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Abnormal permeation behavior of hydrogen through niobium has been investigated in this paper, i.e. the permeation flux saturated with long-term decrease after reaching a maximum. The diffusivity and permeability have been deduced from the decay edge of permeation transient. Three kinds of polycrystalline niobium foils with different annealing temperature have been compared, to verify the effect of defects and grain properties on the permeability and diffusivity. In the temperature range of (773–1023) K, the heat treatment along with the permeation cycles could either reduce or increase the permeability and diffusivity depending sensitively on temperature and showing a temperature threshold around 950 K. The permeation flux is proportional to square root of pressure, revealing that the abnormal permeation was still bulk diffusion-limited. The diffusivity gradually decreased with permeation cycles, and became more and more sensitive to pressure. The niobium foil expanded macroscopically along the gradient of hydrogen concentration, which reveals the strong and unrecoverable lattice distortion in this temperature and pressure range. The X-ray diffraction studies showed that splitting of all the Nb peaks and shifting of Nb-D peaks along with hydrogen loadings. The phase transition was expected to eliminate the lattice strain during hydrogen loading and which in turn acted as a diffusion barrier.

We have theoretically and experimentally studied exciton properties of three normal Nb2O5 polymorphs, including pseudo-hexagonal (TT-), orthorhombic (T-) and monoclinic (H-) phases. The theoretical...

Numerous trap states and low conductivity of compact TiO2 layers are major obstacles for achieving high power conversion efficiency and high-stability perovskite solar cells. Here we report an effe...

The performance of Gamma-ray irradiated silicon devices usually deteriorates due to the total ionizing dose (TID) effect. The common belief is that the TID mainly involves the change of charge states of existing point defects or defect complexes and their subsequent evolution, especially at the widely used amorphous SiO2(a-SiO2)/Si interface, but the TID is not expected to induce new structural defects and change the interface structures. We show in this paper that, contrary to the common belief, gamma-ray irradiation can lead to remarkable structural changes characterized by oxidation and disproportionation of the a-SiO2/Si interface. We present both experimental evidence and theoretical verification of the structural changes. The effective modulation of interfacial structures further suggests the “defective” gamma-ray to be a “constructive” defect engineering method by post-synthesis tuning of the physical performance.

To properly manage nuclear wastes is critical to sustainable utilization of nuclear power and environment health. Here, we show an innovative carbiding strategy for sustainable management of radioactive graphite through digestion of carbon in H

This study conducted a facile solvothermal method along with a dip-coating process to simplify the fabrication and optimize the morphology of Ti/SnO2 and Ti/Sb-SnO2 electrodes. Electrodes a...

Four kinds of well-crystallized tritium permeation barrier coatings, including γ-Al2O3, α-Al2O3, γ-Al2O3/Cr2O3 and α-Al2O3/Cr2O3, were prepared by the metal organic decomposition (MOD) method using a dipping technique. In this study, we concentrated on the preparation and properties of α-Al2O3 and α-Al2O3/Cr2O3 double-layer coatings. The results showed that the α-Al2O3 coating exhibited a pure phase structure, which was entirely and directly transformed from the γ-Al2O3 at an annealing temperature of 1000 °C, and no obvious substrate oxides were formed. An unannealed Cr2O3 MOD layer with a thickness of 0.8 μm featured higher crystallization and was taken as a buffer layer. However, the template effect of Cr2O3 was not obvious because the formation temperature of the α-Al2O3 did not decrease. The corrosion resistance (1.068 × 10−7 A/cm2) and nanohardness (18.49 GPa) of the α-Al2O3/Cr2O3 double-layer coating improved compared to those of γ-Al2O3, α-Al2O3, and γ-Al2O3/Cr2O3 coatings. In contrast, the deuterium permeation test showed that the α-Al2O3 MOD coating had the lowest deuterium ion current at temperatures of 400 ˜ 600 °C of the films considered in this study, demonstrating better resistance to deuterium permeation. Relevant mechanisms and explanations are discussed in detail.

