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In-Situ Synthesis of Nb2O5/g-C3N4 Heterostructures as Highly Efficient Photocatalysts for Molecular H2 Evolution under Solar Illumination
摘要： This work focuses on the synthesis of heterostructures with compatible band positions and a favourable surface area for the efficient photocatalytic production of molecular hydrogen (H2). In particular, 3‐dimensional Nb2O5/g‐C3N4 heterostructures with suitable band positions and high surface area have been synthesized employing a hydrothermal method. The combination of a Nb2O5 with a low charge carrier recombination rate and a g‐C3N4 exhibiting high visible light absorption resulted in remarkable photocatalytic activity under simulated solar irradiation in the presence of various hole scavengers (triethanolamine (TEOA) and methanol). The following aspects of the novel material have been studied systematically: the influence of different molar ratios of Nb2O5 to g‐C3N4 on the heterostructure properties, the role of the employed hole scavengers, and the impact of the co‐catalyst and the charge carrier densities affecting the band alignment. The separation/transfer efficiency of the photogenerated electron‐hole pairs is found to increase significantly as compared to that of pure Nb2O5 and g‐C3N4, respectively, with the highest molecular H2 production of 110 mmol/g·h being obtained for 10 wt % of g‐C3N4 over Nb2O5 as compared with that of g‐C3N4 (33.46 mmol/g·h) and Nb2O5 (41.20 mmol/g·h). This enhanced photocatalytic activity is attributed to a sufficient interfacial interaction thus favouring the fast photogeneration of electron‐hole pairs at the Nb2O5/g‐C3N4 interface through a direct Z‐scheme.
关键词： Z‐Scheme,H2 evolution,hydrothermal synthesis,graphitic carbon nitride,photocatalysis,heterostructures,Niobium(V) oxide
更新于2025-11-14 17:03:37
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On-chip sensor solution for hydrogen gas detection with the anodic niobium-oxide nanorod arrays
摘要： Two types of anodic niobium-oxide nanofilms were synthesized via anodization of an Al/Nb bilayer sputter-deposited onto a SiO2-coated Si wafer. Type I nanofilm was composed of a 200 nm thick NbO2 layer holding the upright-standing 650 nm long, 50 nm wide, and 70 nm spaced Nb2O5 nanorods, of 7·109 cm?2 density, whereas the Type II nanofilm had similarly long but bigger Nb2O5 nanorods, 100 nm wide, 220 nm spaced, and of 8·108 cm?2 density, aligned directly on a niobium metal without any buffering oxide layer, which was achieved for the first time. Each film was then incorporated in an advanced 3-D architecture and multilayer layout on a silicon chip comprising 33 microsensors, with variable sizes and tuned electrical characteristics, by combining the high-temperature vacuum or air annealing, sputter-deposition, and lift-off photolithography to form Pt/NiCr top electrodes and a multifunctional SiO2 interlayer, chemical etching, laser dicing, and ultrasonic wire-bonding. The proposed on-chip sensor solution allowed for a sensitive, fast, and highly selective (toward NH3 and CH4) detection of hydrogen gas. Comprehensive gas sensing tests performed for Type II nanofilm ultimately confirmed the presence of a Schottky-type sensing mechanism, the contribution, however, being substantially weaker than that due to reactions over the surface of the oxide nanorods, especially when the rods show a transition from fully to partially depleted states when interacting with H2 gas. The film formation and chip fabrication technologies may be transferable to other PAA-assisted 1-dimensional metal-oxide nanomaterials suitable for on-chip gas sensing.
关键词： niobium oxide nanorods,anodic alumina,hydrogen,Schottky barrier,anodizing,on-chip sensor
更新于2025-09-23 15:23:52
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Transparent Electrodes Consisting of a Surface-Treated Buffer Layer Based on Tungsten Oxide for Semitransparent Perovskite Solar Cells and Four-Terminal Tandem Applications
摘要： For semitransparent devices with n-i-p structures, a metal oxide buffer material is commonly used to protect the organic hole transporting layer from damage due to sputtering of the transparent conducting oxide. Here, a surface treatment approach is addressed for tungsten oxide-based transparent electrodes through slight modification of the tungsten oxide surface with niobium oxide. Incorporation of this transparent electrode technique to the protective buffer layer significantly recovers the fill factor from 70.4% to 80.3%, approaching fill factor values of conventional opaque devices, which results in power conversion efficiencies over 18% for the semitransparent perovskite solar cells. Application of this approach to a four-terminal tandem configuration with a silicon bottom cell is demonstrated.
