Phase transformations in thin iron oxide films: Spectromicroscopic study of velocity and shape of the reaction fronts

Combining low energy electron microscopy (LEEM) with low energy electron diffraction (LEED) and x-ray photoemission electron microscopy (XPEEM), we studied the phase transformations between Fe3O4, γ-Fe2O3, and α-Fe2O3, grown as 10nm thin oxide films on Pt(111) and Ag(111) single crystals. These tran...

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Bibliographic Details
Published in:Surface science 2016-06, Vol.648, p.177-187
Main Authors: Genuzio, F., Sala, A., Schmidt, Th, Menzel, D., Freund, H.-J.
Format: Article
Language:English
Subjects:
Activation energy
Boundaries
Electron microscopy
Front velocity
Iron oxides
LEEM
Low energy
Moving reaction fronts
Oxide coatings
Phase transformation
Phase transformations
Quantitative analysis
Transformations
XPEEM
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Summary:Combining low energy electron microscopy (LEEM) with low energy electron diffraction (LEED) and x-ray photoemission electron microscopy (XPEEM), we studied the phase transformations between Fe3O4, γ-Fe2O3, and α-Fe2O3, grown as 10nm thin oxide films on Pt(111) and Ag(111) single crystals. These transformations occur as moving reaction fronts in most cases, the shapes and velocities of which show strong dependences on temperature and oxygen pressure, but also on defects like step bunches of the supporting substrate and domain boundaries in the initial oxide film. While the non-uniform moving fronts make quantitative analysis difficult, we have extracted approximate values for the average front velocities. We discuss these as well as the qualitative information on the non-uniform fronts in terms of the known geometric situations and the likely motional steps. [Display omitted] •The phase transformations in thin iron oxide films were studied on mesoscopic scale.•Reaction fronts observed by LEEM, LEED, and XPS vary strongly in shape and velocity.•They are influenced by temperature, O2 pressure, and substrate and film defects.•Apparent activation energies for the various reaction processes were estimated.•Dendritic fronts develop in preferential directions and are connected with fast rates.
ISSN:0039-6028
1879-2758
DOI:10.1016/j.susc.2015.11.016