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The Vacancy-Induced Electronic Structure of the SrTiO <sub/>3?δ</sub> Surface
摘要： The emergence of a 2D electron gas (2DEG) on the (001) surface of oxygen-deficient strontium titanate (SrTiO3?δ) is investigated. Using in situ soft X-ray spectroscopy and effective mass modeling, a series of quantitative band diagrams are developed to describe the evolution of near-surface and bulk carrier concentrations, downward band bending, and Fermi level along a lateral gradient of oxygen vacancies formed on SrTiO3?δ by direct-current resistive heating under ultrahigh vacuum conditions. Electrons are accumulated over a 3 nm region near the surface, confined within a potential well with saturated 300 meV downward band bending. The relation between Fermi levels and carrier concentrations near the surface suggests the density of states near the surface is much lower than the bulk density of states, which is consistent with the quantum-confined subbands of a 2DEG. The quantitative relationship between the surface and bulk electronic structures developed in this work provides a guide for precise engineering of the oxygen-vacancy-induced 2DEG in SrTiO3.
关键词： oxygen vacancies,electronic structure,in-situ x-ray spectroscopy,SrTiO3 surface,effective mass modeling
更新于2025-09-09 09:28:46
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Nanoscale oxygen ion dynamics in SrFeO <sub/>2.5+δ</sub> epitaxial thin films
摘要： A variety of functional properties in transition metal oxides are often underpinned by oxygen vacancies. While the oxygen vacancy concentration and arrangements are well-known to have strong influence on the physical properties of oxides, the oxygen dynamics in oxides—including oxygen ion incorporation and movements during redox reactions—remain elusive. Performing conductive AFM studies of epitaxial thin films of oxygen-deficient SrFeO2.5 treated by air-annealing at various temperatures, we observe oxidation-induced enhancement of local electronic conduction on the higher terraces near the outer step edges at which oxygen ions are preferably incorporated and diffuse into the films. We also show that the local conduction can be reversibly controlled by electric-field-induced redox reactions at room temperature. These results highlight the importance of the nanoscale oxygen dynamics in redox reactions in SrFeO2.5 films.
关键词： SrFeO2.5,transition metal oxides,redox reactions,conductive AFM,oxygen vacancies
更新于2025-09-09 09:28:46
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Properties of percolation channels in planar memristive structures based on epitaxial films of a YBa <sub/>2</sub> Cu <sub/>3</sub> O <sub/> 7? <i>δ</i> </sub> high temperature superconductor
摘要： The transport properties of the percolation channels of memristive structures based on YBa2Cu3O7?δ epitaxial ?lms were studied. Molecular electronics and Andreev re?ection spectroscopy were utilised, and the in?uence of the superconductive transition of electrodes on resistive switching effects in these structures was examined. Based on the analysis of the conductivity mechanisms in the obtained heterostructures, it is assumed that percolation channels form through a chain of domains disordered by oxygen about 10 nm in diameter, with a maximum Tc of 60 K. Zero-bias anomalies of the dynamic resistance of the studied structures display temperature dependence of the critical current of typical superconductor—normal—superconductor weak links within the framework of Kulik–Omel’yanchuk theory in the dirty limit. A simulation was used to determine the physical parameters of the studied heterostructures.
关键词： resistive switching memory,heterostructures,?lms,critical current,high temperature superconductors,oxygen vacancies
更新于2025-09-09 09:28:46
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Photo-induced negative differential resistance in a resistive switching memory device based on BiFeO3/ZnO heterojunctions
摘要： Photo-induced novel effect in a material with multiple physical properties has highly important potential applications in the photo-electric multifunctional electronic devices. In this work, the BiFeO3/ZnO bilayer films were sequentially prepared by magnetron sputtering method, which displays an obvious photo-modulated conversion between resistive switching (RS) memory and negative differential resistance (NDR) effect. Through theoretical analysis and simulation calculation, suggesting the NDR effect can be attributed to the inner electric field and the efficiently separated photogenerated electrons and holes under light-irradiation in the interface of the BiFeO3/ZnO p–n heterojunctions, while the RS memory behavior can be attributed to the formation of oxygen vacancies assisted Ag conductive filaments. This work opens up a new way to preparation a multifunction electronic device with photo-modulated conversion between RS memory and NDR effect for potential applications in optical electrical bifunctional devices, electronic information and optical quantum computers, and so on.
