Temperature and magnetic field dependencies of sheet resistance R # (T,B) in polycrystalline CVD graphene, investigated in the range of 2≤ T≤ 300 K and magnetic fields 0≤ B≤ 8 T, allowed to determine carrier transport mechanisms in single-layered and twisted CVD graphene. It is shown that for R # (T,B) curves for such samples are described by the interference quantum corrections to the Drude conductivity independently on type of precursor and peculiarities of graphene transfer from Cu foil onto the various substrates (glass or SiO 2 ). The twisted CVD graphene samples have demonstrated additional contribution of 2D hopping conductivity into the R # (T,B) dependencies. Keywords: graphene, single layer, twisted layers, CVD, carrier transport, magnetoresistance.

Currently, special attention is paid to the search for new ceramic materials based on wide-gap oxides, as well as to the study of their structure and properties with a view to their application in various areas of electronic and optoelectronic industry. Conventional double-step ceramic technology has been used to obtain samples in this experiment. After compacting at the pressure of 6 GPa of ZnO and ZnO-FexOy powders in different weight relations, the samples were subjected to the procedure of synthesis at 1173 K for 2 h and then to the annealing at 1473 K for 3 h on air. The samples structure was investigated by the Scanning Electron Microscopy (SEM), Energy-dispersive X-ray Spectroscopy (EDX), X-ray Diffraction (XRD) and Raman spectroscopy methods. Temperature dependences of resistivity, magnetoresistance, Hall and Seebeck effects were experimentally studied in the range from 4 to 700 K. As the experiments have shown, the size of grains in the obtained ceramic samples after synthesis was in submicron range. An XRD study showed the saving of the wurtzite structure in Zn1-delta Fe delta O solid solutions where 0.66 < delta < 0.81 at. % regardless of the type of the doping agent. At the same time, the replacement of zinc by iron atoms led to the contraction of the ZnO lattice. All the samples studied (ZnO and Zn1-delta Fe delta O) demonstrate n-type conductivity. The temperature dependencies of resistivity have shown two specific features: the presence of energy level about 0.35 eV below the conduction band bottom for the doped ceramic samples (unknown in literature) and conductance with the changing activation energy at temperatures below 200 K for the undoped ZnO ceramic samples. Seebeck coefficient increased by100-150% with doping due to growth of electron concentration. Some model concepts about scattering mechanisms and reasons of Seebeck effect enhancement have been developed. (C) 2020 Elsevier B.V. All rights reserved.

The study presents frequency dependences of real part of admittance Z' (f) and phase shift angle theta(T, f) in nanogranular films containing CoFeZr nanoparticles with "core-shell" structure embedded into SiO2 matrix. The 3 mu m thicknesses (Co41Fe49Zr10)(x)(SiO2)(100-x) films with 20 <= x <= 80 at.% were deposited in vacuum chamber evacuated either with pure Ar (Set 1 samples) or Ar + O-2 gas mixture (Set 2) using ion-beam sputtering technique. After characterization by X-Ray diffraction, Mossbauer spectroscopy, scanning electron microscopy and magnetization studies, the films both of Set 1 and Set 2 samples were subjected by admittance measurements at 300 K in the frequency range of 0.1-1000 kHz. Mossbauer spectroscopy have shown that oxidized CoFeZr nanoparticles in Set 2 samples contain semiconducting iron-based oxides with Fe3+ charge states of iron ions. The observed Z' (f) and theta(f) dependencies for the Set 2 films below the x(c) have shown dielectric regime of carrier transport. They also exhibited that at weak AC electric fields inductive-like contribution to reactive part of admittance (with positive theta values) prevails over the capacitive one f > 10 kHz. This effect of the so-called "negative capacitance" was explained by the delay of current, formed by electrons hopping between nanoparticles, relative to applied bias voltage. This delay is forced by formation of dipoles of charged FeCoZr nanoparticles with native Fe-based oxide "shells" around them that results in the increase of mean life time of hopping electrons on nanoparticles with "core-shell" structure.

