Ultrathin two-dimensional silica films have been suggested as highly defined conductive models for fundamental studies on silica-supported catalyst particles. Key requirements in this context are closed silica films that isolate the gas phase from the underlying metal substrate and stability under reaction conditions. Here, we present silica bilayer films grown on Pt(111) and Rh(111) and characterize them by scanning tunneling microscopy and X-ray photoelectron spectroscopy. We provide the first report of silica bilayer films on Rh(111) and have further successfully prepared fully closed films on Pt(111). Interestingly, surface and interface silicide phases play a decisive role in both cases: On platinum, closed films can be stabilized only when silicon is deposited in excess, which results in an interfacial silicide or silicate layer. We show that these silica films can also be grown directly from a surface silicide phase. In the case of rhodium, the silica phase is less stable and can be reduced to a silicide in reductive environments. Though similar in appearance to the “silicene” phases that have been controversially discussed on Ag(111), we conclude that an interpretation of the phase as a surface silicide is more consistent with our data. Finally, we show that the silica film on platinum is stable in 0.8 mbar CO but unstable at elevated temperatures. We thus conclude that these systems are only suitable as model catalyst supports to a limited extent.

中文翻译：

---

二维二氧化硅、硅化物和硅烯在 Pt(111) 和 Rh(111) 上稳定性的界面效应


超薄二维二氧化硅薄膜已被建议作为二氧化硅负载催化剂颗粒基础研究的高度定义的导电模型。在这方面的关键要求是封闭的二氧化硅薄膜，其将气相与下面的金属基材隔离，以及反应条件下的稳定性。在这里，我们提出了在 Pt(111) 和 Rh(111) 上生长的二氧化硅双层薄膜，并通过扫描隧道显微镜和 X 射线光电子能谱对其进行表征。我们首次报道了Rh(111)上的二氧化硅双层薄膜，并进一步成功地在Pt(111)上制备了全封闭薄膜。有趣的是，表面和界面硅化物相在这两种情况下都起着决定性的作用：在铂上，只有当硅沉积过量时，封闭的薄膜才能稳定，从而形成界面硅化物或硅酸盐层。我们证明这些二氧化硅薄膜也可以直接从表面硅化物相生长。在铑的情况下，二氧化硅相不太稳定，并且可以在还原环境中还原成硅化物。尽管外观与 Ag(111) 上备受争议的“硅烯”相相似，但我们得出的结论是，将该相解释为表面硅化物更符合我们的数据。最后，我们证明铂上的二氧化硅膜在 0.8 mbar CO 中稳定，但在高温下不稳定。因此，我们得出的结论是，这些系统仅在有限程度上适合作为模型催化剂载体。