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.

Thesis: Ph. D., 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 student-submitted from PDF version of thesis. / Includes bibliographical references. / High temperature (>900°C) industrial waste heat recovery remains a key challenge for thermoelectric (TE) materials. The unique combination of high temperature, low heat-flux, and large surface area of waste heat generation in industrial processes shows that active material cost is the main metric inhibiting application. Low cost molten compounds with semiconducting properties are therefore proposed as a cost-effective addition to solid-state materials for these conditions. The performance of a laboratory-scale TE test cell based on molten SnS is demonstrated which reports Seebeck coefficient, electrical conductivity, thermal conductivity and, for the first time, the Figure of Merit and TE conversion efficiency of a molten semiconductor at the device level. The heat transfer modes of molten SnS in the TE test cell is investigated. The results suggest a domination of natural convection over intrinsic thermal conduction and radiative thermal conduction as primary heat transfer mechanism. In addition, a change of structure and thermophysical properties is found to occur at around 1000'C for molten SnS. The structure and property change is further connected to a semiconductor-to-metal (SC-M) transition, or metallization, which is known to take place in all molten semiconductors at high temperatures. The relationship between SC-M transition and structure/property changes connected by a proposed thermodynamic framework is verified with molten SnS. The outcome of this thesis confirms the opportunity offered by molten thermoelectric compounds and discusses the remaining materials and engineering challenges that need to be tackled in order to envision future deployment of thermoelectric devices based on molten semiconductors. / by Youyang Zhao. / Ph. D.

Thesis: Ph. D., 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. / Includes bibliographical references (pages 131-139). / Photovoltaic (PV) solar cells that constitute semiconducting sunlight absorber and metallic electrical contacts convert solar energy to electricity. Even though silicon represents roughly 90% of installed solar PV capacity as the clear current leader among PV technology, another class of solid-state solar cells, referred to as quantum dot (QD) solar cells, have gained much attentions from both academia and industry with the ability to provide further substantial enhancement of PV efficiency, together with the low possible manufacturing/installation cost. The power conversion efficiencies (P.C.E.) of QD-PVs based on lead sulfide (PbS) have been enhanced dramatically in only several years: current leading groups are able to fabricate reliably QD-PVs with 7-10% P.C.E. owing to favorable optical properties of PbS QDs including facile tunability of bandgaps with the variation in dot sizes or shapes, wide spectral responses, and multiple exciton generation. To date, the efficiency advances of QD solar cells have been carried out almost exclusively through tremendous numbers of trial and error experiments. Examples include materials set variations, donor and acceptor layer thickness optimization, and device structure modification. The core of the work described in this thesis deals with the theoretical understanding and design of PbS QDs with the goal of achieving a deeper and more fundamental understanding of the wide range of material's properties at the atomic scale in these devices. To this end, we employ a technique of computational electronic structure calculation methods, namely density functional theory (DFT) calculations. In this thesis, we select and investigate, using DFT calculations, three important electronic or optical properties: 1) band-edge energy (Chapter 2), 2) trap states (Chapter 3), and 3) Stokes shift (Chapter 4), all of which can contribute to PV performance improvements only if appropriately tailored. It is worth emphasizing that ligands which are used during QD synthesis for prevention of QD agglomeration plays a key role in tuning each property of interest in this thesis. Our theoretical work of band-edge energy shifts presented in Chapter 2 identifies ligand-induced surface dipoles as a hitherto-underutilized means of control over the absolute energy levels in PVs, complementary to well known bandgap tuning. This work have guided our experimental collaborators to build up a device architecture with a novel interfacial band alignment where a surplus loss of current collection can be minimized, leading to "certified" efficiency of 8.6% in 2014. Improvements of JSC presented in Chapter 2 led us to pay much attention to another figure of merit, open-circuit voltage (VOC): maximum Voc of 0.5-0.6 (V) has been achieved in single-junction PVs using PbS QDs with the bandgap of 1.1-1.3 (eV). Such large deficit of Voc in QD-PVs is attributed to the following sources: (1) high density of mid-gap trap states, (2) large Stokes shift, each of which is investigated and elaborated on in Chapters 3 and 4. Based on the fundamental understanding on the origin of these properties obtained from DFT calculations, we together with our experimental collaborators are actively working to develop PbS QD films with improved properties and to incorporate them into PV devices for further performance enhancements. This thesis document is organized as follows: Chapter 1 introduces PbS QDs and PVs, Chapters 2,3, and 4 illustrates theoretical investigations of key electronic and optical properties of PbS QDs (i.e. band-edge energy, trap states, and Stokes shift, respectively) supported by relevant experimental results from collaborators for better understanding of the this thesis. Lastly Chapter 5 closes the thesis with brief summary of works and future impacts to PVs and other optoelectronic applications. / by Donghun Kim. / Ph. D.

Thesis: S.B., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2001. / Cataloged from PDF version of thesis. / Includes bibliographical references (page 31). / Oxygen precipitates in silicon can be used (in a process called internal gettering) as sites of heterogeneous nucleation of precipitates of iron and other transition metal that are harmful to solar cell device operation. Oxygen precipitate densities in p- (10¹⁴ boron atoms/cm³) wafers were quantified using chemical etch techniques. The precipitate densities were then used to estimate times to getter iron based on a diffusion limited precipitation model. Oxygen precipitate densities in p++ (10¹⁹ boron atoms/cm³) wafers were quantified using chemical etch techniques. High levels of boron in p++ wafers make quantifying precipitate densities particularly difficult, via etching, or other methods because precipitate densities in highly doped wafers are very high and the size of precipitates small. / by Ashley Salomon. / S.B.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1997. / Includes bibliographical references (leaf 48). / This paper describes the engineering and development of a process to electrically and mechanically bond a large area, backlit charge-coupled device (CCD) sensor to a metallized substrate, using a materials system compatible with a high vacuum tube configuration. The CCD sensor is used in light sensor and digital camera devices. Currently, CCD devices are mechanically bonded to substrates using a variety of polymeric materials. For maximum resolution, however, the device must operate at high vacuum. Polymers release monomer molecules when exposed to a vacuum, since the polymerization reaction is far from equilibrium. Polymers also release retained solvent and binder molecules into a vacuum. This release of gas pollutes the high vacuum environment and degrades the tube perfomance. The CCD chip used in this research is extremely large, compared with standard semiconductor devices. The CCD chip measures 0.4 x 0.5 inches. At this size scale, thermal expansion mismatch stresses between die and carrier become an important design consideration, particularly for a die thinned to 10 micrometers. The proposed process results in a mechanical bond that is compatible with the high vacuum requirement, and is applicable to substrates of four possible materials: silicon, aluminum nitride, Pyrex, and LZS (a zirconia/ silicon nitride composite). The process also allows for two possible electrical connection techniques. / by Joshua V. Bennett. / M.S.