Charge-transfer (CT) is an important enhancement mechanism in the field of surface-enhanced Raman scattering (SERS) that typically increases the Raman intensity of molecules by as much as 10-100 times. Herein, a low-cost Ag2O aggregates substrate was prepared via a facile chemical precipitation method, and the calculated CT-based enhancement factor of the uranyl ions adsorbed on it reached as high as 105, a metal-comparable value. The efficient photoinduced CT process from the valence band of Ag2O to the LUMO of uranyl ions under appropriate excitation sources resulted in the repulsion of the axial oxygen atoms of the O U O bond, which enhanced its polarizability, creating a more intense Raman mode. To the best of our knowledge, this study firstly reports such a strong photoinduced CT enhancement of uranyl ions, with concentrations of 10−8 mol L−1 or lower being detected using this Ag2O substrate. Most importantly, this research has shown that the photoinduced CT enhancement also contributes to the SERS of uranyl ions on pure Ag substrates which have often been ascribed to the electromagnetic enhancement in previous studies. In addition, Ag2O can be used to selectively detect uranyl ions without interference from many other molecules or ions because of the energy matching rule of the photoinduced CT process, which was readily available for uranyl detection in the environmental aqueous solution.

The synergy between catalysis and plasma chemistry often enhances the yield of chemical reactions in plasma-driven reactors. In the case of CO2 splitting into CO and O2, no positive synergistic effect was observed in earlier studies with plasma reactors, except for dielectric barrier discharges, that do not have a high yield and a high efficiency. Here, we demonstrate that introducing metal meshes into radio frequency-driven plasma reactors increases the relative reaction yield by 20%-50%, while supported metal oxide catalysts in the same setups have no effect. We attribute this to the double role of the metal mesh, which acts both as a catalyst for direct CO2 dissociation as well as for oxygen recombination.

Numerous trap states and low conductivity of compact TiO

Surface modification of tungsten due to the cooling species nitrogen seeded in the divertor region, i.e., by nitrogen ion implantation or re-deposition, is considered to affect the permeation behavior of H isotopes. This work focuses on the effect of nitrogen ion implantation into tungsten (W-N) on the deuterium gas-driven permeation behavior. For comparison, both permeation in tungsten implanted with W ion (W-W) and without implantation (pristine W) are studied. These three samples were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photo-electron spectroscopy (XPS). The SEM results revealed that the W-W sample has various voids on the surface, and the W-N sample has a rough surface with pretty fine microstructures. These are different from the pristine W sample with a smooth and compact surface. The XRD patterns show the disappearance of crystallinity on both W-W and W-N sample surfaces. It indicates that the ion implantation process results in an almost complete conversion from crystalline to amorphous in the sample surfaces. The sputter-depth profiling XPS spectra show that the implanted nitrogen prefers to form a 140 nm thick tungsten nitride layer. In permeation experiments, it was found that the D permeability is temperature dependent. Interestingly, the W-N sample presented a lower D permeability than the W-W sample, but higher than the pristine W sample. Such behavior implies that tungsten nitride acts as a permeation barrier, while defects created by ions implantation can promote permeability. The possible permeation mechanism correlated with sample surface composition and microstructure is consequently discussed in this work.

We report a self-standing NiFe layered double hydroxide/nitrogen doped graphite foam (NiFe LDH/NGF) electrode for the oxygen evolution reaction (OER) prepared via a facile electrodeposition method. The electrode showed high electrocatalytic activity towards OER, exhibiting a low onset overpotential of 0.239 V and a small Tafel slope of 57.9 mV dec−1 in basic electrolytes, as well as a good stability during the long-term cycling test. The outstanding electrocatalytic activity is mainly attributed to the synergy between the abundant catalytically active sites through good dispersion of NiFe LDH across NGF and fluent electron transport arising from NGF.

This paper reports a plasma mediated nitriding method to prepare transition metal nitrides (TMNs) for efficient oxygen evolution reaction (OER). Nickel foam (NF) dipped into FeCl3 solution is treated with N2 plasma, and a composite structure of NiFeN and Ni2Fe2N is obtained with nitride nanoparticles uniformly distributed on the surface of the nickel foam (donated as NiFeNx/NF). The prepared NiFeNx/NF shows a low overpotential of 286 mV at 10 mA cm−2 and 330 mV at 100 mA cm−2, which is lower than RuO2 loaded on NF (0.5 mg cm−2). There is no obvious increase in the overpotential after 20 h stability test. The excellent performance of NiFeNx/NF is attributed to the synergistic effect of NiFe bimetallic nitrides.

