Photoelectron holography of metal adsorbates on semiconductor surfaces
Roesler, James M.
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https://hdl.handle.net/2142/30767
Description
Title
Photoelectron holography of metal adsorbates on semiconductor surfaces
Author(s)
Roesler, James M.
Issue Date
1997
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)
photoelectron holography
branching-ratio photoelectron holography
metal adsorbates
semiconductor surfaces
Language
en
Abstract
Photoelectron holography, a technique used to determine atomic surface structure,
relies on the measurement of interference in the photoelectron wave as a function
of incident photon energy and/or emission direction, namely the interference between the direct path of the photoelectron to the detector and the path which scatters off neighboring atoms. This interference creates oscillations which can be directly
Fourier inverted to yield three-dimensional real-space images. This thesis describes several experiments in which photoelectron holography has been used to study the atomic structure of metal adsorbates on semiconductor surfaces. The surface structure of Pb on Si(lll) has been investigated using photoelectron holography. Angle-resolved photoemission from the Pb 5d core level shows intensity oscillations as a function of photon energy and emission angle. These constant-initial-state spectra were Fourier inverted to yield three-dimensional real-space
images of the emitter's nearest neighbors, showing Pb atoms adsorbed at the T4 site. The surface structure of Pb on Ge(lll) has also been investigated using photoelectron
holography. The resulting images show the emitter bonded at the T4 site.
The use of the small-cone technique for data acquisition or analysis is discussed.
The branching ratio, the photoemission-intensity ratio of two spin-orbit-split
components, has been applied to photoelectron holography in a technique called
branching-ratio photoelectron holography. This technique permits the removal of the
effects of certain experimental variations in a self-normalization of the photoemission
data. Angle resolved photoemission from a monolayer of Bi adsorbed on Si(lll)
shows fine-structure oscillations in the branching ratio of the Bi 5d core level due to
diffraction effects. These oscillations are used to form a holographic image, which
shows that the Bi adatoms are arranged in a trimer structure.
The concept of self-normalization was expanded to include systems without
well resolved spin-orbit splitting in a technique called derivative photoelectron holography.
Ratios of pairs of photoemission intensity data points, from the Bi on Si(lll)
system, were integrated to deduce the underlying constant-initial-state spectra. The
underlying spectra exhibit oscillations which were inverted to yield images which are
compared to images generated using conventional photoelectron holography.
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