Triggering efficient reconstructions of Co/Fe dual-metal incorporated Ni hydroxide by phosphate additives for electrochemical hydrogen and oxygen evolutions.

Alkaline electrochemical water splitting has been considered as an efficient way for the green hydrogen production in industry, where the electrocatalysts play the critical role for the electricity-to-fuel conversion efficiency. Phosphate salts are widely used as additives in the fabrication of electrocatalysts with improved activity, but their roles on the electrocatalytic performance have not been fully understood. Herein, we fabricate Co, Fe dual-metal incorporated Ni hydroxide on Ni foam using NaH2PO4 ((Co, Fe)NiOxHy-pi) and NaH2PO2 ((Co, Fe)NiOxHy-hp) as additive, respectively. We find that (Co, Fe)NiOxHy-hp with NaH2PO2 in the fabrication shows high activity and stability for both HER and OER (a overpotential of -0.629 V and 0.65 V at 400 mA cm-2 for HER and OER, respectively). Further experiment reveals that the reconstructed structures of electrocatalyst by using NaH2PO2 (hp) endow high electrocatalytic performances: (1) in-situ generated active metal improves the accumulation, transportation and activity of hydrogen species in the HER process; and (2) in-situ generated poor-crystalline hydroxide endows superior charge/mass transportation and kinetics improvements in the OER process. Our study may provide an insightful understanding on the catalytic performance of non-precious metal electrocatalysts by controlling additives and guidance for the design and synthesis of novel electrocatalysts.

Trace detection of canine distemper virus based on Michelson-interferometer sensing probe.

A single-mode-fiber (SMF)-multimode-fiber (MMF)-tri-core-fiber (TCF) Michelson probe structure is proposed for trace detection of canine distemper virus (CDV). One end of the TCF is cut flat and fused with the multimode fiber, and the other end is coated with a silver film to enhance the reflection, and an optic-fiber sensing probe with SMF-MMF-TCF structure is obtained. The (PDDA/PSS)3 multilayer film is modified on the surface of the fiber by layer-by-layer self-assembly method as a polyelectrolyte binder to immobilize CDV antibodies to form a (PDDA/PSS)3 /CDV antibody composite membrane for specific detection of CDV antigens. The response-recovery test of the sensor is performed to verify its repeatability. The detection limit, the sensitivity, and the linear fitting degree for CDV antigen are 0.1236 pg/mL, 1.1776 dB/(pg/mL), and 0.9899, respectively. At the same time, the stability, selectivity, and clinical samples of the sensors were also verified.

On-chip Mach-Zehnder interferometer sensor with a double-slot hybrid plasmonic waveguide for high-sensitivity hydrogen detection.

An on-chip Mach-Zehnder interferometer (MZI) hydrogen sensor, applying a double-slot hybrid plasmonic (DSHP) waveguide composed of a Si waveguide and two Pd disks on both sides as the sensing arm, is designed. The optical confinement factor of the sensing area can be up to 87%. For the MZI hydrogen sensor with a DSHP waveguide of 14 µm, the sensitivity can be as high as 11.935 nm/%, corresponding to a free spectral range (FSR) of 15 nm. Furthermore, the sensor sensitivity is influenced by the MZI structure parameters, which is highly adjustable. The extinction ratio of the interference spectra can reach over 30 dB. A feasible solution is provided in this paper for highly sensitive hydrogen detection.

Controlled Epitaxial Growth of (hk1)-Sb2 Se3 Film on Cu9 S5 Single Crystal via Post-Annealing Treatment for Photodetection Application.

Antimony selenide (Sb2 Se3 ) is a promising semiconductor for photodetector applications due to its unique photovoltaic properties. Achieving optimal carrier transport in (001)-Sb2 Se3 by the material of contacting substrate requires in-depth study. In this paper, the induced growth of Sb2 Se3 films from (hk0) to (hk1) planes is achieved on digenite (Cu9 S5 ) films by post-annealing treatment. The flake-like and flower-like morphologies on the surface of Sb2 Se3 films are caused by different thicknesses of the Cu9 S5 films, which are related to the (hk0) and (hk1) planes of Sb2 Se3 surface. The epitaxial growth of Sb2 Se3 films on (105)-Cu9 S5 surfaces exhibits thickness dependence. The results inform research into the controlled induced growth of low-dimensional materials. The device of Sb2 Se3 /Cu9 S5 /Si has good broadband response (visible to near-infrared), self-powered characteristics, and stability. As the crystalline quality of the Sb2 Se3 film increases along the (hk1) plane, the carrier transport is enhanced correspondingly. Under the 980 nm light irradiation, the device has an excellent switching ratio of 2 × 104 at 0 bias, with responsivity, detectivity, and response time up to 17 µA W-1 , 1.48 × 107 Jones, and 355/490 µs, respectively. This suggests that Sb2 Se3 is suitable for self-powered photodetectors and related optical and optoelectronic devices.

