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The modulation of the terahertz (THz) wave is fundamental for its applications in next-generation communications, biological imaging, sensing, and so forth. Searching for higher efficient modulation is still in progress, although plenty of materials have been explored for tuning THz wave. In this work, optical-transparent self-assembled MXene films are used to modulate the THz reflection at the SiO2/MXene/air interface based on the impedance matching mechanism. By adjusting the number of stacked MXene layers/concentrations of MXene dispersions, the sheet conductivity of the MXene films will be changed so that the impedance at the SiO2/MXene/air interface can be tuned and lead to a giant modulation of THz reflection. Particularly, we demonstrate that the MXene films have highly efficient THz modulation from antireflection to reflection-enhancing with a relative reflection of 27% and 406%, respectively. This work provides a new pathway for developing the MXene films with the combination of optical-transparency and high smart THz reflection characteristics, and the films can be applied for THz antireflection or reflection-enhancing.

The equiaxed solidification of Al–20Cu alloy under different cooling rates was investigated using in-situ synchrotron X-ray radiography. The results showed that mean grain size increases rapidly at...

Although coupled plasmonic systems have been extensively studied in the past decades, their theoretical understanding is still far from satisfactory. Here, based on experimental and numerical studies on a series of symmetry-broken nano-patch plasmonic resonators, we found that Fano’s formula, widely used in modeling such systems previously, works well for one polarization but completely fails for another polarization. In contrast, a two-mode coupled-mode theory (CMT) can interpret all experimental results well. This motivated us to employ the CMT to establish a complete phase diagram for such coupled plasmonic systems, which not only revealed the diversified effects and their governing physics in different phase regions, but more importantly, also justifies the applicabilities of two simplified models (including Fano’s formula) derived previously. Our results present a unified picture for the distinct effects discovered in such systems, which can facilitate people’s understanding of the governing physics and can design functional devices facing requests for diversified applications.

In this work, a series of ternary ZnS1-xSex (x = 0–1) nanoparticles with perfectly tunable band gap were synthesized by using a facile low temperature route. The structure, composition, photophysical properties, and morphology of the samples were investigated by XRD, DRS, Nitrogen adsorption, EDS, TEM, and HRTEM. The characterization results indicated that by varying the Se/S molar ratio in the raw solutions the composition of ZnS1-xSex can be easily tailored, which resulted in the tunable band gap and surface areas. Photocatalytic experiments showed the resulting ternary ZnS1-xSex exhibited much higher photocatalytic activity than pure ZnS and ZnSe in methylthionine chloride (MB) degradation, and the superior catalytic activity of ZnS0.9Se0.1 should be attributed to its appropriate band gap and higher surface area. This work mainly deepens on tuning the composition and band gap of ternary ZnS1-xSex by a facile low temperature route for solar energy utilization.

To achieve electrical conductive composites, carbon fibers (CFs) were introduced to polypropylene–thermoplastic polyurethane (PP/TPU) blends. In combination, a definite amount of silica (SiO2) nanoparticles were added as reinforcing agents to impregnate CFs and further improve the mechanical, thermal and electrical properties of CFs-modified PP/TPU composites. These quaternary composites were investigated by X-ray diffractometry technique, thermogravimetric analysis, scanning electron microscopy (SEM), mechanical measurement and electrical conductivity test. The results demonstrated that the crystallinity and flow rate of PP/TPU composites dropped after compounding with CFs, though they increased by the addition of SiO2. Both CFs and SiO2 improved the impact and tensile strength of quaternary composites, which were arising from the large aspect ratio of CFs and the reinforcement effect of SiO2 nanoparticle, respectively. Furthermore, CFs–PP/TPU and (CFs + SiO2)–PP/TPU composites exhibited superior thermal stability over PP/TPU composites, and (3CFs + 3SiO2)–PP/TPU composite exhibited a maximum value. It is attributed to the restriction of polymer chain motion created by the CF fillers and the insulating effect of SiO2. The SEM micrographs revealed the presence of plastic bands for CFs–PP/TPU and (CFs + SiO2)–PP/TPU composites and more refined arrangement of the fibers after incorporation of SiO2. This refinement resulted in higher electrical conductivity of (CFs + SiO2)–PP/TPU composites compared with CFs–PP/TPU composites.

Layered P2-type Na0.67Fe0.5Mn0.5O2 with economic and environmental friendly metal elements is considered to be a candidate cathode for sodium-ion batteries. However, the poor rate performance and cycling stability of the cathode materials are still the pivotal constraints to the commercial development. To address these concerns, a series of different stoichiometric of Mg2+ substitution samples Na0.67(Fe0.5Mn0.5)1-xMgxO2(x = 0.05, 0.1, 0.15, 0.2, 0.25) are synthesised by solid-state reaction. The results indicate that the introduction of Mg2+ in P2 Na0.67Fe0.5Mn0.5O2 cause the transformation of P2 phase to O3 phase with a tremendous influence to the cycling performance. The sample shows P2 phase at x = 0.05. The P2 and O3 phases coexist in the compound while x = 0.1, 0.15, and 0.2. The sample exhibits O3 phase at x = 0.25. The novel composition of P2/O3 biphase Na0.67Fe0.425Mn0.425Mg0.15O2 delivers exceptional rate and cycling performance. Owing to the synergetic effect of P2 and O3 phases, the cathode exhibits excellent capacity retention of 95.7% of its initial capacity after 50 cycles at 1C, and 87.7% after 100 cycles. Therefore, Na0.67Fe0.425Mn0.425Mg0.15O2 with a novel P2/O3 biphase structures may be a promising cathode material for next generation high-performance sodium-ion batteries in the near future.

λ-Ti3O5 is a promising phase-transition metal oxide for the application in rewritable data storage, heat storage and smart optoelectronic devices due to its bistable metal-semiconductor transition (MST) characteristics between λ and β phase. However, λ-Ti3O5 is a room-temperature metastable phase and it's synthesis has been a great challenge. This paper presented a magnesium (Mg)-doping strategy for phase control of Ti3O5 to obtain the λ-Ti3O5 via carbothermal reduction method. The results revealed that Mg-doping induced a crystal-structure modification in Ti3O5 by tuning the Mg-doping content. Particularly, it suggested that the phase-transition temperature (Tc) of β–λ was reduced efficiently by increasing the Mg additive amount, and the λ phase was stabilized at room temperature eventually. Electrical resistivity measurement demonstrated a remarkable decrease in resistivity of Ti3O5, indicating a β–λ–α phase evolution induced by Mg-doping. In-situ temperature-dependent XRD was also employed to confirm the phase evolution and phase-transition characteristic of Ti3O5. This work offered considerable insights into a controllable crystal-structure modification for Ti3O5 by a doping strategy and the mechanism to the stabilization of metastable λ-Ti3O5.

