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.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1994. / Includes bibliographical references (leaves 158-161). / by Kristi L. Fukami. / M.S.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 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 133-147). / Wide band-gap nanowires composed of GaN and ZnO are promising materials for unique designs and potential efficiency improvement of light emitting diodes (LEDs) for solid state lighting. The large surface-to-volume ratio of nanowires provides facile strain-relaxation such that nanowires can be grown on substrates with a large lattice mismatch and remain free of threading dislocations. Specifically, the growth of wide band-gap nanowires directly on Si substrates is a promising platform for the fabrication of wafer-scale nanowire array-based LEDs. While nanowire-based LEDs have been previously demonstrated, there has been no work directly comparing the different potential designs of nanowire-based LEDs addressing how material-specific properties affect the light extraction and internal quantum efficiency (IQE). Furthermore, for scalable fabrication of nanowire array-based LEDs on Si a large degree of control over the nanowire synthesis is necessary, especially with regard to the nanowire length uniformity, vertical alignment relative to the growth substrate and the nanowire areal density. In this work we directly compare feasible designs for GaN-InGaN nanowire-based LEDs using a combination of photonic simulation and modeling. We compared the directed external quantum efficiency of III-nitride LEDs on silicon based on axial and radial nanowire heterostructures, considering m- and c-directional nanowires. The directed extraction efficiency was calculated using photonic simulations and the IQE was estimated using the A-B-C model. We found that m-directional axial heterostructures have the highest directed extraction efficiency, due to the strong polarization anisotropy of III-nitrides, and display similar IQE as c-directional axial heterostructures. By combining IQE and directed extraction, a range of expected directed external quantum efficiencies (EQEs) reveal that m-directional axial heterostructures have EQEs up to three times that of c-directional axial heterostructures, providing guidelines for the design of future III-nitride nanowire-based LEDs. While III-nitride nanowires are promising candidates, ZnO is an alternative with a higher exciton binding energy and excellent optical properties. To create a platform for the fabrication of ZnO nanowire array-based LEDs on Si, the growth of ZnO was investigated primarily using ZnO solution-processed seed-layers in vapor transport and condensation growth at high temperatures. Due to dependency of the carbothermal reduction of ZnO powder, which acts as the precursor source in the growth, the nanowire areal density was dependent on O2 flow. At low nanowire areal density, growth proceeded in a regime in which continuous nucleation of nanowires occurred throughout the growth, resulting in nanowires with a fixed aspect ratio, but widely varying lengths. At higher nanowire areal densities, the nanowires competed for source precursors in a surface-diffusion limited regime of growth in which the growth rate was dependent upon the nanowire diameter. We observed a critical nucleation diameter for nanowires in the continuous-nucleation regime, which was higher at lower oxygen flow rates. Thus, to achieve length uniformity we developed a two-stage growth method in which nanowires are nucleated at low oxygen flow in the continuous nucleation regime to set the nanowire diameter. In the second stage of growth, where conditions were shifted to the surface-diffusion limited regime, the large diameters set by the first stage of growth were designed to be in the range at which the growth rate does not vary substantially with diameter. The concept of this approach was extended to include control over the nanowire areal density, using sparse ZnO seed-layers. These ZnO nanowires retain excellent optical properties and we observed both demonstrative ptype and n-type doping, dependent on processing conditions, using individual nanowire electrical characterization. Thus, by achieving ZnO nanowire arrays with controlled nanowire areal density, excellent length uniformity and vertical alignment relative to the substrate, we have demonstrated a promising platform for the fabrication of scalable ZnO nanowire array-based LEDs. / by Jordan Chesin. / Ph. D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1994. / Includes bibliographical references (leaves 70-71). / by Julia Carmel Duncan. / M.S.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2013. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 39-41). / This thesis seeks to assess the viability of a space qualified shape memory polymer (SMP) mechanical counter pressure (MCP) suit. A key development objective identified by the International Space Exploration Coordination Group, the development of a superior space suit with greater mobility and environmental robustness is necessary to support long-range human space exploration, specifically a mission to Mars. Conceptualized in 1971, a spacesuit utilizing MCP would fulfill these goals but its development was halted due to inadequate mechanical analysis and material limitations at the time. Since then, new active materials have been assessed to potentially further the development of a space qualified MCP space suit, which include quantitative thresholds for minimum pressure production, durability, pressure distribution, mobility range, and ease of garment donning and doffing. Guided by these criteria, a SMP biaxial tubular braid applying MCP through active compression was designed and the prototype manufacturing processes were outlined. To predict the pressure production of this garment, the thermo-mechanics of a SMP was combined with the textile mechanics of a biaxial tubular braid and simulated within design parameter ranges consistent with the design criteria and practical considerations. The pressure production was controllable with the design parameters SMP elastic modulus, garment radial deformation, textile fiber spacing, and operational temperature. Assuming reasonable model accuracy, a SMP garment could achieve the necessary pressure production for a space qualified MCP suit, however, the durability of such a garment would be questionable considering the creep sustained from consecutive spacewalks of four to eight hours. Recommendations are made for methods to increase model accuracy, suggested SMP actuation mechanisms, and alternative textile architectures. / by Brian Wee. / S.B.