Application of magnetic metal/graphene hybrid structures in magnetosensorics requires the formation of high-quality low-ohmic (barrier-free) contacts and understanding of mechanisms of electric charge transfer near and through the metal/graphene contact area. In present paper we fabricate samples of twisted graphene electrochemically decorated with Co particles (Co-G/SiO2) which demonstrate perfect ohmic electric contact between Co and graphene sheets. Temperature and magnetic field dependencies of surface resistance for pure twisted graphene (G/SiO2) and Co-G/SiO2 samples are considered within the models of 3D Mott variable range hopping and 2D weak-localization quantum corrections to the Drude conductivity. Phenomenological model is proposed explaining the experimentally observed transition from predominantly negative magnetoresistive effect in weak magnetic fields B (below 1-2 T) to positive magnetoresistance (PMR) at B beyond 5 T assuming the growth of PMR due to the distortion of current-conducting routes under the influence of Lorentz force which originates from the enhancement of large-scale potential relief in Co-G/SiO2 sample. This work considers the new approach to the application of G/SiO2 decoration with Co particles for creation both metallic (distributed, defragmented) shunts and high-quality ohmic electrodes in magnetic sensing.

As environmental pollution to heavy metals is being increased every year, occurrence of serious risks to health of human, animals and plants can be expected. Heavy metals with all of their destructive effects are the main pollutants in the air of big cities. Hence, this study has been conducted with the objective of analysis of role of tree species in absorption of air pollution caused by copper (Cu), zinc (Zn) and (U) uranium in Tehran. According to the climate of studied stations, especially wind velocity and direction, the sampling operation was taken at the end of March and December. The number of samples was also determined based on number of tree species studied (Pinus eldarica, Cupressus arizonica, Platanus orientails), organs of tree species (leaves), number of stations (Mehrabad Airport, Damavand and Chitgar Park) and sampling time scopes (March and December). Sampling was done in frame of statistical plan of completely random block in 3 iterations and the data analysis was done using analysis of variance and using SAS software. The results obtained from this study show that the absorption of cooper, zinc and uranium metals in the leaves of studied trees in polluted stations is more than control station. According to obtained results, uranium concentration in the leaves of studied species increased respectively in Pinus eldarica Medw, Cupressus arizonica Greene and Platanus orientails. The leaves of Pinus eldarica Medwin Mehrabad Airport station have shown highest absorption of this metal. Moreover, obtained results show that the cooper absorbed by leaves of studied species is increased respectively in Pinus eldarica Medw, Cupressus arizonica Greene and Platanus orientails. In terms of the effect of station on absorption of cooper, the species in the Mehrabad station have shown high absorption of this metal. The concentration of absorbed zinc in leaves of studied species is also increased respectively in Pinus eldarica Medw, Cupressus arizonica Greene and Platanus orientails and the zinc absorbed by species of Mehrabad station has shown the highest level. It is concluded that the absorption level of Cu, Zn and U in leaves of studied trees in polluted stations has been higher than control stations and Pinus eldarica Medw can be used as an index of absorption of heavy metals such as Cu, Zn and U.

According to the abundant use of engineer and factor designer about the function of concrete in different environmental conditions, it's important to analyze the methods and new technologies of factors and concrete and adopted with environmental condition and function of Russia. One of the main causes of destroyed concrete in RCC dams is the alkali-carbon reaction of the aggregates. In this paper, the aggregates are chosen from three well known RCC dams in Russia. Mortar bar method, accelerated mortar bar test, accelerated concrete prism test were performed on experimental samples and some solutions were expressed for the concrete to be remained properly. According to the results, it is concluded that among these three methods, accelerated mortar bar test (choosing appropriate Expansions criterion ) , is the best method to the evaluate Alkali-carbonate reactions. [Masoud Golshani, Ali Arash Ronassi, Vyacheslav Vatslavovich Babitsky. Investigation of physical factors and chemical reactions in Roller compacted concrete dams in Russia. Life Sci J 2013;10(7s):280-285] (ISSN:10978135). http://www.lifesciencesite.com.

The general goal of this work is to study the structure and photoelectrical properties of the electrochemically deposited thin CdTe films. The conducted investigation has shown that (i) as-deposited films have the single-phase structure with a grain size of 1–10 μm and are of the n-type conductivity; (ii) photosensitivity abruptly decreases when the film thickness is over 10 μm; (iii) annealing at temperatures less than 500 °C improves the film quality with retention of the n-type conductivity; and (iv) photosensitivity of the films is not impaired under irradiation by 6 MeV electrons with a fluence of 5 × 10 14 cm − 2 .