Concentration Of Oxygen Vacancy Defects Research Articles

The jump-like PTCR effect in Ca1-xYxCu3Ti4O12 ceramics hot quenched under high-pressure

The PTCR effect is an important application phenomenon in the ferroelectric BaTiO3 electronic ceramic materials. In this work, the PTCR effect is also found in high pressure (HP) hot quenched Ca1-xYxCu3Ti4O12 (CYCTO) ceramics. Compared with the pure CaCu3Ti4O12 (CCTO) ceramic synthesized under ordinary pressure (OP), the low temperature resistivity of HP CYCTO samples is about 3 orders of magnitude lower than that of untreated CCTO samples, showing an obvious PTCR effect. The transition temperature is close to 178 K for x = 0.2 sample. The analysis of crystal and magnetic structures shows that the crystal and magnetic structures of HP CYCTO samples do not change before and after the resistance transition. X-ray photoelectron spectroscopy showed that the concentration of oxygen vacancy defects in HP CYCTO is higher than CCTO. By analyzing the conduction behaviors of HP CYCTO samples, it suggests that oxygen vacancies and Y3+ ions may be the important donors for the decrease of low temperature resistivity of HP CYCTO samples. The results in this work have important reference value for the application of the electrical conduction behaviors in CCTO.

Effects of heterovalent ions doping-induced oxygen octahedral distortion and defect chemical change on piezoelectric characteristics and thermal stability of PHT-PIN ceramics

Electromechanical devices require functional materials possessing excellent piezoelectric properties, good thermal stability, and high electromechanical coupling coefficients. To modulate the piezoelectric, dielectric, and electromechanical characteristics of 0.89Pb(Hf0.47Ti0.53)O3-0.11Pb(In1/2Nb1/2)O3 (PHT-PIN) piezoelectric ceramics, heterovalent ions of lithium (Li) and tungsten (W) were doped through a traditional solid-phase reaction approach. On the one hand, large lattice distortions caused by the doped W6+ resulted in the shortening of BO bonds while an increase in the local displacement of B-site ions. Moreover, a mismatch occurred for the oxygen octahedral dimensions, and a subsequent disruption of the long-ranged ordered ferroelectric domains was observed, which resulted in the formation of microdomains. On the other hand, the changes in the concentration of oxygen vacancy defects induced by the Li and W doping inside the ceramic were comprehensively analyzed. The decrease in the concentration of oxygen vacancies was found to be accompanied by the enhancement of piezoelectric properties of the material. Excellent comprehensive performance (piezoelectric coefficient d33 = 655 pC N−1, Curie temperature Tc = 321.1 °C, dielectric constantεr = 3352.31, electromechanical coupling coefficient kp = 0.67, and residual polarization strength Pr = 55 μC cm−2) was obtained for 0.2 mol % doping amount of Li+ and W6+ ions. This work, therefore, proposes a novel strategy for the origin of piezoelectric properties and inspires doping of other heterovalent ions to improve the piezoelectric properties of ceramics. It further promotes the development of Pb-based piezoelectric ceramics for electromechanical devices that can efficiently operate under high-temperature environments.

Defect assisted self‐reduction and post annealing of Mn ions activated garnet transparent ceramics

AbstractTransition‐metal Mn2+ ion‐doped transparent ceramics (TCs) are promising color‐convertors to improve color rendition for solid‐state lighting. However, the stabilization of Mn2+ remains a challenge owing to the changeable atmosphere in the specific preparation of TC. In this work, the variations of valence states of Mn ions in typical garnet lattice host (YAG and LuAG) throughout the TC fabrication were demonstrated. By combined first principles calculation and experimental investigation, an enhanced self‐reduction of Mn ions was clarified in LuAG host, which was originated from the higher concentration of oxygen vacancy defects. Moreover, the air annealing treatment could significantly weaken and enhance the absorption of Mn2+ and Mn3+ respectively, degrading the orange–red emission peaking at 594 nm. On account of the oxidation of Mn2+ ions, a photoluminescence spectra redshift of 9 nm was observed with increasing air annealing temperature and oxygen content, owing to strengthened crystal field strength surrounding Mn2+ ions. Finally, a high color rendering index of 74.5 of resultant white laser diodes device structured by single‐phase LuAG:Ce,Mn TCs was obtained based on an efficient energy transfer process from Ce3+ to Mn2+. This study will deepen the understanding of the crystal defects inside TCs on luminescence properties, as well as inspiring more exploration on defect control to develop high performance ceramic color‐convertor.

