Department of Physics, National Central University, 300 Jhongda Road, Taoyuan 32001, Taiwan.
Department of Chemistry, National Taiwan Normal University, Taipei, Taiwan.
J Chem Phys. 2017 Jul 28;147(4):044704. doi: 10.1063/1.4995598.
The surface structures and compositions of Au-Rh bimetallic nanoclusters on an ordered thin film of AlO/NiAl(100) were investigated, primarily with infrared reflection absorption spectra and temperature-programmed desorption of CO as a probe molecule under ultrahigh-vacuum conditions and calculations based on density-functional theory. The bimetallic clusters were formed by sequential deposition of vapors of Au and Rh onto AlO/NiAl(100) at 300 K. Alloying in the clusters was active and proceeded toward a specific structure-a fcc phase, (100) orientation, and Rh core-Au shell structure, regardless of the order of metal deposition. For Au clusters incorporating deposited Rh, the Au atoms remained at the cluster surface through position exchange and became less coordinated; for deposition in reverse order, deposited Au simply decorated the surfaces of Rh clusters. Both adsorption energy and infrared absorption intensity were enhanced for CO on Au sites of the bimetallic clusters; both of them are associated with the bonding to Rh and also a decreased coordination number of CO-binding Au. These enhancements can thus serve as a fingerprint for alloying and atomic inter-diffusion in similar bimetallic systems.
采用红外反射吸收谱和 CO 的程序升温脱附作为探针分子，在超高真空条件下，对负载于有序 AlO/NiAl(100) 薄膜上的 Au-Rh 双金属纳米团簇的表面结构和组成进行了研究，同时还基于密度泛函理论进行了计算。双金属团簇是通过在 300 K 下将 Au 和 Rh 的蒸气顺序沉积在 AlO/NiAl(100)上形成的。团簇中的合金化是活跃的，并且无论金属沉积的顺序如何，都会朝着特定的结构发展，即 fcc 相、(100)取向和 Rh 核-Au 壳结构。对于包含沉积 Rh 的 Au 团簇，Au 原子通过位置交换仍保留在团簇表面，并且配位程度降低；而对于反序沉积，所沉积的 Au 只是简单地修饰了 Rh 团簇的表面。对于双金属团簇中的 Au 位上的 CO，吸附能和红外吸收强度都增强了；这两者都与 Rh 的键合以及 CO 结合 Au 的配位数减少有关。因此，这些增强可以作为类似双金属体系中合金化和原子互扩散的特征。
