Electronic structure,optical dielectric constant and born effective charge of EuAlO3

EuAlO₃ (EAO) is synthesized by the sol–gel process. The Rietveld refinement of the X-ray diffraction data shows that the material has orthorhombic structure with Pbnm space group. The density functional theory calculations are initiated with the experimental lattice parameters. The full potential linearized augmented plane wave method and projector augmented wave method are used to investigate the ground state properties of EAO. An indirect band gap of 1.8 eV is observed with the valence band maximum at the Γ point and the conduction band minimum at the R point. The X-ray photoemission spectroscopy (XPS) spectra of EAO are obtained in the energy window of 0–1000 eV. Using the electronic density of states, the valence band (VB) spectrum of EAO is generated and compared with the observed VB-XPS spectrum. The optical dielectric constant and the refractive index of the material are calculated for the photon energy radiation. The optical properties show a considerable anisotropy in the material. The Born effective charge of various elements and the dielectric tensor of EAO have been calculated.     

Effect of size on dielectric constant for low dimension materials

Based on the consideration on size-dependent root of mean-square displacement of vibration of atoms (rms) σ(D), where D denotes the diameter of nanoparticles and nanowires or the thickness of thin films, size-dependent dielectric constants of low-dimensional materials are modeled without any adjustable parameter. The model predicts a decrease or an increase in dielectric constants with drop of D. The predicted results correspond to experimental and other theoretical results for particles and thin films of Si, CdSe, GaAs, H₂O and thiol.     

The effective dielectric constant of a dispersion of clustering spheres

If one measures the dielectric constant of a water in oil microemulsion the large increase of this dielectric constant both as function of the temperature as well as a function of the volume fraction of water suggests that the water droplets will bind together in clusters. In order to analyse this suggestion in more detail we derive a systematic expansion of the Clausius-Mossotti function in terms of integrals over products of excess cluster polarizabilities and correlation functions. It is found that the excess polarizability of a cluster of spherical droplets is zero except when the spheres almost touch each other. Crucial for this property is the fact that the water spheres are conducting or if they are not conducting have a dielectric constant much larger than the dielectric constant of oil. The large increase of the dielectric constant is a consequence of the increase of the number of bound clusters. An explicit formula is given for the resulting temperature and volume fraction dependence of the dielectric constant.Dedicated to Professor Harry Thomas on the occasion of his 60th birthday     

Analytic properties of the effective dielectric constant of a two-dimensional Rayleigh model

Analytic properties of the dimensionless static effective dielectric constant f(p, h) of a two-dimensional Rayleigh model (p is the concentration and h is the ratio of the dielectric constants of components) are considered as a function of the complex variable h. It is shown that the only singularities of the function f(p, h) are first-order poles for real h = h _n < 0 (n = 1, 2, ...) with the condensation point h = ?1, which form an infinite discrete (countable) set. The positions of the first ten poles of the function f(p, h) and the residues at these points are calculated and represented graphically versus the concentration. Based on the results obtained, a pole-type approximate formula is proposed that describes the behavior of the function f(p, h) over a wide range of p and complex h.     

Temperature dependence of the first constant for the crystallographic magnetic anisotropy for polycrystalline lithium-aluminum ferrites

Measurements by approach to saturation are reported for specimens of composition witha = 0; 0. 2; 0. 4; 0. 5; 0. 6, over the range 170 ° to 530 ° K. Modulated fields are used to examine the approach to saturation.     

Multipole contributions to the effective dielectric constant of suspensions of spheres

We study multipole contributions to the effective dielectric constant of dilute suspensions of uniform spheres. It is shown that for frequencies near the plasma resoance multipole contributions are negligible in comparison with the dipole contributions. Outside resoance multipolar corrections to the Clausius-Mossotti formula are of the same order of magnitude as the dipolar ones. We argue that in resonance the dipole approximation should be valid also for more complicated sphere models.     

介电系数对等离子体光子晶体色散的影响

应用多光子非线性Compton散射模型,研究了Compton散射下介电系数对等离子体光子晶体色散的影响,考虑Compton散射对介电系数的影响,给出了一维等离子体光子晶体色散关系式,并进行了数值模拟。结果表明:与散射前相比,当介电系数ε=1时,不出现禁带;当ε<3时,随着ε的增大,一级禁带宽先缓慢增大,再到最大值,后缓慢减小,二级禁带宽先缓慢增大后趋于饱和值0.69,较散射前减小了0.03,两禁带ε临界值为5.4,较散射前减小了0.6;当ε<5.4时,一级禁带宽明显大于二级,较散射前减小了0.04;当ε>5.4时,二级禁带宽大于一级,二者差值比散射前明显减小;截止频率和二级禁带边缘频率均向低频方向较快移动,且二级禁带边缘频率变化幅度明显大于截止频率。     

纳电子器件中的超低介电常数材料与多孔SiCOH薄膜研究

65 nm以下线宽的纳电子器件,要求采用介电常数k小于2的超低介电常数材料作为层间和线间绝缘介质,等离子体增强的化学气相沉积技术制备的硅基纳米多孔薄膜,提供了实现k<2的可能性,多孔SiCOH薄膜成为最具希望的候选材料,但是,纳米孔的引入带来了材料其他性能恶化、集成工艺困难、薄膜微结构分析等许多新问题.文章介绍了多孔SiCOH（超）低k薄膜研究的主要进展及面临的挑战.     

