In situ XPS analysis of various iron oxide films grown by NO2-assisted molecular-beam epitaxy
In situ XPS analysis of various iron oxide films grown by NO2-assisted molecular-beam epitaxy
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DOI：
10.1103/physrevb.59.3195
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发表时间：
1999-01-15
影响因子：
3.7
通讯作者：
Okada, K
中科院分区：
文献类型：
--
作者：
Fujii, T;de Groot, FMF;Okada, K
本文系统地分析了清洁和表征良好的氧化铁薄膜，即α-Fe_2O_3、γ-Fe_2O_3、Fe_3-deltaO_4和Fe_3O_4的X-射线光电子能谱(XPS)的芯态和价态谱。采用NO2辅助分子束外延技术在单晶MgO(100)和α-Al_2O_3(0001)衬底上外延制备了氧化铁薄膜。通过在生长过程中调节NO2压力，可以精确地控制薄膜的物相和化学计量比。每种氧化物的XPS光谱都清楚地显示出卫星结构。用团簇模型模拟了这些卫星结构，考虑了Fe3d到O2p杂化和d-d电子相关能的系统变化，较好地再现了观测结构。α-Fe_2O_3和γ-Fe_2O_3之间卫星结构的微小差异主要是由于Fe-O杂化参数的变化，表明与α-Fe_2O_3相比，γ-Fe_2O_3的共价性增加。随着伽马-Fe_2O_3-Fe_3O_4体系还原程度的增加，XPS中的卫星结构变得不清晰。这不仅是由于Fe2+离子的形成，而且是由于八面体和四面体Fe3+离子之间杂化参数的不均匀变化。[S0163-1829(99)02704-6]。
We report on a systematic analysis of x-ray photoelectron spectroscopy (XPS) core- and valence-level spectra of clean and well-characterized iron oxide films, i.e., alpha-Fe2O3, gamma-Fe2O3, Fe3-deltaO4, and Fe3O4. All iron oxide films were prepared epitaxially by NO2-assisted molecular-beam epitaxy on single crystalline MgO(100) and alpha-Al2O3(0001) substrates. The phase and stoichiometry of the films were controlled precisely by adjusting the NO2 pressure during growth. The XPS spectrum of each oxide clearly showed satellite structures. These satellite structures were simulated using a cluster-model calculation, which could well reproduce the observed structures by considering the systematic changes in both the Fe 3d to O 2p hybridization and the d-d electron-correlation energy. The small difference in the satellite structures between alpha-Fe2O3 and gamma-Fe2O3 resulted mainly from changes in the Fe-O hybridization parameters, suggesting an increased covalency in gamma-Fe2O3 compared to alpha-Fe2O3. With increasing reduction in the gamma-Fe2O3-Fe3O4 system,the satellite structures in XPS became unresolved. This was not only due to the formation of Fe2+ ions, but also to nonhomogeneous changes in the hybridization parameters between octahedral and tetrahedral Fe3+ ions. [S0163-1829(99)02704-6].