Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2001. / Includes bibliographical references (leaves 97-99). / Many transducer technologies would benefit tremendously from the development of shaped, oriented single-crystals, of a high-strain, piezoelectric material. Recently, unusually high electrostrictive and piezoelectric actuation has been observed in polycrystals and flux-grown <100> single-crystals of ... Using seeded, Edgedefined Film-fed Growth (EFG) and the related Stepanov Technique (ST), low-hysteresis, highstrain, <100> and <111> oriented, single-crystals of BNBZT can be grown in rod and fiber form, with direct applications in active fiber composites and related devices. For this work, <100> and <111> oriented, single-crystal rods and fibers were grown via ST and EFG. Fibers, 260-700[mu]m in diameter and over 1.0 meter long, were grown using a custom built EFG machine and a capillary-shaper; rods, 2-3mm in diameter, up to 110mm long were grown using a floating-shaper. In all cases, strontium titanate (STO) was found to be an effective seed crystal. <111> oriented tetragonal crystals generated low hysteresis actuation consistent with a polarization rotation mechanism [14], but with only modest strains: ... <100> oriented tetragonal BNBZT generated high strains up to ... with hysteresis consistent with 90° domain switching. Electromechanical actuation and crystal structure in this system appear to be strongly affected by deviations from stoichiometry (B-site vacancies). Barium segregation and bismuth vaporization can also compromise electromechanical performance. Hypotheses are posed to explain the low actuation seen from <111> oriented ferroelectrics, and the effects of cation deficiencies on phase-stability. Cracks, pores, and other growth challenges encountered in ST and EFG growth of BNBZT are described. / by Benjamin P. Nunes. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1999. / Includes bibliographical references (leaves 89-92). / by Thomas J. Nugent, Jr. / S.M.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2017. / Cataloged from PDF version of thesis. / Includes bibliographical references. / Block copolymer (BCP) self-assembly is attractive because it provides nanoscale long-range ordered structures in a massive quantity. The capability of generating features with size as low as 5 nm is of particular interest in semiconductor fabrication since current photolithography has reached its resolution limitation and the other competing technologies are either too slow such as e-beam lithography or too expensive such as EUV system. In this thesis, BCP lithography is utilized to fabricate magnetic nanostructure and the corresponding magnetic properties are explored. The polystyrene- b-polydimethylsiloxane (PS-b-PDMS) diblock copolymer with different molecule weight is used to generate various sizes of robust silica pattern after solvent annealing and reactive ion etching. Pattern transfer methods are developed to convert the silica pattern into functional materials, including magnetic materials like cobalt, Co/Pd, FePt and CoFeB magnetic tunnel junctions (MTJ), and MoS2 monolayers. For magnetic nanowire arrays, the interactions between neighboring wires are investigated. For perpendicular MTJ nanopillar arrays, the size-dependent switching behavior and magnetostatic effects between two layers are analyzed. MoS 2 monolayers are patterned into features such as nanodots, nanorods and nanomeshs and the corresponding photoluminescence are characterized. Finally, machine learning and deep learning algorithms are the first-time ever demonstrated to model the BCP self-assembly process. The built model is able to recognize different BCP patterns and predicting the resulting morphology and pattern quality based on experimental process parameters. With this model, the BCP self-assembly can be further optimized toward industrial-grade production. / by Kun-Hua Tu. / Ph. D.

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1993. / Includes bibliographical references. / by John R. González. / B.S.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2008. / Includes bibliographical references (p. 107-111). / The development of electric-field-induced optical modulation in the materials capable of monolithically integrated on silicon (Si) substrates offer the possibility of high-speed modulation in a pico second timeframe as well as low power consumption, key requirements for integrated modulator applications. This thesis presents a study of the Franz-Keldysh effect in germanium (Ge) layers epitaxially grown on Si substrates, by using free-space spectral responsivity measurement. Generalized Franz-Keldysh formalism and separately measured Ge material constants were used to calculate theoretical results, which were in agreement with experimental data. The Franz-Keldysh model predicts that the Ge layers on Si substrates will be the best material for phase modulation at nearly 2 [mu]m wavelength, with a value of L, of 3.8 mm and insertion loss of 0.4 dB. In addition, this thesis presents the design of silicon-germanium (SixGe1-x) electroabsorption and phase modulators at 1.55 pLm wavelength from the Franz-Keldysh model. The composition optimized for electroabsorption and phase modulator applications is SixGe1-x with a value of x~0.075 and 0.135, respectively. To achieve high-quality Ge-rich SiGe materials for the modulator applications, deposition of SixGe1-x (0.008<x<0.125) buffers at low temperature was performed, and the growth kinetic was studied. The films were deposited on SiGe buffers to reduce lattice mismatch between the buffers and the remainders of the films, and were in-situ annealed in the same condition as was used for similarly grown Ge films for a reduction of threading dislocation density. Si0.15Ge0.85 p-i-n diodes and Sio.15Geo.ss rib waveguides were fabricated. / (cont.) High leakage current in the Si0.15Ge0.85 p-i-n diodes was due to dislocation defects consistent with measured threading dislocation density from PV-TEM images, which showed