Owing to the abundant storage and environmentally benign of Na, Fe, and Mn elements, FeMn-based O3-type NaFe0.5Mn0.5O2 materials were considered to be a promising cathode for sodium-ion batteries. However, the poor rate performance was barely satisfactory to the commercial production. Here, different Na content O3-type NaxFe0.5Mn0.5O2 (x = 1, 0.9, 0.8) for sodium-ion batteries were synthesized by solid-state reaction. The results illustrated that Na-deficient compound was beneficial to improve the rate performance and discharge capacity. Due to the Na-deficient in the octahedral sites, O3-type Na0.8Fe0.5Mn0.5O2 achieved a discharge capacity of 179 mAh g−1 at 0.1 C, which is relatively higher than that of O3-type NaFe0.5Mn0.5O2 (145 mAh g−1). Besides, the O3-type Na0.8Fe0.5Mn0.5O2 exhibited an initial discharge capacity of 126 mAh g−1 and outstanding capacity retention of 82.6% after 60 cycles at 1C. The excellent performance indicates that nontoxic and earth-abundant Na-deficient O3-type cathode may be a promising cathode for large-scale application and development of sodium-ion batteries.

Temperature can control the degree of hydrogenation of titania (i.e., black TiO2), determining the defect chemistry and hence its optical absorption and electrical conductivity that are key to the photocatalytic activity. However, how pressure affects the two key factors is unknown. In this work, we used a diamond anvil cell to produce the required high pressure (HP) and studied the pressure dependences of the structure change, the electrical conductivity, and the light absorption of black titania using HP X-ray diffraction, Raman/UV–vis spectroscopy, and electrical transport measurements. Results reveal that accompanying the HP phase transition the electrical conductivity exhibits complex variation with pressure, in good accord with the band gap changes of involved HP phases as a function of pressure. This confirms the assumption that pressure affects the electrical conductivity of black titania via controlling the number of free electrons (holes) distributed in the conduction (valence) band, which is in...

The anomalous glasslike behavior of heat transfer in Er:Yb: YCa4O(BO3)3 crystal was explored by means of temperature dependence Raman scattering spectra and synchrotron radiation X-ray topography. Crystal samples were prepared by the Czochralski technique, and the corresponding thermal properties, including thermal expansion, specific heat and thermal conductivity were investigated. The temperature-dependent Raman scattering results indicate the frequencies of Raman peaks as a function of crystal temperature followed a linear dependency on crystal temperature with different slopes. Nevertheless, the temperature-dependent linewidths of different Raman peaks were inconsistent and complicated. The X-ray topography firstly revealed a core situated in the center of crystal. Surrounding the core, a number of other defects like striations and dislocations were observed. The existence of such defects can lead to phonon scattering, which will introduce complicated influence into heat transfer process. As a result, the anomalous behavior of heat transfer can be influenced by disordered structure and crystal defects.

Black TiO2 has received tremendous attention because of its lattice disorder-induced reduction in the TiO2 bandgap, which yields excellent light absorption and photocatalytic ability. In this report, a highly efficient visible-light-driven black TiO2 photocatalyst was synthesized with a mesoporous hollow shell structure. It provided a higher specific surface area, more reaction sites and enhanced visible light absorption capability, which significantly promoted the photocatalytic reaction. Subsequently, the mesoporous hollow black TiO2 with different lattice disorder-engineering degrees were designed. The structure disorder in the black TiO2 obviously increased with reduction temperature, leading to improved visible light absorption. However, their visible-light-driven photocatalytic efficiency increased first and then decreased. The highest value can be observed for the sample reduced at 350 °C, which was 2-, 1.4- and 5-fold that of the samples reduced at 320 °C, 380 °C and 400 °C, respectively. This contradiction can be ascribed to the varied functions of the surface defects with different concentrations in the black TiO2 during the catalytic process. In particular, the defects at low concentrations boost photocatalysis but reverse photocatalysis at high concentrations when they act as charge recombination centers. This study provides significant insight for the fabrication of high-efficiency visible-light-driven catalytic black TiO2 and the understanding of its catalysis mechanism.

Nickel cobalt sulfides (NCS) are regarded as potential energy storage materials due to the versatile valent states and rich electrochemical activity, but their sluggish synthesis process and inferior rate performance hinder them from large-scale application. Herein, microwave-induced strategy has been employed for efficient synthesis of honeycomb-like NCS/graphene composites, which are explored as ultrahigh rate battery-type electrodes for supercapacitors. Due to the internal heat mechanism, the synthesis time of NCS by microwave could be shortened from hours to minutes. Density functional theory was simulated to uncover the interfacial effect between NCS and graphene, and the resulted Schottky barrier is in favor of enhancing redox activity and capacity. Ultimately, the obtained defect-rich nickel cobalt sulfides/graphene with thermal treatment (NCS/G-H) could exhibit a high specific capacitance of 1186 F g−1 at 1 A g−1 and sustain 89.8% capacity even after the increase of current density over 20 times, which is much superior to bare NCS and NCS/graphene. Furthermore, the assembled NCS/G-H hybrid supercapacitor delivers supreme energy density of 46.4 Wh kg−1, and retains outstanding long-term stability of 89.2% after 10 k cycles. These results indicate that the synthesized NCS/G-H by time-saving microwave-induced liquid process could be served as high rate materials for supercapacitors.

