5th Science Workshop of the Program MML

Near-Surface Cation Diffusion in Magnetite studied by advanced Synchrotron and Neutron Methods

Not scheduled

1h 30m

Johann-Gottfried-Tulla-Hörsaal (Karlsruhe Institute of Technology)

Talk RT2 Plenary 2

Speaker

Steffen Tober (Centre for X-ray and Nanoscience (CXNS), Deutsches Elektronen-Synchrotron (DESY), Notkestraße 85, 22607 Hamburg, Germany
 Universität Hamburg, Fachbereich Physik, Luruper Chaussee 129, 22607 Hamburg, Germany, Jülich Centre of Neutron Science (JCNS-2), Forschungszentrum Jülich, Wilhelm-Johnen-Str., 52428 Jülich, Germany
, Deutsches Elektronen-Synchrotron (DESY), Notkestraße 85, 22607 Hamburg, Germany)

Description

With their flexible stoichiometry, magnetic properties and wide abundance, iron oxides are used as catalysts and catalyst components, in medicine, magneto-electronic devices and composite materials. As the surface and interface properties of iron oxides are crucial for these applications, tuning their performance requires a precise understanding of structure and reactions in their near-surface region.
For the stable magnetite (Fe$_3$O$_4$) (001) surface, oxidative regrowth, (partial) lifting of the subsurface cation vacancy reconstruction and the element-specific incorporation of adatoms not only demonstrate a sensitive relation of environmental conditions and defect structure, but also highlight the importance of near-surface cation transport [1,2,3].
We studied the growth, defect structure and cation transport between an isotopically labelled $^{57}$Fe$_3$O$_4$ thin film and a Fe$_3$O$_4$ (001) single crystal substrate by a combination of surface X-ray diffraction (SXRD), neutron reflectivity (NR) and nuclear forward scattering (NFS) [4,5]. While NR provided information about the $^{57}$Fe depth distribution, in situ NFS allowed to determine the lattice site-selective $^{57}$Fe depth distribution and provided independent information about the density and stoichiometry of the near-surface region. The transport experiments are complemented with SXRD to characterise the Fe$_3$O$_4$ homoepitaxy, further emphasizing the link between structure, stoichiometry and transport processes in Fe$_3$O$_4$.
Combining advanced sample preparation at CXNS with methods available at synchrotron and neutron facilities such as PETRAIII, FRMII and SOLEIL allowed to derive characteristics of near-surface cation transport in Fe$_3$O$_4$ that might as well be relevant for the class of spinel-type oxides as a whole.

References: [1] S. Nie et al. JACS 135, 10091 (2013); [2] R. Bliem et al. Science 346, 1215 (2014); [3] B. Arndt et al. Surf. Sci. 653, 76 (2016), [4] S. Tober et al., Phys. Rev. Res. 2, 023406 (2020), [5] S. Tober et al. Phy. Rev. Lett. 134, 236203 (2025).