Effective Impedance Method for In situ Ellipsometry Analysis of Magnetic Films

The method of effective surface impedance is proposed and applied for in situ characterisation of magnetic structures. For any ellipsometry investigations a proper choice of a physical model is important for solving the inverse problem. Reasonable approximations used for in situ ellipsometry monitoring are assumptions of a constant rate of layer growth and stable optical parameters. Standard ellipsometry analysis requires the model response to be calculated from every layer in the structure. Errors from underlying layers propagate through the entire structure and accumulate. In this case a method of a pseudosubstrate is used which approximates the underlying structure as a single interface (so called virtual interface), rather than tracking the entire sample history. The virtual interface is placed at some level and growth is modelled on this interface with no knowledge retained for the underlying structure. There are various methods for describing the virtual interface. In this paper, the concept of the effective impedance is used which requires only three measurement data points and is convenient for combined investigation of optical and magneto-optical properties. The algorithm is based on the calculation of the characteristic matrix of the layer (Abeles matrix) and surface impedance of the virtual interface using two ellipsometric experimental data points. The method is successfully used to analyse Co / SiCo films. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3358

“The Thermal Wave” in Technology of Crystal Growth from the Melt

It was found that the temperature fluctuations at the interface crystal-melt are the main reason for the formation of single crystals inhomogeneity grown by the Czochralski method. To reduce the heterogeneity of the layered method is proposed to reduce temperature fluctuations in the melt through the creation of artificial heat wave formed by the modulation of the heater temperature setting of growing single crystals. This paper describes the experimental technique to measure the temperature directly in the field of crystal growth of gallium arsenide from the melt. We investigated the possibility of special control actions for decreasing the temperature fluctuations at the crystallization front. These actions relate to the modification of the thermal and kinetic control parameters normally used in the Czochralski method of crystal growth, such as heater temperature, as well as crystal and crucible rotation rates. Unsteady low energetic thermal control actions (thermal waves, induced by periodic changes of the heater temperature) are able to eliminate temperature fluctuations near the crystal / melt interface and may be a potential tool for the growth of striation-free gallium arsenide single crystals. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3364

Crystal Growth Mechanism in" Synthesis-solute-diffusion" Method in Ultrasonic Field

Features crystal growth method “synthesis-solute-diffusion”when applied ultrasonic field are consid-ered. Dependence of the crystal optical transmission heterogeneity frequency ultrasonic vibrations deter-mined. System Tests showed that the optimal vibration frequency that provided a homogeneous crystals and permitting the maintenance of the solidification front in a predetermined position with an accuracy of ±5% frequency is 4 MHz±5. Comparison of the optimum frequency ultrasonic vibrations to increase uni-formity in the mode of crystals convective transport under the Czochralski method and conditions of diffu-sive transfer method indicates a significant difference between these frequencies, i.e. character determines the transfer conditions of optimization process. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3632

Morphological Features of Gallium Arsenide Crystals Grown at Low-frequency Influences to the Crystallization Front

It was found experimentally that on the initial part of crystal the fluctuations with amplitude more than 1 mm leads to break of the capillary column melt and close of growth. The physical significance of this functional relationship for this probably lies in the different orientation of surface tension forces. Regar d-less of the direction of stretching and an amplitude -frequency characteristics of development process of the power of the octahedral facets increased with increasing growth rate. Accidents on existing ideas are the result of periodic growth, due, for example, the rotation of the crystal in an asymmetric thermal field. When carrying out the method of crystal growth with perturbations at the interface it to a solid phase, the lateral surface is also composed of corrugations distinguishable to the naked eye.In general, the study of structural defects in the crystals obtained in exacting heat conditions, showed that in this case, low-frequency disturbance of the melt at the interface reduces the average density of dislocations due to the periodic melting of crystallization and partially “heal" the defective portions of the crystals. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3633

