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Electrospinning is a cost-effective but very intricate method of producing polymeric nanofibers at room temperature. Unfortunately however, it is extremely difficult to predict the diameter or other properties of the fibers produced via electrospinning a prior. In this paper, we present a new approach to simulate fiber formation during electrospinning. Our work builds on the mathematical framework that was originally developed by Reneker and Yarin in 2000. Our approach incorporates the 3D electrostatic field that surrounds the fiber in a Lagrangian discrete particle tracking algorithm that tracks the trajectory of the fiber in air and predicts its deposition velocity and diameter. We investigate the effects of electrostatic field spatial variation on fiber electrospinning and compare our results with those obtained using a constant electrostatic field, the traditional approach, and with experiments (conducted using polyurethane). We considered three different electrospinning configurations of single-needle-plate-collector, single-needle-drum-collector, and two-needles-drum-collector to investigate how different electrostatic fields impact fiber formation. The computational model developed in this work helps to advance the current state of the art in modeling the electrospinning process. [ABSTRACT FROM AUTHOR]

Present study reports the role of defects in the electrical transport in BiFeO3 (BFO) multiferroic films and its local electronic structure investigated by near-edge X-ray absorption fine structure. Defects created by high energy 200MeV Ag+15 ion irradiation with a fluence of ~5 x 10 ions/cm² results in the increase in structural strain and reduction in the mobility of charge carriers and enhancement in resistive (I-V) and polarization (P-E) switching behaviour. At higher fluence of ~5 x 1012 ions/cm², there is a release in the structural strain due to local annealing effect, resulting in an increase in the mobility of charge carriers, which are released from oxygen vacancies and hence suppression in resistive and polarization switching. Near-edge X-ray absorption fine structure studies at Fe L3, 2- and O K-edges show a significant change in the spectral features suggesting the modifications in the local electronic structure responsible for changes in the intrinsic magnetic moment and electrical transport properties of BFO. [ABSTRACT FROM AUTHOR]

Present report aims to study the effect of purity, edge length, and growth area on field emission of patterned carbon nanotube (CNT) emitter arrays. For development of four CNT emitter arrays (CEAs), low resistively silicon substrates were coated with thin film of iron catalyst using photolithography, sputtering, and lift off process. Four CEAs were synthesized on these substrates using thermal chemical vapor deposition with minor changes in pretreatment duration. Out of these, two CEAs have 10 μm × 10 μm and 40 μm × 40 μm solid square dots of CNTs with constant 20 μm inter-dot separation. Other two CEAs have ring square bundles of CNTs and these CEAs are envisioned as 10 μm × 10 μm square dots with 4 μm × 4 μm scooped out area and 15 μm × 15 μm square dots with 5 μm × 5 μm lift out area with constant 20 μm inter-dot spacing. Solid square dot structures have exactly constant edge length per unit area with more than four-fold difference in CNT growth area however ring square dot patterns have minor difference in edge length per unit area with approximately two times difference in CNT growth area. Quality and morphology of synthesized CEAs were assessed by scanning electron microscope and Raman characterization which confirm major differences. Field emission of all CEAs was carried out under same vacuum condition and constant inter-electrode separation. Field emission of solid square dot CEAs show approximately identical current density-electric field curves and Fowler-Nordheim plots with little difference in emission current density at same electric field. Similar results were observed for ring square structure CEAs when compared separately. Maximum emission current density observed from these four CEAs reduces from 14.53, 12.23, 11.01, to 8.66 mA/cm2 at a constant electric field of 5 V/μm, according to edge length of 1361.7, 1221.08, 872.20, to 872.16 mm rather than growth area and purity. Although, the 40 μm × 40 μm CEAs possessed highest CNT growth area of 8.7 mm2 and best purity defined in terms of lowest defect band to graphitic band ratio of 0.614, the current observed from this CEAs was least. [ABSTRACT FROM AUTHOR]

We report on the structural and electronic properties of swift heavy ion (SHI) irradiated pristine TiO2 thin films, deposited by radio frequency magnetron sputtering on sapphire substrates. The high resolution x-ray diffraction and Raman measurements show a structural phase transition from anatase to admixture of brookite and rutile phases of TiO2 with increasing SHI fluence followed by a significant distortion in the TiO6 octahedra. The modification in the electronic structure stimulated by SHI irradiation has been investigated using x-ray absorption (XAS) experiments at the O K and Ti L3,2 absorption edges. The O K edge spectra clearly indicate the splitting of the pre-edge spectral features having t2g and eg symmetry bands due to structural disorder/distortion induced by irradiation. The intensity of the SHI generated components at the O K edge increases monotonically, which can be correlated to the modification in unoccupancies associated with O 2 p orbitals hybridized with Ti 3 d states. The XAS spectra at the Ti L3,2 edge further authenticate that SHI creates a controlled structural disorder/distortion in the TiO6 octahedra. [ABSTRACT FROM AUTHOR]

The electronic structure of Cu-doped ZnO thin films, synthesized with a nominal composition of Zn1-xCuxO (x=0.03, 0.05, 0.07, and 0.10) by using spray pyrolysis method, has been investigated using near-edge x-ray absorption fine structure (NEXAFS) experiments at the O K- and the Cu L3,2-edges and resonant inelastic x-ray scattering (RIXS) measurements at Cu L3,2 edge. The Zn1-xCuxO thin films showed single phase wurtzite-hexagonal like crystal structure and ferromagnetic behavior at room temperature (RT). The intensity of the pre-edge spectral feature at the O K-edge increases with the Cu concentration, which clearly reveals that there is strong hybridization of O 2p–Cu 3d orbitals in the ZnO matrix. Spectral features of the Cu L3,2-edge NEXAFS exhibit multiple absorption peaks and appreciable x-ray magnetic circular dichroism signal that persists even at RT. These results demonstrate that Cu is in mixed valence state of Cu2+,3+/Cu1+, substituting at the Zn site and Cu2+/3+ ions are magnetically polarized. RIXS experiments at Cu L3 edge show strong d-d excitations due to localized nature of Cu ions in the ZnO matrix. [ABSTRACT FROM AUTHOR]

We report on the synthesis of Fe-doped ZnO with nominal composition of Zn0.99Fe0.01O by using a coprecipitation method. X-ray diffraction and selective area electron diffraction studies reveal a single phase wurtzite crystal structure without any secondary phase. Field emission transmission electron microscopy measurements infer that Zn0.99Fe0.01O have nanorod-type microstructures. Magnetic hysteresis measurement performed at different temperatures show that Zn0.99Fe0.01O exhibits a weak ferromagnetic behavior at room temperature. A detailed investigation of the electronic and local structure using O K-, Fe L3,2 near edge x-ray absorption fine structure suggests that Fe is substituting Zn in ZnO matrix and is in Fe3+ state. [ABSTRACT FROM AUTHOR]