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New methods in helium atom scattering

This thesis presents developments in both the experimental techniques and in the theoretical understanding of the helium atom scattering. These contributions open the way for more effective experimental investigations and more quantitative analysis of helium - surface scattering data. The introduction starts with an outline of the contents of the thesis, followed by a description of the diffraction geometry of the Cambridge helium scattering apparatus and a method of measuring diffraction intensities at constant incident condition. The next two chapters describe two experimental improvements in the field of helium scattering. In chapter 2 the characterisation of a molecular beam source shows that high performance (velocity spread < 1%) can be achieved with a simple and inexpensive design. Chapter 3 describes the development, testing and characterisation of a 2-dimensional multichannel scalar data acquisition device for use with two experimental methods under development, namely an imaging helium detector and time-of-flight measurements using a double chopper gate helium beam. Chapter 4 describes the investigation of helium scattering from a lattice gas of Pb adsorbed on the Cu(001) surface. Experimental helium diffraction intensities for the Pb/Cu(001) system were previously accounted for by invoking an adsorbate - induced corrugation in the Cu(001) substrate. In this work, a more detailed analysis shows that a substrate corrugation is not necessary to reproduce the experimental results. The investigation includes a review of a range of approximations and methods available for calculating scattered intensities within the hard wall approximation of the helium-surface potential. The remainder of the thesis presents a detailed experimental and theoretical investigation of elastic helium scattering from the Si(111)-(1x1)H surface.

Identiferoai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:597056
Date January 1998
CreatorsBuckland, J. R.
PublisherUniversity of Cambridge
Source SetsEthos UK
Detected LanguageEnglish
TypeElectronic Thesis or Dissertation

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