threading dislocation density of approximately 1.5±0.5 x 109 cm-2. The analysis shows that threading dislocation density below 5 x 107 cm-2 is required for high performance of p-i-n diodes. Furthermore, high optical loss was measured in Si0.15Ge0.85 rib waveguides and strip-load waveguides. The loss is due to light scattering at sidewalls and dislocations. Scattering from dislocations less than 1 x 108 cm-2 is required for loss below materials' interband absorption. This high threading dislocation density shows that the annealing condition used for Ge-on-Si is not effective in reduction of threading dislocation density in Si0.15Ge0.85. Si solutes/dislocations interactions in Si0.15Ge0.85 reduce glide velocity of dislocations as well as the possibility that dislocations run into and annihilate one another. / by Samerkhae, Jongthammanurak. / 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. / Includes bibliographical references (leaves 46-47). / Information processing systems have been getting more powerful over the course of the past three decades due to the scaling of transistor dimensions. Scaling of transistor dimension causes a plethora of technological problems if pursued in the current fashion. Gate-All-Around architecture for transistors has been shown to alleviate many of the problems posed by scaling. Silicon being the material of choice of the semiconductor industry, it is highly desirable to have silicon one dimensional channel in the Gate-All- Around transistor. Silicon nanowires have been fabricated using various methods, in this work Self-Limiting-Oxidation was analyzed for its technological feasibility and found to be satisfactory. Possible value propositions and IP landscape analysis show that this methodology is very much feasible. As the new architecture essentially solves the problems that arise due to aggressive scaling, it becomes vital to look at the relevance of scaling beyond 45 nm technology node. Careful analysis of the semiconductor industry breakdown and top semiconductor foundries' financials reveal that scaling might not be pursued as aggressively as expected. The relevance of Moore's law in the current scheme of things could be that of a Self-fulfilling prophecy. Given this climate, Self Limiting Oxidation based Silicon nanowires have better commercial potential in the field of sensors. Monolithic integration and superior spatial precision makes this methodology ideally suited to the needs of applications which include many different kinds of sensors on the same Lab-on-Chip. / by Rajamouly Swaminathan Omampuliyur. / M.Eng.

Thesis: S.B., Massachusetts Institute of Technology, Department of Materials Science and Engineering, June 2014. / Cataloged from PDF version of thesis. "May 2013." / Includes bibliographical references (pages 86-87). / Connecting structure to properties, and optimizing properties by controlling structure is one of the fundamental goals of materials science and engineering. No where is this connection more apparent than with biomaterials, whose unparalleled properties are the result of the evolution via cumulative selection of highly specialized structures. Beyond biomaterials, cumulative selection offers a generalizable model for materials optimization via accumulative of beneficial mutations in a material's genome that improve the properties for a given function. A genetic algorithm is one method for applying the principals of cumulative selection to material's optimization. One of unique property that cumulative selection generated was the ability of trabecular bone to optimize and adjust its structure in vivo in response to changes in its loading conditions. This work presents a model for trabecular microstructure evolution using a genetic algorithm, the same mechanism through which that ability evolved. The algorithm begins by translating a trabecular genome into a developed structure. It then simulates the structure's response under an applied load and selects for the genome which translates into the best structure. The selected genome is then replicated and mutated. Simulations of microstructure evolution consist of iterating through this process across multiple generations. A series of simulations was conducted demonstrating the ability of the algorithm to improve trabecular architecture. The systems tended to converge to a uniform stress distribution, after which additional generations of evolution had no effect on performance. During the simulations it was found that the length of the computation was most sensitive to the number of offspring per generation. Although focused on trabecular microstructure, this work establishes the use of a genetic algorithm as a general tool for material's optimization. / by Samuel W. L. Shames. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2003. / Includes bibliographical references (p. 135-140). / Packaging is an important aspect of microelectromechanical systems (MEMS) design. As MEMS devices traverse multiple energy domains, sometimes operating in hostile conditions, the need to maintain reliability and functionality makes packaging a challenging problem. Often, the package needs to be specially designed for each device. Given the typically low volume productions, the packaging cost can often exceed the device cost. One way to lower that cost is to package at the wafer-level. This thesis explores a low temperature wafer bonding technique: thermocompression bonding. This technique relies on the applied pressure and temperature to forge a bond. The pressure brings two surfaces into close proximity while the temperature reduces the pressure requirement to deform the surface asperities. In this work, gold thin film was used to bond two silicon substrates. The thesis discusses the fabrication process, its associated challenges, and provides guidelines to achievesuccessful bonding. Characterization of the process focused mainly on the effects of bonding temperature (260 to 300° C), pressure (1.25 to 120 MPa) and time (2 to 90 min). The resultant bond was quantified using a four-point bend-delamination technique. High bond toughness was obtained and the bond quality was found to improve with increases in the bond temperature and pressure. However, non-uniform bonding was observed. Using finite element analysis, correlation between the mask layout and non-uniform pressure distribution was found. The four-point bend-delamination technique was also evaluated for its effectiveness in measuring high toughness bonds. Non-ideality in the load-displacement behavior were observed due to the variation in the bond toughness. A cohesive zone model was used to model the fracture process. The finite element results showed qualitative agreement with experimental data. The results also indicated that the technique is not well suited for bonds with large variations in bond toughness. / by Christine H. Tsau. / Ph.D.