Presentation av mastersarbete i fysik. Titeln på examensarbetet är "Analysis of surface oxides using crystal truncation rods: The RhO2/Rh as a case study".
Characterization of a surface structure is vital when studying catalytic reactions. Surface X-ray diffraction is a powerful tool for studying surface structures due to the strong dependence on the atomic arrangement near the surface. The technique exploits the degradation in periodicity from three-dimensional, as in X-ray diffraction of a bulk structure, to two-dimensional for a surface structure. The change in periodicity causes truncation of the reciprocal lattice points, resulting in intensity lines perpendicular to the surface, known as crystal truncation rods.
This thesis strives to simulate surface X-ray diffraction experiments through a computational study of density functional theory relaxed RhO2 / Rh(111) structures. Structure analyses were made with respect to an ideal structure created with symmetry considerations. It showed that the top substrate layer atoms were lowered by 0.03 Å on average towards the bulk. Furthermore, the in-plane atomic displacements showed destructive interference between the top substrate layer and the surface oxide layers. Rod calculations were analyzed and showed good agreement with experimental data. When calculating with fractional Miller indices, interference between the relaxed top substrate layer and the rhodium layer in the oxide was found. By comparing an ideal structure, two partially relaxed structures, and a completely relaxed structure, it was found that the surface oxide and the top substrate layer had relaxed to form a coincidence lattice.
Opponenter: Fredrik Öhrlund och Muhammad Aqeel.
Handledare: Anders Hellman.
Examinator: Johannes Hofmann.