Synchrotron reflectivity spectra and the optical properties of CuGaS2 crystal

For a CuGaS₂ crystal, the polarized spectra of complete sets of optical functions in the energy range of 0 to 24 eV are obtained for the first time. The calculations are performed using synchrotron reflectivity spectra for E ∥ c and E ⊥ c polarizations in the energy ranges of 0 to 24 eV and of 1 to 5 eV by means of computer programs using the Kramers-Kronig relations. The main features of the spectra of permittivity, characteristic electron loss, and other optical functions are determined. The band maximum energies for the volume and surface plasmons are obtained, and their independence from the type of polarization is found.     

Synthesis,Characterization, and X-Band Permittivity Studies of Polypyrrole–Zirconium Composite

The zirconium dioxide-doped polypyrrole composites with different weight percentage were prepared by in situ polymerization methods. The prepared composites were subjected for characterization with different tools like Fourier transform infrared spectroscopy and scanning electron microscopy. The Fourier transform infrared spectroscopy spectra indicate a characteristic peaks which confirms the formation of composites. Scanning electron microscopy image indicates that the metal oxides are agglomerated with polypyrrole due to that the size of the composite particles increases to 7 µm. The real part of permittivity (?′) at X-band measurements of all samples first decrease and then increase in the higher frequency range. Meanwhile, the values of ?″ for polypyrrole–zirconia composites changes spontaneously due to the scattering of free charges explained by Kramers–Kronig relations. The reflection loss graph shows that the maximum reflection loss (RL) reaches up to ?54.6 dB at 10.8 GHz and the effective absorption bandwidth (RL ≤ ?10 dB) is 6.7 GHz.     

High frequency permittivity dispersion of Fe-based nanocrystallined ferromagnetic flakes

High frequency permittivity of Fe-based nanocrystalline flakes (Fe-Cu-Nb-Si-B) being milled for different hours have been studied. An inverse dependence of peak frequency on the static dielectric constant in dielectric loss spectra is found. The total dielectric loss also increases with milling time. The Havriliak-Negami model is used to study the permittivity dispersion behaviors. It reveals that both the symmetric and asymmetric broadening factors play roles in the deviation of the measured permittivity spectra from the Debye-type theoretical dispersion. The fundamental physics for the dispersion of permittivity is “Maxwell-Wagner-Sillars” interfacial polarization, which arises from the difference in the conductivity of two phases existing in the nanostructures of flakes.     

Characteristic losses of electrons and the electron structure of thallium chloride

The complete set of fundamental optical functions of a thallium chloride crystal is calculated on the basis of the familiar experimental spectrum of volume characteristic losses of electrons using the Kramers-Kronig relations in a range of 0–25 eV. The loss and permittivity spectra are decomposed into elementary components and their main parameters are determined. Basic features of integrated and decomposed spectra are established.     

On the spectrum of large-scale inhomogeneities of the upper ionosphere

The possibility of measuring the large-scale turbulence structure of the upper ionosphere by vertical and oblique short-wave (SW) radio-sounding techniques is considered. General expressions have been derived for the phase fluctuation spectrum of a short-wave signal reflected at the ionospheric layer with an arbitrary regular permittivity profile and given spectrum of inhomogeneities. We have analyzed a number of particular cases which are most typical of phase measurements in the vertical and oblique SW radio-sounding of the randomly inhomogeneous ionosphere. It is shown that when these methods are used the phase fluctuation spectra of reflected signals may critically depend on the form of the ionospheric electron density profiles. The correct interpretation of the measurement data requires use of stations of synchronous vertical and oblique sounding to obtain proper ionograms and calculate the current spectra of a regular permittivity distribution of the ionosphere. Specific difficulties in interpreting the phase measurements of ionospheric inhomogeneity spectra by vertical and oblique radio-sounding methods are mentioned.Radiophysical Research Institute, Nizhny Novgorod. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 38, No. 7, pp. 653–659, July, 1995.     

Influence of rare-earth ions on the dielectric response in stillwellite glasses

Experimental spectra of the dielectric response function of glasses with the composition LnBGeO₅ (Ln = La, Pr, Tb, Er, Sm) in the terahertz and infrared ranges are compared. Absorption bands are identified, and their contributions to permittivity are established. The contours of the boson peak and the dependence of the dielectric loss on the type of rare-earth ion are determined.     

Dependence of microwave absorption properties on ferrite volume fraction in MnZn ferrite/rubber radar absorbing materials

We report the analysis of measurements of the complex magnetic permeability (μ_r) and dielectric permittivity (ε_r) spectra of a rubber radar absorbing material (RAM) with various MnZn ferrite volume fractions. The transmission/reflection measurements were carried out in a vector network analyzer. Optimum conditions for the maximum microwave absorption were determined by substituting the complex permeability and permittivity in the impedance matching equation. Both the MnZn ferrite content and the RAM thickness effects on the microwave absorption properties, in the frequency range of 2-18 GHz, were evaluated. The results show that the complex permeability and permittivity spectra of the RAM increase directly with the ferrite volume fraction. Reflection loss calculations by the impedance matching degree (reflection coefficient) show the dependence of this parameter on both thickness and composition of RAM.     

