Rectification effect in a quantum contact

The rectification of current has been observed in a quasi-one-dimensional ballistic quantum channel. The effect is explained by the asymmetry of the potential profile in the channel. The dependence of the rectified current on the height of the potential barrier in the channel exhibits sharp maxima, which are associated with conductance quantization steps. A model of the rectification is proposed.     

Rectification effect in asymmetric Kerr nonlinear medium

Based on the transfer matrix method, the recursion of an electromagnetic wave propagating in an asymmetric Kerr nonlinear medium is analytically formulated, from which the rectification effect is clearly presented. The effects on the rectification regioh of the linear part and nonlinear coefficient of permittivity are both studied, and the energy densities before and after rectification are discussed. We use a rectifying factor to describe the intensity of the rectification effect. The result shows that every transmission peak is divided into two parts when the symmetry is broken, and nonlinear asymmetry has a more significant effect on the rectification effect than the linear asymmetry. The rectification intensity and area will be enlarged when the asymmetry factor is increased in a certain range.     

Magnetorefractive effect in magnetic nanocomposites

The magnetorefractive effect in ferromagnetic metal-insulator granular nanostructures (CoFeZr)-SiO_n, Co-Al-O, FeSiO_n, and (CoFe)-(Mg-F) is investigated in the infrared spectral region in a wavelength range from 5 to 20 μm. The magnitude of the effect varies from 0.1 to 1.5% for different nanocomposites and strongly depends on the frequency of light and magnetoresistance. It is shown that the reflection coefficient changes in a magnetic field not only due to the magnetorefractive effect, but also due to the even magnetooptical effect. Simple relations describing this effect are given for the case when the reflection from the substrate is insignificant and in the case of a three-layer (insulator-film-substrate) system. The expression for the frequency dependence of the magnetorefractive effect in nanocomposites is derived and its features in the case of high-frequency spin-dependent tunneling are analyzed.     

Synthesis and characterisation: Zinc oxide–sulfide nanocomposites

A novel synthesis method is presented for the preparation of nanosized-semiconductor zinc oxide–sulphide (ZnO/ZnS) core–shell nanocomposites, both formed sequentially from a single-source solid precursor. ZnO nanocrystals were synthesized by a simple co-precipitation method and ZnO/ZnS core–shell nanocomposites were successfully fabricated by sulfidation of ZnO nanocrystals via a facile chemical synthesis at room temperature. The as-obtained samples were characterized by X-ray diffraction and transmission electron microscopy. The results showed that the pure ZnO nanocrystals were hexagonal wurtzite crystal structures and the ZnS nanoparticles were sphalerite structure with the size of about 10 nm grown on the surface of the ZnO nanocrystals. Optical properties measured reveal that ZnO/ZnS core–shell nanocomposites have integrated the photoluminescent effect of ZnO and ZnS. Based on the results of the experiments, a possible formation mechanism of ZnO/ZnS core–shell nanocomposites was also suggested. This treatment is suggested to improve various properties of optoelectronically valuable ZnO/ZnS nanocomposites. These nanosized semiconductor nanocomposites can form a new class of luminescent materials for various applications.     

Superbending effect in two-dimensional graded photonic crystals

We study the superbending effect in a two-dimensional graded photonic crystal (GPC) for both TE and TM modes. We show that the lateral beam shift is extremely sensitive to the wavelength for the TM mode but not TE mode, indicating the potential in designing some special superbending devices, for example, TE/TM splitter and polarization-indifference waveguide at prescribed wavelengths.     

Optical properties of the hybrid nanocomposites consisting of poly-n-phenylvinylene and cadmium sulfide

Thin-film hybrid nanocomposites based on poly-n-phenylvinylene with various contents of the CdS semiconductor nanoparticles are obtained using the pyrolytic polymerization of dichloro-n-xylene from the gas phase and the simultaneous sedimentation of the CdS vapor with the subsequent thermal processing of the precursor. The structure of the nanocomposite is studied, and the optical properties of the materials are analyzed. It is demonstrated that a variation in the concentration of the inorganic component in the polymer matrix leads to a variation in the maximum fluorescence wavelength and optical band gap. The material parameters (degree of conjugation of poly-n-phenylvinylene, band gap, Huang-Rhys factor, Stokes shift, and vibronic energy of molecules) are determined.     

Heating-induced endothermal effect in semiconducting samarium sulfide

The effect of heat absorption is revealed in the temperature range where the thermovoltaic effect occurs in single-crystal samarium sulfide (SmS). It is shown that the heat absorption is caused by the collective injection of electrons from donor levels into the conduction band.     

Production and investigation of layered zinc sulfide(selenide)/insulator nanocomposites

Layered ZnS/SiO₂, ZnS/Al₂O₃, and ZnSe/SiO₂ nanocomposites have been studied. It has been shown that the use of the Maxwell–Garnett and Bruggeman models, as well as the Luyengi formula, in the low dispersion region makes it possible to predict the production of films with a given effective refractive index. Calculated values of the refractive index correlate well with experimental data. The maximal discrepancy between the theoretical and experimental values of the refractive index and the maximal value of the depolarization factor depend on the structure and microstrains.     

