Regensburg 2016 – scientific programme
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O: Fachverband Oberflächenphysik
O 49: Metal Substrates: Structure, Adsorption and Growth
O 49.9: Poster
Tuesday, March 8, 2016, 18:15–20:30, Poster E
Adsorbate nanomesh causes lateral segregation: Ab-initio based Monte–Carlo study for h-BN on Pt50Rh50(111) — •Wolfgang Heckel1, Tobias C Kerscher1, Roland Stania2,3, Thomas Greber2, and Stefan Müller1 — 1Hamburg University of Technology, Institute of Advanced Ceramics — 2Universität Zürich, Physik-Institut — 3Paul Scherrer Institut Villigen, Swiss Light Source
Surface segregation in metal alloys and its adjustability by adsorbates is a well-known phenomenon [1]. In our study, Pt–Rh serves as a substrate for a self-assembled 2d boron nitride (h-BN) layer. The experiments on h-BN/Pt50Rh50(111) show a corrugated, honeycombed 11×11 nanomesh adsorbate layer caused by the lattice constant mismatch of substrate and adsorbate [2].
Using a combined DFT–cluster-expansion approach we elucidate the laterally periodic segregation profile of PtRh(111) caused by h-BN. Our results perfectly confirm the experiment: Beneath pores of the nanomesh the segregation profile shows a strong Rh enrichment, while beneath wires the topmost layer favors platinum.
To quantify the Pt/Rh content per surface layer, we conducted Monte–Carlo simulations accomodating the chemical potential difference of the alloy constituents and the quenched Pt/Rh interdiffusion at low temperatures. In agreement with the experiment, we find that a further Pt enrichment in the top surface layers is favored at elevated temperatures.
[1] Kerscher et al., Phys. Rev. B 86, 195420 (2012)
[2] Stania et al., submitted.