Oxygen Vacancy Defects Research Articles

Correlating the low-temperature photoluminescence with electron transport properties in cerium oxide thin film.

The complex interaction between the intrinsic and extrinsic state variables of strongly correlated insulator thin films is drawing interest as it shows memristive behavior that may be applicable to neuromorphic computing. Cerium oxide is an interesting material as its band structure is modified due to the formation of oxygen vacancy defects. The polaron formation that results from the reduction of the Ce4+ state to the Ce3+ state through oxygen vacancies is crucial for the electron transport in cerium oxide and is strongly influenced by temperature. In this work, we examined the relationship between the change in band structure and the associated conductivity at lower temperatures when ceria is exposed to light. Following light excitation, the creation of oxygen vacancies results in electron localization in the Ce 4f state, followed by the electron transition from 4f1 to 4f0, generating the PL spectra. With decreasing temperature, the lattice vibration decreases, and the splitting in the PL peak at a particular energy state validates the weaker electron-phonon interaction with an exciton trap. This reduces the carrier mobility of the film as observed from the resistance vs temperature curve of ceria under dark conditions. When excited by a particular energy of light, the electrons move more easily from the defect state to the conduction band, increasing conductivity at much lower temperatures than the conductivity under dark conditions.

Reduction of absorption of Ta2O5 monolayers through the suppression of structural defects by employing an appropriate ionic oxygen concentration

Ultralow-absorption laser films have critical applications in high-power continuous-laser and gravitational-wave-detection systems. During film deposition, the ionic oxygen concentration significantly affects the absorption loss of the film. In this study, Ta2O5 monolayers were deposited using an ion-assisted electron beam evaporation technique, and the weak absorption at 1064 nm, temperature rise, optical band gap, element content, and binding energy were tested and analyzed. The band structure and microdefects of the Ta2O5 films were characterized, and their correlation with the absorption properties was established. The analyses revealed that the primary mechanism responsible for reducing the absorption loss in Ta2O5 films was an appropriate ionic oxygen concentration, which improved the optical band gap and stoichiometric ratio and reduced oxygen vacancy defects. For Ta2O5 monolayers deposited with the optimal ionic oxygen concentration, the weak absorption was approximately 7.2 ppm and the temperature rise was approximately 0.6 °C, 1/4 and 1/3 of the values of those deposited with an excessive concentration, respectively—an important finding in the preparation of ultralow-absorption laser films.

Applying hollow octahedron PtNPs/Pd-Cu2O nanozyme and highly conductive AuPtNPs/Ni-Co NCs to colorimetric -electrochemical dual-mode aptasensor for AFB1 detection.

Aflatoxin B1 (AFB1) is a secondary metabolite produced by Aspergillus flavus and Aspergillus parasiticus. This toxin is highly carcinogenic and toxic, posing a serious threat to human and animal health. AFB1 primarily enters the human body through contaminated food, particularly peanuts, corn, nuts, and wheat. These foods are easily contaminated with AFB1 during planting, harvesting, storage, and processing. Therefore, the establishment of an accurate and sensitive method for the detection of AFB1 is essential to safeguard food safety and human health. This study applied catalytic hairpin assembly (CHA), hybridization chain reaction (HCR), hollow octahedron PtNPs/Pd-Cu2O bifunctional nanozyme, and AuPtNPs/Ni-Co NCs to develop a colorimetric-electrochemical dual-mode aptasensor for AFB1 detection. Here, Pd-Cu2O corner-etched octahedra with cavities and oxygen vacancy defects were first designed, followed by the synthesis of PtNPs/Pd-Cu2O through the loading of PtNPs to enhance the peroxidase-like activity of Pd-Cu2O. PtNPs/Pd-Cu2O effectively catalyzed the generation of blue oxidation products from 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide (H2O2). It also enhances the redox reaction of methylene blue (MB) at the electrode and improves the electrochemical signal. AuPtNPs/Ni-Co NCs possess a large specific surface area and excellent conductivity, enhanced the redox signal of MB. Additionally, the aptasensor combined the enzyme-free amplification strategies of CHA and HCR to improve sensitivity. The aptasensor reached limit of detection (LOD) 0.76pg/mL in electrochemical mode and 0.49pg/mL in colorimetric mode. The designed colorimetric-electrochemical dual-mode aptasensor exhibits high selectivity, specificity, stability, and reliability. The dual-mode aptasensor had been successfully applied to the spiked analysis of edible oils, peanuts, and cornmeal, demonstrating excellent recovery rates. Therefore, the dual-mode aptasensor had a wide application prospect in the field of quality supervision and food safety.

