查看更多>>摘要：Pesticides are still abused and overused in agricultural production. Food safety monitoring in terms of reliable detection and quantification of pesticide residues is an ever increasing need. Surface-Enhanced Raman Scattering (SERS)-based chemical sensors and adsorption materials crafted for specific pesticide should provide high sensitivity and selectivity. Herein, zeolitic imidazolate framework (ZIF-8) derived TiO2/ZnO three-dimensional (3D) heterostructures were constructed on FTO substrate and were utilized to assemble silver nanoparticles (AgNPs) to create electromagnetic hot spots. The formation of TiO2/ZnO heterostructure greatly improve the SERS performance of the substrate. The calculated enhancement factor (EF) of the TiO2/ZnO/Ag is 39-fold higher than the TiO2/Ag substrates. Furthermore, the substrate shows high signal sensitivity and reproducibility for rapid detection of multiple pesticides. Even with a portable Raman device, the substrate was found to be highly efficient for model molecules of crystal violet (CV) and 4-mercaptobenzoic acid (4-MBA), and the limit of detection (LOD) for both of 10?9 M was demonstrated. Importantly, real life detection of multiple pesticides residues can be achieved with the TiO2/ZnO/Ag sensor, which was demonstrated by the detection of three common pesticides, thiram, acephate and phoxim at trace concentrations.
查看更多>>摘要：Creating textured front electrodes to improve optical path length is promising to enhance the power conversion efficiency of solar cells. Deposition of transparent conductive oxides with textured surfaces usually requires additional processing steps, such as etching and coating nanoparticles. However, this makes the process complicated and inefficient. We demonstrate a one-step fabrication process to deposit high haze gallium and zirconium co-doped zinc oxides (GZO:Zr) prepared by atmospheric pressure plasma jets. GZO:Zr (2 at%) films achieve a low resistivity (7.88 × 10–4 Ω cm), a high haze (34.8%), and a great FoM (8.22 × 10?3 Ω?1). The haze factor increases from 7.19% to 34.8% (+384%) when 2% Zr is doped into GZO films. Such an enhancement of haze is attributed to the increased surface roughness and deterioration of crystallinity. AFM results show that roughness increases from 18.4 to 122 nm after 2% Zr is doped. SEM images show that spherical particles appeared on the film surface when Zr was doped into GZO films. Unlike conventional methods, our method produces hazy transparent electrodes in one step without changing any operational parameters and is suitable for industrial-scale mass production. Our findings pave the way for new applications of co-doping in transparent conductive oxides.
查看更多>>摘要：0.67(Bi1-xSmx)FeO3-0.33BaTiO3(x = 0.00 ~ 0.12) ceramics were prepared by a standard solid-state sintering method. Effects of Sm substitution on the structure, dielectric and multiferroic properties in 0.67BiFeO3-0.33BaTiO3 ceramics were investigated. Sm substitution destabilized the R3c phase, and deviated the symmetry of the present ceramics from the morphotropic phase boundary of R3c+Pm-3m to Pm-3m+P4mm. With increasing x, enhanced relaxor behaviors were observed with broaden dielectric peaks, and the slimmer P-E hysteresis loops. According to the Raman analysis and temperature dependence P-E hysteresis loops, all the compositions shown relaxor ferroelectricity with local nano-polar domains or clusters, while the domain size and distribution dominated the enhanced relaxor behaviors. Due to change of symmetry and hence the breaking of the spiral cycloidal spin structure of R3c phase, the weak ferromagnetic state with obvious macroscopic remnant magnetization was observed. Noticeable magnetoelectric (ME) coupling with linear ME voltage coefficient of αME ~ 0.55 mV/cm·Oe was achieved for x = 0.03 at room temperature. The origin of the ME properties was discussed according to the symmetry evolution.
