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Atomic-Scale Structure of the Hematite ?-Fe₂O₃(1102) "R-Cut" Surface.

ABSTRACT: The ?-Fe₂O₃(11?02) 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 E_F. 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 E_F. The work function on the (2 × 1) termination is 5.4 ± 0.2 eV.

SUBMITTER: Kraushofer F

PROVIDER: S-EPMC5823487 | biostudies-literature | 2018 Jan

REPOSITORIES: biostudies-literature

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

Kraushofer Florian F Jakub Zdenek Z Bichler Magdalena M Hulva Jan J Drmota Peter P Weinold Michael M Schmid Michael M Setvin Martin M Diebold Ulrike U Blaha Peter P Parkinson Gareth S GS

The journal of physical chemistry. C, Nanomaterials and interfaces 20171208 3

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 × ...[more]

PMID: 29492182

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Project description:Hematite (α-Fe2O3) emerges as an enticing material for visible-light-driven photocatalysis owing to its remarkable stability, low toxicity, and abundance. However, its inherent shortcomings, such as a short hole diffusion length and high recombination rate, hinder its practical application. Recently, oxygen vacancies (Vo) within hematite have been demonstrated to modulate its photocatalytic attributes. The effects of Vo can be broadly categorized into two opposing aspects: (1) acting as electron donors, enhancing carrier conductivity, and improving photocatalytic performance and (2) acting as surface carrier traps, accelerating excited carrier recombination, and deteriorating performance. Critically, the generation rate, distribution, role, and behavior of Vo significantly differ for synthesis methods due to differences in formation mechanisms and oxygen diffusion. This complexity hampers simplified discussions of Vo, necessitating careful investigation and nuanced discussion tailored to the specific method and conditions employed. Among various approaches, hydrothermal synthesis offers a simple and cost-effective route. Here, we demonstrate a hydrothermal synthesis method for Vo introduction to hematite using a carbon source, where variations in the heating rate have not been previously explored in terms of their influence on Vo generation. The analyses revealed that the concentration of Vo was maximized at a heating rate of 16 °C/min, indicative of a high density of surface defects. With regard to photocatalytic performance, elevated heating rates (16 °C/min) fostered the formation of Vo primarily on the hematite surface. The photocatalytic activity was 7.1 times greater than that of the sample prepared at a low heating rate (2 °C/min). These findings highlight the crucial role of surface defects, as opposed to bulk defects, in promoting hematite photocatalysis. Furthermore, the facile control over Vo concentration achievable via manipulating the heating rate underscores the promising potential of this approach for optimizing hematite photocatalysts.

Dataset Information

Atomic-Scale Structure of the Hematite ?-Fe₂O₃(1102) "R-Cut" Surface.

Publications

Atomic-Scale Structure of the Hematite α-Fe<sub>2</sub>O<sub>3</sub>(11̅02) "R-Cut" Surface.

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Dataset Information

Atomic-Scale Structure of the Hematite ?-Fe2O3(1102) "R-Cut" Surface.

Publications

Atomic-Scale Structure of the Hematite α-Fe<sub>2</sub>O<sub>3</sub>(11̅02) "R-Cut" Surface.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets

Atomic-Scale Structure of the Hematite ?-Fe₂O₃(1102) "R-Cut" Surface.