Abstract
The authors study interdiffusion of Fe-cations between homoepitaxially grown 57Fe3O4 films and (001) oriented Fe3O4 substrates in the temperature range of 470-770 K under high vacuum by neutron reflectivity and time-of-flight secondary ion mass spectrometry. The paper estimates diffusion lengths in the order of 20-50 \AA{} and diffusion constants in the order of 10-20 m2/s.
Highlights
Iron oxides are used in catalysis, material science, and in the development of spintronic devices [1]
Growth experiments on Fe3O4 single crystals were performed in a temperature range from room temperature up to approximately 520 K, a temperature commonly chosen for the growth of Fe3O4 on MgO [44,45]
Auger-electron spectra (AES) of the as-prepared crystal and thin films deposited at room temperature [see Fig. 2(a)], 420, and 520 K consistently show a double peak instead of a sharp iron MNN line suggesting the oxide [46]
Summary
Iron oxides are used in catalysis, material science, and in the development of spintronic devices [1]. Under reducing conditions in the absence of oxygen, Frenkel pairs, the combination of a cation vacancy at a regular lattice site and an interstitial atom, are the predominant defects. In this regime, cation motion is proposed to be mediated via an interstitial mechanism with cations hopping along interstitial sites or, more likely, an interstitialcy mechanism [27]. While the bulk cation diffusion at high temperatures is extensively studied and quite-well understood, the transport processes at low temperatures and around the near-surface region are still largely unknown. Isotopically labeled 57Fe3O4 thin films grown homoepitaxially on (001)-oriented natural Fe3O4 crystals by reactive molecular beam epitaxy (MBE) were used to study the near-surface cation diffusion in magnetite in the catalytically relevant temperature range between 470 and 770 K [11].
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