查看更多>>摘要：Single-phase samples of the Bi0.85Ca0.15Fe1?xMnxO3 (0.1 ≤ x ≤ 0.5) perovskites have been prepared by a solid state reaction method and investigated using X-ray and neutron diffraction, scanning electron microscopy, piezoresponse force microscopy, magnetization, and ac susceptibility measurements. It has been found that the increase in Mn concentration induces a modification of crystal and magnetic structures giving rise to the canted antiferromagnetic polar phase → collinear antiferromagnetic polar phase → paramagnetic nonpolar phase transitions at room temperature. The appearance of spontaneous magnetization suggesting a transformation of the room-temperature antiferromagnetic structure characteristic of the ferroelectric Bi0.85Ca0.15Fe1?xMnxO3 compounds near the polar / nonpolar (R3c / Pnma) phase boundary is observed with decreasing temperature. The transformation of the magnetic arrangement can also be driven by a magnetic field application. Such metamagnetic transition can be accompanied by a large (up to ~4 emu/g for the sample with x = 0.4, when measured at T = 2 K) magnetization jump far exceeding that specific to a field-driven cycloidal order → canted order transformation in the pure BiFeO3. Nonpolar samples (x ≥ 0.45) acquire a large (a few emu/g) spontaneous magnetization at low temperature, a value that cannot be explained by a spin canting. It is shown that the low-temperature magnetic behavior of the polar and nonpolar Mn-enriched Bi0.85Ca0.15Fe1?xMnxO3 compounds can be successfully described in terms of an antiferromagnetic phase + glassy magnetic phase coexistence.
查看更多>>摘要：A combination of semi-metallic graphene and photosensitive two-dimensional (2D) transition metal dichalcogenide for heterostructures is ideal for high-performance optoelectronic device applications. Here, we first report semitransparent/flexible photodetectors (PDs) employing trifluoromethanesulfonyl-amide (TFSA)-doped graphene (GR) (TFSA-GR)/WS2 vertical heterostructures. The TFSA-GR/WS2 PDs show a delta-function-like photo-/dark-current (or on/off) ratio-vs-voltage behavior at zero bias, irrespective of wavelength (λ), meaning “self-powered”, mainly resulting from the surface doping of GR. The photoresponse is very sensitive in a wide ultraviolet-to-visible λ range. Maximum key figures of merit obtained for the PDs: responsivity (R), external quantum efficiency, and detectivity are 0.14 AW?1, 40%, and 2.5 × 109 cm Hz1/2 W?1, respectively, comparable to or even larger than those of previously-reported self-powered and/or hetero-structured PDs. The average transmittance of the PDs in the visible region is about 40%, indicating their semitransparency. The PDs maintain 88% of the initial R even after bending tests at 4 mm bending radius for 3000 cycles, demonstrating the excellent flexibility.
查看更多>>摘要：Half-Heusler compounds MNiSn (M = Ti, Zr, Hf) have attracted increasing attentions in the field of thermoelectrics, since their constituent elements are non-toxic and abundant. Meanwhile, it possesses good thermal stability as well as high mechanical strength. Herein, a substantial enhancement to the thermoelectric performance of intrinsic TiNiSn is achieved by passing the pulverized powders through the sieve prior to sintering. The Seebeck coefficient has increased sharply owing to the energy filtering effect, which is induced by the reduction in the average grain sizes, combined with a slightly decreased electrical conductivity, leading to a significant improvement in power factor. Moreover, the lattice thermal conductivity can be further reduced via the enhancement of the grain boundary scattering. Consequently, a maximum figure-of-merit (zT) value of 0.84 at 820 K is achieved for un-doped TiNiSn. This work indicates that the grain boundary engineering may serve as an effective method for improving the thermoelectric performance of other half-Heusler compounds.
