Williams, Ellen D. (1982) Studies of chemical adsorption using low energy electron diffraction. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechETD:etd-09302005-132833
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|
|Thesis Availability:||Public (worldwide access)|
|Defense Date:||10 September 1981|
|Default Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Imported from ETD-db|
|Deposited On:||03 Oct 2005|
|Last Modified:||26 Dec 2012 03:03|
- Final Version
See Usage Policy.
Repository Staff Only: item control page