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Low‐energy ion scattering (LEIS) was used to study the surface composition of a Pt80Fe20(111) alloy surface as a function of temperature. From 700 K onwards, high enough for sufficient atomic mobility to attain equilibrium, the surface consists of nearly pure Pt. These results agree completely with the results from LEED I/V analysis by Beccat et al. [Surf. Sci. 238, 105 (1990)], who also evidenced a monotonic concentration profile over the three top layers, slight relaxations between those layers and a (2×2) superstructure caused by an ordered atomic arrangement in the second layer. Simple expressions for the entropy changes upon segregation in ordered alloys combined with constant pairwise bond energies clearly appear to be inadequate to describe the observed experimental facts. Even when combined with Monte Carlo simulations, the constant bond energies fail to correctly reproduce the results. Only when the Monte Carlo method is combined with the more refined (modified) embedded atom method (MEAM) for energy description of an alloy is satisfactory agreement with experiment obtained. © 1997 by John Wiley & Sons, Ltd.

The growth and thermal stability of an iron oxide overlayer on yttria-stabilized zirconia (YSZ) have been studied using atomic layer deposition (ALD), mainly in combination with low-energy ion scattering (LEIS). These techniques form a powerful combination, where ALD is designed for controlled (sub)monolayer deposition, while LEIS selectively probes the altered outermost atomic layer. The Fe(acac) 3 precursor reacts already at room temperature with YSZ. The reaction proceeds until saturation, which is characteristic for ALD. After the results of repeated ALD cycles, which consist of Fe(acac) 3 deposition followed by an oxidation treatment, have been studied, a model could be proposed which describes the growth mode of the iron oxide layer on YSZ. Oxidation at temperatures of 800 °C and higher causes a migration of Fe 2 O 3 into the bulk, limiting its usefulness in surface catalytic processes at these temperatures. At 800 °C the diffusion coefficient of Fe in YSZ is determined to be 10 -23 m 2 /s. The reaction mechanism of Fe(acac) 3 with the YSZ surface is studied using infrared diffuse reflectance. The results reveal more than one reaction mechanism, but there seems to be a preference for the reaction via coordinatively unsaturated sites.