Photoemission studies of noble metal semiconductor systems
Wachs, Alan Leonard
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https://hdl.handle.net/2142/25214
Description
Title
Photoemission studies of noble metal semiconductor systems
Author(s)
Wachs, Alan Leonard
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
nobel metal semi-conductor systems
thin metallic films
Language
en
Abstract
The study of the structural and electronic properties of semiconductor
surfaces and of thin metallic films deposited upon them is a topic of
fundamental and practical interest. Clean and Au and Ag covered surfaces
of Ge(lll)-c(Zx8), Si(lll)-(7x7), Ge(lOO)-(Zxl), and Si(lOO)-(Zxl) are
studied in this work with high-resolution core-level, valence-band, and
angle-resolved photoemission, and high-energy electron diffraction (HEED).
In conjunction with the results of other surface studies, notably of scanning
tunneling microscopy (STM), the findings reveal significant details
of, and correlations between, these systems' structural and electronic
properties. Dispersive bulk-derived transitions are observed with angleresolved
photoemission and mapped along high-symmetry directions in the
Brillouin zone for most of the clean substrates. The previous surfacestate
assignments are rigorously confirmed. Quantitative structural details
for these surfaces are deduced with the aid of core-level line shape
analysis. The results agree with recent STM topographs. Valence-band
density-of-states spectra show the familiar bulk and surface-derived features.
A study is made of the initial stages of Au and Ag adsorption upon
these surfaces. Overlayer growth morphologies are investigated with HEED.
The deposition of noble-metal atoms induces significant modifications of
surface structural and electronic properties. The results establish correlations
between the electronic and structural properties of the substrate
surfaces and have implications for possible growth models of Au and
Ag upon them. This experimental approach is of general utility and adoptable
for studies of other systems. The thin-film overlayers are studied
in detail. A novel labeling technique unambiguously shows that less than
0.1 monolayer (ML) Ge segregates on top of thin films of Ag on Ge(ll1).
Angle-resolved photoemission studies are performed for Ag(111) films
0-17 ML thick on Si(111). The Ag(l11) L-gap surface-state precursor is
evident in films as thin as 2 ML. Bulk-like, dispersive Ag-4d band transitions
are observed and mapped along the [111] direction of the Brillouin
zone. Ag sp-band thin-film states are probed and their associated quantum
defects measured.
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