Bhavana N. Joshi

Flexible, Freestanding, and Binder-free SnOx–ZnO/Carbon Nanofiber Composites for Lithium Ion Battery Anodes

Here, we demonstrate the production of electrospun SnO(x)-ZnO polyacrylonitrile (PAN) nanofibers (NFs) that are flexible, freestanding, and binder-free. This NF fabric is flexible and thus can be readily tailored into a coin for further cell fabrication. These properties allow volume expansion of the oxide materials and provide shortened diffusion pathways for Li ions than those achieved using the nanoparticle approach. Amorphous SnO(x)-ZnO particles were uniformly dispersed in the carbon NF (CNF). The SnO(x)-ZnO CNFs with a Sn:Zn ratio of 3:1 exhibited a superior reversible capacity of 963 mA·h·g(-1) after 55 cycles at a current density of 100 mA·g(-1), which is three times higher than the capacity of graphite-based anodes. The amorphous NFs facilitated Li2O decomposition, thereby enhancing the reversible capacity. ZnO prevented the aggregation of Sn, which, in turn, conferred stable and high discharge capacity to the cell. Overall, the SnO(x)-ZnO CNFs were shown to exhibit remarkably high capacity retention and high reversible and rate capacities as Li ion battery anodes.

Enhanced Photoelectrochemical Solar Water Splitting Using a Platinum-Decorated CIGS/CdS/ZnO Photocathode.

A Cu(InGa)Se2 film was modified with CdS/ZnO for application to solar water splitting. Platinum was electrodeposited on the ZnO layer as a hydrogen evolution catalyst. The effects of the electroplating time and acidity level of the electrolyte on the photocurrent density were studied. The highest photocurrent density of -32.5 mA/cm(2) under 1.5 AM illumination was achieved with an electroplating time of 30 min at a pH of 9. This photocurrent density is higher than those reported in previous studies. The markedly high performance of the CIGS/CdS/ZnO photocathode was rationalized in terms of its type II cascade structure that facilitated efficient charge separation at the interface junction.

Highly efficient wettability control via three-dimensional (3D) suspension of titania nanoparticles in polystyrene nanofibers.

Electrospinning is a simple and highly versatile method for the large-scale fabrication of polymeric nanofibers. Additives or fillers can also be used to functionalize the nanofibers for use in specific applications. Herein, we demonstrate a novel and efficient way to fabricate superhydrophobic to hydrophilic tunable mats with the combined use of electrospinning and electrospraying that may be suitable for mass production on the merits of rapid deposition. The tunable nanocomposite mats were comprised of hydrophobic polystyrene nanofibers and hydrophilic titania nanoparticles. When the electrical conductivity of the electrospinning solution was increased, the surface morphology of the mats changed noticeably from a bead-on-string structure to an almost bead-free structure. Polystyrene (PS)-titania nanocomposite mats initially yielded a static water contact angle as high as 140° ± 3°. Subsequently exposing these mats with relatively weak ultraviolet irradiation (λ = 365 nm, I = 0.6 mW/cm²) for 2 h, the unique 3D suspension of the photoactive titania nanoparticles maximized the hydrophilic performance of the mats, reducing the static water contact angle to as low as 26° ± 2°. The tunable mats were characterized by scanning electron microscopy (SEM), static water contact angle (WCA) measurements, and energy-dispersive X-ray spectroscopy (EDX). Our findings confirmed that the tunable mats fabricated by the simultaneous implementation of electrospraying and electrospinning had the most efficient ultraviolet (UV)-driven wettability control in terms of cost-effectiveness. Well-controlled tunable hydrophobic and hydrophilic mats find potential applications in functional textiles, environmental membranes, biological sensors, scaffolds, and transport media.

Self-cleaning superhydrophobic films by supersonic-spraying polytetrafluoroethylene–titania nanoparticles

Spherical water drops show little or no adhesion to superhydrophobic surfaces due to the strong water repellence. Polytetrafluoroethylene (PTFE)–titania (TiO2) nanocomposite films were fabricated using a scalable, rapid and cost-effective technique: supersonic spray coating at room temperature. The wettability of the supersonic spray-coated nanocomposite films can be tuned to the Cassie–Baxter or Wenzel wetting states by simply varying the relative content of titania. This wettability tuning can also be used to adjust the surface morphology of the films, resulting in either a rough compact structure or a porous morphology. The static water contact angle and roll-off angles were measured for the nanocomposite films as a function of the titania content. Furthermore, water drop rebounding and water jet impact tests were performed on the nanocomposite films and their self-cleaning properties were investigated.

Heterojunction photoanodes for solar water splitting using chemical-bath-deposited In2O3 micro-cubes and electro-sprayed Bi2WO6 textured nanopillars

In2O3 micro-cubes were fabricated via chemical bath deposition (CDB) on an indium tin oxide (ITO) substrate, over which highly textured Bi2WO6 nanopillars were grown via a diffusion-and-aggregation phenomenon by electrostatic spraying deposition (ESD). The resulting heterojunction bilayer exhibited a photocurrent density value of 1.03 mA cm−2 under visible light of 100 mW cm−2 intensity. Widening the light absorptivity spectrum and reducing the charge recombination enhanced the performance of the heterojunction bilayer films for solar water splitting.

