Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2007. / Includes bibliographical references (p. 295-303). / Multilevel copper metallization for Ultra-Large-Scale-Integrated (ULSI) circuits is a critical technology needed to meet performance requirements for advanced interconnect technologies with sub-micron dimensions. It is well known that multilevel topography resulting from pattern dependencies in various processes, especially copper Electrochemical Deposition (ECD) and Chemical-Mechanical Planarization (CMP), is a major problem in interconnects. An integrated pattern dependent chip-scale model for multilevel copper metallization is contributed to help understand and meet dishing and erosion requirements, to optimize the combined plating and polishing process to achieve minimal environmental impact, higher yield and performance, and to enable optimization of layout and dummy fill designs. First, a physics-based chip-scale copper ECD model is developed. By considering copper ion depletion effects, and surface additive adsorption and desorption, the plating model is able to predict the initial topography for subsequent CMP modeling with sufficient accuracy and computational efficiency. Second, a compatible chip-scale CMP modeling is developed. / (cont.) The CMP model integrates contact wear and density-step-height approaches, so that a consistent and coherent chip-scale model framework can be used for copper bulk polishing, copper over-polishing, and barrier layer polishing stages. A variant of this CMP model is developed which explicitly considers the pad topography properties. Finally, ECD and CMP parts are combined into an integrated model applicable to single level and multilevel metallization cases. The integrated multilevel copper metallization model is applied to the co-optimization of the plating and CMP processes. An alternative in-pattern (rather than between-pattern) dummy fill strategy is proposed. The integrated ECD/CMP model is applied to the optimization of the in-pattern fill, to achieve improved ECD uniformity and final post-CMP topography. / by Hong Cai. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2008. / Includes bibliographical references (p. 46-48). / We present a general outline for automating cluster expansions of configurational energetics in systems with crystallographic order and well defined space group symmetry. The method presented herein combines constrained optimization techniques of positive-definitive quadratic forms with the mathematical tool of Tikhonov regularization (kernel smoothing) for automated expansions of an arbitrary general physical property without compromising the underlying physics. Throughout the thesis we treat formation energy as the fundamental physical observable to expand on since the predominant application of cluster expansions is the extraction of robust approximations for configurational energetics in alloys and oxides. We therefore present the implementational aspects of the novel algorithmic route on a challenging material system NaxCoO2 and reconstruct the corresponding GGA ground state line with arbitrary precision in the formation energy-configuration space. The mathematical arguments and proofs, although discussed for cases with arbitrary spin assignments and multiple candidate species for single site occupancy, are eventually formulated and illustrated for binary systems. Various numerical challanges and the way they are resolved in the framework of kernel smoothing are addressed in detail as well. However, the applicability of the procedure described herein is more universal and can be tailored to probe different observables without resorting to modifications in the algorithmic implementation or the fundemantal mathematical construction. The effectiveness in recovering correct physics shall than be solely tied to the presence of superposable nature (of the physical property of interest) of local atomic configurations or lackthereof. / by Osman Burak Okan. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2010. / 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 (p. 145-151). / The synthesis of Si and III-V nanowires using the vapor-liquid-solid (VLS) growth mechanism and low-cost Si substrates was investigated. The VLS mechanism allows fabrication of heterostructures which are not readily attainable using traditional thin-film metalorganic chemical vapor deposition (MOCVD). In addition to these heterostructures, the VLS mechanism allows exploration of Si substrates as platforms for advanced III-V devices, a long-standing goal of the III-V research community, because of the potential for significant cost reductions. The approach to nanowire development first began by focusing on the binary Au/Si system. This system allowed us to understand critical parameters of our process including e-beam evaporation of Au thin-films, deposition of Au-colloid particles, pregrowth cleaning procedures and CVD growth conditions and times. Once controllable and repeatable Si nanowire epitaxy on Si substrates was established, we were able to focus on development of both III-V wires on Si substrates as well as Si substrates with topographic features and silicon-on-insulator (SOI) wafers. Growth abnormalities between Au-colloid nanoparticle catalysts and Au thin-film catalysts revealed a correlation between Au coverage on the substrate surface and Si nanowire growth rate. We found an increasing growth rate with increasing concentrations of Au catalyst particles on the wafer surface. Systematic experiments relating the nanowire growth rate to the proximity of nearest-neighbor Au-particles and Au-reservoirs were carried out and the results were found to be in good agreement with a SiH4 reaction model which associates decomposition to form SiH2 with higher nanowire growth rates. III-V nanowire growth on Si substrates was investigated as a possible route to the realization of high performance compound semiconductor devices on low cost substrates. For this study, GaP and InP were chosen as starting points for III-V nanowire integration with Si. Initial studies which focused on III-V wire epitaxy found that when Au-catalyst particles were treated with the group-III precursors before growth, there was an increase in the fraction of catalyst particles yielding wire growth and in the number of wires growing vertically from the substrate. Axial nanowire heterostructures of GaP(w)/InP(w)/GaP(w) were fabricated using MOCVD on Si (111) substrates. Growth temperature was found to be critical in the formation of GaP/InP axial heterostructures with minimal simultaneous lateral 3 overgrowth of InP. Analysis of the second GaP segment on InP suggests that an increase in growth temperature while Au is in direct contact with InP results in the InP dissolving into the Au particle and disappearance of the heterostructure. Si substrates were used as a foundation to explore more complex silicon structures, such as ordered arrays and SOI architectures. Although several routes initially looked promising for ordered array development, inverted pyramid arrays on Si (100) substrates were found to be the most successful. Silicon-on-insulator substrates were also explored for VLS nanowire growth and both Si nanowire field effect transistors and GaP nanowire cantilevers were successfully demonstrated on this platform. / by Steven Tyler Boles. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1993. / Includes bibliographical references (leaves 153-158). / by Susan Patricia James. / Ph.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2001. / Includes bibliographical references. / (cont.) The vectorial energy transfer design of sensory films to harvest and direct energy to the surface detection layer toward ultimate signal amplification has been discussed. Third, the role of chemical structure of a sensory polymer in the selectivity of a conjugated polymer-based fluorescent sensor has been examined. In two different sensory systems for the detection of potassium ions and a nitroaromatic explosive TNT, respectively, key chemical design parameters governing their selectivity have been rationalized. Finally, the combination of the conclusions of this thesis provided an idealized structure of a fluorescent conjugated polymer-based sensory film with optimized sensitivity and selectivity. / A sensor is one of the many important applications of conjugated polymers. Poly(p-phenylene ethynylene)s (PPEs) have been studied for fluorescence-based sensor applications. The chemical structure and nano-structure of a polymer in the solid-state are two critical parameters that determine sensitivity and selectivity of a conjugated polymer-based sensor. In this thesis, both parameters have been systematically investigated. First, the Langmuir-Blodgett method was used to control the nano-structure of PPEs in the solid-state. Rational design of surfactant PPEs made it possible to control the conformation of a single polymer strand and interpolymer spatial arrangement at the air-water interface. In situ UV-Vis and fluorescence spectroscopy on the Langmuir film in controlled nano-structures revealed the effects of conformation and spatial arrangement of conjugated polymers on their intrinsic optical properties. Since the controlled structure of a monolayer at the air-water interface can be transferred to a solid substrate, structurally well-defined multilayer LB films of PPEs with confined optical properties were fabricated. This made it possible to study the role of interpolymer aggregation in the photophysical properties of conjugated polymer films. The results provided a general design principle to make a highly emissive conjugated polymer film. Second, an ideal thickness of a sensory film for optimizing sensitivity was determined by experimental and theoretical analysis of energy transport phenomena in multilayer PPE films. / y Jinsang Kim. / Ph.D.

