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Highly conductive two-dimensional electron gas at the interface of Al2O3/SrTiO3
摘要： We create a two-dimensional electron gas at the Al2O3/SrTiO3/LaAlO3 heterostructures using pulsed laser deposition, which exhibits a decreasing sheet resistance with increasing growth temperatures of Al2O3 films. Structural characterizations of films are confirmed by cross-sectional transmission electron microscopy. Compared with these heterostructures with Al2O3 films deposited on pristine SrTiO3 and TiO2-terminated SrTiO3 substrates, the Al2O3/SrTiO3/LaAlO3 heterostructures are more conductive. X-ray photoelectron spectroscopy indicates the formation of oxygen vacancies at the SrTiO3 side of the interface, which results from the redox reactions by reducing SrTiO3 films. Furthermore, the existence of oxygen vacancies on the SrTiO3 side is verified by a blue-light emission.
关键词： Al2O3/SrTiO3/LaAlO3 heterostructures,pulsed laser deposition,oxygen vacancies,two-dimensional electron gas,conductivity
更新于2025-09-23 15:21:21
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Mesoporous black TiO2 array employing sputtered Au cocatalyst exhibiting efficient charge separation and high H2 evolution activity
摘要： The separation and transfer of photogenerated carriers are the key issue in the design of high performance TiO2 photocatalysts. In order to overcome the kinetic limitations and achieve rapid charge transfer, TiO2-related multi-component catalysts have been extensively studied. Among all the TiO2 supports, the impressive black TiO2 (BT) with broad visible light absorption spectrum and oxygen vacancies are preferable, but still suffers from low quantum efficiency. Meanwhile, poor control of cocatalyst placement by conventional loading method can also severely impede photocatalytic efficiency. Herein a fast and simple metal magnetron sputter approach was used to place highly-uniformed Au nanoparticles cocatalyst on the top of the mesoporous TiO2-BT nanotube array fabricated by in situ electrochemical anodization approach on a Ti film. This confined plasmonic photocatalyst with highly uniformly distributed Au cocatalysts exhibited greatly enhanced charge-separation and charge-transfer behavior, and a remarkable 10 times enhancement of the photocatalytic H2 evolution reactivity over conventional TiO2 nanotube. The TiO2-BT-Au electron transfer cascade structure is proposed in which black TiO2 acts as a buffer layer for TiO2 conduction band electrons, allowing efficient photogenerated electrons to be transferred to Au nanoparticles and then into the TiO2 pores that suitable for H2 generation. Since the nanotube walls themselves are curved upwards, the short diffusion length allows electrons to be easily transferred to the cocatalyst, where recombination of photogenerated electron pairs is limited. The metal magnetron sputter technique for noble metal cocatalyst immobilization and the unique TiO2-BT-Au electron-transfer system are promising and can be extended to the design of other supported catalysts.
关键词： Metal magnetron sputter,TiO2 nanotube arrays,Oxygen vacancies,Hydrogen evolution,Au nanoparticle,Black TiO2
更新于2025-09-23 15:21:01
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Resistive switching and electric field control of ferromagnetism in SnO2 films deposited at room temperature
摘要： The SnO2 film deposited at room temperature (RT) on the substrate of Pt/Ti/SiO2/Si is nano-crystallized, which exhibits room temperature ferromagnetism (FM) due to the oxygen vacancies of SnO2 film. The bipolar and multilevel resistive switching (RS) can be observed in the Ta/SnO2/Pt devices, where SnO2 film was deposited at RT. The Ta/SnO2/Pt device has a large ON/OFF ratio (27000) and multilevel RS, which is of great significance for high-density data storage applications. The saturation magnetization of Ta/SnO2/Pt/Ti/SiO2/Si (Ta/SnO2/Pt device) is almost the same as SnO2/Pt/Ti/SiO2/Si, which implies that the influence of Ta top electrodes on the saturation magnetization of Ta/SnO2/Pt/Ti/SiO2/Si is much less. The Ta/SnO2/Pt device shows the non-volatile and reversible saturation magnetization modulation between low resistance state (LRS) and high resistance state (HRS), which results from the formation/rupture of oxygen vacancy filaments. The saturation magnetization at LRS is higher than that at HRS. In addition, the saturation magnetization also enhances with an increase the magnitude of positive DC sweeping voltage. Without DC loop current, the saturation magnetization of Ta/SnO2/Pt increases with an application of positive electric field and drops again with an application of certain negative electric field. The saturation magnetization of Ta/SnO2/Pt can be reversibly modulated in non-volatile by only electric voltage without DC loop current. Such modulation of Ms by only electric voltage without loop DC current is connected with the change in Vo+ density in a certain range of SnO2 films.
