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O: Fachverband Oberflächenphysik

O 87: Metal Substrates: Structure, Epitaxy and Growth

O 87.4: Vortrag

Donnerstag, 10. März 2016, 16:00–16:15, S053

Atomic diffusion through vacancies as driving mechanism for structure formation of bimetallic surface alloys — •Luis Mancera and Axel Gross — Institute of Theoretical Chemistry, Ulm University, D-89069 Ulm, Germany

The local catalytic activity of surface alloys is usually investigated using periodic DFT calculations, and the energetics of the surface structure is based on periodic arrangements. Still, real surface alloys are often far away from having regular atomic distributions. Furthermore, it is not clear whether the resulting structures are governed by thermodynamics, i.e., whether these structures correspond to a minimum of the free energy, or whether their arrangement is a consequence of kinetic hindering that does not allow the system to reach thermal equilibrium. Thus a generalized approach is necessary in order to understand the stability of surface alloys for different mixing ratios of the constituents. Therefore, we investigate the structure formation of surface alloys by generalizing the local description provided by periodic DFT into a kinetic Monte Carlo (kMC) approach that allows to address the temporal evolution of bimetallic structures. As self-diffusion in metals is usually mediated via vacancies, as a first step we concentrate on the determination of transition rates for vacancy diffusion processes taking variations in the local environment into account.