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Title: Study of X-ray photoelectron diffraction in crystals
Author: Khudheyer, F. Y.
Awarding Body: University of Wales Swansea
Current Institution: Swansea University
Date of Award: 2000
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Photoelectron diffraction pattern is one of a number of surface-structure probes to knowledge of the atomic positions, identities and bonding mechanisms within few layers of the surface. The high-energy forward scattering version of photoelectron diffraction called X-Ray photoelectron diffraction (XPD). XPD features can be described theoretically by a simple single-scattering cluster model (SSC), which used either spherical wave (SW) or plane wave (PW) approximation. X-Ray photoelectron diffraction offers a direct method of determining interatomic bond directions in the surface region of a solid. Single Scattering Cluster theory with Plane Wave approximation (SSC-PW) is simple and reliable mean of interpreting XPD data, but it tends to overestimate the peak heights. The plane wave approximation developed by Lee and Fadley, but this developing is appropriate for photoemission from a s-core orbital. Parry modified this theory which takes account of the core sub-shell having non-zero orbital angular momentum lc. At typical XPD energies, k is large enough to make many partial waves phase shifts significant and this has encouraged use instead of scattering amplitudes as in Fadley's theory. This implies ignoring all terms in each Hankel function expansion, apart from the leading one eikr/r. The corrections become progressively more important with increasing l. We are investigating, in this thesis, the importance of including, order by order, successive non-asymptotic terms in each Hankel function expansion and to see if thereby a successful theory can be set up without having to modify mean free path, and possibly without the complication of Debye-Waller factors. The new technique needs phase shifts to describe all the scattering processes that arise. In this thesis, we give a description of our fitting method and tabulate the phase shifts in an appendix. Trial calculations on simple systems (C-C, Cu-Cu, Ni-Ni and Si-Si) have been made and compared with predictions of Fadley theory. This work include application to some simple well defined cases e.g. photoemission from monolayer of Cu on Ni substrate and sandwich structure. We compared the results with experiment results. Photoemission from single crystals of elements (Cu and Si), and binary compounds (NaCl, LiF, ZnSe and GaAs) has been studied by our new technique and comparison with another experiment data and theoretical calculations has been made.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available