关键词： semitransparent solar cells,perovskite-silicon tandem,niobium oxide,tungsten oxide,perovskite solar cells
更新于2025-09-23 15:21:01
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Crystalline structure, electronic and lattice-dynamics properties of NbTe2
摘要： Layered-structure materials are currently relevant given their quasi-2D nature. Knowledge of their physical properties is currently of major interest. Niobium ditelluride possesses a monoclinic layered-structure with a distortion in the tellurium planes. This structural complexity has hindered the determination of its fundamental physical properties. In this work, NbTe2 crystals were used to elucidate its structural, compositional, electronic and vibrational properties. These findings have been compared with calculations based on density functional theory. The chemical composition and elemental distribution at the nanoscale were obtained through atom probe tomography. Ultraviolet photoelectron spectroscopy allowed the first determination of the work function of NbTe2. Its high value, 5.32 eV, and chemical stability allow foreseeing applications such as contact in optoelectronics. Raman spectra were obtained using different excitation laser lines: 488, 633, and 785 nm. The vibrational frequencies were in agreement with those determined through density functional theory. It was possible to detect a theoretically-predicted, low-frequency, low-intensity Raman active mode not previously observed. The dispersion curves and electronic band structure were calculated, along with their corresponding density of states. The electrical properties, as well as a pseudo-gap in the density of states around the Fermi energy are characteristics proper of a semi metal.
关键词： Electronic band structure,Ultraviolet photoelectron spectroscopy,Density functional theory,Atom probe tomography,Niobium ditelluride,Layered-structure materials,Raman spectra,Density of states,Semimetal
更新于2025-09-23 15:21:01
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One-Step Plasma Synthesis of Nb <sub/>2</sub> O <sub/>5</sub> Nanofibers and their Enhanced Photocatalytic activity
摘要： Fiberform nanostructured niobium (Nb) was fabricated by one step helium (He) plasma irradiation. He ion implantation formed He nano-bubbles on a Nb plate and led to formation of protrusions while migrating in Nb matrix; fiberform nanostructures (FN) were grown when the fluence became high (> 1026 m?2). The necessary conditions for the formation of Nb FN were revealed to be the surface temperature range of 900–1100 K and the incident ion energy higher than 70 eV. The sample was oxidized at 573–773 K in an air atmosphere, and Pt nanoparticles were photo-deposited on the Nb2O5 samples. The surface was analyzed by scanning electron microscope, transmission electron microscope, x-ray photoelectron spectroscopy, and ultraviolet-visible spectrophotometry. Photocatalytic activity of the fabricated materials was studied using methylene blue (MB) decolorization process. An enhanced photocatalytic performance was identified on FN Nb2O5 substrate with Pt deposition.
关键词： helium bubble,photocatalysis,niobium oxide,plasmas
更新于2025-09-23 15:21:01
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Multifunctional behavior of Ca-doped niobium-based double perovskite for photovoltaic/solar cell devices
摘要： Smart materials of oxide ceramics are usually in the form of single- or polycrystalline. The present ceramic belongs to the polycrystalline compound of Pb1.5Ca0.5BiNbO6 which has a double perovskite structure with the general form of A1.5A′0.5BB′O6. For synthesis and characterization of the sample, a solid solution casting method, X-ray diffraction, scanning electron micrography, Infra-red spectroscopy, etc., have been utilized. Different characterization reveals that the material has a higher value of room-temperature dielectric constant remnant polarization useful for energy storage devices. Optical equities of the ceramic were further analysed by UV–Vis and PL spectroscopy analysis which reveals that the material can be useful for energy harvesting devices like photovoltaic/solar cells. The estimated thermistor parameter suggests that the material can also be useful for thermal sensor devices.
