Reversible metamorphosis from Fe3O4 to FeO of epitaxial iron oxide films grown on the Fe-p(1 × 1)O surface

M Capra,A Lodesani,M Finazzi,F Ciccacci,L Duò,A Picone,A Brambilla

doi:10.1039/d0ra10650j

Abstract

The reduction and oxidation of epitaxial Fe3O4 films grown by reactive deposition on a Fe-p(1 × 1)O surface have been investigated by means of Auger electron spectroscopy (AES), low energy electron diffraction (LEED) and scanning tunneling microcopy (STM). The as-grown iron oxide samples display a square LEED pattern with a lattice constant compatible with a p(1 × 1) bulk terminated Fe3O4(001) surface. STM topographic images of Fe3O4 are characterized by atomically flat terraces separated by highly oriented steps running along the (010) and (100) crystallographic directions of the substrate. Upon annealing at 800 K in an ultra-high vacuum, AES reveals that magnetite transforms to FeO. The sample exposes the (001) surface of the rock salt structure, with a lattice parameter close to that of bulk wüstite. The Fe3O4 phase can be recovered by oxidation at 10−6 mbar of molecular oxygen.

Highlights

Iron oxides have been investigated for decades in several scienti c disciplines, spanning physical chemistry[1,2,3] to medicine.[4]
The stabilization of Fe3O4(001) is supported by the Auger electron spectroscopy (AES) and scanning tunneling microcopy (STM) data presented in the following
The subsequent ultra-high vacuum (UHV) annealing at 800 K li s the p(2 Â 2) phase and a square lattice similar to that of the Fe-p(1 Â 1)O substrate appears in Fig. 1(c), with different spot intensities and unit mesh dimensions

Summary

Introduction

Iron oxides have been investigated for decades in several scienti c disciplines, spanning physical chemistry[1,2,3] to medicine.[4]. The Fe-p(1 Â 1)O surface was obtained by following a well-established procedure, exposing the Fe(001) sample to 30 L of molecular oxygen (O2) and annealing in UHV to 800 K for 5 minutes.[5] Fe3O4 lms were grown by evaporating Fe in a 10À6 mbar O2 atmosphere, with the sample kept at 500 K during the deposition, as measured by a thermocouple positioned close to the sample.

Results

Conclusion