Optoelectronic properties and optical transitions in low concentrated aluminum-doped tin oxide thin films

The structural, chemical, surface morphology, and optoelectronic characteristics of Al-doped SnO2 (ATO) films are investigated and a comprehensive analysis of the obtained results is presented. All films are shown to have a polycrystalline tetragonal rutile structure by X-ray diffraction (XRD) measurements, and the single-phase nature of the structure is proved by detailed X-ray photoelectron spectroscopy (XPS) investigations. Two mechanisms of Al incorporation into the SnO2 lattice were evident by XRD and XPS measurements. Comprehensive XPS, XRD, and Hall effect investigations showed a clear relation between the charge carrier concentration, crystallite size, and the concentration of oxygen vacancy defects. Through a comprehensive analysis of the photoluminescence (PL) measurements, we determined the positions of various defect states within the bandgap. Using a thorough analysis of the optical absorption measurements, we have successfully demonstrated the presence of four direct optical transitions with energies ranging from 3.84 to 5.10 eV, and by considering the Moss–Burstein effect and the Urbach tailing phenomenon, it was shown that the first transition energy (E1) corresponds to the direct optical transition across the Γ3+−Γ1+ forbidden energy gap. The other three transitions are ascribed to electronic transitions from the valence band states Γ5− and Γ5+ to different defect states within the bandgap.

Multi-scale simulation of the fracture behavior of non-stoichiometric gadolinia-doped ceria solid electrolytes under the coupled mechanical and electrochemical field

Solid oxide fuel cell (SOFC) works in a complex working environment, which is affected by many factors such as temperature, load and electrochemical reaction. When there are cracks in the material, the multi-field coupling effect will cause the electrolyte performance degradation, even failure and damage. In this paper, the coupling effects of mechanical and electrochemical field on mechanical behavior of gadolinia-doped ceria (GDC) electrolyte are investigated by using the Atom-to-Continuum (AtC) multi-scale method combining molecular dynamics (MD) and finite element method (FEM). Based on the electrochemomechanical coupling theory, we derive the defect diffusion equation of the finite element form. The non-stoichiometry of the cracked GDC electrolyte is calculated, and it is found that the stress concentration at the crack tip will induce non-stoichiometric effects, causing further concentration of oxygen vacancy defects at the crack tip. Subsequently, the effect of electrochemomechanical coupling effect on the fracture toughness of GDC electrolyte is studied by using the AtC multi-scale method. At 800°C under oxygen partial pressure logPO2=−22, this multi-field coupling effect reduces the fracture toughness of 10GDC and 20GDC by 16.13% and 23.33%, and this effect is more apparent with the increase of oxygen partial pressure gradient and external load.

Ternary CuCrCeOx Solid Solution Enhances N2‐Selectivity in the NO Reduction with CO in the Presence of Water and Oxygen

AbstractCo‐doping of ceria with Cu and Cr forming a ternary CuCrCeOx solid solution enhances N2‐selectivity as well as NO and CO conversions compared to the corresponding singly doped ceria, CuCeOx and CrCeOx, and pristine ceria, in the absence as well as presence of water and oxygen. The comparative study of these solid‐solution catalysts indicates that the doping of ceria results in the coupling of different transition metal redox cycles, which has a strong effect on the surface population of oxygen vacancies. The temperature required to reach 95 % N2‐selectivity is shown to be nearly linearly correlated to the concentration of oxygen vacancy defects. The oxygen defect population is highest for the ternary CuCrCeOx solid solution, which exhibits the best catalytic performance, reaching 100 % N2‐selectivity at around 100 °C. Three redox cycles (CrVI/CrIII, CuII/CuI, and CeIV/CeIII) have been identified in this catalyst leading to a synergistic effect. The ternary CuCrCeOx catalyst exhibits good water tolerance and long‐term stability while the SO2 tolerance is limited due to selective blocking of the active surface oxygen defects forming SO32− species, resulting in catalyst deactivation.

