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In this work, we demonstrate a novel In0.52Al0.48As based top-illuminated avalanche photodiode (APD), designed to circumvent the problem of serious bandwidth degradation under high gain (>100) and high power operation and significantly enhance the dynamic range in the established frequency modulated continuous wave (FMCW) lidar system. In our APD design, the carriers transiting through the dual multiplication (M-)layers are subjected to a stepped-up electric field profile, so they can be energized by the first step and propagate to the second step to trigger the avalanche processes. Such a cascade avalanche process leads to an ultra-high gain bandwidth product (460 GHz) with a 1 A/W responsivity at unit gain. Compared to the high-performance and commercial p-i-n PD and photo-receiver (PD + trans-impedance amplifier (TIA)) installed in the same lidar test bed, our demonstrated APD receiver (without TIA) has a larger S/N ratio under high operation gain (33 A/W) with less optical local-oscillator (LO) power required (0.25 vs. 0.5 mW), while exhibiting a wider dynamic range in each pixel. These advantages in turn lead to the construction of a better quality of 3-D lidar image by using the demonstrated APD.

This paper presents a new kind of adjustable dielectric waveguide resonator (DWR), based on which integrated designs of filtering circuits are conducted. The DWR is composed of a dielectric part as the main resonating body and a printed circuit board (PCB) part as the cover. An unmetallized blind hole is carved at the upper surface of the dielectric part. A tuning screw is installed on the PCB and inserted into the unmetallized blind hole to adjust the resonant frequency the DWR. This adjusting method is flexible and reversible. By using the proposed adjustable DWR, a fourth order bandpass filter (BPF) is designed, fabricated and measured. The measured results show that the BPF is with an in band insertion loss of 0.8 dB and an in band return loss better than 19 dB. A capacitive cross coupling structure is constructed on the PCB so that two transmission zeros are introduced close to the passband to improve the filtering selectivity. In addition, a Wilkinson power divider is realized on the PCB and integrated with the above BPF, forming a filtering power divider. The measured in band insertion loss of the filtering power divider is 1.1 dB. The isolation is better than 24 dB and the maximum phase imbalance is 1circ in the passband.

Novel microring based optical phase-shifters on Si-photonic platforms for microwave photonic applications are demonstrated. By using an add-drop microring structure in combination with an additional multimode interferometer (MMI), pure phase modulation with an ultrahigh modulation efficiency can be realized. Comparison is made to the reference all-pass ring design with both the same radius (5 m) and coupling coefficient (: ~0.2). The demonstrated structure minimizes the residual amplitude modulation (0.9 vs. 1.8 dB) for nearly 2 phase shifting over a wide optical window (1520 to 1570 nm) at the expense of a larger insertion loss (0.06 dB) due to the additional MMI. The demonstrated phase shifter structure is implemented in a Mach-Zehnder interferometer (MZI) for further study of its dynamic and linearity performance. Under forward bias, it exhibits a low V/I(0.4 V/12.7 mA), fast rise-time (3 ns), low insertion loss (0.2 dB), low residue-amplitude-modulations (

Based on the previous work on Si3N4-ZrB2, the addition of 2.5 vol.% ZrB2 promoted α- to β-Si3N4 phase transformation, bimodal microstructure, and toughness and strength improvement after hot-pressing at 1500 °C. However, the mechanism needed to be further explored. In the present work, the effect of ZrB2 and its oxide impurities (ZrO2 and B2O3) on phase composition, microstructure and mechanical properties of Si3N4 ceramics with MgO-Yb2O3 additives were studied. Results showed that the addition of B2O3 had no influence on Si3N4 ceramics, whereas the addition of ZrO2 inhibited the α- to β-Si3N4 phase transformation, formed an uniform equiaxed microstructure, and deceased the toughness and strength. The positive effect of oxide impurities can be eliminated. Based on the STEM analysis, the possible reason was that the addition of ZrB2 led to the formation of Si-Mg-O-N-Yb-Zr-B liquid phase, and then promoted α- to β-Si3N4 phase transformation.

Chiral Pb(Sn)-I hybrid organic-inorganic perovskites exhibit outstanding chiral-induced spin selectivity (CISS) performance, but the nontoxic lead-free hybrid materials with high stability are still greatly desired for spin filtering in spintronic applications. We synthesize chiral hybrid copper halides (R/S-MBA)2 CuX4 (MBA=methylbenzylammonium; X=Cl, Br) with characteristic 0D CuX4 tetrahedral structural motifs, combining the low toxicity of Cu2+ and air stability of halide ions (Cl- and Br- ). Despite similar structural and electronic features, (R/S-MBA)2 CuBr4 shows much smaller chiroptical activity than the chloride counterpart. Magnetically conductive atomic force microscopy measurements display a typical spin-polarized charge-transport property with high efficiency up to 90 % for both copper halides. Our work expands the CISS effect into eco-friendly and stable metal-organic halides, which is promising for applications in spintronics based on transition-metal hybrid systems.

Highly c-axis textured β-silicon nitride (β-Si3N4) ceramic with fine grains was prepared by a new method of hot extrusion for the first time. The (002) pole figure on the section plane vertical to extruding direction showed a characteristic of center rotational symmetry. The average cline angle between elongated β-Si3N4 grains and hot extruding direction was about 14.4°. The degree of c-axis texturing by hot extrusion was comparable to that achieved by rotating magnetic field. The hardness and toughness anisotropy in different direction was apparent and relatively higher hardness was achieved in the present work mainly due to the finer grain size. Therefore, many different compositions of c-axis aligned Si3N4-based ceramics with tailored mechanical properties could be achieved by the strategy of hot extrusion.

