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Effect of oxygen vacancy on structural, optical, and photocatalytic properties of ceria films grown by magnetron sputtering deposition
摘要： Cerium oxide is of crucial importance for intrinsic redox reaction, which is attributed to the active sites neighboring oxygen vacancies. However, the role of oxygen vacancy (Ov) on the various properties of ceria ?lms remains to be elucidated. Herein, ceria ?lms were deposited by magnetron sputtering and the e?ect of electric current intensity on the creation of Ov was systematically investigated. X-ray photoelectron spectroscopy (XPS) results show that the Ce4+ concentration decreases with the increase of current intensity, which demonstrates that Ov can be created and tuned during ?lm deposition by controlling electric current intensity. The ?lm fabricated by 6 A current intensity has 42% Ce4+, approaching that of rhombohedral-Ce7O12, which is a stabilized bulk phase ceria. X-ray di?raction patterns reveal that 6 A ?lm shows mixed crystalline phases with the majority of peaks very close to rhombohedral-Ce7O12, while 1 A, 2 A, and 4 A ceria ?lms show simple crystalline phase. Raman analysis presents that dioxygen species are heavily absorbed on the surface of 6 A ?lm with more active sites on di?erent crystalline surfaces, which is con?rmed by photocatalytic degradation of Methylene Blue. The calculated bandgap by DFT (density functional theory) + U is consistent with that obtained from Tauc plots curves. This work demonstrates that Ov plays an important role on the properties of the ceria ?lm.
关键词： XPS,Raman,Oxygen vacancy,Magnetron sputtering,Cerium oxide
更新于2025-09-23 15:21:01
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Ferromagnetic Properties of N-Doped and Undoped TiO2 Rutile Single-Crystal Wafers with Addition of Tungsten Trioxide
摘要： In this work, undoped, N-doped, WO3-loaded undoped, and WO3-loaded with N-doped TiO2 rutile single-crystal wafers were fabricated by direct current (DC) magnetron sputtering. N-doping into TiO2 and WO3 loading onto TiO2 surface were used to increase and decrease oxygen vacancies. Various measurements were conducted to analyze the structural and magnetic properties of the samples. X-ray diffraction results showed that the N-doping and WO3 loading did not change the phase of all samples. X-ray photoelectron spectroscopy results revealed that W element loaded onto rutile single-crystal wafers existed in the form of WO3. UV-Vis spectrometer results showed that the absorption edge of WO3-loaded undoped and WO3-loaded with N-doped TiO2 rutile single-crystal wafers had red shift, resulting in a slight decrease in the corresponding band gap. Photoluminescence spectra indicated that oxygen vacancies existed in all samples due to the postannealing atmosphere, and oxygen vacancies density increased with N-doping, while decreasing with WO3 loading onto TiO2 surface. The magnetic properties of the samples were investigated, and the saturation magnetization values were in the order N-doped > WO3-loaded with N-doped > undoped > WO3-loaded undoped rutile single-crystal wafers, which was the same order as the oxygen vacancy densities of these samples. N-doping improved the saturation magnetization values, while WO3-loaded decreased the saturation magnetization values. This paper reveals that the magnetic properties of WO3-loaded with N-doped rutile single-crystal wafers originate from oxygen vacancies.
关键词： rutile TiO2 single-crystal wafers,WO3-loaded,oxygen vacancy,ferromagnetic properties
更新于2025-09-23 15:21:01
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Fluorescent Nanodiamonds || Producing Fluorescent Nanodiamonds
摘要： Natural diamonds in colors are commonly known as fancies, or fancy color diamonds, in gemstone industries. They are rare, beautiful, and some even carry impressive price tags in the jewelry market. By comparison, micro‐ and nanoscale diamond powders are low in price, with or without colors and fluorescent or not. These powders have been used as abrasives for grinding and polishing purposes since ancient time, mainly because of their extraordinary hardness. Little or no attention has been paid over the centuries to other properties of nanodiamonds such as their innate biocompatibility and light‐emitting capability. The invention of fluorescent nanodiamond (FND) in 2005 has revolutionized the field, opening a new area of research and development with diamonds. Experiments with FNDs in the last decade have demonstrated various promising applications of surface‐functionalized FNDs in diversified fields, ranging from physics and chemistry to biology and medicine. It is worthy of noting that as originated from the discovery of Radium by Marie Sk?odowska Curie (Section 3.2), FNDs may very well be called Madame Curie’s gemstones, valued appropriately as a scientist’s best friend.
