Neutron standing waves in layered systems

A theory of propagation of neutron waves in multilayer magnetic and nonmagnetic systems is presented. It is shown how a system forms the wave function of a neutron, how the wave function formed can be controlled, and how this function can be used to investigate materials. The results of experimental investigations of the neutron reflection from multilayer systems with simultaneous measurement of different types of secondary radiation are reported.     

Efficiency of excitation of dimensional resonances of magnetoelastic waves in layered structure

This paper reports the study of elastic and magnetoelastic waves in two-layered structure: magnetic film – non-magnetic substrate, restricted in one dimension. We have investigated behavior of elastic and magnetoelastic standing waves resonant frequencies dependent on the relative thicknesses of magnetic and non-magnetic layers. Magnetic susceptibility of magnetic film placed on non-magnetic substrate and character of its behavior in the vicinity of frequencies of dimensional resonances of magnetoelastic and elastic waves are studied. We have explored susceptibility dependence on the relation between magnetic and non-magnetic layers parameters. By change of the thickness of magnetic layer relative to overall thickness of a sample we can regulate magnetic susceptibility and therefore efficiency of excitation of definite harmonics of standing magnetoelastic and elastic waves. If even number of magnetoelastic half waves falls to magnetic layer corresponding harmonics of magnetoelastic and elastic wave disappears. In particular odd harmonics disappear when magnetic film occupies half space of a sample. Magnetic susceptibilities reveal peculiarities in their behavior dependent on material parameters change.     

Configurations of the zero-birefringence and zero-dichroism lines of electromagnetic waves in weakly anisotropic crystals

Configurations of two types of lines—those of zero birefringence and zero dichroism—drawn by the end of the directional vector of the wave normal over the unit sphere, which correspond to the coincident phase velocities or the absorption coefficients of isonormal electromagentic waves in weakly anisotropic crystals, have been studied analytically. It is shown that under the conditions of weak dielectric anisotropy, even slight changes in anisotropy result in the dramatic deformation of the lines of both types. The corresponding evolution of the configurations with the change of the anisotropy parameters is considered by example of absorptive orthorhombic crystals.     

On existence of one-partial bulk waves in semi-infinite piezoelectric media

The conditions for the existence of one-partial bulk waves satisfying the boundary conditions on a mechanically free surface of a semi-infinite piezoelectric medium have been analyzed. In purely elastic media, similar wave solutions are known to exist along the propagation directions m which form lines on the sphere m ? m = 1, passing through all the available degeneracy points (acoustic axes). It is shown that in a triclinic piezoelectric half-space with a metallized surface, one-partial bulk waves may exist solely along isolated propagation orientations, whereas for a nonmetallized surface, such waves can exist only if an additional condition for the material constants of the medium is fulfilled. It is also shown that the one-partial bulk solution may not exist along an arbitrary acoustic axis in a piezoelectric. These conclusions are valid in the general case of unrestricted anisotropy, i.e., they do not take into account the material symmetry. In addition, the orientations providing the propagation of one-partial bulk waves because of the existing symmetry are specified for piezoelectric media of various symmetry classes.     

Spectrum of natural electromagnetic waves in a periodic ferromagnet-dielectric structure

The specific features of propagation of natural TE waves in a periodic ferromagnet-dielectric structure are investigated in the following geometry: a bias magnetic field is parallel to the ferromagnet/dielectric interface and perpendicular to the wave propagation direction. The transformation matrix for the period of the structure, the dispersion relation, and the energy reflection coefficient are obtained for the case of normal incidence of a wave on a semi-infinite periodic medium by solving the boundary-value problem. It is shown that an external field can be used to control the spectrum and characteristics of reflected waves.     

