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Title: Epitaxial growth and surface morphology of some metal and semiconductor structures.
Authors: Johnson, Andrew David.
Award date: 1989
Presented at: University of Leicester
Abstract: Forward focussing of medium energy Auger and photoelectrons have been used along with LEED and Auger electron spectroscopy to investigate the initial stages of growth of both Cr and Co on Ag(001). Cr was found to grow epitaxially on Ag in the bcc phase up to ~2ML, in agreement with previous results. Co also grows epitaxially on Ag up to 3ML although it is proposed that the Co lattice is in the FCC phase but no comment can be made as to whether the overlayer is laterally expanded. Polarised Neutron Reflection measurements have been made on Ag/Cr/Ag sandwich structures with varying thicknesses of Cr. It is shown that for Cr thicknesses of 2 and 3.3ML the Cr is ordered non-ferromagnetically and it is proposed that at these thicknesses the Cr has reverted to its bulk antiferromagnetic order. However measurements on samples with Cr thicknesses of 0.33ML indicate ferromagnetic ordering with a greatly enhanced magnetic moment per atom over the bulk Cr value, in partial agreement with previous theoretical predictions. PNR measurements on a Ag/Fe/Ag (001) structure with thickness of Fe of 8ML have yielded an accurate measurement of the magnetic moment per atom for the Fe film of 1.0 +; 0.15microB, indicating a reduced value from that of bulk Fe of 2.22microB. x-ray scattering from a Ge (001) surface has been used to show that the surface undergoes a reversible phase transition at T = 954 +; 7K. It is proposed that the transition occurs due to the formation of vacancy-adatom pairs as some of the surface dimers break with increasing temperature. The data is explained in terms of a three level model used to describe the vacancy-adatom creation. The three level model results are compared with results from a simple Monte-Carlo simulation and an energy of 0.41 +; 0.05eV is deduced as the energy required to break the dimer bonds on the surface of Ge (001). Further X-ray scattering from a miscut Ge (001) surface shows that the surface is made up of regularly spaced steps of double atomic height, in agreement with theoretical and previous experimental studies. It is shown that perpendicular to the steps the reconstructed domains are limited in dimension by the steps, although both orientations of the reconstruction are possible.
Type: Thesis
Level: Doctoral
Qualification: Ph.D.
Rights: Copyright © the author. All rights reserved.
Appears in Collections:Theses, Dept. of Physics and Astronomy
Leicester Theses

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