insidious greenhouse gas emissions, the need to harness abundant and renewable energy sources is never more urgent than now. The sun is the champion of all energy sources and photovoltaic cell production is currently the world's fastest growing energy market. Dye-sensitized solar cells (DSCs) are photoelectrochemical cells which mimic the natural photosynthesis process to generate solar electricity. Typically, a monolayer of dye sensitizer molecules is anchored onto a semiconductor mesoporous film such as TiO₂ to generate charges on exposure to illumination. The nanocrystalline particulate threedimensional network provides high surface area coverage for the photogeneration process and percolation of charges. In the thesis, we will review the current research efforts to optimize the DSC performance and develop probable applications to complement existing solid-state photovoltaic technologies. We believe the large and rapidly expanding solar market offers a prime commercial opportunity to deliver a DSC product for mass adoption by consumers. DSC is kept at a low production cost because it bypasses conventional vacuum-based semiconductor processing technologies, instead relying on solution and chemical processing routes. However, our cost modeling analysis show the TCO glass substrate and ruthenium dyes could constitute more than 90% of the overall materials cost. / (cont.) Thus, we recommend new technological approaches must be taken to keep the substrate pricing low and continuously improve the energy conversion efficiencies to further lower the production cost. / by Kwan Wee Tan. / M.Eng.