Fachbereich Physik, Universität Osnabrück, Barbarastr. 7, 49076 Osnabrück, Germany.
Phys Chem Chem Phys. 2013 Nov 14;15(42):18589-99. doi: 10.1039/c3cp52688g.
The structural changes of a (111) oriented CeO2 film grown on a Si(111) substrate covered with a hex-Pr2O3(0001) interface layer due to post deposition annealing are investigated. X-ray photoelectron spectroscopy measurements revealing the near surface stoichiometry show that the film reduces continuously upon extended heat treatment. The film is not homogeneously reduced since several coexisting crystalline ceria phases are stabilized due to subsequent annealing at different temperatures as revealed by high resolution low energy electron diffraction and X-ray diffraction. The electron diffraction measurements show that after annealing at 660 °C the ι-phase (Ce7O12) is formed at the surface which exhibits a (√7 × √7)R19.1° structure. Furthermore, a (√27 × √27)R30° surface structure with a stoichiometry close to Ce2O3 is stabilized after annealing at 860 °C which cannot be attributed to any bulk phase of ceria stable at room temperature. In addition, it is shown that the fully reduced ceria (Ce2O3) film exhibits a bixbyite structure. Polycrystalline silicate (CeSi(x)O(y)) and crystalline silicide (CeSi1.67) are formed at 850 °C and detected at the surface after annealing above 900 °C.
研究了在覆盖有六方 Pr2O3(0001) 界面层的 Si(111) 衬底上生长的 (111) 取向 CeO2 薄膜在沉积后退火过程中的结构变化。X 射线光电子能谱测量揭示了近表面化学计量比表明，薄膜在长时间热处理后不断还原。由于在不同温度下随后退火，稳定了几种共存的结晶氧化铈相，因此薄膜不均匀还原，如高分辨率低能电子衍射和 X 射线衍射所揭示的。电子衍射测量表明，在 660°C 退火后，表面形成了 ι-相 (Ce7O12)，其具有 (√7 × √7)R19.1°结构。此外，在 860°C 退火后，稳定了具有接近 Ce2O3 化学计量比的 (√27 × √27)R30°表面结构，这不能归因于室温下稳定的任何氧化铈体相。此外，表明完全还原的氧化铈 (Ce2O3) 薄膜具有尖晶石结构。多晶硅酸盐 (CeSi(x)O(y)) 和结晶硅化物 (CeSi1.67) 在 850°C 形成，并在退火温度高于 900°C 时在表面检测到。