The first all-amidinate-protected gold nanocluster [Au28 (Ph-form)12 ](OTf)2 (Ph-form=N,N'-diphenylformamidinate) (Au28 ) has been synthesized and structurally resolved. Single crystal X-ray diffraction reveals that Au28 has a compact Au4 @Au24 tetrahedral core-shell structure of T symmetry, which is fully protected by 12 bridging formamidinate ligands. This cluster is quite robust as indicated by the fact that it can stay intact in solution at 80 °C for 6 d. It exhibits excellent catalytic performance for the electroreduction of CO2 with 96.5 % Faradaic efficiency (FE) at -0.57 V and a maximum TOF of 1731 h-1 at -0.87 V. Its superior stability is also manifested in the fact that the supported catalyst Au28 /CNTs maintains stable potentials at ca. -0.69 V for 40 h with FE(CO)s>91 %. A superatomic electron configuration of 1S2 1P6 2S2 1D4 has been clarified by DFT computations, and the strong gold-ligand binding and geometric shell closure account for the superior stability of Au28 .

The coronavirus disease 2019 (COVID-19) can present a similar syndrome to an influenza infection, which may complicate diagnosis and clinical management of these two important respiratory infectious diseases, especially during the peak season of influenza. A rapid and convenient point-of-care test (POCT) for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and influenza virus is of great importance for prompt and efficient control of these respiratory epidemics. Herein, a multichannel electrochemical immunoassay (MEIA) platform was developed based on a disposable screen-printed carbon electrode (SPCE) array for the on-site detection of SARS-CoV-2 and A(H1N1). The developed MEIA was constructed with eight channels and allowed rapid detection on a single array. On the SPCE surface, monoclonal antibodies against influenza A(H1N1) hemagglutinin (HA) protein or SARS-CoV-2 spike protein were coated to capture the target antigens, which then interacted with a horseradish peroxidase (HRP)-labeled detection antibody to form an immuno-sandwich complex. The results showed that the MEIA exhibited a broader linear range than ELISA and comparable sensitivity for A(H1N1) HA and SARS-CoV-2 spike protein. The detection results on 79 clinical samples for A(H1N1) suggested that the proposed MEIA platform showed comparable results with ELISA in sensitivity (with a positive rate of 100% for positive samples) but higher specificity, with a false-positive rate of 5.4% for negative samples versus that of 40.5% with ELISA. Thus, it offers great potential for the on-the-spot differential diagnosis of infected patients, which would significantly benefit the efficient control and prevent the spread of these infectious diseases in communities or resource-limited regions in the future.

To improve the interfacial mass-transfer efficiency, microporous layers (MPLs) containing CeO2 nanorods and the CeO2 nano-network were prepared for proton exchange membrane fuel cells (PEMFCs). In order to minimize the contact resistance, the three-dimensional (3D) graphene foam (3D-GF) was used as the carrier for the deposition of CeO2 nanorods and the nano-network. The CeO2-doped 3D-GF anchored at the interface between the catalyst layer and microporous layer manufactured several novel functional protrusions. To evaluate the electrochemical property, the normal MPL, the MPL containing raw 3D-GF, and MPLs containing different kinds of CeO2-doped 3D-GF were used to assemble the membrane electrode assemblies (MEAs). Measurements show that the CeO2-doped 3D-GF improved the reaction kinetics of the cathode effectively. In addition, the hydrophilic CeO2-doped 3D-GF worked as the water receiver to prevent the dehydration of MEAs at dry operating condition. Besides, at a high current density or humid operating condition, the CeO2-doped 3D-GF provided the pathway for water removal. Compared with the CeO2 nanorods, the CeO2 nano-network on 3D-GF revealed a higher adaptability at varying operating conditions. Hence, such composition and structure design of MPL is a promising strategy for the optimization of high-performance PEMFCs.

Joining of SiC ceramics was successfully achieved at a relatively low temperature of 1500 °C without any pressure using pure polycarbosilane (PCS) as the joining material, which was distributed homogenously on the surface of SiC monolith through a screen printing method. The XRD pattern shows that the pyrolysis product of PCS is single-phase SiC. The interlayer thickness of the SiC joint is approximately 2 μm. This ultra-thin interlayer with lower possibility of the existence of defects contributes to the average shear strength of 105.8 ± 10.4 MPa, higher than that of other works using other preceramic polymers to the best of our knowledge. Due to the simplicity, low cost and high joining strength, the screen printing method using PCS as the joining material has good practicality in SiC ceramics joining.

We report an Ag1 single-atom catalyst (Ag1 /MnO2 ), which was synthesized from thermal transformation of Ag nanoparticles (NPs) and surface reconstruction of MnO2 . The evolution process of Ag NPs to single atoms is firstly revealed by various techniques, including in situ ETEM, in situ XRD and DFT calculations. The temperature-induced surface reconstruction process from the MnO2 (211) to (310) lattice plane is critical to firmly confine the existing surface of Ag single atoms; that is, the thermal treatment and surface reconstruction of MnO2 is the driving force for the formation of single Ag atoms. The as-obtained Ag1 /MnO2 achieved 95.7 % Faradic efficiency at -0.85 V vs. RHE, and coupled with long-term stability for electrochemical CO2 reduction reaction (CO2 RR). DFT calculations indicated single Ag sites possessed high electronic density close to Fermi Level and could act exclusively as the active sites in the CO2 RR. As a result, the Ag1 /MnO2 catalyst demonstrated remarkable performance for the CO2 RR, far surpassing the conventional Ag nanosized catalyst (AgNP /MnO2 ) and other reported Ag-based catalysts.

Dense pressure-sintered reaction-bonded Si3N4 (PSRBSN) ceramics were obtained by a hot-press sintering method. Precursor Si powders were prepared with Eu2O3–MgO–Y2O3 sintering additive. The addition of Eu2O3–MgO–Y2O3 was shown to promote full nitridation of the Si powder. The nitrided Si3N4 particles had an equiaxial morphology, without whisker formation, after the Si powders doped with Eu2O3–MgO–Y2O3 were nitrided at 1400 °C for 2 h. After hot pressing, the relative density, Vickers hardness, flexural strength, and fracture toughness of the PSRBSN ceramics, with 5 wt% Eu2O3 doping, were 98.3 ± 0.2%, 17.8 ± 0.8 GPa, 697.0 ± 67.0 MPa, and 7.3 ± 0.3 MPa m1/2, respectively. The thermal conductivity was 73.6 ± 0.2 W m−1 K−1, significantly higher than the counterpart without Eu2O3 doping, or with ZrO2 doping by conventional methods.

