D. Mangalaraj

Characterization of transparent conducting CdO films deposited by spray pyrolysis

Transparent conducting cadmium oxide (CdO) films have been deposited by spray pyrolysis. The film thicknesses have been determined using Rutherford backscattering spectrometry. X-ray diffraction measurements show that the films are polycrystalline with a preferential orientation along the (111) diffraction plane and the lattice parameter has been calculated. The dislocation density and strain have also been evaluated. The films possess a transmittance of about 75% in the visible and near-infrared region. The refractive index is found to vary between 1.68 and 2.84 in the wavelength range 500-1500 nm. The values of indirect and direct bandgaps obtained are 1.98 and 2.32 eV respectively. Hall effect measurements have been carried out in the temperature range 304-349 K. Resistivity, carrier concentration and mobility of the films at room temperature have been evaluated as 6.6*10-5 Omega m, 1.4*1025 m-3 and 0.68*10-2 m2 V-1 s-1 respectively. Thermoelectric power values from thermoelectric power measurements carried out in the temperature range 304-376 K have been found to be about 19.7-89 mu V K-1. Laser damage studies performed at a wavelength of 1.06 mu m indicate that the films possess a damage threshold density of about 2.37*104 J m-2.

Shape evolution of perovskite LaFeO3 nanostructures: a systematic investigation of growth mechanism, properties and morphology dependent photocatalytic activities

Shape evolution of nanostructured LaFeO3 with fascinating morphologies like cubes, rods and spheres was successfully synthesized by a facile and environmentally friendly hydrothermal process. Tuning the morphologies was achieved using different surfactants. The prepared samples were systematically characterized using X-ray diffraction, micro-Raman spectroscopy, scanning electron microscopy and high-resolution transmission electron microscopy for structural, morphological and chemical composition analysis by X-ray photoelectron spectroscopy. The optical properties of prepared samples were studied employing UV-Vis diffusion reflectance analysis. Brunauer–Emmett–Teller measurement reveals a large surface area for all the prepared nanostructures. Most importantly, the visible-light photocatalytic activities of the three LaFeO3 nanostructures were evaluated by photocatalytic decolorization of Rhodamine B in aqueous solution. The enhanced photocatalytic activity of LaFeO3 nanospheres compared to other nanostructures and commercial Degussa P25 TiO2 can be ascribed to high specific surface area, pore size distribution and the smaller particle size. The underlying growth mechanism responsible for the formation of LaFeO3 nanostructures is also discussed. The results from this study illustrate the morphology-dependent photocatalytic performance of LaFeO3.

Highly mesoporous α-Fe2O3 nanostructures: preparation, characterization and improved photocatalytic performance towards Rhodamine B (RhB)

Single-crystalline porous hematite nanorods and spindle-like nanostructures were successfully synthesized by a low temperature reflux condensation method. Two different iron sources, namely, FeCl3?6H2O and Fe(NO3)3?9H2O, were hydrolyzed in the presence of urea to selectively prepare nanorods and spindle-like nanostructures. Initially, the akagenite phase was obtained by refluxing the precursor for 12?h and then the as-prepared akagenite nanostructures were transformed to porous hematite nanostructures upon calcination at 300??C for 1?h. The shape and the aspect ratio of the 12?h refluxed sample was retained even after calcination and this shows the topotactic transformation of the nanostructure. TEM and HRTEM investigations have shown the porous nature of the prepared sample. Brunauer?Emmett?Teller and Barret?Joyner?Halenda measurements have shown a large surface area and distribution of mesopores in the nanorods sample. The photocatalytic activity of the prepared nanostructures towards RhB has reflected this variation in the pore size distribution and specific surface area, by showing a higher activity for the nanorods sample. Magnetic studies by VSM have shown a weak ferromagnetic behaviour in both the samples due to shape anisotropy.

Magnetron sputtered transparent conducting CdO thin films

Thin films of cadmium oxide have been produced by dc reactive magnetron sputtering in nitrogen and oxygen atmosphere. The structural, optical, and electrical characterization of these films are investigated. Structural analysis indicates that the films are polycrystalline and cubic. Composition analysis by Rutherford backscattering spectrometry has been made and it is found that the films contain excess cadmium and deficient oxygen. It is observed from the optical properties that the films possess a transmittance of about 85% in the visible and near infrared regions of the spectrum and direct bandgap values in the range 2.50 to 2.68 eV for films of thicknesses 146 to 177 nm. Electrical measurements point out that the films have resistivity, carrier concentration, and mobility in the range 2.65 to 6.64 × 10-6 Ωm, 1.60 to 2.35 × 1026 m-3, and 57.65 to 100.48 × 10−4 m2 v−1 s−1 respectively.

Fabrication of CeO2/Fe2O3 composite nanospindles for enhanced visible light driven photocatalysts and supercapacitor electrodes

Hybrid CeO2/Fe2O3 composite nanospindles (CNSs) are synthesized by a simple and cost effective co-precipitation method. CeO2/Fe2O3 CNSs used as an efficient recyclable photocatalyst for degrading Eosin Yellow (EY) dye under visible light irradiation possess a high degradation rate of 98% after 25 min. The estimated electrical energy efficiency of CeO2/Fe2O3 CNSs shows the consumption of less energy (6.588 kW h m−3 per order) in degrading EY. Besides, the CeO2/Fe2O3 CNS exhibits a specific capacitance of 142.6 F g−1 at a scan rate of 5 mV s−1. Moreover, the composite displays an excellent capacitance retention of 94.8% after 1000 cycles. This newly designed CeO2/Fe2O3 CNS with enhanced visible light-driven photocatalytic activity and good supercapacitive cycling stability has great potential for use in wastewater treatment and energy storage applications.

