<i>In-situ</i> x-ray diffraction studies on post-deposition vacuum-annealing of ultra-thin iron oxide films

Bertram, Florian; Deiter, C.; Pflaum, K.; Suendorf, M.; Otte, Christian; Wollschläger, J.

doi:10.1063/1.3661655

Cited by 21 publications

(17 citation statements)

References 12 publications

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“…The transition temperatures observed in this study are consistent with those from previous in situ X-ray diffraction experiments of iron oxide thin films. 37,38 Although the effects of electron beam damage during in situ TEM studies, such as oxygen vacancy formation, cannot be neglected for this study, the observed systematic reduction of iron oxide nanochains is in good agreement with previous studies. In-situ TEM heating experiments of individual iron oxide nanoparticles under the same conditions reported in this study have revealed the elimination of the FeO phase, and demonstrate equilibrium between Fe 3 O 4 and metallic Fe.…”

Section: A Reduction-oxidation Reactionssupporting

confidence: 90%

Reduction reactions and densification during in situ TEM heating of iron oxide nanochains

Bonifacio

Das

Kennedy

et al. 2017

Journal of Applied Physics

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The reduction reactions and densification of nanochains assembled from -FeO nanoparticles were investigated using transmission electron microscopy (TEM). Morphological changes and reduction of the metal oxide nanochains were observed during TEM annealing through simultaneous imaging and quantitative analysis of the near-edge fine structures of Fe L absorption edges acquired by spatially resolved electron energy loss spectroscopy. A change in the oxidation states during annealing of the iron oxide nanochains was observed with phase transformations due to continuous reduction from FeO over FeO, FeO to metallic Fe. Phase transitions during the heating experiments were accompanied with morphological changes in the nanochains, specifically rough-to-smooth surface transitions below 500 °C, neck formation between adjacent particles around 500 °C, and subsequent neck growth. At higher temperatures, coalescence of FeO particles was observed, representing densification.

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Section: A Reduction-oxidation Reactionssupporting

confidence: 90%

Reduction reactions and densification during in situ TEM heating of iron oxide nanochains

Bonifacio

Das

Kennedy

et al. 2017

Journal of Applied Physics

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“…However, in the second series the vertical layer distance of Fe 3 O 4 relaxes with increasing Fe 3 O 4 film thickness until it reaches nearly the bulk value, although the magnetite has not reached the critical film thickness. Our previous studies [33][34][35][36] on the growth of magnetite on MgO(001) confirm this observation. In these studies the strain of the magnetite films has relaxed with increasing film thickness and the critical film thickness is very small.…”

Section: Discussionsupporting

confidence: 80%

Structure and morphology of epitaxially grown Fe3O4/NiO bilayers on MgO(001)

Schemme

Kuschel

Bertram³

et al. 2015

Thin Solid Films

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Crystalline Fe 3 O 4 /NiO bilayers were grown on MgO(001) substrates using reactive molecular beam epitaxy to investigate their structural properties and their morphology. The film thickness either of the Fe 3 O 4 film or of the NiO film has been varied to shed light on the relaxation of the bilayer system. The surface properties as studied by X-ray photoelectron spectroscopy and low energy electron diffraction show clear evidence of stoichiometric well-ordered film surfaces. Based on the kinematic approach X-ray diffraction experiments were completely analyzed. As a result the NiO films grow pseudomorphic in the investigated thickness range (up to 34 nm) while the Fe 3 O 4 films relax continuously up to the thickness of 50 nm. Although all diffraction data show well developed Laue fringes pointing to oxide films of very homogeneous thickness, the Fe 3 O 4 /NiO interface roughens continuously up to 1 nm root-mean-square roughness with increasing NiO film thickness while the Fe 3 O 4 surface is very smooth independent on the Fe 3 O 4 film thickness. Finally, the Fe 3 O 4 /NiO interface spacing is similar to the interlayer spacing of the oxide films while the NiO/MgO interface is expanded.

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“…Phase stability for CoO was reported during reduction reactions of thin films [30]. The relatively low Fe 3 O 4 to FeO transition temperature of 400°C is consistent with previous indirect observations for thin metal-oxide films [31].…”

Section: For Individual Nanoparticles and Nanochains The Phase Transfsupporting

confidence: 90%

Stabilization of metal(II)oxides on the nanoscale

Bonifacio

Majidi

et al. 2019

Materials Research Letters

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Increasing surface-to-volume ratios for nanoscale materials may cause metal(II)oxides phases to be thermodynamically unstable compared to their bulk counterparts. For instance, previous studies have found FeO to be unstable for nanoparticles with dimensions below 100 nm. In this study insitu TEM was used to gradually reduce nanoparticles and nanochains of Fe 2 O 3. Electron energy-loss spectroscopy and selected area diffraction at different temperatures not only confirm earlier predictions, but also reveal the unexpected stabilization of the FeO phase for nanochains with a minimal critical length. Hence, dimensionally constrained phases were stabilized on length-scales that were previously considered unattainable. IMPACT STATEMENT This study provides direct experimental evidence for the previously unanticipated stabilization of metal(II)oxides with dimensions well below 100 nm, which has exciting potential for catalyst technologies and next generation memory devices.

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In-situ x-ray diffraction studies on post-deposition vacuum-annealing of ultra-thin iron oxide films

Cited by 21 publications

References 12 publications

Reduction reactions and densification during in situ TEM heating of iron oxide nanochains

Reduction reactions and densification during in situ TEM heating of iron oxide nanochains

Structure and morphology of epitaxially grown Fe3O4/NiO bilayers on MgO(001)

Stabilization of metal(II)oxides on the nanoscale

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