In this work, we demonstrate the high-power and high-responsivity performance of the dual multiplication (M-) layers in In0.52Al0.48As based avalanche photodiode (APD). The dual M-layer design in our APD structure effectively constrains the multiplication process to a thin high-field region rather than the whole thick M-layer. It thus minimizes the space charge effect (SCE) within and avoids increasing the tunneling dark current for the case of directly shrinking M-layer thickness in APD. Furthermore, by combining the specially designed mesa shape with this dual M-layer structure, the edge breakdown can be well suppressed. These benefits lead to an ultra-high gain-bandwidth product (450 GHz; 1 A/W at unit gain) and a high saturation current (>12 mA) can be simultaneously achieved in our device. By nonlinearly driving a wavelength sweeping laser in the self-heterodyne lidar setup, it can generate an optical pulse train-like waveform, providing an effective optical modulation depth of 200% to feed into our demonstrated APD at the receiver-end. Under such scheme, the photo-generated RF (1 GHz) power from our APD with a 6.3 A/W responsivity can be as high as +6.95 dBm at a high (7 mA) output photocurrent. Such high-power and high-responsivity characteristics of our APD can further improve the signal-to-noise (S/N) ratio and dynamic range performances in each pixel of the lidar image. A high-quality 3-dimensional (D) FMCW lidar image is constructed based on our APD, without the integration of any electrical amplifier at the receiver end.

The joining of liquid-phase sintered SiC (LPS-SiC) ceramics was conducted using spark plasma sintering (SPS), through solid state diffusion bonding, with Ti-metal foil as a joining interlayer. Samples were joined at 1400 °C, under applied pressures of either 10 or 30 MPa, and with different atmospheres (argon, Ar, vs. vacuum). It was demonstrated that the shear strength of the joints increased with an increase in the applied joining pressure. The joining atmosphere also affected on both the microstructure and shear strength of the SiC joints. The composition and microstructure of the interlayer were examined to understand the mechanism. As a result, a SiC-SiC joining with a good mechanical performance could be achieved under an Ar environment, which in turn could provide a cost-effective approach and greatly widen the applications of SiC ceramic components with complex shape.

Cellulose-based films have attracted significant attention in the fields of flexible photoelectric products and energy equipment by virtue of their abundant sources, biodegradability, renewability, sustainability, and optical properties, of which high transmittance and high haze are important parameters. In this study, we proposed a green and efficient defibrillation and carboxylation method of KMnO4 synergized with slight homogenization to produce fine carboxylated cellulose nanofibrils (COOH-CNFs) with a high yield of 96%. The oxidation reaction was carried out under mild conditions (50 °C, 2 h). The as-prepared COOH-CNFs well-retained the crystalline structure of the pulp with coexisting crystalline and amorphous regions. This structure gave the COOH-CNF film unique optical properties, including a transmittance above 80% at a wavelength of 550 nm, a haze reaching 97.45%, and no obvious absorption in the ultraviolet-visible range. The resulting COOH-CNFs were characterized in terms of fibrillation yield, morphological features, crystal structure, surface chemistry, and mechanical behavior. This CNF preparation approach is advantageous over traditional methods owing to a reduced reactant dosage and enhanced efficiency, which represents a potential green route in industry and makes it a promising candidate for fabricating films for flexible lighting, energy, and sensing devices.

The shape of gas flow field determines the distribution of reactive gas and the drainage performance so it has a significant impact on cold start performance. This work designs three novel cathode flow fields of stacks through variable cross-section design to improve drainage, which are the single variable section serpentine flow field, the variable section interdigitate flow field and the variable section parallel flow field. The cold start characteristics and internal behavior of diverse novel stack flow fields are investigated by segmented cell technology. The results show that stack with the single variable section serpentine flow field realizes the fastest cold start when the temperature is below −5 °C. However, the variable section interdigitate flow field displays the shortest cold start time when the temperature is above −5 °C. The evolution of the current density distribution of the single cell in different position of the same stack is inconsistent during cold start. The key regions with strong electrochemical performance of different stack flow fields are found. The performance degradation of the stack with the single variable section serpentine flow field is the lowest when start fails. This work can supply experimental support for the selection of flow fields for cold start.

We demonstrate a novel optical phase shifter with a bipolar junction transistor (BJT) type of device structure based on the silicon photonics foundry platform. By operating such a device in saturation mode, we obtain measured output IEC-VEC characteristics very similar to those of an ideal diode, which has a nearly zero turn-on voltage and an extremely small differential resistance. The huge amount of injected current under a small voltage swing (0.1 V) in the operation window makes it possible to obtain significant plasma induced change of the refractive index in the optical waveguide with an extremely small driving-voltage. The device has a small foot-print (500 μm in length), but exhibits small static power consumption for the π phase-shift (Pπ: 4.1 mW), reasonable propagation loss (0.02 dB/μm), small driving-voltage (Vπ: 0.12 V), fast switching time (rise/fall

A novel high conversion ratio bidirectional C-dual transformers-LC (CDT-LC) resonant dc–dc converter is proposed in this paper. Based on the traditional LLC, an auxiliary transformer and an extra resonant capacitance are employed in the CDT-LC structure. It not only harvests high efficiency, but exhibits a good voltage gain feature. Especially for the case of light load, CDT-LC still harvests a high efficiency, compared with traditional converters. Also, it can achieve a fast gain reduction when the switching frequency is higher than resonant frequency. In this paper, the operating principles of the converter are analyzed in both bidirectional operation modes. In addition, its dual-transformers structure feature and voltage gain characteristics are discussed in details. Furthermore, the parameter design method is provided. Moreover, the loss breakdown for the converter is given in details. Finally, a 2.5-kW prototype is established to verify the performance of the CDT-LC converter, and its maximum efficiency reaches 97%.