Broadband high-performance vertical WS1.08Se0.92/Si heterojunction photodetector with MXene electrode.

Vertical semiconductor van der Waals heterojunctions are essential for fabricating high-performance photodetectors. However, the range of the spectral response and defect states of semiconductor materials are two critical factors affecting the performance of photodetectors. In this work, the spectral response range of WS2was changed through WS2band gap regulation, and a self-powered vertical WS1.08Se0.92/Si heterojunction photodetector with MXene electrode was prepared by synthesizing WS1.08Se0.92film on Si substrate and vertically stacking Ti3C2TxMXene on the film. Due to the electron collection of MXene and the wonderful junction quality of WS1.08Se0.92/Si, the photodetector can detect near-infrared light in the range of 980-1310 nm, which exceed the detection limit of WS1.08Se0.92. And the device had high sensitivity in the broadband. The responsivity was 4.58 A W-1, the specific detectivity was 4.58 × 1011Jones, the on/off ratio was 4.95 × 103, and the fast response time was 9.81/9.03µs. These properties are superior to previously reported WS2-based photodetectors. Vertical structure, Energy band tuning, and MXene electrode provide a new idea for preparing broadband high-performance and self-powered photodetector.

Electronic and magnetic properties of layered M3Si2Te6(M = alkaline earth and transition metals).

Recently, a new layered material, Mn3Si2Te6, was identified to be a semiconductor with nodal-line topological property and ferrimagnetic ground state. In this work, we propose a series of structures, M3Si2Te6(M = alkaline earth and transition metals), and systematically investigate their mechanical, magnetic and electronic properties, and the strain effect to enrich the family of the layered materials for practical applications. We find 13 stable M3Si2Te6, including 5 semiconductors (M = Ca, Sr, Fe, Ru and Os) and 8 metals (M = Sc, Ti, Nb, Ta, Cr, Mo, W and Tc). Two structures (M = Ti and Cr) are antiferromagnetic (AFM), while other structures are non-magnetic (NM). Similar to Mn3Si2Te6, the AFM structures exhibit magnetic anisotropy energies (MAEs) and semiconductors have anisotropic electron effective masses. We further show that compressions along thez-axis can effectively tune the electronic and magnetic properties, such as the semiconductor-metal and NM-AFM transition in Fe3Si2Te6, the two-fold degeneracy of the valence band maximums in Sr3Si2Te6, as well as the reduced MAE for all magnetic structures. These results demonstrate the diverse properties of the layered M3Si2Te6family and provide promising theoretical predictions for the future design of new layered materials.

Advances in Spin Catalysts for Oxygen Evolution and Reduction Reactions.

Searching for high effective catalysts has been an endless effort to improve the efficiency of green energy harvesting and degradation of pollutants. In the past decades, tremendous strategies are explored to achieve high effective catalysts, and various theoretical understandings are proposed for the improved activity. As the catalytic reaction occurs at the surface or edge, the unsaturated ions may lead to the fluctuation of spin. Meanwhile, transition metals in catalysts have diverse spin states and may yield the spin effects. Therefore, the role of spin or magnetic moment should be carefully examined. In this review, the recent development of spin catalysts is discussed to give an insightful view on the origins for the improved catalytic activity. First, a brief introduction on the applications and advances in spin-related catalytic phenomena, is given, and then the fundamental principles of spin catalysts and magnetic fields-radical reactions are introduced in the second part. The spin-related catalytic performance reported in oxygen evolution/reduction reaction (OER/ORR) is systematically discussed in the third part, and general rules are summarized accordingly. Finally, the challenges and perspectives are given. This review may provide an insightful understanding of the microscopic mechanisms of catalytic phenomena and guide the design of spin-related catalysts.