Expedient Red Emitting and Transparency Dual Modulation in KNN-Based Transparent Ceramics via Sensitive Photothermochromic Behavior

An up-conversion luminescence (UCL) transparent ferroelectric oxide (KNN) introduced by rare-earth ions (Er3+ and Bi3+) has been demonstrated to exhibit a unique, high-purity, red emitting, high transparency, reversible, photothermochromic (PTC) reaction. And, its associated transmittance/red emitting modulations are realized via the continuous alternating of UV light irradiation and heat treatment (200 °C). The effects of the phase structure, microstructure, and oxygen vacancy defects on their optical transmittances and the corresponding optical modulation based on PTC reaction at different sintering temperatures were systematically studied. Because of the sufficiently small grain size, dense structure, and appropriate concentration of oxygen vacancy defects, excellent optical transparency (∼70%, at 900 nm) and moderate PTC modulation contrast (ΔAbs = 13.9%, ΔR = 48.9%) are obtained in KNNEB-1155. The decreased and increased transmittance/red emitting can represent two pairs of “off” and “on” codes, which makes the red-emitting KNNEB transparent ceramics very competitive in the application of multifunctional transparent sustainable warning equipment and optical storage materials.

Influence of sintering parameters on transparency of reactive SPSed Nd3+:YAG ceramics

Fine-grained 4 at% Nd3+:YAG transparent ceramics were prepared by reactive spark plasma sintering using a two-step heating profile. The effect of key sintering parameters (heating rate, external pressure, sintering and post-annealing temperatures) on densification peculiarities, optical and mechanical properties was investigated. Special attention was paid to the behavior and nature of carbon contaminations, dispersed in the yttrium aluminum garnet matrix. It was established that the optimal heating rate to the isothermal exposure temperature was 15 °C min−1. In this case, supporting the uniformity of temperature field distribution between the punches ensures the synthesis of the single-phase product and positive densification dynamics throughout the sintering trajectory for the disk geometry of samples. It was shown that an increase in applied pressure from 30 to 70 MPa changed the color of ceramics: the samples darkened and became dark brown. This may be due to an increase in the concentration of oxygen vacancy defects (color centers). The formation of silicon oxycarbides SiOxCy (where x + y = 4; x,y ≥ 1) in ceramics at sintering temperatures T > 1400 °C was revealed by X-ray photoelectron spectroscopy. It was found that these impurity phases demonstrated a thermal stability and resistance to decomposition during post-annealing. The study showed that 4 at% Nd3+:YAG ceramics obtained by reactive spark plasma sintering at 1350°С//10 min//30 MPa//15 °C min−1 and post-annealed at 900 °C for 1 h possessed a mean grain size of 0.74 μm, a microhardness of 13.2 GPa, a residual porosity of 0.0192 vol% and in-line optical transmittance 73.7% at λ = 1064 nm, which is 0.87 from the theoretical value for a single crystal.

Significantly enhanced piezoelectric performance in Bi4Ti3O12-based high-temperature piezoceramics via oxygen vacancy defects tailoring

Bismuth titanate (Bi4Ti3O12, BIT) piezoelectric materials have attracted increasing attention due to their high-temperature applications. However, it is quite challenging to simultaneously achieve outstanding piezoelectric properties and high Curie temperature in BIT-based systems. In this study, oxygen vacancy defects tailoring strategy was utilized to solve this problem, excellent piezoelectric coefficient (32.1 pC/N), and ultrahigh Curie temperature (659 °C) are gotten in Bi4Ti3-x(Mn1/3Nb2/3)xO12 (BTMN) ceramics, which are among the top values in the BIT-based ceramics. More importantly, the (Mn1/3Nb2/3)(4+δ)+ complex-ion modified Bi4Ti3O12-based ceramics are characterized with excellent piezoelectric stability up to 500 °C (d33 > 30.0 pC/N at 500 °C)) and significantly reduced conductivity (only ∼ 10−7 Ω−1 cm−1 at 500 °C). Moreover, enhanced ferroelectricity and good dielectric stability were also obtained. The better comprehensive properties can be ascribed to two aspects. First, the concentration of oxygen vacancy defects is obviously reduced, and their distribution is effectively controlled in BITMN ceramics. Second, the introduction of (Mn1/3Nb2/3)(4+δ)+ complex-ion gives rise to the antiphase boundaries and massive ferroelectric domain walls. This works not only reveal the high potential of BITMN ceramics for high-temperature piezoelectric applications but also deepen the understanding of the structure-properties relationship in BIT-based materials.

