Substrate-termination and H2O-coverage dependent dissociation of H2O on Fe3O4(111)

Cutting, Richard S; Muryn, C. A.; Vaughan, David J.; Thornton, G.

doi:10.1016/j.susc.2008.01.012

Cited by 40 publications

(44 citation statements)

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“…A similar shoulder feature with a chemical shift of 1.0-1.3 eV from the Ox peak was often observed on clean iron oxide surfaces in UHV. [82][83][84] This feature has been suggested to be due to nonstoichiometric oxygens or hydroxyl species formed by residual water in the vacuum chamber or to finalstate effects such as shake-up, but it is still under debate. [82][83][84] When the surface is exposed to 3 × 10 -8 Torr of water vapor, a significant shoulder is observed at ∼531.5 eV.…”

Section: Resultsmentioning

confidence: 99%

Water Adsorption on α-Fe₂O₃(0001) at near Ambient Conditions

et al. 2010

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We have investigated hydroxylation and water adsorption on R-Fe 2 O 3 (0001) at water vapor pressures up to 2 Torr and temperatures ranging from 277 to 647 K (relative humidity (RH) e 34%) using ambient-pressure X-ray photoelectron spectroscopy (XPS). Hydroxylation occurs at the very low RH of 1 × 10 -7 % and precedes the adsorption of molecular water. With increasing RH, the OH coverage increases up to one monolayer (ML) without any distinct threshold pressure. Depth profiling measurements showed that hydroxylation occurs only at the topmost surface under our experimental conditions. The onset of molecular water adsorption varies from ∼2 × 10 -5 to ∼4 × 10 -2 % RH depending on sample temperature and water vapor pressure. The coverage of water reaches 1 ML at ∼15% RH and increases to 1.5 ML at 34% RH.

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Section: Resultsmentioning

confidence: 99%

Water Adsorption on α-Fe₂O₃(0001) at near Ambient Conditions

et al. 2010

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“…a similar process to a TPD experiment) the surface remained hydroxylated at 400 K, and STM images suggest this hydroxylation was restricted to the Fe tet1 termination. Cutting et al [411] suggest that these results show that Joseph et al [303] were not measuring the Fe tet1 termination. Given that Cutting et al prepared their single crystal sample by sputter/anneal cycles without annealing in oxygen, it could also be that their surface exhibited reduced terminations.…”

Section: H 2 O/fe 3 O 4 (100)mentioning

confidence: 87%

Iron oxide surfaces

Parkinson

2016

Surface Science Reports

501

463

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The current status of knowledge regarding the surfaces of the iron oxides, magnetite (Fe 3 O 4 ), maghemite (γ-Fe 2 O 3 ), hematite (α-Fe 2 O 3 ), and wüstite (Fe 1-x O) is reviewed. The paper starts with a summary of applications where iron oxide surfaces play a major role, including corrosion, catalysis, spintronics, magnetic nanoparticles (MNPs), biomedicine, photoelectrochemical water splitting and groundwater remediation. The bulk structure and properties are then briefly presented; each compound is based on a close-packed anion lattice, with a different distribution and oxidation state of the Fe cations in interstitial sites. The bulk defect chemistry is dominated by cation vacancies and interstitials (not oxygen vacancies) and this provides the context to understand iron oxide surfaces, which represent the front line in reduction and oxidation processes. The atomic-scale structure of the low-index surfaces of iron oxides is the major focus of this review. Fe 3 O 4 is the most studied iron oxide in surface science, primarily because its stability range corresponds nicely to the ultra-high vacuum environment, and because it is an electrical conductor, which makes it straightforward to study with the most commonly used surface science methods such as photoemission spectroscopies (XPS, UPS) and scanning tunneling microscopy (STM). The impact of the surfaces on the measurement of bulk properties such as magnetism, the Verwey transition and the (predicted) half-metallicity is discussed.The best understood iron oxide surface at present is probably Fe 3 O 4 (100); the structure is known with a high degree of precision and the major defects and properties are well characterised. A major factor in this is that a termination at the Fe oct -O plane can be reproducibly prepared by a variety of methods, as long as the surface is annealed in 10 Such straightforward preparation of a monophase termination is generally not the case for other iron oxide surfaces. All available evidence suggests the oft-studied (√2×√2)R45° reconstruction results from a rearrangement of the cation lattice in the outermost unit cell in which two octahedral cations are replaced by one tetrahedral interstitial, a motif conceptually similar to well-known Koch-Cohen defects in Fe (0001) is the most studied hematite surface, but 2 difficulties preparing stoichiometric surfaces under UHV conditions have hampered a definitive determination of the structure. There is evidence for at least three terminations: a bulk-like termination at the oxygen plane, a termination with half of the cation layer, and a termination with ferryl groups. When the surface is reduced the so-called "bi-phase" structure is formed, which eventually transforms to a Fe 3 O 4 (111)-like termination. The structure of the bi-phase surface is controversial; a largely accepted model of coexisting Fe 1-x O and α-Fe 2 O 3 (0001) islands was recently challenged and a new structure based on a thin film of Fe 3 O 4 (111) on α-Fe 2 O 3 (0001) was proposed. The merits of the compet...

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“…Initially 1/4 ML of Fe, in other words the Fe tet O Fe oct O [3][4][5], has been suggested as the terminating layer in ultra-high vacuum (UHV) conditions, but later on thermal desorption and infrared spectroscopy studies of adsorbed CO have indicated that 1/2 ML Fe terminations, Fe oct Fe tet O Fe oct O, were more likely the case [6,7]. Larger molecules that can coordinate more than one adsorption site potentially give additional information.…”

Section: Introductionmentioning

confidence: 99%

Determination of the surface electronic structure of Fe3O4(1 1 1) by soft X-ray spectroscopy

2015

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Please cite this article in press as: S. Kaya, et al., Determination of the surface electronic structure of Fe 3 O 4 (1 1 1) by soft X-ray spectroscopy, Catal. Today (2014), http://dx.The determination of surface terminations in transition metal oxides is not trivial because many structural configurations could be possible. They exhibit various terminations depending on the oxidation states of metal cations exposed to the surface. Fe 3 O 4 is one example in which octahedrally and tetrahedrally coordinated Fe 2+ and Fe 3+ cations coexists with oxygen anions. For the identification of the surface termination of Fe 3 O 4 (1 1 1) grown on Pt(1 1 1) we have employed surface sensitive synchrotron based X-ray photoelectron and absorption spectroscopy. It has been shown that the topmost surface is octahedrally coordinated Fe 3+ rich.

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Substrate-termination and H2O-coverage dependent dissociation of H2O on Fe3O4(111)

Cited by 40 publications

References 32 publications

Water Adsorption on α-Fe₂O₃(0001) at near Ambient Conditions

Water Adsorption on α-Fe₂O₃(0001) at near Ambient Conditions

Iron oxide surfaces

Determination of the surface electronic structure of Fe3O4(1 1 1) by soft X-ray spectroscopy

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Substrate-termination and H2O-coverage dependent dissociation of H2O on Fe3O4(111)

Cited by 40 publications

References 32 publications

Water Adsorption on α-Fe2O3(0001) at near Ambient Conditions

Water Adsorption on α-Fe2O3(0001) at near Ambient Conditions

Iron oxide surfaces

Determination of the surface electronic structure of Fe3O4(1 1 1) by soft X-ray spectroscopy

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Water Adsorption on α-Fe₂O₃(0001) at near Ambient Conditions

Water Adsorption on α-Fe₂O₃(0001) at near Ambient Conditions