关键词： fluorescent nanodiamonds,magnetically modulated fluorescence,fluorescence lifetime,size reduction,FND,ion irradiation,H3 centers,nitrogen-vacancy centers,electron irradiation,NV centers
更新于2025-09-23 15:21:01
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Influence of Oxygen Vacancy Behaviors in Cooling Process on Semiconductor Gas Sensors: A Numerical Analysis
摘要： The in?uence of oxygen vacancy behaviors during a cooling process in semiconductor gas sensors is discussed by the numerical analysis method based on the gradient-distributed oxygen vacancy model. A diffusion equation is established to describe the behaviors of oxygen vacancies, which follows the effects of diffusion and exclusion in the cooling process. Numerical analysis is introduced to ?nd the accurate solutions of the diffusion equation. The solutions illustrate the oxygen vacancy distribution pro?les, which are dependent on the cooling rate as well as the temperature interval of the cooling process. The gas-sensing characteristics of reduced resistance and response are calculated. Both of them, together with oxygen vacancy distribution, show the grain size effects and the re-annealing effect. It is found that the properties of gas sensors can be controlled or adjusted by the designed cooling process. The proposed model provides a possibility for sensor characteristics simulations, which may be bene?cial for the design of gas sensors. A quantitative interpretation on the gas-sensing mechanism of semiconductors has been contributed.
关键词： numerical analysis,oxygen vacancy,gas sensor,semiconductor,diffusion equation
更新于2025-09-23 15:21:01
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Strong polarization of individual nuclear spins weakly coupled to nitrogen-vacancy color centers in diamond
摘要： We experimentally demonstrate high degree of polarization of 13C nuclear spins weakly interacting with nitrogen-vacancy (NV) centers in diamond. We combine coherent microwave excitation pulses with optical illumination to provide controlled relaxation and achieve a polarity-tunable, fast nuclear polarization of degree higher than 85% at room temperature for remote 13C nuclear spins exhibiting hyperfine interaction strength with NV centers of the order of 600 kHz. We show with the aid of numerical simulation that the anisotropic hyperfine tensor components naturally provide a route to control spin mixing parameter so that highly efficient nuclear polarization is enabled through careful tuning of nuclear quantization axis by external magnetic field. We further discuss spin dynamics and wide applicability of this method to various target 13C nuclear spins around the NV center electron spin. The proposed control method demonstrates an efficient and versatile route to realize, for example, high-fidelity spin register initialization and quantum metrology using nuclear spin resources in solids.
关键词： nitrogen-vacancy (NV),nitrogen-vacancy center,spin initialization,hyperfine interaction,spin polarization
更新于2025-09-23 15:19:57
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Efficient generation of nitrogen vacancy centers by laser writing close to the diamond surface with a layer of silicon nanoballs
摘要： We proposed a method to effectively fabricate negatively charged nitrogen vacancy (NV?) centers close to the diamond surface by applying femtosecond laser writing technique. With a thick layer of silicon (Si) nanoballs coated, diamond surface was irradiated by high-fluence femtosecond laser pulses. A large number of NV? centers were created around the laser ablation crater area without thermal annealing. The distribution of the NV? centers was expanded to about 50 μm away from the crater center. To demonstrate the function of Si nanoballs, we performed the exactly same laser illumination process on the bare region of the sample surface. In this case, only a few NV? centers were generated around ablation crater. At distance of 32 μm away from crater centers, the NV? density for the case with nanoballs was up to 15.5 times higher compared to the case without nanoballs. Furthermore, we also investigated the influence of laser fluence and pulse number on the NV? density for the case with Si-nanoball layer. Finally, the formation mechanism of NV? centers and the role of Si nanoballs were explained via Coulomb explosion model. The method is demonstrated to be a promising approach to efficiently and rapidly fabricate NV? centers close to the surface of the diamond, which are significant in quantum sensing. Furthermore, the results provide deep insights into complex light-matter interactions.
关键词： single emitters,nitrogen vacancy centers in diamond,silicon nanoballs,femtosecond laser technique
更新于2025-09-23 15:19:57
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Embedding of WO3 nanocrystals with rich oxygen-vacancies in solution processed perovskite film for improved photovoltaic performance
摘要： Seeking strategies of promoting the charge separation and transport of the photo-active layer has been always of significance for the development of high-performance optoelectronic devices. We herein demonstrate an effective way of decorating WO3 nanocrystals in perovskite films for boosted photogenerated carriers transport. The WO3 nanocrystals are generated by a simple technique of pulsed laser irradiation in liquid, then introduced into the perovskite film based on the anti-solvent approach. Such decoration is found helpful for the increase of the short-circuit current density (Jsc) of the device, which leads to the increase of the photoconversion efficiency (PCE) from 17.72% to 19.29%. The improved PCE is mainly due to the decoration of the WO3 at the grain boundaries of perovskite films that facilitates the charge transport between the adjacent grains, which is evidenced by the quenching of the film photoluminescence, shortened carrier lifetime, and increased carrier mobility. We thus believe our study provides an effective way of embedding ordinary metal oxides in perovskite films for enhanced optoelectronic performance.
