Dispersion of surface polaritons in uniaxial CdS

The dispersion of ordinary and extraordinary surface polaritons in uniaxial CdS has been measured using the ATR technique. The results have been compared with theoretical dispersion curves based on a classical oscillator model. The dielectric dispersion has also been generated. Comparison is made between the bulk phonons derived from Raman, infrared and from the surface mode data. Infrared measurements of small crystallites of CdS are in good agreement with the frequencies predicted for surface modes of small isolated spheres.     

Some dynamical properties of a two-dimensional Wigner crystal

Results for the static part of the ground state energy of the square and hexagonal two-dimensional Wigner lattices are given. The hexagonal lattice has the lower energy. Phonon dispersion curves and the vibrational zeropoint energy are calculated for the hexagonal lattice. The dielectric susceptibility tensor of a two-dimensional Wigner crystal χ_αβ(q) has been determined in the long wavelength limit in the presence of a static magnetic field perpendicular to the crystal, and explicit expressions have been obtained for the hexagonal lattice. Applying the analysis developed by Chiu and Quinn, the results for the susceptibility have been used to obtain the dispersion relation for the plasma oscillations in the electron crystal on the assumption that the crystal is embedded in a dielectric medium. The dispersion curves have been calculated for differing magnitudes of the applied magnetic field.     

Surface plasma waves in the noble metals

The dispersoon curves for surface plasma waves (SPW) in Ag have been determined from calculated reflectivity minima as exhibited by attenuated total reflection (ATR spectra) for the prism-metal-air (PMA) configuration and from the direct calculation of the dispersion relation for the same configuration. Comparison is made with published results. The dispersion curves for Au and Cu have been determined for the same configuration from calculated ATR spectra and verified experimentally. Comparison is made with the direct calculation of the dispersion relation. The direct calculation yields two types of modes; namely the surface or Brewster mode and the virtual mode. Both modes are discussed. The marked effect of small electronic damping as exhibited by Ag and moderate electronic damping as exhibited by Au and Cu upon the PMA dispersion curves from ATR spectra is examined. Finally the direct calculation of the dielectric shift (perturbing effect of the prism-metal surface upon the active metal-air surface dispersion curve) is presented for the three metals as a function of film thickness and photon energy.     

Ab initio calculations of the elastic, electronic, optical, and vibrational properties of PdGa compound under pressure

The structural, elastic, electronic, optical, and vibrational properties of cubic PdGa compound are investigated using the norm-conserving pseudopotentials within the local density approximation (LDA) in the framework of the density functional theory. The calculated lattice constant has been compared with the experimental value and has been found to be in good agreement with experimental data. The obtained electronic band structures show that PdGa compound has no band gap. The second-order elastic constants have been calculated, and the other related quantities such as the Young’s modulus, shear modulus, Poisson’s ratio, anisotropy factor, sound velocities, and Debye temperature have also been estimated. Our calculated results of elastic constants show that this compound is mechanically stable. Furthermore, the real and imaginary parts of the dielectric function and the optical constants such as the electron energy-loss function, the optical dielectric constant and the effective number of electrons per unit cell are calculated and presented in the study. The phonon dispersion curves are also derived using the direct method.     

Surface plasma waves in silver and gold

The dispersion curves for surface plasma waves (SPW) in Ag have been determined from calculated reflectivity minima as exhibited by attenuated total reflection (ATR spectra) for the prism-air-metal (PAM) configuration and from the direct calculation of the dispersion relation for the same configuration. The dispersion curves for Au have been determined by measuring the ATR spectra for the prism-dielectric-metal (PDM) configuration, by calculating the ATR spectra from published optical constants and from the direct calculation of the despersion relation for the PDM configuration. We have found two general types of solutions from the direct calculation of the dispersion relation for both configurations. The two solutions are the surface or Brewster modes and the virtual modes. The characteristics of both modes are discussed. The effect of electronic damping upon the dispersion curves for Ag which exhibits low electronic damping and Au which exhibits moderate electronic damping is demonstrated. Finally the perturbing effect of the dielectric (referred herein as dielectric shift) upon the displacement of the dispersion curves to higher wave number for the PAM configuration for Ag and for the PDM configuration for Au is shown.     

The Analysis of the Microstrip Dispersion with Multi-Layers Dielectric

The paper analyses the dispersion of microstrip with multi-layers dielectric substrate in theory mainly. Giving the dispersion equation of the structure. And the dispersion curves of the microstrip with dual-layers dielectric substrate are calculated in 2GHz~6GHz.     