Sodium-ion batteries have attracted increasing attention due to the preponderance of nontoxicity, naturally elemental abundance, and low cost of the metal sodium. However, the electrochemical performance, including rate capability and cycling performance of the cathodes are still the pivotal shortcomings for the large scale application. Herein, a series of layered Na0.67(Fe0.5Mn0.5)1-χCoχO2 (χ = 0, 0.2, 0.4, 0.5) used as cathodes for sodium-ion batteries were synthesized via a solid-state reaction. Owing to the Co-substitution into the Na0.67Fe0.5Mn0.5O2, the rate performance and capacity retention of the cathodes for sodium-ion batteries were significantly elevated. Compared to the Na0.67Fe0.5Mn0.5O2 cathode, the Na0.67Fe0.3Mn0.3Co0.4O2 cathode exhibited an exceptional capacity retention (retaining 85.5% of its initial capacity after 100 cycles at 1C), as well as excellent rate capabilities (136.7 mAh g−1 at 0.2C, and 81.1 mAh g−1 at 5C). Such an outstanding electrochemical performance endows the P2-type Na0.67Fe0.3Mn0.3Co0.4O2 to be a promising cathode material for high-performance sodium-ion batteries in the near future.

Flexible and lightweight shielding materials recently have attracted increasing attention for terahertz wave due to the deteriorated performance of electronic equipment interferenced by electromagnetic yielding. Herein, flexible reduced graphene oxide (rGO) papers were prepared by solution evaporation method to attenuate the electromagnetic wave in terahertz field. They exhibited excellent electrical conductivity and remarkable electromagnetic interference shielding effectiveness. The electrical conductivity of the rGO papers was improved from 54.07 to 78.67 S/cm after annealing at 400 °C. The rGO paper annealed at 400 °C was only ~ 370 µm in thickness and particularly exhibited an outstanding absorption performance of 17.6 dB at 0.7 THz. It has been found that the maximum absorption performance of rGO papers was basically equivalent to that of the metamaterials. Moreover, electromagnetic interference shielding effectiveness of 72.1 dB of the rGO papers was obtained at 0.6 THz, which indicated that ~ 99.99% of the power was shielded. Thus, the flexible rGO papers maybe a promising candidate for optimized electromagnetic shielding materials in the terahertz band.

Transparent AlON ceramics are intriguing window materials with excellent mechanical strength and superb optical transparency from the near ultraviolet to the mid-infrared range. However, previous studies focused their investigations in the visible range; therefore, the application of transparent AlON ceramics to tunable windows has yet to be reported. In this work, a VO2 thin film with a characteristic semiconductor-metal phase transition (SMT) was fabricated on a transparent AlON ceramic, which exhibited remarkable tunable switching properties in the infrared and terahertz ranges. The transparent AlON ceramic was prepared by a two-step method, which included carbothermal reduction and pressureless sintering. The resulting ceramic exhibited high transparency of over 70% in the visible-infrared range and a notable THz transmission of 64.5–73.9% at 0.1–1.5 THz. The VO2 thin film was prepared on a transparent AlON ceramic using the sol-gel method and showed excellent optical and electric switching performance. The square resistance variance was close to four orders of magnitude, and an infrared switching ratio of over 40% was obtained. Furthermore, the combined structure showed an efficient THz switching ratio of approximately 70.9%. This study proposes a composite material combined with a transparent ceramic and a phase transition oxide and provides great insights into their application in infrared and terahertz smart windows as well as in switching devices.

VO2 with reversible semiconductor–metal phase transition properties is particularly available for the application in smart opto-electrical devices. However, there are rare reports on comparing its phase transition properties at different ranges. In this study, the VO2 films are designed with the similar crystalline structure and stoichiometry, but different morphologies by inorganic and organic sol-gel methods, and their phase transition characteristics are compared both at infrared and terahertz range. The results indicate that the VO2 film prepared by inorganic sol-gel method shows more compact nanostructure. It results in larger resistivity change, infrared and terahertz switching ratio in the VO2 film. Moreover, it presents that the phase transition intensity of VO2 film in terahertz range is more sensitive to its microstructure. This work is helpful for understanding the susceptibility of terahertz switching properties of VO2 to its microstructure. And it can provide insights for the applicat...

Black TiO2 has attracted great attentions due to its wide application potentials in visible-light photocatalysis, solar-thermal conversion for water evaporation, photothermal therapy and so on because of its controllable band gap using lattice disorder engineering. In this work, we proposed the design of microporous hollow structure in black TiO2 with thickness-controllable nano-shells to further optimize its photocatalytic ability. The hollow shells were produced from the evaporation-induced self-assembly (EISA) followed by NaBH4 reduction, and the shell thicknesses could be adjusted from ~20 to ~145 nm. The prepared microporous hollow shells showed excellent light absorption and enhanced photocatalysis performance with decreased shell thickness. Under visible light irradiation, the photocatalytic efficiency of the 20-nm shells was ~8 times higher than that of the 145-nm shells, revealing the strong promotion effect of the nano-shell design on the photocatalytic activity of hollow black TiO2. This great effect can be attributed to the higher surface area, more catalytic active sites and less diffusing distance in pore channels of the thinner shells. Our work demonstrates a scheme for the porous hollow structural design of black TiO2 with ultrathin nano-shell, and provides significant insights for its applications in higher efficiency of visible-light utilization and photocatalysis.

In this paper, a facile chemical bath deposition method was utilized to synthesize three-dimensional nanostructured CoNi 2 S 4 /Co 9 S 8 (CNSCS) composites as advanced electrode materials for high performance supercapacitors. CNSCS composites showed remarkable electrochemical performance owing to the high porosity, appropriate pore size distribution, novel architecture and synergistic effect of Ni/Co ions. The electrochemical tests revealed that CNSCS composites exhibited high specific capacitance (1183.3 Fg −1 at the current density of 2 Ag −1 ), excellent rate performance (74.9% retention with tenfold current density increase) and outstanding cycle life stability. Moreover, the effect of temperature on electrochemical performance of CNSCS composites was investigated and the results indicated the specific capacitance of CoNi 2 S 4 /Co 9 S 8 can keep relatively stable in a wide temperature from 0 °C to 50 °C. These results indicated that the synthesized CNSCS composites can be a promising electrode materials candidate for supercapacitors and chemical bath deposition is a promising processing route for CNSCS composites production.

