Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1994. / Includes bibliographical references (p. 109-113). / by Michael Charles Zody. / M.S.

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2009. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 144-150). / To build an electric car plus renewable energy system for Singapore, solar thermal technologies were investigated in this report in the hope to find a suitable "green" energy source for this small island country. Among all existing solar thermal technologies, parabolic trough power plants represent a well established technology with more than twenty years of operation experiences. This report reviewed recent progress of research in this field. It was found that significant progresses have been made in solar collector, heat transfer fluid and thermal storage. An economic assessment of the parabolic trough power plant technology was also carried out. By comparing a parabolic trough power plant and a concentrating photovoltaic solar farm, both advantages and limitations of these plants were indentified. Based on these findings, the niche market for parabolic trough power plants was analyzed. It was found that in the next few years, the deployment of parabolic trough plants would mainly occur in south-western U.S. and Mediterranean countries. However, it was found that concentrating solar thermal technologies were not suitable for Singapore, due to this country's limited land and high fraction of diffuse solar radiation. Therefore, PV technology was selected as a "clean" energy source. Based on PV electricity, a few electric vehicle (XEV) models were developed and evaluated. / by Xiaogang Liu. / M.Eng.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2014. / 116 / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 147-159). / This thesis focuses on the development of synthetic methods to create application ready quantum dots (QDs) in the infrared for biological imaging and optoelectronic devices. I concentrated primarily on controlling the size and size distribution of indium arsenide and cadmium arsenide QDs. In the nanocrystal community, classical nucleation and growth is often invoked to explain size focusing. However, this model lacks predictive power and contradicts what is known about the chemistry of QD growth. I try to relate my experimental approach and my conclusions to our understanding of the mechanism of particle growth. This approach led me to explore the role of precursor conversion rate in the growth of III-V QDs and to develop a continuous injection synthesis method that I used to make both III-V and cadmium arsenide QDs. Cadmium arsenide (Cd 3As 2 ) is a narrow gap semiconductor that can form QDs with tunable emission between 530nm and 2000nm. I developed a synthetic strategy to precisely control the size of Cd3As 2 QDs while maintaining a narrow size distribution. Continuous precursor injection was used to drive growth and suppress size broadening. The quantum yields of Cd3As 2 QDs produced using this method ranged as high as 80%, and their emission is tunable over a broad range with narrow linewidths. However, they were found to be unstable in ambient conditions. Nevertheless, by processing in inert conditions we were able to make a crude photodetector that demonstrates that Cd3As 2 QDs are sufficiently stable for use in optoelectronic devices. Although growth of a Cd3 P2 shell provided enough added stability to observe emission after ligand exchange into water, these core-shell structures do not seem to be robust enough for biological applications. Indium arsenide (InAs) QDs are more easily stabilized with a core-shell structure. However, the spectral linewidths are broad and existing synthetic techniques produce only small particles with limited spectral tunability. Models predicted that decreasing precursor reactivity would produce larger, more monodisperse particles. Therefore, I chemically modified the group-V precursor to reduce reactivity. I made a library of group-V precursors, and I developed a framework for comparing the QDs that they produced and measuring the kinetics of precursor conversion and particle growth. Although we successfully reduced precursor reactivity, we found that the effect on particle size was minimal and that the least reactive precursors produced particles with inferior size distributions. To find another way to try to improve III-V synthesis, I adapted the continuous injection method developed for making Cd3As 2. Using this strategy, I was able to produce InAs QDs with broadly tunable size and narrow spectral features. However, continuous injection ceases to drive particle growth beyond about 5nm in diameter. We examined why particle growth stops, and proposed a strategy to prolong growth and size focusing. Ultimately, the continuous injection technique allowed us to produce InAs QDs with infrared emission and narrow spectral features that were ideally suited for producing QDs optimized for deep tissue imaging in mice. By adding a shell of CdSe, CdS, or ZnSe, the quantum yield and stability were enhanced. These emitters allowed us to see biodistribution and biological processes occurring inside live mice. Although we found that precursor chemistry did not affect particle growth to the degree we hoped, we were able to produce application ready QDs via a continuous injection procedure. Continuous injection synthesis of QDs is a precise way to tune QD size while maintaining narrow size distributions. We have used this technique to produce QDs with the specifications required for high impact applications. / by Daniel Kelly Harris. / Ph. D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2017. