Photoelectron holography of metal adsorbates on semiconductor surfaces

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.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Physics

Year dc:date

2012

Author dc:creator

• Roesler, James M.

Contributors dc:contributor

• Chiang, Tai-Chang

• photoelectron holography
• branching-ratio photoelectron holography
• metal adsorbates
• semiconductor surfaces

Statement dc:rights

• © James M. Roesler, 1997

Language dc:language

en

Identifier

4038107

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/30767