关键词： oxygen vacancies,electric field control,room temperature ferromagnetism,resistive switching,SnO2 film
更新于2025-09-23 15:21:01
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Oxygen Vacancies-Enhanced CeO2:Gd Nanoparticles for Sensing Tumor Vascular Microenvironment by Magnetic Resonance Imaging
摘要： The specific characteristics of the tumor vascular microenvironment such as microvascular permeability and water diffusion have been demonstrated to play essential roles in the evaluation of infiltration of tumors. However, at present, there are few contrast agents (CAs) for magnetic resonance imaging (MRI) to enhance the sensitivity to acquire this vital information. Herein, we develop Gd doped (CeO2:Gd) nanoparticles as CA to detect the tumor vascular microenvironment with high sensitivity. The lattice oxygen vacancies on the surface of CeO2:Gd nanoparticles could bind considerable water molecules to improve the r1 value, achieving an excellent dynamic contrast-enhanced perfusion weighted imaging (DCE-PWI) performance for the measurement of microvascular permeability. The water molecules’ diffusion limited by oxygen vacancies of CeO2:Gd nanoparticles further enhance the diffusion-weighted magnetic resonance imaging (DWI) signal in vitro and in vivo. Excitingly, the strategy is not only essential for obtaining tumor vascular microenvironment information but also offers a way for further research of how to design magnetic resonance CAs.
关键词： CeO2:Gd nanoparticles,oxygen vacancies,microvascular,tumor microenvironment,DWI/DCE-PWI
更新于2025-09-23 15:21:01
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In situ fluorine doped ZrO2?x nanotubes for efficient visible light photocatalytic activity
摘要： The F-doped ZrO2?x nanotubes are synthesized by anodic oxidization in a F-containing electrolyte and following a low temperature annealing process. The F-doped ZrO2?x nanotubes exhibit a dramatic increase in visible light absorption and efficient visible light photocatalytic activity which are not possessed to normalized ZrO2. The fluorine in anodic ZrO2 nanotubes plays a vital role in the formation of abundant anion vacancies during the annealing. Combining the doping effect of the residual fluorine element, the band gap of the F-doped ZrO2?x nanotubes reduced from 5.13 to 2.35 eV. Moreover, the transient photocurrent response plots and the photocatalytic experiments reveal the highly effective electrons–holes separation of the F-doped ZrO2?x nanotubes and enhanced visible-light photocatalytic degradation for RhB. The degradation rate of RhB in the presence of the F-doped ZrO2?x nanotubes catalyst has reached up to 83% under 2 h low-power LED light irradiation. In addition, the possible photocatalytic mechanism of the F-doped ZrO2?x nanotubes has been proposed via studying the band structure. It is believed that the F-doped ZrO2?x nanotubes will have a bright future for sustainable energy sources and cleaning environment.
关键词： oxygen vacancies,F-doped ZrO2?x nanotubes,anodic oxidization,visible light photocatalytic activity,band gap narrowing
更新于2025-09-23 15:21:01
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Memristive Behavior Enabled by Amorphousa??Crystalline 2D Oxide Heterostructure
摘要： The emergence of memristive behavior in amorphous–crystalline 2D oxide heterostructures, which are synthesized by atomic layer deposition (ALD) of a few-nanometer amorphous Al2O3 layers onto atomically thin single-crystalline ZnO nanosheets, is demonstrated. The conduction mechanism is identified based on classic oxygen vacancy conductive channels. ZnO nanosheets provide a 2D host for oxygen vacancies, while the amorphous Al2O3 facilitates the generation and stabilization of the oxygen vacancies. The conduction mechanism in the high-resistance state follows Poole–Frenkel emission, and in the low-resistance state is fitted by the Mott–Gurney law. From the slope of the fitting curve, the mobility in the low-resistance state is estimated to be ≈2400 cm2 V?1 s?1, which is the highest value reported in semiconductor oxides. When annealed at high temperature to eliminate oxygen vacancies, Al is doped into the ZnO nanosheet, and the memristive behavior disappears, further confirming the oxygen vacancies as being responsible for the memristive behavior. The 2D heterointerface offers opportunities for new design of high-performance memristor devices.