Gallium Arsenide Czokhralski Crystal Growth with High Oscillatory Influences

The influence of ultrasound introduced into the melt during the growth of single crystals of gallium ar-senide. Ultrasonic vibrations had a frequency of 820 kHz and amplitude of 0.1-0.2 micrometer. Found an increase in the homogeneity of impurity distribution of the bands growth without change of the dislocation structure of single crystals. In the simulation result of the ultrasonic wave interaction with the melt in the crucible on the basis of the theory of formation of phases is established that nucleation rate associated with the frequency and amplitude of the ultrasonic vibration acting on the melt. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3632

The Synthesis of Metalcarbon Nanocomposite Ni / C on the Basis of Polyacrylonitrile

Metalcarbon nanocomposites based on polyacrylonitrile and nickel chloride are synthesized under the influence of infrared heat. The resulting materials represent a system of carbon matrix formed during the carbonization of PAN, and distributed in it nickel nanoparticles. The average size of the nanoparticles in the nanocomposite was 15-25 nm. It was found that the distribution of nickel nanoparticles sizes is determined by temperature synthesis nanocomposite. Thus with increasing temperature, the predominant average particle size of the metal increases, and the distribution is spread and shifted toward larger sizes. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3360

Obtaining Hexagonal Ferrites for Substrates Microstrip Microwave Devices of mm-Range of LTCC-technology

In the work by the method low temperature co-fired ceramics (LTCC) obtained samples of isotropic and anisotropic polycrystalline hexaferrite BaFe12O19 and SrFe12O19. Using in the LTCC-technology the pressing operation for samples (tablets) in a magnetic field produces anisotropic hexaferrites, pressing without a magnetic field - isotropic hexaferrites. Application in the LTCC-technology molding process tape produces exclusively isotropic samples

The Structure and Content Peculiarities of Carbon Material Obtained under the Polyacrylonitrile Infra-red Heating

It is first determined by the semiempirical quantum chemical model MNDO for a carbon material (CM) structure based on polyacrylonitrile (PAN) heat-treated that the increase of a content N from 14 to 18 atoms in CM monolayers C46N14H10, C44N16H12, and C42N18H14 and a content H from 12 to 22 atoms in CM monolayers C44N16H12 and C44N16H22 leads to the decrease of the binding energy (EB) from 7.40; 7.12 to 6.88 and 6.25 eV, respectively; and to the increase of the differences between the maximum and minimum bond lengths (∆l), between the maximum and minimum valence angles (∆Θ), and between the maximum and minimum local charges (∆q) from 0.176 Å; 12.0°, and 0.487 to 0.238 Å; 20.8°, and 0.613, respectively, and promotes the CM structure curvature. Quantum chemical simulation results are confirmed by the element analysis of CM samples and a nanocomposite FeNi3 / C. As the IR heating temperature is increased from 30 to 500 °С, concenrations N (СN) and H (СH) in the CM and nanocomposite FeNi3 / C are decreased from 27 to 18 and 10 wt % and from 6 to 1 and 0.5 wt %, respectively. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3364

LTCC-technology for Producing Hexaferrites

In the review examined the possibility of using LTCC-technology for obtaining hexaferrites as reaction additives glasses Bi2O3-B2O3-SiO2-ZnO (BBSZ) and BaCu (B2O5) (BCB) to reduce the sintering temperature. It is shown that compatibility between hexaferrites with the addition BBSZ, BCB and silver paste, which is a key requirement in the manufacturing process LTCC-components. Considered the possibility of co-sintering of ferrites and dielectric tape composites. It was established that for the realization of defectfree LTCC-composite need to control the shrinkage of the two tapes. In this connection becomes an important concept of zero shrinkage and limiting sintering

Influence of Magnetic Pulseprocessing on Oxide Materials Physics and Mechanical Properties

Internal stresses, specific single-crystal blocks, stoichiometric impurity of oxides composition and other factors lead to low strength properties of ferromagnetic iron oxides. Weakening of such defects and increa s-ing iron oxides microhardness, their fracture and mechanic strength are possible by using magnetic pulse processing. The results of experimental studies of the magnetic pulse field effecting on the iron oxides strength properties are shown. Mössbauer spectroscopy, porosimetry, X-ray structure analysis are used to find the mechanisms of this effect. The strength properties change is the result of set of microscopic and quantum effects superposition. It provides easy defects restructuring of solids: vacancies, dislocations, voids. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3636