FOR 2213: Subproject "Quantum mechanically based quantitative description of metal alloy surfaces as function of the environment
The goal of this project is to predict and understand the structural properties of metal alloy surfaces containing Au as function of their environment. This includes properties as the segregation profile of the surface, the crystallographic structure and its stability. Here, "environment" may stand for temperature, bulk concentration, or the influence of adsorbates. Based on these studies, we will be able to control the influence of the individual parameter, e.g. by analyzing the electronic structure, on the surfaces properties. Starting point will be the alloy surfaces of Ag-Au and Cu-Au, because they belong to the most promising candidates for the making of nanoporous Au. They will be studied via the combination of first-principles methods based on Density Functional Theory (DFT) with methods from statistical physics, namely the so-called Cluster Expansion method (CE) and Monte-Carlo (MC) simulations.While the CE allows for scanning huge parameter spaces, MC simulations will give us access to finite temperatures. In that way, the influence of temperature on atomic ordering phenomena in the near-surface regime will be studied by implementation of the CE Hamiltonian into Monte-Carlo programs. Then, on the basis of the stabilized cluster expansion, surface phase diagrams and ordering parameters will be constructed. These diagrams will provide a look-up-table for experimental studies, because they allow us to detect at which temperature and concentration the highest enrichment/depletion of Au in the near surface layer is reached. This also includes short-range order. In parallel, the structural results will be supported by the quantitative analysis of intensity spectra received from Low Energy Electron Diffraction (LEED) measured in the project SP5. Such structure determinations may reach accuracy smaller than one percent of the atomic diameter. This will allow for a detailed understanding of the alloy surface structures.