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 153-161). / Gallium Nitride (GaN) belongs to a class of materials called wide band-gap semiconductors. In recent years, the versatile nature of this material has been exploited for a wide range of applications from solid state lighting to RF and microwave communication, as well as high power switching. The first part of this thesis discusses planar AlGaN/GaN transistors. GaN is a piezoelectric material, and changes in mechanical stress result in a change in the charge density which in turn affects the maximum current in AlGaN/GaN transistors. Finite element modelling techniques were applied to quantify the mechanical stress distribution in planar AlGaN/GaN RF transistors resulting from device fabrication, and operation in the on- and off-state. Thereafter, two important surface and interface effects were studied in this thesis. In the first one, the impact of surface cleanings, surface treatments and plasma-based dry etch conditions on two different types of ohmic contact technologies was investigated. Contact resistance measurements were correlated with surface characterization results. The second was that of interface positive charges at the Al₂O₃-GaN interface and the increase in electron density in the device resulting from them. In both these problems, a combination of device electrical measurements and material characterization techniques was used to establish direct correlations between device behavior and material properties. The second part of the thesis deals exclusively with nano-ribbon (NR) or fin-like AlGaN/GaN transistors. Fundamental transport properties of charge density and mobility in NR devices were studied in order to understand the difference in behavior of these devices from planar devices. The influence of passivation films on the charge density in these structures was investigated, using Al₂O₃ passivation as a specific example. Electron mobility degradation due to sidewall-scattering in NR devices was quantified using different mobility extraction methods based on device measurements. The thesis concludes with a potential application of NR AlGaN/GaN transistors for high linearity power amplification. A new kind of transistor with varying threshold voltages along the gate width is proposed to improve the DC and RF linearity of GaN-based devices. / by Sameer Jayanta Joglekar. / Ph. D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2001. / "February 2001." / Includes bibliographical references (p. 149-157). / This thesis examines novel photonic materials systems possessing order in the atomic, microscopic, and macroscopic dimensional regimes. In the atomic order regime, a structure-property investigation is done for Er203 in which the first report of room temperature photoluminescence (PL) is provided. Thin films of the rare earth oxide were deposited via reactive sputtering of Er metal in an Ar/02 ambient, and subsequently annealed to promote grain growth. Heat treatment consisting of a 650°C followed by 1000°C anneal produces maximum crystallinity as measured by glancing angle x-ray diffraction. These films show characteristic PL at [lambda]=1.54 [mu]m. In the microscopic order regime, omnidirectional reflectors and thin film microcavities are demonstrated using sol-gel and solid-state materials. A first demonstration of omnidirectional reflectivity in sol-gel structures was accomplished using a dielectric stack consisting of 12 spin-on Si02/Ti02 quarterwave sol-gel films. Similarly, solid-state dielectric stacks consisting of 6 Si/Si02 sputtered films were used to demonstrate the same principle. Microcavities were formed using sol-gel structures, producing a low quality factor Q=35 due to limitations in film thickness control and lossy interfaces from stress-induced cracks. The high index contrast Si/Si02 microcavities enabled Q ~1000 using 17 total layers following hydrogenation of dangling bonds within the amorphous Si films. Combining fabrication processes for the solid-state microcavity and Er20 3 films, a device was fabricated to demonstrate photoluminescence enhancement of an Er20 3 film embedded in a microcavity. The structure consisted of 3-bilayer mirrors on either side of an Si02/Er203/Si02 cavity. The Q~300 was near the theoretical value for such a structure. At room temperature, PL of