Asymmetries in physisorbed systems give rise to interesting phases and phase transitions in two-dimensional (2D) monolayer and multilayer systems. The effects of asymmetric adsorbate and substrate interactions in monolayers of dipolar molecules on ionic substrates and N2 on graphite are studied.
In the case of dipolar molecules on ionic substrates, 2D dielectric phase transitions using a modified Blume-Emery-Griffiths (BEG) model are determined theoretically. A dipole adsorbed vertically above a metal ion lattice site, and pointing up (down), is assigned a spin s=+1 (s=-1). An empty lattice site is assigned a spin S=0. Analytic solutions for both ferroelectrically and antiferroelectrically ordered systems are found. The model is applied to CO adsorbed on MgO and NaCl, and preliminary results for the phase diagram of CH3F on NaCl, are presented.
Multilayer phase transitions for N2 on graphite are studied experimentally using synchrotron x-ray diffraction. The system is measured to undergo layering transitions, where the number of layers increases as the temperature of the system increases. A new multilayer phase diagram based on our results and the combined results published by other researchers is presented. The effects of capillary condensation on this multilayer system are quantified, and it is determined that its primary effect is to broaden the discrete layering transitions. The results for both studies are put into context with other adsorption systems with asymmetric interactions.
| Identifer | oai:union.ndltd.org:UTAHS/oai:digitalcommons.usu.edu:etd-3097 |
| Date | 01 August 1994 |
| Creators | Burns, Teresa Ellen |
| Publisher | DigitalCommons@USU |
| Source Sets | Utah State University |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | All Graduate Theses and Dissertations |
| Rights | Copyright for this work is held by the author. Transmission or reproduction of materials protected by copyright beyond that allowed by fair use requires the written permission of the copyright owners. Works not in the public domain cannot be commercially exploited without permission of the copyright owner. Responsibility for any use rests exclusively with the user. For more information contact Andrew Wesolek (andrew.wesolek@usu.edu). |
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