Energy exchange between electromagnetic waves on the director diffraction grating in planar waveguide with nematic layer

The energy exchange between two coupled TE modes on the diffraction grating of the director in a planar waveguide containing a nematic liquid crystal layer is calculated. The diffraction grating is induced by an external electric field in the nematic layer with periodic anchoring energy at the waveguide surface. The intensity of the signal mode at the output of the nematic layer is calculated as a function of the amplitude and period of the anchoring-energy modulation, the nematic layer sizes, and the electric-field strength. The cases of modes with the same and opposite directions are considered. Analytical expressions for the maximum intensities of the signal mode are derived. In both cases the maximum intensity of the signal mode increases with an increase in the electric-field strength.     

Developments in the bulk growth of Cd1−xZnxTe for substrates

Single crystal of CdTe or dilute alloys of Cd_1−yZn_yTe (y < 0.04) and CdTe_1−zSe_z (z < 0.04) with low defect density, high purity, and large single-crystal area (>30 cm²) are required as substances for high-quality epitaxial Hg_1−xCd_xTe thin films in the infrared (IR) detector industry. Bridgman or gradient freeze is the most common technique used for commercial production of these materials because of its success in producing large-area substrates of good quality and reproducibility. For epitaxial growth of Hg_1−xZn_xTe, which has been of considerable interest in recent years as an IR detector material, the substrate of choice has been Cd_0.80Zn_0.20Te, for lattice matching with long-wavelength Hg_1−xZn_xTe epitaxial layers (x = 0.15). The primary focus of this paper is on CdZnTe, which is currently the preffered subtrate material and most widely used for both HgCdTe and HgZnTe epitaxy. This paper reviews the current status of bulk substrate technology for IR detector applications, highlighting critical issues and essential research areas for further improvement of these materials.     

Bulk polaritons in a biaxial crystal at the interface with a perfect metal

The orientation of the plane where the tangential electric field component becomes zero is indicated for any plane bulk electromagnetic wave propagating in an infinite transparent medium of arbitrary anisotropy. Thus, the existence of this wave (bulk polariton) in this plane (interface with an ideal conductor) is ensured. The characteristics of such polaritons of two independent branches with coinciding wave normals (isonormal polaritons) or Poynting vector directions (isoray polaritons) are compared.     

Modern application packages for rigorous solution of problems of light propagation in anisotropic layered media: II. Optically active crystals

The matrix Δ suggested by Berreman for optically active crystals of various symmetry classes has been calculated with the use of the Mathematica-4.1 package. It is shown that the eigenvalues of this matrix are the refractive indices, whereas its eigenvectors determine the polarization states of eigenwaves propagating in the crystal. The relation between the components of the gyration tensors obtained on the basis of various constitutive equations is established. The essential differences in the optical activity described on the basis of these equations are also discussed.     

Theory and computer simulation of the reflection and refraction of bulk acoustic waves in piezoelectrics under the action of an external electric field

The basic equations describing the conditions for reflection and refraction of bulk acoustic wave at the interface between acentric crystals subjected to the action of a uniform external electric field are reported. Numerical analysis of the effect of this field on the reflection and refraction anisotropy of bulk acoustic waves at the crystal/vacuum and piezoelectric/elastic-isotropic-medium interfaces is performed.     

Specific features of localization of magnetic TM polaritons in the ferroelectric-nongyrotropic-magnet structure

The conditions are determined under which virtual slot magnetic TM polaritons are formed as a result of the quadratic magnetooptic interaction near a ferroelectric layer embedded in an easy-axis antiferromagnet.     

Thermooptical excitation of sound by Bessel light beams in crystalline media with internal stress

The thermooptical excitation of sound by Bessel light beams in crystalline media with internal stress has been studied. The dependence of the thermoelastic coupling coefficient, which is due to the modulated absorption of laser radiation, on the initial strain in a crystalline sample is taken into account. The expression for the photoacoustic signal amplitude is obtained, and it is shown that, in the range of high modulation frequencies of TE modes of Bessel light beams, resonant phenomena occur which can be used to increase the resolution of laser photoacoustic diagnostics of elastically strained crystals.     