Er20 3 was enhanced by a factor of 1000 in the microcavity compared to a single thin film. In the macroscopic order regime, self-assembly of micron-sized Si02 and polystyrene latex colloidal particles into 2D crystals is presented. The colloidal assemblies offer a relatively easy processing route for fabrication of photonic bandgap structures. Large (> 1 mm diameter) single crystal grains of colloids were formed using controlled evaporation and fluid flow techniques. A novel solution enabling postprocessing of the fragile ordered assemblies is presented in which polyelectrolyte multilayers serve as adsorption platforms that anchor the colloidal assemblies. Tailorability of the polyelectrolyte surface properties (charge density, morphology) enables tuning of the colloid adsorption behavior. The polyelectrolyte surface affects colloid adsorption by influencing its surface diffusion. Observations of colloid surface diffusion were made using optical microscopy. Use of polyelectrolytes patterned via rnicrocontact printing enables fabrication of colloid assemblies containing predesigned point and line defects. The patterned polyelectrolyte adsorption template allows placement of colloids in specific geometric arrangement, making possible the realization of sensors or functional photonic bandgap devices such as waveguides or photon traps. Three mechanisms were used to control· adsorption: (1) pH of the colloid suspension, which determines the ionization of the uppermost surface of the polyelectrolyte multilayer; (2) ionic strength of the suspension, which determines the extent of charge screening about the colloid and polyelectrolyte; and (3) concentration of added surfactant, which causes charge screening and introduces hydrophobic interactions between the surfactant and polyelectrolyte. / by Kevin Ming Chen. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1989. / Includes bibliographical references (leaves 175-184). / by Fred Daniel Gealy III. / 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 (p. 223-230). / The field of texture analysis is fundamentally concerned with measuring and analyzing the distribution of crystalline orientations in a given polycrystalline material. Traditionally, the orientation distribution function describing crystallographic orientation information is written as a linear combination of the generalized spherical harmonics. Since the use of generalized spherical harmonics requires that orientations be described by sets of Euler angles, the field of texture analysis suffers from the inherent limitations of Euler angles. These include difficulty of presentation and interpretation, discontinuous changes in the description of a changing orientation, and singularities in many equations of Euler angles. An alternative expansion of the orientation distribution function as a linear combination of the hyperspherical harmonics is therefore proposed, with the advantage that this expansion allows rotations to be described by angles that directly relate to the axis and angle of a rotation. Apart from the straightforward and intuitive presentation of orientation statistics that this allows, the utility of the hyperspherical harmonic expansion rests on the fact that the orientation distribution function inherits the useful mathematical properties of the hyperspherical harmonics. The relationship of the hyperspherical harmonics to the three- and four-dimensional rotation groups is investigated, and expressions for the matrix elements of the irreducible representatives of these rotation groups as linear combinations of the hyperspherical harmonics are found. / (cont.) These expressions allow an addition formula for the hyperspherical harmonics to be derived, and provide the means to write a simple conversion between the generalized spherical harmonic and hyperspherical harmonic expansions. This allows results derived via the hyperspherical harmonic expansion to be related to the texture analysis literature. Furthermore, a procedure for calculating the symmetrized hyperspherical harmonics consistent with crystal and sample symmetries is indicated, and used to perform the expansion of an orientation distribution function significantly more efficiently. The capability of the hyperspherical harmonic expansion to provide results not traditionally accessible is demonstrated by the generalization of the Mackenzie distribution to arbitrary textures. Finally, further areas where the application of the hyperspherical harmonic expansion is expected to advance the field of texture analysis are discussed. / by Jeremy K. Mason. / Ph.D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2014. / 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 259-284). / Nanoparticles (NPs) have recently emerged as a versatile new materials platform for biomedical applications. By tuning their surface functionality, NPs can be engineered to resemble proteins in terms of size, shape, and chemistry, making them ideal for use in vivo. However, a theoretical