A new type plasma generator based on hollow cathode discharge has been designed and installed on the linear magnetic device, for the researches on helium and hydrogen plasma interaction with plasma facing components. The hollow cathode plasmas for argon/helium/hydrogen discharges were realized. The performances of the hollow cathode source were analyzed based on argon discharges, such as the electron temperature and electron density with respect to radial position, gas flow rate and magnetic field. The plasma parameters have been measured with Langmuir probe on the linear magnetic device. It shown that this hollow cathode source could provide ion flux density up to 10 22 m −2 s −1 with high gas efficiency and energy efficiency. Typically, for argon plasmas, it could reach an electron density of 2 × 10 19 m −3 and an electron temperature of 3.5 eV in core region, with a power dissipation of 1 kW and gas flow rate of 0.25 standard liters per minute. The plasma beam with a radius of 2.5 cm was confined very well with a magnetic field around 0.05 T. By the virtue of these properties, this plasma generator is a good candidate for the fusion related plasma-surface-interaction researches.

Laser cladding provides a widely applicable method for the preparation of metallic glass matrix composite (MGMC) coatings, where the mechanical property and the corrosion resistance can be tailored by the in-suit precipitated crystalline phases. Thus, the investigation on the microstructure evolution and corrosion mechanism of MGMC coating to achieve superior performance is of great importance. In the presented work, Zr50.7Cu28Ni9Al12.3 MGMC coatings, which are constituted by Zr&Cu enriched dendrites and Ni&Al enriched metallic glass (MG) matrix, were prepared by laser cladding. The effect of the laser power on the microstructure and the corrosion property of the MGMC coatings was investigated. It has been found that the MG content increases and the size of the dendrites decreases with decreasing laser power. Increasing MG content in the coating can decrease the self-etching current density due to the rapid surface oxidation, and decrease the open-circuit-potential due to the higher chemical activity of MG. Besides that, a probable corrosion mechanism of the Zr-Cu-Ni-Al MGMC coating in the NaCl solution was proposed. The segregation of Cu could be the main inducement for pitting. The increasing MG phase content can suppress the segregation of Cu and therefore increase the pitting corrosion resistance of the coating.

Thermal desorption spectroscopy (TDS) measurement of tungsten (W) exposed to tritium (T2) under a series of conditions was conducted, and the peak of T2 desorption reached as high as 895 K at the heating rate of 20 K/min. The detrapping energy of T in W was then determined experimentally to be 2.18 ± 0.22 eV, suggesting that T was mainly trapped by vacancy clusters which may be formed during manufacturing and enhanced by charged T atoms.

The microstructure of tungsten, a primary candidate for the first wall of Tokamak devices, affects the retention and permeation of hydrogen isotopes. These have a close connection to the tritium inventory. In this work, the tungsten microstructure was tuned by annealing and intense 15,700 displacements per atom (dpa) keV-W-self-ion implantation. The samples were characterized by x-ray diffraction (XRD) and scanning electron microscopy (SEM). The results reveal that the annealing treatment has little influence on the crystallite size but decreases the number of defects such as vacancies, which relates to the bulk microstructure. Moreover, ion implantation changes the sample surface from a smooth quasi-mirror to a grey morphology with various voids. The deuterium retention is suppressed by the decrease of bulk defects due to annealing, but does not present a saturation with the displacement damage increase. It is interesting to note that in permeation, the rate limiting step is bulk diffusion while the deuterium permeability is enhanced for samples with a surface modification. The possible permeation mechanisms and their relation with the sample microstructure are discussed in this work.

TiO2 powder was modified by the afterglow of plasma of pure N2 or H2, and mixed N2 + H2 gas. The ion species in plasma afterglow were measured by an ion-energy analyzer. It is found that the main ion is N2+ in N2 afterglow and the yield is changed to NH4+ with a six times higher concentration, when 10% H2 was input. The modified TiO2 shows significant differences of microstructure and optical properties depending on the plasma gas used. This work enables one to find a correlation between active species in the plasma afterglow and TiO2 microstructure/optical properties.

Defects engineering is a promising and versatile method to improve solar-light-driven photocatalytic activity of photocatalysts. Mesoporous materials possess a versatile defective structure as well as a large exposed surface, which are particularly important in photocatalysis. Still, the underlying impact of defects in mesoporous photocatalysts remains elusive, as limited studies detail the exact atomistic surface structure and how the concentration of defects is directly related to the photocatalytic activity. Here, we successfully synthesized ultra-thin mesoporous-structured anatase TiO2 and changed the overall concentration of defects by improving the crystallinity. Without Pt deposition, the highest H2 production of ~3.507 mmol h−1g−1 was obtained under simulated solar light. We interrogated the atomic structure using scanning transmission electron microscopy, which directly revealed the coexistence of the lattice distortions and point defects in the mesoporous TiO2. Improving the crystallinity in TiO2 reduced these defects and slightly enhanced the H2 yield from water splitting, while the charge-transfer resistance increased. Further introduction of Ti3+ atomic defects decreased the charge-transfer resistance and facilitated the separation of electron-hole pairs in the photocatalysis. This study offers inspiration for designing efficient photocatalysts and provides valuable insights towards defect engineering in photocatalysts.

