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In the first part, the defect states of amorphous silicon (a-Si) and a-Si:H material are studied using density functional theory (DFT). I first employ simulated annealing using molecular dynamics (MD) to create stable configurations of a-Si:H, and then analyze the atomic and electronic structure to investigate which structural defects interact with H, and how the electronic structure changes with H addition. I find that H atoms decrease the density of mid-gap states and increase the band gap of a-Si by binding to Si atoms with strained bonds. My results also indicate that Si atoms with strained bonds creates high-localized orbitals in the mobility gap of a-Si, and the binding of H atoms to them can dramatically decrease their degree of localization.
In the second part, I explore the effect of the H binding configuration on the electronic properties of a-Si:H/c-Si heterostructure using density functional theory studies of models of the interface between a-Si:H and c-Si. The electronic properties from DFT show that depending on the energy difference between configurations, the electronic properties are sensitive to the H binding configurations.
In the last part, I examine the electronic structure of GaP/Si(001) heterojunctions and the effect of hydrogen H passivation at the interface in comparison to interface mixing, through DFT calculations. My calculations show that due to the heterovalent mismatch nature of the GaP/Si interface, there is a high density of localized states at the abrupt GaP/Si interface due to the excess charge associated with heterovalent bonding, as reported elsewhere. I find that the addition of H leads to additional bonding at the interface which mitigates the charge imbalance, and greatly reduces the density of localized states, leading to a nearly ideal heterojunction.
Four-dimensionalism is a popular philosophical view of how we persist through time. However, some philosophers, such as Mark Johnston and Eric Olson, argue that four-dimensionalism has perverse implications on our practical ethics. This is because, if four-dimensionalism is true, then there exist entities called personites. And if personites exist, then many of the ordinary prudential, social, and moral habits we engage in, like present self-sacrifice for future benefit, promising to do something painful in the future, or being held responsible for something the we did in the past, subjects personites to suffering without sufficient compensation, consent, or desert. And this would be immoral according to our common-sense morality. In this paper, I argue that if four-dimensionalism is true, and personites exist, then we are still morally permitted to engage in the above practices. If four-dimensionalism turns out to be true, it has no perverse implications on how we ought to live.
The premise of this essay is that the study of ethics is an essential component in teaching all forms of “non-market entrepreneurship,” that is, all forms of entrepreneurship not undertaken solely for commercial purposes. In non-market entrepreneurship, such as arts entrepreneurship, social enterprise, or social entrepreneurship, at least one other purpose instead of or in addition to profit motivates acting entrepreneurially. In this essay we show how we add an ethical component to teaching social entrepreneurship in a discussion-based seminar in an American university. The thrust of our effort is to require students read Fyodor Dostoevsky’s “The Grand Inquisitor” and the Father Zossima portions from The Brothers Karamazov, originally published in Russian in 1863 as a seminal work in the golden age of Russian literature. Through the instructor’s structured and directed discussion of the text, students are presented with the argument that a personal ethic of “loving humility” as embodied in the character of Father Zossima might serve as an appropriate ethical guide for non-market entrepreneurship.