Swarup Biswas

Optical and structural properties of amorphous and heat treated In0.4Se0.6 film of different thicknesses

The optical gap (Egopt) of as-deposited In0.4Se0.6 film is found to increase with the thickness of the film. The optical gap attains a steady value after several heat treatments of the films at elevated temperatures. The values of optical gaps of In0.4Se0.6 films are found to depend on the temperature of the heat treatment. The effect of thickness and temperature of heat treatment on the optical gap of the film is interpreted in terms of creation or elimination of defects in the amorphous structure of In0.4Se0.6 film. X-ray diffraction spectra are taken for both as deposited and heat treated In0.4Se0.6 films. From the results related to the radial distribution functions of the specimens it is noted that in the case of In0.4Se0.6 a transition from amorphous to crystalline states takes place at 523 K and above. The results also show that both the optical gap and the coordination number decrease with increasing temperature of heat treatment. Therefore it is evident that the heat treatment improves the long range order of In0.4Se0.6 but reduces the coordination in the short range.

Correlation between nucleation, phase transition and dynamic melt-crystallization kinetics in PAni/PVDF blends

In this study, polyaniline (PAni)/poly(vinylidene fluoride) (PVDF) blends of different compositions were prepared by in situ chemical polymerization of aniline in a mixture of PVDF and dimethylformamide (DMF). Fourier transform infrared spectroscopy (FT-IR), thermo-gravimetry (TG) and differential scanning calorimetry (DSC) were utilized to understand the effect of different amounts of in situ PAni loading on the crystalline structure, phase transition and dynamic melt-crystallization kinetics of PVDF. The images for morphology obtained using scanning electron microscopy and polarizing optical microscopy also provided the confirming evidences. FT-IR studies revealed that the transition of the crystalline structure (from β- to α-phase) of pure PVDF during recrystallization is hindered by the incorporation of PAni within the matrix. The dynamic crystallization kinetics data were analysed with different macroscopic models to describe the polymer crystallization, and the parameters obtained from the analyses were correlated with the structural evidence to verify their applicability for the systems under investigation. Values for the effective activation energy (EX) of the crystallization process of PVDF and its blends were calculated by the differential isoconversional methods of Friedman. It was observed that, although PAni acted as an effective nucleating agent to induce a great number of heterogeneous nuclei within the blends, it actually delayed the overall crystallization process. The increased values of the crystal growth parameters obtained from the analysis of the temperature-dependent EX by the modified Hoffman–Lauritzen theory also support the above mentioned interpretations.

Dependence of the carrier mobility and trapped charge limited conduction on silver nanoparticles embedment in doped polypyrrole nanostructures

The present article demonstrates an intensive study upon the temperature dependent current density (J)-voltage (V) characteristics of moderately doped polypyrrole nanostructure and its silver nanoparticles incorporated nanocomposites. Analysis of the measured J–V characteristics of different synthesized nano-structured samples within a wide temperature range revealed that the electrical conduction behavior followed a trapped charge-limited conduction and a transition of charge transport mechanism from deep exponential trap limited conduction to shallow traps limited conduction had been occurred due to the incorporation of silver nanoparticles within the polypyrrole matrix. A direct evaluation of carrier mobility as a function of electric field and temperature from the measured J–V characteristics illustrates that the incorporation of silver nanoparticles within the polypyrrole matrix enhances the carrier mobility at a large extent by reducing the concentration of traps within the polypyrrole matrix. The c...

Correlation of carrier localization with relaxation time distribution and electrical conductivity relaxation in silver-nanoparticle-embedded moderately doped polypyrrole nanostructures

The electrical conductivity relaxation in moderately doped polypyrrole and its nanocomposites reinforced with different proportion of silver nanoparticles was investigated in both frequency and time domain. An analytical distribution function of relaxation times is constructed from the results obtained in the frequency domain formalism and is used to evaluate the Kohlrausch-Williams-Watts (KWW) type decay function in the time domain. The thermal evolution of different relaxation parameters was analyzed. The temperature-dependent dc electrical conductivity, estimated from the average conductivity relaxation time is observed to depend strongly on the nanoparticle loading and follows Mott three-dimensional variable range hopping (VRH) conduction mechanism. The extent of charge carrier localization calculated from the VRH mechanism is well correlated to the evidences obtained from the structural characterizations of different nanostructured samples.

On the compositional dependence of the optical gap and structural properties of amorphous In x Se1−x thin films

The optical gap of the amorphous InxSe1−x thin film has been observed to decrease with increasing content of indium in the film (x). An attempt is made to interpret the compositional dependence of the optical gap in amorphous InxSe1−x thin film in an alloy-like approach. It has been found that introduction of higher concentrations of indium imparts greater stability to the structure of the indium selenium alloy. From the study of the radial distribution function (RDF) by X-rays it is observed that there is a correlation between the coordination number and the optical gap of indium selenide thin films.