Analysis of a random system of dislocations in a deformed crystal

Structure of deformed crystals is modeled by dislocation loops of random size nonuniformly randomly distributed in natural slip planes. This model is used to determine structure parameters from the harmonics of the diffraction line of a polycrystal. Practical analysis of the dislocation structure under real conditions of the diffraction experiment is performed.     

X-ray quantitative determination of the phases in a batch for the synthesis of poly- and monocrystal yttriumaluminium garnet

For the synthesis of ceramics and single crystals of yttriumaluminium garnet, a batch consisting of Y₂O₃ and Al₂O₃ is first treated thermally in order to obtain the garnet phase Y₃Al₅O₁₂. It is possible to make a choice of the optimum technological parameters of the batch if the amounts of all oxide phases, present during the synthesis, are well known. A combined X-ray quantitative method is suggested for this purpose. The initial oxides and a garnet phase are determined by the method with external standard. The rest two impurity oxide phases are determined as binary system. The specific diffraction characteristics of the present compounds were taken into account. The amounts of all phases in the batch, treated thermally from 1373 to 2075 K at every 100 K are shown.     

Is it possible to use ion exchange in glasses for producing effective diffraction gratings?

The characteristics of light diffraction by graded index diffraction gratings, formed in glasses by ion-exchange techniques, and the minimum periodicity of such gratings are theoretically evaluated on the basis of a simple physical model. It is shown that spontaneous thermal ion-exchange can be used for the formation of gratings demonstrating Raman–Nath type light diffraction only. Electrically stimulated ion exchange can be applied for the formation of gratings diffracting ∼60–80% of incident light in one diffraction order. However, thick diffraction gratings demonstrating high angular selectivity can hardly be formed by this method. The range of achievable grating periodicities and phase modulation depths are estimated based on the glass parameters, the temperature of the ion-exchange process, and driving electric field strength.     

Spectrometer of Synchrotron Radiation Based on Diffraction Focusing a Divergent Beam Formed by a Compound Refractive Lens

The results of the first experimental realization of a spectrometer based on the effect of diffraction focusing of X rays by a flat single crystal are discussed. A secondary X-ray source with a relatively high angular divergence and small sizes was formed at the focus of a compound refractive lens having 50 beryllium biconcave elements with a curvature radius of 50 μm. The silicon spectrometer crystal was cut in the form of a wedge of variable thickness, oriented perpendicular to the diffraction plane. The reflection 111 was used for energies of 8.3 and 12 keV. To simulate the experiment, a computer program was developed, which takes into account accurately and for the first time the focusing of radiation by the lens and its subsequent diffraction in the crystal. A calculated curve for a monochromatic beam has made it possible to determine the monochromator spectrum with high resolution from experimental data for a polychromatic beam. It is shown that monochromator resolution increases with an increase in the distance from the compound refractive lens to the crystal.     

High Stability and Uniformity Polymeric Thin-Film Transistor Arrays Fabricated by Directly Subtractive Photolithography

We prepared polymer thin film on a diffraction grating by electrochemical polymerization in cholesteric liquid crystal (ChLC). The polymer thin film synthesized in ChLC shows diffraction function due to periodic structure produced by imprinting of the matrix ChLC. Combination of diffractions from the substrate (prepared by top-down technique) and the polymer having fingerprint structure (prepared by bottom-up technique) provides double diffraction grating function.     

A Novel Method for the Improved Skin Whitening Effect Based on Nanostructured Lipid Carrier

The effect of humidity on the holographic grating diffraction efficiency and transmittance kinetics in the E204Q BR gelatin film is investigated. We found a correlation between the accumulation of the red-light absorbing O intermediate in the later part of the E204Q BR photocycle and sharpness (decay to the steady-state) of the holographic recording kinetics. As shown, at humidity exceeding 95% the ratio between the peak and steady-state of the diffraction efficiency for the weak probe beam (670 nm) can reach 8.7 in the E204Q BR film, which is sufficient for realization of an efficient novelty filter.     

Organic light-emitting transistors with a thin metal layer covering a diffraction grating

We fabricated organic light-emitting transistors (OLETs) characterized by an Ag layer deposited on a one-dimensional (1D) or two-dimensional (2D) diffraction grating that acts as a combined gate insulator with SiO₂. The Ag layer was entirely covered with an organic crystal. Upon photoexcitation that crystal showed narrow linewidth emissions (NLEs) parallel to the substrate plane. The narrowed lines were either redshifted or blueshifted with rotation of the crystal around a normal to its surface with respect to the grating wave vector. Strong emissions (～10⁴–10⁶ cd m^?2) accompanied by current-injected NLEs were observed from the 1D and 2D grating OLETs.     

Crystal structure refinement from electron diffraction data

A procedure of crystal structure refinement from electron diffraction data is described. The electron diffraction data on polycrystalline films are processed taking into account possible overlap of reflections and two-beam interaction. The diffraction from individual single crystals in an electron microscope equipped with a precession attachment is described using the Bloch-wave method, which takes into account multibeam scattering, and a special approach taking into consideration the specific features of the diffraction geometry in the precession technique. Investigations were performed on LiF, NaF, CaF₂, and Si crystals. A method for reducing experimental data, which allows joint electron and X-ray diffraction study, is proposed.     

