Photoemission studies of surfaces and thin film systems of silver and gold
Hsieh, Tzu Chiang
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https://hdl.handle.net/2142/25212
Description
Title
Photoemission studies of surfaces and thin film systems of silver and gold
Author(s)
Hsieh, Tzu Chiang
Issue Date
1987
Doctoral Committee Chair(s)
Chiang, Tai-Chang
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
photoemission studies
thin-film systems
silver
gold
zone-center surface state
Language
en
Abstract
Angle-integrated photoemission spectroscopy was used to study the properties
of Au 4f7; 2 core level in several systems: Au overlayers on Ag(lll),
Au overlayers on Ag(lOO), and an Au monolayer buried in Ag(lll). Properties
of a zone-center surface state were also investigated with the use of angle
resolved photoemission spectroscopy for many related systems: the clean
Ag(lll) surface, Ag overlayers on Au(lll), and Au overlayers on Ag(lll).
For Au epitaxial overlayers on Ag, the binding energies of Au 4f7; 2 core
level were measured as a function of overlayer thickness. The Au 4f 7/2 core
level associated with the top layer is shifted relative to the underlayers.
With increasing Au coverages on Ag(lOO) beyond 5 monolayers, the surface
reconstruction changes from (lXl) to (SX20), and the binding energies change
correspondingly. The measured binding energies are related to the variation
of the one-electron potential within the overlayer. For the Au monolayer
buried in Ag(lll), the Au 4f7/2 core-level binding energies were measured as
a function of the depth below the surface. The measured Au 4f7/2 binding
energy converges asymptotically to a constant value for depths greater than
about three atomic monolayers. The measured spatial range of the surface
effect is significantly greater than what is expected from a jellium calculation.
This result implies that significant subsurface-core-level shifts
can occur for close-packed metal surfaces. For the studies of the zone
center surface state of Au overlayers on Ag(lll), it was observed that this
surface state evolves continously from Ag(lll)-like to Au(lll)-like for
increasing Au coverages on Ag, and a similar behavior was also observed for
Ag on Au(lll). The shifts of the binding energies as a function of
overlayer thickness can be related to the z-dependence of the surface state
wave function. The envelope function of this surface state in Ag(lll) was
further determined by use of Ag(lll) samples with one subsurface atomic
layer substituted by a matched Au atomic layer. Using this technique, the
decay length of this surface state is determined to be about 28 A. The
photoemission cross section of the Ag(lll) surface state was also measured
over the photon energy range of 36 - 65 ev. A resonance at 54 eV was
observed. The energy position of this resonance is in agreement with the
prediction of a theoretical model based on an extension of the directtransition
model for bulk states.
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