Vertically oriented ReS2(1-x)Se2x nanosheet-formed porous arrays on SiO2/Si substrates for ultraviolet-visible photoelectric detection.

Rhenium (Re)-based transition metal dichalcogenides (TMDs) have excellent in-plane anisotropic optical and electrical properties. However, their distorted octahedral (1T') structure and weak interlayer coupling easily lead to anisotropic and out-of-plane growth, which makes it particularly difficult to prepare large-area Re-based TMD continuous porous films on SiO2/Si substrates. In this work, ReS2 films are synthesized on SiO2/Si substrates by using tellurium (Te) powder-assisted chemical vapor deposition, and then the films are selenized to synthesize a series of continuous large-area ReS2(1-x)Se2x (x = 0, 0.34, 0.56, 0.84, and 0.91) nanosheet-formed porous films. Furthermore, prototype ReS2(1-x)Se2x photodetectors with different Se compositions are fabricated. The surface morphology, high quality crystallization and compositions are confirmed by various characterization techniques. The ReS2(1-x)Se2x photodetectors based on these films show excellent ultraviolet-visible (UV-vis) spectral responses and self-powered characteristics. The response time is faster, and the photocurrent increases with the Se composition. Due to the Schottky barrier generated by the Ag-ReS2(1-x)Se2x interface, the device without bias voltage has a superior responsivity (121.9 mA W-1), high detectivity (5.27 × 1012 Jones), good on/off ratio (1.2 × 103) and fast response time (rising/decay times, 30/60 ms) under 365 nm light irradiation. This simple and controllable method opens up a new way to produce high-quality vertically oriented ReS2(1-x)Se2x porous arrays on SiO2/Si substrates for next-generation application in UV-vis photodetectors.

M4 B6 X6 as a New Family of High-Efficient Electrocatalysts: The Role of Surface Reconstruction in Water Oxidization.

Searching for highly-efficient electrocatalysts for water splitting has been greatly endowed due to the huge demand for green energy sources. Two-dimensional (2D) materials are widely explored for the purpose because of their unique physical and chemical properties, abundant active sites, and easy fabrication. Here, we present a new family of 2D M4 B6 X6 (2D Boridenes) and investigate their physical and chemical properties for their potential applications into electrocatalysis based on first-principles calculations. We demonstrate that 2D M4 B6 X6 (M=Cr, Mo, and W; X=O and F) are dynamically, thermodynamically, and mechanically stable, and show intriguing electronic and catalytic properties. Importantly, we find that M4 B6 O6 are intrinsically active for oxygen evolution reaction (OER). Our results demonstrate that: (1) the adsorbate-escape mechanism dominates the OER process with a low overpotential of 0.652 V on Cr4 B6 O6 ; (2) the partial surface-oxidization can improve the catalytic performance of M4 B6 F6 dramatically; and (3) the surface reconstruction greatly affects the OER performance of M4 B6 X6 . Our findings illustrate that the surface reconstruction is critical to the OER activity, which may provide a new strategy on the design of 2D materials for electrocatalysis and offer theoretical insight into the catalytic mechanism.

Hollow terbium metal-organic-framework spheres: preparation and their performance in Fe3+ detection.

Hollow metal-organic framework (MOF) micro/nanostructures have been attracting a great amount of research interest in recent years. However, the synthesis of hollow metal-organic frameworks (MOFs) is a great challenge. In this paper, by using 1,3,5-benzenetricarboxylic acid (H3BTC) as the organic ligand and 2,5-thiophenedicarboxylic acid (H2TDC) as the competitive ligand and protective agent, hollow terbium MOFs (Tb-MOFs) spheres were synthesized by a one-pot solvothermal method. By comparing the morphology of Tb-MOFs in the presence and absence of H2TDC, it is found that H2TDC plays a key role in the formation of the hollow spherical structure. Single crystal analyses and element analysis confirm that H2TDC is not involved in the coordination with Tb3+. Interestingly, Tb-MOFs can be used as the luminescent probes for Fe3+ recognition in aqueous and N,N-dimethylformamide (DMF) solutions. In aqueous solution, the quenching constant (K SV) is 5.8 × 10-4 M-1, and the limit of detection (LOD) is 2.05 µM. In DMF, the K SV and LOD are 9.5 × 10-4 M-1 and 0.80 µM, respectively. The sensing mechanism is that the excitation energy absorption of Fe3+ ions reduces the energy transfer efficiency from the ligand to Tb3+ ions.

