Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2016. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 113-120). / Efficient mechanical energy harvesters enable various wearable devices and may also act as auxiliary energy supply to isolated area. In this thesis, I present a novel class of mechanical energy harvesters based on stress-voltage coupling in electrochemically alloyed electrodes. The device consists of two identical Li-alloyed Si as electrodes, separated by electrolyte-soaked polymer membranes. Bending-induced asymmetric stresses generate chemical potential difference, driving lithium ion flux from the compressed to the tensed electrode to generate electric current. Unbending the device reverses the ion flux, generating electrical current in the opposite direction. The thermodynamic analyses reveal that the ideal energy-harvesting efficiency of this device is dictated by the Poisson's ratio of the electrodes. For the thin-film-based energy harvester used in this study, the device has achieved the overall efficiency of 0.6% and a generating capacity of 15%. The device also presents unique characteristics over the existing type of mechanical energy harvesters. Compared to piezoelectric or triboelectric generators, the prototype demonstrates low internal impedance of the order of 300[omega] as opposed to 100M[omega] in the other two types, and continuous electric current of the order of 3 seconds as opposed to 50ms in the other two types. From kinetics analysis, we show that the device's electric current generation is limited by lithium diffusion inside the LixSi electrode for sufficiently thick electrodes and by electrolyte diffusion for thin electrodes below 400nm. Tuning the current peak widths between 5s and 22s was demonstrated experimentally. The framework developed in the kinetics analyses also suggests that the device may be used as a spectroscopic tool to measure lithium diffusivity inside electrochemical alloys. The experimentally observed kinetics suggests lithium diffusivity on the order of 10-¹⁰cm² /s in Li₃.₁Si. The device demonstrates a practical use of stress-composition coupling in electochemically active alloys to harvest low-grade mechanical energies from various lowfrequency motions, such as everyday human activities. The analyses present the quantitative strategies to optimize the device in terms of its total energy output, kinetic behavior and ultimately the design principles for an energy harvester optimized for harvesting a specifically targeted frequency motion. / by Sangtae Kim. / Ph. D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2006. / Includes bibliographical references (p. 256-260). / Microprocessors have truly revolutionized the efficiency of the world due to the high-volume and low-cost of complimentary metal oxide semiconductor (CMOS) process technology. However, the traditional scaling methods by which chips improve are soon to end. The continued drive towards smaller circuit elements and dense chip architecture has yielded to power consumption, heat production, and electromagnetic interference (RC-delay) limitations. A logical solution to surmounting this electronic interconnect bottleneck is to utilize photonic interconnects. Photonic interconnects (waveguides) offer high data bandwidths with low signal attenuation and virtually zero heat dissipation. Strategic replacement of RC speed-limited electronic interconnects with photonic interconnects is a logical step to improving data processing performance in future microprocessors. Integration of photonic circuits onto electronic chips also enables sought after networking technologies that have higher complexity and unique functionality. Similar to the integrated microchip, the employment of CMOS technology in the fabrication of integrated photonic chips enables high yield, low cost, and increased performance. Essentially, the development of an integrated CMOS compatible photonic circuit technology is an enabler of improved communication. / (cont.) However, there are many challenges in realizing a viable, integrated photonic circuit technology. The constraints associated with fabrication of CMOS compatible, high-index-contrast, planar, thin-film photonic devices add difficulty in realizing the necessary components for a complete photonic circuit. Of these components: light source, waveguide, modulator, splitter, filter, and detector; all are limited in performance and functionality by optical transmission loss. As a result, this thesis has focused on diagnosing and addressing the various loss mechanisms that exist in fabricating CMOS compatible channel waveguides. As the building block of higher order photonic devices, waveguides are useful as diagnostic tools with which one can characterize photonic loss mechanisms. Waveguide test methodologies are developed to accurately diagnose the waveguide loss