Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2004. / Includes bibliographical references (p. 288-294). / (cont.) Er-based gain. We reported the first infrared photoluminescence PL study of Er₂O₃ and found a 7 ms lifetime at 4 K, attributed to a metastable FCC or HCP phase. We showed the thermodynamically stable BCC crystal phase has PL emission lines at 1537 nm and 1550 nm, and metastable FCC and HCP crystal phases result in PL emission lines at 1542 nm and 1533 nm. Upconversion coefficient measurements on the BCC phase and 7 ms lifetime metastable phase gave values of 10⁻¹⁷ and 10⁻¹⁸ cm³/s, respectively. Comparison of room temperature absorption versus 4 K PL of Er₂O₃ and an SiO₂:Er reference showed the BCC phase to be the dominant volume fraction. The calculated WOA power requirements for 3 dB gain in the metastable phase were found to be 450 mW. We examined SiON and Si₃N₄ for high index difference ([delta]n=0.1-0.7) Er host materials. Samples were grown by sputtering, and we investigated the optical materials quality of this process by studying sputtered SiO₂:Er; we report a record co-sputtered SiO₂:Er room temperature lifetime of 14 ms. PL versus heat treatment results strongly indicate the nitride environment of Si₃N₄ favors a higher Er solubility and lower cooperative upconversion than the oxide environment of SiO₂. We measure a 2.4 ms radiative lifetime in co-sputtered Si₃N₄:Er, [approximately] 4x smaller than radiative lifetime reports in ion implanted Si₃N₄:Er PL samples; we attribute this enhancement to an optimized Er ligand field from the sputter process ... / Si Microphotonics is a micron-scale planar processing technology compatible with the fabrication tools of Si Microelectronics. The first demonstration of an integrated set of microphotonic devices replicating the function of an entire fiber optic link, dubbed a Planar Lightwave Circuit (PLC), is being developed to solve the Integrated Circuit (IC) interconnection bottleneck problem: the project proposes replacing time delaying metal interconnects with optical interconnects, i.e. a PLC integrated onto the IC chip. This work requires the development of compact micron-scale analogs to fiber optic link device elements. In this thesis, we take example from commercially available Erbium Doped Waveguide Amplifiers (EDWAs), to investigate the use of high Er concentration doped materials and device design optimization to create gain efficient Waveguide Optical Amplifiers (WOA) in the PLC, at 1.55 [micro]m light. We develop a waveguide index difference An scaling methodology with which to optimally design a WOA into as small a planar footprint as possible and using as little optical pump power as required. We observe that device gain efficiency and footprint have a power-law dependence, summarized in a cumulative Figure-of-Merit, of [delta]n²·⁶. This strong improvement in WOA performance is dependent on the requirement of strip waveguide propagation losses < 0.2 dB/cm, a requirement demonstrated in SiON waveguides. We conclude that a 10 mW-powered 3 dB or 30 dB gain WOA can be fit into a 425x425 [micro]m² or 3x3 mm² footprint, respectively, using an SiON [delta]n=0.155 Er-doped strip waveguide. The impact of [delta]n scaling shows the WOA to be feasible for dense PLCs and low cost planar EDWAs. We examined Er₂O₃ as a materials candidate for ultra-high / by Sajan Saini. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2008. / Includes bibliographical references (p. 95-97). / This project aims to develop MEMS actuators to aid in the study of insect flight mechanics. Specifically, we are developing actuators that can stimulate the antennae of the crepuscular hawk moth Manduca Sexta. The possible mechanosensory function of antennae as airflow sensors has been suggested, and recent discoveries of our collaborators reveal that mechanosensory input from the antennae of flying moths serves a similar role to that of the hind wings of two-winged insects, detecting Coriolis forces and thereby mediating flight stability during maneuvers. Early evidence suggests that mechanical stimulus of the antennae may enable flight control. In addition, the crepuscular hawk moth Manduca Sexta has a wide wingspan (~110 mm) and is capable of carrying at least one quarter of its own weight. Thus, studying the flight of Manduca Sexta by attachment of microsystems seems plausible. The goal of our project is to design and fabricate micromechanical actuators, which will be mounted onto the moth antennae. Our collaborators will study the flight control mechanism by mechanical stimulation. Our first step was to fabricate "dummy" silicon rings for our biologist collaborators for implant experiment. A series of mounting kits were developed, and due to the nature of the moth antennae, ring-beam-ring construction was finally designed and fabricated, like a "shackle", to meet the mounting requirements. Next, we integrated actuators onto the mounting kit. Piezoelectric film/sheet, piezoelectricbender and piezoelectric-stack were considered as the actuators. Live testing was also taken while the moth was resting or flapping its wings. The moth apparently responds to the mechanical stimulus under both circumstances, by swinging its wings and abdomen. Actuation amplifier was also modeled and tested, which might be used for future mechanical stimulators. / by Hui Zhou. / S.M.

