Search

In the present paper the investigations of the influence of swift heavy ion irradiation on the magnetotransport in the antimony (Sb) d-layer in silicon are reported. Temperature and magnetic field dependences of the resistance R(T,B) and the Hall coefficient RH(T,B) in the temperature range of 2K < T < 300K and B = 8T before and after the 167 MeV Xe+26 ion irradiation (ion fluence of 108 cm-2) were measured. At the temperatures below 50K there is observed the transition from the Arrhenius log R(1/T) to a logarithmic R ≈-log(T) dependence both before and after the swift heavy ion exposure which confirms the assumption that the carrier transport goes through the d-layer mainly. Moreover, the transition from the positive to negative magnetoresistance was observed with the temperature decrease that is characteristic of the two-dimensional quantum corrections to the conductivity in the case of weak localization regime. The appropriate Thouless lengths LTh(T) ≈ × Tp (where p and A are dependent on the scattering mechanism) indicated their ≈ 25-30% decrease after the swift heavy ion exposure. It was shown that the exponent p values were close to the theoretical one of p = 1, confirming the realization of 2D weak localization regime in the carrier transport. [ABSTRACT FROM AUTHOR]

We investigate the transport properties of n-type noncompensated silicon below the insulator-metal transition by measuring the electrical and magnetoresistances as a function of temperature T for the interval 2–300 K. Experimental data are analyzed taking into account possible simple activation and hopping mechanisms of the conductivity in the presence of two impurity bands, the upper and lower Hubbard bands (UHB and LHB, resp.). We demonstrate that the charge transport develops with decreasing temperature from the band edge activation (110–300 K) to the simple activation with much less energy associated with the activation motion in the UHB (28–90 K). Then, the Mott-type variable range hopping (VRH) with spin dependent hops occurs (5–20 K). Finally, the VRH in the presence of the hard gap (HG) between LHB and UHB (2–4 K) takes place. We propose the empiric expression for the low T density of states which involves both the UHB and LHB and takes into account the crossover from the HG regime to the Mott-type VRH with increasing temperature. This allows us to fit the low T experimental data with high accuracy. [ABSTRACT FROM AUTHOR]

Copyright of Przegląd Elektrotechniczny is the property of Przeglad Elektrotechniczny and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this paper the results of examinations of nanocomposites Cux(SiOy)100-x produced by ion beam sputtering using argon ions were presented. The examinations were performed by the use of ac devices for measuring frequency in the range 50 Hz-1 MHz and temperatures from 81 K to 273 K. The measurements were performed for the samples directly after production. Based on temperature dependences of conductivity σ, which were determined at the frequency 100 Hz, the Arrhenius graphs were prepared. From these graphs conductivity activation energies ΔE were calculated. Dependences of conductivity and activation energy of electrons on the metallic phase content x at the frequency 100 Hz were determined. Analysis of the obtained dependences shows that conductivity is a parabolic function of the metallic phase content x in nanocomposites. Changes of activation energies of nanocomposites, in which metallic phase contents are in the ranges x < 12 at.% and x > 68 at.%, demonstrate negative values - metallic type of conductivity. In the range 12 at.% < x < 68 at.% activation energies have positive values - the dielectric type of conductivity. It was established that for the metallic phase content of about 68 at.% the real percolation threshold occurs, and the conduction changes from dielectric to metallic type. [ABSTRACT FROM AUTHOR]

In this paper the results of investigations of electrical properties of metal-dielectric nanocomposites (FeCoZr)x(CaF2)100-x are presented. The samples with the metallic phase content x = 45.7 at.% were produced by ion-beam sputtering method in pure argon atmosphere, and subsequently annealed at. 398 K for 15 min. The measurements of electrical properties were performed in the frequency range from 50 Hz to 1 MHz. The frequency dependences of phase angle θ, capacity Cp, conductivity a and dielectric loss factor tanδ were measured at seven different, temperatures ranging from 148 K to 263 K. It was found that, the nanocomposite exhibits the phenomena of voltage resonance and current, resonance, characteristic of the conventional RLC circuits with series and parallel connections of elements. [ABSTRACT FROM AUTHOR]

The present paper investigates the temperature/frequency dependences of admittance Z in the granular Cux(SiO2)1-x nanocomposite films around the percolation threshold xC in the temperature range of 4-300 K and frequencies of 20-106 Hz. The behavior of low-firequency ReZ(T) dependences displayed the predominance of electrons hopping between the closest. Cu-based nanoparticles for the samples below the percolation threshold xC ≈ 0.59 and nearly metallic behaviour beyond the xC. The high-frequency curves ReZ(f) at temperatures T > 10 K for the samples with x < xC exhibited behavior close to ReZ(f) ≈ f-s with s ≈ 1.0 which is very similar to the known Mot.t law for electron hopping mechanism. For the samples beyond the percolation threshold (x > xC), the frequency dependences of ReZ(f) displayed inductive-like (not capacitive) behaviour with positive values of the phase shift, angles. [ABSTRACT FROM AUTHOR]

