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The Structure of Oxygen Vacancies in the Near-Surface of Reduced CeO2 (111) Under Strain.

ABSTRACT: Strain has been widely recognized as important for tuning the behavior of defects in metal oxides since properties such as defect configuration, electronic structure, excess charge localization, and local atomic distortions may be affected by surface strain. In CeO2, the most widely used promoter in three-way catalysts and solid state electrolyte in fuel cells, the behaviors of oxygen vacancies, and associated Ce3+ polarons are crucial in applications. Recent STM and AFM investigations as well as DFT-based calculations have indicated that in the near-surface of CeO2 (111), at low temperatures and vacancy concentrations, subsurface oxygen vacancies are more stable than surface ones, and the Ce3+ ions are next-nearest neighbors to both types of vacancies, which can be explained by the better ability of the system to relax the lattice strain induced by vacancy formation as well as by the excess charge localization. The results also revealed that the interaction between first-neighbor vacancies is repulsive. In this work, the relative stability of surface and subsurface oxygen vacancies at the CeO2 (111) surface under in-plane strain is investigated by means of DFT+U calculations. The tensile strain favors isolated surface vacancies with next nearest neighbor polarons, whereas isolated subsurface vacancies with nearest neighbor polarons are energetically favored under compressive strain. In addition, the formation of both surface and subsurface dimers is favored over having corresponding isolated species under compressive strain, which implies the possibility of controlling the formation of vacancy clusters using strain. In many applications, ceria is employed as a supported thin film or within a heterostructure in which ceria can be strained, and this study shows that strain can be a useful handle to tune properties of such materials.

SUBMITTER: Han ZK

PROVIDER: S-EPMC6592146 | biostudies-literature | 2019

REPOSITORIES: biostudies-literature

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The Structure of Oxygen Vacancies in the Near-Surface of Reduced CeO2 (111) Under Strain.

Han Zhong-Kang ZK Zhang Lei L Liu Meilin M Ganduglia-Pirovano Maria Verónica MV Gao Yi Y

Frontiers in chemistry 20190618

Strain has been widely recognized as important for tuning the behavior of defects in metal oxides since properties such as defect configuration, electronic structure, excess charge localization, and local atomic distortions may be affected by surface strain. In CeO2, the most widely used promoter in three-way catalysts and solid state electrolyte in fuel cells, the behaviors of oxygen vacancies, and associated Ce3+ polarons are crucial in applications. Recent STM and AFM in ...[more]

PMID: 31275923

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Project description:Two-dimensional (2D) topological insulators have fascinating physical properties which are promising for applications within spintronics. In order to realize spintronic devices working at room temperature, materials with a large nontrivial gap are needed. Bismuthene, a 2D layer of Bi atoms in a honeycomb structure, has recently attracted strong attention because of its record-large nontrivial gap, which is due to the strong spin-orbit coupling of Bi and the unusually strong interaction of the Bi atoms with the surface atoms of the substrate underneath. It would be a significant step forward to be able to form 2D materials with properties such as bismuthene on semiconductors such as GaAs, which has a band gap size relevant for electronics and a direct band gap for optical applications. Here, we present the successful formation of a 2D Bi honeycomb structure on GaAs, which fulfills these conditions. Bi atoms have been incorporated into a clean GaAs(111) surface, with As termination, based on Bi deposition under optimized growth conditions. Low-temperature scanning tunneling microscopy and spectroscopy (LT-STM/S) demonstrates a well-ordered large-scale honeycomb structure, consisting of Bi atoms in a √3 × √3 30° reconstruction on GaAs(111). X-ray photoelectron spectroscopy shows that the Bi atoms of the honeycomb structure only bond to the underlying As atoms. This is supported by calculations based on density functional theory that confirm the honeycomb structure with a large Bi-As binding energy and predict Bi-induced electronic bands within the GaAs band gap that open up a gap of nontrivial topological nature. STS results support the existence of Bi-induced states within the GaAs band gap. The GaAs:Bi honeycomb layer found here has a similar structure as previously published bismuthene on SiC or on Ag, though with a significantly larger lattice constant and only weak Bi-Bi bonding. It can therefore be considered as an extreme case of bismuthene, which is fundamentally interesting. Furthermore, it has the same exciting electronic properties, opening a large nontrivial gap, which is the requirement for room-temperature spintronic applications, and it is directly integrated in GaAs, a direct band gap semiconductor with a large range of (opto)electronic devices.

Dataset Information

The Structure of Oxygen Vacancies in the Near-Surface of Reduced CeO2 (111) Under Strain.

Publications

The Structure of Oxygen Vacancies in the Near-Surface of Reduced CeO<sub>2</sub> (111) Under Strain.

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