Dresden 2017 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 87: Metal Substrates: Structure, Epitaxy and Growth
O 87.3: Vortrag
Donnerstag, 23. März 2017, 11:15–11:30, WIL C307
Spectroscopic observation and molecular dynamics simulation of Ga surface segregation in liquid Pd-Ga alloys — •Mathias Grabau1, Jannis Erhard2, Nicola Taccardi3, Sandra Krick Calderon1, Andreas Görling2, Peter Wasserscheid3, Christian Papp1, and Hans-Peter Steinrück1 — 1Physikalische Chemie II, Friedrich-Alexander Universität Erlangen-Nürnberg (FAU) — 2Theoretische Chemie, FAU — 3Chemische Reaktionstechnik, FAU
Pd-Ga alloys with 0.8, 1.8 and 4.7 at.% of Pd were examined as a function of temperature between 400 and 750 K using angle-resolved x-ray photoelectron spectroscopy (XPS). The Pd surface concentration is found to depend on temperature. This is explained by the transition from a liquid phase to a two-phase system, consisting of a buried solid Ga5Pd phase and a liquid Pd-Ga alloy, which leads to Pd depletion of the liquid phase. In the liquid phase, Pd was depleted from the vacuum/liquid interface, as deduced from the comparison of XPS data obtained in 0 and 80∘ emission; this observation is independent of temperature and Pd concentration of the liquid phase. It is interpreted as an inhomogeneous depth distribution function of Pd, that is, Pd depletion in the topmost layer and enrichment in the next layer. In line with experiment, a DFT-based molecular dynamics simulation (MD) shows interfacial stratification of Ga and an inhomogeneous Pd distribution along the surface normal. The experimental data was evaluated by using a rigid layer model leading to excellent agreement with the results of the MD simulation. We acknowledge the financial support by the Cluster of Excellence ’Engineering of Advanced Materials’.