64,428 research outputs found
An analysis of the energy efficiency and economic viability of expanded magnesium utilization
No full textThesis: Sc. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 1979Vita.Includes bibliographical references.by George Brian Kenney.Sc. D.Sc. D. Massachusetts Institute of Technology, Department of Materials Science and Engineerin
Study of nanocomposite thin film fabrication on graphoepitaxial templates
No full textThesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2017.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 159-169).Block copolymers (BCPs) are a class of soft materials consisting of two (or more) different chains joint together by covalent bond. This special chemical structure leads to microphase separation and consequently a variety of highly controllable self-assembly patterns. Directed self-assembly (DSA) of BCPs has therefore emerged as one of the most promising technologies to fabricate functional nanostructures and is able to produce patterns with ultra-small resolution (sub-10 nm) while maintaining high throughput and order. However, existing DSA methods depend mostly on carbon or silicon-based BCPs, thus lack functionality for sophisticated applications. This work aims at expanding the capability of DSA techniques by exploring new ways of incorporating functional materials into the BCP matrix and by imposing non-native symmetries on the BCP patterns. First, we focused on constructing nanocomposite thin films composed of BCPs and various types of functional materials (i.e., inorganic ions, inorganic-organic complex, organic compounds and nanoparticles). Based upon this methodology, we developed novel ways of fabricating mesoporous thin film structures with rectangular, triangular and quasicrystalline symmetries by means of graphoepitaxial post array templates. On the other hand, we also examined the limits of DSA by introducing artificial noise to mimic fabrication errors and studied the corresponding responses from BCP. This study demonstrates the potential of DSA of BCP in building thin film nanostructure of unconventional symmetries with functional components.by Yi Ding.Ph. D
First-principles studies of defects in colloidal nanocrystals
No full textThesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2019Cataloged from PDF version of thesis.Includes bibliographical references (pages 91-102).Solar energy is one of the few renewable, low-carbon sources with both the maturity and accessibility to meet the ever-increasing global demand for energy. There are also accounting for an increasing percentage of our energy output due to increased adoption in both industrial and residential areas. Wafer based silicon photovolatics (PV) technology has dominated the solar market, whereby its price has increased significantly over the last decades. In order to fully capture the solar energy from the sun and extend the flexibility of PV technology, there is a need for constant innovation for new materials. Currently, there is a class pf emerging PV technologies that offer the potential of increased scalability, flexibility and lower prices. They include hybrid organic-inorganic lead halide perovskite PV, organic PV and colloidal quantum dot (CQD) PV. Colloidal quantum dots are semiconducting nanocrystals that exhibit size tunable electronic and optical properties.Owing to their versatility and facile synthesis, they have seen wide application photovoltaics, light emitting diodes, solar concentrators and bio-imaging. In particular, their PV power conversion efficiency has grown rapidly over the last 9 years from 3% to 16.6%. Despite the rapid progress, the search for better PV materials has been carried out almost exclusively through tremendous numbers of trial and error experiments. This is due to the fact that many fundamental aspects of the materials has not been fully understood, especially the role of defects and trap states. Due to the nature of wet chemistry synthesis, vacancies, intersitial and other extended defects inevitably form. These defects often cause in gap states within the semiconductor bandgap, which sensitively impact the performance of the PV devices. In addition, defects are difficult to measure directly using experimental techniques, and we often rely on spectroscopic and imaging to probe their properties indirectly.The core of the work described in this thesis deals with the theoretical understanding of nanocrystals with the goal of achieving a deeper and more fundamental understanding of the material's properties at the atomic scale, focusing on the roles of defects. To this end, we employ a technique of computational electronic structure calculation methods, namely density functional theory (DFT) calculations. In this thesis we will use DFT to investigate and find the role that defects play at controlling the 1) Stokes shift and 2) trap states in PbS quantum dot, as well as the 3) luminescent properties of CuAlS₂ nanocrystals. While we show that points defects can cause excessive Stokes shift in single PbS CQDs, and dimer defects are a source of detrimental trap states in PbS CQD solids, the presence of point defects are the source of high luminescence in CuAl₂ nanocrystals.We have also provided insights and design guidelines to control defects to design ever more efficient PV devices at an atomic level. This thesis document is organized as follows: Chapter 1 introduce CQD and their applications in PV and other optoelectronic devices. Chapter 2 summarizes the computational techniques employed in this thesis work. Chapter 3 focuses on the origins of the Stokes shift in PbS nanocrystal. Chapter 4 focuses on the PbS superlattice solids, and highlight the origin of trap states in these solids as due to the presence of dimers. Chapter 5 studies the defect physics of CuAlS₂, and identifies the defect states responsible for the high photoluminescene.by Yun Liu.Ph. D.Ph.D. Massachusetts Institute of Technology, Department of Materials Science and Engineerin