The successful development of artificial photosynthesis requires finding new materials able to efficiently harvest sunlight and catalyze hydrogen generation and carbon dioxide reduction reactions. Plasmonic nanoparticles are promising candidates for these tasks, due to their ability to confine solar energy into molecular regions. Here, we review recent developments in hybrid plasmonic photocatalysis, including the combination of plasmonic nanomaterials with catalytic metals, semiconductors, perovskites, 2D materials, metal-organic frameworks, and electrochemical cells. We perform a quantitative comparison of the demonstrated activity and selectivity of these materials for solar fuel generation in the liquid phase. In this way, we critically assess the state-of-the-art of hybrid plasmonic photocatalysts for solar fuel production, allowing its benchmarking against other existing heterogeneous catalysts. Our analysis allows the identification of the best performing plasmonic systems, useful to design a new generation of plasmonic catalysts.

Tailoring optical properties in photocatalysts by nanostructuring them can help increase solar light harvesting efficiencies in a wide range of materials. Whereas plasmon resonances are widely employed in metallic catalysts for this purpose, latest advances of nonradiative, dielectric nanophotonics also enable light confinement and enhanced visible light absorption in semiconductors. Here, a design procedure for large-scale nanofabrication of semiconductor photoelectrodes using imprint lithography is developed. Anapole excitations and metasurface lattice resonances are combined to enhance the absorption of the model material, amorphous gallium phosphide (a-GaP), over the visible spectrum. It is shown that cost-effective, high sample throughput is achieved while retaining the precise signature of the engineered photonic states. Photoelectrochemical measurements under hydrogen evolution reaction conditions and sunlight illumination reveal the contributions of the respective resonances and demonstrate an overall photocurrent enhancement of 5.7, compared to a planar film. These results are supported by optical and numerical analysis of single nanodisks and of the upscaled metasurface.https://onlinelibrary.wiley.com/doi/10.1002/aenm.202102877

In the process of construction and service, high-grade line pipes will get defective, e.g. dents, which will change its stress and strain distribution characteristics and impact its service reliability. In this paper, a X80 line pipe was taken as the research object. The distribution characteristics of the strain field in the X80 line pipe with plain dents with the change of dent depth under external load were analyzed using the finite element analysis software ABAQUS. Then, the strain distribution and microstructure characteristics in the dent zone were explored by conducting prefabrication test on physical dent. Finally, combined with the finite element simulation results, the strain distribution laws of the X80 line pipe with plain dent were discussed. And the following research results were obtained. First, under the same internal pressure, the strain distribution characteristics in the dent zone at different dent depths are similar, i.e., the strain increases with the increase of the distance from the center of the dent, and decreases rapidly with the increase of the distance after the peak strain. Second, the strain increases with the increase of dent depth, and under the same internal pressure and dent depth, the axial strain is larger than the radial strain at the same location. Third, the greater the dent depth, the stronger the superposition effect of internal pressure and depth on the strain. Fourth, strain hardening occurs on the materials in the initial stage of the dent deformation. With the aggravation of deformation and the extension of dent radius, the strain response ability of materials increases, the grains at the bottom and side walls of the dent zone are elongated along the direction of maximum deformation, the lattice is distorted and strain hardening occurs. As a result, the dislocation density in this zone increases and the interaction occurs between dislocations, as a result, the strength of line steel is enhanced. In conclusion, the research results do well in predicting the stress–strain evolution laws in the process of dent, and provide a theoretical foundation and an experimental basis for studying the influence of mechanical damage on the service safety of pipelines. Keywords: X80 line pipe, Finite element simulation, Dent, Dent depth, Strain, Strain hardening, ABAQUS, Microstructure characteristic

Nonwovens are widely applied in the air filtration field for their multi-layered fibrous structures and interconnected pores. Despite their intensive use, conventional microfiber nonwovens usually suffer from low filtration efficiencies due to their large pore size, while most nanofiber nonwovens are still confined within the laboratory due to the difficulties of reconciling the comprehensive requirements (such as low pressure drop, high fluffiness, strength and long-term reliability) raised from practical applications. Herein, we report a simple and scalable method that can generate more nanofibrils in a para-aramid microfiber nonwoven without interfering with the three-dimensional nonwoven structure. The success of this method relies on treating the whole nonwoven, rather than individual fibers, with phosphoric acid to trigger a surface fibrillation process of para-aramid microfibers. The structural reinforcement from microfibers, in combination with the enlarged surface area and the reduced pore size brought by nanofibrils, improves the filtration efficiency of the fibrillated nonwoven by 84.7% and maintains the pressure drop at an ultralow value of 3.5 Pa. Further synthesis and loading of a novel catalyst (CuO–CeO2) onto the nonwoven demonstrates a higher catalyst-loading capacity after fibrillation. The resulting nonwoven filter shows high elimination rates against a variety of solid and gaseous pollutants (including particulate matter, carbon monoxide and toluene), and is applicable at both room and elevated temperatures. We believe that the generation of nanofibrils in microfiber nonwovens and the subsequent loading of catalysts will find extensive utility in the purification of industrial emissions, automobile exhausts and indoor air.

A three-port optical phase-shifter and Mach-Zehnder modulator (MZM) based on PNP-type bipolar junction transistor (BJT) is demonstrated. Significant plasma (injected carrier) induced changes of the refractive index for the optical waveguide become possible with an extremely small driving-voltage and a compact device size during operation of this BJT between the saturation and forward active modes. Devices with a standard MZM structure and a small foot-print (0.5 mm) exhibit a moderate optical insertion loss (2 dB), extremely small Vπ (0.18V) and Pπ (0.21mW), fast rise/fall time (~1ns), and a residue-amplitudemodulation (RAM) as small as 0.18 dB. Furthermore, thanks to the ultra-high modulation efficiency characteristic of our device, a +4.0 dB net RF-linking gain can be obtained under dynamic operation. Compared to 2-port (base-collector) forward bias operation, under three-port operation, the extra bias current from the base-emitter junction provides a lower Vπ (0.18 vs. 0.22 V), a smaller RAM (0.18 vs. 0.6 dB), and a larger RF-linking gain (+4 vs. -3.2 dB). The superior performances of the three-port to two-port operations can be attributed to the additional forward bias B-E junction being able to provide more injected carriers to induce stronger plasma effects for optical phase-shifting.