International audience; Rare earth (RE) ions doped in Si-based materials, compatible with Si technology, are promising compounds with regards to optical communication and energy conversion. In this article, we show the emission properties of Nd-doped Si-rich Si oxynitride (Nd-SRSON) films, and their dependence on the dangling bond density and the nature of the sensitizer. These films were prepared by reactive magnetron sputtering and post-annealing. The film composition, microstructure, and emission properties were investigated as a function of deposition parameters and annealing temperatures. Both Fourier transform infrared (FTIR) and ellipsometry spectroscopy measurements have confirmed that the sample composition (Si/N ratio) can be carefully tuned by varying the ratio of reactive nitrogen to argon in the sputtering plasma. Moreover, FTIR and x-ray photoelectron spectroscopy measurements demonstrate the existence of both nitrogen and oxygen dangling bonds (N· and O·) in as-deposited samples. These dangling bonds were passivated during annealing. Under non-resonant excitation at 488 nm, the films exhibit a significant photoluminescence (PL) signal from Nd3+ ions demonstrating the occurrence of an effective sensitization of Nd$^{3+}$ ions in the host matrix. Both PL excitation and ellipsometry results (the energy band gap from new amorphous model) exclude the sensitization by an exciton with energy over the band gap, whereas the presence of Si agglomerates, at the atomic scale, have been identified as effective sensitizers towards Nd$^{3+}$ ions. This work not only provides knowledge to optimize Si-based materials for favorable emission properties, but also, presents a universal methodology to investigate the nature of sensitizers for RE emitters. This allows one to find correlations between composition, microstructure, and emission properties.

Tritium permeation barrier (TPB) is a promising solution to reduce fuel loss and environmental contamination caused by tritium permeation in fusion reactor. A multilayered Al2O3/Y2O3 TPB coating containing a total of 10 nanolayers was prepared by magnetron sputtering technology. The Auger electron spectroscopy, field emission scanning electron microscopy, and X-ray diffraction demonstrated the formation of the multilayer structure with crystalline Y2O3 and amorphous Al2O3 sublayers. Further, the effect of Ar/O2 flow ratio (?) during Al2O3 sublayer deposition on the phase structure, surface morphology, nano-hardness, corrosion resistance, He ion irradiation resistance and deuterium permeation behavior of the multilayered coating was explored systematically. The results showed that the Al2O3 sublayer with lower ? benefits the (222) preferred orientation of Y2O3 sublayer. The nano-hardness of Al2O3/Y2O3 coating gradually increased with the decrease of ?. The coating with ? =1:1 performs the best corrosion resistance and He ion irradiation tolerance. The deuterium permeation test shows a lower deuterium ion current of the Al2O3/Y2O3 coating compared to their single-layer counterparts, where the deuterium gas-driven permeation process was controlled by a combination regime of recombination and diffusion. Our study could provide a potential coating material for the TPB design of fusion reactor.

One-dimensional tubes and rough-sphere particles of Fe-Co Prussian blue analogue with different structures were prepared from the cationic surfactant cetyltrimethyl ammonium bromide in an ethanol and water solution. The products were characterized by x-ray diffraction, energy-dispersive x-ray spectroscopy, infrared spectrum, transmission electron microscopy, field emission scanning electron microscopy, and vector network analysis. The experimental results clearly show that the reaction temperature is the dominant processing factor in controlling the morphologies of the resulting products. These compounds mainly consist of an Fe2+-CN-Co2+ entity, but some of them would be converted into Fe2+-CN-Co3+ with the addition of RbCl. The real parts of permeability (ϵ′) of these samples with different structures are in the range from 2.4 to 3.9. Furthermore, the synthesis mechanism and the influencing factors on dielectric properties are discussed.