Thesis: S.B., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 55-56). / Carbon nanotubes have generated much research interest and potential applications due to their unique properties such as their high tensile strength, high thermal conductivity, and unique semiconductor properties. Vertically-aligned carbon nanotubes (VA-CNTs) have been used in applications for electrochemical systems in energy storage systems and desalination systems. Typical methods of characterizing the morphology and composition of CNTs are limited in providing information on the packing density of CNTs, and therefore, an effective method for in situ characterization of VA-CNT electrodes is needed. This method explores the use of impedance spectroscopy and other electrochemical methods to characterize VA-CNTs in situ. VA-CNTs forests were grown via chemical vapor densification on pre-oxidized silicon wafers, mechanically densified to achieve varying volume fractions (1%, 2%, 5%, and 10%), and tested in a three-electrode electrochemical cell. Electrochemical techniques (cyclic voltammetry, impedance spectroscopy, and potentiostatic techniques) were used to measure the performance of the VA-CNTs in 1 M and 500 mM electrolyte solutions. Optimization of the experimental setup design and data collection methods yielded data that resulted in the expected cyclic voltammetry response and impedance behavior of porous electrodes. A transmission line model-pore size distribution (TLM-PSD) model was applied to the data collected in order to predict and model porosimetry characteristics. Porous behavior was observed in the VA-CNT electrodes of all volume fractions tested, and the impedance spectra showed that the volume fraction affected the overall impedance but not the characteristic shape of the spectra. Comparison between the impedance data collected in 1 M NaCl and 500 mM NaCl showed the expected corresponding inverse correlation with solution conductivity. Parameters that describe the VA-CNT electrode porosity were calculated and predicted using electrochemical data and the TLM-PSD model. The porous volume Vtot and total ionic conductance Yp values calculated using the model applied to the impedance spectroscopy data showed trends as expected for the different volume fractions of VA-CNT. The results show that electrochemical impedance spectroscopy can be used to characterize certain physical characteristics of the VA-CNT electrodes and further development of the model can yield insights into the porous geometry of VA-CNT forests. / by Yuan Lu. / S.B.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1996. / Includes bibliographical references (leaves 123-125). / by J. Morgan Slade. / M.S.

Thesis: S.B., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2014. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 35-37). / The study was conducted to characterize the effects of xanthan gum on gluten-free bread formulations. An improved gluten-free flour blend consisting of brown rice flour, quinoa flour, and sorghum flour was used with the aim of developing a gluten-free bread formulation comparable to traditional gluten-based bread and commercial gluten-free bread mix. Rheological measurements were taken to analyze the effects of xanthan gum on pre-baked dough formulations. Higher concentrations of xanthan gum were found to decrease the loss factor thus strengthening the elastic properties of the dough, elongating the linear viscoelastic region and increasing the viscosity of the dough. Furthermore, the xanthan gum samples were not independent of frequency and the loss factor decreased as frequency increased. Porosity of samples was also analyzed using imaging technology to determine the average pore size. Pore size increased as xanthan gum concentration increased indicating the ability for xanthan gum to retain gas during the proofing stage before baking. It was concluded that xanthan gum was necessary for a loaf with nice crumb texture, loaf color, and moisture content though different than gluten-based and commercial brand gluten-free bread mix. 0.3% xanthan gum concentration provided the most desirable post-baked crumb texture, loaf volume, and moisture content / by Rebecca Y. Lin. / S.B.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 131-134). / We describe the fabrication and study of bulk heterojunction solar cells composed of PbS quantum dots and TiO2. In particular, we study the effects that bulk heterojunction composition and structure have on resulting device performance. We find that PbS and titania are extremely evenly distributed throughout our bulk heterojunction devices, such that charge carriers generated anywhere within the blend are well within a carrier collection length of the charge separating driving force required to separate them and enable their collection. Of the compositions we studied, we found that devices with a TiO2 rich bulk heterojunction composition outperformed devices employing other compositions. As a result of the size difference between the PbS quantum dots and the titania nanocrystals which compose the blends, the likelihood of forming a truly complete, bicontinuous bulk heterojunction network is maximized at a TiO2-rich blend composition. We find that diffuse interfaces exist between adjacent layers of our devices as a result of interfacial surface roughness. Rather than being deleterious, this increased interfacial area extends the spatial extent of the depletion region over a greater volume of our devices. Our bulk heterojunction blends form well packed, high density binary particle mixtures, particularly at a TiO2-rich composition. Device efficiency was maximized for bulk heterojunctions employing the smallest titania nanocrystals, an indication that at constant volume fractions, larger titania nanocrystals decrease the total number of titania particles available to form complete and continuous pathways through the depth of the bulk heterojunction. Furthermore, a peak in device performance was observed at intermediate blend layer thicknesses. This results from the balance between two opposing effects: an increase in light absorption and photocurrent with thicker bulk heterojunctions and an increased likelihood of charge carrier recombination with thicker bulk heterojunctions. Finally, enhanced light absorption and current generation was observed at red and infrared wavelengths, validating the ability of bulk heterojunctions to spatially extend the reach of the charge separating driving force, such that the previously missed red and infrared photons may be captured. / by Kevin J. Huang. / Ph. D.