Vanadium dioxide (VO2) with reversible metal-semiconductor transition is one of the most researched smart materials due to its near room-temperature transition at around 68 °C. Coating VO2 (M) nanoparticles onto substrate is superior to fabrication of VO2 (M) thin films owing to its advantages on large-scale preparation and flexible shaping. In this study, freeze-drying has been applied in a convenient precipitating and following annealing process of fabricating VO2 (M) nanoparticles. More importantly, effects of freeze-drying and pre-freezing temperature on phase composition, size distribution and phase-transition temperature of synthesized particles have been systematically researched by varying the pretreatment conditions. It is observed that the application of freeze-drying is crucial to the formation of pure VO2 (M), meanwhile, phase-transition temperature and size distribution of VO2 (M) nanoparticles can be effectively reduced with lowered pre-freezing temperatures. Besides, the influence of different annealing temperatures on nanocrystallite size has been investigated, and it has been found that both the crystallinity and particle size increased as the annealing temperature was increased. Finally, the as-fabricated VO2 (M) particles were coated onto microscopic glass substrate to characterize mid-infrared modulation performance. The coated film (made from sample pre-frozen at −50 °C) exhibits an excellent mid-infrared transmittance change of 23.3% at a fixed wavelength of 4 μm. This work demonstrates the effect of freeze-drying on the fabrication of VO2 (M) nanoparticles and provides a facile method for large-scale preparation of VO2 (M) nanoparticles.

Effect of the melt superheat on equiaxed solidification of Al-20 wt% Cu alloy was investigated by in-situ synchrotron radiography at Beijing Synchrotron Radiation Facility. For comparison, the corresponding DSC analysis was also conducted. It was found that the grain size decreased with increasing the melt superheat. The relationship between the final mean grain size and the melt superheat can be expressed as: d = 4919.3 × Δ T - 0.33 . During solidification, the mean grain size increased sharply in the first 70 s, then reached the final grain size gradually. Furthermore, with increasing the melt superheat, the mean nucleation rate increased, which can be attributed to the fact that increasing the melt superheat led to an increase in nucleation undercooling, and the growth rate and the duration of free growth stage decreased. As the melt superheat increased from 100 °C to 160 °C, the mean nucleation rate increased by 78.2% while the mean growth rate only decreased by 19.3%, which indicated that the high mean nucleation rate and the consequent low mean growth rate may be the real reasons for grain refinement. The increased nucleation density caused earlier growth deceleration due to solutal impingement effects.

In situ synchrotron X-ray radiography was used to study the effect of direct current (DC) on the grain nucleation and growth of Sn-50 wt.%Pb alloy. The results showed that applying DC adequately during solidification could effectively enhance the grain nucleation and inhibit its growth. Imaging of comparative experiments with varying DC intensity indicated that the final grain size, determined by the competition between grain nucleation and growth, was sensitively dependent on the DC intensity. It was found that the average grain size was decreased from 1632 to 567 μm with DC density of 1.5 A/mm 2 compared to the case without DC. Beyond this value, raising the current density may cause a significant decrease in the nucleation rate, and thus lead to a coarsening of the grain structure.

Ag/C is evaluated as a cathode catalyst for a bipolar membrane fuel cell (BPMFC). The microstructure of the cathode catalyst layer is modulated via ionomer content, and the effects on BPMFC performance are studied. When the ionomer content is increased from 10 wt% to 30 wt%, the fuel cell performance is optimized at 19.3 mW/cm2 with an ionomer content of 20 wt%. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) are conducted on the catalyst layer. EIS indicates that the charge transfer resistance is minimum, while CV suggests that the highest electrocatalytic activity of the catalyst is achieved with an ionomer content of 20 wt%. The microstructure of the catalyst layer is characterized using scanning electron microscopy (SEM) and nanometer-scale X-ray computed tomography (nano-CT). The SEM results show that excess ionomer cover on the surface of the catalyst, and the catalyst seems to form larger aggregates. Nano-CT, however, produces quite different results. The reconstructed 3D image of the catalyst layer reveals that the Ag/C catalyst tends to aggregate at low ionomer content. When the ionomer content is increased from 10 wt% to 30 wt%, the average diameter of the catalyst aggregation decreases from 313 nm to 210 nm.

The high purity γ-Ti3O5 thin films deposited on single-crystal SiO2 substrates are firstly prepared via sol–gel method combined with hydrogen reduction processing. In this reported work, the influences of reduction of temperature, hydrogen flow rate and holding time on the reduced phases are investigated. The as-prepared materials are characterized by glancing incident angle X-ray diffraction, scanning electron microscopy. Based on the results of single factor and orthogonal tests, the optimum condition for synthesizing high purity Ti3O5 thin films are as follows: the hydrogen gas flow rate is 0.8 L min−1, the reduction temperature is 1150 °C and the holding time is 1 h. Temperature dependence of PXRD patterns and electrical conductivity (σ) variation demonstrates that the temperature of phase transition between monoclinic I2/c crystal structure of γ-Ti3O5 thin film and monoclinic P2/a crystal structure of δ-Ti3O5 thin film was 225 K. The four-point probe test shows that the room-temperature conductivity of γ-Ti3O5 thin film is 202.1 S m−1.

Hydrangea-like NiCo 2 S 4 as electrode materials for high performance supercapacitors was synthesized by using a facile low temperature (90 °C) two-step hydrothermal technique without surfactant or template. The special hydrangea-like structure and large specific surface area (74.8 m 2 /g) provided plenty of electro active sites which were beneficial to superior pseudocapacitive performance of NiCo 2 S 4 . The supercapacitors performance of NiCo 2 S 4 was investigated by a three-electrode system. NiCo 2 S 4 exhibited high specific capacitance with 1475 F g −1 at a current density of 3 A g −1 , and a fairly high rate capacity with 1152 F g −1 at 20 A g −1 . These results indicate that low temperature hydrothermal is a very promising method to prepare electrode materials for supercapacitors.

Constructing high-density hotspots is of crucial importance in surface enhanced Raman scattering (SERS). In this paper, we present a large-area and broadband porous Au-Ag hybrid nanoparticle array which was fabricated by an ultra-thin alumina mask (UTAM) technique incorporated with annealing and galvanic replacement techniques. Experimental results and numerical simulations demonstrated that the porous Au-Ag hybrid nanoparticle array possessed enormous hotspots for high sensitivity, uniformity, and stability in SERS analysis. A large Raman enhancement factor of 2.2 × 107 was achieved with a relative standard deviation (RSD) of 7.7%, leading to excellent reliability for Raman detection. Furthermore, this novel substrate exhibited a long shelf time in an ambient environment and promising practical applications in many SERS-based quantitative analytical and biomedical sensing techniques.

