Zarraga-Colina Jeannette, Nix Roger M, Weiss Helmut
Department of Chemistry, Queen Mary, University of London, Mile End Road, London E1 4NS, United Kingdom.
J Phys Chem B. 2005 Jun 2;109(21):10978-85. doi: 10.1021/jp0508296.
The growth of ceria (CeO2) films by oxidation of evaporated Ce metal on Si(111) and on CaF2(111) epilayers on Si(111) is compared. By use of XPS, UPS, and LEED, it has been demonstrated that the application of a CaF2 buffer layer between the ceria and Si substrate prevents the formation of an amorphous oxidized Si layer at the interface and permits the growth of a well-defined epitaxial ceria layer of (111) surface orientation. The thermal stability of the CeO2/CaF2/Si(111) interface structure is limited by the solid-state reaction between CaF2 and ceria. This leads to gradual migration of fluorine into the oxide at elevated temperatures to give a solid-state solution of fluorine in the partially reduced oxide. An analysis of the composition observed after extensive annealing in a vacuum suggests that, with initial layers of CaF2 and CeO2 of similar thickness, the ultimate product may be CeOF. The onset of this solid-state reaction can, however, be significantly delayed by annealing under an oxygen atmosphere.
比较了通过在Si(111)以及Si(111)上的CaF2(111)外延层上蒸发Ce金属进行氧化来生长二氧化铈（CeO2）薄膜的情况。通过使用X射线光电子能谱（XPS）、紫外光电子能谱（UPS）和低能电子衍射（LEED），已证明在二氧化铈和Si衬底之间施加CaF2缓冲层可防止在界面处形成非晶态氧化Si层，并允许生长具有(111)表面取向的明确外延二氧化铈层。CeO2/CaF2/Si(111)界面结构的热稳定性受CaF2与二氧化铈之间的固态反应限制。这导致在高温下氟逐渐迁移到氧化物中，从而在部分还原的氧化物中形成氟的固态溶液。对在真空中进行长时间退火后观察到的成分分析表明，对于初始厚度相似的CaF2和CeO2层，最终产物可能是CeOF。然而，在氧气气氛下退火可显著延迟这种固态反应的开始。