Study of the properties of artificial anisotropic structures with high chirality

The chiral properties of an artificial anisotropic structure composed of microhelices are numerically simulated using the example of a sample developed by a team of authors from the Institute of Semiconductor Physics of the Russian Academy of Sciences. It is shown that this artificial structure can exhibit strong chiral properties in the THz range. Analytical expressions for the dielectric, magnetic, and chiral susceptibilities of the structure are derived on the condition of strong gyrotropy. The calculated values of the angle of the electromagnetic-wave polarization plane rotation and the circular dichroism are compared with the experimental results.     

Modern application packages for rigorous solution of problems of light propagation in anisotropic layered media. I. General solution of boundary problems in crystal optics

A new approach to the solution of the boundary problems of light propagation in optically active anisotropic absorbing media has been suggested. Unlike a number of already existing approaches, the new approach is based on the use of a computer mathematical system—the integrated application package Mathematica-4.1 and the method suggested by Berreman. It is shown that the special functions integrated into the package allow one to calculate the characteristics of the reflected and transmitted light for an arbitrary class of crystals and construct their dependences on various optical parameters. The examples of the application of the package Mathematica-4.1 for solving various problems of crystal optics are considered.     

Deposition of bulk GaN from solution in gallium under high N2 pressure on silicon carbide and sapphire substrates

Results of high-pressure directional growth of GaN on foreign substrates: SiC, sapphire and GaN/sapphire MOCVD templates are presented. The role of nitrogen pressure and supersaturation in the growth process is discussed. The conditions for stable growth of the nitride are determined. The results of the crystallization process are compared with those obtained for directional growth on pressure grown GaN crystals.     

Surface matter waves caused by the absorption of nonrelativistic particles

The existence of surface states of nonrelativistic particles at the interface between a vacuum and a layer of a material on a reflecting substrate, which are caused by the absorption in the layer rather than the presence of discrete levels, is established. The wave functions of such states (surface matter waves) are found and the domains of their existence in the complex plane of the “optical” potential (both attractive and repulsive) of the layer are determined. Threshold effects of the count of microparticles at the intersection of the boundaries of these domains are revealed. The spatial characteristics of the surface matter waves are calculated. An example of the layer composition providing the existence of such waves is given for ultracold neutrons. The increase in the loss of trapped ultracold neutrons owing to the excitation of the surface matter waves of these particles in the trap walls is discussed.     

On iodine behaviour in bulk crystals of PbTe and SnTe synthesized by the iodide method

In order to explain the peculiar characteristics of iodidely synthesized PbTe and SnTe crystals a model for their interaction with iodine is suggested. It is based on the assumption that PbI and I, respectively SnI and I, resulting from the PbI₂ (SnI₂) dissociations, are incorporated independently and specifically in the crystals: in PbTe prevails the PbI-incorporation; in SnTe — the incorporation of I + V_Sn. This difference is connected with the thermodynamic stability of the PbTe and SnTe crystal lattices.     

A study of mechanical homogeneity in as-cast bulk metallic glass by nanoindentation

A surface softening effect induced during copper-mould suction casting of bulk metallic glass is investigated as a function of rod diameter and glass fragility index, m, by nanoindentation. A reduction in hardness and reduced modulus at the rod surface is found to be favoured in small diameter castings and in fragile systems, respectively resulting from limited in-situ annealing and from a greater diversity of metastable atomic environments in the potential energy landscape of fragile glasses. Enhanced propensity for shear transformation zone nucleation in the low moduli surface is explained in terms of reduced atomic connectivity arising from a reduction in local co-ordination number and a lowering of the shear modulus. Finally, the structure and mechanical diversity that is possible in as-cast bulk metallic glass rods is explored through a relative quantification of shear modulus and plastic zone size across the whole as-cast state and in a single rod. These findings illustrate the sensitivity of bulk metallic glass to preparation, especially in respect of thermal history, potentially making replication of mechanical data between researchers problematic.