Computer simulations of quantum films on surfaces.
Item
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Title
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Computer simulations of quantum films on surfaces.
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Identifier
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AAI9820547
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identifier
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9820547
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Creator
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Jaiswal, Ajit Kumar Singh.
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Contributor
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Adviser: Brian B. Schwartz
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Date
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1998
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Language
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English
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Publisher
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City University of New York.
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Subject
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Physics, Condensed Matter
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Abstract
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In this thesis we present a study of the ground states of helium films, on a range of binding surfaces. We represent the system as a weakly interacting boson gas under the influence of an attenuating external field, which represents the force due to the surface. Monte-Carlo simulations, with periodic boundary conditions have been used to model an infinite system in the plane of the surface, but finite in the normal direction.;We study the film structure and energetics. The surfaces studied range from the experimentally well studied and strongly attracting surface of graphite to the very weak and barely binding surface of cesium. The study ignores the effects of surface structure, specially important for graphite.;Energetics suggests two different types of weak-binding surfaces. Type I are those with a single atom binding energy less than the binding energy per particle in the bulk fluid. Such surfaces will support a fluid monolayer. An example is the surface of lithium, for which we present our calculations. We find that a lithium surface is not strong enough to support a solid monolayer. Those surfaces that have a binding energy greater than the per particle binding energy in the bulk fluid, we refer to as of Type II. Such surfaces will be non-wetting, and our calculations of the fluid density on this surface seems to indicate this. A good example is the Sodium surface potential, for which we find that the minimum stable coverage corresponds to two layers.;We then calculate the equations of states for the graphite, lithium and sodium surfaces and show different qualitative regimes. For Type I surfaces, there are two qualitatively distinct regimes. Above the equilibrium areal-density there is the regime of stable coverages. Below this density the negative value of the slope signals instability and a phase transition, and our simulation model is no longer valid.;Our data for layering on graphite shows reasonably good agreement with the experimental layer promotion data. Onset and disappearance of superfluidity in the second layer of graphite, is in good agreement with experimental reports.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