Controlled growth of single-crystalline, nanostructured dendrites and snowflakes of α-Fe2O3: influence of the surfactant on the morphology and investigation of morphology dependent magnetic properties

Single-crystalline, nanostructured dendrites, single and double-layered snowflakes of hematite (α-Fe2O3) were synthesized by a well controlled, surfactant-assisted hydrothermal reaction of K3[Fe(CN)6]. By varying the preparatory conditions such as precursor concentration and type of surfactant, we could establish precise control on the morphology of the sample. X-Ray diffraction, Raman analysis and X-ray photoelectron spectroscopic studies have confirmed that the as grown morphologies were hematite. Dendrites were obtained due to weak dissociation of the precursor and controlled diffusion of α-Fe2O3 nanoparticles under non-equilibrium conditions which attach and grow along certain preferred crystal facets. In the presence of a surfactant, single and double-layered snowflakes were formed. The type of surfactant and the nature of micelle formation were proposed to be the key factor for the observed snowflakes and the single or double-layered growth. Magnetic studies have shown morphology dependent magnetic properties with variation in the coercivity values for dendrites, single and double-layered snowflakes.

Growth, structure, dielectric and AC conduction properties of solution grown PVA films

Abstract Polyvinyl alcohol (PVA) films were deposited on pre-cleaned glass substrates using an isothermal immersion technique. Sandwich structures of the type Al-PVA-Al were formed to study the dielectric and conduction properties of PVA films. Aluminium electrodes were deposited by vacuum evaporation method. Thicknesses ( d ) of the dielectric films were measured by an electronic linear thickness measuring instrument (Tesatronic TTD20 model) and a gravimetric method and cross checked by a capacitance method. The dependence of the thickness of the PVA films on the immersion time, concentration and temperature of the solution had been studied. From the X-ray diffraction studies the structure of the deposited film was found to be amorphous. The dielectric properties were studied in the frequency range 1–30 kHz at various temperatures in the range 303–423 K. The capacitance, though dependent on frequency and temperature, was found to be almost invariant at room temperature for all frequencies. The dielectric constant e ′ of the films was found to be increasing with increase in thickness of the film. The loss factor e ″ was found to be increasing with increase in temperature up to the glass transition temperature ( T g ) and decreasing above that ( T g ). From AC conduction studies it was confirmed that the mechanism responsible for conduction is mostly due to ionic hopping. The films showed very high transmittance in the visible to near IR region.

Pulsed laser deposited vanadium oxide thin films for uncooled infrared detectors

Vanadium oxide thin films were deposited by pulsed laser deposition (PLD) technique using V 2O5 as target. A new deposition parameter has been extracted to deposit vanadium oxide thin films at room temperature for uncooled microbolometers. Temperature coefficient of resistance (TCR) is one of the vital bolometric parameters, which influences the performance of the uncooled microbolometer infrared detectors was determined. The TCR values of vanadium oxide films deposited by PLD at room temperature are coinciding with the reported TCR values of successful vanadium oxide thin films deposited at elevated temperatures by other techniques for bolometric applications. We further investigated the influence of laser fluence on the electrical property of the vanadium oxide films.

Conducting polyaniline-graphene oxide fibrous nanocomposites: preparation, characterization and simultaneous electrochemical detection of ascorbic acid, dopamine and uric acid

Polyaniline/graphene oxide (PANI-GO) fibrous nanocomposites have been prepared and the electrochemical catalytic activity towards the electro-oxidation of ascorbic acid (AA), Dopamine (DA) and Uric acid (UA) has been investigated. The nanocomposites were synthesized via an in situ chemical polymerization method. The morphology, composition, thermal and electrochemical properties of the resulting nanocomposites were characterized by scanning electron microscopy, X-ray diffraction, Raman spectroscopy, FT-IR spectroscopy, thermo gravimetric analysis and cyclic voltammetry. The catalytic behavior of PANI-GO nanocomposite modified glassy carbon electrode (GCE) towards AA, DA and UA has been investigated by cyclic voltammetry (CV), differential pulse voltammetry (DPV). The PANI-GO/GCE showed excellent catalytic activity towards electrochemical oxidation of AA, DA and UA compared to the bare GCE. The electrochemical oxidation signal of AA, DA and UA are well separated into three distinct peaks with peak potential separation of 343 mV, 145 mV and 488 mV between AA-DA, DA-UA and AA-UA respectively in CV studies and the corresponding peak potential separation in DPV mode are 320 mV, 230 mV and 550 mV. Under the optimized DPV experimental conditions, the peak current of AA, DA and UA give linear response over the range of 25–200 μM (R2 = 0.9955), 2–18 μM (R2 = 0.9932) and 2–18 μM (R2 = 0.9902) with detection limit of 20 μM, 0.5 μM and 0.2 μM at S/N = 3, respectively. The attractive features of PANI-GO provide potential applications in the simultaneous detection of AA, DA and UA. The excellent electrocatalytic behavior of PANI-GO may lead to new applications in electrochemical analysis.

Structural characterization of cadmium oxide thin films deposited by spray pyrolysis

Abstract A series of CdO thin films have been prepared by spray pyrolytic technique at different substrate temperatures. X-ray diffraction scans confirmed the polycrystalline structure of the films. The films exhibit preferential orientation along the (111) plane. To describe the preferential orientation, the texture coefficient has been calculated and the standard deviation factor has also been evaluated to explain the growth mechanism. Various structural parameters such as lattice parameter, crystallite size, strain, dislocation density and stacking fault probability have been calculated. From the optical measurements, the void concentration has been determined and the results are discussed.