Thesis: S.B. in Archaeology and Materials, Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2014. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 46-49). / Obsidian is known to have been used for tool making in Kenya since the Early Stone Age, appearing as early as 974 thousand years ago (Durkee and Brown, in press). Past research has shown that the study of obsidian artifacts, and the determination of their provenance, can be very useful in reconstructing past civilizations and analyzing the spread of technology and trade. A number of different analytical techniques have previously been utilized to characterize obsidian sources for such studies, including magnetic analysis. This thesis reports the results of a preliminary study to explore the potential of utilizing magnetic analysis for the characterization of obsidian sources in Kenya. A total of 192 samples from 23 localities, belonging to 6 broadly defined petrologically distinct source groups, were analyzed using a vibrating sample magnetometer to test saturation magnetization (Ms), remanence magnetization (Mr), and coercivity (Hc). Comparing the ratio of Mr/Ms with Hc allowed clear differentiation among three of the analyzed obsidian sources (Groups 14, 19, and 29 from Merrick and Brown 1984a). The magnetic signatures reveal clues about the microscopic Fe mineral grains present in the samples, suggesting that magnetic characterization also has the potential to provide additional value as a supplementary technique to chemical analysis. Based on these preliminary results, it is proposed that future studies could examine the temperature dependence of the magnetic properties of obsidian to provide more complete characterization of the obsidian sources. / by Elizabeth A. Krueger. / S.B. in Archaeology and Materials

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1990. / Vita. / Includes bibliographical references (leaves 221-229). / by Hee-Kyung Moon. / Ph.D.

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1994. / Includes bibliographical references (leaves 73-74). / by Jun Funatsu. / B.S.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, June 2004. / "May 2004." / Includes bibliographical references (leaves 18-19). / Magnetostriction measurements were taken on samples of Fe-Ga alloys (Galfenol) containing between 18% and 35% Ga in fields of 5 kOe to 24 kOe from room temperature to liquid nitrogen temperature. In addition, room temperature magnetic anisotropy measurements were conducted on samples between 8% Ga and 25% Ga. No major hysteresis was found in any of the samples and the field dependence was found to be modest (-2%). Anomalous temperature dependence was found in 22-24% Galfenol, where magnetostriction decreased with decreasing temperature, and 35% Galfenol, where magnetostriction increased dramatically (over 50% to values up to about 250 parts per million) with decreasing temperature. Quenching to retain [alpha]-iron and B2 (CsCl) phases was found to increase magnetostriction, with the B2 structure creating the largest magnetostriction. The reasons for the atypical temperature dependence and the B2 structure enhancing magnetostriction are still unexplained. K anisotropy constants were found to decrease with increasing Ga concentration, but more samples need to be measured to validate this trend. / by Jenny Lichter. / S.B.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2004. / Includes bibliographical references. / by Whitney Gaynor. / S.B.