P.K. Kahol

High Per formance and Flexible Supercapacitors based on Carbonized Bamboo Fibers for Wide Temperature Applications

High performance carbonized bamboo fibers were synthesized for a wide range of temperature dependent energy storage applications. The structural and electrochemical properties of the carbonized bamboo fibers were studied for flexible supercapacitor applications. The galvanostatic charge-discharge studies on carbonized fibers exhibited specific capacity of ~510F/g at 0.4 A/g with energy density of 54 Wh/kg. Interestingly, the carbonized bamboo fibers displayed excellent charge storage stability without any appreciable degradation in charge storage capacity over 5,000 charge-discharge cycles. The symmetrical supercapacitor device fabricated using these carbonized bamboo fibers exhibited an areal capacitance of ~1.55 F/cm2 at room temperature. In addition to high charge storage capacity and cyclic stability, the device showed excellent flexibility without any degradation to charge storage capacity on bending the electrode. The performance of the supercapacitor device exhibited ~65% improvement at 70 °C compare to that at 10 °C. Our studies suggest that carbonized bamboo fibers are promising candidates for stable, high performance and flexible supercapacitor devices.

Biobased Polyols Using Thiol-Ene Chemistry for Rigid Polyurethane Foams with Enhanced Flame-Retardant Properties

Biobased polyol was synthesized using 1-thioglycerol and limonene, an extract of orange peel, via thiol-ene chemistry as an alternative to petrochemical-based polyol for preparation of rigid polyurethane foams (RPFs). Fire-retardant polyurethane foams were prepared by addition of different amounts of dimethyl methyl phosphonate (DMMP) in the polyol. The effect of DMMP on the properties of RPFs was studied. All the biobased RPFs maintained a regular cell structure with uniform cell distribution and over 90% of closed cell. The RPFs showed excellent compressive strength of ~230 kPa without addition of DMMP. These RPFs almost retained their specific compressive strength even when 2 parts by weight (pbw) of DMMP was added but with significant improvement in fire retardancy. Horizontal burning test of RPFs containing only 2 pbw of DMMP showed reduction in burning time by ~83% compared to the neat sample. Weight loss during the burning test for the control sample was nearly 50% and this was reduced significantly by addition of 2 pbw of DMMP to merely 7%. TGA analysis indicated that the improved flame retardancy could be attributed to the release of DMMP at the temperature range of 100 °C to 250 °C.

Electrical and Optical Properties of High Mobility W-doped In2O3 Thin Films

Transparent conducting oxides (TCO) have been widely used for opto-electronic devices such as light emitting diodes, photo-detectors, touch panels, flat panel displays, and solar cells. Low resistivity, high mobility, and good transparency are the prime requirements for these devices. There is an increasing interest in TCO with high mobility to decrease their electrical resistivity without a significant decrease in the optical transparency. Highly conducting and transparent tungsten doped indium oxide thin films were deposited on quartz substrate by ablating the sintered In 2 O 3 target containing WO 3 with a KrF excimer laser (λ = 248 nm and pulsed duration of 20 ns). The effect of growth temperature and oxygen pressure on structural, optical, and electrical properties has been studied. The transparency of the films largely depends on the growth temperature. The electrical properties are found to depend strongly on the growth temperature as well as on oxygen pressure. The temperature dependence resistivity measurement shows the transition from semiconductor to metallic behavior as the growth temperature increases from room temperature to 500 °C. The high mobility (up to 358 cm 2 V −1 s −1 ), low resistivity (1.1 × 10 −4 Ω.cm), and relatively high transmittance of ∼90 % have been observed on the optimized film grown at 500 °C and under oxygen pressure at 1 × 10 −6 bar.

Properties of ZnO/W-doped In2O3/ZnO multilayer thin films deposited at different growth temperatures

Multilayer thin films of zinc oxide and tungsten-doped indium oxide are deposited by the pulsed laser deposition technique using a KrF excimer laser. The effect of growth temperature on the properties of multilayer films is studied. It is observed that these films are highly transparent and the transparency of the films increases with growth temperature. X-ray diffraction study reveals that films grown at high growth temperature are crystalline, while films grown at low growth temperature are amorphous in nature. The electrical properties such as conductivity and electron mobility of the multilayer films increase with growth temperature.

Effect of Growth Temperature on Structural and Magneto-Transport Properties of Co-Doped In2O3 Diluted Magnetic Semiconductors

Thin films of Co-doped In 2 O 3 diluted magnetic semiconductor have been grown on c-plane sapphire single crystals using pulsed laser deposition technique. Different characterizations such as x-ray diffraction, atomic force microscopy, and magneto-transport have been carried out to study the effect of growth temperature on structural, electrical, and magneto-transport properties of these films. Crystalinity of the films increases with the growth temperature. The films grown at high temperature have preferred orientation along (222) direction, while films grown at low temperature behave more like to nanocrystaline. It is observed that electrical properties of the films strongly depend on growth temperature. The resistivity and magnetoresistance of the films decreases with increase in growth temperature. On the other hand, mobility of the films increases with increase in growth temperature. This could be due to improvement in crystalinity of the films.

