Micro & Nano Letters最新文献

Multi-needle electrospinning is a simple and general method for mass preparation of nanofiber membrane, which has great industrial potential. However, the bending instability produced in the electrospinning process makes that the deposition uniformity of the nanofiber is still a big concern, resulting in non-uniform nanofiber membrane, which seriously affects the application of electrospun membrane in environmental filtration, new energy and medical fields. In order to improve the uniformity of nanofiber deposition in multi-needle electrospinning, an auxiliary flow field system (AFF) is proposed, which can effectively improve the uniformity of nanofiber deposition. After image processing, the uniformity of nanofiber deposition is quantified with the index of grey distribution, and the effectiveness of this method is verified. Combined with the multi-physical field analysis, the influence mechanism of cross-wind field on the uniformity of fibre deposition was revealed. By optimizing the experimental parameters, the non-uniformity of nanofiber deposition was reduced by 49.19%. Based on multi-needle electrospinning technology, a reliable idea (AFF) and experimental basis are provided for the uniform preparation of nanofiber membrane.

Nickel cobalt layered double hydroxides (NiCo LDHs) have emerged as ideal electrode materials for supercapattery due to their high specific surface area and excellent cycling stability. Morphology control plays a unique role in regulating the performance of the NiCo LDHs. Herein, the morphology of NiCo-LDHs electrode is optimized for enhancing energy storage by a simple activation process with different concentrations of the electrolyte. During the activation process, electrochemical morphology reconstruction occurs on the electrode surface. With a 2 m KOH electrolyte, the NiCo-LDH electrode transforms from nanosheets to nanoflower, which aids in reducing the distance of ion transport. The reconstructed NiCo-LDH exhibits an ultra-high specific capacity of 2809 C g⁻¹ at a current density of 1 A g⁻¹, outperforming most of NiCo LDHs. At a high current density of 10 A g⁻¹, the capacity retention rate remains above 72.7% after 3000 cycles. An asymmetric supercapacitor is fabricated with activated carbon material as the negative electrode, the energy density is 36 Wh kg⁻¹ at the power density of 732 W kg⁻¹. The strategy proposed in the study, which involves concentration-controlled morphology optimization for energy storage enhancement, holds great practical significance for the field of supercapatteries.

The wavelength tunability of a general transmittance function (GTF) is investigated in a first-order fibre multiwavelength filter based on a polarisation-diversified fibre loop, which utilised a composite combination of wave retarders. The filter consists of a polarisation beam splitter, two equal-length high birefringence fibre (HBF) segments, and two different sets of wave retarders with each set positioned before each HBF segment. Specifically, a combination of a set of dual quarter-wave retarders (QWRs) and another set of a QWR and a half-wave retarder is focused upon. By considering the effect of the four wave retarders and two HBF segments on the output polarisation state (OPS) of each element in the filter, the four wave retarder angles (WRAs) are identified that caused all polarisation states on the OPS trace of the second HBF move in the direction of wavelength decrease, resulting in a redshift of the GTF. 360 WRA sets are derived that enabled tuning the GTF by one free spectral range S_R. For eight sets chosen from the WRA sets, inducing a wavelength shift of S_R/8 for each set order, wavelength-shifted spectra are calculated. Finally, this theoretical prediction is experimentally verified, confirming the wavelength tunability of the GTF of the filter.

Silver (Ag) nanoparticles (NPs) are perceiving remarkable progress during the past few periods due to its exclusive properties in many applications. Recently, green synthesis method of NPs is racing against traditional chemical and physical methods by avoiding the use of many toxic chemicals, and expensive devices. Accordingly, in this study, dry and fresh Portulaca-oleracea L. leaf extract has been employed for producing AgNPs as a reducing, capping and stabilizing agents. This process is simple, eco-friendly and green. UV–vis spectra showed the formation of AgNPs represented by the change of a colorless liquid to brownish solution. The crystallinity of the AgNPs, was confirmed by X-ray diffraction (XRD). The contribution of the available functional groups of the leaf extract in the reduction and capping process of NPs was demonstrated using Fourier transform infrared spectroscopy (FTIR). This study showed that fresh Portulaca-oleracea L. leaf extract provides better NPs in terms of stability, purity, degree of crystallinity and spherical shape. The biosynthesized AgNPs from both procedures were coated on the indium tin oxide (ITO) glass substrates to enhance the reflectivity property. It has been shown that the utilized AgNPs, from fresh Portulaca-oleracea L. extract, has smaller size and negligeable agglomeration, consequently lower light transmittance.

Multi-walled carbon nanotubes (MWCNTs) were successfully synthesized and functionalized by chemical vapour deposition and acid reflux methods, respectively. Chitosan (CTS) was prepared by a chemical extraction method from waste prawn shells. Various weight fractions of functionalized multi-walled carbon nanotubes (f-MWCNTs) have been used as reinforcing agent in CTS biopolymer matrix. Fourier transform infrared spectroscopy analysis was done, which confirms the presence of absorption bands of the various functional groups of chitin, CTS, and MWCNTs. Raman spectra revealed the quality of MWCNTs, the extent of their functionalization, and the quality of nanocomposites. The X-ray diffraction analysis showed the distinctive peaks for f-MWCNTs’ and also revealed the formation of CTS/f-MWCNTs nanocomposites. Transmission Electron Microscopy (TEM) analysis also exhibited that the CTS/f-MWCNTs nanoparticles have a well-defined crystalline structure. The highest coercivity and magnetization (Ms) of the CTS/5%f-MWCNTs nanocomposite are 602 Oe and 0.1202 emu/g, respectively that have been enhanced by 3.83 and 5.27 times compared to the pure CTS respectively. It showed that the conductivity is getting higher with the addition of f-MWCNTs in the CTS matrix. CTS/5% f-MWCNTs composites exhibit the highest conductivity than other composites and the conductivity of CTS/5% f-MWCNTs composite is 4.0×10⁻⁴ S/m.