Electronic structure of C60 fullerite

The complete systems of fundamental optical functions of single crystals and polycrystalline films of fullerite (C₆₀) are calculated on the basis of known reflection spectra and the imaginary and real parts of the permittivity. The integrated permittivity spectra are decomposed into elementary components. The three basic parameters of each component (the energy of the maximum, the half-width, and the oscillator strength) are determined. The nature of these components of the permittivity is discussed on the basis of existing theoretical calculations of fullerite bands. Fiz. Tverd. Tela (St. Petersburg) 41, 1124–1125 (June 1999)     

Electromagnetic properties of random material

Abstract

This work addresses the relationship between grain properties and the permeability and permittivity spectra of non-crystalline materials or aerosols.

The scattered multipolar fields about a single sphere are related to the polarizability of a random collection of such spheres. Using the Clausius–Mossotti relation the effective permeability and permittivity spectra of an amorphous material is determined for arbitrary permittivity and permeability of the individual spheres, packing density, and sphere size. Although the author considers the spectra over a range where the product of the external wavevector and sphere radius is kept small, typically less than one-tenth, the product of the internal wavevector and sphere radius is unconstrained and seen to have a large effect on predicted spectra.

The result is a variety of possible spectral types which include resonances, relaxations and certain complex. conglomerate spectra that have been measured and far which no direct explanation is otherwise available.     

Atomic and electronic structures of lutetium oxide Lu2O3

The chemical composition, electronic structure, structure, and physical properties a lutetium oxide Lu₂O₃ film are studied by X-ray photoelectron spectroscopy, ellipsometry, and X-ray absorption spectroscopy. The short-range order in Lu₂O₃ is found to correspond to its cubic modification. The binding energies of the 1s and 2p levels of oxygen and the 4d _5/2 and 4f _7/2 levels of lutetium are 529.2, 5.0 and 7.4, 195.9 eV, respectively. The energy gap determined from the electron energy loss spectrum of the film is 5.9 eV. The electron energy loss spectra have two peaks at 17.4 and 22.0 eV, which can be attributed to the excitation of bulk plasma oscillations. The dispersion of the refractive index is measured by spectral ellipsometry. The refractive index is shown to increase from 1.82 at 1.5 eV to 2.18 at 5.0 eV, and the high-frequency permittivity of Lu₂O₃ is 3.31.     

Comparative analysis of characteristic electron energy loss spectra and inelastic scattering cross-section spectra of Fe

The inelastic electron scattering cross section spectra of Fe have been calculated based on experimental spectra of characteristic reflection electron energy loss as dependences of the product of the inelastic mean free path by the differential inelastic electron scattering cross section on the electron energy loss. It has been shown that the inelastic electron scattering cross-section spectra have certain advantages over the electron energy loss spectra in the analysis of the interaction of electrons with substance. The peaks of energy loss in the spectra of characteristic electron energy loss and inelastic electron scattering cross sections have been determined from the integral and differential spectra. It has been shown that the energy of the bulk plasmon is practically independent of the energy of primary electrons in the characteristic electron energy loss spectra and monotonically increases with increasing energy of primary electrons in the inelastic electron scattering cross-section spectra. The variation in the maximum energy of the inelastic electron scattering cross-section spectra is caused by the redistribution of intensities over the peaks of losses due to various excitations. The inelastic electron scattering cross-section spectra have been analyzed using the decomposition of the spectra into peaks of the energy loss. This method has been used for the quantitative estimation of the contributions from different energy loss processes to the inelastic electron scattering cross-section spectra of Fe and for the determination of the nature of the energy loss peaks.     

Measurements of electron energy losses and VUV-reflectivity of anthracene single crystals

Anisotropic behaviour of the electron energy loss spectra is discussed in terms of the oriented gas model. These measurements are compared with electron energy loss spectra in the vapour phase and normal incidence VUV-reflectivity from the (ab) plane for 2 directions of polarization. The VUV measurements were made at DESY using synchrotron radiation.     

Generation and amplification of terahertz electromagnetic waves in a plasma waveguide with a dielectric rod and an annular degenerate plasma

The theoretical investigation of terahertz waves and their excitation by electron beam injection in a cylindrical metallic plasma waveguide is investigated. This metallic waveguide includes a cold collisionless unmagnetized annular degenerate plasma and a dielectric rod. The dispersion characteristics of these waves, the frequency spectra of fast and slow E-modes waves (transverse magnetic field), are studied. Also, the effects of the dielectric permittivity, the radius of the dielectric rod and the radius of the plasma on the frequency spectra and the time growth rate of waves are simulated. In addition, the electric field profiles in this waveguide are plotted.     

