Hsu Po-Wei, Liao Zhen-He, Hung Ting-Chieh, Lee Hsuan, Wu Yu-Cheng, Lai Yu-Ling, Hsu Yao-Jane, Lin Yuwei, Wang Jeng-Han, Luo Meng-Fan
Department of Physics, National Central University, 300 Jhongda Road, Taoyuan 32001, Taiwan.
Phys Chem Chem Phys. 2017 Jun 7;19(22):14566-14579. doi: 10.1039/c7cp02524f.
Self-organized alloying of Au with Rh in nanoclusters on an ordered thin film of AlO/NiAl(100) was investigated via various surface probe techniques under ultrahigh-vacuum conditions and calculations based on density-functional theory. The bimetallic clusters were formed on the sequential deposition of vapors of Au and Rh onto AlO/NiAl(100) at 300 K. The formation was more effective on the oxide seeded with Rh, since all post-deposited Au joined the pregrown Rh clusters; for metal deposition in the reverse order, some separate Rh clusters were formed. The contrasting behavior is rationalized through the easier nucleation of Rh on the oxide surface, due to the stronger Rh-oxide and Rh-Rh bonds. The alloying in the clusters proceeded, regardless of the order of metal deposition, toward a specific structure: an fcc phase, (100) orientation and Rh core-Au shell structure. The orientation, structural ordering and lattice parameters of the Au-Rh bimetallic clusters resembled Rh clusters, rather than Au clusters, on AlO/NiAl(100), even with Rh in a minor proportion. The Rh-predominated core-shell structuring corresponds to the binding energies in the order Rh-Rh > Rh-Au > Au-Au. The core-shell segregation, although active, was somewhat kinetically hindered, since elevating the sample temperature induced further encapsulation of Rh. The bimetallic clusters became thermally unstable above 500 K, for which both Rh and Au atoms began to diffuse into the substrate. Moreover, the electronic structures of surface elements on the bimetallic clusters, controlled by both structural and electronic effects, show a promising reactivity.
在超高真空条件下，通过各种表面探针技术以及基于密度泛函理论的计算，研究了在AlO/NiAl(100)有序薄膜上纳米团簇中Au与Rh的自组织合金化。在300 K下，将Au和Rh的蒸气依次沉积到AlO/NiAl(100)上时形成了双金属团簇。在以Rh为籽晶的氧化物上形成更为有效，因为所有后沉积的Au都加入了预生长的Rh团簇；对于金属以相反顺序沉积的情况，则形成了一些单独的Rh团簇。这种对比行为通过Rh在氧化物表面更容易成核得到合理解释，这是由于Rh-氧化物和Rh-Rh键更强。无论金属沉积顺序如何，团簇中的合金化都朝着特定结构进行：面心立方相、(100)取向以及Rh核-Au壳结构。即使Rh含量较少，Au-Rh双金属团簇在AlO/NiAl(100)上的取向、结构有序性和晶格参数也更类似于Rh团簇，而不是Au团簇。以Rh为主的核壳结构对应于Rh-Rh > Rh-Au > Au-Au顺序的结合能。核壳偏析虽然活跃，但在动力学上受到一定阻碍，因为升高样品温度会导致Rh进一步被包裹。双金属团簇在500 K以上变得热不稳定，此时Rh和Au原子都开始扩散到衬底中。此外，受结构和电子效应共同控制的双金属团簇表面元素的电子结构显示出有前景的反应活性。