关键词： Oxygen vacancies,Conducting filament,Negative differential resistance,RRAM,Photo-induced
更新于2025-09-09 09:28:46
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Controlling the white phosphorescence ZnGa2O4 phosphors by surface defects
摘要： White phosphorescence that lasted ≈ 212 seconds, being the longest phosphorescence time reported so far for any Ga based material, has been observed in undoped ZnGa2O4 (ZGO) phosphors. The samples were synthesized by a simple combustion method by using two different Gallium precursors (Gallium nitrate and Gallium Acetylacetonate). According to the X-ray diffraction analysis, the samples prepared with the two different precursors presented the same single cubic phase. TEM images demonstrated that the ZGO phosphors made with both precursors are formed by nanoparticles with quasi-spherical shape, and they have nanoparticle sizes in the range of 17-43 nm. When excited with UV light (400 nm), these phosphors produced a broad blue-green-yellow luminescence. The blue band was associated to transitions from the Ga-O levels, while that of green-yellow band was attributed to radiative transitions from oxygen vacancies. Particularly, the sample synthesized with Gallium acetylacetone precursor presented the highest phosphorescent emission intensity and had a CIE coordinates of (x= 0.27, y= 0.33), which is close to that for pure white light (x=0.33, y=0.33). Since the ZGO presented a white phosphorescent emission without doping with rare earths, they could be good candidates for lighting or signaling applications.
关键词： White emission,Zinc-gallate,phosphorescence,Oxygen-vacancies,luminescence
更新于2025-09-09 09:28:46
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Identification of the nature of traps involved in the field cycling of Hf0.5Zr0.5O2 -based ferroelectric thin films
摘要： The discovery of ferroelectricity in hafnium oxide has revived the interest in ferroelectric memories as a viable option for low power non-volatile memories. However, due to the high coercive field of ferroelectric hafnium oxide, instabilities in the field cycling process are commonly observed and explained by the defect movement, defect generation and field induced phase transitions. In this work, the optical and transport experiments are combined with ab-initio simulations and transport modeling to validate that the defects which act as charge traps in ferroelectric active layers are oxygen vacancies. A new oxygen vacancy generation leads to a fast growth of leakage currents and a consequent degradation of the ferroelectric response in Hf0.5Zr0.5O2 films. Two possible pathways of the Hf0.5Zr0.5O2 ferroelectric property degradation are discussed.
关键词： leakage currents,oxygen vacancies,defects,luminescence,ferroelectric Hf0.5Zr0.5O2
更新于2025-09-04 15:30:14
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Ionic Radii and Concentration Dependency of RE <sup>3+</sup> (Eu <sup>3+</sup> , Nd <sup>3+</sup> , Pr <sup>3+</sup> and La <sup>3+</sup> ) Doped Cerium Oxide Nanoparticles for Enhanced Multi-Enzyme Mimetic and Hydroxyl Radical Scavenging Activity
摘要： The anti-oxidant activity of cerium oxide nanoparticles (CNPs) depends on the concentration of oxygen vacancies and Ce3+ active sites. In the present work, we report the impact of 5 mol% tri-valent rare earth doped (RE3+ = Eu3+, Nd3+, Pr3+ and La3+) CNPs on the oxidation state modulation and anti-oxidant property with respect to ionic radii. An increase in lattice parameter, strain and oxygen vacancy concentration was observed as a function of ionic radii. Among the various dopants in CNP, La3+ with higher ionic radii having smaller crystallite size (7.9 nm) and higher vacancy displayed better peroxidase, oxidase and hydroxyl radical (HO?) scavenging activity. The kinetic parameters for the peroxidase and oxidase activity was found to be superior with Km = 0.217 mM and 0.261 mM, respectively, for 5 mol% La3+ doped CNPs. In order to divulge the role of dopants concentration on structural properties, we also explored using 10 and 20 mol% La3+ doping in CNP. Due to smaller crystallite size (6.7 nm) and higher defect level (3.12 x 1021 cm-3), 20% La3+ doping showed superior peroxidase and oxidase activity as shown by the low Km values. CNPs exhibit both peroxidase and oxidase activity in a concentration dependent manner. Moreover, CNPs exhibit a concentration dependent peroxidase and oxidase activity that can be selectively activated for various theranostic applications. Thus, our results demonstrate the crucial role of ionic radii and concentration of RE3+ dopants on the defect formation in cerium oxide nanoparticles for improved anti-oxidant properties of ceria.
