Materials Science and Engineering - Ph.D. / Sc.D.
http://hdl.handle.net/1721.1/7837
Sat, 17 Nov 2018 19:43:24 GMT2018-11-17T19:43:24ZCation self-diffusion in Zn0.
http://hdl.handle.net/1721.1/118577
Cation self-diffusion in Zn0.
Kim, Kee Soon
Massachusetts Institute of Technology. Dept. of Metallurgy and Materials Science. Thesis. 1971. Sc.D.; Vita.; Includes bibliographical references.
Fri, 01 Jan 1971 00:00:00 GMThttp://hdl.handle.net/1721.1/1185771971-01-01T00:00:00ZResonant Raman scattering in graphene
http://hdl.handle.net/1721.1/118567
Resonant Raman scattering in graphene
Narula, Rohit
In this thesis we encounter the formulation of a rigorous theory of resonant Raman scattering in graphene, the calculation of the so-obtained Raman matrix element K2f,1o for the 2D Raman mode with the full inclusion of the matrix elements and a physically appealing bridge between theory and experiment by eschewing the problematic ascription of graphene with a finite thickness. Finally, we elucidate an experimental study of the Raman D and G modes of graphene and highly-defected pencil graphite over the visible range of laser radiation. Marking a departure from the usual practice for light scattering in semiconductors of including only the dynamics of the electrons and holes separately, we show via fourth-order quantum mechanical perturbation theory using a Fock state basis that for resonant Raman scattering in graphene the processes to leading order are those that involve the simultaneous action of the electrons and holes. Such processes are indeed an order of magnitude stronger than those prevalent in the literature under the double resonance [1, 2, 3] moniker. We translate our perturbation theoretic analysis into simple rules for constructing Feynman diagrams for processes to leading order and we thereby enumerate the 2D and D modes. Using expressions for the terms to leading order obtained from our theoretical treatment we proceed to evaluate the Raman matrix element [4] for the Raman 2D mode by using state-of-the-art electronic [5] and iTO phonon dispersions [6] fit to ab initio GW calculations. For the first time in the literature we include the variation of the light-matter and electron-phonon interaction matrix elements calculated via an ab initio density functional theory (DFT) calculation under the local density approximation (LDA) for the electronic wavefunctions. Our results for the peak structure, position and intensity dependence are in excellent agreement with experiments [7, 8, 9, 10]. Strikingly, our results show that depending on the combination of the input (polarizer) and output (analyzer) polarization of the laser radiation, very different regions of the phonon dispersion are accessed. This has a direct impact on the dominant electronic transitions according to the pseudo-momentum conservation condition satisfied by the scattering of an electron by a phonon ki = kf + q. Using sample substitution [11] we deconvolve the highly wavelength dependent response of the spectrometer from the Raman spectra of graphene suspended on an SiO2 - Si substrate and graphite for the D and G modes in the visible range. We derive a model that considers graphene suspended on an arbitrary stratified medium while sidestepping its problematic ascription as an object of finite thickness and calculate the absolute Raman response of graphene (and graphite) via its explicitly frequency independent Raman matrix element [K'2f10]2 vs. laser frequency. For both graphene and graphite the [K'2f10]2 per graphene layer vs. laser frequency rises rapidly for the G mode and less so for the D mode over the visible range. We find a dispersion of the D mode position with laser frequency for both graphene and graphite of 41 cm-YeV and 35 cm-YeV respectively, in good agreement with Narula and Reich 131 assuming constant matrix elements, the observed intensity follows the joint density states of the electronic bands of graphene. Finally, we show the sensitivity of our calculation to the variation in thickness of the underlying SiO2 layer for graphene.
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, February 2011.; Cataloged from PDF version of thesis.; Includes bibliographical references (pages 131-144).
Sat, 01 Jan 2011 00:00:00 GMThttp://hdl.handle.net/1721.1/1185672011-01-01T00:00:00ZTechno-economical evaluation of intra-datacenter optical transceiver designs
http://hdl.handle.net/1721.1/118038
Techno-economical evaluation of intra-datacenter optical transceiver designs
Yu, Wei, Ph. D. Massachusetts Institute of Technology
The evolution of data center network interconnects is based: at the component level, on cost, power, and bandwidth density; and at the system level, on cost, unit count, footprint, and implementation time. The decision for iterative vs. transformational design depends critically on the product horizon view that amortizes R&D, manufacture tooling and infrastructure preparation. An iterative platform can be implemented earlier, but it may present limited performance scalability. A transformational design can have large creation and implementation costs that are amortized over a longer time window. A framework for quantitatively capturing these variables using a new technology inventory model is developed. Scenarios for deployment of six different transceiver package platforms to meet the projected data center capacity scaling ramp are constructed. The iterative designs provide better return on investment for a 3-year time window, while the transformational designs are optimized for a 20-year window.
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2018.; Cataloged from PDF version of thesis.; Includes bibliographical references.
Mon, 01 Jan 2018 00:00:00 GMThttp://hdl.handle.net/1721.1/1180382018-01-01T00:00:00ZDesign of stable nanostructure configurations in ternary alloys
http://hdl.handle.net/1721.1/117947
Design of stable nanostructure configurations in ternary alloys
Xing, Wenting, Ph. D. Massachusetts Institute of Technology
The development of stable nanocrystalline binary alloys, which possess a large volume fraction of grain boundaries at elevated temperatures, is a promising route to high yield strength materials. Previous studies have focused on alloying by selecting solute elements that segregate at grain boundaries to stabilize the nanostructure. A selection criterion has been established for designing stable binary nanocrystalline materials. This thesis explores the extension of this concept to the design of multicomponent nanostructured systems. In contrast to the simplicity of a binary system where not many topological possibilities are accessible, multicomponent nanostructured systems are shown to occupy a vast space where the large majority of interesting configurations will be missed by a regular solution approximation. This thesis describes research to develop a conceptual basis for the thermodynamic properties of multicomponent nanocrystalline alloys, and to design interesting ternary configurations not accessible in binary systems. The conditions necessary to achieve the desired nanostructure configurations are developed in a model that takes solute interactions into consideration. Based on the model, we performed a systematic case study on one alloy system expected to exhibit nanocrystalline stability: Pt-Pd-Au. As a control, two binary systems (Pt-Au, Pt-Pd) were produced for comparison. While a uniform distribution of Pd is observed in binary Pt-Pd alloys at 400 °C, the results from scanning transmission electron microscopy (STEM) reveal that Pd segregation behavior was induced by the Au grain boundary segregation in the ternary system at 400 °C. Our work on induced co-segregation behavior of Pt-Pd-Au alloy is just a simple example of solute interaction in nanocrystalline alloys. Our approach more generally presents a new design framework to control the complex configurations possible in nanocrystalline materials by alloying element selection.
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2018.; Cataloged from PDF version of thesis.; Includes bibliographical references (pages 129-135).
Mon, 01 Jan 2018 00:00:00 GMThttp://hdl.handle.net/1721.1/1179472018-01-01T00:00:00Z