Rational optimization design for the structure of materials on the self-supported electrode usually be an effective strategy for the development of advanced supercapacitors. Herein, the Co3O4/CoVxOy nanosheets composed of interweaved nanowires with core-shell structure were prepared through the two-step hydrothermal process combined with annealing treatment. These electrode materials exhibited a high specific capacitance of 1162.2 F g−1 at 1 A g−1, a good rate capability and a satisfactory cycling life. Asymmetric devices were fabricated using an as-prepared electrode as a positive electrode and activated carbon as a negative electrode, which delivered the highest energy density of 26.1 Wh kg−1 with a power density of 400 W kg−1 in the voltage range of 0–1.6 V. This work with the encouraging results point out the as-obtained Co3O4/CoVxOy composites not only can be a promising candidate for the energy storage system but also present a practicable route to design nanosheets core-shell structures for other transition metal oxides.

Metal-nitrogen-carbon (M-N-C) materials show great advantages for catalyzing the oxygen reduction reaction (ORR) in proton-exchange membrane fuel cells (PEMFCs). However, both the low density of single atomic (SA) MNx active sites and restricted mass transfer render these M-N-C based air electrodes inferior in cell performance. In this study, a new ZIF8-derived Fe-N-C catalyst/electrode design combining local chemistry tuning and primary morphology tailoring to address the above two critical issues is shown. The introduction of nitrogen-carbon defects in ZIF8 host enables a controlled atomic-scale dispersion of FeNx moieties, increasing their content in support materials. Also, the simultaneous structural arrangement of individual ZIF8 nano-grains endows the catalyst with a unique porous micro-spheric morphology. This result in an advanced 3D air electrode featuring dense SA FeNx sites and ample, multiscale macro-sized pore channels, which can significantly increase the intrinsic catalytic activity, facilitate bulk mass transport, and generate more effective triple-phase interfaces for ORR. The present catalyst/electrode design exhibits a record large peak power density of ca. 0.60 W cm−2 under practical air conditions. This approach provides a feasible way for boosting the air cathode interfacial ORR and further enlightens electrode designs for energy devices involving multiphase electrochemical reactions.

Vanadate nanomaterials with unique amorphous phase possess more active sites and isotropic nature, which is in favor of facilitating the diffusion of electrolyte ions into the electrode materials during the charge/discharge process and providing high capacitance for samples. Hereby, we report the preparation of the amorphous NiCozVxOy(NCVO) nanosphere as electrode materials for supercapacitors via a facile method using ethanol as the agent for assembly materials. The NCVO delivers a specific capacitance of 1449.3 F/g at 2 A/g with excellent rate capability. And the asymmetric supercapacitor devices achieve a high energy density of 45 Wh/kg at 1 A/g, a power density of 8000 W/kg at 10 A/g and good capacitance retention of 91.4% after 2000 cycles compared with its initial value under the voltage window of 1.6 V. The amorphous NCVO nanosphere prepared by the facile route exhibits attractive electrochemical properties and provides a potential candidate as energy storage materials for supercapacitors.

Vanadium dioxide (VO2), with reversible metal–semiconductor transition near room temperature, is a compelling candidate for thermochromic windows. Nanocomposite coatings derived from VO2 nanoparticles are particularly superior to VO2 films due to their advantages in large-scale preparation, flexible shaping, and regulation of optical properties. In this work, we developed a novel method for one-step hydrothermal synthesis of W-doped VO2 (M) nanorods and studied their application in large-scale infrared smart windows. On introducing tartaric acid as a new reductant, VO2 underwent a two-stage phase evolution from the pure phase comprising VO2 (A) nanobelts to VO2 (M) nanorods, instead of the conventional three-stage B–A–M phase evolution during hydrothermal synthesis. This transition is very favorable for the large-scale hydrothermal synthesis of VO2 (M). The phase-transition temperature of VO2 (M) nanoparticles can be regulated systematically by W doping, with a reduction efficiency of about 24.52 °C/atom ...

Aluminum oxynitride (AlON) transparent ceramics were prepared through aqueous gel-casting forming technique. To prevent hydrolysis, the homemade AlON powder was treated in 1% phosphoric acid at 70 °C for 30 min. Then the surface-treated AlON powder was dispersed in an aqueous-organic solution to prepare low viscosity slurry with 40 vol% solids loading, which was shaped by gel-casting forming technique. The hydrolysis of AlON powder was prevented effectively and the transmittance of sintered ceramics had been significantly improved by introducing hydrolysis protection of the powder. The sample sintered with the treated powder can reach an ultimate infrared transmittance of 78% with 2 mm thickness. The surface modification of AlON powder with phosphoric acid was confirmed by various techniques such as scanning electron microscopy (SEM), pH, Viscosity, X-ray photoelectron spectroscopy (XPS) and infra-red spectroscopy (IR). The related hydrolysis protection mechanism via this available method was discussed.

Epoxy/graphene nanoplatelets (GNPs) powder coatings were fabricated using ultrasonic predispersion of GNPs and melt-blend extrusion method. The isothermal curing kinetics of epoxy/GNPs powder coating were monitored by means of real-time Fourier transform infrared spectroscopy (FT-IR) with a heating cell. The mechanical properties of the epoxy/GNPs cured coatings had been investigated, by evaluating their fracture surfaces with field-emission scanning electron microscopy (FE-SEM) after three-point-bending tests. The thermal stability of the epoxy/GNPs cured coatings was studied by thermo-gravimetric analysis (TGA). The isothermal curing kinetics result showed that the GNPs would not affect the autocatalytic reaction mechanism, but the loading of GNPs below 1.0 wt % additive played a prompting role in the curing of the epoxy/GNPs powder coatings. The fracture strain, fracture toughness and impact resistance of the epoxy/GNPs cured coatings increased dramatically at low levels of GNPs loading (1 wt %), indicating that the GNPs could improve the toughness of the epoxy/GNPs powder coatings. Furthermore, from FE-SEM studies of the fracture surfaces, the possible toughening mechanisms of the epoxy/GNPs cured coatings were proposed. TGA result showed that the incorporation of GNPs improved the thermal stability of the cured coatings. Hence, the GNPs modified epoxy can be an efficient approach to toughen epoxy powder coating along with improving their thermal stability.