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2005. / Includes bibliographical references (leaf 38). / Several parameters that affect the formation, size and spatial distribution of micelles of poly(styrene-block-acrylic acid) (PS-b-PAA) in organic solvents or assembled on solid substrates have been investigated. The micelles were characterized in the solvated state using Dynamic Light Scattering, and were imaged and characterized in the dry thin film state using Atomic Force Microscopy. Micelle size in solution followed scaling laws based on the ratio of the two block copolymer segments. Micelle size was not affected by the addition of PS homopolymer or salt, whereas micelle diameter did increase with the addition of PAA homopolymer both in solution and in the dry state on sold supports. Furthermore, micelles formed in toluene, but they did not form in tetrahydrofurane, chloroform or hexane. In terms of spatial distribution in the dry state, the only parameters which affected spacing, and therefore density, were annealing conditions and addition of PAA homopolymer. Annealing near or below the glass transition temperature for 16 hours increased the order of the films, as was demonstrated by Fast Fourier Transforms of their AFM images. Annealing for longer periods of time or at temperatures significantly above the glass transition temperature destroyed the micelles. / by Naomi Kohen. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2008. / Includes bibliographical references (leaves 111-122). / Surfaces with reversible stimulus-responsive properties have great potential for a wide variety of applications, such as transport, separation, and detection of biomolecules, controlled adhesion, friction, and lubrication in microfluidic systems, and force or displacement generation in micro- and nanoscale devices. Surface bound stimulusresponsive polymers are ideal candidates for above applications due to their conformational sensitivity to many stimuli with controlled molecular weight, composition, architecture and topology. In this thesis, one particular class of stimulus-responsive polymers, pH-sensitive comb-type graft copolymers with ionizable main chain segments was investigated. Mono(end)-functional thiol-terminated poly(methacrylic acid-gethylene glycol) (HS-poly(MAA-g-EG)) with three different macromolecular architectures (number average molecular weight, Mn = 27K, PEG graft density, PEG(%) = 7.7%, backbone contour length, Lcontour= 41.1 nm; Mn= 15K, PEG(%) = 8.8%, Lcontour = 22.1 nm; Mn = 17K, PEG(%)= 1.9%, Lcontour = 39.8 nm) have been synthesized via atomic transfer radical polymerization and characterized by 'H NMR, GPC and FT-IR. Stimulus responsive surfaces were prepared via chemically end-attached "brush-brushes" formed by chemisorption of the copolymers on Au substrates. Chemically specific high resolution force spectroscopy (HRFS) was carried out with probe tips (end radius-50 nm) functionalized with HS(CH2)10COOH (a carboxy-terminated selfassembling monolayer or COOH-SAM) to measure the normal nanoscale interaction forces, F, as a function of probe-tip sample separation distance, D,in a series of aqueous buffer solutions of varied pH (=4-9) and constant ionic strength (IS=0.005M NaC1). / (cont.) The higher PEG grafting density surfaces (27K, 15K) exhibited the unique property of "nanomechanical switching" with pH, i.e. the normal intersurface force inverted from net repulsive (high pH, ionized uncomplexed side chains) to net attractive (low pH, sidechain/main-chain hydrogen bonding complexation). The 17K polymer brushes did not exhibit nanomechanical switching and maintained a slightly repulsive intersurface force at low pH. Surface plasmon resonance (SPR) was employed to assess the adsorption of human serum albumin (HSA) to these poly(MAA-g-EG) brushes in aqueous buffer solutions of varying pH. Polymers with a higher grafting density of hydrophilic PEG side chains and longer polymer backbones showed much less HSA adsorption at high pH and more protein adsorption at low pH. Surprisingly, HSA adsorption was found to be greatly amplified at intermediate pH6 (~1.4-1.8 x greater than that of the hydrophobic state of polymer layers at pH4). Higher PEG grafting density and a longer polymer backbone demonstrated larger protein adsorption amplification at pH6, which may be due to increased molecular mobility/disorder at a metastable state of the conformational transition. For the lateral force interaction between the end-grafted polymer layers and a probe tip (nominal radius - 50 nm) functionalized with OH-SAM (HS(CH2)11OH), as pH decreased, both the 27K and 17K polymer layers exhibit an abrupt change in lateral proportionality coefficient (ratio of lateral force to normal force) between pH7.1 and pH6 with larger lateral proportionality coefficients, [mu] ~ 0.63-0.89 at pH 4-6 and decreased [mu] ~ 0.12-0.34 at pH 7.1-9. / (cont.) The 27K polymer had relatively higher p values at pH < 6 (0.89±0.19) but smaller [mu] at pH > 7.1 (0.21±0.04) than the 17K polymer, indicating that a more dramatic change in lateral force coefficient is expected for stimulus-responsive graft copolymers with higher side chain grafting densities. / by Miao Ye. / Ph.D.