The Influence of the X-ray Wavelength on the Behaviour of Polar Kossel Reflections

The Kossel effect permits a determination of polar directions in non-centrosymmetrical structures. To identify polar reflections unambiguously, differences — as large as possible — in their fine structures are necessary. These differences considerably depend on both the diffraction geometry and the characteristic X-ray wavelength applied. The reasons of such behaviour are deliberated upon hereinafter and a good harmony achieved of theoretical predictions and experimental findings.     

Birth-and-spread growth on the Kossel and a non-Kossel surface

A birth-and-spread growth model is derived for an anisotropic crystal surface and fitted to growth rate data obtained from Monte Carlo simulations of an isotropic and anisotropic Kossel (0 0 1) surface and a non-Kossel (0 0 1) surface. Only the step free energy is used as a fit parameter. All growth rate sets are nicely fitted by the new expression and the fitted values of the step free energy are in the physically relevant regime.     

X-ray divergent-beam (Kossel) technique: A review

The development of the X-ray divergent-beam (Kossel) technique over the last 50 years is traced. The fundamentals of this technique and ways to implement it experimentally are considered, and its potential for studying the real structure of crystals is analyzed in detail.     

Measurements of Residual Stresses in Micron Regions by Using Synchrotron Excited Kossel Diffraction

In 1996, we performed the first measurements of residual stresses by using synchrotron excited Kossel diffraction (at the beamline L of the HASYLAB, Hamburg). Our first findings as well as the principle of the determination procedure for obtaining residual stresses from Kossel lines are presented. The Kossel technique is a very suitable method for fast measurements of local residual stresses in micron regions. Because of the high lateral resolution even residual stresses of third order (inhomogeneities of the stress state within a grain) can be proved and calculated.     

Estimation and Correction of Effects of Simultaneous Reflections on Intensity Data Collected with the Four‐Circle Diffractometer

A procedure based on the kinematical theory has been developed to estimate and correct the effects of simultaneous reflections on intensity data collected with the four‐circle single crystal X‐ray diffractometer through minimizing the scatter of the corrected structure factor (intensity) values of equivalent reflections.     

Intensity and Anisotropy of the Dynamic Ligh Scattering in Nematic Liquid Crystals

The dependence on voltage of the correlation length of turbulence in the dynamic scattering mode in an ac excited nematic liquid crystal has been measured and discussed. The influence of a high frequency stabilizing field has been shown. The total anisotropy of the turbulent medium has been demonstrated, using measurements on a wedge-shaped sample.     

Temperature and Intensity Behaviour of the pAl0.7Ga0.3As-pGaAs-nGaAs Concentrator Solar Cell

A semiempirical approch for calculation of pAl_0.7Ga_0.3As-pGaAs-nGaAs concentrator solar cell behaviour in a very wide range of operating temperatures (77 K – 490 K) is developed. Experimental values of cell collection efficiency, short circuit current and open circuit voltage are given, while cell fill factor and overall conversion efficiency are calculated. Optimum cell operating conditions are found both for AM 1 and AM 0 radiation.     

Light Intensity Variation Studies of MoS2/Electrolyte Interface

Photoelectrochemical characterization of natural and synthetic molybdenum disulphide prepared by direct vapour transport technique have been carried out. The quality of the MoS₂/electrolyte junction for photovoltatic applications was assessed examining the effect of varying light intensity on current voltage behaviour. For measurements at low intensity a broad light source was used. The ideality factor (n) was determined for these junctions by modelling the MoS₂/electrolyte junction in terms of a Schottky barrier. The effect of intensity in the efficiency of the PEC solar cells has also been studied in detail. All the observations have been described and the implications have been discussed.     

Characterization of the Intensity Distribution in a Single Laser Spot Applied to the Annealing of Ion-Implanted Silicon

By means of the annealing events of ion-implanted p-type silicon in liquid phase epitaxy (implantation dose 2.5 × 10¹⁶ As⁺/cm²) the degree of homogeneity of a bent quartz rod diffuser for single pulses of a Q-switched Nd-glass laser (λ = 1.06 μm) is investigated using SEM-EBIC, TEM and RBS. Starting from discrete distributions of EBIC signal heights in the annealing spot the specific distribution of recrystallized monocrystalline and polycrystalline regions as well as the transition between them are proved by TEM diffraction contrast studies. The perfect recrystallization for a locally optimum laser energy density as well as the rectangular shape of the carrier concentration profile are proved by RBS measurements. At different positions of the measuring point within the annealing area RBS, too, renders it possible to point out local inhomogeneities of the energy density distribution in the case of low-quality beam diffusers.     

