Surface structure of MBE-grown α-Fe 2 O 3 (0001) by intermediate-energy X-ray photoelectron diffraction

Thevuthasan, S.; Kim, Y.J.; Yi, Sang I.; Chambers, Scott A.; Morais, Jonder; Denecke, R.; Fadley, C. S.; Liu, P.; Kendelewicz, T.; Brown, Gordon E.

doi:10.1016/s0039-6028(99)00200-9

Cited by 122 publications

(84 citation statements)

References 28 publications

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“…[63], Mackrodt et al [153], and Reeves and Mann [154]. In Table 1, we summarize the optimized interlayer spacings compared with previous theoretically predicted values and experimentally observed interlayer spacings (Thevuthasan et al) using X-ray photoelectron diffraction [151]. Generally, our calculated inward relaxations of the layer spacings of the single-Fe terminated α-Fe 2 O 3 (0001) surface are consistent with the X-ray photoelectron diffraction results and with earlier theoretical calculations [62,65] but the magnitude of the relaxation differs.…”

Section: The Structure Of α-Fe 2 O 3 Surfacesmentioning

confidence: 85%

“…Earlier investigations of the (0001) surface of both bulk α-Fe 2 O 3 and epitaxial thin films, using qualitative low energy electron diffraction (LEED) [140][141][142][143][144] and scanning tunneling microscope (STM) [145][146][147][148][149][150], have shown significant variations in the nature of the surface ordering depending on the method of surface preparation. Detailed structural characterization of the {0001} surface under ultrahigh vacuum and clean conditions revealed that both Fe-and O-terminations coexist under different conditions of temperature and oxygen partial pressure [149][150][151][152]. Theoretical calculations by Trainor et al [61] and Wang et al [62] showed that the {0001} surface can be terminated by either a single or double Fe layer or by oxygen ions, although the unreconstructed double Fe-termination and oxygen-terminated surface are dipolar.…”

Section: The Structure Of α-Fe 2 O 3 Surfacesmentioning

confidence: 99%

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A Density Functional Theory Study of the Adsorption of Benzene on Hematite (α-Fe2O3) Surfaces

2014

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Abstract:The reactivity of mineral surfaces in the fundamental processes of adsorption, dissolution or growth, and electron transfer is directly tied to their atomic structure. However, unraveling the relationship between the atomic surface structure and other physical and chemical properties of complex metal oxides is challenging due to the mixed ionic and covalent bonding that can occur in these minerals. Nonetheless, with the rapid increase in computer processing speed and memory, computer simulations using different theoretical techniques can now probe the nature of matter at both the atomic and sub-atomic levels and are rapidly becoming an effective and quantitatively accurate method for successfully predicting structures, properties and processes occurring at mineral surfaces. In this study, we have used Density Functional Theory calculations to study the adsorption of benzene on hematite (α-Fe 2 O 3 ) surfaces. The strong electron correlation effects of the Fe 3d-electrons in α-Fe 2 O 3 were described by a Hubbard-type on-site Coulomb repulsion (the DFT+U approach), which was found to provide an accurate description of the electronic and magnetic properties of hematite. For the adsorption of benzene on the hematite surfaces, we show that the adsorption geometries parallel to the surface are energetically more stable than the vertical ones. The benzene molecule interacts with the hematite surfaces through π-bonding in the parallel adsorption geometries and through weak hydrogen bonds in the vertical geometries. Van der Waals interactions are found to play a significant role in stabilizing the absorbed benzene molecule. Analyses of the electronic structures reveal that upon benzene adsorption, the conduction band edge of the surface atoms is shifted towards the valence bands, thereby considerably reducing the band gap and the magnetic moments of the surface Fe atoms. OPEN ACCESSMinerals 2014, 4 90

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Section: The Structure Of α-Fe 2 O 3 Surfacesmentioning

confidence: 85%

Section: The Structure Of α-Fe 2 O 3 Surfacesmentioning

confidence: 99%

A Density Functional Theory Study of the Adsorption of Benzene on Hematite (α-Fe2O3) Surfaces