Synthesis of vertically-aligned large-area MoS2nanofilm and its application in MoS2/Si heterostructure photodetector.

Van der Waals heterostructures based on the combination of 2D transition metal dichalcogenides and conventional semiconductors offer new opportunities for the next generation of optoelectronics. In this work, the sulfurization of Mo film is used to synthesize vertically-aligned MoS2nanofilm (V-MoS2) with wafer-size and layer controllability. The V-MoS2/n-Si heterojunction was fabricated by using a 20 nm thickness V-MoS2, and the self-powered broadband photodetectors covering from deep ultraviolet to near infrared is achieved. The device shows superior responsivity (5.06 mA W-1), good photodetectivity (5.36 × 1011Jones) and high on/off ratioIon/Ioff(8.31 × 103at 254 nm). Furthermore, the V-MoS2/n-Si heterojunction device presents a fast response speed with the rise time and fall time being 54.53 ms and 97.83 ms, respectively. The high photoelectric performances could be attributed to the high-quality heterojunction between the V-MoS2and n-Si. These findings suggest that the V-MoS2/n-Si heterojunction has great potential applications in the deep ultraviolet-near infrared detection field, and might be used as a part of the construction of integrated optoelectronic systems.

Cadmium-ion detection: a comparative study for a SnO2, MoS2, SnO2/MoS2, SnO2-MoS2 sensing membrane combination with a fiber-optic Mach-Zehnder interferometer.

A novel fiber-optic Mach-Zehnder interferometer based on SnO2, MoS2, SnO2/MoS2, and SnO2-MoS2 sensing film for cadmium-ion (Cd2+) detection is proposed and fabricated. The photonic-crystal fiber (PCF) is sandwiched between the no-core-fiber-1 (NCF1) and no-core-fiber-2 (NCF2), forming the Mach-Zehnder interferometer with the NCF1-PCF-NCF2 structure, which is regarded as the sensing unit. The SnO2, MoS2, SnO2/MoS2, and SnO2-MoS2 sensing films are, respectively, coated on the surface of two NCFs' claddings. The comparative experiment results of the sensors with four membranes (SnO2, MoS2, SnO2/MoS2, SnO2-MoS2) show that the sensors have good sensing performance for Cd2+ in the concentration range of 0-100 µM. When these sensing films adsorbed Cd2+, the monitoring wavelength shows blueshift of 0.6931 nm, 1.0252 nm, 1.9505 nm, respectively, and redshift of 3.0258 nm, and the sensitivities are 6.931 pm/µM, 10.252 pm/µM, 19.505 pm/µM, and 30.258 pm/µM, respectively. The sensor with SnO2-MoS2 bilayer film exhibits the optimal response to Cd2+ with excellent selectivity and stability. The proposed sensor has the advantages of simple structure, easy fabrication, small size, etc., having potential application in the monitoring of Cd2+ in aqueous solution.

Broadband InSb/Si heterojunction photodetector with graphene transparent electrode.

Silicon-based Schottky heterojunction photodetectors are promising due to their compatibility with the semiconductor process. However, the applications of these devices are usually limited to wavelengths shorter than 1.1 µm due to the low absorption of electrode materials at infrared. In this report, silicon-based compound semiconductor heterojunction photodetectors with graphene transparent electrodes are fabricated. Due to the high absorption of InSb at infrared, as well as the good transparency and excellent electrical conductivity of the graphene, the as-prepared photodetectors show a broadband photoresponse with high performance which includes a specific detectivity of 1.9 [Formula: see text]1012 cm Hz1/2 W-1, responsivity of 132 mA W-1, on/off ratio of 1 [Formula: see text]105, rise time of 2 µs, 3 dB cut-off frequency of 172 kHz, and response wavelengths covering 635 nm, 1.55 µm and 2.7 µm. This report proves that graphene as a transparent electrode has a great effect on the performance improvement of silicon-based compound semiconductor heterojunction photodetectors.

Hydrogen sulfide gas sensor based on copper/graphene oxide coated multi-node thin-core fiber interferometer.