Thermally Dependent Metastability of Indium-Tungsten-Oxide Thin-Film Transistors

Abstract Indium tungsten oxide (IWO) has been investigated as an oxide semiconductor candidate for next-generation thin-film transistors (TFTs). Bottom-gate TFTs were fabricated with a 30-nm IWO channel material sputter-deposited with oxygen partial pressure (PO2) ranging from 2.5% to 10% of the total ambient pressure. Annealing was conducted at temperatures ranging from 100ºC to 275ºC. Device transfer characteristic measurements revealed a pronounced interaction between the sputter PO2 setting and passivation annealing conditions. Devices annealed at 100ºC in air ambient demonstrated characteristics with a strong dependence on PO2, attributed to differences in oxygen vacancy defects and semiconductor electronic properties. Devices annealed at 200ºC in air ambient demonstrated characteristics like those of unannealed devices, with operation far in depletion mode. Donor state passivation is possible following additional annealing at 275ºC in air, with reduced sensitivity to the initial sputter PO2 setting. A hypothesis on the mechanism of metastability is proposed.

Quantitative Enhancement of Arsenate Immobilization Induced by Vacancy Defects on Various Exposed Lattice Facets of Hematite.

Defects are common features in hematite that arise from deviations from the perfect mineral crystal structure. Vacancy defects have been shown to significantly enhance arsenate (As) immobilization by hematite. However, the contributions from vacancy defects on different exposed facets of hematite have not been fully quantified. In this study, hematite samples with various morphologies were pretreated with sodium borohydride (NaBH4) to generate oxygen vacancy defects (OVDs), analyzed quantitatively using extended X-ray absorption fine structure (EXAFS) and thermogravimetric analysis (TG). Batch experiments revealed that the OVDs on different exposed facets showed significant variations in improving arsenate adsorption, i.e., the quantitative enhancement of arsenate adsorption amount per unit OVD concentration (ΔQm/Cdefect) followed the sequence of (110) facet (80.05 μmol/mmoldef) > (001) facet (31.85 μmol/mmoldef) > (012) facet (13.14 μmol/mmoldef). The underlying mechanism by which OVDs affect arsenate adsorption across different exposed facets of hematite was studied. The results reveal that the tremendous improvement of arsenate adsorption caused by OVDs on the (110) facet compared to (001) and (012) facets was attributed to their stronger bonding strength of As to under-coordinated Fe atoms, thus significantly promoting the immobilization of arsenate. The findings of this study enhance our ability to precisely understand the migration and fate of As while also aiding in the design of highly efficient iron mineral materials for mitigating As pollution.

Effective control of conductivity in lutetium orthoferrite with cobalt doping measured by terahertz time-domain spectroscopy

The effective control of conductivity in LuFeO3 (LFO) with Co3+ doping is explored by terahertz (THz) time-domain spectroscopy. It is demonstrated that the conductivity of 5% Co-doped LFO (LFO:Co 5%) is lower than that of LFO, while that of 15% Co-doped LFO (LFO:Co 15%) is significantly higher than LFO. Furthermore, LFO exhibits two lattice vibration peaks at 0.58 and 1.61 THz, LFO:Co 5% shows only one lattice vibration peak at 1.61 THz, while no distinct vibration peak is observed in LFO:Co 15%. The disappearance of lattice vibration at 0.58 THz is attributed to the shortened Fe (Co)-O bond length resulting from Co3+ doping, thus suppressing magnetic resonance effect of Fe3+. With 15% Co3+ doping, structural stability is enhanced, and the asymmetric vibration of Lu3+ at surface/interface/boundary is suppressed, resulting in the disappearance of vibration peak at 1.61 THz. The conductivity of LFO:Co 5% is lower than that of LFO, mainly because the lattice vibration at 1.61 THz and oxygen vacancy defects introduced by doping jointly increase the degree of carrier back-scattering, which decreases carrier movement, while the enhancement of conductivity by electronegativity at 5% Co3+ doping is very limited. The significantly higher conductivity of LFO:Co 15% compared to LFO is due to the obvious increase in overall electronegativity and suppression of lattice vibration by 15% Co3+ doping, thereby improving carrier mobility. The insights of this investigation provide important experimental data and theoretical basis for design and production of high-conductivity and stable solid oxide fuel cells cathode.