Synchrotron X-ray radiography was used to in situ study the solute distribution and the dendritic growth during the bottom-up solidification of Sn–50 wt%Pb alloy under a traveling magnetic field (TMF) for the first time. The buoyance driven evolution and motion of the plumes containing Sn-rich melt are directly observed in the solidification front before the application of TMF. A forced melt flow from left to right is induced with the application of TMF, which results in the redistribution of the solute concentration (facilitate the solute transportation and reduce the local fluctuations considerably) and the change of the dendrite morphologies (promote/suppress the growth of the secondary arms, remelting and fragmentation of dendrites). Meanwhile, the concentration variations of Sn around the solidification front are quantitatively analyzed through the extraction of gray level from sequenced X-ray images.

Although microstrip reflectarrays/transmitarrays have been extensively studied in the past decades, most previous designs were confined to monofunctional operations based on either transmission or reflection. In this communication, we propose a scheme to design multifunctional arrays that can simultaneously exhibit the functionalities of a reflectarray and a transmitarray on the basis of the appealing feature of a polarizer we discovered (i.e., constant phase difference between its cross-polarization transmission and copolarization reflection within a broadband). To demonstrate the proposed scheme, we designed and fabricated a multifunctional device comprising a $15 \times 15$ array of twisted complementary dual-split ring resonators, each carefully designed to exhibit the desired transmission phase satisfying a parabolic distribution. Feeding the device by a Vivaldi antenna at its focus, we numerically and experimentally demonstrated that our system functioned as a directive emitter working in a transmission/reflection mode for cross-polarization/copolarization radiation at low/high frequencies, and it can radiate directively in both directions with different polarizations at intermediate frequencies. The half-power beamwidth of the array antenna was $\sim 15^{\circ }$ , which is 40° narrower than that of a bare Vivaldi antenna. Moreover, the gain was higher than 13 dB in all cases studied, which is at least 7 dB higher than that of the Vivaldi antenna.

Li 4 SiO 4 pebbles have been widely studied as attractive tritium breeding materials in the fusion reactor blanket of international thermonuclear experimental reactor (ITER). In this work, surfactant-assisted hydrothermal method was first employed to prepare ultrafine ceramic powders for fabricating attractive Li 4 SiO 4 pebbles. SEM analysis revealed that the introduction of sodium dodecyl sulfate could eliminate the particle aggregation to prepare monodispersed precursor powders, and thus generated the green bodies of pebble with homogeneous microstructure, which was helpful to eventually obtain high-quality Li 4 SiO 4 pebbles. Moreover, the effects of sintering temperature on the grain size, relative density, and crush load of Li 4 SiO 4 pebbles were also investigated. Li 4 SiO 4 pebbles sintered at 700 °C had a high crush load (average value 27.39 N), small grain size (average value 0.57 μm), satisfactory density (88.13%T.D.) and abundant pore structure, which were expected to show favorable tritium release behavior as a promising tritium breeding material for fusion reactor blanket.

Non-covalent functionalized reduced graphene oxide (rGO) with l-tryptophan was rapidly fabricated by reducing graphene oxide (GO), using l-ascorbic acid as reducer under microwave heating. Atomic force microscope, scanning electron microscope, ultraviolet–visible spectroscopy, X-ray diffraction, Raman spectroscopy and Fourier transform infrared spectroscopy were employed to investigate the morphologies and structures of the samples. The average particle sizes and zeta potentials of rGO were measured by means of dynamic light scattering spectroscopy. Furthermore, the maximum dispersibility of rGO dispersion was calculated from Lambert–Beer law. It was shown that oxidative debris of GO were cleaned after ammonia wash process, and ultimately improving the water dispersibility through enhancing the π–π interaction between l-tryptophan molecules and rGO sheets. The maximum dispersibility of the functionalized rGO dispersion with cleaning oxidative debris was increased by 95 % (from 0.44 to 0.86 mg mL−1) compared to that without cleaning oxidative debris. This investigation proposed an effective method to fabricate the non-covalent functionalized rGO, as well as the method to improve its water dispersibility.

Strontium Calcium titanate (SCT) Sr1−xCaxTiO3 nanopowders have been successfully synthesized by sol–gel method. The effect of Ca2+ ion content from 0 to 1 on their crystal structure, microstructure, transmission and dielectric properties in terahertz range was systematically investigated. The results revealed that single SCT phases with well crystallinity were formed at 900 °C for 2 h. The grain size of the SCT powders was decreased by increasing the Ca2+ ion molar ratios. X-ray diffraction (XRD) and Raman spectra measurement results demonstrated that obvious reduction of symmetry and Raman modes related to structural information varied with the Ca2+ ion composition x. The sequence of SCT phase transitions with increasing Ca content is from cubic through tetragonal I4/mcm to orthorhombic Pbnm. The THz transmission of SCT revealed by terahertz time-domain spectroscopy was changed by varying the Ca2+ ion composition. Meanwhile, the time lag between reference and the SCT could be adjusted between around 20 ps and 30 ps, which increased with increased Ca content. The permittivity of stressed Sr1−xCaxTiO3 powders was obtained by terahertz time-domain spectroscopy. These results revealed that the Ca2+ ion in SCT led to tuning of dielectric response in terahertz range. Sr0.9Ca0.1TiO3 exhibited a smeared-out maximum; for x ≥ 0.3, the real and imaginary components of dielectric permittivity (e′) and (e″) decreased with increasing x. These results may offer considerable insights into the application of Sr1−xCaxTiO3 in smart THz device.