Röntgenographische Untersuchungen zum Abbau von bleihaltigen Stabilisatoren im PVC

Investigation methods of X-ray diffraction cannot only be used for characterizing technical crystalline admixtures of plastic material. In the case of stabilizers „dibasic lead stearate”︁ and „three-basic lead sulphate”︁ in PVC, there has been shown that the degradation of these substances at thermal stress of the material can be illustrated by diffractograms proving basic lead oxichlorides in cristalline intermediate stages. As final product of the reaction of lead stabilizers with HCl liberated when PVC decomposes, lead chloride appears, and in this connection the conversion of the sulphate part of th three-basic lead sulfate in this compound must also be taken into account. The intensities of the interferences of the three-basic lead sulphate and of the lead chloride on the X-ray diffractograms show the degree of degradation of the material after a processing operation due to the thermal stress. There is also the possibility of comparing the thermal stability of various lead stabilized PVC materials.     

X-ray diffraction in thick perfect crystals with deformed subsurface layers

The diffraction of X-rays in thick perfect crystals with deformed subsurface layers has been investigated. It was shown that the kinematic scattering of X-rays took place in deformed layers, while the dynamical one occurred in the perfect part of the crystal, -its bulk; also, that in beams of X-rays diffracted on surface defects, the role played by the second harmonics of the applied characteristic radiation MoKα₁ was essential.     

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.     

Failure Distribution on Semiconductor Wafers

Investigation of the distribution of dislocations intersecting the free surface of (1, 0, 0), Si-doped Bridgman-grown GaAs wafers. The defect densities were determined by using molten KOH as the defect-revealing etch. Their distribution can well be described by the compound Poisson-gamma distribution. The corresponding formula for the chip-yield is derived and it is shown, under which conditions it goes over into that for the simple Poisson distribution. Further, it is shown how the finite dimension of failures can be taken into account.     

Effect of the ultrasonic frequency on the multiple X-ray scattering from a LiNbO<Subscript>3</Subscript> crystal modulated by a surface acoustic wave

The effect of multiple scattering on the formation of the θ-2θ scan curves for a crystal modulated by a surface acoustic wave (SAW), depending on the ultrasonic frequency, has been investigated in the frame-work of the dynamical theory of X-ray diffraction. A model of a Rayleigh surface wave has been analyzed as applied to X-ray diffraction with allowance for the transverse and longitudinal elastic lattice strains. Using the example of the 127° Y′ cut of the LiNbO₃ crystal, it is established that the effects of multiple scattering can be neglected for ultrasonic frequencies above 650 MHz; this finding significantly simplifies the numerical calculations of X-ray diffraction from a crystal modulated by a short-wavelength SAW. A comparative quantitative analysis of the experimental data on synchrotron scattering from the 127° Y′ cut of a LiNbO₃ crystal modulated by a 952-MHz SAW have been performed, both taking into account and neglecting the effects of multiple scattering. It is shown that the computation time can be reduced by 2 to 3 orders of magnitude.     

Impurity Striations During Bridgman Growth of InSb

InSb single crystals have been grown by the gradient freeze method. Striations close to the seeding interface have been evidenced by X-ray topography and correlated to temperature and growth rate oscillations. It is shown that these striations are related to light impurity segregations and that a non-linear process should be taken into account to explain the phenomena.     

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.     

Investigation of the accuracy of modeling the orientation distribution function of polycrystalline materials from individual orientations

The accuracy of reconstructing the orientation distribution function of grains in polycrystalline materials by the kernel method from a set of individual orientations has been studied. In particular, the influence of choosing the smoothing kernel in the kernel method and the influence of the dependence on the resulting distribution are taken into account. The rotations obeying the normal distribution on the group SO(3) and obtained by the statistical test method are used as an orientation set. Some aspects of electron backscattering diffraction measurements are considered. This problem is urgent in view of the expanding potential of the experimental study of the texture of polycrystalline materials, especially for electron microscopy, which makes it possible to measure the orientations of individual grains.     

A Model for Structures Growth by Sodium Electrodiffusion in Quartz Crystals

Dendritic structures were grown inside the quartz crystal by electrodiffusion of sodium ions from a NaCl layer at the anode. The electric field was applied along the optical axis Z and the structures were grown in the xy plane. An experimental arrangement using a pointed cathode and a graphite plate anode was employed. X ray diffraction analysis shows that the structures' chemical composition is a mixture of sodium silicates. To explain the structures' growth a model is proposed. The model is a bidimensional one. The transport of the particles along the Z axis structural channels by the electric field was taken into account by introducing a probability of generating the particles in the growth plane as a function of the distance to the cathode. The computer generated results and the experimental ones were compared and a good correlation was found.     

Simulated diffraction on TiN coatings with gradients

A method of computer simulated X-ray diffraction patterns has been applied to TiN coatings assuming different gradients of lattice parameters, microstrain or grain size in the direction normal to the substrate surface. The generated diffraction patterns have been compared with experimental ones and a possibility of real occurrence of such gradients is discussed. This method is superior to the methods based on intensity weighted average quantities which do not take into account actual profiles of diffraction peaks.     

X-ray diffraction and X-ray standing-wave study of the lead stearate film structure

A new approach to the study of the structural quality of crystals is proposed. It is based on the use of X-ray standing-wave method without measuring secondary processes and considers the multiwave interaction of diffraction reflections corresponding to different harmonics of the same crystallographic reflection. A theory of multiwave X-ray diffraction is developed to calculate the rocking curves in the X-ray diffraction scheme under consideration for a long-period quasi-one-dimensional crystal. This phase-sensitive method is used to study the structure of a multilayer lead stearate film on a silicon substrate. Some specific structural features are revealed for the surface layer of the thin film, which are most likely due to the tilt of the upper layer molecules with respect to the external normal to the film surface.     

Nonidentified Kikuchi lines with reverse contrast

Electron diffraction patterns of silicon in transmission with contrast reversal from bright to dark for an unidentified Kikuchi line along its length have been obtained. The contrast reversal of an unidentified line is explained within the elementary mechanism of Kikuchi pattern formation taking into account the Kikuchi electron double diffraction.