Medium energy ion scattering investigation of the structures formed by deposition of sub-monolayer platinum group metals on the copper(110) surface
thesisposted on 30.01.2012, 12:24 by Thomas P. Fleming
In order to distinguish essays and pre-prints from academic theses, we have a separate category. These are often much longer text based documents than a paper.
This thesis reports a medium energy ion scattering investigation (MEIS) of platinum, palladium, and rhodium deposited upon the copper (110) surface using 100 keV hydrogen ions. The Daresbury National MEIS facility was used to take blocking curve and energy profiles of the structure formed by e-beam deposition of various thicknesses of platinum, palladium, and rhodium upon an atomically clean and ordered copper (110) crystal face. Quantitative analysis was conducted using an in-house version of the IGOR macro widely used within the MEIS community, adapted to analyse these systems. Sub-monolayer deposits of palladium and platinum were found to preferentially occupy subsurface sites, predominantly in the second layer below a copper first layer. This process occurred at room temperature. The interlayer separation between the deposited species and first layer copper were found in all three cases, being 1.21±0.04 Å for platinum, 1.17±0.06 Å for palladium and 1.16±0.06 Å for rhodium. These are contractions when compared to bulk interlayer spacing for copper which in 1.278 Å but are comparable to the first interlayer spacing from literature for relaxed copper which is 1.18 Å. A c(2x2) LEED pattern was observed in the case of the 0.3 ML platinum deposit which is an interesting comparison to the (1x2) reconstruction observed for sub-monolayer palladium in some literature sources. Upon annealing, the deposited species were observed to occupy third and fourth layer sites despite the temperature not being sufficient for diffusion deeper into the copper substrate. A process of burying through substrate adatom diffusion upward onto step edges is suggested as an energetically favoured process.