The structure-dependent magnetic properties of cobalt-iron Prussian blue analogues (PBAs) with different morphologies synthesized in microemulsion were systematically explored by the characterization of XRD, IR, SQUID techniques, etc. And it was observed that both the w (water-to-surfactant molar ratio) and reactant concentrations had a significant effect on the morphologies and structures of the products. The magnetic nanoparticles of cobalt-iron Prussian blue analogues (PBAs) with novel morphologies, e.g., hollow particles in the form of FeIII-CN-CoII, FeII-CN-Co,II and FeII-CN-CoIII entity were prepared. Our results indicated that the nanomaterials possessed distinct magnetic properties in that their coercivities were intensely dependent on sample structure, which was determined by cobalt-to-iron ratios and potassium contents.

Mn-Zn ferrite nanoparticles about 15 nm with various amounts of Co substituting for Mn were synthesized in microemulsion at 50°C. The samples were characterized by energy-dispersive X-ray spectroscopy, X-ray diffraction, scanning electron microscope, and vibrating sample magnetometer. The experimental results indicate the formula for all samples can be derived as CoxMn1−xZn0.5Fe1.504, and the presence of single-phase spinel ferrite is in all the samples without annealing at high temperature. The saturation magnetization increases with Co content (x = 0 to 0.31) followed by a decrease with further enhancement of Co (x = 0.39 and 0.48). Compared with that of Mn-Zn ferrite annealed at 600°C for 4 h, the saturation magnetization of the synthesis sample without annealing is larger, but the coercivity force is smaller.

We synthesized a series of cobalt-iron Prussian blue analogues in the form of nanocubes with which we tuned the amount of Cesium cation in the tetrahedral sites of the structure and varied nature of the alkali cation in the compound adopting a single microemulsion technique. Structure and morphology of the compound had been investigated by combining energy-dispersive X-ray spectroscopy (EDS), inductively coupled plasma (ICP), thermo-gravimetry analysis (TGA), infrared spectroscopy (IR), powder X-ray diffraction (XRD) and Transmission electron microscopy experiments (TEM). To directly determine the coercivity, remanence and Curie temperature, superconducting quantum interference device magnetometer (SQUID) was performed. Our investigation suggests that the amount and nature of the alkali cation are critical parameters for understanding the magnetic properties of the nanoparticles.

We report a successful synthesis of nanostructure phase-pure TiO2(B) by one-step hydrothermal process. The process was performed in a 10 mL ethanol and 30 mL glycol solution at 200°C for 24 h using 0.3 mL titanium tetrachloride. The prepared materials were characterized by TEM and XRD, which provide evidence that nanostructure phase-pure TiO2(B) can be directly produced without ion exchange or further thermal treatment. Furthermore, the morphology and the phase of resultant materials can be controlled easily through changing reaction conditions.

International audience; This paper aims to study the excitation mechanism of Nd3+ ions in Nd-SiOx (x 1000 °C), the visible emission emanates from recombination of excitons in Si nanoclusters. When doped with Nd3+ ions, the visible PL behaviors of Nd-SiOx films follow the same trends. Nd3+ PL was investigated and its decay rate was analyzed in detail. Depending on the annealing conditions, two types of sensitizers have been evidenced. Finally, maximum Nd3+ PL emission has been achieved at around 750 °C when the number of Nd3+ ions excited by the two types of sensitizers reaches a maximum.

International audience; Planar waveguides made of Nd3+-doped silicon rich silicon oxide (SRSO) and silicon rich silicon nitride (SRSN) have been fabricated by reactive magnetron sputtering and characterized with special emphasis on the comparison of the guided photoluminescence (PL) properties of these two matrices. Guided fluorescence excited by top surface pumping at 488 nm on planar waveguides was measured as a function of the distance between the excitation area and the output of the waveguide, as well as a function of the pump power density. The PL intensity increased linearly with pump power without any saturation even at high power. The linear intensity increase of the Nd3+ guided PL under a non-resonant excitation (488 nm) confirms the efficient coupling between either Si-np and rare-earth ions for SRSO or radiative defects and rare earth ions for SRSN. The guided fluorescences at 945 and 1100 nm were observed until 4 mm and 8 mm of the output of the waveguide for Nd3+ doped SRSO and SRSN waveguides, respectively. The guided fluorescence decays of Nd3+-doped-SRSO and -SRSN planar waveguides have been measured and found equal to 97 μs ±7 and 5 μs ± 2, respectively. These results show notably that the Nd3+-doped silicon rich silicon oxide is a very promising candidate on the way to achieve a laser cavity at 1.06 μm.