Three different kinds of rutile TiO2 nanoparticles with different surface coating conditions were prepared by precipitation method for synthesizing λ-Ti3O5. The effect of surface layers on nano rutile TiO2 particles on the preparation of λ-Ti3O5 was firstly investigated. X-ray diffraction, scanning electron microscope, energy dispersive spectrometer and transmission electron microscope were used to characterize these powders. The nano rutile TiO2 powders were mixed with carbon black separately and then annealed at an isothermal heat condition. The phase structures of the products demonstrate that high purity nanocrystalline λ-Ti3O5 powders can be synthesized by carbothermal reduction of the Al2O3–SiO2 dual-coated TiO2 powders, but not by the uncoated and SiO2-coated TiO2 powders. Thus, the coating layers of the TiO2 nanoparticles played a decisive role in the formation of nanocrystalline λ-Ti3O5. It proposed that both of the coating layers and metal ion (i.e. Al3+) make a contribution to stabilize the metastable phase λ-Ti3O5 to ambient temperature in the carbothermal reduction of the TiO2/C system. This study provided considerable insights into the preparation of nanocrystalline λ-Ti3O5.

Tungsten trioxide/reduced graphene oxide (WO3/RGO) nanocomposite film was fabricated by the sol–gel spin-coating technique, using a mixed colloidal dispersion of WO3 precursor and GO. The structure, surface morphology and optical properties of WO3 and WO3/RGO films were investigated by means of X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, high-resolution transmission electron microscopy and UV-visible spectrophotometry. The electrochemical and electrochromic performances of the WO3 and WO3/RGO films were studied by chronoamperometry, in situ optical transmittance and cyclic voltammogram analysis. In the WO3/RGO nanocomposite film, monoclinic WO3 nanoparticles were grafted onto the surface of RGO sheets via C–W and C–O–W chemical bonds. The results showed that the WO3/RGO nanocomposite film exhibited shorter coloration–bleaching times (tc = 9.5 s and tb = 7.6 s), higher coloration efficiency (75.3 cm2 C−1 at 633 nm), larger optical modulatory range (59.6% at 633 nm) and better cyclic stability compared with WO3 films, which are attributed to faster Li+ ion diffusion and electron transfer rate. The methodology provides a facile and industrially scalable approach to obtain fast switching electrochromic materials.

λ-Ti3O5 was a newly discovered material with intriguing phase transition characteristics, which exhibits huge potential in the application of memory and tunable optoelectronic devices. However, the fabrication of λ-Ti3O5 still presents a great challenge and its application needs further investigation. In this work, we developed a novel method to fabricate nanocrystalline λ-Ti3O5 by carbothermal reduction of nano-TiO2, and explored its terahertz transmission properties through a temperature induced phase transition. A second phase was introduced to inhibit the grain growth of titanium oxide during the carbothermal reduction, by performing a surface modification of the precursor nano-TiO2 particles with Al2O3. This process was proved to be critical for the formation of nanocrystalline λ-Ti3O5. An in situ XRD analysis combined with a first-principles calculation based on plane wave DFT indicated that the nanocrystalline λ-Ti3O5 exhibited a semimetallic λ phase to metallic α phase transition across a large temperature range. The phase transition was accompanied by continuous, slow and reversible tuning of the terahertz transmission amplitude. This work provides considerable insights into the synthesis of λ-Ti3O5 and opens up studies on the applications of λ-Ti3O5 in the THz range, such as but not limited to sensors and smart windows.

The application of the subwavelength planar structure to control the propagation direction of surface plasmon polaritons (SPPs) has attracted many interests in recent years. However, the traditional unidirectional transmission devices of SPPs are limited by the low extinction ratio, narrow working band and the incapability of controlling the transmission directions. In this study, a novel SPPs unidirectional transmission device based on metallic aperture arrays of the right triangle (RT) is proposed and demonstrated by numerical simulations (finite-difference time-domain method). The maximum extinction ratio of the unidirectional transmission device can reach upto 33 dB under the irradiation of linearly polarized light, and the device possesses a wide operating band ([Formula: see text] nm) while the extinction ratio is greater than 10 dB. Moreover, the transmission direction of SPPs can be flexibly controlled by tuning the polarization of the incident beam. This broadband, polarization-mediated and high extinction ratio unidirectional transmission device shows great potential in the compact plasmonic devices.

λ-Ti3O5 with unique phase transition properties is prosperous functional materials for application in data storage, thermal storage and optoelectronic devices. However, the synthesis of λ-Ti3O5 nanocrystal has long been a great challenge. In this work, the λ-Ti3O5 nanocrystals were obtained by a PEG assisted sol-gel method, in which Polyethylene glycol 600 (PEG-600) was used as a reducing agent. Subsequently, the as-prepared λ-Ti3O5 nanocrystals were characterized by X-ray diffraction, scanning electron microscope, transmission electron microscopy, X-ray photoelectron spectroscopy and Raman spectrum. We also investigated the thermal-induced phase transition characteristics of λ-Ti3O5 by in-situ temperature-dependent XRD. This work provides a facile method to fabricate λ-Ti3O5 and would be significant for the further investigation and application of λ-Ti3O5.

In this work, rapid chemical precipitation assisted annealing method is used to prepare flower-like NiCo2S4. And the flower-like structure after polyethylene glycol (PEG) modification yields an excellent specific capacitance (2198.9 F g−1 at 1 A g−1). And an asymmetric supercapacitor assembled with NiCo2S4 (PEG-modified) and activated carbon (AC) shows an energy density of 38.2 Wh kg−1 at 400 W kg−1, and outstanding stability (80% remained after 3000 cycles at 5 A g−1). Benefited by a larger specific surface area and suitable pore size of the aggregate structure, the specific capacitance of prepared NiCo2S4 is increased by about 2 times. This uncomplicated preparation method is proved to be suitable for NiCo2S4 with a high specific capacitance of supercapacitors.

With the rapid development of integrated optics, bulky and curved traditional lenses cannot meet the requirements of on-chip optical systems. Alternatively, the metalenses based on the artificial subwavelength structure possess ultra-thin and lightweight characteristics, providing a potential candidate for on-chip optical systems. Nonetheless, most metalenses have a limited field-of-view (FOV) due to the prevalence of severe off-axis aberrations. In this work, we propose and design an on-chip metalens with wide FOV based on the quadratic phase. The metalens modulates the phase of the incident light with different lengths of gold nano-bands placed on the silicon-on-insulator substrate; thus, the quadratic distribution of the phase of the output light can be achieved by shifting the lengths of gold nano-bands and the output light is focused. The metalens can be focused on a large angle (∼120°, ranging from −60° to +60°). Furthermore, the metallic strips in the metalens are very thin with a thickness of 50 nm, which can be easily integrated into a chip. The monolithic metalens of broad FOV and ultrathin thickness will have great potential for applications in areas of sensing, imaging, and on-chip information processing.