Rectification effect for spin- and charge-currents in a shuttled molecule transistor

We have investigated the spin-dependent electronic transports through a shuttled molecule, a molecule self-excitedly oscillating due to suffering an external electric field. When the shuttled molecule is coupled asymmetrically to a ferromagnetic and a normal metal leads, a pronounced dual rectification effect is predicted for both spin- and charge-currents in the Coulomb blockade regime. As compared to the conventional rectifier based on a static quantum dot, the proposed rectifier based on a movable individual molecule has higher rectification efficiency.     

Cochlea's graded curvature effect on low frequency waves

In the ear, sound waves are processed by a membrane of graded mechanical properties that resides in the fluid-filled spiral cochlea. The role of stiffness grading as a Fourier analyzer is well known, but the role of the curvature has remained elusive. Here, we report that increasing curvature redistributes wave energy density towards the cochlea's outer wall, affecting the shape of waves propagating on the membrane, particularly in the region where low frequency sounds are processed.     

The effect of intragranular microstress in A1203-SiC nanocomposites

A theoretical model is established to investigate the intragranular particle residual stress in A1203-SiC nanocom-posites. Using this model, we calculate the average compressive stress on the A1203 grain boundary （GB） and the average tensile stress within A1203 grains caused by SiC nanoparticles. The normal compressive stress strengthens the GB, and the average tensile stress weakens the grains. The model gives a reasonable interpretation of the strength changes of A1203-SiC nanocomposites with the number of SiC particles.     

Focusing effect of a graded index photonic crystal lens

We present a new graded-index photonic crystal (GRIN PhC) structure which can be made by laser interference lithography (LIL). It can be applied as miniaturized focusing lens. Numerical simulations are carried out on the structures with different widths, lengths, and modulations. In the qualitative analysis of the focal length, focusing of a GRIN PhC was proved to originate from both the graded sizes of the rods and multimode interference. Multimode interference dominates the focusing effect when a GRIN PhC has a small length or a small difference in the rod sizes. Intensity distributions in different cases were given to support the conclusion.     

双层纳米磁电薄膜模型及分析

以层状磁电复合材料弹性力学模型为基础,建立了自由状态下双层纳米磁电薄膜的弹性力学模型,并以此为基础简单介绍了推导其磁电电压系数表达式的方法.计算了CoFe₂Ｏ₄/Pb（Zr_0．52Ti_0．48）Ｏ₃双层纳米复合薄膜的磁电电压系数理论值,分析结果表明基片对薄膜存在强烈的夹持效应,而且基片对压电与磁致伸缩两相材料间最佳体积比有一定的影响. 关键词： 磁电理论 磁电薄膜 铁电材料 磁致伸缩     

Rectification in Luttinger liquids

We investigate the rectification of an ac bias in Luttinger liquids in the presence of an asymmetric potential (the ratchet effect). We show that a strong repulsive electron interaction enhances the ratchet current in comparison with Fermi-liquid systems, and the dc I-V curve is strongly asymmetric in the low-voltage regime even for a weak asymmetric potential. At higher voltages the ratchet current exhibits an oscillatory voltage dependence.     

Large positive magnetoresistance effect in metal-insulator nanocomposites in weak magnetic fields

Studies of the magnetoresistance of granular Fe/SiO₂ films within the compositional range corresponding to insulators revealed a large positive magnetoresistance. The positive magnetoresistance reaches 10% in magnetic fields ～100 Oe at room temperature and exhibits slow response times (～2 min) to stepped magnetic-field variation. The nature of the effect is apparently associated with the influence of ferromagnetic cluster aggregates of iron nanoparticles on the magnetoresistance.     

High-frequency spin-dependent tunnelling in magnetic nanocomposites: Magnetorefractive effect and magnetoimpedance

Since the dielectric permittivity is linear with frequency-dependent conductivity, high-frequency properties for any kind of magnetic materials with the high magnetoresistance depend on magnetization. It manifests as magnetorefractive effect (MRE) in the infrared region of spectrum and as magnetoimpedance (MI) in the frequency range between radio and microwaves. The main mechanism of both MRE and MI in nanocomposites with tunnel-type magnetoresistance is high-frequency spin-dependent tunnelling. We report on recent results of theoretical and experimental investigations of MRE and MI in nanocomposites Co_51.5Al_19.5O₂₉, Co_50.2Ti_9.1O_40.7, Co_52.3Si_12.2O_35.5 and (Co_0,4Fe_0,6)₄₈(MgF)₅₂. Most of the obtained experimental data for MRE and MI are consistent with the theory based on considering the tunnel junction between adjacent granules in percolation cluster as a capacitor.