ANALYSIS OF CAPACITANCE ACROSS INTERCONNECTS OF LOW-K DIELECTRIC USED IN A DEEP SUB-MICRON CMOS TECHNOLOGY

The paper presents the detailed analysis of the intercon- nect capacitance, crosstalk time and peak crosstalk voltage. The de- pendency of the couple capacitance and fringe capacitance on the in- terconnect layer dimensions affects significantly to the interconnect ca- pacitance. The peak crosstalk time obtained to be 13 femtoseconds for 9.6 femtoseconds of propagation delay, while the maximum crosstalk voltage obtained to be 178 mV.

Chemical-Bath-Deposited Indium Oxide Microcubes for Solar Water Splitting

We fabricated films of cubic indium oxide (In2O3) by chemical bath deposition (CBD) for solar water splitting. The fabricated films were characterized by X-ray diffraction analysis, Raman scattering, X-ray photoelectron spectroscopy, and scanning electron microscopy, and the three-dimensional microstructure of the In2O3 cubes was elucidated. The CBD deposition time was varied, to study its effect on the growth of the In2O3 microcubes. The optimal deposition time was determined to be 24 h, and the corresponding film exhibited a photocurrent density of 0.55 mA cm(-2). Finally, the film stability was tested by illuminating the films with light from an AM 1.5 filter with an intensity of 100 mW cm(-2).

Monomer methylmethacrylate (MMA) incorporated hybrid low-k thin films

Low-dielectric-constant hybrid thin films were deposited by sol-gel spin coating technique, using methyl methacrylate and tetraethyl orthosilicate as organic and inorganic precursors, respectively. The deposited hybrid thin films were annealed at different temperatures in the range 200°C–500°C. Fourier transform infrared spectroscopic study reveals the presence of Si-O-Si and C=C bonds, which confirms the successful assimilation of carbon in the deposited hybrid thin film. The carbon incorporation is responsible for lowering the dielectric constant (k) in the deposited film. The k value was determined to be 2.51, as measured from the highfrequency capacitance-voltage curve. This is a significant contribution, since the deposition method did not involve polymerization. The electrical characteristics, such as border trap charge, interface trap density, and fixed oxide charge were estimated to be 4.10 × 1015 cm−2, 1.94 × 1011 cm−2 eV−1, and 1015 cm−2, respectively, indicating the optimum annealing temperature to be 200°C.

Ni-core CuO-shell fibers produced by electrospinning and electroplating as efficient photocathode materials for solar water splitting

Charge recombination in CuO photocathodes inhibits efficient electron flow and limits the photo-electrochemical performance of these cathodes for solar water splitting. To circumvent this shortcoming, we introduce highly conductive Ni/CuO core-shell structured fibers. The photocurrent density (PCD) achieved with these core-shell fibers exceeded that of fibers without a Ni core by a factor of 2.6. The PCD enhancement arises from increased acceptor concentration and electron-hole recombination time, as measured by electrochemical impedance spectroscopy. These core-shell nanofibers were fabricated via electrospinning and electroplating. First, a polyacrylonitrile fiber was electrospun and then seeded with metal via sputtering. Second, electroplating was used to encase and metalize the fiber with Ni and Cu. Finally, the outermost Cu shell was oxidized to CuO, which is an effective photocathode for solar water splitting. The Ni-CuO, core-shell layers were characterized by scanning electron microscopy, elemental mapping, X-ray diffraction, and X-ray photoelectron spectroscopy. The core Ni content and number of core-shell fibers per area were optimized through parametric studies.

Polyacrylonitrile nanofibers with added zeolitic imidazolate frameworks (ZIF-7) to enhance mechanical and thermal stability

Zeolitic imidazolate framework 7/polyacrylonitrile (ZIF-7/PAN) nanofiber mat of high porosity and surface area can be used as a flexible fibrous filtration membrane that is subjected to various modes of mechanical loading resulting in stresses and strains. Therefore, the stress-strain relation of ZIF-7/PAN nanofiber mats in the elastic and plastic regimes of deformation is of significant importance for numerous practical applications, including hydrogen storage, carbon dioxide capture, and molecular sensing. Here, we demonstrated the fabrication of ZIF-7/PAN nanofiber mats via electrospinning and report their mechanical properties measured in tensile tests covering the elastic and plastic domains. The effect of the mat fabrication temperature on the mechanical properties is elucidated. We showed the superior mechanical strength and thermal stability of the compound ZIF-7/PAN nanofiber mats in comparison with that of pure PAN nanofiber mats. Material characterization including scanning electron microscope, energy-dispersive X-ray spectroscopy, tensile tests, differential scanning calorimetry, and Fourier transform infrared spectroscopy revealed the enhanced chemical bonds of the ZIF-7/PAN complex.