Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2003. / Includes bibliographical references. / Addition cure (X1-2672) and condensation cure (4-3136) silicone resins have been studied for their mechanical property change with temperature. Properties include maximum flexural stress, flexural modulus and fracture toughness K[sub]IC. Temperature effect on mechanical properties of addition cure resin is substantial and also depends on the crosslinkers used. Generally the maximum stress and flexural modulus decrease with temperature, and the dependence upon crosslinkers in addition cure resin is obvious. Fracture toughness data of addition cure silicone resins have a peaking behavior with the peak appearing [approximately] 58-101C̊ (depending on the crosslinker) below their glass transition temperatures. This can be explained by the competing effect between network mobility and rigidity of the silicone polymer. Rate effect on fracture toughness of silylphenylene crosslinked 2672 has also been studied. It is concluded that the temperature effect on such a system is more dominant compared to the rate effect. The condensation resins also experience decrease in modulus and strength but the toughness changes little with temperature. This is due to its tight network structure. Silylphenylene crosslinked addition cure resin (2672B) and the toughened condensation cure resin (3136T) were used to make silicone fiberglass laminates. They have been successfully processed with a vacuum bagging technique. Silicone resin composites are proved to be thermally stable, moisture resistant and fire resistant. However, they have weak strength and modulus. Their temperature dependence of mechanical properties is also big and results in poor property retention at high temperatures. 2672B was used to produce hybrid composites with an organic resin-vinyl ester. The processes of curing the hybrid composites in both sequential cure and co-cure methods prove to be successful. The hybrid composites are stronger and their property retention at elevated temperatures is improved compared to silicone resin composites. They also have improved moisture resistance, thermal stability and fire resistance over vinyl ester composites. The co-cured V/B 8/4 structure has excellent strength and rigidity and also extraordinary property retention at high temperatures, which can be explained by the chemical reaction at the silicone resin and vinyl ester resin interface. The hybrid composites prove to be successful in having balanced mechanical and environmental properties. / by Yuhong Wu. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2006. / Includes bibliographical references (p. 190-195). / We have conducted a study of the optical properties of sputtered silicon-rich silicon dioxide (SRO) thin films with specific application for the fabrication of erbium-doped waveguide amplifiers and lasers, polarization sensitive devices and devices to modify the polarization state of light. The SRO thin films were prepared through a reactive RF magnetron sputtering from a Si target in an O2/Ar gas mixture. The film stoichiometry was controlled by varying the power applied to the Si target or changing the percentage of 02 in the gas mixture. A deposition model is presented which incorporates the physical and chemical aspects of the sputtering process to predict the film stoichiometry and deposition rate for variable deposition conditions. The as-deposited films are optically anisotropic with a positive birefringence (nTM > nTE) that increases with increasing silicon content for as-deposited films. The dependence of the birefringence on annealing temperature is also influenced by the silicon content. After annealing, samples with high silicon content (>45 at%) showed birefringence enhancement while samples with low silicon content (<45 at%) showed birefringence reduction. A birefringence of more than 3% can be generated in films with high silicon content (50 at% Si) annealed at 11000C. / (cont.) We attribute the birefringence to the columnar film morphology achieved through our sputtering conditions. Er was incorporated through reactive co-sputtering from Er and Si targets in the same O2/Ar atmosphere in order to investigate the energy-transfer process between SRO and Er for low annealing temperatures. By studying the photoluminescence (PL) intensity of Er:SRO samples annealed in a wide range of temperatures, we demonstrated that the Er sensitization efficiency is maximized between 600°C and 700°C. Temperature-resolved PL spectroscopy on SRO and Er:SRO samples has demonstrated the presence of two different emission sensitizers for samples annealed at 6000C and 1 100°C. This comparative study of temperature-resolved PL spectroscopy along with energy Filtered Transmission Electron Microscopy (EFTEM) has confirmed that the more efficient emission sensitization for samples annealed at 6000C occurs through localized centers within the SRO matrix without the nucleation of Si nanocrystals. Er-doped SRO slab waveguides were fabricated to investigate optical gain and loss for samples annealed at low temperatures. / (cont.) Variable stripe length gain measurements show pump dependent waveguide loss saturation due to stimulated emission with a maximum modal gain of 3 ± 1.4 cm-1 without the observation of carrier induced losses. Pump and probe measurements on ridge waveguides also confirms the presence of SRO sensitized signal enhancement for samples annealed at 6000C. Transmission loss measurements demonstrate a significant loss reduction of 1.5 cm-1or samples annealed at 600°C compared to those annealed at 1000°C. These results suggest a possible route for the fabrication of compact, high-gain planar light sources and amplifiers with a low thermal budget for integration with standard Si CMOS processes. / by Michael Anthony Stolfi. