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Title: Low energy He⁺ and Li⁺ ion scattering from surfaces
Author: Ashwin, Mark John
ISNI:       0000 0001 3430 6380
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 1990
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A 150° ion scattering spectrometer has been commissioned and utilized to investigate several adsorbate systems on Cu(110). Firstly, the experimental parameters were determined by using 3keV Li+ ions in the ICISS mode to investigate the clean Cu(110) surface. The inelastic background normally observed in Li+ ion scattering energy distributions was found to be more sensitive to the sublayer shadowing conditions than was the substrate’s elastic scattering peak. Most of the observed lower layer scattering features corresponded to multiple scattering events. Using computer modelling it was deduced that for the clean Cu(110) surface the 1st to 2nd layer spacing was compressed by (8±3)%, and the 2nd to 3rd was expanded by (11±8)% compared to the bulk values. 3keV Li+ and 2keV He+ ions were then used to study the Cu(110)(2x1)-O and Cu(110)(2x3)-N adsorbate systems. In the former case the Li+ data exhibited a doubling of the Cu-Cu distance in the <110> and the <211> azimuths and were found to favour a missing row type reconstruction, in which every other <100> row had been removed. In addition. He+→ O scattering indicated that the oxygen atoms resides in the <100> long bridge site (0.0±0.2)A above the surface. Li+ ion scattering from the Cu(110)(2x3)-N indicated a substantial reconstruction of the surface, with an apparent reduction in the Cu-Cu spacing in the <110> azimuth and an increase in the <211> azimuth. Many of the observations are found to be quantitatively consistent, and all are qualitatively consistent, with a reconstruction in which a local Cu(100)c(2x2)-N structure is formed. Additionally, the He+→N scattering results favour a N adsorption site slightly above the surface. Adsorption of Na, K and Cs onto Cu(110) at room temperature was studied using 1keV He+ ions, 1keV Li+ ions were used to investigate Cs adsorption. The intensity of the alkali elastic scattering signal exhibited a ‘dip’ with increasing alkali coverage. For lithium this was attributed to the change in the reionization probability with changes in the surface's work function. For helium this was thought to be due to changes in the neutralization mechanism within the alkali adlayer. Additionally, the alkali metal adsorbates induced an inelastic background in the He+ ion energy distributions, and this is ascribed to changes in the neutralization probability as the ion returns through the alkali metal overlayer.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QC Physics