A hydrogen sulfide gas sensor based on a copper/graphene oxide (Cu/GO) coated multi-point thin-core fiber Mach-Zehnder interferometer is proposed and experimentally demonstrated. The single-mode fiber (SMF) is sandwiched between the thin-core-fiber-1 (TCF-1) and thin-core-fiber-2 (TCF-2), and the SMF-TCF-1-SMF-TCF-2-SMF Mach-Zehnder interferometer is obtained. In order to detect the concentration of hydrogen sulfide, Cu/GO composite sensitive film was coated on the outside surface of two thin-core fibers. When the composite film absorbs the gases, it leads to a change of the effective refractive index of the cladding and causes the regular shift of dip wavelength. The result indicates that the thickness of the sensitive film is 1.6 µm. With the increase of concentration of hydrogen sulfide, the transmission spectra appear blueshift in the range of 0-60 ppm H2S. The linearity of 0.9884 and sensitivity of 4.83 pm/ppm are achieved. In addition, the dynamic response time and recovery time of the hydrogen sulfide sensor are about 32 s and 52 s, respectively. This sensor has the advantages of the small size, simple structure, and easy manufacture, and it is suitable for the detection of trace hydrogen sulfide.

Infrared Photodetector Based on the Photothermionic Effect of Graphene-Nanowall/Silicon Heterojunction.

Because of the slow relaxation process according to weak acoustic phonon interaction, the photothermionic effect in graphene could be much more obvious than in the metal film, so a graphene heterojunction photodetector based on the photothermionic effect is promising for infrared imaging applications. However, the 2.3% absorption rate of the graphene film presents a severe limitation. Here, in situ grown graphene nanowalls (GNWs) were integrated on the silicon substrate interfaced with Au nanoparticles. Because of the strong infrared absorption and hot-carrier relaxation process in GNWs, the as-prepared GNWs/Au/silicon heterojunction has a photo to dark ratio of 2 × 104, responsivity of 138 mA/W, and linear dynamic range of 89.7 dB, with a specific detectivity of 1.4 × 1010 and 1.6 × 109 cm Hz1/2/W based on calculated and measured noise, respectively, in 1550 nm at room temperature, and has the best performance among silicon-compatible infrared photodetectors without any complicated waveguide structures. Obvious photoresponses are also detected in the mid-infrared and terahertz band. The interface Au particle is found to reduce the barrier height and enhance absorption. The device structure in this report could be compatible with the semiconductor process, so that infrared photodetectors with high integration density and low cost could be potentially realized.

Hybrid graphene heterojunction photodetector with high infrared responsivity through barrier tailoring.

The graphene/Si heterojunction is attractive for high gain and broadband photodetection through photogating effect. However, the photoresponsivity in these devices are still limited to under 1 A W-1 if no narrowband absorption-enhanced nanostructures were used. In this paper, the effects of barriers on photoresponse are systematically studied at 1550 nm wavelength. Different barrier heights are obtained through selection of substrates, graphene doping and electrical tuning. Lower barrier height for graphene side and higher barrier height for silicon side are found to be beneficial for better infrared photoresponse. Through Polyetherimide doping of graphene and back-gated electrical modulation, the responsivity finally reached 5.71 A W-1, which to our knowledge is among the best results for graphene-based infrared photodetectors with graphene adopted as a light-absorption material. It is found that the thermionic emission efficiency of indirect transition in graphene is related to the difference in emissioin barrier height, and the lifetime of photoinduced carriers in the channel can be enhanced by built-in potential. These results lay the foundation for the photodetection applicatioins of graphene/Si heterojunction in the longer-wavelength infrared region.

Hydrogen sulfide sensor based on tapered fiber sandwiched between two molybdenum disulfide/citric acid composite membrane coated long-period fiber gratings.

In this work, a novel hydrogen sulfide detection scheme based on tapered fiber seeded in two long-period fiber gratings (LPGs) coated by a molybdenum disulfide/citric acid composite membrane is proposed and fabricated. The input light of a broadband source is coupled twice by passing through two LPGs with identical parameters, from which a Mach-Zehnder interferometer can be formed. The composite sensitive membrane was prepared with molybdenum disulfide and citric acid, which was coated on the surface of the two LPGs. The experimental results show that in the range of 0-70 ppm of hydrogen sulfide, with the increase of gas concentrations the interference spectra appear to blueshift. In addition, a high sensitivity of 16.65 pm/ppm, an excellent linear relationship (R2=0.97721), and high selectivity for hydrogen sulfide are achieved. The effect of temperature is also discussed. The sensor has the advantages of low cost and small volume, and can be used for detection applications at sites where hydrogen sulfide is produced, such as natural gas plants, areas of magmatic activity, coal mines, etc.

