Order–disorder phase transition of the subsurface cation vacancy reconstruction on Fe3O4(001)

• Published in: Physical chemistry chemical physics : PCCP Vol. 22; no. 16; pp. 8336 - 8343
• Main Authors: Arndt, Björn, Lechner, Barbara A J, Bourgund, Alexander, Grånäs, Elin, Creutzburg, Marcus, Krausert, Konstantin, Hulva, Jan, Parkinson, Gareth S, Schmid, Michael, Vonk, Vedran, Esch, Friedrich, Stierle, Andreas
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 28.04.2020
• Subjects: Cations; Crystals; Ion scattering; Iron oxides; Long range order; Microscopy; Phase transitions; Photoelectric emission; Reconstruction; Scanning tunneling microscopy; Vacancies; X-ray diffraction
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/d0cp00690d

We present surface X-ray diffraction and fast scanning tunneling microscopy results to elucidate the nature of the surface phase transition on magnetite (001) from a [Formula Omitted] reconstructed to a non-reconstructed surface around 720 K. In situ surface X-ray diffraction at a temperature above the phase transition, at which long-range order is lost, gives evidence that the subsurface cation vacancy reconstruction still exists as a local structural motif, in line with the characteristics of a 2D second-order phase transition. Fast scanning tunneling microscopy results across the phase transition underpin the hypothesis that the reconstruction lifting is initiated by surplus Fe ions occupying subsurface octahedral vacancies. The reversible near-surface iron enrichment and reduction of the surface to stoichiometric composition is further confirmed by in situ low-energy ion scattering, as well as ultraviolet and X-ray photoemission results.