A comparative study of dispersion relation of EM waves in ternary one-dimensional plasma photonic crystals having two different structures

In this paper, a rigorous theoretical analysis has been made to study the dispersion relation of EM waves in periodic ternary one-dimensional photonic crystal having two different structures. In one case we have chosen glass-plasma and ZnS in one unit cell and in other case we have considered glass-plasma and M_gF₂ in one unit cell. Using Kronig-Penney model the dispersion relation for proposed structures has been obtained and numerical results are presented in the form of dispersion curves. The dependence of photonic band gap (PBG) characteristics on plasma frequency, plasma width and the width of dielectric media are discussed in the light of frequency gap and cutoffs of binary one-dimensional plasma photonic crystal. An attempt has been made to show how the PBG characteristic of a particular structure changes when the dielectric materials of its unit cell is changed by the other dielectric material. It is found that the structure having glass-plasma-ZnS in unit cell is more useful for broad band filtering and other plasma functioning devices compared to the structure having glass-plasma-MgF₂ in one unit cell.     

Successive phase transitions in the highly ordered complex perovskite PbLu1/2Nb1/2O3

The structural phase transitions and the electrical behaviour of the complex perovskite PbLu_1/2Nb_1/2O₃ have been investigated using X-ray powder diffraction, dielectric constant measurements, differential scanning calorimetry and measurement of the polarisation as a function of applied electric field. The high-temperature paraelectric phase is highly ordered. A first-order paraelectric-antiferroelectric phase transition occurs at 270°C and an antiferroelectric-ferroelectric phase transition, characterised by dispersion in the curves of dielectric constant as a function of temperature, occurs at ≈ 30°C. The antiferroelectric phase is isostructural with the orthorhombic form of PbYb1/₂Nb1/₂O₃. The low-temperature ferroelectric phase also has an orthorhombic crystal structure.     

Application of three body force shell model to the lattice dynamics of transition metal oxides MnO,CoO and NiO

Lattice dynamics of some transition metal oxides has been studied using the three body force shell model. Reasonably good fits with the experimental phonon dispersion curves have been obtained by choosing values of molecular electronic polarisability substantially lower than those derived from the dielectric constant. This result is similar to those obtained in many other crystals which are not ideally ionic.     

Lattice dynamics of cubic SrZrO3

Using density functional perturbation theory, the optical dielectric constant, Born effective charges and phonon dispersion curves of cubic SrZrO₃ have been calculated. The obtained dispersion curves show a soft phonon branch spreading from R to M points of the cubic Brillouin zone. An analysis based on the symmetry relationships indicates that the experimentally observed low-symmetry phases of SrZrO₃ can be considered as results of the soft mode condensation at R and M points.     

Theoretical study on the band structure and optical properties of 4H-SiC

We have studied the band structure and optical properties of 4H-SiC by using a full potential linearized augmented plane waves (FPLAPW) method. The density of states (DOS) and band structure are presented. The imaginary part of the dielectric function has been obtained directly from the band structure calculation. With band gap correction, the real part of the dielectric function has been derived from the imaginary part by the Kramers－Kronig (KK) dispersion relationship. The values of reflectivity for normal incidence as a function of photon energy have also been calculated. We found the theoretical results are in good agreement with the experimental data.     

Surface plasmons on corrugated metal films

The dispersion relation for a surface plasmon, propagating across a corrugated metal film on a dielectric substrate, is obtained by the method of reduced Rayleigh equations. It is found that the surface plasmon dispersion curve has an infinite number of branches. Numerical solutions of the dispersion relation are obtained for a film, characterized by a free-electron metal dielectric function and a sinusoidal profile function.     

Singularities of the dielectric function of InN in the region of a direct optical transition

The dispersion of the dielectric function of InN with the wurtzite structure in the frequency region near the fundamental energy gap has been analyzed with the inclusion of temperature and carrier density effects. The linearity of the electron spectrum in a wide energy range leads to a logarithmic singularity of the real part of the dielectric function, which is associated with the direct electronic transitions and, correspondingly, to an anomalously large dielectric constant. The imaginary part becomes constant above the absorption threshold. The values calculated without any free parameters are in good agreement with the experimental data and ab initio calculations.     

