Quantum mechanically based quantitative description of metal alloy surfaces as function of the environment

该项目的目标是预测和了解含Au的金属合金表面的结构特性随其环境的变化。这包括表面的偏析轮廓、晶体结构及其稳定性等特性。在这里，“环境”可能代表温度、体积浓度或吸附物的影响。在这些研究的基础上，我们将能够控制单个参数对表面性质的影响，例如通过分析电子结构。Ag-Au和Cu-Au的合金表面是制备纳米Au最有希望的候选材料，因此将以它们为起点。它们将通过基于密度泛函理论(DFT)的第一性原理方法与统计物理方法相结合来研究，即所谓的团簇展开方法(CE)和蒙特卡罗(MC)模拟。当CE允许扫描巨大的参数空间时，MC模拟将使我们能够访问有限的温度。通过在蒙特卡罗程序中实现CE哈密顿量，研究了温度对近表面区域原子有序化现象的影响。然后，在稳定团簇展开的基础上，构建表面相图和有序化参数。这些图解将为实验研究提供一个查询表，因为它们允许我们探测在什么温度和浓度下，金在近表层达到最高的富集度/贫化率。这也包括短线买单。同时，结构结果将得到SP5项目中测量的低能电子衍射(LEED)强度谱的定量分析的支持。这种结构测定的精度可能小于原子直径的百分之一。这将允许对合金表面结构的详细了解。

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.