Bergbreiter A, Hoster H E, Sakong S, Gross A, Behm R J
Institute of Surface Chemistry and Catalysis, Ulm University, D-89069, Ulm, Germany.
Phys Chem Chem Phys. 2007 Oct 7;9(37):5127-32. doi: 10.1039/b705237p. Epub 2007 Jul 31.
The energetics determining the distinct short-range order in two-dimensional (2D) monolayer Cu(x)Pd(1-x) surface alloys on a Ru(0001) substrate were investigated by Monte Carlo simulations and density functional theory calculations. Using a 2D lattice gas Hamiltonian based on effective pair interaction (EPI) parameters, the EPIs were derived for different Cu concentrations with Monte Carlo (MC) simulations by comparing with the atomic distributions obtained from atomic resolution STM images and the related Warren-Cowley short-range order parameters (Hoster et al., Phys. Rev. B, 2006, 73 165413). The ground state structures and mixing energies at 0 K derived from these EPIs agree well with mixing energies determined from DFT calculations of different ordered surface alloys. Additional MC simulations yield rather low transition temperatures which explain the absence of ordered 2D phases in the experiments. The consequences of our findings for the use of alloy surfaces and surface alloys as model systems for adsorption and catalytic reaction studies are discussed.
通过蒙特卡罗模拟和密度泛函理论计算，研究了决定Ru(0001)衬底上二维(2D)单层Cu(x)Pd(1 - x)表面合金中独特短程有序的能量学。基于有效对相互作用(EPI)参数使用二维晶格气体哈密顿量，通过与从原子分辨率STM图像获得的原子分布以及相关的沃伦 - 考利短程有序参数进行比较，利用蒙特卡罗(MC)模拟得出不同Cu浓度下的EPI（霍斯特等人，《物理评论B》，2006年，73 165413）。由这些EPI得出的0 K基态结构和混合能与不同有序表面合金的密度泛函理论计算确定的混合能非常吻合。额外的MC模拟产生了相当低的转变温度，这解释了实验中不存在有序二维相的原因。讨论了我们的研究结果对于将合金表面和表面合金用作吸附和催化反应研究模型系统的影响。