Radiation‐Enhanced Annealing of Vacancy–Oxygen Defects in Cz n‐Si: Features of the Experiment, Factor of the Radiation Ionization, and a Possible Annealing Mechanism

The results of the detailed study of the accumulation and/or annealing of vacancy–oxygen (VO) complexes kinetics in the Czochralski‐grown n‐type silicon (Cz n‐Si) are presented. The samples are irradiated by electron beam pulses of different energies and intensities (J) at VO effective annealing temperatures (>300 °C). It is shown that: 1) upon high‐temperature (so‐called “hot”) irradiation Cz n‐Si at temperatures >300 °C, J can significantly stimulate VO annealing and a maximum concentration of accumulated VO defects ([VO]max, when the rates of formation and simultaneous annealing of VO complexes are equal) increases with increasing J and decreases with increasing irradiation temperature. Accelerated annealing of VO slows down sharply the growth rate of [VO]max as a function of J; 2) the VO defects introduced into Cz n‐Si at room temperature can also be annealed faster if the annealing is accompanied by additional electron irradiation of a certain intensity. It has been established that the radiation‐accelerated annealing of VO is characterized by a decrease in the activation energy from ≈1.7 to ≈0.5 eV due to radiation ionization of the Si crystal. A model of the enhanced VO annealing process is proposed.

Multiscale Simulation of the Impact of Defects on Elevated-Metal Metal-Oxide IGZO TFTs

This study explores the impact of oxygen vacancy defects on elevated-metal metal-oxide (EMMO) IGZO TFTs under positive bias stress (PBS) using TCAD and DFT simulation. Findings reveal that oxygen vacancies accumulating at the channel/passivation layer interface and within the channel under PBS lead to negative threshold voltage shifts and reduced mobility. Additionally, higher tail state densities contribute to a positive Vth shift. These results provide important insights into the defect-related reliability of EMMO IGZO TFTs, guiding the design of more reliable devices.

Lattice Distortions Promoting the In-Depth Reconstruction of Ni-Based Electrocatalysts with Enriched Oxygen Vacancies for the Electrochemical Oxidation of 5-Hydroxymethylfurfural toward 2,5-Furandicarboxylic Acid.

The electrocatalytic 5-hydroxymethylfurfural (HMF) oxidation reaction (HMFOR) toward 2,5-furandicarboxylic acid (FDCA) has been considered a promising approach for the substitution of the energy-consuming and hazardous oxygen evolution reaction and for the valorization of renewable biomass. However, it is limited by the susceptibility of HMF to the oxidative environment and requires efficient electrocatalysts. Herein, a NiMo complex (NiMo-N) is provided as the precatalyst for the HMFOR, exhibiting favorable performances with a current density of 450 mA·cm-2 achieved at an anodic potential of 1.4 V vs RHE (similarly hereinafter) with 50 mmol/L (mM) HMF and over 95% HMF conversion and FDCA FE for at least five cycles. Combined with quasi situ and in situ analysis, it is confirmed that the extensive lattice distortions in the precatalyst facilitate the in-depth reconstruction, increasing the accessible Ni sites and defective oxygen vacancies (Ov), which would promptly convert to high-valence Ni and active O species during the reaction. The improved performance is then attributed to the incorporation of the improved chemisorption and dehydrogenation ability of HMF by the as-evolved active sites.

What Is the Mechanism by which the Introduction of Amorphous SeOx Effectively Promotes Urea-Assisted Water Electrolysis Performance of Ni(OH)2?