纳电子器件中的超低介电常数材料与多孔SiCOH薄膜研究

65nm以下线宽的纳电子器件，要求采用介电常数k小于2的超低介电常数材料作为层间和线间绝缘介质，等离子体增强的化学气相沉积技术制备的硅基纳米多孔薄膜，提供了实现k〈2的可能性，多孔SiCOH薄膜成为最具希望的候选材料，但是，纳米孔的引入带来了材料其他性能恶化、集成工艺困难、薄膜微结构分析等许多新问题．文章介绍了多孔SiCOH（超）低k薄膜研究的主要进展及面临的挑战．     

A comparative study of the effective dielectric constant of a medium containing randomly distributed dielectric spheres embedded in a homogeneous background medium

The effective dielectric constant ∈_eff of a medium containing randomly distributed dielectric particles has been analysed by conventional methods: Foldy's approximation, the quasi-crystalline approximation (QCA) and the QCA with coherent potential. These conventional methods, however, have been indicated to become invalid for particles with a high dielectric constant; we have thus presented a new method that is valid for them. This paper compares ∈_eff of our method with those of the conventional methods by changing the volume fraction and the dielectric constant of spheres. As a result, our method is shown to be more powerful for the analysis of ∈_eff than the conventional methods.     

Effective dielectric constant of two-dimensional photonic crystals in optical bands

By using the Fourier expansion method, we have developed an approach to calculate the effective dielectric index of a two-dimensional photonic crystal. The approach is very general: it can take into account various Bravais lattice structure as well as arbitrary spatial variation of the dielectric index. It has been found that near a nondegenerate frequency ω_n(Γ) at Γ point, the transverse magnetic (TM) mode is ordinary, as it is independent of the propagation direction, whereas in general the transverse electric (TE) mode depends on the propagation direction, it is extraordinary. Therefore, a two-dimensional photonic crystal can always be described by an effective dielectric index for TM mode near the nondegenerate frequency ω_n(Γ). However, the TE mode is much more complicated unless the lattice structure is highly symmetric. Moreover, a two-dimensional square photonic crystal has been identified as an effective birefringent crystal having two negative refractive indexes from the perspective of Snell's law.     

A comparative study of the effective dielectric constant of a medium containing randomly distributed dielectric spheres embedded in a homogeneous background medium

Abstract

The effective dielectric constant ∈_eff of a medium containing randomly distributed dielectric particles has been analysed by conventional methods: Foldy's approximation, the quasi-crystalline approximation (QCA) and the QCA with coherent potential. These conventional methods, however, have been indicated to become invalid for particles with a high dielectric constant; we have thus presented a new method that is valid for them. This paper compares ∈_eff of our method with those of the conventional methods by changing the volume fraction and the dielectric constant of spheres. As a result, our method is shown to be more powerful for the analysis of ∈_eff than the conventional methods.     

Variation of optical dielectric constant with carrier concentration: PbSnTe

Free carrier contribution to the optical dielectric constant of PbSnTe has been calculated. Our results suggest that the increase of optical dielectric constant with increase in carrier concentration may result on account of the two carrier effects contributing to the optical dispersion at wavelengths shorter than that of the fundamental absorption edge.     

Multipolar corrections to the Clausius-Mossotti formula for the effective dielectric constant of a polydisperse suspension of spheres

We study multipolar corrections to the Clausius-Mossotti formula for the effective dielectric constant of a polydisperse suspension of spheres with identical uniform dielectric constant embedded in a uniform background. The first few moments of the spectral density occurring in the Bergman representation are evaluated exactly to second order in the volume fraction. We present numerical results for a log-normal distribution of sphere radii.     

Surface optical sensitization of a thin polycrystalline silver iodide film by brilliant green molecules

The effect of the surface optical sensitization (SOS) of silver iodide in a multilayer structure by trace amounts of gaseous molecules of brilliant green dye is demonstrated. Using the surface plasmon resonance excitation, it is shown that the SOS causes changes in the surface layer parameters and can be used to develop highly sensitive and selective gas sensors.     

Evolution of the optical reflectivity of a monolayer of nanoparticles during its growth on a dielectric thin film

The reflectivity variations of a dielectric thin film during the deposition of a disordered monolayer of metallic nanoparticles are studied. We present experimental results and provide theoretical physical insight into the behavior of the reflectivity signal and its dependence on the dielectric thin-film thickness and structural features of the monolayer of nanoparticles. A closed-form expression is used to describe the reflectivity of a disordered monolayer of particles on a flat substrate within the frame of a coherent-scattering model approach. It is shown that the model reproduces qualitatively the behavior of the reflectivity signal during the experiment. Finally we study the optical response in the limit of small particles for low surface coverage fractions of the monolayer to evidence the main parameters that dictate the evolution of the reflectivity signal during the growth of a monolayer of nanoparticles.