In this work, we demonstrate a novel top-illuminated avalanche photodiode (APD) with high-speed and wide dynamic range performance for coherent lidar applications, which needs simultaneous processing of weak light reflections from the object and a strong optical local-oscillator (LO) signal at the receiving end. By taking advantage of a partially depleted p-type In0.53Ga0.47As absorbing layer and a thin In0.52Al0.48As multiplication layer (88 nm), the demonstrated APDs exhibit a wide optical-to-electrical bandwidth (16 GHz) and high responsivity (2.5 A/W at 0.9 Vbr) near the saturation output current which is as high as >8 mA. Furthermore, the measured low excess noise (k = 0.14) characteristics of this device ensure its wide dynamic range performance. In addition, it should be noted that the measured nonlinear behaviors of these APDs are quite different from those of typical fast p-i-n photodiodes (PDs), which always show serious degradation in their O-E bandwidths at their saturation output. On the other hand, the measured bias dependent 3-dB O-E bandwidth of the demonstrated APDs can be pinned at 16 GHz without any degradation at around the saturation current output. Such distinct nonlinear APD behaviors can be attributed to the space-charge-screening effect induced gain reduction under high-power operation.

By using nano-infiltration and transient eutectic (NITE) phase with nanosized SiC and the addition of CeO2–Al2O3 as joining material, liquid-phase-sintered SiC ceramics were joined at the relatively low temperature of 1500 °C and 1700 °C. For comparison purpose, Al2O3–Y2O3 and SiO2–Al2O3–Y2O3 were used as the additives to join SiC ceramics. The shear strength of SiC assembly with the interlayer thickness of ~70 μm and addition of CeO2–Al2O3 after joining at 1700 °C was measured to be 163.9 MPa but decreased to 57.4 MPa when joining at 1500 °C. It was revealed that the joining status could be improved by decreasing the thickness of the interlayer to ~35 μm and SiC joint finishing at 1500 °C possessed the comparatively high shear strength of 113.2 MPa. NITE phase containing other additives (Al2O3–Y2O3 and SiO2–Al2O3–Y2O3) showed the much lower shear strength after joining at 1500 °C.

Ni-rich layered oxides (LiNi1-x-yCoxMnyO2, 1-x-y ≥ 0.5) are attracting great attention due to their high capacity and operating voltage. However, Ni-rich layered oxides still face long-standing challenges, such as incomplete capacity release and fast capacity fade, especially at high C rates. Herein, we implement a wet chemical method to dope Ti into LiNi0.8Co0.1Mn0.1O2 (NCM811). We discover that NCM811 with the homogeneously distributed Ti can effectively enhance ion transfer kinetics and thus greatly improve capacity delivery at high C rates. The Ti-doped NCM811 exhibits a capacity of 196 mAh/g and 157 mAh/g at 0.5C and 2C in voltage range of 2.8–4.6 V, 5% higher (188 mAh/g at 0.5C) and 15% higher (136 mAh/g at 2C) than the pristine NCM811. Ti-doped NCM811 cathodes also exhibit enhanced cycling stability with capacity retention of 84% after 100 cycles at 1C, which shows that our methodology for Ti doping is potentially competitive for a practical production of Ni-rich layered oxides.

This paper investigates the cold start characteristic of the polymer electrolyte membrane fuel cell stack in the constant voltage startup mode. The stack is used in actual vehicle working conditions, so it is practical significance to study the cold start characteristics of the stack. The evolution of the temperature and current density distribution at different regions in the constant voltage mode of the stack are studied. Consistency analyzes from two dimensions, in-plane and through-plane are studied. Then, the performance degradation of the stack after the cold start is explored through the polarization curve and the voltage consistency. The cold start characteristics and performance degradation mechanism of the stack are found. The stack has better cold start performance than that of the single cell, which can realize a rapid cold start at −15 °C in 95 s. Also, the performance of the single cell in the middle position is obviously better than that of the single cell on both sides. The internal behavior of each single cell during cold start process is different and the performance consistency is poor after the failed cold start. The performance degradation gradually decreases from the single cell near the inlet to the single cell far away from the inlet. This paper can provide direction for the optimization cold start strategy.

Under the vehicle working conditions, operating temperature and relative humidity (RH) of gas supplies have an important influence on the performance and durability of PEMFC. In this paper, the influence of hydrogen RH, air RH, operating temperature and air stoichiometric ratio on the performance of PEMFC was studied with the help of 5 factors and 4 levels orthogonal test table. The fifth factor was set to be empty to carry out the variance analysis. Using variance analysis method, the influence degree of random errors on the experiments was analyzed. The credibility of the experimental results was verified along with the polarization curve and the electrochemical impedances spectroscopy (EIS) results. The experiment results show that the most important factor which affects the performance of PEMFC is air stoichiometric ratio, followed by air RH, and then the operating temperature. The effect of hydrogen RH on PEMFC performance is minimal and negligible. Low hydrogen RH can be used during operation to reduce energy consumption of auxiliary system.

