Nonlinear properties of two-phase composite films with a fractal structure

Inhomogeneous two-phase conducting films whose structure is intermediate between three-and two-dimensional configurations are discussed. The longitudinal film size exceeds the correlation length, and its thickness is less than the correlation length. In the case of weak nonlinearity, we found dependences of the film resistivity on the concentration and size of conducting particles, as well as on the film thickness, in the framework of a percolation approach.     

A phenomenological theory of the thermal conductivity of thin films

A phenomenological theory is presented for the lattice thermal conductivity of thin plates (or films) in a contact with another material (e.g. a thin plate covered by an oxide film, a thin film evaporated on a substrate, etc.). In such heterogeneous systems, it is necessary to consider — besides reflections — the exchange of phonons between the phases of which the system is composed. Boundary conditions are formulated for the phonon distribution functions. It is shown that the surrounding material (or the substrate) can exert considerable influence upon the effective thermal conductivity of the plate (film).In conclusion, the authors express their sincere gratitude to . Bárta for valuable discussions on the subject of this paper.     

The influence of the structure of thin antimony films on their electrical conductivity

The eletrical conductivity of antimony films of different thicknesses was studied at different temperatures. For small thicknessd, whereL is the electron mean-free path, the film resistances varies asd ^?n , wheren=2. However, ford?L the value ofn becomes smaller than 2 which is in agreement with the theory.     

The crystalline structure,conductivity and optical properties of Co-doped ZnO thin films

Transparent conductive Co-doped ZnO thin films were deposited by ultrasonic spray technique. Conditions of preparation have been optimized to get good quality. A set of cobalt (Co)-doped ZnO (between 0 and 3 wt%) thin films were grown on glass substrate at 350 °C. The thin films were annealed at 500 °C for improvement of the physical properties. Nanocrystalline films with hexagonal wurtzite structure and a strong (0 0 2) preferred orientation were obtained. The maximum value of grain size G = 63.99 nm is attained with undoped ZnO film. The optical transmissions spectra showed that both the undoped and doped ZnO films have transparency within the visible wavelength region. The band gap energy decreased after doping from 3.367 to 3.319 eV when Co concentration increased from 0 to 2 wt% with slight increase of electrical conductivity of the films from 7.71 to 8.33 (Ω cm)⁻¹. The best estimated structure, optical and electrical results are achieved in Co-doped ZnO film with 2 wt%.     

Electrical conductivity and band structure of thin polycrystalline EuS films

A study of the electrical resistance of thin polycrystalline EuS films (0.4–0.8 μm thick) in the temperature range 120–480 K has provided the basis for a model of the band structure of this substance. It has been shown that the main impurity levels in thin polycrystalline EuS films are those related with localized states near the conduction band bottom, as well as the E _i donor levels of Eu ions outside regular lattice sites. The “tail” of the localized states extends in energy up to at least ?0.45 eV.     

Thermal conductivity of a composite medium with a disperse graphene filler

The possibility of decreasing the effective heat-transfer coefficient of insulating materials due to the introduction of small amounts of graphene-like clusters is considered. It is shown that the effect of screening thermal radiation by introduced clusters at their low concentration significantly exceeds the effect of increasing the thermal conductivity     

The conductivity transition of aggregated Bi films

By analyzing the recent experimental and theoretical results, we find that the abrupt conductivity transition of an ultrathin aggregated film of bismuth during its growth is not describable by the Anderson transition or quantum percolation, but instead can be well described by a two-dimensional continuum model of classical percolation.     

High-frequency conductivity of films with different surfaces

The high-frequency conductivity of films with different surfaces and spherically symmetric energy band is calculated. General expressions are obtained for the conductivity for arbitrary values of the following quantities: the film thickness, the frequencies of the incident wave, and the specularity parameters with allowance for the bulk scattering mechanisms. A detailed analysis is made of the influence of the boundedness of the sample and the different surfaces on the conductivity in limiting cases with respect to the film thickness and the frequency of the incident wave. In particular, it is shown that in the case of thin films and low frequencies the conductivity decreases with decreasing thickness. The influence of different surfaces on the conductivity is also considered. The dependence of the coefficient of absorption of the wave on the film thickness and the carrier density is analyzed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 88–92, July, 1980.We are sincerely grateful to Professor B. M. Askerov for his interest in the work and a helpful discussion of the obtained results.     

Studying the structure and electrical conductivity of thin granulated bimetallic films

The surface resistance of bimetallic granular films prepared by means of laser-induced deposition is studied. The possibility of modeling their conductivity is demonstrated, depending on their morphological properties.     