Superconducting DC-sputtered Nb3Ge films : fabrication, structure, and properties
No full textThesis (Sc.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1979.MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE.Vita.Includes bibliographical references.by James Allen Gregory.Sc.D
Finding Aid for Social Science Department Records, 1931-
No full textThis collection includes department meeting minutes, course descriptions, outlines, bibliographies, course materials, correspondence of department chair, and miscellaneous materials from the Social Science Department
Structure and relaxation studies of high performance thermoplastics
Full text linkThesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1995.Includes bibliographical references (leaves 221-229).by Xin Lu.Ph.D
The World of Materials, Fall 1998
No full textThis is the biannual newsletter for the Department of Materials Science and Engineering
The World of Materials, Spring 1999
No full textThis is the biannual newsletter for the Department of Materials Science and Engineering
Self-assembly of silicon-containing triblock copolymer and terpolymers
No full textThesis: S.M., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2019Cataloged from PDF version of thesis.Includes bibliographical references.The block copolymer (BCP) self-assembly has garnered significant interest due to its ability to generate periodic nanostructures with a variety of morphologies. Compared to diblock copolymers that have been extensively studied to form the conventional morphologies such as spheres, cylinders, and lamellae depending on the block volume fraction, more complex polymer architectures are expected to offer additional degrees of freedom and a wider range of structures. Solvent vapor annealing (SVA) using a continuous gas flow system allows a precise control over the annealing condition, which can capture intermediate morphologies including perforated lamellae and gyroids and can create unique nanostructures that have not been observed in diblock copolymers. Combining with self-consistent field theory (SCFT) modeling and in situ grazing-incidence small-angle X-ray scattering (GISAXS) measurement, the phase behavior of advanced polymer architectures can be revealed in details.Here, the self-assembly behavior of silicon-containing triblock copolymer and terpolymers in multi-layered films under SVA is presented. Using both experimental and SCFT approaches, the phase behavior of poly(stryrene-b-dimethylsiloxane-b-styrene) (PS-b-PDMS-b-PS or SDS32) thin films was investigated as a function of the as-cast film thickness and the ratio of two different solvent vapors, toluene and heptane. In comparison with diblock PS-b-PDMS with same molecular weight, the SDS32 offers a simple route to produce a diversity of well-ordered bilayer structures with smaller feature sizes, including the formation of bilayer perforated lamellae over a large process window. In addition, the morphological evolution of core-shell cylinder-forming triblock terpolymers during SVA was monitored in situ using GISAXS. A reversible order-order phase transformation between spheres and cylinders occurred during the annealing process.One of the final morphologies consisted of the regions of in-plane cylinders, with the majority of the film comprising vertical core-shell cylinders passing through perforated lamellae of poly 1,1-dimethyl silacyclobutane (PDMSB).by Sangho Lee.S.M.S.M. Massachusetts Institute of Technology, Department of Materials Science and Engineerin
Life-cycle analysis of hazardous chemicals in the Department of Materials Science & Engineering
No full textThesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2013.Cataloged from PDF version of thesis.Includes bibliographical references (p. 29).MIT policies set forth by the Department of Environment, Health, and Safety (EHS) require that all laboratories maintain a chemical inventory to properly document the use of hazardous chemicals. While EHS has provided a chemical inventory management tool called ChemTracker to help labs to do so, it is estimated that less than 20% of laboratories utilize the software. As a result, an EHS committee has been formed to re-evaluate ChemTracker and explore other options for inventory management. RFPs have been sent to potential vendors to determine if alternatives can better satisfy the goals of EHS and attain the benefits of effective chemical management. To analyze the problem of low usage rates of ChemTracker, interviews were conducted with research groups within the Department of Materials Science & Engineering (DMSE). These revealed that the largest variables were the number of chemicals used by the lab and the user-friendliness of the software. The initial time investment to switch from current, simpler methods to ChemTracker discouraged many smaller labs from pursuing that option. Current users of ChemTracker also expressed frustration with auto-fill features that weren't comprehensive and thus hindered the process of entering and updating inventory. Future work should expand into other departments to observe usage behavior and concerns and compare to those within DMSE. Any chemical inventory management software should be user-tested prior to full Institute implementation to ensure adoption by a larger proportion of groups around campus. While compulsory software would also ensure adoption, a one-size-fits-all approach is not appropriate for chemical tracking due to the hassle it could create and the potential impact on productivity of research itself. Thus, further analysis of user concerns and better marketing of the tools to address those concerns are required for a successful solution to the problem.by Valerie Jing-chi Chia.S.B
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