Applications of electron energy loss spectroscopies to the study of surface chemistry
Dai, Qing
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Permalink
https://hdl.handle.net/2142/19236
Description
Title
Applications of electron energy loss spectroscopies to the study of surface chemistry
Author(s)
Dai, Qing
Issue Date
1992
Doctoral Committee Chair(s)
Gellman, A.J.
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Physical
Physics, Condensed Matter
Language
eng
Abstract
Two different kinds of electron energy loss spectroscopies have been used in this thesis to the study of surface chemistry. In the first part of the thesis which includes the first four chapters, Extended Electron Energy Loss Fine Structure (EXELFS) has been used to study the bonding of (1) oxygen atom in NiO film grown on Ni(100) and Ni(110) surface and (2) nitrogen atom overlayer on Cu(100) and Cu(110) surfaces. EXELFS spectra obtained from the K-level of oxygen in NiO film grown on both the Ni(100) and Ni(110) surfaces reveal that the NiO films grown on both surfaces have the same structure as bulk NiO. The Ni-O bond lengths are 2.08 A in both cases. EXELFS spectra obtained above the K-edge of nitrogen atoms adsorbed on the Cu(100) (c(2x2) overlayer) and Cu(110) (p(2x3) overlayer) indicate N-Cu bond lengths of 1.84 and 1.81 A for N on Cu(100) and Cu(110) surfaces, respectively. The difference is within the resolution of the experiment and does not indicate significant differences between the two adsorbate systems.
In the second part of the thesis, HREELS and TDS measurements have been used to investigate the surface chemistry of straight chain hydrocarbon alcohols (n-C$\sb{\rm n}$H$\sb{\rm 2n+1}$OH, n = 1,2,3,4,5) and fluorocarbon alcohols (C$\sb{\rm n}$F$\sb{\rm 2n+1}$CH$\sb2$OH, n = 1,2,3) on Ag(110), Cu(100) and Cu(111) surfaces. It has been found that on clean surfaces, both hydrocarbon alcohols and fluorocarbon alcohols adsorb reversibly without dissociation. When Ag or Cu surfaces are pre-covered with atomic oxygen, alcohols (both hydrocarbon and fluorocarbon alcohols) adsorb dissociatively and form alkoxides and water. At higher temperatures, alkoxides decompose into aldehydes and hydrogen.
One of the major differences between fluorocarbon and hydrocarbon alcohols is their surface bond alkoxide stability. Fluorinated alkoxides are more stable on Cu and Ag surfaces studied. This has been attributed mostly to the fact that the alkoxide decomposition transition state involves a carbon cation and that fluorination of the alkyl group destabilizes the transition state and therefore increases the decomposition energy barrier.
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