Fritz-Haber-Institut der MPG, Faradayweg 4-6, 14195 Berlin, Germany.
Phys Rev Lett. 2013 Nov 15;111(20):206101. doi: 10.1103/PhysRevLett.111.206101. Epub 2013 Nov 12.
The role of surface and subsurface O vacancies for gold adsorption on crystalline CeO2(111) films has been investigated by scanning tunneling microscopy and density functional theory. Whereas surface vacancies serve as deep traps for the Au atoms, subsurface defects promote the formation of characteristic Au pairs with a mean atom distance of two ceria lattice constants (7.6 Å). Hybrid density functional theory calculations reveal that the pair formation arises from a titration of the two Ce3+ ions generated by a single O vacancy. The Au-Ce3+ bond forms due to a strain effect, as the associated charge transfer from the spacious Ce3+ into the adgold enables a substantial relaxation of the ceria lattice. Also the experimentally determined Au-pair length is reproduced in the calculations, as we find a Ce3+-Ce3+ spacing of two ceria lattice parameters to be energetically preferred. Single Au atoms can thus be taken as position markers for Ce3+ ion pairs in the surface, providing unique information on electron-localization phenomena in reduced ceria.
通过扫描隧道显微镜和密度泛函理论研究了表面和亚表面 O 空位对金在晶态 CeO2(111) 薄膜上吸附的作用。表面空位作为 Au 原子的深陷阱，而亚表面缺陷则促进了具有两个 CeO2 晶格常数（7.6 Å）平均原子距离的特征 Au 对的形成。杂化密度泛函理论计算表明，对单个 O 空位产生的两个 Ce3+ 离子进行滴定，导致了对形成。Au-Ce3+ 键的形成是由于应变效应，因为从宽敞的 Ce3+ 到 adgold 的相关电荷转移使 CeO2 晶格得以充分松弛。此外，实验确定的 Au 对长度也在计算中得到了再现，因为我们发现 Ce3+-Ce3+ 间距为两个 CeO2 晶格参数在能量上是优选的。因此，单个 Au 原子可以作为表面上 Ce3+ 离子对的位置标记，为还原 CeO2 中的电子局域化现象提供了独特的信息。
