Institute of Surface Chemistry and Catalysis, Ulm University, Ulm, Germany.
Chemphyschem. 2011 Apr 18;12(6):1148-54. doi: 10.1002/cphc.201001087. Epub 2011 Apr 1.
The stability of PdRu/Ru(0001) and PtRu/Ru(0001) surface alloys and the tendency for surface segregation of Pd and Pt subsurface guest metals in these surface alloys is studied by scanning tunneling microscopy (STM) and Auger electron spectroscopy (AES). Atomic resolution STM imaging and AES measurements reveal that upon overgrowing the surface alloys with a 1-2 monolayer Ru film and subsequent annealing to the temperatures required for initial surface alloy formation, the Ru-covered Pd (Pt) atoms float back to the outermost layer. The lateral distribution of these species is also essentially identical to that of the initial surface alloys, before overgrowth by Ru. In combination, this clearly demonstrates that the surface alloys represent stable surface configurations, metastable only towards entropically favored bulk dissolution, and that there is a distinct driving force for surface segregation of these species. Consequences of these data on the mechanism for surface alloy formation are discussed.
通过扫描隧道显微镜 (STM) 和俄歇电子能谱 (AES) 研究了 PdRu/Ru(0001) 和 PtRu/Ru(0001) 表面合金的稳定性以及这些表面合金中 Pd 和 Pt 次表面客金属表面偏析的趋势。原子分辨率 STM 成像和 AES 测量表明，在将表面合金用 1-2 单层 Ru 膜外延生长并随后退火到初始表面合金形成所需的温度后，覆盖 Ru 的 Pd(Pt)原子会浮回到最外层。这些物种的横向分布与 Ru 外延生长之前的初始表面合金基本相同。结合起来，这清楚地表明，表面合金代表稳定的表面构型，仅对熵有利的体溶解处于亚稳状态，并且这些物种的表面偏析存在明显的驱动力。讨论了这些数据对表面合金形成机制的影响。
