Electrical transport,optical and thermal properties of polyaniline–pumice composites

In this study, electrical conductivity, photoconductivity, absorbance and thermal properties of polyaniline (PANI) and polyaniline–pumice composites were investigated. Temperature dependent conductivity and photoconductivity measurements were carried out in the temperature range of 80–400 K. The measurements revealed that the dominant conduction mechanisms in polyaniline and 15% pumice doped composite were hopping conduction. The low activation energies calculated for 36% pumice doped composite indicated that this sample has highly defective and degenerate structure due to the high pumice content. Polyaniline and pumice doped composites showed semiconductor behavior with the exponential variation of inverse temperature dependence of electrical conductivity. Photoconductivities of the PANI and PANI–pumice composites under various illumination intensities were studied and it was found for all samples that the conductivity increased with increasing temperature and light intensity, but decreased with increasing pumice content in the structure. Absorbance spectrum has been determined in the wavelength range of 300–700 nm and it was found that the band gap values decreased as the pumice content was increased. Thermogravimetric analysis have shown for all samples that the mass loss has started above around 300 K due to the loss of moisture from the structures. As a result of this work, it was found that polyaniline and polyaniline–pumice composites had low resistivity and high band gaps and could be used as a window layer semiconductor in heterojunction solar cell applications.     

Synthesis,characterization and studies on optical properties of hierarchical ZnO–CdS nanocomposites

Cadmium sulfide coated zinc oxide hierarchical nanocomposites have been synthesised at room temperature by a simple solution based method. CdS nanoparticles were deposited on the surface of ZnO without using any surfactant, ligand or chelating agents. The nanocomposites were synthesised using different concentrations of thioacetamide, cadmium salts, and also by varying the reaction time. After characterization of the nanocomposites, optical properties were investigated by UV–visible diffuse reflectance and photoluminescence spectroscopy techniques. It was found that band gap of the ZnO–CdS nanocomposites is tunable between 2.42 and 3.17 eV.     

Electrical and optical studies on γ-irradiated pure and chromium-chloride-doped polyvinyl alcohol

Measurements of optical absorption, electrical conductivity and of the dielectric constant were used to study the changes that occur due to -radiolysis of pure and CrCl₃-doped polyvinyl alcohol (PVA) thin films. Identification of the structure and assignments of energy bands were derived in terms of ligand field theory. Induced changes in the absorbance at 282 and 222 nm bands in pure and doped PVA samples, respectively, appeared to be dose dependent. The direct-current (d.c.) electrical conductivity of the samples was measured in the temperature range 296–433 K, and the results obtained revealed that -irradiation enhances the conductivity. The calculated activation energy in the lower temperature region also proved to be dose dependent. Plots of the dielectric constant, , against temperature show an interesting behaviour which depends on the dopant concentrations and exposure to -irradiation. The results obtained suggest that these materials may have an application in dosimetry.     

Characterization and catalytic activity studies of sol–gel Co–SiO2 nanocomposites

Silica embedded with transition metals exhibits adequate properties for applications in catalysis, sensors and optics. Cobalt–silica (Co–SiO₂) nanocomposites were prepared by the sol–gel method and thermally treated at 700, 900, 1100 and 1250 °C. Characterization of the samples was performed by XRD and BET nitrogen adsorption. The performance of the nanocomposites was investigated by catalysis reactions of oxidation. These catalysts were found to be recyclable showing a catalytic activity even after a third recovering. The results indicate that thermal treatment of sol–gel nanocomposites at temperatures higher than 900 °C is essential for the preparation of active heterogeneous catalysts.     

Polyaniline–CuO hybrid nanocomposites: synthesis, structural, morphological, optical and electrical transport studies

Thin films of semiconducting polyaniline (PANi) nanofibers reinforced with copper oxide (CuO) nanoparticles (NPs) were prepared on glass substrate using spin coating technique. Polyaniline (PANi) have been synthesized by chemical oxidative polymerization method with monomer aniline in presence of (NH₄)₂S₂O₈ as an oxidant at 0 °C. The copper oxide (CuO) nanoparticles were synthesized by sol–gel method. Physical properties of nanocomposite (NCs) films were characterized and analyzed by X-ray diffraction, Scanning electron microscopy, Fourier transform infrared (FTIR) spectroscopy, UV–vis spectroscopy, Two probe resistivity measurement technique and Thermo-emf measurement. Structural analysis showed that the crystal structure of CuO is not disturbed in the PANi–CuO hybrid nanocomposite. Surface morphology study shows the uniform distribution of CuO nanoparticles in PANi matrix. FTIR and UV–Visible studies confirm the presence of polyaniline in emeraldine base form in the composites and suggest incorporation of CuO in polymer. Two probe electrical resistivity measurements of nanocomposites (NCs) film revealed that the resistivity of PANi increases with increasing content of CuO NPs.     

