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Density Functional Theory and Accelerated Dynamics Studies of the Structural and Non-equilibrium Properties of Bulk Alloys and Thin-Films

Khatri, Indiras
http://orcid.org/0000-0002-5677-4369
http://rave.ohiolink.edu/etdc/view?acc_num=toledo1651500257656618

Abstract Details

2022, Doctor of Philosophy, University of Toledo, Physics.
In this dissertation the structural properties of bulk alloys and thin-films are studied using a variety of di erent techniques including density functional theory (DFT) and accelerated dynamics. The first part of this dissertation involves the use of DFT calculations. In particular, in Chapter 3 the stability and mechanical properties of 3d transitional metal carbides in zincblende, rocksalt, and cesium chloride crystal structures are studied. We find that the valence electron concentration and bonding configuration control the stability of these compounds. The filled bonding states of transition metal carbides enable the stability of the compounds. In the second part of this dissertation we use a variety of accelerated dynamics techniques to understand the properties of growing and/or sublimating thin-films. In Chapter 4, the results of temperature-accelerated dynamics (TAD) simulations of the submonolayer growth of Cu on a biaxially strained Cu(100) substrate are presented. These simulations were carried out to understand the e ects of compressive strain on the structure and morphology. For the case of 4% compressive strain, stacking fault formation was observed in good agreement with experiments on Cu/Ni(100) growth. The detailed kinetic and thermodynamic mechanisms for this transition are also explained. In contrast, for smaller (2%) compressive strain, the competition between island growth and multi-atom relaxation events was found to lead to an island morphology with a mixture of open and closed steps. In Chapter 5, we then study the general dependence of the diffusion mechanisms and activation barriers for monomer and dimer diffusion as a function of strain. The results of TAD simulations of Cu/Cu(100) growth with 8% tensile strain are also presented. In this case, a new kinetic mechanism for the formation of anisotropic islands in the presence of isotropic diffusion was found and explained via the preference for monomer diffusion via exchange over hopping. In Chapter 6, we then study the early stages of CdTe thin- lm deposition. In particular, molecular dynamics simulations based on a bond-order potential are used to investigate the dependence of the attachment probability and deposition site for Cd and Te2 clusters deposited on Cd-terminated and Te-terminated (100) and (111) surfaces of zincblende CdTe on deposition angle, energy, and substrate temperature. In general, we  nd that the deposition of Cd atoms and/or Te2 dimers on the oppositely terminated surface leads to an attachment probability which is close to 1 and relatively independent of deposition conditions. In contrast, deposition on the same terminated surface leads to a significantly lower attachment probability which generally decreases with increasing deposition angle, energy, and substrate temperature. Our results also indicate that vapor deposition on both the (100) and (111) surfaces as well as sputter deposition on the (111) surface leads to a significant excess Te sticking probability. In Chapter 7 we then use the same bond-order potential, along with two different accelerated dynamics methods to study the process of CdTe sublimation, which is important in the deposition of CdTe thin- lm solar cells. Our results explain the temperature dependence of the experimentally observed activation energies and also elucidate the key mechanisms involved in CdTe(100) sublimation. An analysis of our results also leads to good agreement with experimental results for the total sublimation rate at high temperatures (T > 360 C). They also provide a possible explanation for the lower effective activation energy observed for T < 360 C. Finally, in Chapter 8 we summarize our results and discuss possible future work.
Jacques Amar, Professor (Advisor)
173 p.
Physics
Density Functional Theory; Temperature Accelerated Molecular Dynamics; Thin-Film Growth, Solar Cell, Close-Spaced Sublimation; Electronic Properties; Mechanical Properties; CdTe; Island Morphology; Activation Barrier; Sputtering; Stacking Fault; Isotropic Diffusion; Anisotropic Island;

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Citations

  • Khatri, I. (2022). Density Functional Theory and Accelerated Dynamics Studies of the Structural and Non-equilibrium Properties of Bulk Alloys and Thin-Films [Doctoral dissertation, University of Toledo]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1651500257656618

    APA Style (7th edition)

  • Khatri, Indiras. Density Functional Theory and Accelerated Dynamics Studies of the Structural and Non-equilibrium Properties of Bulk Alloys and Thin-Films. 2022. University of Toledo, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=toledo1651500257656618.

    MLA Style (8th edition)

  • Khatri, Indiras. "Density Functional Theory and Accelerated Dynamics Studies of the Structural and Non-equilibrium Properties of Bulk Alloys and Thin-Films." Doctoral dissertation, University of Toledo, 2022. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1651500257656618

    Chicago Manual of Style (17th edition)

toledo1651500257656618
103
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