Unconventional properties of nanometric FeO(111) films on Ru(0001): stoichiometry and surface structure

Martín-García, Laura; Bernal-Villamil, Iván; Oujja, M.; Carrasco, Esther; Gargallo-Caballero, R.; Castillejo, Marta; Marco, José F.; Gallego, S.; Figuera, Juan de la

doi:10.1039/c5tc03871e

Cited by 26 publications

(32 citation statements)

References 40 publications

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“…Moreover, the new structure shows mixed coordination: it comprises one close-packed Fe layer with octahedral coordination at the center of the film and two close-packed Fe layers with Fe tetrahedrally coordinated next at the film/substrate and film/gas-phase interfaces. Such surface layer arrangements are of the same tetrahedral/wurtzite type as previously reported for rocksalt FeO on Ru(0001) [18,19] and CoO on Ir(100) [20][21][22]. However, the layer stacking sequence is different from that in previous reports [18][19][20][21][22], as the stacking faults effectively cancel when the structure is only three layers thick.…”

Section: Introductionsupporting

confidence: 74%

“…Such surface layer arrangements are of the same tetrahedral/wurtzite type as previously reported for rocksalt FeO on Ru(0001) [18,19] and CoO on Ir(100) [20][21][22]. However, the layer stacking sequence is different from that in previous reports [18][19][20][21][22], as the stacking faults effectively cancel when the structure is only three layers thick. Thus, the new phase has a tetrahedral-octahedral-tetrahedral (TOT) layer combination with the close-packed Fe layers ordered in an ABC stacking sequence.…”

Section: Introductionsupporting

confidence: 74%

“…1(f)]. This type of ordering is analogous to that found for the FeO and CoO wurtzite terminations previously modeled with DFT + U [18,19,21]. The two final configurations for TOT1 are a ferrimagnetic (FiM) structure [see Fig.…”

Section: Magnetic Ordersupporting

confidence: 66%

“…However, as discussed in Refs. [18,19], the local spin structure may differ in the proximity of surfaces with Fe ions in tetrahedral positions. Thus, to identify the lowest-energy configuration, we investigate different spin orderings.…”

Section: Magnetic Ordermentioning

confidence: 99%

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Stability, magnetic order, and electronic properties of ultrathin Fe3O4 nanosheets

2020

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We study the stability, magnetic order, charge segregation, and electronic properties of a novel three-layered Fe 3 O 4 film by means of Hubbard-corrected density functional theory calculations. The stable film is predicted to consist of close-packed iron and oxygen layers, comprising a center layer with octahedrally coordinated Fe sandwiched between two layers with tetrahedrally coordinated Fe. The film exhibits an antiferromagnetic type I spin order. A charge analysis confirms that the stable structure has distinct charge segregation, with Fe 2+ ions in the center layer and Fe 3+ in the tetrahedral surface layers. Examination of the electronic band structures and densities of states shows that the bandgap is substantially reduced, from 2.4 eV for the bulk rocksalt to 0.3 eV for the film. The reduction in the bandgap is a consequence of the 2+ to 3+ change in oxidation state of Fe in the surface layers.

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Section: Introductionsupporting

confidence: 74%

Section: Introductionsupporting

confidence: 74%

Section: Magnetic Ordersupporting

confidence: 66%

Section: Magnetic Ordermentioning

confidence: 99%

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Stability, magnetic order, and electronic properties of ultrathin Fe3O4 nanosheets

2020

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“…It has to be mentioned that such a growth mode was already predicted for FeO(111)/Ru(0001) in Ref. [ 24 ] based on the six-fold symmetry observed in LEED of few-nanometers-thick FeO(111) films. The 180° rotation is related to the structure of stepped Ru(0001) surfaces, as described in the Introduction (see Figure 1 ).…”

Section: Resultsmentioning

confidence: 66%

Symmetry-Induced Structuring of Ultrathin FeO and Fe3O4 Films on Pt(111) and Ru(0001)

et al. 2018

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Iron oxide films epitaxially grown on close-packed metal single crystal substrates exhibit nearly-perfect structural order, high catalytic activity (FeO) and room-temperature magnetism (Fe3O4). However, the morphology of the films, especially in the ultrathin regime, can be significantly influenced by the crystalline structure of the used support. This work reports an ultra-high vacuum (UHV) low energy electron/synchrotron light-based X-ray photoemission electron microscopy (LEEM/XPEEM) and electron diffraction (µLEED) study of the growth of FeO and Fe3O4 on two closed-packed metal single crystal surfaces: Pt(111) and Ru(0001). The results reveal the influence of the mutual orientation of adjacent substrate terraces on the morphology of iron oxide films epitaxially grown on top of them. On fcc Pt(111), which has the same mutual orientation of adjacent monoatomic terraces, FeO(111) grows with the same in-plane orientation on all substrate terraces. For Fe3O4(111), one or two orientations are observed depending on the growth conditions. On hcp Ru(0001), the adjacent terraces of which are ‘rotated’ by 180° with respect to each other, the in-plane orientation of initial FeO(111) and Fe3O4(111) crystallites is determined by the orientation of the substrate terrace on which they nucleated. The adaptation of three-fold symmetric iron oxides to three-fold symmetric substrate terraces leads to natural structuring of iron oxide films, i.e., the formation of patch-like magnetite layers on Pt(111) and stripe-like FeO and Fe3O4 structures on Ru(0001).

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Effect of wavelength, deposition temperature and substrate type on cobalt ferrite thin films grown by pulsed laser deposition

Oujja

Martín-García

Rebollar

et al. 2018

Applied Surface Science

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In pulsed laser deposition, the laser irradiation wavelength and the substrate nature and temperature crucially affect the composition, crystallinity, structure and magnetic properties of the grown deposits. In this work, cobalt ferrite (CoFe 2 O 4) thin films were deposited on Si (100) and SrTiO 3 (100) single crystal substrates at room temperature and 770 K using laser wavelengths of 213, 532 and 1064 nm. The deposited films were characterized by atomic force microscopy to determine the surface morphology, by Xray diffraction to examine their crystallinity, and by micro-Raman, scanning electron microscopy/energy-dispersive X-ray spectroscopy, X-ray photoelectron and Mössbauer spectroscopies to investigate their composition and stoichiometry. Magnetic characterization was carried out by superconducting quantum interference device magnetometry. At 770 K and 1064 nm, the films consisted of single-crystal CoFe 2 O 4 ((100) orientation) when grown on SrTiO 3 , and of polycrystalline CoFe 2 O 4 when grown on Si. The composition of the films became more complex at shorter wavelengths as they contained magnetite and other minority phases in different concentrations. The crystalline quality of the films also decreased with decreasing wavelength even including superparamagnetic species. In general, for the same wavelength, the deposits obtained at room temperature were less crystalline than those produced with the substrate heated at 770 K.

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Unconventional properties of nanometric FeO(111) films on Ru(0001): stoichiometry and surface structure

Abstract: FeO(111) films have been synthesized by PLD revealing unexpected properties explained by a wurtzite-like environment at the surface.

Cited by 26 publications

References 40 publications

Stability, magnetic order, and electronic properties of ultrathin Fe3O4 nanosheets

Stability, magnetic order, and electronic properties of ultrathin Fe3O4 nanosheets

Symmetry-Induced Structuring of Ultrathin FeO and Fe3O4 Films on Pt(111) and Ru(0001)

Effect of wavelength, deposition temperature and substrate type on cobalt ferrite thin films grown by pulsed laser deposition

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