2014

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“…An Fe terminated surface was found to be completely unstable in presence of excess water (>67% coverage) and was predicted to relax, leaving an O terminated hydrated layer with Fe(OH) 3 subunits behind [300]. OH species on the (0001) face of hematite were found to be difficult to remove (in contrast to surface OH groups on other hematite planes) and were thermally stable up to at least 1073 K in O 2 atmosphere as evidenced by infrared spectroscopy [303], and OH on Fe terminated α-Fe 2 O 3 (0001) could not be removed by excessive heating at 900K without reducing the near-surface region to Fe(II) [301]. Also the isostructural α-Al 2 O 3 (0001) surface has been found to get hydroxilated easily [63,297,298,[304][305][306][307][308].…”

Section: Discussionmentioning

confidence: 97%

“…Indeed, α-Fe 2 O 3 (0001) hydroxylation was found to be facile [298,301]. For an Fe terminated and even more for a defective O terminated α-Fe 2 O 3 (0001) surface, the hydroxylation energy was calculated to be very large (-298.1kJ/mol) [302].…”

Section: Discussionmentioning

confidence: 98%

Surface chemistry and catalysis on well-defined epitaxial iron-oxide layers

Weiß

Ranke

2002

Progress in Surface Science

579

610

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Metal-oxide based catalysts are used for many important synthesis reactions in the chemical industry. A better understanding of the catalyst operation can be achieved by studying elemantary reaction steps on well-defined model catalyst systems. For the dehydrogenation of ethylbenzene to styrene in the presence of steam both unpromoted and potassium promoted iron-oxide catalysts are active. Here we review the work done over unpromoted single-crystalline FeO(111), Fe 3 O 4 (111) and α-Fe 2 O 3 (0001) films grown epitaxially on Pt(111) substrates. Their geometric and electronic surface structures were characterized by STM, LEED, electron microscopy and electron spectroscopic techniques. In an integrative approach, the interaction of water, ethylbenzene and styrene with these films was investigated mainly by thermal desorption and photoelectron emission spectroscopy. The adsorptiondesorption energetics and kinetics depend on the oxide surface terminations and are correlated to the electronic structures and acid-base properties of the corresponding oxide phases, which reveal insight into the nature of the active sites and into the catalytic function of semiconducting oxides in general. Catalytic studies, using a batch reactor arrangement at high gas pressures and post reaction surface analysis, showed that only α-Fe 2 O 3 (0001) containing surface defects is catalytically active, whereas Fe 3 O 4 (111) is always inactive. This can be related to the elementary adsorption and desorption properties observed in ultrahigh vacuum, which indicates that the surface chemical properties of the iron-oxide films do not change significantly across the "pressure-gap". A model is proposed according to which the active site involves a regular acidic surface sites and a defect site next to it. The results on metal-oxide surface chemistry also have implications for other fields, such as environmental science, biophysics and chemical sensors.-2 -"2kyEi9FYSQjBVrZxIPQ.FHIAC_WRa02_review.doc", Datum: 19.02.03

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“…In order to produce the full range of iron oxide phases and crystal surface orientations required for studies of Cr(VI) aq reduction reactions, we used oxygen-plasma-assisted molecular beam epitaxy (OPA-MBE) to prepare well-defined epitaxial films ( 300-500 Å thick) on two kinds of oxide substrates -α-Al 2 O 3 for α-Fe 2 O 3 (4)(5)(6)(7)(8)(9)(10) Figure 1 shows an empirically derived phase diagram that illustrates these values (12). Points on the border between Fe 2 O 3 and Fe 3 O 4 represent growths that resulted in a mixed phase in the film.…”

Section: B Epitaxial Growth and Characterization Of Model Iron Oxidementioning

confidence: 99%

Molecular-Level Processes Governing the Interaction of Contaminants with Iron and Manganese Oxides - Final Report

Brown¹,

Chambers²

1999

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Surface structure of MBE-grown α-Fe 2 O 3 (0001) by intermediate-energy X-ray photoelectron diffraction

Cited by 122 publications

References 28 publications

A Density Functional Theory Study of the Adsorption of Benzene on Hematite (α-Fe2O3) Surfaces

A Density Functional Theory Study of the Adsorption of Benzene on Hematite (α-Fe2O3) Surfaces

Surface chemistry and catalysis on well-defined epitaxial iron-oxide layers

Molecular-Level Processes Governing the Interaction of Contaminants with Iron and Manganese Oxides - Final Report

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