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1990. / Includes bibliographical references (leaves 29-30). / by Eric D. Ditmars. / B.S.

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2006. / Includes bibliographical references (leaves 82-85). / While light emitting devices, such as laser diodes (LDs) and light emitting diodes (LEDs), were first introduced decades ago, they have been the subject of continuing research and improvements due to their relatively poor performance. Evolution has occurred in both the design of light emitting devices and in the materials from which they are made. This thesis examines new proposals for use of templated arrays of heterostructural semiconductor nanowire light emitting devices, from both engineering and business points of view. The effects of wire spacing and diameter on reliability and performance (both the internal quantum efficiency and the extraction efficiency) are evaluated. Business models for development of nanowire arrays for light emitting devices are discussed. / by Ting Zou. / M.Eng.

Thesis: S.M., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2017. / Cataloged from student-submitted PDF version of thesis. / Includes bibliographical references (pages 42-44). / Free-moving "floating" grains have been linked to macrosegregation in direct-chill (DC) aluminum castings. The presence of these grains in the sump of a solidifying ingot has been acknowledged based on measurements of cast microstructures and by recent work using a turbulent jet to suspend solute-poor grains and minimize macrosegregation.1,2 Experiments in this study were designed to sample grains from the mushy region of two ingots, one cast by the standard method and another stirred with a turbulent jet. Measurements of floating grain size, concentration, morphology, and chemical composition are reported. The observations from the standard ingot offer a point of comparison for floating grain theories and casting models. The measurements from the stirred ingot show how the turbulent jet modifies the distribution, concentration and morphology of the floating grains. / by Carolyn M. Joseph. / S.M.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, February 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 211-223). / The physical and chemical properties of nanoscale materials derive largely from structure and composition at interfaces. The possibility to electrically modify these interfacial characteristics would provide a powerful means to control material properties. Of particular recent scientific and technological interest are metal/metal-oxide bilayers, in which properties as varied as catalytic activity, charge and spin transport, ionic exchange, mechanical behavior, thermal conductivity, and magnetism all depend sensitively on oxygen stoichiometry and defect structure at the metal/metal-oxide interface. The possibility to dynamically control interface characteristics through electric-field-induced oxygen transport and electrochemical interface reactions paves the way towards voltage control of these properties in solid-state devices. Here, we focus on ferromagnetic metal/metal-oxide bilayers that exhibit strong perpendicular magnetic anisotropy derived from interfacial oxygen hybridization. In these materials, we directly observe, in situ voltage-driven oxygen migration at room temperature and show that electrical switching of the interfacial oxidation state allows for voltage control of magnetic properties to an extent never before achieved through conventional magneto-electric coupling mechanisms. By engineering the electrode and metal-oxide layers for efficient ionic exchange and transport, we improve the response time by six orders of magnitude and switch perpendicular magnetic anisotropy at the millisecond timescale. Based on this magneto-ionic coupling mechanism we demonstrate a printer-like system to reversible pattern magnetic properties and realize a prototype nonvolatile memory device in which voltage-controlled domain wall traps facilitate electrical bit selection in a magnetic nanowire register. Moreover, we report on voltage control over electronic transport properties in the same bilayer structures and show that solid-state switching of interface oxygen chemistry provides a path towards voltage-gating the wide range of phenomena governed by metal/oxide interfaces. / by Uwe Bauer. / Ph. D.