Surface and interface structural studies using medium energy ion scattering

• Main Author: Sheppard, Daniel Crispin
• Published: University of Warwick 2010
• Subjects: 530.417; QC Physics
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.532153

The technique of medium energy ion scattering (MEIS) can be used to elucidate the structural details of surfaces, both in general terms and in a more qualitative manner, in order to help solve a number of outstanding uncertainties relating to the structures of a number of surface systems. MEIS, involving the back-scattering of light ions from a material of interest, in this case 100 keV H+ ions from adsorbate covered single crystal metal surfaces, can potentially be a powerful tool for obtaining either depth-dependent compositional information or quantitative structural details. MEIS has been used to study the surface relaxations at the Cu(410)-O stepped surface. The results have been compared to a number of models favoured by previous studies, and an optimisation of the structural parameters associated with the outermost Cu atoms was undertaken so as to determine the positions of these atoms to a reasonable degree of precision. In this thesis, MEIS has also been used to probe the surface reconstructions triggered by the adsorption of the methylthiolate species on the Cu(100), Au(111) and Pd(111) surfaces. Methylthiolate is derived from the n-alkylthiol molecule methylth- iol, the simplest molecule of a species which ubiquitously form so called self-assembled monolayers (SAMs) on single crystal metal surfaces. In the case of Cu(100), our study confirms the existence of a radial lateral distortion of the outermost Cu layer, and we quantify this distortion. For Au(111), two competing structural models for the methylth- iolate overlayer have been proposed, namely the Au-adatom-monothiolate (AAM) and Au-adatom-dithiolate (AAD). MEIS has been used to compare these two models, and we find in favour of the AAD model. Additionally, evidence has been found for a significant reconstruction of the Pd(111) surface triggered by adsorption of methylthiolate. We have carried out a MEIS investigation of the (3×2)-alaninate phase formed by adsorption of the chiral molecule alanine on Cu(110). Evidence is found for a small degree of lateral surface distortion.