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2008. / Includes bibliographical references (p. 154-165). / To facilitate commercialization of fuel cell systems as alternative energy device, the enhancement of Pt electrocatalysts activity is one of the most challenging issues. The first step to the solution is elucidating relationship between surface structure and chemical reactivity as electrocatalysis occurs on its surface. However, in spite of concerted experimental and theoretical research over the last decades, the detailed mechanism is still in debate. This thesis explores a structural sensitivity of the chemical reactivity in the Pt-based alloy electrocatalysts by combining ab-initio density functional theory (DFT) with relevant thermodynamic and kinetic approach. We developed a rigorous statistical mechanical formalism, which can parameterize the energetics obtained by first principles calculations as a function of surface topologies. This methodology enables kinetic Monte Carlo simulations to provide thermally equilibrated structures as a function of partial pressures of adsorbates and alloy compositions. With our consistent methods, we characterize surface structures on the atomic scale, and quantify chemical reactivity of various Pt-alloy model systems. Our methodology reproduced accurate and consistent results of available experimental measurements. We find that our methodology is considerably useful for studying the structural effect on the heterogeneous catalysis. Through the thesis, we understood better how surface structures evolve according to environmental conditions and hence, the structure-activity relationship, which is useful for design of electrocatalysts. / by Byungchan Han. / Ph.D.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2007. / Includes bibliographical references (p. 21). / Soluble protein antigens used in vaccines have shown lower immune responses when compared with certain particulate forms of these same antigens. For example, it has been shown that micro- and nano-particle mediated delivery of protein antigen can use up to 100 times less protein and still produce an effective immune response [1]. In order to use this phenomenon to make vaccines more efficient, we need a biodegradable delivery particle. This thesis modifies a particle created by Jain et al., which consists of a polymer network surrounding and trapping a protein, by removing the non-degradable crosslinker used in the original particle design and replacing it with a poly (ethylene glycol) acrylate molecule attached to ovalbumin protein. When a dendritic cell degrades the particle, the ovalbumin protein will be degraded, as will the connections between the polymer network that holds the particle together [2]. The particles degraded to 56% of their original size in 3 days, while the non-degradable particle degraded to only 80% of its original size. / by Kendall Werts. / S.B.

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2004. / Includes bibliographical references. / (cont.) portable consumer electronics, such as PDAs, cell phones, music players, digital cameras, etc. make a relatively modest but fast growing market for ultrahigh areal density HAMR-based HDDs. HAMR-based HDD for portable applications could very well be a disruptive technology in the magnetic recording industry. Companies that intend to profit from this technology need to invest on its development and must try to be first-to-volume production to benefit from economies of scale and to build the necessary expertise that could give them leadership roles in future magnetic recording. / The magnetic recording industry keeps up with the demand of high capacity hard disk drives by improving the areal recording density of these devices. The use of conventional longitudinally magnetized media will be truncated by the challenges it faces nowadays, which are related to the instability of the stored information, produced by the aggressive decrease in the volume of the grains in the media. To overcome this problem, the use of large magnetic anisotropy energy density alloys is necessary, but the write fields that are required by such alloys can be prohibitively large, rendering these media effectively unwritable. Fortunately, the magnetocrystalline anisotropy energy density decreases with increasing temperature and so does the required write field. Heat assisted magnetic recording allows the use of such magnetically hard alloys by using both a magnetic and a thermal field during the writing process. Research in HAMR is centered in three major fields: the heat delivery system, the magnetic recording media and the heat dissipation technology. Based on an analysis of several US patents related to HAMR, one can see the real value of such patents is in negotiating and cross-licensing between companies to guarantee the right to participate in the manufacture of HDDs. Trade secrets and know-how are valuable assets for corporations. However, information exchange exists due to the great mobility of highly trained personnel between competing companies. Because the basic application of HAMR is in supplying the computer industry with affordable storage devices, there is a well established market that makes the research efforts in HAMR advisable for individuals, universities and companies. Besides that traditional market, / by Diego A. Méndez del la Luz. / M.Eng.