CNT–CdSe QDs nanocomposites: synthesis and photoluminescence studies

In this study, synthesis of carbon nanotube (CNT)–CdSe Quantum dots (QDs) nanocomposites has been investigated. CdSe QDs were synthesized via hydrothermal process. The chemical tendency of CNT and QDS was increased by precipitation after surface functionalization of CNTs (by carboxylated groups) and CdSe QDs (by silane groups), separately. The structure of nanocomposites was amorphous with a little amount of nanocrystalline cubic CdSe. The Fourier-transform infrared (FTIR) spectra and Raman spectrum revealed the strong chemical tendency of linkage between CNTs and QDs after functionalization on the surface of them. The morphology of nanocomposites depended on the QDs concentration and changed from aggregates of CNTs to the marvelous decoration of quantum dots on the ropes of CNTs. Transmission electron microscope (TEM) and atomic force microscope (AFM) images confirmed the adorable coatings of CNTs with CdSe QDs. The nanocomposites emitted in blue–green region with a maximum peak at 490 nm under the exposure of Ultraviolet (UV) light. Below 50 wt% QDs, the emission was quenched completely.     

In situ prepared polypyrrole–Ag nanocomposites: optical properties and morphology

Polypyrrole–silver (PPy–Ag) nanocomposites with various silver contents have been synthesized via a kinetically favorable one-step chemical oxidative polymerization process. The oxidant, ammonium persulfate, was used to oxidize pyrrole monomer for growing chains of PPy. And AgNO₃ was used as a precursor for metallic silver nanoparticles. The detailed characterization techniques, UV–Vis–NIR, fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction spectroscopy, field-emission scanning electron microscopy, and transmission electron microscopy (TEM), have been used to reveal electronic environment, structure, and morphology of composites as well as as-synthesized PPy. The synthesis environment prior to polymerization has also been investigated by absorption spectroscopy. The TEM images of PPy–Ag nanocomposites reveal that silver nanoparticles are deeply embedded into the polymer matrix in addition to surface adsorption. It is observed that the size distribution of inorganic nanoparticles (ca. 4–10 nm, depending on the metal ion concentrations) as well as structural morphology is altered by the initial concentrations of silver ions.     

Dielectric studies on hybridised PVDF–ZnO nanocomposites

Nanocomposites of polyvinylidene fluoride (PVDF) and nano-ZnO were prepared using the solution casting method for different concentrations of nano-ZnO and were characterised by X-ray diffraction and atomic force microscopy. Optical properties of these nanocomposites were determined by using UV-Vis absorption spectroscopy and Fourier transform infrared analysis. The variation of dielectric properties such as dielectric constant, dielectric loss and electric modulus of the hybrid films based on the content of ZnO studied for various microwave frequencies at room temperature showed that the dielectric constant of PVDF–ZnO hybrid films increased with increasing ZnO content at room temperature.     

Ultrafast optical and magneto-optical studies of III–V ferromagnetic semiconductors

Abstract

We use ultrafast optical techniques to investigate the dynamics of charge and spin carriers and coherent phonons as well as magnetic order in III-V ferromagnetic semiconductors. We observe a rich array of dynamical phenomena that are absent in traditional nonmagnetic semiconductors or metallic ferromagnets. Very short charge and spin lifetimes of the photoinjected carriers (～2ps) and multi-level charge decay dynamics are observed, which are attributed to a large density of mid-bandgap states introduced during low temperature molecular beam epitaxy (LT-MBE) growth and highly p-type Mn doping. During the very short free carrier lifetime, the coercivity of the system is seen to be reduced. We attribute this photo-induced ‘softening’ to the transient modification of carrier-mediated ferromagnetic exchange coupling between Mn spins. After the photogenerated free electrons are trapped by defects, periodic oscillations appear in differential reflectivity due to the coherent generation of acoustic phonon wavepackets.     

Electrical and optical properties of µc-SiH films

Microcrystalline silicon films have been found quite useful in amorphous silicon solar cells as a contact material in n-i-p cells. Microcrystalline silicon films are obtained when amorphous silicon films are prepared by R.F. glow discharge of SiH₄ + H₂ at higher power ratings. These films possess higher conductivity as well as high transmission than amorphous silicon films. The present paper reports the preparation technique ofμc-SiH films using R.F. capacitive glow discharge of hydrogen-diluted silane. X-ray studies andtem studies of the films indicate microcrystallinity of the films. The electrical and optical properties are also reported.     

