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Studies of chemical adsorption using low energy electron diffraction


Williams, Ellen D. (1982) Studies of chemical adsorption using low energy electron diffraction. Dissertation (Ph.D.), California Institute of Technology.


Both experimental and computational studies based on low-energy electron diffraction (LEED) have been performed to determine the nature of order in chemically adsorbed overlayers. These studies have been directed towards obtaining a better understanding of adatom-adatom interactions by measurement of their most obvious manifestations; change in overlayer order during adsorption and co-adsorption, island formation, and order-disorder phenomena.

The effect of the co-adsorption of hydrogen on the ordering of CO on Rh(111) has been studied using LEED and thermal desorption mass spectrometry. The results indicate that the adsorption of CO proceeds via a physically adsorbed intermediate. In addition, there is a strong repulsive interaction between CO molecules and hydrogen atoms co-adsorbed on Rh(111). This interaction is apparent at distances up to 2.7 - 3.1 A indicating that it is a through-metal effect.

A series of LEED patterns has been observed during the adsorption of sulfur on the reconstructed IR(110)-(1x2) surface. The structure observed at lowest coverages has a p2mg symmetry. This allows a determination of the absolute coverage, and indicates a probable binding site for the sulfur atoms.

A Monte Carlo simulation of the order-disorder behavior of oxygen on W(110) has been performed. General expressions relating the values of the interaction energies to the transition temperatures for a lattice gas with first, second and third neighbor interactions have been determined. Symmetry considerations in selecting a model for the interaction energies are discussed.

The effect of the ordering of adsorbed molecules into small islands on the LEED beam profile has been determined. In the limit of a random distribution of island positions the overall intensity is shown to be the weighted sum of the intensities from the individual islands. Computer simulations of island-containing overlayers have been used to determine the effect on the beam profiles of deviations from a random distribution of islands.

Experimental studies of island formation for CO on Ru(001) have been performed. The finite size of the ordered islands has a strong effect on the order-disorder behavior. Quantitative measurements of this effect have allowed a determination of the island size distribution and thus, the mean island size as a function of coverage.

Item Type:Thesis (Dissertation (Ph.D.))
Degree Grantor:California Institute of Technology
Division:Chemistry and Chemical Engineering
Major Option:Chemistry
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Weinberg, William Henry
Thesis Committee:
  • Unknown, Unknown
Defense Date:10 September 1981
Record Number:CaltechETD:etd-09302005-132833
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:3840
Deposited By: Imported from ETD-db
Deposited On:03 Oct 2005
Last Modified:26 Dec 2012 03:03

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PDF (Williams_ed_1982.pdf) - Final Version
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