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Measurement and analysis of LEED fine structure

Hitchen, Gregory James (1990) Measurement and analysis of LEED fine structure. PhD thesis, Murdoch University.

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Abstract

LEED fine structure features arise from an interference between the measured beam and a pre-emergent beam internally reflected at the surface potential barrier. Such features are observed at very low energies (typically 0-40eV) and usually consist of a rydberg-like series of peaks converging on the emergence energy of the pre-emergent beam. These features provide a means of determining the shape of the surface potential barrier of a metal.

It is possible to calculate theoretical fine structure spectra by using a barrier model with adjustable parameters. These parameters can be altered to give the best fit to experiment. To obtain an unambiguous fit it is necessary to perform this matching over a range of angles and for multiple peaks within the structure. Thus a good data base for analysis consists of high resolution intensity versus energy spectra at various angles of incidence and azimuths. For this work an electron spectrometer capable of fulfilling these requirements designed and was built. It was used to measure fine structure features from the clean and oxygen covered surfaces of Cu(00l) and Cu(lll).

The success of LEED fine structure analysis depends upon a precise knowledge of the quantities that characterize each spectrum, namely the incidence angle, the azimuth angle and the contact potential difference between the filament emitting the electrons and the crystal surface. These need to be known to a precision that reflects the total resolution of the experiment. In this work techniques were developed for determining these values and these were applied to the data collected from the Cu(00l) and Cu(111) surfaces.

Analysis of this data yielded information regarding the shape of the surface potential barrier. It was also possible to reach some conclusions about the chemisorption sites for oxygen adsorption. The importance of using the full LEED theory for substrate scattering effects in the analysis of fine structure features is also demonstrated.

Item Type: Thesis (PhD)
Murdoch Affiliation: School of Mathematical and Physical Sciences
Notes: Note to the author: If you would like to make your thesis openly available on Murdoch University Library's Research Repository, please contact: repository@murdoch.edu.au. Thank you.
Supervisor(s): Thurgate, Stephen and Jennings, Philip
URI: http://researchrepository.murdoch.edu.au/id/eprint/51661
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