For high quality imaging of materials in nanoscale by hard X-ray optics, high resolution lenses with high focusing/imaging efficiency are needed. Refraction based conventional Kinoform lenses with 1D linear configuration in Si has been attempted for decades, but there has still been no sign of success due to the enormous difficulty in fabrication. This paper proposes a novel configuration of golden Kinoform lenses with round shape on a plate, in which each zone maintains the typical 3D parabolic profile as seen in the traditional 1D counterpart. The major focus in this work is on the generation of the 3D profile in e-beam resist through greyscale electron beam lithography (EBL) as the template for the golden Kinoform lens. Systematic study of the greyscale lithography conditions, including the comparisons of resists, developers and charge distributions, has been conducted by using Monte Carlo simulation as well as e-beam lithography. Initial results have been achieved for replicating the desired 3D profile of the golden Kinoform lens in the resist. Using the generated profile in resist as templates, the golden Kinoform lens with 200 μm diameter and 3.5 μm height has been successfully fabricated, for the first time, which will hopefully replace the existing Fresnel zone plates for hard X-ray imaging with high resolution and high efficiency.

High yield 3-hydroxy benzaldehyde-N-methyl 4-stilbazolium tosylate (3-HBST) was synthesized by optimizing the reaction temperature. High-quality bulk crystals of 3-HBST were grown by slow evaporation technique and spontaneous nucleation method, respectively. The crystal structure of 3-HBST was determined by single crystal X-ray diffraction (XRD) technique and belongs to monoclinic system. The defects of the 3-HBST crystals were observed by the synchrotron radiation X-ray topography. 3-HBST crystal remains stable until 305 °C, with a melting point of 214.1 °C from the TG-DTG and DSC techniques. The dielectric constant of 3-HBST crystal was also studied. The grown crystal had good optical transparency and the optical transmittance was investigated by UV-vis-NIR spectral analysis. Photoluminescence (PL) indicated green emission occurred at 478 nm. Based on the growth technical analysis and performance parameters measurements, 3-HBST crystal was verified to be a promising organic nonlinear optical crystal.

Vanadium dioxide (VO2) is considered to be one of the most competitive thermochromic materials, due to its semiconductor-metal phase transition characteristics. And the doping of tungsten (W) into the lattice of VO2 can significantly reduce the phase transition temperature to near room temperature. However, the reduction efficiency dependent on doping amount is quite different in previous reports. In this work, we proposed an in-situ stirring assisted hydrothermal to synthesize W-doped VO2 nanorods with improved doping efficiency. The effects of in-situ stirring during the hydrothermal synthesis on phase composition, sample morphology, and phase-transition temperature of VO2 with different W doping amounts were studied systematically. The phase transition temperature reduction efficiency of W-doped VO2 prepared by hydrothermal synthesis without in-situ stirring was at % W. By contrast, the phase transition temperature of W-doped VO2 prepared by in-situ stirring hydrothermal synthesis was depressed as much as 24.55 °C/at % W when W/V ranged in 0.75–2.0 at %. Further research found that the phase transition temperature of W-doped VO2 (M) could be simply tuned by changing the in-situ stirring time. Then, the 1 at% W-doped VO2 (M) (with phase transition temperature of around 41.5 °C) nanorods and acrylic resin were mixed to prepare VO2 composite film. It exhibited suitable infrared transmission (>60%) and excellent mid-infrared transmission switching performance (23.77%). This work proposed an in-situ stirring hydrothermal method for high efficiency synthesis of W-doped VO2 (M) and provided significant insights for its application in thermochromic windows.

Synchrotron radiation X-ray computed tomography (CT) enables nondestructive visualization of 3D morphological and chemical changes inside a sample and has become a powerful analysis tool to monitor reactive parts and their chemical states. However, synchrotron radiation CT imaging of specimens with lateral extensions much larger than the acceptance window of detectors is rather problematic due to strong absorption of X-rays in the lateral directions. On the other hand, X-ray computed laminography (CL) permits 3D imaging of flat samples while X-ray diffraction enhanced imaging (DEI) can provide high-quality results with different imaging contrasts such as absorption, phase and dark-field for samples with weak absorptions. Combining CL and DEI together, we have developed a multi-contrast DEI-CL system at the 4W1A beamline of the Beijing Synchrotron Radiation Facility for this kind of sample. Here we reported its design, implementation, and preliminary experimental results of carbon fiber reinforced polymer laminates with three kinds of imaging contrasts. The results have demonstrated the validity of this DEI-CL system. It will be helpful to push the applications of the state-of-the-art synchrotron radiation methods and instruments towards cutting-edge research. Graphical abstract ᅟ.

A three-image algorithm is proposed in order to retrieve the absorption, refraction and ultra-small-angle X-ray scattering (USAXS) properties of the object in X-ray analyzer-based imaging. Based on the Gaussian fitting to the rocking curve, the novel algorithm is theoretically derived and presented, and validated by synchrotron radiation experiments. Compared with multiple-image radiography, this algorithm only requires a minimum of three intensity measurements, and is therefore advantageous in terms of simplified acquisition procedure and reduced data collection times, which are especially important for specific applications such as in vivo imaging and phase tomography. Moreover, the retrieval algorithm can be specialized to particular cases where some degree of a priori knowledge on the object is available, potentially reducing the minimum number of intensity measurements to two. Furthermore, the effect of angular mis-alignment on the accuracy of the retrieved images was theoretically investigated, which can be of use in image interpretation and optimization of the data acquisition procedure.

Li4SiO4 has been widely studied as attractive tritium breeding materials due to its innate merits. Considering the potential advantages of nanostructure in tritium breeding materials, a distinctive process was developed to obtain nanostructured Li4SiO4 pebbles. In brief, ultrafine precursor powders were synthesized by solvothermal method without using surfactants, and then indirect wet method was adopted to generate the green spheres with homogeneous microstructure. After that, the suitable sintering conditions were defined by studying the effects of sintering parameters on the grain size evolution, and nanostructured Ti-doped Li4SiO4 pebbles were first obtained by two-step sintering method. This study will be expected to provide references for fabricating other Li-based tritium breeding materials. Accepted version