查看更多>>摘要：The crystalline Sm-Co alloys show excellent hard magnetic properties, while the amorphous Sm-Co alloys have a poor performance. In this paper, Sm12Co76-xFe4Zr7Cu1Bx (x = 0, 2, 4, 5, 5.2) ribbons were melt-spun at 40 m/s, and the effects of B content on the phase composition, microstructure, and magnetic properties of the ribbons were studied. The results show that the main phase of all ribbons with different B content is Sm(Co, M)7. With an increase in B content, the content of amorphous and fine soft magnetic phases increases. Besides, nano-scale crystalline clusters are embedded in the amorphous matrix, forming different forms of exchange coupling microstructures between the soft and hard magnetic phases. The x = 5 ribbons have the finest grains, the most uniform grain distribution, and the strongest exchange coupling effect. Without heat treatment, their coercivity reaches 19.5 ± 0.9 kOe, and the other magnetic properties are also excellent, Mr = 24.8 ± 1.7 emu/g, M2T = 29.0 ± 1.7 emu/g, and Mr/M2T = 0.858 ± 0.015.
查看更多>>摘要：The amorphous NiFeOx(OH)y is synthesized on Fe, Ni, and Cu foam substrates to study the effects of the metal substrates on activity and stability for the electrochemical oxygen evolution reaction (OER) from water. The metal substrate for NiFeOx(OH)y catalyst does not merely perform the physical role of loading the catalyst, but actively participates in the activation process of the catalyst phase by controlling the charge transfer during the OER. The Ni foam substrate is found to be the best to make NiFeOx(OH)y/Ni foam the most active and the most stable electrode for OER in an alkaline medium due to its multiple functions. The nickel substrate forms the thinnest oxide layer on its surface to allow facile charge transfer, and stabilizes the M–Ox(OH)y structure of high oxidation degree of metals and balanced Ox/(OH)y responsible for excellent OER performance. The high intrinsic corrosion resistance of Ni and its ability to stabilize a thick layer of M–Ox(OH)y structure can also minimize the metal dissolution during the OER and provide superior long-term stability. Finally, oxidation of the Ni substrate itself results in more NiOOH phase formation to achieve an optimum NiFe composition.
查看更多>>摘要：The effect of annealing temperature on crystalline structure and magnetic behaviors are experimentally investigated for Co(Cr0.9Fe0.1)2O4 with cubic spinel structure (space group Fd3ˉm, No. 227). The average crystallite size shows an increase with the increased annealing temperature (700–1200 oC). Magnetic compensation effect and negative magnetization are observed in temperature dependent magnetization M(T) curves of samples S3-S6 with larger crystallite size, which are respectively characterized by M(T) = 0 and M(T) < 0 under a stable positive magnetic field of 100 Oe. However, the phenomena are absent in S1-S2 due to the reduction of spontaneous magnetization in samples with smaller crystallite size. Furthermore, magnetization reversal occurs to be almost the same as compensation temperature Tcomp characterized by an abrupt change in M(T) curves under a higher magnetic field. This work provides a route for the manipulation of magnetism or magnetization state by annealing the sample at different temperatures.
查看更多>>摘要：With high theoretical energy density, rechargeable lithium-oxygen (Li-O2) batteries are considered to be the most promising energy storage and conversion system. However, its development is seriously hampered by the sluggish kinetics of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), resulting in notorious overpotential and mediocre cycle stability. Here, we elaborately design the free-standing NiSe2 @NiO heterostructure on conductive carbon cloth as oxygen electrode for Li-O2 batteries. The electronic redistribution at the interface between NiSe2 and NiO caused by the strong electronic interaction can strengthen electron transfer and optimize the adsorption energy of reaction intermediates, thereby immensely boosting the ORR/OER kinetics. Therefore, Li-O2 batteries with NiSe2 @NiO oxygen electrodes show the highly discharge capacity of 11512 mAh g?1 at 500 mA g?1 and outstanding stability of over 360 h. This work enriches the understanding on the influence of electronic structure modulation of heterostructural transition metal dichalcogenides on their catalytic activity towards oxygen electrode reactions in Li-O2 batteries.
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Elsevier