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2007. / Includes bibliographical references (p. 111-119). / The ductile behavior of metals requires dislocation nucleation, from either homogeneous or heterogeneous sources, in order to produce the large number of dislocations necessary for extensive plastic deformation. As with the majority of the defect processes that comprise deformation and failure of materials, dislocation nucleation is well described in the framework of transition state theory as a stress-mediated, thermally activated process. We have used reaction pathway sampling methods and well-fit empirical potentials to determine the stress-dependent behavior of and atomistic mechanisms for dislocation nucleation at stresses much lower than typically accessible to atomistic techniques. We have shown that a significant range of stresses exist for which homogeneous dislocation loop nucleation is feasible because the critical nucleate transitions to an in-plane shear perturbation where the shear displacement of most particles is significantly less than the Burger's vector. We have also revealed that the common structural conception of activation volume for dislocation nucleation does not apply for all stresses and in general over-predicts the stress-dependence of activation by considering only the shear displacement of the critical defect. / (cont.) Furthermore, by considering the full reaction pathway for dislocation nucleation in perfect crystals and at a vacancy, we have provided a fully atomistic description of shear localization via an expanded one-dimensional chain analysis of the wave-steepening behavior. Lastly, both breaking the local atomic symmetry and increasing the extent of heterogeneous nucleation sites are shown to lower the activation energy for dislocation nucleation. In general we have applied reaction pathway sampling to the problem of dislocation nucleation in Cu not only for a perfect crystal, but also in the presence of point defects, vacancy clusters and nanowire surfaces. As a result the strength of a variety of nucleation sites in mediating activation as well as specific atomistic mechanisms for dislocation nucleation have been discussed from both structural and energetic perspectives. / by Robert D. Boyer. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2007. / Includes bibliographical references (p. 221-231). / Along with scaling down in size, novel materials have been introduced into the semiconductor industry to enable continued improvements in performance and cost as predicted by Moore's law. It has become important now more than ever to include an environmental impact evaluation of future technologies, before they are introduced into manufacturing, in order to identify potentially environmentally harmful materials or processes and understand their implications, costs, and mitigation requirements. In this thesis, we introduce a methodology to compare alternative options on the environmental axis, along with the cost and performance axes, in order to create environmentally aware and benign technologies. This methodology also helps to identify potential performance and cost issues in novel technologies by taking a transparent and bottoms-up assessment approach. This methodology is applied to the evaluation of the MIT 3D IC technology in comparison to a standard CMOS 2D IC approach. Both options are compared on all three axes - performance, cost and environmental impact. / (cont.) The "handle wafer" unit process in the existing 3D IC technology, which is a crucial process for back-to-face integration, is found to have a large environmental impact because of its use of thick metal sacrificial layers and high energy consumption. We explore three different handle wafer options, between-die channel, oxide release layer, and alternative low-temperature permanent bonding. The first two approaches use a chemical handle wafer release mechanism; while the third explores solid liquid inter-diffusion (SLID) bonding using copper-indium at 2000C. Preliminary results for copper-indium bonding indicate that a sub-micron thick multi-layer copper-indium stack, when bonded to a 300 nm thick copper film results in large voids in the bonding interface primarily due to rough as-deposited films. Finally, we conduct an overall assessment of these and other proposed handle wafer technologies. The overall assessment shows that but the oxide release layer approach appears promising; however, each process option has its strength and weaknesses, which need to be understood and pursued accordingly. / by Ajay Somani. / Ph.D.