关键词： Hybrid perovskite solar cell,Pulsed laser irradiation in liquid,WO3 nanocrystals,Charge transport,Oxygen-vacancy
更新于2025-09-23 15:19:57
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Visible Light CO2 Reduction to CH4 Using Hierarchical Yolk@shell TiO2-xHx Modified with Plasmonic Au-Pd Nanoparticles
摘要： Engineering of advanced semiconductor photocatalysts for CO2 conversion to solar fuels is a promising strategy to solve the greenhouse effect and energy crisis. Herein, hierarchical urchin-like yolk@shell TiO2-xHx decorated with core/shell Au-Pd plasmonic nanoparticles (HUY@S-TOH/AuPd) have been prepared using a multi-step process and employed as advanced visible light active photocatalyst in CO2 conversion to CH4 with rate of 47 μmol/gcat.h (up to 126 μmol/gcat after 7h). Different engineered sites in this structure for high gas adsorption, powerful visible light activation and intense electron transportation are responsible for the observed high photocatalytic CO2 conversion efficiency. The present smart designing process can produce a considerable cooperation, not only to disclose the architectural engineering to improvement of photo-conversion efficiency, but also as a viable and appropriate photocatalytic process to sustainable energy production.
关键词： nanoarchitecture,Plasmonic nanoparticles,Photocatalysis,CO2 Conversion,Oxygen vacancy
更新于2025-09-23 15:19:57
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Tapered ultra-high numerical aperture optical fiber tip for nitrogen vacancy ensembles based endoscope in a fluidic environment
摘要： Fixing a diamond containing a high density of Nitrogen-Vacancy (NV) center ensembles on the apex of a multimode optical fiber (MMF) extends the applications of NV-based endoscope sensors. Replacing the normal MMF with a tapered MMF (MMF-taper) has enhanced the fluorescence (FL) collection efficiency from the diamond and achieved a high spatial resolution NV-based endoscope. The MMF-taper’s high FL collection efficiency is the direct result of multiple internal reflections in the tapered region caused by silica, which has a higher refractive index (RI) than the surrounding air. However, for applications involving fluidic environments whose RI is close to or higher than that of the silica, the MMF-taper loses its FL collection significantly. Here, to overcome this challenge and achieve a high spatial resolution NV-based endoscope in a fluidic environment, we conceptually proposed a tapered ultra-high numerical aperture microstructured optical fiber (MOF) whose air capillaries at the tapered end are sealed. Since the end-sealed air capillaries along the tapered MOF (MOF-taper) have isolated the MOF core from the surrounding medium, the core retains its high FL collection and NV excitation efficiency in liquids regardless of their RI values. Replacing the MMF-taper with the MOF-taper will achieve a versatile NV-based endoscope that could potentially find widespread applications in fluidic environments where many biological processes and chemical reactions occur.
关键词： fluidic environment,Nitrogen-Vacancy (NV) center,fluorescence collection,endoscope,optical fiber
更新于2025-09-23 15:19:57
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Recovery kinetics in high temperature annealed AlN heteroepitaxial films
摘要： Based on the experimental dislocation annihilation rates, vacancy core diffusion-controlled dislocation climb was found as a dominant recovery mechanism in high temperature annealing of AlN heteroepitaxial films. Dislocation annihilation mechanisms via dislocation glide (with or without kinks) and vacancy bulk diffusion were found to be less significant. Cross-slip was also ruled out as a possible mechanism as a majority of dislocations in heteroepitaxial AlN films are threading edge dislocations. While dislocation climb through both vacancy bulk and core diffusion could offer a plausible explanation of the recovery process, the activation energy for the vacancy core diffusion-controlled dislocation climb was relatively low (4.3 ± 0.1 eV), as estimated from an Arrhenius plot. The validity of the vacancy core diffusion mechanism was also supported by a large vacancy mean free path (～240 nm), which was comparable to the sample thickness and thus the average dislocation length. Finally, the experimentally observed dislocation density reduction as a function of the annealing temperature and time was in good agreement with the vacancy core diffusion mechanism.
关键词： dislocation annihilation,high temperature annealing,AlN heteroepitaxial films,recovery kinetics,vacancy core diffusion
更新于2025-09-23 15:19:57