TY - JOUR
T1 - Interconversion of α-Fe2O3 and Fe3O4 thin films
T2 - Mechanisms, morphology, and evidence for unexpected substrate participation
AU - Genuzio, Francesca
AU - Sala, Alessandro
AU - Schmidt, Thomas
AU - Menzel, Dietrich
AU - Freund, Hans Joachim
N1 - Publisher Copyright:
© 2014 American Chemical Society.
PY - 2014/12/18
Y1 - 2014/12/18
N2 - The reversible transformations of thin magnetite (Fe3O4) and hematite (α-Fe2O3) films grown on Pt(111) and Ag(111) single crystals as support have been investigated by a combined low energy electron microscopy (LEEM) and low-energy electron diffraction (LEED) study. The conversions were driven by oxidation, annealing in ultrahigh vacuum (UHV), or Fe deposition with subsequent annealing. As expected, the oxidation of a Fe3O4 film yielded an α-Fe2O3 structure. Unexpectedly, the annealing in UHV also led to a transformation from Fe3O4 into α-Fe2O3, but only if Pt(111) was used as substrate. In contrast, on a Ag(111) substrate the inverse reaction, a slow transformation from α-Fe2O3 into Fe3O4, was observed, as expected for oxygen desorption. Fe deposition on α-Fe2O3 and subsequent annealing in UHV transformed the film into Fe3O4. As the most probable explanation we propose that the UHV conversion on Pt(111) supports proceeds by Fe cation diffusion through the film and Fe atom dissolution in the substrate, decreasing the Fe concentration within the iron oxide film. This process is not possible for a Ag(111) substrate. The interconversions, which were best observable in mixed films containing domains of both oxides, occurred by growth of one domain type with well-defined boundaries and growth rates.
AB - The reversible transformations of thin magnetite (Fe3O4) and hematite (α-Fe2O3) films grown on Pt(111) and Ag(111) single crystals as support have been investigated by a combined low energy electron microscopy (LEEM) and low-energy electron diffraction (LEED) study. The conversions were driven by oxidation, annealing in ultrahigh vacuum (UHV), or Fe deposition with subsequent annealing. As expected, the oxidation of a Fe3O4 film yielded an α-Fe2O3 structure. Unexpectedly, the annealing in UHV also led to a transformation from Fe3O4 into α-Fe2O3, but only if Pt(111) was used as substrate. In contrast, on a Ag(111) substrate the inverse reaction, a slow transformation from α-Fe2O3 into Fe3O4, was observed, as expected for oxygen desorption. Fe deposition on α-Fe2O3 and subsequent annealing in UHV transformed the film into Fe3O4. As the most probable explanation we propose that the UHV conversion on Pt(111) supports proceeds by Fe cation diffusion through the film and Fe atom dissolution in the substrate, decreasing the Fe concentration within the iron oxide film. This process is not possible for a Ag(111) substrate. The interconversions, which were best observable in mixed films containing domains of both oxides, occurred by growth of one domain type with well-defined boundaries and growth rates.
UR - http://www.scopus.com/inward/record.url?scp=84918771081&partnerID=8YFLogxK
U2 - 10.1021/jp504020a
DO - 10.1021/jp504020a
M3 - Article
AN - SCOPUS:84918771081
SN - 1932-7447
VL - 118
SP - 29068
EP - 29076
JO - Journal of Physical Chemistry C
JF - Journal of Physical Chemistry C
IS - 50
ER -