Propagation of SH-waves in two anisotropic layers bonded to an isotropic half-space under gravity

This study reports a theoretical investigation of the propagation of SH-wave in a piezoelectric layer superimposed on a self-reinforced layer overlying an isotropic gravitational half-space. The expressions of the dispersion relation of SH-wave have been established for electrically open and electrically short conditions in closed form. For the purpose of numerical computation, lithium niobate piezoelectric material has been considered. The dispersion curves have been depicted graphically and the prominent impacts of piezoelectric constant, dielectric constant, reinforced parameter, width ratio, and Biot’s gravity parameter on the phase velocity of SH-wave have been unraveled for both the electrical conditions. As a special case of the problem, it is found that the obtained dispersion relation concurs with classical Love wave equation for both the electrical conditions. Moreover, some important peculiarities have also been traced out through numerical computations for both the electrical cases.     

Ab initio lattice dynamics and piezoelectric properties of MgS and MgSe alkaline earth chalcogenides

We have studied structural, elastic, dielectric, vibrational, and piezoelectric properties of rock-salt and zinc-blende Mg alkaline earth chalcogenides (MgS, and MgSe) by using the plane-wave pseudopotential method within the local density approximation. The calculated lattice constant, bulk modulus, and elastic constants for these compounds are found to be in good agreement with experiment. The density functional perturbation theory has been employed to derive the Born effective charge and high-frequency dielectric constant and to calculate phonon dispersion curves and density of states. The piezoelectric constant has also been determined. The calculated results are compared with theory and experiment when available and showed reasonable agreement. In other cases, our results are predictions. The pressure dependence of the studied quantities has been examined and discussed. The pressure coefficients and mode Grüneisen parameters are determined.     

Phonon dispersion and dielectric behaviour of mixed alkali halide crystal NaCl0.5Br0.5

In the present paper we have calculated the phonon dispersion curves and dielectric constants, their volume derivatives and the Gruneisen parameters of the mixed alkali halide NaCl_0.5Br_0.5, using the extended three body force shell model. The results of dielectric constants, their volume derivatives and Gruneisen parameters are found to agree reasonably well with the experimental values, which establishes the validity of the three body charge transfer parameter. With this concept the phonon dispersion curves are obtained in all the three symmetry directions (q,o,o), (q,q,o) and (q,q,q), which will be of interest for experimental workers, since no experimental values have so far been obtained for phonon frequencies.     

X波段介质和金属膜片混合加载行波加速结构的传播特性计算及模型腔的有关研究

计算了X波段(f=9.37GHz)介质和金属膜片混合加载行波加速结构的TM₀₁模和HEM₁₁模的色散曲线, 结果表明HEM₁₁模的截止频率比TM₀₁模的低, 说明与盘荷波导相比, 该种新加速结构单束团的BBU效应得到改善.实验研究优选得到了适用于该种新加速结构的介质(ε_r=5.812). 采用MAFIA程序优化设计了模型腔, 测试频率与设计的数值吻合得很好.     

THE DIELECTRIC FUNCTION OF AN ELECTRON SYSTEM IN A PERIODIC STRUCTURE: VAA THEORY+

A general expression for the dielectric function of an electron system in a period structure has been derived by using linear response theory with the assumption that the equilibrium electronic density differs slight1y from its average value. Starting from the BBGKY equations,the theory is formulated in the Velocity Average Approximation.Numerical results for the dispersion and damping of plasmons and for the longitudinal dielectric function are given in the case of sinusoidally modulated structures.     

Lattice dynamics of ZnO

Some phonon dispersion curves in ZnO have been determined by inelastic neutron scattering. Shell model calculations with 10 parameters were fitted to the neutron data, to optical frequencies and to dielectric constants. Good agreement was obtained including some elastic constants which were calculated from the model.     

First-principles study of the structural, elastic, electronic, optical, and vibrational properties of intermetallic Pd2Ga

The structural, elastic, electronic, optical, and vibrational properties of the orthorhombic Pd₂Ga compound are investigated using the norm-conserving pseudopotentials within the local density approximation in the frame of density functional theory. The calculated lattice parameters have been compared with the experimental values and found to be in good agreement with these results. The second-order elastic constants and the other relevant quantities, such as the Young's modulus, shear modulus, Poisson's ratio, anisotropy factor, sound velocity, and Debye temperature, have been calculated. It is shown that this compound is mechanically stable after analysing the calculated elastic constants. Furthermore, the real and imaginary parts of the dielectric function and the optical constants, such as the optical dielectric constant and the effective number of electrons per unit cell, are calculated and presented. The phonon dispersion curves are derived using the direct method. The present results demonstrate that this compound is dynamically stable.