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The structures of clean rhodium surfaces studied by low-energy electron diffraction

University of British Columbia

This thesis describes the determination of the structures of the (111), (100) and (110) surfaces of rhodium by low-energy electron diffraction (LEED). In this work the photographic method of Stair et al «as refined so that LEED patterns stored on photographic film were analysed by a computer-controlled Vidicoa T.V. camera system to give intensity v. energy, or I(E), curves for the various diffracted beams. This approach was tested for a Cu(111) surface; I(E) curves determined in this new say were compared with intensities measured previously with a Faraday cup collector., Structural analyses were performed by comparing experimental intensities with those calculated with the multiple-scattering programs of Van Hove and long. Checks were made against some previously published calculations to ensure that the programs were running correctly. For calculations on surfaces of both rhodium and copper, an ion-core scattering potential from a band structure calculation- was compared with one constructed by superposing the charge densities of a cubo-octahedral cluster of metal atoms. The degree of agreement between experimental and calculated diffracted beam intensities was determined with a reliability-index proposed recently by Zanazzi and Jona. Here, the analysis of Zanazzi and Jona was extended to enable assessments to be made of the uncertainties in the structural parameters which give the best correspondence between experimental and calculated I(E) curves. The effects of independent measurements of intensities, and of changes in the non-structural parameters for the calculations upon the reliability of the derived structural results were also examined in some detail. All three rhodium surfaces sere found to be unreconstructed at room temperature and above, each surface being a simple termination of the bulk crystalline stacking sequence. However, the topmost interlayer spacing did show some variation from the bulk value. The (110) surface showed a contraction of 2.7 ± 2.0% relative to the bulk interlayer separation, while the (111) and (100) surfaces showed small (-1 ± 3%) and 0 ± 2.5% contractions respectively.

Text

2010-03-18

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http://hdl.handle.net/2429/22062

Chemistry

University of British Columbia

Graduate