High-performance Schottky heterojunction photodetector with directly grown graphene nanowalls as electrodes.

Schottky heterojunctions based on graphene-silicon structures are promising for high-performance photodetectors. However, existing fabrication processes adopt transferred graphene as electrodes, limiting process compatibility and generating pollution because of the metal catalyst. In this report, photodetectors are fabricated using directly grown graphene nanowalls (GNWs) as electrodes. Due to the metal-free growth process, GNWs-Si heterojunctions with an ultralow measured current noise of 3.1 fA Hz-1/2 are obtained, and the as-prepared photodetectors demonstrate specific detectivities of 5.88 × 1013 cm Hz1/2 W-1 and 2.27 × 1014 cm Hz1/2 W-1 based on the measured and calculated noise current, respectively, under ambient conditions. These are among the highest reported values for planar silicon Schottky photodetectors. In addition, an on/off ratio of 2 × 107, time response of 40 µs, cut-off frequency of 8.5 kHz and responsivity of 0.52 A W-1 are simultaneously realized. The ultralow current noise is attributed to the excellent junction quality with a barrier height of 0.69 eV and an ideal factor of 1.18. Furthermore, obvious infrared photoresponse is observed in blackbody tests, and potential applications based on the photo-thermionic effect are discussed.

Synaptic plasticity in the facial nucleus in rats following infraorbital nerve manipulation after facial nerve injury.

The aim of this study is to investigate the effect of sensory input on the neural plasticity in the facial nucleus following facial nerve injury. Adult male Wistar rats were randomly assigned to four groups: (1) sham control; (2) facial nerve crush (FNC); (3) nerve crush plus daily manual vibrissal stimulation (FMS); and (4) nerve crush with infraorbital nerve transection plus daily manual stimulation (FIMS). Plasticity related proteins in the facial nucleus were evaluated by western blot at 7, 14, and 28 days postsurgery (n = 6/group per timepoint). Synaptophysin-positive terminals were evaluated by immunohistochemistry in a second set of animals (n = 6/group) at 14 days. Quantitation of synaptophysin immunostaining showed that rats in the FNC group had a significantly lower mean number of pixels compared to control animals (29.1 ± 2.6 × 10(6) vs. 34.2 ± 2.3 × 10(6); P < 0.05). Values in the FMS group (33.2 ± 1.7 × 10(6)) were similar to that of the control group, while the mean number in the FIMS group (26.5 ± 2.4 × 10(6)) was significantly lower than in the control group. Synapsin I phosphorylation was reduced to 70-83 % in FNC rats, but increased to 121-132 % in the FMS group (P < 0.05 vs. controls). Phosphorylation of cAMP response element-binding protein was similarly reduced by facial nerve crush, which was delayed in FMS animals (P < 0.05 vs. controls at 28 days). Expression and phosphorylation of all proteins were reduced to the lowest in the FIMS group (all P < 0.05). Sensory input from the IoN have a strong effect on synaptic plasticity within the facial nucleus, which is necessary to achieve the benefit of manual stimulation.

Photonic crystal fiber in-line Mach-Zehnder interferometer for explosive detection.

We report a photonic crystal fiber (PCF) in-line Mach-Zehnder interferometer used as a gas sensor device which exhibits high sensitivity to the explosive trinitrotoluene (TNT). The interferometric sensor head is formed by embedding a segment of large-mode-area/grapefruit PCF between standard single-mode fibers via butt coupling, which produces two small air gaps in between terminated fiber ends with ceramic ferrule connectors as coupling regions, which also serve as inlet/outlet for the gas. The spectral response of the interferometer is investigated in terms of its wavelength spectrum. The selectivity to TNT vapor is achieved by immobilizing a molecular recognition ployallylamine layer on the inner surface of the holey region of the PCF. The TNT-induced variations of the interference fringes are measured and the sensing capability of the proposed sensor is demonstrated experimentally.