understanding of how NPs interact with the biological milieu has lagged far behind experiments. In particular, it is critical to gain physical insight into the behavior of NPs at cell surfaces in order to minimize cytotoxic side effects while maximizing NP efficacy. In this thesis, I use several biomolecular simulation techniques to model the interactions of amphiphilic, monolayer-protected NPs with lipid bilayers. This work is motivated by the recent experimental finding that certain gold NPs can penetrate into cells via an unexplained non-endocytic, non-disruptive mechanism. I propose that such a penetration process is possible if the surface properties of the NP can effectively reorganize in the presence of the lipid bilayer. I show that such environmentally-responsive NPs can stably insert into lipid bilayers as a precursor to cell penetration. The thesis divides this study into three Parts. In Part I, I study the thermodynamics of NP-bilayer interactions using both a coarse-grained methodology and a novel implicit bilayer, implicit solvent model. I show that NPs with flexible ligands can fuse with lipid bilayers by "snorkeling" charged end groups out of the bilayer core and into solution. Several experimental studies confirm aspects of this fusion hypothesis and indicate that fusion may be a precursor to cellular internalization. In Part II, I use atomistic molecular dynamics simulations to uncover the kinetic pathway for NP-bilayer fusion. Fusion occurs spontaneously if the NP comes into contact with lipid tail protrusions which occur stochastically over long timescales. In Part III I perform initial studies on cooperative NP behavior. I first show that NPs must be carefully engineering to avoid aggregation in solution prior to contact with the bilayer. I then show that embedded NPs induce membrane deformations similar to those around transmembrane proteins, a finding that implies thats NPs may aggregate due to membrane-mediated forces. On the basis of these results, I propose several examples of cooperative interactions that bear future investigation. The findings of this thesis are a comprehensive study of novel nano-bio interactions that reveal a previously unknown pathway for NP-bilayer fusion. Moreover, the physicochemical similarity between the NPs studied here and both other NP formulations and proteins implies that the results may generalize to a large variety of other synthetic and biological systems. This work will be essential in guiding the design of novel biomaterial systems for bioimaging, biosensing, and drug delivery applications and provides significant physical insight into behavior at the cell surface. / by Reid Chi Van Lehn. / Ph. D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2003. / Includes bibliographical references (p. 245-263). / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Predicting macroscopic properties of materials starting from an atomistic or electronic level description can be a formidable task due to the many orders of magnitude in length and time scales that need to be spanned. A characteristic of successful approaches to this problem is the systematic coarse-graining of less relevant degrees of freedom in order to obtain Hamiltonians that span larger length and time scale. Attempts to do this in the static regime (i.e. zero temperature) have already been developed, as well as thermodynamical models where all the internal degrees of freedom are removed. In this thesis, we present an approach that leads to a dynamics for thermodynamic-coarse-grained models. This allows us to obtain temperature-dependent and transport properties. The renormalization group theory is used to create new local potential models between nodes, within the approximation of local thermodynamical equilibrium. Assuming that these potentials give an averaged description of node dynamics, we calculate thermal and mechanical properties. If this method can be sufficiently generalized it may form the basis of a Multiscale Molecular Dynamics method with time and spatial coarse-graining. In the second part of the thesis, we analyze the problem of crystal structure prediction, by using quantum calculations. / (cont.) This is a fundamental problem in materials research and development, and it is typically addressed with highly accurate quantum mechanical computations on a small set of candidate structures, or with empirical rules that have been extracted from a large amount of experimental information, but have limited predictive power. In this thesis, we transfer the concept of heuristic rule extraction to a large library of ab-initio calculated information, and demonstrate that this can be developed into a tool for crystal structure prediction. In addition, we analyze the ab-initio results and prediction for a large number of transition-metal binary alloys. / by Stefano Curtarolo. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1990. / Includes bibliographical references (leaves 245-258). / by Glenn R. Romanoski, Jr. / Ph.D.