Electronic and optical features of silicon carbide nanoparticles and nanocomposites
Electron paramagnetic resonance (EPR) investigations were carried out on hybrid Core-Shell nanomaterials associating silicon carbide nanoparticles and conducting polyaniline. The performed experiments compare the paramagnetic centres, the electronic transport features and the interface effects in two classes of materials, bare polymers and core-shell nanocomposites. By EPR, large doping rates were demonstrated in the bare doped polymers through important saturation phenomena which alter significantly the EPR spectrum features. Furthermore, memory effects were involved in the bare doped polymer with regard to the EPR spectrum features depending on the conditions of its thermal treatments. In the hybrid core-shell nanocomposites nor such saturation and nor memory effects were found on the EPR signals even if similar paramagnetic centres exist in both classes of samples. These behaviors were discussed taking into account the thermal stability and the doping efficiency in the considered classes of materials. Optimal doping levels were then realized and their effects on the polymers and the nanocomposites were clarified by using EPR and DRS (dielectric relaxation spectroscopy) measurements. Also, it is demonstrated that the charge carriers consist in polarons in the nanocomposites while bipolarons contributions dominate the electrical conductivity in the bare doped polymers.
New aspects of the low-concentrated aniline polymerization in the solution and in SiC nanocrystals dispersion.
Results of the simultaneous in-situ UV-vis and open-circuit potential (OCP) monitoring of the low-concentrated aniline (An) polymerization in the presence of camphorsulfonic acid (CSA) suggested that during the induction period (IP) step a transition state formed, which probably included anilinium cation and the oxidant anion, antecedent to a propagation step. No aniline oligomers were registered at this stage but they appeared at the beginning of the propagation step under the investigation conditions. The moments of formation of insoluble pernigraniline phase and appearance of emeraldine units in the growing pernigraniline chains were ascertained by the comparison of kinetic and OCP profiles of the polymerization process both in the solution and in SiC dispersion water mediums. It is deduced that pernigraniline reduction by aniline molecules begins earlier than it is generally accepted (i.e., earlier than OCP maximum is reached) and probably in parallel to a continuing appearance of pernigraniline units even in the same chains that undergo the reduction. It was found that an addition of the SiC dispersion phase into the polymerization mixture accelerates differently all stages of the aniline polymerization. Finally, this polymerization process leads to the formation of polyaniline (PANI)-CSA shell with thickness in the range from 0.5 nm to a few nm at the SiC nanocrystals surface.
Photoconductivity of CdS nanocluster-doped polymers
Abstract We report the first demonstration of photoconductivity of a polymer film doped with nanometer-sized semiconductor clusters (quantum dots). In such a composite, the semiconductor cluster acts as a sensitizer for the photogeneration of carriers and the polymer serves as the carrier-transporting medium. In this study we have measured the wavelength and field dependence of the charge generation efficiency of a polyvinylcarbazole film doped with ≈ 16 A CdS clusters and discussed the mechanism for photoconduction. We believe this approach may be extended to include many other semiconductor nanoclusters to create a novel class of photoconductive material.