mechanisms (e.g. bulk absorption and interface roughness-scattering) by analyzing transmission loss (T) as a function of signal wavelength (x), waveguide width (w), waveguide height (h), effective index (neff), number of bends (N), and optical power (P). / (cont.) Four high index waveguide materials are investigated: silicon on insulator (SOI), amorphous silicon (a-Si), polycrystalline silicon (poly-Si), and Silicon Nitride. The dominant loss mechanism for each material system is different and as a result, unique process and design techniques are developed for each. For SOI waveguides, the loss is dominated by sidewall roughness. As a result, a novel post-etch wet chemical oxidation smoothing method is developed to reduced sidewall roughness and improve waveguide transmission. The employment of a hybrid waveguide design further reduces SOI waveguide losses to 0.35 dB/cm. For a-Si waveguides, loss is dominated by bulk absorption arising from dangling bonds. Loss reduction is achieved by increasing the H-content in the films, thereby satisfying the dangling bonds and reducing the number of absorption sites. Amorphous silicon bulk losses are reduced from 15.2 ± 2 dB/cm to < 1 dB/cm, representing a tractable path for integrating high index contrast waveguides onto multiple chip levels. For SiN waveguides, N-H bond absorption at %=1510 nm is the dominant loss mechanism. Here the use of low H-content precursors is investigated to reduce the number of N-H bond absorption sites. / (cont.) A total of six SiN materials are compared with losses as low as 1.5 dB/cm. Ring resonator devices, comprised of channel waveguides, are also investigated. Ring resonators serve as filters for multiplexing and demultiplexing broadband optical signals, dispersion compensators for accurately controlling phase, lasers, and ultrafast all-optical switches. In realizing these devices a ring trimming method is developed to compensate for non-deterministic pattern transfer errors which limit dimensional precision and preclude the fabrication of identical devices across an entire wafer. In this work, a novel photo-oxidation trimming method, using a UV-sensitive, polysilane top cladding material, is employed. The UV-induced refractive index decrease of polysilane (4%) enables accurate and localized trimming of ring resonators. Ring modulator devices are modeled as well. The employment of integrated SiGe ring modulators that utilize the fast Franz-Keyldish effect is discussed. The design constraints involved in monolithically integrating photonic and electronic components are discussed. In particular, the CMOS process challenges: material limitations, epitaxial compatibilities, thermal-budget imposed process order, and device communication requirements are utilized in arriving at an optimal application specific, electronic-photonic integrated chip (AS-EPIC) architecture. / by Daniel Knight Sparacin. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1996. / Includes bibliographical references (leaves 96-98). / by Kenneth D. Zemach. / Ph.D.

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2010. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 55-58). / A new method to quantify hepatitis C (HCV) viral particles when present in ultra low concentrations is being developed. Hepatitis C is a viral infection that affects the liver. There are 3.2 million people in the United States with an active hepatitis C infection. Untreated HCV can lead to cirrhosis, liver failure and liver cancer. HCV treatments can be very costly and physically taxing for patients; the side-effects of treatment are comparable to persistent flu-like symptoms. Physicians are looking to shorten the duration of the standard treatment, typically 24 to 48 weeks, for patients who respond quickly. Physicians must have more sensitive testing equipment to truly know when a patient has been cured and be able to successfully shorten the length of treatment. Current diagnostic tests are insufficiently sensitive when the patient begins to positively respond to treatment and the amount of the virus present in his/her blood dramatically decreases. This limitation can be overcome by employing an in-vivo sampling technique, where a device is placed in a vein to trap HCV viral particles present in the blood. These particles are then subsequently quantified with a commercially available test. This technique allows at least 40,000 times more blood to be sampled in 30 minutes than with a traditional blood draw, greatly increasing the effective sensitivity of the test. The approach provides significant medical benefit to the patient being treated and a strong financial incentive to the entity paying for the treatment. / by Gregory J. Ekchian. / M.Eng.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2009. