Wire Melt Electrospinning of Thin Polymeric Fibers via Strong Electrostatic Field Gradients

Here, a novel melt electrospinning method to produce few‐micron and nanometer thick fibers is presented, in which a polymer‐coated wire with a sharp tip is used as the polymer source. The polymer coating is melted via Joule heating of the source wire and extracted toward the target via electrostatic forces. The high viscosity and low charge density of polymer melts lower their stretchability in melt. The method relies on confining the Taylor cone and reducing initial jet diameter via concentrated electrostatic fields as a means to reduce the diameter of fibers. As a result, the initial jet diameter and the final fiber diameter are reduced by an order of magnitude of three to ten times, respectively, using wire melt electrospinning compared to syringe‐ and edge‐based electrospinning. The fiber diameter melt electrospun via this novel method is 1.0 ± 0.9 µm, considerably thinner than conventional melt electrospinning techniques. The generation of thin fibers are explained in terms of the electrostatic field around the wire tip, as obtained from finite element analysis (FEA), which controls the size and shape of the melt electrospun jet.     

Facile synthesis and characterization of potassium-doped MnO2 nanowires

A new type of potassium doped manganese oxide nanowires were synthesized using a simple hydrothermal route. The reduction of MnO4- in the presence of acetate species led to the formation of the Multi-filamentous nanowire structure. Detailed TEM and chemical characterizations indicated that potassium ions were homogeneously distributed in the nanowires. XPS results show a clear binding energy shift (1 eV) for K(2p) peak in nanowires compared with its starting material of KMnO4. Detailed synthetic condition investigation indicated that the presence of acetate ions played an important role in the formation of such a type of nanowires other than layered structures.     

Effects of Annealing Temperature on the Structural,Optical,and Electrical Properties of ZnO Thin Films Grown on n-Si<100>Substrates by the Sol–Gel Spin Coating Method

The effects of annealing temperature on the sol–gel-derived ZnO thin films deposited on n-Sh100 i substrates by sol–gel spin coating method have been studied in this paper.The structural,optical,and electrical properties of ZnO thin films annealed at 450,550,and 650 °C in the Ar gas atmosphere have been investigated in a systematic way.The XRD analysis shows a polycrystalline nature of the films at all three annealing temperatures.Further,the crystallite size is observed to be increased with the annealing temperature,whereas the positions of various peaks in the XRD spectra are found to be red-shifted with the temperature.The surface morphology studied through the scanning electron microscopy measurements shows a uniform distribution of ZnO nanoparticles over the entire Si substrates of enhanced grain sizes with the annealing temperature.Optical properties investigated by photoluminescence spectroscopy shows an optical band gap varying in the range of 3.28–3.15 eV as annealing temperature is increased from 450 to 650 °C,respectively.The fourpoint probe measurement shows a decrease in resistivity from 2:1 10 2to 8:1 10 4X cm with the increased temperature from 450 to 650 °C.The study could be useful for studying the sol–gel-derived ZnO thin film-based devices for various electronic,optoelectronic,and gas sensing applications.     

Mn-Doped Zn<Subscript>2</Subscript>SiO<Subscript>4</Subscript> Phosphors Synthesis Using Flame Spray Pyrolysis

Zn₂SiO₄:Mn²⁺ particles are used as green phosphors in plasma display panels and cathode ray tubes. In this study, we report the synthesis of zinc silicate phosphors by flame spray pyrolysis using different Zn-sources and under different process conditions. The XRD and luminescence measurement showed the phosphors prepared from Zn-nitrate source to have better crystallinity and emission characteristics. The luminescence properties of the phosphor particles were found to improve both at higher methane flow rates during pyrolysis and at higher annealing temperatures.     

First-principles investigation of elastic and electronic properties of double transition metal carbide MXenes

We use first-principles-based density functional theory (DFT) calculations to investigate the structural, elastic, and electronic properties of various pristine and oxygen (O)-functionalized double transition metal (DTM) MXenes with general formulas of M₂′M′′C₂ and M₂′M′′C₂O₂, where M′ = Mo, Cr and M′′ = Ti, V, Nb, Ta. The dynamic stability of the DTM MXenes are assessed and elastic stiffness constants (C_ij) are used to investigate the mechanical stability and properties of the compositions. The calculated elastic properties of the pristine Mo-based MXenes are found to be superior compared to Cr-based compounds. Furthermore, the O-functionalized MXenes exhibit improved in-plane elastic constants, Young's moduli, and shear moduli compared to their pristine counterpart. We observe that the hybridization of the energy states results in stronger covalent interactions as such increased elastic properties for the M₂′M′′C₂O₂ MXenes. Ashby plot clearly demonstrates superior materials properties of O-functionalized Mo-based DTM MXenes compared to other commonly known two-dimensional materials. All the MXenes exhibit metallic character evident from the density of states (DOS) calculations. Additionally, the work functions are studied and the calculated values are higher in the case of O-functionalized MXenes. Overall, this work will be a guide for future investigations on the mechanical properties of DTM MXenes for their targeted applications in structural nanocomposites.     

Improvement of Plasma Performance with Lithium Wall Conditioning in Aditya Tokamak

Lithiumization of the vacuum vessel wall of the Aditya tokamak using a lithium rod exposed to glow discharge cleaning plasma has been done to understand its effect on plasma performance. After the Li-coating, an increment of ～100 eV in plasma electron temperature has been observed in most of the discharges compared to discharges without Li coating, and the shot reproducibility is considerably improved. Detailed studies of impurity behaviour and hydrogen recycling are made in the Li coated discharges by observing spectral lines of hydrogen, carbon, and oxygen in the visible region using optical fiber, an interference filter, and PMT based systems. A large reduction in O I signal (up to ～ 40% to 50%) and a 20% to 30% decrease of H α signal indicate significant reduction of wall recycling. Furthermore, VUV emissions from O V and Fe XV monitored by a grazing incidence monochromator also show the reduction. Lower Fe XV emission indicates the declined impurity penetration to the core plasma in the Li coated discharges. Significant increase of the particle and energy confinement times and the reduction of Z eff of the plasma certainly indicate the improved plasma parameters in the Aditya tokamak after lithium wall conditioning.