Nickel hydroxide (Ni(OH)2) is considered to be one of the most promising electrocatalysts for urea oxidation reaction (UOR) under alkaline conditions due to its flexible structure, wide composition and abundant 3D electrons. However, its slow electrochemical reaction rate, high affinity for the reaction intermediate *COOH, easy exposure to low exponential crystal faces and limited metal active sites that seriously hinder the further improvement of UOR activities. Herein it is reported electrocatalyst composed of rich oxygen-vacancy (Ov) defects with amorphous SeOx-covered Ni(OH)2 (Ov-SeOx/Ni(OH)2). Surprisingly, at 100 mA cm-2, compared with Ni(OH)2 (1.46 V (vs RHE)), Ov-SeOx/Ni(OH)2 has a potential of 1.35 V. Meanwhile, Ov-SeOx/Ni(OH)2 catalyst also showed good hydrogen evolution reaction (HER) performance, so it is used as the electrolytic cell assembled by UOR and HER bifunctional catalysts and only 1.57 V could reach 100 mA cm-2. Density functional theory (DFT) study revealed that introduce of amorphous SeOx optimizes the electronic structure of the central active metal, amorphous/crystalline interfaces promote charge-carrier transfer, shift d-band center and entail numerous spin-polarized electrons during the reaction, which speeds up the UOR reaction kinetics.

Organic Crosslinked Tin Oxide Mitigating Buried Interface Defects for Efficient and Stable Perovskite Solar Cells

AbstractTin dioxide (SnO2) stands as a promising material for the electron transport layer (ETL) in perovskite solar cells (PSCs) attributed to its superlative optoelectronic properties. The attainment of superior power conversion efficiency hinges critically on the preparation of high‐quality SnO2 thin films. However, conventional nanoparticle SnO2 colloids often suffer from inherent issues such as numerous oxygen vacancy defects and film non‐uniformity. In this study, we report a strategy to homogenize SnO2 with reduced defects for high‐performance PSCs. The commercial SnO2 colloid is modulated with bisphenol S (BPS) crosslinking to achieve a better annealing intermediate state. The phenolic hydroxyl groups on BPS bond with the hydroxyl groups on the SnO2 surface, passivating defects as well as promoting superb regularity of the films by forming a network of the SnO2 nanoparticles. Additionally, the sulfone groups on BPS coordinate with Pb2+, regulating the crystallization of PbI2 and FAPbI3, which leads to better interface contact at the buried interface. The FAPbI3 perovskite solar cells based on BPS‐crosslinked SnO2 layers achieved a champion efficiency of 24.87 % and retained 95 % of their initial PCE after 1000 hours of continuous light soaking under N2 atmosphere.

A Novel Methodology for the Accelerated Desalination of Seawater Utilizing Up‐ and Down‐Conversion Phosphors

Solar evaporators are fabricated by coating coconut/agave fibers with graphene. Those ones are utilized to desalinate seawater brought from Vallarta beach, Mexico. The graphene‐based evaporators exposed to sunlight produce a maximum evaporation rate/efficiency of 2.13 kg m−2 h−1/83%. The addition of Fe2O3 particles to the evaporators enhances the evaporation rate/efficiency up to 2.36 kg m−2 h−1/88.5%. The higher presence of oxygen vacancies defects in the evaporators made with Fe2O3 improves the absorption of light in the UV‐Vis range, which in turn, accelerates the desalination of seawater. Moreover, the performance of the solar evaporators is evaluated in absence of solar light. In this case, upconversion (UC) and downconversion (DC) phosphors are attached to the evaporators and such phosphors are excited with near‐infrared (980 nm) or ultraviolet (360 nm) light. Consequently, green light is produced by DC/UC, which is absorbed by the evaporators to be heated and the seawater evaporation is induced. The maximum evaporation rate/efficiency produced by the evaporators is 0.738 kg m−2 h−1/84.9%. In general, this research offers a novel strategy to continue the desalination of seawater in absence of solar light or in cloudy days. This can be useful to design new types of desalination plants without using complex/expensive filtration systems.