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 147-153). / In this thesis two unique carbon based nanoelectromechanical switches or carbon nano-relays are demonstrated as a toolkit for investigating NEMs based low power switching. The first is a vertical carbon nano-relay, consisting of a vertically aligned carbon nanotube/fiber (CN) between two contacts and operated by pull-off, and the second, a double graphene switch, consisting of two electromechanically actuated stacked layers of polycrystalline graphene. Vertical carbon nano-relays were initially prototyped by inserting a CN between two contacts through the use of a nanopositioner. The prototype demonstrated pull-off operation and multiple switching. To our knowledge this is the only example to date of a multiple-use NEMs switch that operates with pull-off. Next a wafer integrated device was fabricated. Although pull-in was demonstrated in these integrated devices, pull-off was not possible primarily due to limitations in CN growth, which were also investigated. In the work on a double graphene switch we demonstrated an electromechanical switch comprising two polycrystalline graphene films, each deposited using ambient pressure chemical vapor deposition (CVD). The top film is pulled into electrical contact with the bottom film by application of approximately 5V between the layers. Contact is broken by mechanical restoring forces after bias is removed. The device switches several times before tearing. Demonstration of multiple switching at low voltage confirms that graphene is an attractive material for electromechanical switches. / by Kaveh Mehdi Milaninia. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1996. / Includes bibliographical references (leaves 216-221). / by Kevin Glenn Ressler. / Ph.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2000. / Includes bibliographical references (p. 253-261). / Graded buffers oflnxGa1-xP on GaP ([Delta]x[lnxGa1-x]P/GaP) can be used to fabricate potentially high performance, epitaxial transparent substrates light-emitting diodes (ETSLEDs ). Practical devices have thus far been limited by poor quality: reports of [Delta]x[lnxGa1-x]P/GaP show sharp declines in device and material quality above x - 0.3. This study revisits the challenge of engineering high-quality [Delta]x[lnxGa1-x]P/GaP grown by metal-organic vapor phase epitaxy. A new planar defect microstructure oriented 10-15° off the (1-10), which we call branch defects, was discovered via transmission electron microscopy. Branch defects feature sharp strain fields and dominate the microstructure. causing dislocation pinning and escalation. Branch defects occur later in growth with increasing temperature; however, they are stronger when formed at higher temperatures. Branch defects do not appear to be directly related to other co-existing microstructures in lnxGa1.xP. In the phase space where branch defects are absent, the intrinsic dislocation dynamics of[Delta]x[lnxGa1-x]P/GaP were explored. Dislocation density decreases exponentially with increasing temperature, supporting a kinetic glide model for graded buffers. Dislocation glide velocities also appear to increase dramatically while grading from GaP to InP. Optimizing the co-evolution of dislocation dynamics and branch defects has achieved dislocation densities of [Delta]x106 cm-2 out to x = 0.54, the highest quality [Delta]x[lnxGa1-x]P/GaP reported to date. Reciprocal space mapping reveals three distinct regimes of crystallographic tilt. Qualitative to semi-quantitative models were developed for each regime to elucidate the changing dislocation dynamics during V x[lnxGai-x]P/GaP growth. Critical reanalysis of earlier reports provides further evidence for the kinetic glide model. Overall, discovery of tilt regimes demonstrates the need for a dynamic approach to tilt analysis. A series of ETS-LEDs with emission wavelengths ranging from 575 to 655 nm was fabricated from optimized [Delta]x[lnxGa1-x]P/GaP and shows continuing good performance for [Delta]x 0.3, in contrast to earlier reports. A second, subtle process optimization to better suppress branch defects increases efficiency 60% and drops spectral width 8 meV. Since self-absorption in [Delta]x [lnxGai-x]P/G<t.P is >90%, a fully transparent [Delta]x,y [inx(AlyGa1_y)i-x]P/GaP technology was also developed and initial results promise an order of magnitude improvement in device efficiency. The improvements from subtle process changes suggest a good outlook for achieving practical ETS-LEDs. / by Andrew Y. Kim. