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

本项目的目标是预测和了解金属合金表面的结构特性包含Au作为其环境的功能。这包括表面偏析分布、晶体结构及其稳定性等特性。这里，“环境”可以代表温度、体积浓度或吸附物的影响。基于这些研究，我们将能够控制单个参数的影响，例如通过分析电子结构，对表面性质的影响。银-Au和铜-Au的合金表面是研究的出发点，因为它们属于制备纳米多孔Au的最有希望的候选材料。我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学方法（即所谓的簇展开方法（CE）和蒙特-卡罗（MC）模拟）相结合来研究它们。虽然CE允许扫描巨大的参数空间，但MC模拟将使我们能够访问有限的温度。这样，在近表面制度的原子有序现象的温度的影响将通过实施CE哈密顿量到蒙特-卡罗程序进行研究。然后，在稳定的团簇展开的基础上，构建表面相图和有序化参数。这些图将提供一个查找表的实验研究，因为它们使我们能够检测在温度和浓度的最高富集/耗尽的Au在近表面层达到。这也包括短期订单。同时，结构结果将得到SP 5项目中测量的低能电子衍射（LEED）强度谱定量分析的支持。这样的结构测定可以达到小于原子直径的百分之一的精度。这将允许详细了解合金表面结构。

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.