Vol 52, No 4 (2016)

Results of a study of the structure of porous carbon materials (PCMs) prepared by the carbonization of plant raw materials and the modification of oxidized or thermally expanded graphite have been described. It has been experimentally found that the studied materials have a porous fractal structure with an average micropore radius of 17–37 Ǻ. Based on this finding and results of previous studies, it is reasonable to state that the studied materials can be effectively used as supercapacitor electrodes. Adsorption/desorption of vapors and an aqueous solution of ethyl alcohol has revealed that the resulting materials are not inferior to pharmaceutical activated carbon with respect to the studied parameter. At a temperature of 37°C, carbonized sunflower seed shells retain the adsorbate three times longer than activated carbon does; this feature makes it suitable for use in medical applications.

In this study, intercalated polypyrrole/montmorillonite nanocomposite was synthesized by a facile and simple solution intercalation method. The method is based on the exchanging of pyrrole monomers with sodium interlayer cations followed by polymerization by adding ammonium persulfate as oxidant. To avoid the spontaneous polymerization of pyrrole outside the clay, the proportions of pyrrole to clay and that of monomer to oxidant were varied. Several techniques have been used to study the structure and conductivity of the obtained materials: Fourier transform infrared spectroscopy, X-ray diffraction, Energy-dispersive X-ray spectroscopy analysis, scanning electron microscopy, Brunaner–Emmet–Teller technique, impedance spectroscopy and ultraviolet–visible spectroscopy. It was shown that it is not necessary to subject clay to organophilation with quaternary alkylammonium or to ultrasonic activation, or to treat it thermally to form intercalated nanocomposite. By increasing the amount of clay to that pyrrole, an intercalated polypyrrole clay nanocomposite is formed. Theevidence of the intercalation of polypyrrole is deduced from the X-ray diffraction and the Brunaner–Emmet–Teller technique specific surface. Both the expansion of the basal interlayer distance to 14 Å and the decrease of the specific surface area from 78.2 for the clay to 48 m² g^–1 prove the formation of an intercalated structure. The conductivity has been measured using impedance spectroscopy. The dc conductivity was in the range of 2–10^–3 S/cm.

Studies of boron-gluconate electrolyte for obtaining nanocrystalline Co–W coatings and its separation by molecular weights of the components is carried out by gel filtration. It is shown that boric acid (as a buffer agent) and sodium chloride (as the agent increasing conductivity) after being introduced into the electrolyte form certain gluconate complexes in the solution. The boron-gluconate complex has a larger molecular weight. Three fractions with different molecular weights including the fractions that contain Co-boron-gluconate and W-boron-gluconate complexes were obtained. It is shown that the formation of certain macromolecular complexes is a slow process, the consequence of which is the dependence of the bulk properties of the electrolyte on time.

Undoped zinc oxide and iron-doped zinc oxide thin films have been deposited by the sol-geldipcoating method. The Fe/Zn nominal volume ratio was 5% in the solution. The effects of Fe incorporation on morphological, structural, and optical properties of ZnO films were investigated. The scanning electron microscopy measurements showed that the surface morphology of the prepared thin films was affected by Fe doping. The X-ray diffraction patterns of the thin films showed that doped incorporation leads to substantial changes in the structural characteristics of ZnO thin films. The optical absorption measurements indicated a band gap in the range of 3.31 to 3.19 eV. The X-ray photoelectron spectroscopy demonstrated that Fe is incorporated in the ZnO matrix with 6.5 atomic percent (at %). The energy dispersive spectroscopy studies indicated the formation of ZnO with high efficiency.

The focus of this research is on the investigation of structural changes in the As₂S₃–Se multilayer nanostructure and on the examination of a relative contribution of As₂S₃ and Se layers to nanostructuring by measuring the Raman spectra. The formation of the As₂S₃-Se nanostructure by an alternate As₂S₃ and Se layers deposition was applied. The diffraction efficiency dependence on the exposure of a CW DPSS laser were monitored in a transmission mode of the1st order diffracted beam intensity and measured in real-time at the normal incidence of the laser diode beam (λ = 650 nm). From the comparison of these dependences for a set of samples we have chosen the multilayer nanostructure As₂S₃–Se with optimal recording properties meaning maximum both the value and the rate of diffraction efficiency. Our results are found to be of practical interest as they allow a significant improvement of the diffraction efficiency of the directly recorded relief gratings.

Modern physical vapor deposition and chemical vapor deposition technologies intended for the protection of surfaces of products, in particular, the pyrolytic deposition of chromium carbide coatings using organometallic compounds as precursors, are discussed.

In this study, resistive switching behaviors of Ag/SiN/p⁺-Si device were investigated by adjusting nitrogen concentration and layer thickness. The device with a nitrogen concentration of 50% and a thickness of 10 nm has a typical bipolar resistive switching behavior with a low forming voltage (~4 V), a high on/off ratio (~10²), an excellent endurance (>10²) and a long retention time (>10⁵ s). According to I–V characteristics analyses, electric transports in both a high resistance state and a low resistance state are dominated by hot electron emission which is caused by the electron trapping and detrapping through immovable nitrogenrelated traps. The temperature dependence of a resistive switching behavior not only illustrates the existence and importance of the traps, but also discovers a new phenomenon of the transition about the polar of a resistive switching method. Surely, more efforts need to be made for deeper understanding of the carrier transport in SiN thin films.