Photocatalytic oxidation has been widely employed in organic synthesis, by virtue of the green, mild and simple reaction conditions as well as high selectivity. Introducing oxygen vacancies (OVs) with proper concentrations into the photocatalysts has been proven as an effective strategy to boost the catalytic performances. However, the currently used treatment method under high temperature at reducing atmosphere inevitably introduces a large number of OVs at the interior of the catalyst and serving as the recombination centers of carriers. To address this issue, here we develop a facile solvothermal process to prepare ultrathin BiOBr nanosheets with rich surface OVs. This method effectively decreases the bulk of the material and the ratio of interior OVs, rendering most of the OVs exposed on the surfaces which act as exposed catalytic sites and enhance the separation of carriers, therefore significantly elevates the photocatalytic performances. For the photo-oxidation reaction of secondary amines, under the conditions of visible light, ambient temperature and atmosphere, the BiOBr nanosheets featuring rich surface OVs deliver a doubled conversion compared to those with low OV concentrations, and a high selectivity of 99%, a high stability as the performance shows no reduction after 5 times of circular reaction.

Aristolochia and related plants contain nephrotoxins and mutagens in the form of aristolochic acids (AAs). However, there is still lack of a fast and specific method for monitoring AAs in biological samples. Herein, we synthesized a hybrid magnetic mesoporous carbon-molecularly imprinted polymers (MMC@MIPs) as a novel magnetic solid-phase extraction (MSPE) adsorbent for selective recognition of aristolochic acid I and II from rat urine samples. The choline chloride/glycol-based deep eutectic solvent (DES) and indomethacin were used as the eluent and dummy template molecule accordingly. The morphology, structure property and surface groups of the prepared materials were investigated in sequence, and the optimum conditions of the MMC@MIPs-MSPE procedure were also optimized well. Results showed that the proposed method had a relatively satisfactory recovery (86.7-94.3%), with low standard deviation (

Pressureless joining of SiC ceramics at low temperature was developed using Ti powder interlayer. Phase assemblage and microstructure of SiC joint revealed that the products after diffusion bonding mainly consisted of Ti5Si3 and TiC owing to the comparatively low joining temperature. Additionally, Si and C elements were found to be with higher penetration depth in the Ti interlayer. Benefitting from the lower proportion of the brittle Ti5Si3 phase and porosity, shear strength reached a relatively higher value of 41 MPa after joining at 1200 °C for 30 min.

To study the oxygen reduction reaction (ORR) at different through-plane position in catalyst layer, a multiple catalyst layer (MCL) was designed in which the reaction area could move from proton exchange membrane (PEM) to gas diffusion layer (GDL). The reaction layer (layer Y) was sandwiched between proton conduct layer (layer X) and air diffusion layer (layer Z) to simulate the real reacting process in an ordinary catalyst layer. Three MEA samples with MCL were made, the reaction area was set near the PEM, in the middle of catalyst layer and near the GDL, respectively. According to the polarization curves, the position of reaction area in catalyst layer has obvious influence on cell performance and the output current at the same working voltage increased when the reaction area moved towards GDL. Besides, how the charge transfer resistance and mass transport resistance of reaction area at different position in CL changed when output current increased has also been studied in this work using EIS. Simulation results about current and proton distribution have also been verified in this work.

Proton Exchange Membrane Fuel Cell can have a large active area, and the working condition in different areas can be entirely different. Localized electrochemical impedance spectroscopy can directly observe the proton exchange membrane fuel cell internal reaction conditions. In this work, localized electrochemical impedance spectroscopy test system based on print circuit board is implemented in a 50 cm2 multi-channel serpentine flow fields. The localized electrochemical impedance spectroscopy performances of different segments with different cathode stoichiometry (1.8, 2.3 and 2.8) at different current density (100 mA cm−2, 500 mA cm−2 and 900 mA cm−2) are studied. The result demonstrates that the fuel cell may suffer from local drying and flooding at the same time. To make full use of the potential of a fuel cell, a suitable cathode stoichiometry should be identified to control the drying of the inlet and the flooding of the outlet at the same time. It is shown that a cathode stoichiometry of 2.3 is close to the optimum cathode stoichiometry to keep the fuel cell in good consistency without gas waste. Besides, a current density distribution measurement is performed to verify the conclusions of this work.

The flow velocity and pressure distribution of the three cathode flow fields are simulated in this study. Larger pressure drop and more rapid flow rate reduce residual water, resulting in minimal ice formation during the cold start process. The simulation results show that the single variable cross section serpentine flow field has the largest pressure drop and the most rapid flow rate. The evolution of the temperature and the segment current density characteristics of three different cathode flow fields during cold start process is studied by printed circuit board technology. The results show that the 2 to 1 serpentine flow field has the best cold start performance and the best current density uniformity when cold start at constant voltage mode above −5 °C. However, the single variable cross section serpentine flow field has the best performance when cold start temperature is below −5 °C. Based on these results, cold start at −30 °C can be realized in 97s by using hot antifreeze liquid.

Heterojunctions modulated internal electric field (IEF) usually result in suboptimal efficiencies in carrier separation and utilization because of the narrow IEF distribution and long migration paths of photocarriers. In this work, we report distinctive bismuth oxyhydroxide compound nanorods (denoted as BOH NRs) featuring surface-exposed open channels and a simple chemical composition; by simply modifying the bulk anion layers to overcome the limitations of heterojunctions, the bulk IEF could be readily modulated. Benefiting from the unique crystal structure and the localization of valence electrons, the bulk IEF intensity increases with the atomic number of introduced halide anions. Therefore, A low exchange ratio (~10%) with halide anions (I–, Br–, Cl–) gives rise to a prominent elevation in carrier separation efficiency and better photocatalytic performance for benzylamine coupling oxidation. Here, our work offers new insights into the design and optimization of semiconductor photocatalysts., Research on the bulk internal electric field (IEF) regulation is significant for designing high-efficiency photocatalysts. Here, the authors report distinctive bismuth oxyhydroxide nanorods photocatalyst and increase the bulk IEF intensity by halogen ions exchange.