The Effect of Metal Ions as Dopants on OMS-2 in the Catalytic Degradation

Here we first designed, synthesized and compared Ni, Ag and Ce doped manganese oxide octahedral molecular sieves, (Ni-OMS-2, Ag-OMS-2 and Ce-OMS-2) for the catalytic degradation of organic dyes, such as reactive red 2, acid orange 7, methylene blue, and rhodamine B, in the presence of potassium peroxymonosulfate in aqueous solutions. These results show that the catalytic efficiency increases in the order of Ce-OMS-2 < OMS-2 < Ag-OMS-2 < Ni-OMS-2 for organic dyes degradation, which is in accordance with the concentration of oxygen vacancy defects on the surface of materials. Then pH condition and various amounts of Ni-OMS-2, organic dye and potassium peroxymonosulfate concentration have also been investigated for the reactive red 2 degradation. In addition, TEM and XRD have confirmed the heterogeneous catalyst Ni-OMS-2 has been successfully recycled at least 5 times with a very slight reduction efficiency by the simple filtration. We have designed, synthesized and compared Ni, Ag and Ce doped OMS-2, (Ni-OMS-2, Ag-OMS-2 and Ce-OMS-2) for the degradation of organic dyes. And they show the catalytic efficiency increases in the order of Ce-OMS-2 < OMS-2 < Ag-OMS-2 < Ni-OMS-2 for the degradation.

Flexible Femtojoule Energy-Consumption In-Ga-Zn-O Synaptic Transistors With Extensively Tunable Memory Time

A neuromorphic electronic system requires the component devices to not only mimic typical synaptic behaviors but also be energy-efficient, together with excellent uniformity and tunable memory time. For this purpose, we fabricated amorphous In-Ga-Zn-O (a-IGZO) thin-film transistors with plasma-enhanced atomic layer deposition AlO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> :H dielectrics, successfully demonstrating typical synaptic behaviors, such as excitatory and inhibitory postsynaptic current, pair-pules facilitation, dynamic filter, learning and forgetting abilities and spike-timing dependent plasticity. In particular, such synaptic transistors exhibit ultralow energy consumption down to 3.18 fJ per synaptic event and tunable extensive memory time ranging from 76.6 ms to at least thousands of seconds. The ultralow energy consumption is realized by electron trapping and releasing at and near the interface between a-IGZO channel and AlO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> :H dielectric under low voltages. By adjusting the concentration of oxygen vacancy defects in the a-IGZO domain adjacent to the interface by means of changing the growth temperature of the AlOx:H dielectrics, the memory time of the device can be further tuned on a large scale. Device flexibility was also demonstrated by fabricating the synaptic transistors onto polymer substrates at room temperature.

Enhancement of catalytic activity by UV-light irradiation in CeO2 nanocrystals

Ultraviolet (UV) light irradiation on CeO2 nanocrystals catalysts has been observed to largely increase the material’s catalytic activity and reactive surface area. As revealed by x-ray absorption near edge structure (XANES) analysis, the concentration of subvalent Ce3+ ions in the irradiated ceria samples progressively increases with the UV-light exposure time. The increase of Ce3+ concentration as a result of UV irradiation was also confirmed by the UV-vis diffuse reflectance and photoluminescence spectra that indicate substantially increased concentration of oxygen vacancy defects in irradiated samples. First-principle formation-energy calculation for oxygen vacancy defects revealed a valence-hole-dominated mechanism for the irradiation-induced reduction of CeO2 consistent with the experimental results. Based on a Mars-van Krevelen mechanism for ceria catalyzed oxidation processes, as the Ce3+ concentration is increased by UV-light irradiation, an increased number of reactive oxygen atoms will be captured from gas-phase O2 by the surface Ce3+ ions, and therefore leads to the observed catalytic activity enhancement. The unique annealing-free defect engineering method using UV-light irradiation provides an ultraconvenient approach for activity improvement in nanocrystal ceria for a wide variety of catalytic applications.

Effects on structure, surface oxygen defects and humidity performance of Au modified ZnO via hydrothermal method

In this paper, different approaches for the preparation of gold (Au) modified zinc oxide (ZnO) humidity sensors were investigated. Experimental results show that ZnO modified with gold nanoparticles (AuNPs) or chloroauric acid (HAuCl4) enhances the concentration of oxygen vacancy defects on the surface of ZnO, which can improve the sensitivity of such a ZnO humidity sensor. As compared to AuNPs-modified ZnO, the modification of HAuCl4 reduces the size of ZnO and Au particles and exhibits better humidity performance. This is due to that smaller Au particles can further promote dissociation and electrolysis conduction processes so as to enhance the adsorption activity of HAuCl4-modified ZnO nanocomposites. Humidity experiments indicate that HAuCl4-modified ZnO acquires more than 4 orders of magnitude for the impedance changes in RH range from 11% to 95% with high sensitivity, good linearity, small hysteresis (~2.35%) and short response/recovery time (15 s/6 s). The results indicate that smaller Au particle can improve the hysteresis and response of the ZnO humidity sensor. Thus, Au particles with small size are a key parameter for the design of Au modified ZnO humidity sensors with high performance, which has a potential in the fast detection of humidity.

