In situ RHEED and XPS studies of epitaxial thin α-Fe2O3(0001) films on sapphire

Fujii, Toru; Alders, D.; Voogt, F. C.; Hibma, T.; Thole, B. T.; Sawatzky, G. A.

doi:10.1016/0039-6028(96)00844-8

Cited by 74 publications

(34 citation statements)

References 20 publications

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“…The hematite slab consists of a × × 2 2 1 bulk structure super cell with 30 atoms each excluding terminations, while the water layer has 92 water molecules. Previous simulations have shown that this system size is sufficiently large to ensure bulk-like properties in the middle of the slabs [18] which is supported by experiment [28].…”

Section: Computational Detailssupporting

confidence: 66%

Hematite(001)-liquid water interface from hybrid density functional-based molecular dynamics

Rudorff

Jakobsen

Rosso

et al. 2016

J. Phys.: Condens. Matter

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The atom-scale characterisation of interfaces between transition metal oxides and liquid water is fundamental to our mechanistic understanding of diverse phenomena ranging from crystal growth to biogeochemical transformations to solar fuel production. Here we report on the results of large-scale hybrid density functional theory-based molecular dynamics simulations for the hematite(001)-liquid water interface. A specific focus is placed on understanding how different terminations of the same surface influence surface solvation. We find that the two dominant terminations for the hematite(001) surface exhibit strong differences both in terms of the active species formed on the surface and the strength of surface solvation. According to present simulations, we find that charged oxyanions (-O−) and doubly protonated oxygens (-OH) can be formed on the iron terminated layer via autoionization of neutral -OH groups. No such charged species are found for the oxygen terminated surface. In addition, the missing iron sublayer in the iron terminated surface strongly influences the solvation structure, which becomes less well ordered in the vicinity of the interface. These pronounced differences are likely to affect the reactivity of the two surface terminations, and in particular the energetics of excess charge carriers at the surface.

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Section: Computational Detailssupporting

confidence: 66%

Hematite(001)-liquid water interface from hybrid density functional-based molecular dynamics

Rudorff

Jakobsen

Rosso

et al. 2016

J. Phys.: Condens. Matter

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“…5 (0001) substrates [36][37][38]. In the present study we do not find detectable amounts of Al or Mg at the surface of any of our films.…”

Section: B Surface Composition Structure and Morphologycontrasting

confidence: 42%

Effects of unreconstructed and reconstructed polar surface terminations on growth, structure, and magnetic properties of hematite films

et al. 2012

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The effects of polar surface stabilization mechanisms on the film growth, phase composition, surface and interface structure, and magnetic properties are explored for polar (1×1) surfaces under equivalent conditions. This study suggests that in addition to the customary strain, spin, and band-gap engineering, control of surface polarity stabilization could also be important for electronic and magnetic device engineering.Cheung et al.2

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“…Moreover, while the positions of the satellite features that accompany the Fe 2p main ionization peaks are characteristic for Fe 2 O 3 , their intensities are definitely lower than those reported for 100 monolayers of Fe 2 O 3 grown on sapphire and even lower than the corresponding spectrum for one monolayer. [73] Notice that for this last sample, a negative shift for the Fe 2p BE with respect to bulk Fe 2 O 3 has also been reported. Fe 2 O 3 or FeOOH have been distinguished in the XPS literature only for their (slightly) different valence-band photoemission spectra.…”

Section: X-ray Photoelectron Spectroscopy (Xps)mentioning

confidence: 55%

“…Such a variation has been assigned in the literature, also on the basis of results from theoretical calculations, to a modification in FeÀO mean distance, the decrease in satellite intensity being related to a decrease in the distance, that is, a decrease in the plane distance. [73] An additional explanation for the negative BE shifts for the alumina-embedded nanoparticles stems from consideration of the peculiar environment in which the iron oxide and titania particles are confined to grow. The potential inside the small cavities of the alumina membrane can be thought of as a Madelung term, operating on the photoelectrons kinetic energy (hence on the final binding energy) while they are escaping the particle.…”

Section: Xps On Tio 2 Particles In a Mesoporous Alumina Membranementioning

confidence: 99%

Metallorganic Routes to Nanoscale Iron and Titanium Oxide Particles Encapsulated in Mesoporous Alumina: Formation, Physical Properties, and Chemical Reactivity

et al. 2000

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Iron and titanium oxide nanoparticles have been synthesized in parallel mesopores of alumina by a novel organometallic "chimie douce" approach that uses bis(toluene)iron(0) (1) and bis(toluene)titanium(0) (2) as precursors. These complexes are molecular sources of iron and titanium in a zerovalent atomic state. In the case of 1, core shell iron/iron oxide particles with a strong magnetic coupling between both components, as revealed by magnetic measurements, are formed. Mössbauer data reveal superparamagnetic particle behavior with a distinct particle size distribution that confirms the magnetic measurements. The dependence of the Mössbauer spectra on temperature and particle size is explained by the influence of superparamagnetic relaxation effects. The coexistence of a paramagnetic doublet and a magnetically split component in the spectra is further explained by a distribution in particle size. From Mössbauer parameters the oxide phase can be identified as low-crystallinity ferrihydrite oxide. In agreement with quantum size effects observed in UV-visible studies, TEM measurements determine the size of the particles in the range 5-8 nm. The particles are mainly arranged alongside the pore walls of the alumina template. TiO2 nanoparticles are formed by depositing 2 in mesoporous alumina template. This produces metallic Ti, which is subsequently oxidized to TiO2 (anatase) within the alumina pores. UV-visible studies show a strong quantum confinement effect for these particles. From UV-visible investigations the particle size is determined to be around 2 nm. XPS analysis of the iron- and titania- embedded nanoparticles reveal the presence of Fe2O3 and TiO2 according to experimental binding energies and the experimental line shapes. Ti4+ and Fe3+ are the only oxidation states of the particles which can be determined by this technique. Hydrogen reduction of the iron/iron-oxide nanoparticles at 500 degrees C under flowing H2/N2 produces a catalyst, which is active towards formation of carbon nanotubes by a CVD process. Depending on the reaction conditions, the formation of smaller carbon nanotubes inside the interior of larger carbon nanotubes within the alumina pores can be achieved. This behavior can be understood by means of selectively turning on and off the iron catalyst by adjusting the flow rate of the gaseous carbon precursor in the CVD process.

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In situ RHEED and XPS studies of epitaxial thin α-Fe2O3(0001) films on sapphire

Cited by 74 publications

References 20 publications

Hematite(001)-liquid water interface from hybrid density functional-based molecular dynamics

Hematite(001)-liquid water interface from hybrid density functional-based molecular dynamics

Effects of unreconstructed and reconstructed polar surface terminations on growth, structure, and magnetic properties of hematite films

Metallorganic Routes to Nanoscale Iron and Titanium Oxide Particles Encapsulated in Mesoporous Alumina: Formation, Physical Properties, and Chemical Reactivity

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