Quantum dots (QDs) as a promising optical probe have been widely used for in vivo biomedical imaging; especially enormous efforts recently have focused on the potential toxicity of QDs to the human body. The toxicological effects of the representative InP/ZnS QDs as a cadmium-free emitter are still in the early stage and have not been fully unveiled. In this study, the DPPC/DPPG mixed monolayer was used to simulate the lung surfactant monolayer. The InP/ZnS-COOH QDs and InP/ZnS-NH2 QDs were introduced to simulate the lung surfactant membrane’s environment in the presence of InP/ZnS QDs. The effects of InP/ZnS QDs on the surface behavior, elastic modulus, and stability of DPPC/DPPG mixed monolayer were explored by the surface pressure-mean molecular area isotherms and surface pressure-time curves. The images observed by Brewster angle microscope and atomic force microscope showed that the InP/ZnS QDs affected the morphology of the monolayer. The results further demonstrated that the InP/ZnS QDs coated with different surface groups can obviously adjust the mean molecular area, elastic modulus, stability, and microstructure of DPPC/DPPG mixed monolayer. Overall, this work provided useful information for in-depth understanding of the effects of the −COOH or −NH2 group coated InP/ZnS QDs on the surface of lung surfactant membrane, which will help scientists to further study the physiological toxicity of InP/ZnS QDs to lung health.

A novel polarization-independent electro-absorption graphene modulator is proposed. Two layers of graphene structure are transferred on the inclined arsenic selenide and then covered with arsenic selenide to form a partially inclined graphene-arsenic selenide waveguide structure. According to the simulation results, TE and TM effective mode in the waveguide have almost the same change under different Graphene chemical potentials near the 3 μm wavelength. For the 100-μm-long waveguide structure, the extinction ratio (ER) of about 20 dB can be achieved through the selection of low absorption ("ON") and high absorption ("OFF") state points, and the gap between the two modes’ ER is less than 1.2 dB. The dependency of these two polarization states in "ON" state is lower than 0.112 dB, which indicates that the device can be used as polarization independent modulation. And combined with simulation calculations, the theoretical 3 dB modulation bandwidth (f3dB) of the proposed modulator reaches 43.5 GHz.

Durability is an important factor in evaluating the performance of a catalyst. In this work, the spatial protection of the carrier to nanoparticles was considered to improve the durability of the catalyst. It is found that a honeycombed graphene with a three-dimensional (3D)-hierarchical porous structure (3D HPG) can help to reduce the shedding of Pt-Co nanoparticles (Pt-Co NPs) because 3D HPG can form a protective layer to reduce the direct erosion of Pt-Co NPs on the interface by an electrolyte. Then, appropriate oxygen groups were introduced on the 3D reduced hierarchical porous graphene oxide (3D rHPGO) to improve the dispersion of Pt-Co NPs on the surface of the carrier. It was found that the Pt d-band of the catalyst was anchored by π sites of carbonyl of an oxygen group. After optimization, the catalyst (referred to as Pt-Co/3D rHPGO) achieved a 2-fold enhancement in mass activity than that of a commercial Pt/C catalyst. More importantly, after the accelerated durability test (ADT) of 20 000 cycles, the Pt-Co/3D rHPGO catalyst can almost sustain this level of performance, whereas other catalysts showed a comparatively large loss of activity. According to the results, the high durability of Pt-Co/3D rHPGO was attributed to spatial protection of Pt-Co NPs and the defects on the surface allowed the electrolyte to enter. In addition, oxygen groups provided an anchoring effect on nanoparticles. Thus, the Pt-Co/3D rHPGO electrocatalyst exhibited splendid durability, holding a potential to be applied in PEMFC for long-term work.

A polarization-insensitive graphene-based mid-infrared optical modulator is presented that comprised SiO2/ Ge23Sb7S70, in which two graphene layers are embedded with a semiellipse layout to support transverse magnetic (TM) and transverse electric (TE) polarizing modes with identical absorption. The key performance index for the polarization independent modulator is polarization-sensitivity loss (PSL). The waveguide of our device just supports basic TE and TM modes, and the PSL between two modes is of

The wide application of multi-frequency atomic force microscopy (AFM) places higher demands on the higher-order modes response of the cantilever. The response of the higher modes however is generally weaker than that of the fundamental mode in air. Researchers have proposed many methods, most of which involve cantilever modification, to enhance higher-order eigenmodes response. These previous results are proved to be effective, but the microfabrication is expensive. In this article, we propose a novel model based on bridge/cantilever coupled system to enhance the higher-order modes response of AFM cantilever. The segmented beam model provides a new thinking to explain the appearance of undesired peaks in mode analysis of cantilever. Through theoretical analysis and simulation, we find that higher resonance modes are enhanced by tuning the bridge to match the high resonances of the single clamped cantilever. The length, thickness of the coupled system and the location of excitation can affect the enhancement. In summary, this model provides a new way to improve higher mode response for multi-frequency and other high bandwidth applications of AFM.

In this work, we demonstrate In0.52Al0.48As top/backside-illuminated avalanche photodiodes (APD) with dual multiplication layers for high-speed and wide dynamic range performances. Our fabricated top-illuminated APDs, with a partially depleted p-type In0.53Ga0.47As absorber layer and thin In0.52Al0.48As dual multiplication (M-) layer (60 and 88 nm), exhibit a wide optical-to-electrical bandwidth (16 GHz) with high responsivity (2.5 A/W) under strong light illumination (around 1 mW). The measured bias dependent 3-dB O-E bandwidth was pinned at 16 GHz without any serious degradation near the saturation current output. To further increase the speed, we downscaled the active diameter and adopted a back-side illuminated structure with flip-chip bonding for batter optical alignment tolerance. A significant improvement in maximum bandwidth was demonstrated (25 versus 18 GHz). On the other hand, we adopted a thick dual M-layer (200 and 300 nm) and 2 μm absorber layer in the APD design to circumvent the problem of serious bandwidth degradation under high gain (&gt, 100) and high-power operation which significantly enhanced the dynamic range. Due to dual M-layer, the carriers could be energized in the first M-layer then propagate to the second M-layer to trigger the avalanche process. In both cases, despite variation in thickness of the absorber and M-layer, the cascade avalanche process leads to values close to the ultra-high gain bandwidth product (GBP) of around 460 GHz with a responsivity of 0.4 and 1 A/W at unit gain for the thin and thick M-layer devices, respectively. We successfully achieved a good sensitivity of around −20.6 dBm optical modulation amplitude (OMA) at a data rate of 25.78 Gb/s, by packaging the fabricated APDs (thin dual M-layer (60 and 88 nm) version) with a 25 Gb/s trans-impedance amplifier in a 100 Gb/s ROSA package. The results show that, the incorporation of a dual multiplication (M) layer structure in the APD opens a new window to obtaining the higher GBP in order to meet the requirements for high-speed transmission without the need of further downscaling the multiplication layer.