Investigating the impact of gamma radiation on structural and optical properties of Eu3+ doped rare-earth hafnate pyrochlore nanocrystals

A proposed method for treating nuclear high level radioactive (NHLW) is to encapsulate it in a matrix made of complex oxide materials, such as pyrochlores with the general formula A2B2O7. Rare-earth hafnate pyrochlores have the potential to advance the current methods of NHLW disposal due to their robust chemical stability in radioactive environments, their high thermal stability, and their natural structural compatibility with radionuclide species. In this study, RE2Hf2O7:Eu3+ (RE = Y, La, Pr, Gd, Er, Lu) nanoparticles synthesized by a molten salt method were exposed to highly energetic gamma-ray irradiation. La2Hf2O7:Eu3+ and Lu2Hf2O7:Eu3+ underwent the order pyrochlore-disorder fluorite structural phase transition after exposure to gamma-ray irradiation. There was a change in the O-Eu charge transfer band (CTB) position as a function of gamma-ray dose. There was no change in the local symmetry of the Eu3+ dopant in Y2Hf2O7, Gd2Hf2O7 and Lu2Hf2O7, but in La2Hf2O7:Eu3+ gamma-ray dose reduced the symmetry around the Eu3+. For Y2Hf2O7:Eu3+ and La2Hf2O7:Eu3+, the lifetime and emission intensity were found to degrade possibly due to creation of gamma ray-induced defects which provides non-radiative pathways. Regarding Gd2Hf2O7:Eu3+, the concentration of oxygen vacancy defects predominated over other defects leading to enhanced emission and lifetime after gamma-ray irradiation. This study is of utmost importance for the design of a robust rare earth hafnate pyrochlore to be used as a nuclear waste host or gamma-ray based scintillator material.

Tremendous effect of oxygen vacancy defects on the oxidation of arsenite to arsenate on cryptomelane-type manganese oxide

Manganese oxide as a benign and low-cost oxidant has been widely investigated for the oxidation of As(III) to As(V), but its As(III) oxidation rate is easily hindered due to the thermodynamically favorable adsorption of the As(V) species produced and coexisting ions. Herein, we develop a novel strategy of tremendously increasing the As(III) oxidation activity via tuning the concentration of oxygen vacancy defects (OVD) in cryptomelane-type manganese oxides (OMS-2). The result of the batch experiment of the As(III) oxidation on OMS-2 shows that increasing the concentration of oxygen vacancy defects in OMS-2 remarkably increases the specific As(III) oxidation rate from 0.12 to 0.22μmolm−2min−1, and dramatically reduces the unfavorable effect of the As(V) adsorption on the As(III) oxidation activity. The origin of the tremendous effect of OVD in OMS-2 on the As(III) oxidation activity is experimentally and theoretically investigated by the adsorption of the As(III) and As(V) species on OMS-2, the point of zero charge (pHPZC), the evolution of the concentration of Mn2+ ions dissolved in the solution, and density functional theory (DFT) calculations. The results reveal that the presence of OVD in OMS-2 not only makes the adsorption of As(III) on OMS-2 more thermodynamically favorable, but also accelerates the charge transfer from As(III) to Mn atom, thus significantly improving the As(III) oxidation activity.

Anodic luminescence, structural, photoluminescent, and photocatalytic properties of anodic oxide films grown on niobium in phosphoric acid

This article reports on properties of oxide films obtained by anodization of niobium in phosphoric acid before and after the dielectric breakdown. Weak anodic luminescence of barrier oxide films formed during the anodization of niobium is correlated to the existence of morphological defects in the oxide layer. Small sized sparks generated by dielectric breakdown of formed oxide film cause rapid increase of luminescence intensity. The luminescence spectrum of obtained films on niobium under spark discharging is composed of continuum radiation and spectral lines caused by electronic spark discharging transitions in oxygen and hydrogen atoms. Oxide films formed before the breakdown are amorphous, while after the breakdown oxide films are partly crystalline and mainly composed of Nb2O5 hexagonal phase. The photocatalytic activity of obtained oxide films after the breakdown was investigated by monitoring the degradation of methyl orange. Increase of the photocatalytic activity with time is related to an increase of oxygen vacancy defects in oxide films formed during the process. Also, higher concentration of oxygen vacancy defects in oxide films results in higher photoluminescence intensity.