关键词： zinc oxide,2D heterostructures,memristors,atomic layer deposition,oxygen vacancies
更新于2025-09-23 15:19:57
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High-Performance Silicon Photoanode Enabled by Oxygen Vacancy Modulation on NiOOH Electrocatalyst for Water Oxidation
摘要： Silicon (Si) is an attractive photoanode material for photoelectrochemical (PEC) water splitting. However, Si photoanode is highly challenging due to its poor stability and catalytic inactivity toward oxygen evolution reaction (OER). Integration of highly active electrocatalysts with Si photoanodes has been considered as an effective strategy to improve OER performance through accelerates reaction kinetics and inhibits Si photocorrosion. In this work, ultra-small NiFe nanoparticles are deposited onto n-Si/Ni/NiOOH surface to improve the activity and stability of Si photoanode by engineering the electrocatalyst and Si interface. Ultra-small NiFe can introduce oxygen vacancies via modulating the local electronic structure of Ni hosts in NiOOH electrocatalyst for fast charge separation and transfer. Besides, NiFe nanoparticles also can serve as co-catalyst exposure more active sites and as protection layer prevents Si photocorrosion. The as-prepared n-Si/Ni/NiOOH/NiFe photoanode exhibits excellent OER activity with an onset potential of 1.0 V versus reversible hydrogen electrode (RHE) and a photocurrent density of ～25.2 mA cm-2 at 1.23 V versus RHE. This work provides a promising approach to design high-performance Si photoanodes by surface electrocatalyst engineering.
关键词： photoelectrochemical water splitting,oxygen vacancies,OER activity,NiFe nanoparticles,Silicon photoanode
更新于2025-09-23 15:19:57
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Optical band gap and dielectric abnormality in (Sr, Ce, Zr)TiO3 composite ceramics sintered in nitrogen
摘要： The crystal-chemical structure, band gap-grain structure and dielectric properties of (1?x)SrTiO3-xCe0.95Zr0.05O2 [(Sr,Ce,Zr) TiO3, for x = 0.0, 0.3 and 0.4] ceramics were investigated. Samples with 0.3 ≤ x ≤ 0.4 appeared cubic by X-ray diffraction (XRD), however, splitting of the peaks along with Rietveld refinement indicated tetragonal structure. The change in the band gap energy with Ce(x) have been investigated and are related to variation in the grain size, activation energy and octahedral tilting. The reduction in band gap energy with Ce0.95Zr0.05O2 ions (x = 0.4) is attributed to the widening of conduction band with octahedral tilting. The absence of TO2 (175 cm?1) mode while the existence of TO4 (521.72 cm?1) mode has been considered as sign of relaxor-like-dielectric behavior. The ε′?T curve and the P–E loop analysis confirms that there is no signature of the ferroelectric phase in all samples. Base on the X-ray photoelectrons spectroscopy (XPS) and high temperature ac conductivity analysis, the dielectric anomalies were due to the formation of lattice defects and defect dipoles ( Ti4+ ? e? ? V ?? o ) generated by the Ti3+ ions and ionized oxygen vacancies.
关键词： Crystal-band gap structure,Dielectric properties,Oxygen vacancies
更新于2025-09-19 17:15:36
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Preparation, structural and functional properties of PbTiO3-δ ceramics
摘要： In the present study, oxygen deficient PbTiO3-d ceramics were prepared by solid state-reaction method. The formation of the pure perovskite phase with tetragonal structure was confirmed for the 800°C/2h calcined sample by using X-ray diffraction analysis at room temperature. Energy dispersive X-ray spectroscopy analyses confirm the creation of oxygen vacancies in the system for charge compensations, as demonstrated by the percentage of O atoms of ~53%. The complex impedance data reveals important contributions of the oxygen vacancies to the total dielectric response that are homogeneous distributed within the sample. The room temperature magnetic properties show a weak ferromagnetic character in all the samples that might be attributed to the oxygen vacancies defects and to surface effects.
关键词： oxygen vacancies,EDX spectra,magnetic properties,ceramics,dielectric properties
更新于2025-09-19 17:15:36
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Surface ferromagnetism in ZnO single crystal
摘要： We report on the room temperature surface ferromagnetism in undoped ZnO bulk single crystal. Typical ferromagnetic saturation behavior is clearly demonstrated by magnetization loops, and the saturated magnetization can be manipulated by annealing under argon atmosphere. A strongly correlation, between the saturated magnetization and the concentration of singly occupied oxygen vacancies on the surface of ZnO single crystal, is established by means of the Raman spectra, photoluminescence, electron paramagnetic resonance and atomic force microscope. It is suggested that the observed room temperature ferromagnetism in ZnO single crystal should be attributed to the effect of surface oxygen vacancy defects. This finding may help to get further insight into the ferromagnetic origin in other undoped oxide semiconductor materials.
关键词： D. Annealing,A. ZnO single crystal,C. Oxygen vacancies,B. Surface ferromagnetism
更新于2025-09-19 17:15:36