关键词： Photovoltaic/solar cell devices,Energy storage devices,Ca-doped niobium-based double perovskite,Multifunctional behavior,Thermal sensor devices
更新于2025-09-23 15:19:57
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Study on mechanical and metallurgical properties of fiber laser welded Nb-1% Zr-0.1% C alloy
摘要： Laser welding of Nb-1% Zr-0.1% C was attempted in butt-welding configuration using top and bottom sided inert gas shielding. The precautionary measure during welding was to limit the reactivity of niobium alloy in ambient atmosphere. The ranges of input parameters, that is, laser power (P), welding speed (V) and beam diameter (D) for full penetration welding were attempted by carrying out bead-on-plate (BOP) experiments. The selection of the combination of process parameters was such that the formed weld area could be minimized without hampering the depth of penetration. Bead-geometry, hardness and tensile strength were quantified to study the influence of input process parameters during laser welding. Base metal had an average hardness of 108 VHN and the average hardness of fusion zone (FZ) was found to lie between 278 and 546 VHN. The steeper increment in microhardness value of the FZ could be due to the grain refinement, dissolution of precipitates and formation of brittle intermetallic phases of carbide and oxides, which were evident by the result of energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) phase analysis. The weld joint that failed in the weld zone exhibited the brittle failure, and ductile mode was achieved in the joint, where failure occurs at base metal. The range of elongation in laser welded joints varied in between 1.97 and 5.73 mm. The reduction of tensile strength and ductility of the joints could be due to marginal enhancement of microhardness and increment of brittle phase density in fusion zone, as were evident from XRD phase analysis. The main focus of the present work was intended towards the establishment of laser welding as an alternative technique for fabrication of reactive niobium alloy in ambient atmosphere.
关键词： Cooling rate,Laser welding,Grain refinement,Niobium alloy,Mechanical properties,Nb-1% Zr-0.1% C
更新于2025-09-23 15:19:57
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Interaction between CO2 and NbO2+: Infrared photodissociation spectroscopic and theoretical study
摘要： The mass-selected infrared photodissociation (IRPD) spectroscopy combined with quantum chemical calculations was utilized to study the interactions between niobium dioxide cation and carbon dioxide molecules. Experimental and calculated results indicate that the CO2 molecules are weakly bound to the NbO2+ cation in an end-on configuration via a charge-quadrupole electrostatic interaction. For n ≥ 6, CO2 molecules in the second shell no longer have contribution to CO2 activation. The similarity of experimental spectra for n ≥ 7 also indicates that ion cores of NbO2+(CO2)n cluster have not changed. Compared with the congeneric YO+ complexes (Phys. Chem. Chem. Phys., 2018, 20, 19314–19320), NbO2+ is found to be thermodynamically and kinetically more difficult to react with CO2.
关键词： Niobium dioxide cation,Infrared photodissociation spectroscopy,Structure,Quantum chemical calculation,Carbon dioxide
更新于2025-09-23 15:19:57
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Study on laser annealing of niobium films deposited on copper for RF superconducting cavities
摘要： Niobium sputtered copper cavities were proposed as a kind of promising next generation superconducting cavities, but were still challenged by the Q-slope effect under high acceleration gradients. Current solutions focus on improving the film quality to make it more bulk-like, for which a higher substrate temperature is required. However, due to the limitation of the melting point of the copper substrate, both the deposition process and the post-annealing process cannot be performed at a high temperature. The laser annealing mentioned in this paper uses nanosecond pulsed laser as the heat source, and the local temperature field generated within the thickness scale of the niobium film can anneal the film without affecting copper substrate. Laser annealing system has been set up in Peking University, and experiments with niobium thin film on copper (Nb/Cu) samples have been carried out. Superconducting performance, surface topography and other properties of Nb/Cu samples before and after annealing are compared. Recrystallization of niobium films happened and various factors that may cause Q-slope have been suppressed according to the results. All these indicate the effectiveness of laser annealing and the possibility of being used in niobium sputtered copper cavities in the future.
关键词： Surface topography,Surface roughness,Recrystallization,Niobium thin film,Superconducting cavity,Laser annealing
更新于2025-09-23 15:19:57
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Preparation of SiC Powders by Carbonthemal Reduction Method at Low Temperature
摘要： The stable slurry was prepared by ball-milling with a certain proportion of silica fume as silicon source, glucose as carbon source and metal niobium (Nb) as additives mixed with alcohol water. After the slurry was dried and pulverized, put the powder into a tubular furnace heated to 650℃ for 2h under nitrogen atmosphere to prepare precursor, the heating rate was 5℃ /min. Treated the precursor under vacuum by carbothermal reduction method to prepare silicon carbide (SiC) powder. The effect of temperature and additive content on the morphology of synthesised silicon carbide and the impurity removal order on product purity were explored. After firing at 1300℃, 1400℃, 1500℃ for 2 h, the 3C-SiC powders are detected, and as the temperature increased, the crystallinity of the product become better. When the content of the additive is 1% of the quality of the silica fume, the particle size of the silicon carbide synthesized at the temperature of 1500℃ is even and the dispersion is better. As for the impurity removal order, removed SiO2 first, then removed C can effectively remove the impurities in the product.
关键词： metal niobium,carbothermal reduction,silica fume,glucose,SiC powders,low temperature
更新于2025-09-23 15:19:57