Surface and interface effects in valence band photoemission of noble metals
Hansen, Evan D.
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https://hdl.handle.net/2142/30817
Description
Title
Surface and interface effects in valence band photoemission of noble metals
Author(s)
Hansen, Evan D.
Issue Date
1998
Director of Research (if dissertation) or Advisor (if thesis)
Chiang, Tai-Chang
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Noble metals
Copper
Valence Band Photoemission
Photoemission
Language
en
Abstract
Angle-resolved photoemission probes sample initial and final states involved in direct
transitions within the valence bands of the noble metals. Experiments studying these direct
transitions have yielded fundamental understanding of the electronic structure of noble metals and
of the valence band photoemission process. Recently, however, it has become apparent that the
standard valence band photoemission treatment of the noble metals has not satisfactorily explained
available data. At the same time photoemission experiments have made it increasingly obvious
that interfaces can dramatically change the electronic structure of noble metal thin films. This
thesis addresses the effects of the surface and interfaces on electronic structure and on the
photoemission process in the noble metals copper and silver.
One section of this thesis addresses the surface and interface effects on the electronic
structure of the noble metal copper on different single crystal cobalt substrates. Careful
comparison of the photoemission data with the band structure of the metals shows that the
interface can be transparent or barrier-like depending on the valence band electronic structure.
If the interface is transparent, the electronic structure of a copper film is very similar to that of
bulk copper. If the interface is not transparent the surface and interface provide a confinement
potential which results in quantum well states not found in bulk copper.
Another section presents the solution to a long standing question about the asymmetric line shape of inter-band transitions in the noble metals. The asymmetry of this direct transition peak
is a result of the involvement of the surface in the photoemission process. This is known as the
surface photoemission effect. The change in dielectric function at the surface affects the photon
field such that there are two resultant contributions to the line shape which interfere to produced
the observed asymmetry.
The third and final effect discussed in this thesis is also related to the line shape of the
noble metal direct transition peak. The width of this peak is determined by the band structure and
the orientation of the surface with respect to the propagation direction of the state of interest.
Transitions from bands which are non-dispersive along the direction of the surface normal are
found to have no contribution from the final state. Resultant direct transition peaks from silver
are in fact narrower than the inverse lifetime limit.
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