Room Temperature Quantum Emitters in van der Waals α-MoO3.

Quantum emitters in solid-state materials are highly promising building blocks for quantum information processing and communication science. Recently, single-photon emission from van der Waals materials has been reported in transition metal dichalcogenides and hexagonal boron nitride, exhibiting the potential to realize photonic quantum technologies in two-dimensional materials. Here, we report the generation of room temperature single-photon emission from exfoliated and thermally annealed single crystals of van der Waals α-MoO3. The second-order correlation function measurement displays clear photon antibunching, while the luminescence intensity exceeds 0.4 Mcts/s and remains stable under laser excitation. The theoretical calculation suggests that an oxygen vacancy defect is a possible candidate for the observed emitters. Together with photostability and brightness, quantum emitters in α-MoO3 provide a new avenue to realize photon-based quantum information science in van der Waals materials.

Visual Location of Oxygen Vacancies on Bismuth Titanate Nanosheets with Periodic Quantum Well and Promoting H2O2 Photosynthesis.

Oxygen vacancy (OV) defect engineering plays a crucial role in enhancing photocatalytic efficiency. However, the direct visual characterization of oxygen vacancies still remains technically limited. Herein, a bismuth titanate (Bi4Ti3O12, BTO-OV) model photocatalyst containing oxygen vacancies is constructed through density functional theory (DFT) calculations to reveal the influence mechanism of distinctive periodic quantum well and oxygen vacancies on the charge transfer behavior in BTO. Notably, the distribution of oxygen vacancies is directly observed using the low-dose integrated differential phase contrast-scanning transmission electron microscopy (iDPC-STEM), providing visual evidence for the location of these oxygen vacancies in BTO-OV. Furthermore, the theoretical calculation results are verified by characterizing the photoelectric properties and conducting performance tests on the hydrogen peroxide (H2O2) photosynthesis. Specifically, the oxygen vacancies and distinctive periodic quantum well in BTO-OV accelerate charge separation, leading to a H2O2 photosynthesis efficiency reaching 5278 µm g-1 h-1, which is 5 times that of the original BTO. This work offers theoretical and experimental references for the visual characterization of oxygen vacancies and the improvement of the charge transfer mechanism.

Exceptionally Low-Coordinated Bismuth–Oxygen Vacancy Defect Clusters for Generating Black In2O3 Photocatalysts with Superb CO2 Reduction Performance

Exceptionally Low-Coordinated Bismuth–Oxygen Vacancy Defect Clusters for Generating Black In₂O₃ Photocatalysts with Superb CO₂ Reduction Performance

Broadband nonlinear optical response and ultrafast carrier dynamics in defect-engineered Fe-Co3O4 for photonics

In this paper, Fe-doped Co3O4 (Fe-Co3O4) with oxygen vacancy defects, which was derived from Fe-doped ZIF-67, was successfully synthesized via high-temperature calcination and verified using several special characterization methods. Femtosecond-resolved...

Oxygen‐Vacancy Rich Co3O4/CeO2 Interface for Enhanced Oxygen Reduction and Evolution Reactions

Oxygen reduction and evolution reactions (ORR and OER, respectively) are the two most extensively studied reactions in electrochemistry. Herein, we report the synthesis of Co3O4/CeO2/GNP (GNP=graphene nanoplatelet) electrocatalyst for ORR and OER that exhibits an early onset potential (0.85 V) and half‐wave potential (E1/2) of 0.69 V for ORR. The reported catalyst is highly durable with 87.6% retention of its initial current after a 6 h chronoamperometry test compared to 72.5% by Pt/C. It exhibits a negligible shift of E1/2 after 10,000 potential cycles for ORR. Heterogeneous oxide/oxide interfaces, oxygen vacancies and semicrystalline nature are inferenced to play a dominant role in altering the collective catalytic efficiency of Co3O4/CeO2/GNP. High concentration of oxygen vacancy defects (68%) in Co3O4/CeO2/GNP is presumed to play a dominant role here. The catalyst is bifunctional for ORR and OER with a bifunctionality index of 0.98 V and operates at an overpotential of ƞ10= 440 mV for OER. Ex‐situ X‐ray absorption studies indicate an increased average oxidation state of Co by 15% in Co3O4/CeO2/GNP compared to Co3O4/GNP, aiding in preserving its inherent catalytic nature of spinel Co3O4.