关键词： ionic radii,RE3+ doping,oxygen vacancies,peroxidase activity,oxidase activity,hydroxyl radical scavenging,cerium oxide nanoparticles,anti-oxidant properties
更新于2025-09-04 15:30:14
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Hydrothermal synthesis of flower-like Na-doped α-Bi2O3 and improved photocatalytic activity via the induced oxygen vacancies
摘要： Na-doped α-Bi2O3 with a hierarchical flower-like shape was successfully prepared via a facile hydrothermal reaction. The samples consisted of well-crystalized nanoplates with smooth surfaces and a thickness of tens of nanometers. The phase formation was investigated via X-ray powder diffraction (XRD) patterns and structural refinements. The formations of oxygen vacancies were verified and its effects on the optical and photocatalysis were discussed. The band gap of α-Bi2O3 was narrowed via forming the local energy levels by oxygen vacancy defect complexes in the lattices. The photocatalytic activities on photo-degradation of Rhodamine B (RhB) were significantly improved. The effective photocatalysis was discussed on the improved visible-light response, band structure, and dynamic luminescence decay. The photocatalysis of Na-doped α-Bi2O3 was improved via the induced oxygen vacancies. The reported hydrothermal synthesis was advantageous approach to prepare α-Bi2O3 by considering the simplicity, low reaction temperature, no post-sintering, without using any template or surfactant, large-scale production, low cost, etc.
关键词： Photocatalysis,Semiconductor,Hydrothermal synthesis,Optical properties,Oxygen vacancies
更新于2025-09-04 15:30:14
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Non-Stoichiometric Redox Active Perovskite Materials for Solar Thermochemical Fuel Production: A Review
摘要： Due to the requirement to develop carbon-free energy, solar energy conversion into chemical energy carriers is a promising solution. Thermochemical fuel production cycles are particularly interesting because they can convert carbon dioxide or water into CO or H2 with concentrated solar energy as a high-temperature process heat source. This process further valorizes and upgrades carbon dioxide into valuable and storable fuels. Development of redox active catalysts is the key challenge for the success of thermochemical cycles for solar-driven H2O and CO2 splitting. Ultimately, the achievement of economically viable solar fuel production relies on increasing the attainable solar-to-fuel energy conversion ef?ciency. This necessitates the discovery of novel redox-active and thermally-stable materials able to split H2O and CO2 with both high-fuel productivities and chemical conversion rates. Perovskites have recently emerged as promising reactive materials for this application as they feature high non-stoichiometric oxygen exchange capacities and diffusion rates while maintaining their crystallographic structure during cycling over a wide range of operating conditions and reduction extents. This paper provides an overview of the best performing perovskite formulations considered in recent studies, with special focus on their non-stoichiometry extent, their ability to produce solar fuel with high yield and performance stability, and the different methods developed to study the reaction kinetics.
关键词： solar fuel,concentrating solar technologies,non-stoichiometric materials,perovskites,CO2/H2O splitting,hydrogen,thermochemical cycles,oxygen vacancies
更新于2025-09-04 15:30:14
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Point defect chemistry of donor-doped bismuth titanate ceramic
摘要： This communication reports on the defect chemistry at room temperature of barium (Ba) doped bismuth titanate (Bi4Ti3O12), emphasizing the influence of the point defects on its electrical properties. Pure and Ba doped Bi4Ti3O12 were prepared by a conventional solid-phase reaction technique. The addition of Ba into the crystal structure of Bi4Ti3O12 was monitored by X-ray diffraction measurements combined with Rietveld refinement studies where it was determined that Ba occupies the bismuth (Bi) lattice sites as well as the presence of oxygen vacancies (V??O). The characterization of the point defects was carried out using impedance and electron spin resonance spectroscopies where the results support the models of compensation mechanisms dominated by electrical positive charges (h?) and oxygen vacancies (V??O).
关键词： defect chemistry,X-ray diffraction,Rietveld refinement,impedance spectroscopy,solid-phase reaction,barium doped bismuth titanate,electron spin resonance spectroscopy,electrical properties,oxygen vacancies
更新于2025-09-04 15:30:14