Clean and water-covered sapphire (11̄02) surfaces: structure and laser-induced desorption

Schildbach, M. A.; Hamza, A. V.

doi:10.1016/0039-6028(93)90936-e

Cited by 47 publications

(19 citation statements)

References 39 publications

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“…Low-intensity combinational losses of bulk and surface plasmons ( b ) are also barely visible. The lower spectrum, taken after surface oxidation using electron bombardment, is almost identical with spectra obtained from sapphire surfaces 21 and clearly indicates heavy surface oxidation. The dominating loss feature is the characteristic aluminum oxide plasmonlike loss, b ͑Al 2 O 3 ͒, at 23.5 eV.…”

Section: Film Thicknesssupporting

confidence: 65%

Electron-impact-induced oxidation of Al(111) in water vapor: Relation to the Cabrera-Mott mechanism

Ebinger

Yates

1998

Phys. Rev. B

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The oxidation of an Al͑111͒ single-crystal surface induced by 100 eV electron bombardment in water vapor at room temperature has been studied using x-ray photoemission spectroscopy and electron-energy-loss spectroscopy. Electron bombardment significantly increases the growth rate and changes the observed growth-rate law in comparison to the oxidation without the electron beam. The aluminum oxide film grows with linear rather than parabolic time-dependent kinetics up to a thickness of about 25 Å. After reaching this thickness, the growth rate slows down significantly. During oxidation the oxide film becomes electrically charged on its surface and the normal electric field in the oxide remains constant. The results are discussed in the framework of a Cabrera-Mott type oxidation mechanism.

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Section: Film Thicknesssupporting

confidence: 65%

Electron-impact-induced oxidation of Al(111) in water vapor: Relation to the Cabrera-Mott mechanism

Ebinger

Yates

1998

Phys. Rev. B

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“…31 By contrast, Schildbach and Hamza found that the ͑2 ϫ 1͒ surface reconstruction of ␣-Al 2 O 3 ͑1102͒ is removed by the water adlayer upon exposure to an electron beam. 32 Previous theoretical studies investigations have focused on structures consistent with the adsorption of water to the fivefold-coordinated iron sites of the ͑1 ϫ 1͒ stoichiometric surface. 15,33,34 The energy minimization calculations of Rustad et al, using parametrized classical potentials, show that approximately 75% of the adsorbed water molecules dissociate heterolytically on the ͑1 ϫ 1͒ surface.…”

Section: Introductionmentioning

confidence: 99%

Density functional theory study of the clean and hydrated hematite(11¯02)surfaces

Tanwar

Chaka

et al. 2007

Phys. Rev. B

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The structures of the clean and hydrated hematite ␣-Fe 2 O 3 ͑1102͒ surfaces were investigated using density functional theory, and the free energies of the surfaces in chemical equilibrium with water were calculated as a function of temperature and oxygen partial pressure using ab initio thermodynamics. At 298.15 K, the predicted lowest-energy surface, in equilibrium with 20 Torr H 2 O has a stoichiometry of ͑H 2 O͒ 2 -X-͑HO͒ 2 -Fe 2 -O 2 -R, where X denotes a vacancy of an atomic layer of Fe and R represents the bulk stoichiometric repeat ͑Fe 2 O 3 ͒. This surface stoichiometry results in three types of ͑hydr͒oxo functional groups: Fe-OH 2 ,Fe 2 -OH, and Fe 3 -O. At temperatures above 435 K, maintaining equilibrium with the same water partial pressure, the predicted lowest-energy stoichiometry is ͑HO͒ 2 -͑HO͒ 2 -Fe 2 -O 2 -Fe 2 -O 2 -R, consistent with water dissociated on the stoichiometric bulk termination. These results suggest that the experimentally observed surface termination is highly sensitive to thermal annealing and water reaction. Furthermore, differences in protonation states or the surface hydroxyl groups are shown to lead to large differences in energetic stability and layer relaxations of the oxide substrate. Prediction of the stable surface termination and its dependence on environmental variables such as water, O 2 , and thermal treatment provide a base line for understanding surface reactivity.

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“…In closing, we note that a (2 × 1) reconstruction has also been observed on the r-cut surface of α-Al 2 O 3, which also has the corundum structure. 74,75 It is possible that a similar alternating trench structure might be present there.…”

Section: Discussionmentioning

confidence: 99%

Atomic-Scale Structure of the Hematite α-Fe₂O₃(11̅02) “R-Cut” Surface

et al. 2018

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The α-Fe2O3(11̅02) surface (also known as the hematite r-cut or (012) surface) was studied using low-energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), scanning tunneling microscopy (STM), noncontact atomic force microscopy (nc-AFM), and ab initio density functional theory (DFT)+U calculations. Two surface structures are stable under ultrahigh vacuum (UHV) conditions; a stoichiometric (1 × 1) surface can be prepared by annealing at 450 °C in ≈10–6 mbar O2, and a reduced (2 × 1) reconstruction is formed by UHV annealing at 540 °C. The (1 × 1) surface is close to an ideal bulk termination, and the undercoordinated surface Fe atoms reduce the surface bandgap by ≈0.2 eV with respect to the bulk. The work function is measured to be 5.7 ± 0.2 eV, and the VBM is located 1.5 ± 0.1 eV below EF. The images obtained from the (2 × 1) reconstruction cannot be reconciled with previously proposed models, and a new “alternating trench” structure is proposed based on an ordered removal of lattice oxygen atoms. DFT+U calculations show that this surface is favored in reducing conditions and that 4-fold-coordinated Fe2+ cations at the surface introduce gap states approximately 1 eV below EF. The work function on the (2 × 1) termination is 5.4 ± 0.2 eV.

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Clean and water-covered sapphire (11̄02) surfaces: structure and laser-induced desorption

Cited by 47 publications

References 39 publications

Electron-impact-induced oxidation of Al(111) in water vapor: Relation to the Cabrera-Mott mechanism

Electron-impact-induced oxidation of Al(111) in water vapor: Relation to the Cabrera-Mott mechanism

Density functional theory study of the clean and hydrated hematite(11¯02)surfaces

Atomic-Scale Structure of the Hematite α-Fe₂O₃(11̅02) “R-Cut” Surface

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Clean and water-covered sapphire (11̄02) surfaces: structure and laser-induced desorption

Cited by 47 publications

References 39 publications

Electron-impact-induced oxidation of Al(111) in water vapor: Relation to the Cabrera-Mott mechanism

Electron-impact-induced oxidation of Al(111) in water vapor: Relation to the Cabrera-Mott mechanism

Density functional theory study of the clean and hydrated hematite(11¯02)surfaces

Atomic-Scale Structure of the Hematite α-Fe2O3(11̅02) “R-Cut” Surface

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Product

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Atomic-Scale Structure of the Hematite α-Fe₂O₃(11̅02) “R-Cut” Surface