A theory of the microwave ac conductivity of superionic conductors with randomly modulated structure

Localized resonant absorbing states of ions due to a random potential modulating the structure of superionic conductors are shown to be responsible for ac current response maxima in high frequency tails. The theory allows for interpretation of the microwave maxima found in samples of α-AgI and β-Cu Br exhibiting strain-induced texture, and also in some polycrystalline ionic structures.     

Thermodynamic functions of a two-sublattice ferrite in a magnetic field

This paper considers the effect of the magnetic field on the specific heat, entropy, and temperature behavior of the magnetization in a two-sublattice ferrite in the collinear phase. It is shown that the specific heat and entropy vary nonmonotonically with the magnetic field, while at low temperatures the magnetization increases with the temperature when the magnetic field takes values in the range H₁/2 < H h₁, where H₁ is the value of the magnetic field for which deviation from the collinear structure begins [1, 2].Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 33–36, January, 1977.In conclusion, the author wishes to express his indebtedness to G. M. Nedlin and to thank him for his valuable appraisal of the work.     

Electrical conductivity of a two-dimensional model for a composite material with structural anisotropy

The electrical conductivity of a structurally anisotropic two-dimensional model for a composite material is considered. The model represents an isotropic matrix with a system of nonconducting inclusions in the form of mutually perpendicular scratches of various lengths. The centers of the scratches are chaotically distributed in plane (x, y). The approximate effective medium method is used to derive an expression for effective conductivity tensor $\hat \sigma _e$ that satisfactorily describes the electrical conductivity of this model over a wide concentration range. The model conductivity in the critical region is considered in terms of the similarity hypothesis.     

The effective conductivity of composite materials with cubic arrays of multi-coated spheres

Two premeditated resistor models have been developed and tested for the prediction of the effective thermal conductivity of a periodic array of multi-coated spheres embedded in a homogeneous matrix of unit conductivity. The results have been compared and evaluated with the exact solution, as obtained by extending a method originally devised by Zuzovski and Brenner. The results for the two models were found to yield bounds for the exact solution. For some situations, the model results match well with the exact solution, but in other cases the results for one of the models could deviate from the exact solution. PACS 41.20.Cv; 44.10.+i; 72.80.Tm     

Heisenberg-type ferromagnetic films with a sandwich structure

Green’s function theory is applied to an alternating two-element multilayer ferromagnetic film. The Hamiltonian is based on the Heisenberg model with a second-order uniaxial single-ion anisotropy and with the interaction between the layer in the interfaces. Magnetization and the phase transition in such system are derived for several sets of material parameters.     

Properties of carbon films with high conductivity anisotropy

Carbon films with high conductivity anisotropy were obtained via sputtering a graphite target with an accelerated argon ion beam. The film structure was studied using Raman spectroscopy (combination scattering spectroscopy), transmission high-resolution electron microscopy, chemical analysis, X-ray photoelectron spectroscopy, and tunnel spectroscopy. We found conductivity anisotropy along and across the film chains of the order of 10⁴, which is associated with a high content of linear carbon chains with sp hybridization of bonding orbitals.     

The theory of atomic and magnetic ordering in ternary alloys with fcc lattice

We consider the theory of the mutual influence of atomic and spin ordering phenomena in ternary alloys of transition elements with fcc lattice. The case of quasibinary alloys B₃A-B₃D is considered in detail. Concentration dependences of the critical temperature of the order-disorder phase transition are considered for cases of atomic and magnetic ordering.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 48–57, December, 1970.     

Electrical conductivity and electromagnetic interference shielding characteristics of multiwalled carbon nanotube filled polyacrylate composite films

Multiwalled carbon nanotubes (MWCNTs) were homogeneously dispersed in pure acrylic emulsion by ultrasonication to prepare MWCNT/polyacrylate composites applied on building interior wall for electromagnetic interference (EMI) shielding applications. The structure and surface morphology of the MWCNTs and MWCNT/polyacrylate composites were studied by field emission scanning microscopy (FESEM) and transmission electron microscopy (TEM). The electrical conductivity at room temperature and EMI shielding effectiveness (SE) of the composite films on concrete substrate with different MWCNT loadings were investigated and the measurement of EMI SE was carried out in two different frequency ranges of 100-1000 MHz (radio frequency range) and 8.2-12.4 GHz (X-band). The experimental results show that a low mass concentration of MWCNTs could achieve a high conductivity and the EMI SE of the MWCNT/polyacrylate composite films has a strong dependence on MWCNTs content in both two frequency ranges. The SE is higher in X-band than that in radio frequency range. For the composite films with 10 wt.% MWCNTs, the EMI SE of experiment agrees well with that of theoretical prediction in far field.