The Cu_3.96Ag_0.04 nanoparticles were synthesized using the essence of Foeniculum vulgare Mill for the first time. The particles were fully analysed by conventional characterization methods such as powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), dynamic light scattering (DLS). The results have shown the crystal structure of silver copper particles and the crystallite size obtained by the Scherer equation was 23.2 nm. The TEM images interestingly displayed the formation of nanorods in the solid phase with nearly 5 nm widths and different lengths up to 100 nm. The hydrodynamic size is also compatible with the solid phase and crystallite sizes. Biologically, the particles were tested against infective gram negative and gram positive bacteria. The synthetic NPs show strong antibacterial properties against gram negative bacteria. Also, the synthesized nanoparticles had an inhibitory effect on the growth of cancer cells, which was dose- and time-dependent.

This research aims at investigating the idea of anti-bacterial self-healing coatings based on polyurea formaldehyde microcapsules (MCs), with the repair agent being ZnO-containing linseed oil. ZnO nanoparticles were added to the repair agent with the idea of developing an antibacterial coating. The idea was to entrap some ZnO nanoparticles inside microcapsules, aiming for some local release of ZnO nanoparticles where the coating is damaged. The corrosion resistances of the coatings were studied using the Tafel polarization test. The structure of the coating samples was evaluated using a scanning electron microscope. To check the antibacterial properties of ZnO-containing self-healing samples, Escherichia coli and Staphylococcus aureus bacteria were used. Results showed that ZnO nanoparticles were distributed not only inside microcapsules but also over the walls, inferring that overall protection can also be attained in addition to local anti-bacterial performance. Results showed that the proposed multi-functional coating has promising antibacterial and self-healing responses.

The auto-combustion technique was employed to synthesize nano particles of B_xFe_(3−x)O₄ (x = 0.0, 0.7, 1.18, 1.36 and 1.54). The resulting structural and dielectric properties of the boron doped Fe₃O₄ were evaluated. XRD analysis confirmed the presence of a single spinel structure with crystallite dimensions ranging from 21.18 to 26.43 nm and lattice parameters of 8.211 to 8.487 Ǻ. The morphological images revealed homogenous and spherical grain sizes, while EDX confirmed the presence of constituent elements used. The X-ray density increased whereas the bulk density and the porosity decreased with boron substitution. The study of dielectric properties and AC conductivity (σ_AC) was demonstrated and the AC conductivity decreased with increasing boron concentration, indicating a hopping mechanism. Moreover, noticeable variations in dielectric loss, AC conductivity, and dielectric permittivity with temperature and frequency were observed. These observations were attributed to the Maxwell–Wagner interfacial polarization and the hopping of charges between Fe³⁺ and Fe²⁺ ions.

In many physics and engineering applications requiring exceptional precision, the presence of highly reflective coatings with low thermal noise is of utmost significance. These applications include high-resolution spectroscopy, optical atomic clocks, and investigations into fundamental physics such as gravitational wave detection. Enhancing sensitivity in these experiments relies on effectively reducing the thermal noise originating from the coatings. While ion beam sputtering (IBS) is typically employed for fabricating such coatings, electron beam evaporation can also be utilized and offers certain advantages over IBS, such as versatility and speed. However, a significant challenge in the fabrication process has been the limitations of the quartz crystal monitor used to measure the thickness of the deposited layers. This paper showcases how, through hardware and software upgrades, it becomes achievable to create high-density coatings with layers as thin as a few angstroms by using electron beam evaporation (OAC75F coater) with a deposition rate of 1 Å/s and ion-assisted source with a gas mixture of oxygen and argon, using a pressure of about 4 × 10⁻⁴ mbar. Furthermore, these upgrades enable the attainment of high levels of precision and uniformity in the thickness of the coatings.

The quasi-Z-source H-bridge grid-connected inverter (QHGCI) is well known for its advantages of the void of the shoot-through problem and the high DC-voltage utilization. But the existence of the common-mode leakage current in the power frequency cycle, lower power density, and higher thermal stress make it hard applicable to the grid-penetrating application. Thus with the purpose to conquer the problem relating to the QHGCI, an innovative transformerless Z-source photovoltaic grid-connected inverter with a coupled inductor coil (TZPGCI-CIC) is proposed. The circuitry topology and an unipolar sine pulse width modulation strategy are first introduced in short. Thereafter, the common-mode voltage in the whole working process is derived and evaluated through the detailed operating mode analysis, in which a constant value of it has been theoretically revealed. Lastly, a prototype platform of TZPGCI-CIC is set up and its good performance on leakage current suppression, and lower thermal stress are validated with the experimental results.