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2008. / Includes bibliographical references (leaves 43-44). / Solar energy has become a hot prospect for the future replacement of fossil fuels, which have limited reserves and cause environmental problems. Solar cell is such a device to directly generate electricity from this clean and renewable energy source. Today's photovoltaic market is dominated by Si flat-plate solar modules, but its production cost is still much higher than that of fossil-fuelled power plant. To reduce this cost, sunlight concentrator, which is made of cheap materials like glass, polymers and metals, can be used together with the solar cell. It is able to focus a wide column of sunrays onto a small piece of solar cell, thus the required dimension of the cell is greatly reduced. The cost analysis showed that it is preferable to use high-end solar cells with higher concentration ratio, since this leads to great increase in output power and less significant increment in overall cost, as this cell cost is small compared with the entire solar unit cost. The best concentration system with most efficient solar cell is found to be able to achieve a lower average price than Si flat-plates, and with sufficient market penetration, its average cost may even be comparable to that of a newly established coal-fired power plant. Therefore, concentration solar module has great potential to secure its share in the fast-growing photovoltaic market, serving as supplement to currently dominating fossil fuels and even replacement for them. Existing IP was also carefully reviewed to find out possible aspects for future developments. Finally, possible business strategies were studied and discussed. It was recommended to start as an IP company, which may expand to manufacturing company in the long run. / by Tao An. / M.Eng.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2009. / 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. / Monolayer patterns of block copolymer (BCP) microdomains have been pursued for applications in below sub-30 nm nanolithography. BCP selfassembly processing is scalable and low cost, and is well-suited for integration with existing semiconductor fabrication techniques. The two critical issues are how to obtain reliable long-range ordering of features with minimum defect densities and how to successfully transfer the patterns into other functional materials. Exceptionally well-ordered and robust nanoscale patterns can be made from poly(styrene-b-dimethylsiloxane) (PS-PDMS) BCPs, which have a very large Flory-Huggins interaction parameter between the blocks compared to other commonly used BCPs. Cylinder- or sphere-forming BCP films were spincoated over silicon substrates patterned with shallow steps using optical lithography or nanoscale posts made by electron-beam lithography, and solvent-annealed to induce ordering. This generates patterns with a correlation length of at least several micrometers. The annealed film was treated with plasma to obtain oxidized PDMS patterns with a lateral dimension of 14 - 18 nm. These can be used as an etch mask or an easily removable template for patterning functional materials. Solvent vapor treatments can tune the pattern dimension and morphology. Different degrees of solvent uptake in BCP films during solvent-annealing can manipulate the interfacial interaction between the two blocks, and a mixed solvent vapor can change the effective volume fraction of each block. The self-assembled patterns can be transferred into various kinds of functional materials. / (cont.) For example, arrays of parallel lines were used as a mask to pattern poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) conducting polymer thin films. The resulting PEDOT:PSS nanowire array was used as an chemiresistive-type ethanol-sensing device. Metallic films such as Ti, Pt, Ta, W, and magnetic Co and Ni were structured using a pattern-reversal process. Coercivity enhancements were observed for the fabricated ferromagnetic nanostructures such as wires, rings, and antidots. These functional nanostructures can be utilized for a variety of devices such as high-density and high performance sensor or memory devices. / by Yeon Sik Jung. / Ph.D.

Thesis: S.B., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2017. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 48-49). / There exists a need to detect methane (CH₄) gas, and optical sensors provide many advantages over electronic sensors. Single-walled carbon nanotubes (SWNT) can be used as optical sensors, as SWNTs emit fluorescence upon photoexcitation. The photoluminescent (PL) intensity upon excitation depends on the electronic structure of the SWNT. Here, SWNTs are loaded with palladium (Pd) nanoparticles using sodium dodecyl sulfate (SDS). The Pd-loaded SWNTs offer a detection mechanism for methane (CH 4) by comparing the PL intensity before and after exposure to CH₄.A significant PL change (relative to the experiment) indicates a "turn-on" response to CH₄ Preliminary experiments showed no response to CH4 at zero and high (>10mM) Pd loading in both aqueous solution and film, indicating that there must be an optimal Pd concentration in the middle. This optimal loading for methane response was found to be in the range 2.61mM - 5.21mM Pd²+. The Pd-SWNTs in aqueous solution showed selectivity to CH₄ over nitrogen gas (N₂ and ambient air (20-22% O₂). SDS-SWNT (the control) showed a significant response to N₂ and air while Pd-SWNTs in aqueous solution showed the greatest response to methane. In film, the optimal Pd-loading (5.21mM) for sensitivity was found to exhibit an inexplicable high response to N₂ but still displayed selectivity to methane over ambient air. Pd-SWNTs in aqueous solution and film showed stability of response over time. Pd- SWNTs in aqueous solution maintained the PL intensity with a minor decrease (3- 19% decrease) in Day 14 as compared to Day 1. Pd-SWNT in aqueous solution showed turn-on response under the methane gas in Day 14. In film, the optimal Pd-loading (5.21mM) and a lower Pd-loaded SWNT (2.61mM) displayed a turn-on response to methane after 14 days, showing stability in response over time. This work has thus demonstrated an optimally Pd-loaded SWNT that is sensitive, selective, and stable over time to methane gas. / by Melissa Keiko McGee. / S.B.