Electrical properties of rectifying contacts on selectively carrier controlled grown ZnO thin films

Controlled decrease in carrier concentration (Nd) through postdeposition annealing of ZnO is shown to provide a crossover from Ohmic to rectifying junction behavior. Highly oriented (002) ZnO films with silver contact yield nonlinear I-V characteristics below a carrier concentration of ∼1023 m−3 and linear Ohmic behavior above 1023 m−3. The specific differential resistance around zero bias is practically independent of carrier concentration up to 1023 m−3 and then decreases with increase in carrier concentration. These results are in excellent agreement with standard theoretical models of current transport phenomena in metal–semiconductor contacts. While the differential junction resistance at lower carrier concentrations gradually becomes less governed by carrier concentrations and current transport is dominated by thermionic emission and diffusion mechanism, it decreases as a function of carrier concentration at higher carrier concentrations. These results show that metal–oxide semiconductor junctions b...

Derivation and evaluation of the fourth moment of NMR lineshape in zero-field

An expression for the fourth moment in zero-field NMR has been analytically derived and numerically evaluated for a rigid cubic lattice. Model simulations have been performed to calculate the second moment, the fourth moment, the ratio of the fourth moment to the square of the second moment, and the width of the resonance line for a crystal and a polycrystalline material in high-field as well as in zero-field NMR. The simulation results allow us to draw two conclusions: (1) zero-field NMR gives sharper and better defined spectra than the high-field NMR and (2) the ratio of the high- to zero-field resonance line-widths is 4 for a crystal, whereas it is 11 for a polycrystalline material.

Electrical and Magneto‐Transport Properties of Gd‐Doped In2O3 Thin Films Prepared by Pulsed Laser Deposition

Dilute Magnetic Semiconductors (DMS) are a rare group of promising materials that utilize both the electronic charge‐a characteristic of semiconductor materials‐and the electronic spin‐a characteristic of magnetic materials. Oxide based DMS show promise of ferromagnetism (FM) at room temperature. It has been found that doping metal oxides such as ZnO, TiO2, and In2O3 with magnetic ions such as Fe, Co, Mn, and Cr produces DMS, which exhibit FM above room temperature. In2O3, a transparent opto‐electronic material, is an interesting prospect for spintronics due to a unique combination of magnetic, electrical, and optical properties. High quality thin films of rare earth magnetic gadolinium (Gd) doped oxide‐based DMS materials have been grown by pulsed laser deposition (PLD) technique on various substrates such as single crystal of sapphire (001) and quartz under suitable growth conditions of substrate temperature and oxygen pressure in the PLD chamber. The effect of rare earth magnetic doping on the structur...

Magneto-Transport Properties of Nonmagnetic Doped (Zn,Mn) O Dilute Magnetic Semiconductor

In this paper, nonmagnetic elements (Al and Cu) doping effect on the structural and magneto-transport properties of Zn0.85Mn0.15O (ZnMnO) dilute magnetic semiconductors were reported. The structural characterization was performed using XRD, Raman spectroscopy, AFM and SEM. Temperature dependent electrical resistivity, Hall effect, and were carried out using a standard magneto-transport set-up.

Effect of Substrate Variation on Electrical and Magnetic Properties of Mn Doped ZnO of Dilute Magnetic Semiconductors

In this paper, the effect of substrate on the domain structure growth and electrical and magnetic properties of epitaxial Mn-doped Zn 0.8 Mn 0.15 O ( ZnMnO ) thin films has been investigated. Epitaxial thin films of ZnMnO dilute magnetic semiconductors ( DMS ) were grown on various substrates such as single crystal sapphire, single crystal silicon, and quartz substrates using Pulsed Laser Deposition ( PLD ) technique . Structural, surface, magnetic, and optical properties have been observed on these films using X-Ray diffraction ( XRD ), Atomic Force Microscopy ( AFM ), Scanning Electron Microscopy ( SEM ), and Raman spectroscopy. X-Ray Diffraction shows that films are highly epitaxial and c-axis oriented with some induced strain. AFM images show that film surface is smooth with RMS roughness of the order of 1-2 nm over 5*5sq.micron. Magnetic characteristic properties such as carrier concentration, mobility, and temperature dependent resistivity were also investigated. Carrier concentration decreases and mobility increases for both the films on silicon and quartz substrates when compared to film on sapphire.