Electrical and FTIR studies on Al substituted Mn–Zn mixed ferrites

Mixed ferrites of manganese and zinc with the substitution of aluminum are prepared by the ceramic double-sintering method. Confirmation of single-phase and polycrystalline ferrites is made from X-ray diffraction patterns and experimental and theoretical values of lattice constant are compared. Distribution of cations on A and B sites is concluded. A.c. conductivity and FTIR characterizations are done and the logarithm of conductivity (log ) dielectric constant () and tan at various frequencies () and temperatures (T) are reported. Hopping of electrons between localized d bands of ions is the interesting feature of these ferrites and the mechanism of hopping is discussed. Activation energy and vibration frequencies are discussed as a function of aluminum concentration.     

Dispersion assessment and studies on AC percolative conductivity in polymer-derived Si–C–N/CNT ceramic nanocomposites

Nanocomposites comprise polysilazane-derived SiCN ceramic charged with carbon nanotubes (CNTs) have been prepared by dispersion of multi-walled CNTs with a diameter of 80 nm in a cross-linked polysilazane (HTT 1800, Clariant) using a simple roll-mixer method. Subsequently, the composites were warm pressed and pyrolyzed in argon atmosphere. Scanning electron microscopy (SEM) and 3D Raman imaging techniques were used as major tools to assess the dispersion of CNTs throughout the ceramic matrix. Furthermore, studies on the effect of the volume fraction of CNTs in the nanocomposites on their electrical properties have been performed. The specific bulk conductivities of the materials were analyzed by AC impedance spectroscopy, revealing percolation thresholds (ρ_c) at CNT loadings lower than 1 vol%. Maximum conductivity amounted to 7.6 × 10⁻² S/cm was observed at 5 vol% CNT. The conductivity exponent in the SiCN/CNT composites was found equal to 1.71, indicating transport in three dimensions.     

Effect of annealing temperature on optical and electrical properties of ZrO2–SnO2 nanocomposite thin films

ZrO₂–SnO₂ nanocomposite thin films were deposited onto quartz substrate by sol–gel dip-coating technique. Films were annealed at 500, 800 and 1,200 °C respectively. X-ray diffraction pattern showed a mixture of three phases: tetragonal ZrO₂ and SnO₂ and orthorhombic ZrSnO₄. ZrSnO₄ phase and grain size increased with annealing temperature. Fourier transform infra-red spectroscopy spectra indicated the reduction of –OH groups and increase in ZrO₂–SnO₂, by increasing the treatment temperature. Scanning electron microscopy observations showed nucleation and particle growth on the films. The electrical conductivity decreased with increase in annealing temperature. An average transmittance greater than 80 % (in UV–visible region) was observed for all the films. The optical constants of the films were calculated. A decrease in optical band gap from 4.79 to 4.59 eV was observed with increase in annealing temperature. Photoluminescence (PL) spectra revealed an emission peak at 424 nm which indicates the presence of oxygen vacancy in ZrSnO₄. PL spectra of the films exhibited an increase in the emission intensity with increase in temperature which substantiates enhancement of ZrSnO₄ phase and reduction in the non-radiative defects in the films. The nanocomposite modifies the structure of the individual metal oxides, accompanied by the crystallite size change and makes it ideal for gas sensor and optical applications.     

Electrical conductivity studies of Bi2O3–Li2O–ZnO–B2O3 glasses

Ac conductivity measurements and its analysis has been performed on xBi₂O₃–(65?x)Li₂O–20ZnO–15B₂O₃ (0 ≤ x ≤ 20) glasses in the temperature range 30–300 °C and a frequency range of 100 Hz to 1 MHz. The dc conductivity increased and the activation energy decreased with lithium content. The frequency dependent conductivity has been analyzed employing conductivity and modulus formalisms. The onset of conductivity relaxation shifts towards higher frequencies with temperature. The Almond–West conductivity formalism is used to explain the scaling behavior, and the relaxation mechanism is independent of temperature.     

Changes in electronic and optical characteristics of halogen–alkali adsorbed WSe2 monolayer

Journal of Materials Science: Materials in Electronics - Adsorbing halogen and alkali metals atoms modify the optical and electrical characteristics of WSe2 monolayer (2D). The electrical and...     

Photocatalytic decomposition of VOCs by AC–TiO2 and EG–TiO2 nanocomposites

Clean Technologies and Environmental Policy - In this study, TiO2 nanoparticles (NPs)-based catalysts were prepared for the photocatalytic removal of toluene as a model VOC from air under UV light....