X-ray diffraction study on CU(111)/electrolyte interfaces
Chu, Yong Song
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Permalink
https://hdl.handle.net/2142/30776
Description
Title
X-ray diffraction study on CU(111)/electrolyte interfaces
Author(s)
Chu, Yong Song
Issue Date
1997
Doctoral Committee Chair(s)
Robinson, Ian K.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
X-ray diffraction
CU(111)/electrolyte interfaces
Pb monolayer
free-electron gas model
Language
en
Abstract
"An experimental study of the interfacial structures at the Cu(111) surface under
various electrochemical environments is presented. The interfacial structures have been
examined with the synchrotron x-ray diffraction. Three different Cu(111)/electrolyte
systems are discussed.
In the first experiment, the properties of the underpotentially deposited (UPD) Ph
monolayer on the Cu(111) surface were studied. The Pb UPD monolayer formed an
incommensurate hexagonal closed-packed structure, aligned with the Cu(111) substrate.
Both in-plane and surface-normal structures ofPb/Cu(111) were studied as a function of
the electrochemical potential. While the surface-normal structure exhibited no potential
dependence, the in-plane structure of the Pb monolayer responded sensitively to the
potential. The compression behavior the Ph monolayer showed excellent agreement with
the free-electron gas model.
Experiments on of the bare Cu(111) surface in 0.1 M HCl04 (pH :::::1) revealed that
there were two distinct interfacial structures. For a wide potential range negative of the
Nernst potential, the Cu(111) surface was, in fact, not bare but adsorbed with oxygen or
hydroxide. The bare Cu(lll) surface was observed only at the onset of the hydrogen
evolution. CTR (crystal truncation rods) analysis showed that the oxygen atoms are
adsorbed at 3-fold hollow sites of the Cu(lll) substrate. The observed bond length was
111
consistent with the known Cu-0 bond length. The presence of the oxygen adlayer in the
pH regions (pH <3. 5 ), in which the bulk oxide is forbidden, has significant
thermodynamic implications, and the adsorbed oxygen monolayer can be interpreted as
the precursor to the bulk oxide.
In a less acidic electrolyte (pH=4.5), the growth of aqueous oxide was observed.
The aqueous oxide exhibited an epitaxial cubic Cu20 (cuprite) structure. Two distinct
epitaxial structures were found: the ""aligned' cuprite with its ( 1 T 0) axis parallel with the
substrate ( 1 T 0) axis and the ""reversed"" cuprite with its ( 11 0) axis anti-parallel with the
substrate ( 1 T 0) axis. While the ""reversed"" cuprite was found to grow into a thick film,
the ""aligned"" cuprite remained as a thin two-dimensional film. The growth of the aqueous
oxide showed a distinct growth behavior, which was different from the that of the
previously reported ""dry"" oxide grown under vacuum."
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