This paper studies the temperature dependences (2 < T < 300 K) of the DC conductivity σ(T) for the (Co0.45Fe0.45Zr0.10)x(Al2O3)1-x nanocomposites (30 < x < 65 at.%) sputtered in Ar + O2 atmosphere. It is shown that at temperatures lower than 100-150 K dependences of DC conductance on temperature for all the studied samples are due to the Shklovski-Efros variable range hopping mechanism. It was also observed that σ(x,T) dependences can be attributed to the formation of FeCo-based oxide "shells" around metallic alloy nanoparticles due to incorporation of oxygen in the vacuum chamber during the deposition procedure. [ABSTRACT FROM AUTHOR]

We describe here structure and temperature dependences of conductivity σ(T), the Seebeck coefficient α(T), thermal conductivity λ(T) and figure-of-merit ZT(T) in Ca3Co4O- ceramics, doped with Fe and Y, depending on compacting pressure (0.2 or 6 MPa) and temperature (300 < T < 700 K). It is shown that introduction of iron and yttrium to ceramics does not alter the crystalline structure of the material. Increasing the pressure in the compacting process before the additional diffusion annealing leads to a smaller-grained structure and increase σ and λ due to reducing of the synthesized samples porosity. The Seebeck coefficients of nanocomposite ceramics Ca3Co3.9Fe0.1O9 and (Ca2.9Y0.1) (Ca3Co3.9Fe0.1O9 have linear dependences on temperature is not changed after increase of compacting pressure. Electrical-to-heat conductivity ratio (σ/λ) for the samples compacted at high (6 GPa) pressure increases not more than 20-30% in comparison with ones compacted at low (0.2 GPa) pressure, whereby ZT is increased more than 50%. The main reason for this effect is samples porosity reduction with the compacting pressure increase. [ABSTRACT FROM AUTHOR]

The effect of oxygen-containing ambient arising at sputtering of granular nanocomposites (Fe0.45Co0.45Zr0.10)x(Al2O3)1−x (30 at.%≤x≤65 at.%) on their magnetic state and phase composition has been investigated. It was shown that the presence of oxygen resulted in the formation of oxide shells preventing the ferromagnetic interaction between Co0.45Fe0.45Zr0.10 nanoparticles and also the formation of metallic percolative net beyond the percolation threshold (as opposed to the films prepared in pure argon atmosphere). [ABSTRACT FROM AUTHOR]

In this work anisotropic magnetoresistance in lianogranular Ni films and Ni lianorods on Si(100) wafer substrates was studied in wide ranges of temperature and magnetic field. To produce Ni films and lianorods we used electrochemical deposition of Ni clusters either directly on the Si substrate or into pores in SiO2 layer on the Si substrate. To produce mesopores in SiO2 layer, SiO2/Si template was irradiated by a scanned beam of swift heavy 350 MeV 197AU26+ ions with a fluence of 5 x 108 cm-2 and then chemically etched in diluted hydrofluoric acid. Pores, randomly distributed in the template have diameters of 100 250 urn and heights about. 400 500 urn. Comparison of temperature dependences of resistance and magnetoresistance in Ni films and n-Si/SiO2/Ni structures with Ni lianorods showed that, tliey are strongly dependent. 011 orientation of magnetic field and current, vectors relative to each other and the plane of Si substrate. Moreover, magnetoresistance values in n-Si/SiO2/Ni nanostructures can be controlled not. only by electric field applied along Si substrate but. also by additionally applied transversal bias voltage. [ABSTRACT FROM AUTHOR]

A study of magnetotransport in the n-Si/SiO2/Ni nanostructures with granular Ni nanorods in SiO2 pores was performed over the temperature range 2-300 K and at the magnetic fields induction up to 8 T. The n-Si/SiO2/Ni Schottky nanostructures display the enhanced magnetoresistive effect at 25 K due to the impurity avalanche mechanism. [ABSTRACT FROM AUTHOR]

Abstract: The paper reports on the results of a comparative study of magnetic and magnetotransport properties of granular nanocomposite films FeCoZr–Al2O3 synthesized in pure Ar and Ar+O sputtering atmosphere. Effects of oxygen incorporation on the temperature and magnetic field dependencies of magnetization and electrical resistance of the films are discussed with respect to the “core–shell” structure formation. Peculiarities of coercive force variation with temperature are analyzed and discussed. [Copyright &y& Elsevier]

The effect of oxygen-containing ambient arising at sputtering of granular nanocomposites (Fe0.45Co0.45Zr0.10)x(Al2O3)1−x (30 at.%≤x≤65 at.%) on their magnetic state and phase composition has been investigated. It was shown that the presence of oxygen resulted in the formation of oxide shells preventing the ferromagnetic interaction between Co0.45Fe0.45Zr0.10 nanoparticles and also the formation of metallic percolative net beyond the percolation threshold (as opposed to the films prepared in pure argon atmosphere). [ABSTRACT FROM AUTHOR]