Double-segregation effect inAgxPd1−x∕Ru(0001)thin film nanostructures

Abstract

We study the structural properties of ultrathin Ag x Pd 1−x films on top of a Ru͑0001͒ substrate. Effective interatomic interactions, obtained from first-principles calculations, have been used in Monte Carlo simulations to derive the distribution of the alloy components in a four-monolayer ͑4-ML͒ Ag-Pd film. Though Ag-Pd alloys show complete solubility in the bulk, the thin film geometry leads to a pronounced segregation between Ag and Pd atoms with a strong preference of Ag atoms toward the surface and Pd atoms toward the interface. The theoretical prediction of this double-segregation effect is strongly supported by photoelectron spectroscopy experiments carried out for 4-ML thin films. We also show, in an additional experiment, that even in the case where initially 1 ML Ag is buried under 6 ML Pd, the whole Ag ML segregates to the surface.

First principle calculations of core-level binding energy and Auger kinetic energy shifts in metallic solids

“…More specifically considering core-level shifts, there are several experiments [6,80,50], while theoretical works include results for bulk [16][17][18], surface [23] and thin films [25,91]. A difference between older and newer experimental values was attributed to measurements performed on surface alloys rather than bulk in the older study [50].…”

“…Apart from interface qualities, there is a possibility of considering CLSs as a way to monitor special interface states. Also, one interesting option is to consider Monte Carlo methods, see for example the computation of the double segregation effect in AgPd alloy on Ru(0001) [91], in order to determine candidate structures for CLS calculations. In future work, it would be of interest to study the effect of the local environments in more detail, for instance using supercell techniques.…”

Reversed Hysteresis during CO Oxidation over Pd75Ag25(100)

“…For nanoparticles and extended surfaces, it has been demonstrated that reactions may drive restructuring and segregation. In the case of PdAg alloys, silver segregation to the surface under ultra high vacuum (UHV) conditions has been observed experimentally, 11,12 and predicted from calculations. [13][14][15][16][17][18][19] The segregation originates from the lower surface energy of Ag as compared to Pd 15,17,20,21 and from the reduction of stress owing to the slightly larger Ag atoms.…”

Core-level shifts at the Pt/W(110) monolayer bimetallic interface

“…Core-level photoemission has also been used to probe the substrate atoms at group-10/early-transitionmetal interfaces [8,[19][20][21][22][23], but except for core-level measurements of W(111) by Tao et al [20], none of this work has been particularly systematic. This is unfortunate because the substrate shifts provide a view of the interface that is complementary to the adlayer shifts.…”