RUI: Structure and Kinetics of Epitaxially-Grown Surface Alloys

这是一个本科院校研究奖（RUI），涉及本科生在拟议的研究。 使用动力学蒙特卡罗模拟，仔细分析实验研究和国家的最先进的总能量计算扩散障碍相结合，主要研究者（PI）最近已经证明，通过异质外延沉积生长的表面合金的结构和发展可以充分占。 这样的系统，涉及一个以上的原子物种和混合的沉积物种的几个层到衬底中，是具有挑战性的准确建模，所以取得的成功是值得注意的。 也有强大的技术动机，将这项工作扩展到其他双金属系统，因为其中几个具有重要的相关性，表面磁性和催化。 在原子水平上处理这样的系统的表面动力学开发的模型是基于一个简单的，协调相关的，参数化近似的能量障碍管理本地原子的安排。 直接移动和交换（协调，两个原子）移动都包括在内。 必要的参数推导出从实验信息结合总能量计算使用VASP协议和轻推弹性带的方法绘制扩散途径和障碍。 基于这些移动和相关障碍的表面合金系统的动力学发展和演变通过动力学Monte Carlo模拟（BLK算法）确定，该模拟也忠实地对待沉积过程。 这种方法已经成功地完全解释了Rh/Ag（001）体系中所观察到的有趣的覆盖度依赖结构，并且关于这项工作的第一份报告最近发表在《表面科学》杂志上。Jurgen在乌尔姆，德国，它具有广泛的实验能力，研究双金属生长系统，并为Rh/Ag（001）系统的STM数据的来源。 第一个扩展将是在较高温度下的Rh/Ag（001）系统，然后是具有不同基底对称性的其他软金属基底表面合金。 在此之后，我们将扩展该方法，以更硬的基板的情况下，工业意义。 这类系统应该类似地发展，但需要更高的温度来实现必要的流动性。 在对模型进行这些扩展的过程中，我们还将测试对我们的模型进行扩展的必要性，以确定活化能势垒的配位依赖性。该小组还对金属平台上的吸附原子和空位进行了详细的分析。 我们已经表明，在低覆盖率的访问概率函数可以通过简单的松弛方法计算得到，并将继续工作，将这种方法应用到各种表面过程催化的移动的吸附原子或空位。 这是一个本科院校研究奖（RUI），涉及本科生在拟议的研究。 使用动力学蒙特卡罗模拟，仔细分析实验研究和最先进的总能量计算的扩散障碍相结合，主要研究者（PI）最近证明，通过沉积生长的表面合金的结构和发展可以完全解释。 在本研究中，这种处理和模型将与R.位于德国乌尔姆的Jurgen拥有研究双金属生长系统的广泛实验能力，并且是之前研究的大部分数据的来源。*

This is an award for Research at Undergraduate Institutions (RUI) that involves undergraduate students in the proposed research. Using a combination of kinetic Monte Carlo simulation, careful analysis of experimental studies and state-of-the-art total energy calculations for diffusion barriers, the principal investigator (PI) has recently demonstrated that the structure and development of surface alloys grown via heteroepitaxial deposition can be fully accounted for. Such systems, involving as they do here more than one atomic species and mixing of the deposited species several layers into the substrate, are challenging to model accurately and so the success achieved is noteworthy. There are also strong technological motivations for extending this work to other bi-metallic systems since several of them have important relevance for surface magnetism and catalysis. The model developed for treating the surface kinetics of such systems at the atomic level is based on a simple, coordination dependent, parametrized approximation for the energy barriers governing local atomic arrangements. Both direct moves and exchange (coordinated, two-atom) moves are included. The necessary parameters are deduced from experimental information combined with total energy calculations using the VASP protocol and the nudged elastic band method of mapping out diffusion pathways and barriers. The kinetic development and evolution of the surface alloy system based on these moves and the associated barriers are determined via a kinetic Monte Carlo simulation (BLK algorithm), which also treats the deposition process faithfully. This approach has succeeded in fully accounting for the interesting coverage dependent structures seen for the Rh/Ag(001) system, and a first report on this work has recently appeared in the journal Surface Science.In the present research this treatment and model will be extended to other regimes and systems in collaboration with the experimental group of R. Jurgen in Ulm, Germany, which has extensive experimental capability for study of bi-metallic growth systems and was the source of much of the STM data for the Rh/Ag(001) system. The first extension will be to the Rh/Ag(001) system at higher temperature and then to other soft-metal substrate surface alloys of differing substrate symmetry. After that we will extend the method to harder substrate cases of industrial significance. Such systems should evolve similarly, but require higher temperatures to achieve the necessary mobility. In making these extensions to the model we will also test for the necessity of extensions to our model for the coordination dependence of the activation energy barriers.The group also has underway a detailed analysis of adatoms and vacancies on metallic terraces. We have shown that the visit probability function at low coverage can be obtained via simple relaxation method calculations and will continue work to apply this approach to various surface processes catalyzed by mobile adatoms or vacancies. %%%This is an award for Research at Undergraduate Institutions (RUI) that involves undergraduate students in the proposed research. Using a combination of kinetic Monte Carlo simulation, careful analysis of experimental studies and state-of-the-art total energy calculations for diffusion barriers, the principal investigator (PI) has recently demonstrated that the structure and development of surface alloys grown via deposition can be fully accounted for. In the present research this treatment and model will be extended to other regimes and systems in collaboration with the experimental group of R. Jurgen in Ulm, Germany, which has extensive experimental capability for study of bi-metallic growth systems and was the source of much of the data for the previous research.***