Dual multiplication-layers APDs with large bandwidth-responsivity product (460GHz-A/W), saturation-current (>10mA), and IF-power (+4.5dBm) are demonstrated in self-heterodyne FWCW lidar systems with ~285% modulation depths. Constructed images show 9.5dB larger SNRs than that of p-i-n PD.

Inspired by nature, many functional surfaces have been developed with special structures in biology, chemistry, and materials. Many research studies have been focused on the preparation of surfaces with static structure. Achieving dynamical manipulation of surface structure is desired but still a great challenge. Herein, a polyelectrolyte film capable of regional and reversible changes in the microporous structure is presented. Our proposal is based on the combination of azobenzene (Azo) π-π stacking and electrostatic interaction, which could be affected respectively by ultraviolet (UV) irradiation and water plasticization, to tune the mobility of polyelectrolyte chains. The porous patterns can be obtained after regional ultraviolet irradiation and acid treatment. Owing to the reversibility of Azo π-π stacking and electrostatic interaction, the patterns can be repeatedly created and erased in the polyelectrolyte film made by layer-by-layer (LbL) self-assembly of poly(ethyleneimine)-azo and poly(acrylic acid). Furthermore, through two rounds of porous pattern formation and erasure, different functional species can be loaded separately and confined regionally within the film, showing potential applications in the functional surface. This work highlights the coordination of two noncovalent interactions in thin films for regional and reversible controlling its structure, opening a window for more in-depth development of functional surfaces.

Solar-powered water splitting is expected to be a promising route for sustainable hydrogen production. However, its wide implementation is hampered by expensive electrocatalysts and photovoltaic apparatus. Herein, we designed a low-cost overall water splitting system combining flexible catalyst electrodes and one novel organic solar cell. The flexible electrodes contain carbon fabric functionalized with nitrogen-doped carbon encased iron-cobalt bimetallic phosphide and sulfide nanohybrids as electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. The electrolyzer for overall water splitting can realize a current density of 10 mA cm−2 at a low cell voltage of 1.60 V and remain stable in long-time durability test in alkaline media. Moreover, when driven by one organic solar cell, our system yields a record high water-splitting current density of 7.5 mA cm−2 with a solar-to-hydrogen efficiency of 9.2%. The above results demonstrate its potential as a real-life solar-powered hydrogen production system.

To optimize the interface of the catalyst layer (CL) and gas diffusion layer (GDL) in polymer electrolyte membrane fuel cells (PEMFCs), microporous layers (MPLs) with different decorative patterns were prepared. Carbon paper treated with polytetrafluoroethylene was used as a substrate for the coating of MPLs. To accelerate water removal and gas permeation, ammonium chloride was utilized to improve the porous structure of MPLs. Owing to the recrystallization and pyrolysis of ammonium chloride with different contents, the surface of MPLs exhibited point-, line-, and flowerlike patterns. Membrane electrode assemblies (MEAs) were assembled to evaluate the performance of MPLs with different decorative patterns. From measurements, an MEA containing a porosity-graded MPL (MPL-G) with a flowerlike pattern exhibited the best electrochemical performance. It is because that graded porosity accelerates the removal of excessive water. The flowerlike pattern facilitates the diffusion of the reactant gas at the interface of the catalyst layer and MPL. With the measurement of segmented cell technology, such MEAs revealed an improved redispersion of reactant gases. Furthermore, the produced water was compressed to the gas outlet, providing a larger active region for reaction. These results indicate that pattern design of MPLs is a promising strategy to improve the mass-transfer efficiency at the interface of the catalyst layer and gas diffusion layer.

We experimentally demonstrate the generation of 107-Gbit/s net-rate optical discrete multitone signal using a 1.5- μ m single-mode vertical cavity surface emitting laser (VCSEL) with modulation bandwidth of 22 GHz. Utilizing a nonlinearity-tolerant channel equalization algorithm for digital signal processing, total net-rates of 726.6-Gbit/s over 2.5-km dispersion-uncompensated 7-core fiber and 533.1-Gbit/s over 10-km dispersion-compensated 7-core fiber below 7% overhead hard-decision forward error correction limit have been experimentally achieved with a 1.5- μ m VCSEL-based intensity-modulation direct-detection system. The features of the 1.5- μ m single-mode VCSEL, 2.5-km/10-km multi-core fibers, and fan-in/fan-out modules are presented. Besides, the Volterra series-based nonlinearity-tolerant channel equalization algorithm, which improves the signal-to-noise ratio with more than 5 dB, is mathematically described and experimentally validated. The results have demonstrated that 1.5- μ m single-mode VCSEL and multi-core-fiber-based transmission can be a promising candidate to solve the capacity challenges in short-reach optical interconnects.

CuCo2S4 synthesized on the nitrogen-doped double-layer graphite (NDG) inter-layer revealed more uniform and smaller size than synthesized directly on Ni foam. From electrochemical measurements, the specific capacitance of CuCo2S4@NDG electrode was 1244 F g−1 at a current density of 50 A g−1, which was twice higher than the CuCo2S4@Ni electrode. In addition, the reduced graphene oxide (rGO) was used to assemble CuCo2S4@NDG//rGO asymmetric supercapacitor, revealing a high energy density (58.4 W h kg−1) for practical applications. Significantly, the NDG inter-layer improved the properties of asymmetric supercapacitor at high-rate and high energy density conditions effectively.