Photoabsorption, photoluminescence, and chromaticity properties of pure CuO and CuO-Y2O3 composites for white light-based emitting diode applications

The primary goal of the present exploration is to test the photoluminescence (PL) responses and chromaticity features of pure CuO and CuO-Y2O3 composites for white light-emitting devices. The aforementioned compounds were synthesized using copper acetate and oxalic acid in the absence and presence of different weights of yttrium nitrate salt via the co-precipitation method. Using powder XRD study, the pure CuO sample has identified the monoclinic structure; however, the primary phase-monoclinic structure of CuO with the secondary phase-yttrium oxide appeared for the synthesized composites samples. Experimentally scrutinize the microstructure and the presence of chemical bonds in the synthesized compounds by employing selected tools such as SEM, FT-IR, and EDX studies. To confirm with the optical absorption spectra study, optical band gap values have increased in the CuO-Y2O3 samples when compared to the pure CuO. Blue, green, and red emission peaks have been recorded through photoluminescence (PL) measurements for the pure CuO and all synthesized CuO-Y2O3 composites. PL results reveal that oxygen vacancy defects were increased in all synthesized CuO-Y2O3 composites when compared to the pure CuO. With the help of the obtained photoluminescence spectra data, we made the CIE 1931 chromaticity diagram for the synthesized pure CuO and CuO-Y2O3 composites suitable for LED devices.

Annealing construction of in situ heterojunction for photocatalytic degradation of bisphenol A

Here, we report the synthesis of bismuth oxyiodide (BiOI) photocatalysts with oxygen vacancy defects by a one-pot solvothermal method followed by annealing in a nitrogen atmosphere. This method allows the oxygen vacancy concentration to be tuned and provides new insights into defect engineering of photocatalytic materials. We found that the Bi2O3/BiOI heterojunction formed after annealing at 400°C significantly improves the photocatalytic performance, which provides a new strategy for the optimal design of structures for efficient photocatalysts. Using a combination of characterization techniques such as X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), and ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS), as well as density-functional theory (DFT) calculations, we have elucidated the photocatalytic mechanism of the Bi2O3/BiOI heterojunctions, highlighting their role in facilitating the photogenerated charge-carrier separation and transfer. The optimized A-B40 samples exhibited photocatalytic degradation efficiencies of up to 99.7% for bisphenol A (BPA), highlighting their potential for remediation of environmental pollutants. This study presents a method for the preparation of high-performance BiOI-based photocatalysts, which offers valuable theoretical and experimental prospects for the development of eco-friendly photocatalytic materials.

Rational desig of hierarchical defect-rich NiSe2/Se-NiCuOx heterostructures: Modulating electronic structure for exceptional ammonia oxidation performance

Direct ammonia oxidation reaction (AOR) is a promising route for efficiently removing ammonia–nitrogen from wastewater. However, the sluggish kinetics and poor N2 selectivity present significant challenges for AOR catalysts. Herein, a novel cost-effective hierarchical catalyst was constructed by selenizing NiCuOx nanorods on nickel foam support (NiSe2/Se-NiCuOx/NF) via the hydrothermal-calcination selenization method. The selenizing procedure radically manipulates the surface structure of NiSe2/Se-NiCuOx/NF, enriching it with oxygen vacancy defects and heterostructures to achieve high efficiency towards AOR. Consequently, the optimal NiSe2/Se-NiCuOx/NF only requires 1.50 V to achieve a current density of 65mA cm−2. Furthermore, the N2 selectivity was up to 98.18 % after 5 h of electrolysis. Density functional theory (DFT) calculation elucidates that the defects and heterostructures effectively facilitates electron transfer between NiSe2 and Cu2O, significantly reduces the energy barrier of the rate-determining step (RDS) of O-S mechanism. This work demonstrates the feasibility of metallic selenides as efficient electrocatalysts for AOR.