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Structure, Magnetism, and the Interaction of Water with Ti-Doped Fe3O4 Surfaces
journal contribution
posted on 2019-10-18, 17:04 authored by Kelsey A. Stoerzinger, Carolyn I. Pearce, Timothy C. Droubay, Vaithiyalingam Shutthanandan, Zhi Liu, Elke Arenholz, Kevin M. RossoThe functionality
of magnetite, Fe3O4, for
catalysis and spintronics applications is dependent on the molar ratio
of Fe2+ and Fe3+ and their distribution at the
surface. In turn, this depends on a poorly understood interplay between
crystallographic orientation, dopants, and the reactive adsorption
of atmospheric species such as water. Here, (100)-, (110)-, and (111)-oriented
films of titano-magnetite, Fe(3–x)TixO4, were grown by pulsed
laser deposition and their composition, valence distribution, magnetism,
and interaction with water were studied by ambient pressure X-ray
photoelectron spectroscopy (AP-XPS) and X-ray magnetic circular dichroism.
Although the bulk compositions match the desired stoichiometry, the
surfaces were found to be enriched in Ti4+, especially
the top 1 nm. The highest surface energy (110) film was the most reduced,
tied to local Ti enrichment, and a corresponding decreased magnetic
moment. AP-XPS showed that incorporation of x = 0.25
Ti dramatically lowered the propensity to form hydroxyl species at
a given relative humidity, and also that hydroxylation is relatively
invariant with orientation. In contrast, the affinity for water is
similar across orientations, regardless of Ti incorporation, suggesting
that relative humidity controls its uptake. The findings may help
demystify the interactions that lead to specific distributions of
Fe2+ and Fe3+ at magnetite surfaces, toward
design of more deliberately active catalysts and magnetic devices.
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Keywords
spintronics applicationsform hydroxyl species1 nmhumidity controlsmagnetite surfacesTi enrichmentTi x O 4AP-XPSreactive adsorptionTi incorporation0.25 TiFe 3 O 4bulk compositionsTi-Doped Fe 3 O 4 Surfaceslaser depositionambient pressure X-ray photoelectron spectroscopyorientationvalence distributionmolar ratio
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