Heights of Overlapping X-ray Reflections and Phase Analysis

The influence of reflections overlapping on the heights of their maxima is investigated using the Lorentzian profile approximation. This influence should be taken into account in automatic powder diffractometer programs of phase analysis based on the peak heights.     

Analysis of Changes in the Intensity of the Intrinsic Luminescence after the Copper Diffusion into Semi-Insulating Undoped GaAs Crystals

An analysis is made of the effect of the copper diffusion into semi-insulating undoped GaAs crystals on the intensity of the intrinsic luminescence. It is shown that the copper diffusion into semi-insulating undoped GaAs crystals could lead both to an increase and to a decrease in the intrinsic luminescence intensity. Analytical expressions connecting the value and the sign of the effect observed with the recombination parameters of crystals pointed and also with the intensity of luminescence excitation are obtained.     

Electric-Field Enhancement of Fluorescence Intensity of Cholesteric Liquid Crystals Containing Aromatic Chromophores

Fluorescence from cholesteric liquid-crystalline mixture containing cholesteryl 3-(l-pyrenyl)propanoate was measured under dc and ac electric field applied parallel to the helix axis. The excimer fluorescence of the pyrenyl chromophore increased and decreased its intensity reversibly upon turning the electric field on and off. Similar electric field effects were observed for such chromophores as tetracene, perylene, and 9,10-diphenylanthracene doped in the cholesteric mixture. The electric-field effect was observed only for fluorescence transitions which show left-handed circularly polarized fluorescence, indicating that only transitions which are polarized perpendicular to the optic axis in a quasi-nematic layer exhibit the effect. The experimental results were found to be intimately connected to the onset of the Helfrich periodic distortion of a planar structure.     

Intensity parameters and laser analysis of Pr and Dy in oxide glasses

Intensity parameters ($\text{Ω}{}_{\mathrm{\Lambda }}$) of Pr³⁺ and Dy³⁺ have been obtained in tellurite, borate and phosphate glasses. It has been found that $\text{Ω}{}_{\mathrm{\Lambda }}$ calculated by exlusion of hypersensitive transitions, gives a better fit between measured and calculated lifetimes and branching ratios than those including hypersensitive transitions. Using these parameters and calculated matrix elements U^(Λ), radiative transition probabilities, branching ratios and integrated cross sections for stimulated emission were calculated for ³P₀, ³P₁ and ¹D₂ excited states of Pr³⁺ and ${}^4\text{F}\text{9}\text{2}$ excited state of Dy³⁺. Potential transitions are indicated.     

Effect of Neutron Irradiation and Annealing on the Intensity of the Copper Related 1.01 eV Emission Band in n-type GaAs

Effect of neutron irradiation (E = 2 MeV, ϕ ≤ 10¹⁵ n/cm²) and subsequent annealing (T ≤ 700 °C, t = 30 min) on the intensity of the copper-related peaked at hvm =1.01 eV emission band in n-type GaAs (n₀ = 2 × 10¹⁸ cm⁻³) is studied. A strong irradiation-induced increase of the above emission intensity was observed testifying about the irradiation-stimulated growth in the concentration of copper-related 1.01 eV radiative centres (Cu_GaV_As pairs). A model is presented to explain this effect.     

Structural Studies of Antimony Pentahalide Graphite Intercalation Compounds Using 001 Reflections

X-ray diffraction studies at room temperature are reported of stages 1, 2 and 3 SbCl_mF_5-m graphite intercalation compounds (m = 0, 2, 4, 5). The analysis of the 001 reflection inten-sities shows the periodic stacking of carbon, chlorine and antimony layers in all compounds. The results are in good agreement with the structural model recently found in other metal halide graphites. But we have found that the antimony atoms are not located on the mirror plane (z = O) in the centre of the intercalate layer. In case of dilute SbCl₅ graphites, the identity period along c axis I_c increases with SbCl₅ concentration in the stage 2 com-pound. Interlayer distances were determined in dependence on SbCl₅ concentration. A molecular layer form consisting of SbX₅ molecules which are linked by halogen bridges is suggested to fill the galleries in the graphite lattice.     

Degenerate Reflections in Acoustics of Solids. II: Orthorhombic Crystals

Crystallography Reports - The conditions under which a bulk acoustic wave, incident on a crystal at a certain angle and reflected from the crystal boundary with vacuum, generates two or one...