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Polypyrrole nanotubes: mechanism of formation

This article presents a contribution to better understanding of the processes which take place during the synthesis of polypyrrole nanotubes using a structure-guiding agent, methyl orange. Polypyrrole was prepared by oxidation of pyrrole monomer with iron(III) chloride. In the presence of methyl orange, the formation of nanotubes was observed instead of the globular morphology. Two reaction schemes with reversed additions of oxidant and monomer have been tested and they show remarkable influence on the produced morphology. Nanotubes with circular or rectangular profiles and diameters from tens to hundreds of nanometres have been obtained. FTIR and Raman spectra were used to assess the molecular structure of polypyrrole and detect residual methyl orange in the samples. The conductivity of nanotubes compressed into pellets was as high as 68 S cm−1. The mechanism of nanotubular formation starting at the nucleus produced with the participation of organic dye is proposed. The growth of a nanotube, however, proceeds in the absence of a template. An alternative mechanism for the formation of nanotubes, the coating of solid templates with a polypyrrole overlayer, is also discussed.

Synthesis of silver-anchored polyaniline–chitosan magnetic nanocomposite: a smart system for catalysis

A simple route was employed for the fabrication of a polyaniline (PANI)–chitosan (CS)–magnetite (Fe3O4) nanocomposite (PANI–CS–Fe3O4) via the in situ polymerization of aniline in the presence of CS using anhydrous iron(III) chloride as an oxidizing agent. The magnetic character of the nanocomposite results from the presence of iron oxide nanoparticles, which were formed as side products during the synthesis of the PANI–CS nanocomposite. The synthesized PANI–CS–Fe3O4 nanocomposite was fully characterized using Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), energy dispersive X-ray (EDX), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and vibrating sample magnetometry (VSM). The reduction of silver nitrate by the synthesized nanocomposite enables the anchoring of silver (Ag) nanoparticles onto its surface. The catalytic properties of the Ag-decorated nanocomposite (Ag@PANI–CS–Fe3O4) toward the reduction of 4-nitrophenol was investigated using sodium borohydride as a reducing agent.

Methodology of evaluating the influence of the resistance of contact regions in the measurements of sheet resistance on stripes of ultrathin high-resistance materials

The paper reviews the problems of measurement of sheet resistance of ultrathin high-resistance layers of organic semiconductors and the essential underlying problems. Particular attention is paid to potential influence of the resistance of contact regions on the results of direct measurement of sheet resistance of stripe-shaped layers. In this connection, we present a methodology of double length stripe resistance measurement (DLSRM), used above all to minimise the influence of contact regions on the measurement results. We deduce theoretical as well as practical possibilities of DLSRM in the diagnostics and quantitative characterisation of unsuitable or even faulty contacts on high-resistance layers. The application efficiency of the DLSRM method is documented by the results of sheet resistance measurement on zinc phthalocyanine with cathode sputtered planar contacts of noble metals (gold, platinum, or palladium). As expected, gold is the best contact material, but even in its application one cannot neglect the influence of contact regions. The presented method is universal and generally applicable to all materials where sheet resistance is the relevant parameter, and its assessment is based on measurements of the layer resistance in stripe arrangement.

Polypyrrole active layers of gas sensors prepared by MAPLE technology

Thin layers of polypyrrole (PPY) were deposited by MAPLE (Matrix Assisted Pulse Laser Evaporation) technology. The deposition was carried out by KrF excimer laser from water and dimethylsulfoxide matrixes. Ablation thresholds (Fth) were determined to be Fth ~ 0.3 J.cm−2for dimethylsulfoxide matrix and Fth ~ 0.45 J.cm−2for water matrix. The roughness of deposited layers was measured by AFM and their chemical composition was characterized by FTIR spectroscopy. Finally, resistance of sensors with PPY active layer was measured in dependence on working temperature and relative humidity of surrounding atmosphere.

Reversible switching of PEDOT:PSS conductivity in the dielectric–conductive range through the redistribution of light-governing polymers

One of the biggest challenges in the field of organic electronics is the creation of flexible, stretchable, and biofavorable materials. Here the simple and repeatable method for reversible writing/erasing of arbitrary conductive pattern in conductive polymer thin film is proposed. The copolymer azo-modified poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) was synthesized to achieve reversible photo-induced local electrical switching in the insulator–semimetal range. The photoisomerization of the polymer was induced by grafting nitrobenzenediazonium tosylate to the PSS main chains. While the as-deposited PEDOT:PSS thin films showed good conductivity, the modification procedure generated polymer redistribution, resulting in an island-like PEDOT distribution and the loss of conductivity. Further local illumination (430 nm) led to the azo-isomerization redistribution of the polymer chains and the creation of a conductive pattern in the insulating polymer film. The created pattern could then be erased by illumination at a second wavelength (470 nm), which was attributed to induction of reverse azo-isomerization. In this way, the reversible writing/erasing of arbitrary conductive patterns in thin polymer films was realized.

The Fe-Au interface: Hyperfine interactions of 57Fe by Mössbauer transmission and conversion electron spectroscopy

We studied the effect of interfaces character in 57Fe/Au thin layers on iron hyperfine parameters using Mossbauer spectroscopy. Four samples of bilayers (57Fe covered by Au) were prepared on MgO substrate by pulsed laser deposition (PLD) with varying 57Fe layer thickness (∼10–95 nm), covered by Au layer with constant thickness of ∼8.7 nm. Mossbauer spectra were acquired in transmission and conversion electron geometry. The hyperfine parameters of α–Fe layer, Fe/Au and MgO/Fe interfaces were determined.

Conductive Gas Sensors Prepared Using PLD

This contribution deals with conductive thin film gas sensors fabricated using laser technology. The principles of the pulsed laser deposition (PLD) technology is explained. Hybrid PLD systems, based on a combination of PLD and magnetron sputtering, PLD and RF discharges, and PLD with two laser targets are also presented. The growing layers can be modified by an ion beam. Organic films can be grown using the cryogenic MAPLE technology. Nanocrystalline and nanocomposite thin films for gas sensors can be deposited. Examples of layer fabrication and testing of layer properties for gas sensors are given.