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1988. / Includes bibliographical references. / by Tsung-Eong Hsieh. / Ph.D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, February 2014. / Cataloged from PDF version of thesis. "February 2014." / Includes bibliographical references. / The ability to characterize and control cellular responses in vitro has far reaching implications for basic science and applied medical research. For well over 125 years, researchers have studied the behavior of biological cells under in vitro conditions where rigid glass or plastic Petri dishes and defined media in the laboratory replace the compliant solids and crowded fluids of the human body in vivo. While these tools have enabled several important advances in understanding cell functions and pathological mechanisms, the behavior of tissue cells in vitro can differ remarkably from those observed in in vivo tissue microenvironments. It is becoming increasingly appreciated that there is a close coupling between the chemical and mechanical microenvironments of the cell (i.e., the chemomechanical niche). Therefore, the biochemical reactions and conditions responsible for generating mechanical stresses and attendant cell behaviors may not be well represented in typical in vitro assays. In several key respects, particularly in terms of cell proliferation, adhesion, migration and phenotypic metabolism, in vitro assays often misrepresent the major characteristics of these behaviors in vivo. Most physiological processes are defined in part by mechanical force, mechanical microenvironment, and chemical stimuli (e.g., in angiogenesis or regulation of stern cell differentation), and therefore require an updated methodology to studying cellular mechanics and behavior. This thesis aims to address the molecular- to cellular-level chemical and mechanical environments that modulate cell function in vivo at the cell-cell and cell-matrix interfaces, while aiming to more accurately reproduce these cell responses in vitro. The experiments and analyses described in this work investigate two key questions at the heart of angiogenesis. First, how does the protein dense nature of tissue nicroenvironments affect extracellular matrix organization and, in turn, direct cell-matrix guided functions and cytoskeletal organization? This will be addressed by the addition of inert crowders which artificially enhance the effective concentration of relevant macromolecules and proteins in vitro. Second, how do the mechanically couplings and biochemical signals between adjacent, dissimilar cell types in the microvasculature coordinate and guide angiogenesis? Multiple types of deformable substrata will be used to investigate the mechanical strain and soluble growth factors generated by perivascular cells and the response of microvascular endothelial cells to those cues. This includes the development of a novel uniaxial strain-generating device and tissue culture surfaces for endothelial cells. Atomic force microscopy enabled imaging and nanoindentation, mechanically and chemically defined substrata, immunocyto-chemistry, and novel quanitification and analysis techniques are used concomitantly to answer these questions. Ultimately, this thesis aims to close the gap between in vitro cell culture and in vivo cell physiology, especially in directing and characterizing chemomechanical cues implicated in angiogenesis, and to inform the design of future experiments and microenvironments with non-dilute culture media and deformable substrata. / by Adam Scott Zeiger. / Ph. D.

Thesis: S.B., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2014. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 43-45). / This study sought to evaluate hard carbon's fracture characteristics under different cycling rates due to its lithium solid solubility and isotropic nature. In addition to the evaluation, an electrochemical shock map was modified from a previous study to try and predict what conditions of particle size and C-rate are necessary to cause brittle fracture events in hard carbon. Subsequently, hard carbon anodes were created using a formulation of hard carbon, carbon black, and Kureha binder and subjected to two or three cycles of C-rates varying from C/10 to 5 C. Data evaluation suggests that for every C increase approximately nine more percent of the particles in the system will develop cracks. Further analysis of the data shows that low C-rate anodes may have been affected by inhomogeneous mixtures, skewing the linear relationship to a higher than accurate value in the linear plot. Additionally, a C-rate limit that prevents any brittle fracture from occurring can be found at c/10 or lower. When comparing the anodes to the model, the model shows accuracy in C predicting failure conditions for the higher C-rate anodes. When applied to lower C-rates (below c/2), the 2 accuracy of the model begins to fall. Possible solutions to this problem include finding more accurate material properties for hard carbon or redefining the model to account for some unique value (i.e. - the hard carbon's geometry) associated with the hard carbon. Additionally, more anodes should be tested to create a larger sampling that can average cells that have inhomogeneous mixtures. / by Thomas A. Villalón Jr. / S.B.