Zirconia films formed by plasma electrolytic oxidation: Photoluminescent and photocatalytic properties

In this paper, we have investigated photoluminescence and photocatalytic properties of zirconia films formed by plasma electrolytic oxidation (PEO) of zirconium foil in 0.1M water solution of citric acid. Zirconia films with diverse morphology and phase structure are formed varying the time of PEO process. Characterization by atomic force microscopy and X-ray diffraction shows that obtained zirconia films mostly consist of monoclinic ZrO2 phase, while corresponding roughness and crystallite size increases with PEO time. Diffuse reflectance spectroscopy has shown that zirconia films have a broad absorption band in the range from 200nm to 330nm, indicating that zirconia films could be used as a photocatalyst using ultraviolet radiation. Strong photoluminescence bands are present in spectra featuring four distinct peaks in the 300–600nm range. The peaks are centered at about 418nm, 440nm, 464nm, and 495nm. Apparent increase of photoluminescence intensity with PEO time is related to an increase of oxygen vacancy defects in zirconia films formed during the process. Also, higher concentration of oxygen vacancy defects in zirconia films result in higher photocatalytic activity.

Zn, Ga, and Ca substituted transition-metal-free oxides with K2NiF4structures

Recently, an oxide with K2NiF4 structure but free of transition metals was developed with the intent of creating a new solid electrolyte material. Here, the original composition, La1.6+xSr0.4−xAl0.4Mg0.6O4+x/2, was modified by replacing Sr, Al, or Mg, with the isovalent substitutes Ca, Ga, or Zn, respectively. The phase stability of these compounds was investigated to determine, specifically, the maximum concentration of oxygen defects allowed by the crystal structure. It was found that a greater concentration of oxygen vacancy defects than interstitials could be created in all of the compositions. In addition, the influence of the cation substitutions on the lattice parameters and the electrical conduction behavior was analyzed. At 650 °C in air, the highest conductivity achieved for B-site substituted compositions was 2.63 × 10−4 S cm−1 in La1.5Sr0.5Al0.4Zn0.6O3.9, much higher than 5.82 × 10−7 S cm−1 in La1.65Sr0.35Al0.4Mg0.6O4.025, while the highest value for A-site substituted compositions was only 7.55 × 10−7 S cm−1 in La1.65Ca0.35Al0.4Mg0.6O4.025. The electrochemical results indicated that A-site substituted compositions, although with low conductivity, were possible oxygen ion conductors, while B-site substituted compositions exhibited either mixed ionic and hole conductivity or pure hole conductivity.

First-principles study on anatase TiO2 (101) surface adsorption of NO

In this paper, the stable structure and the electronic and optical properties of nitric oxide (NO) adsorption on the anatase TiO2 (101) surface are studied using the plane-wave ultrasoft pseudopotential method, which is based on the density functional theory. NO adsorption on the surface is weak when the outermost layer terminates on twofold coordinated oxygen atoms, but it is remarkably enhanced on the surface containing O vacancy defects. The higher the concentration of oxygen vacancy defects, the stronger the adsorption is. The adsorption energies are 3.4528 eV (N end adsorption), 2.6770 eV (O end adsorption), and 4.1437 eV (horizontal adsorption). The adsorption process is exothermic, resulting in a more stable adsorption structure. Furthermore, O vacancy defects on the TiO2 (101) surface significantly contribute to the absorption of visible light in a relatively low-energy region. A new absorption peak in the low-energy region, corresponding to an energy of 0.9 eV, is observed. However, the TiO2 (101) surface structure exhibits weak absorption in the low-energy region of visible light after NO adsorption.

Improvement in Photo-Bias Stability of High-Mobility Indium Zinc Oxide Thin-Film Transistors by Oxygen High-Pressure Annealing

This letter examines the effect of oxygen (O2) high-pressure annealing (HPA) on indium zinc oxide (IZO) thin-film transistors (TFTs) with a high-quality Al2O3 passivation layer. The IZO TFTs anneal under an O2 atmosphere at 9 atm exhibits a high field-effect mobility, low subthreshold gate swing, moderate threshold voltage (Vth), and high ION/OFF ratio of 30.4 cm2/Vs, 0.10 V/decade, 0.79 V, and 108, respectively. In addition, the O2 HPA-treated IZO TFT has superior reliability (ΔVth= -0.5 V) to that of the 0.2-atm-annealed device (ΔVth=-3.7 V) under negative bias illumination stress conditions. This improvement can be attributed to the reduced concentration of oxygen vacancy defects in the IZO channel layer during the O2 HPA treatment.