A study of the orientation dependence of the electron energy loss spectra for single crystal films of copper and silver

Apart from two peaks caused by bulk and surface plasmons, four or five peaks (depending on the crystal type) of electron energy losses due to inter- and intraband electron transitions are observed in the investigation of the electron energy loss spectra for metals (Cu, Ag). A comparative analysis of the spectra for Cu or Ag films reveals a shift of bulk plasmon loss peaks to higher values for polycrystals, as in the case of transition metals and semiconductors. In a study concerning the orientation dependence of the energy loss spectra (ELS) for electrons scattered from the copper and silver surface, the anisotropy of the bulk plasmon peak is found when the incident beam’s polar angle or the sample’s azimuthal angle are altered. The anisotropy of the primary electron energy loss for plasmon excitation is also observed, depending on the sample orientation relative to the direction incident electrons. The energy losses are found to increase with an increasing atomic packing density of planes and crystal transparency relative to the incident beam.     

Development of polyurethane multiwall carbon nanotubes (MWCNTs) novel polymeric nanodielectric material

Polyurethane/multi-walled carbon nanotube nanodielectric thin films of 25 μm thick were prepared by solution grown method. The microstructure of the nanodielectric was examined by scanning electron microscopy. The MWCNTs are observed to be dispersed in PU matrix well apart from a few of clusters. The MWCNTs/polymer nanodielectrics characterized with decrease in energy band gap and crystallinity. The analysis of dielectric properties of the composite samples of different weight ratio was studied by measuring the permittivity and tangential loss at room temperature. The frequency dependent permittivity obeys the percolation theory. Further, it has been observed that the dielectric properties of PU and PU nanodielectric are unaffected by UV-irradiation. XRD characteristics confirm the formation of PU/MWCNTs nanodielectrics.     

Effect of optical pump on the dielectric properties of SrTiO_3 in terahertz range

Tuning the dielectric permittivity spectra of strontium titanate （SrTiO3） single crystals in an extemal optical field is investigated at room temperature by means of terahertz time-domain spectroscopy. The application of the optical field leads to an appreciable tuning of the permittivity, reaching up to 2.8%, with the dielectric loss changing about 3%. The observed behavior is interpreted in terms of soft-mode hardening due to the anharmonic character of its potential. We also find that the change of the refractive index responds linearly to the applied light power. These findings are attributed to a linear electro-optical effect of the internal space charge field of the crystal.     

Choice of a dielectric relaxation model of a substance by hypothesis testing

A procedure for processing of measured complex permittivity spectra of a substance for the main Debye, Cole-Cole, Cole-Davidson, and Havriliak-Negami relaxation models is described. The most probable model is chosen by hypothesis testing. The results of processing of experimental permittivity spectra for methyl alcohol and water mixtures are presented. Tomsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 15–22, November, 1999.     

Dielectric properties of CdS nanoparticles synthesized by soft chemical route

CdS nanoparticles have been synthesized by a chemical reaction route using thiophenol as a capping agent. The frequency-dependent dielectric dispersion of cadmium sulphide (CdS) is investigated in the temperature range of 303-413 K and in a frequency range of 50 Hz-1 MHz by impedance spectroscopy. An analysis of the complex permittivity (ɛ′ and ɛ″) and loss tangent (tan δ) with frequency is performed by assuming a distribution of relaxation times. The scaling behaviour of dielectric loss spectra suggests that the relaxation describes the same mechanism at various temperatures. The frequency-dependent electrical data are analysed in the framework of conductivity and modulus formalisms. The frequency-dependent conductivity spectra obey the power law.     

Theoretical Study on Inner Shell Electron Impact Excitation of Lithium

Cross sections for electron impact excitation of lithium from the ground state 1s^22s to the excited states 1s2s^2, 1s2p^2, 1s2snp （n = 2-5）, 1s2sns （n = 3 5）, 1s2pns （n = 3-5）, and 1s2pnp （n = 3-5） are calculated by using a full relativistic distorted wave method. The latest experimental electron energy loss spectra for inner-shell electron excitations of lithium at a given incident electron energy of 2500 eV [Chin. Phys. Lett. 25 （2008）3649] have been reproduced by the present theoretical investigation excellently. At the same time, the structures of electron energy loss spectra of lithium at low incident electron energy are also predicted theoretically, it is found that the electron energy loss spectra in the energy region of 55-57eV show two-peak structures.     

Nature of electronic states and optical functions of sodium oxyanionic compounds

The band structure, the density of states, the partial electron densities, and optical functions (such as permittivity, refraction index, reflection and absorption coefficients) of sodium nitrite, nitrate, carbonate, chlorate, sulfite, perchlorate, and sulfate are calculated in a local approximation of the density-functional theory using the Troullier-Martins pseudopotentials in the basis of numerical pseudoatomic orbitals. The nature of the upper valence bands and the lower empty bands is established. It is shown that the specific features of the optical functions at energies of up to 8 eV and at E> 8 eV are due to the excitation of electrons into a localized anionic conduction band and into the bands of anion-cation states, respectively. The results are compared to experimental photoelectron spectra and reflection and absorption spectra.