Investigations of the energy flow of X-ray wavefields in crystals

The energy flow of the X-ray wavefields in the Laue case of diffraction and its importance for X-ray topography and interferometry are discussed.     

Investigations on noncubic crystals with the divergent X-ray beam technique

The divergent X-ray beam technique is very useful for the study of small monocrystalline sample regions. The diffraction patterns are cone-shaped. The size of the cone angle and the direction of the cone axis depend form the lattice parameters and the orientation of the investigated crystal. An appropriate evaluation permits the simple determination of lattice parameters, even of those of noncubic crystals and the determination of crystal orientation. The comparison of X-ray divergent beam patterns of different regions of the sample makes it possible to discover changes in the imperfect crystal structure such as local lattice parameter variations, disorientations, and twinnings in regions up to 10 μm in diameter. Suitable methods for utilization will be shown here.     

Curved focusing crystals for hard X-ray astronomy

A lens made by a properly arranged array of crystals can be used to focus x-rays of energy ranging from 30 to 500 keV for x-ray astronomy. Mosaic or curved crystals can be employed as x-ray optical elements. In this work self standing curved focusing Si and GaAs crystals in which the lattice bending is induced by a controlled damaging process on one side of planar crystals are characterized. Diffraction profiles in Laue geometry have been measured in crystals at x-ray energies E = 17, 59 and 120 keV. An enhancement of diffraction efficiency is found in asymmetric geometries.     

X-ray Investigations of Shape Memory Alloys

The investigation aims to analyse the influence of different kinds of thermal treating on the structure of martensite. Maxima of the X-value are observed at 60–70 minutes for the sample aged at 200°C and 90 minutes for that aged at 375 °C and minima for Y after almost the same time. We consider that with these results the discussion on the processes occurring during short ageing times will be activated, because in the literature there is lack of such a results.     

X-ray investigation of NPOOB crystals

Results of a series of experimental investigations by means of X-rays of NPOOB crystals are reported. These results refer to the anisotropy of thermal expansion, to the smectic-nematic phase transition and to critical scattering accompanying that phase transition. It is suggested that the smectic-nematic phase transition is continuous.     

X-ray crystal orientation determination for semiconductor single crystals

An improved method to measu reorientation angles of flat single crystals was developed taking Buerger precession technique. The method is described and compared with Laue- and goniometer techniques. Advantages are low costs and short measuring time. An easy evaluation of the records allows to take this method as a routine angle determination for semiconductor manufacturing.     

X-ray two-crystal diffractometer for testing of plane analyser crystals

A two-crystal diffractometer (TCD) for testing the mosaic structure of LiF crystals is presented. Peculiarities are the adapted sensivity (angular minutes), short measuring times, large registered areas and the possibility of application for various kinds of surface treatment.     

Investigations on the structural perfection of bridgman-grown PbTe single crystals

It is reported on the possibility of improving the structural perfection by the Bridgman method, shown with the example of the influence on the low-angle grain boundary substructures in PbTe arranged in growth direction. In the employed crystal growth apparatus temperature gradients from 15 to 100°C/cm and solidification rates from 0.33 to 4.2 mm/hr could be achieved. The low-angle grain boundary substructure was characterized by X-ray-topographic and etch investigations on (100)-orientated ingots. The thermal conditions during the growth affect the structural perfection decisively. An axial spot dependence of etch pit density and substructure abundance was observed. By reducing the cooling rate during growth — expressed by the product of temperature gradient G and solidification rate V — it is possible to obtain more perfect PbTe-crystals. It seems that the diameter l of the substructure cells which was lying between 0.5 and 2 mm, is related to the cooling rate G · V by the functional coherency l ≈ 1/√G · V. The choice of different initial melt combinations up to 1 at.% Te-surplus exerted no influence on the abundance of the low-angle grain boundaries. The in literature suggested connection of low-angle grain boundary substructure with phenomena resulting from a constitutional supercooling could not be established.     

Investigations on the Nucleation Kinetics of L-Arginine Phosphate single crystals

The nucleation parameters, such as radius of the critical nucleus and critical free energy change have been evaluated for LAP single crystals. The interfacial tension determined by conducting the induction period measurements has been used for the evaluation of nucleation parameters. The determined interfacial tension is found to be comparable with theoretical literature values.     

X-ray determination of the polarity of zincblende-structure crystals

An X-ray diffraction procedure for the determination of the polarity of noncentrosymmetric crystals by measuring the integrated reflections of opposite polarity on one surface of the crystal is described. The observed intensities must be corrected for the different asymmetries of the two reflections. To estimate the influence of crystal perfection on the correction factor, the ratios of the integrated reflections were calculated numerically for dynamic diffraction. The method has been applied for determining the polarity of CdTe.     

Investigations of impurity striations in potassium bichromate crystals

Impurity striations in potassium bichromate crystals (KBC, lopezite) formed during crystal growth from aqueous solution were revealed by chemical etching and analyzed. Striations were revealed as etch grooves, as rows of dislocation etch pits and as rows of flat‐bottomed etch pits. Various types and groups of striations have been visualized. Some striations were due to lateral segregation of impurities caused by convection flow of the mother solution, other were formed during growth stoppages whereas induced striations were generated by changes in hydrodynamical conditions. Growth rates changes resulted in zonal distribution of impurities, formation of planar lattice strain, rows of clusters of point defects and rows of dislocations. Generation of striations with different intensities in various sectors is a proof of the selective capture of impurities. Ratios of growth rates of various faces of KBC crystals growing in forced and free convection regimes were determined by induced striations. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

X-ray characterization of detached-grown germanium crystals

Germanium (1 1 1)-oriented crystals have been grown by the vertical Bridgman technique, in both detached and attached configurations. Microstructural characterization of these crystals has been performed using synchrotron white beam X-ray topography (SWBXT) and double axis X-ray diffraction. Dislocation densities were measured from X-ray topographs obtained using the reflection geometry. For detached-grown crystals, the dislocation density is on the order of 10⁴ cm⁻² in the seed region, and decreases in the direction of growth to less than 10³ cm⁻², and in some crystals reaches less than 10² cm⁻². For crystals grown in the attached configuration, dislocation densities were on the order of 10⁴ cm⁻² in the middle of the crystals, increasing to greater than 10⁵ cm⁻² near the edge. The measured dislocation densities are in excellent agreement with etch pit density (EPD) results. Broadening and splitting of the rocking curve linewidths was observed in the vicinity of subgrain boundaries identified by X-ray topography in some of the attached-grown crystal wafers. The spatial distribution of rocking curve linewidths across the wafers corresponds to the spatial distribution of defect densities measured in the X-ray topographs and EPD micrographs.     

Investigations for the improvement of the radial doping homogeneity of dislocation-free floating zone silicon crystals

In order to improve the doping inhomogeneities of dislocation free FZ Silicon crystals with diameters ≧ 75 mm investigations were carried out to influence the shape and curvature of the crystallization interface during the crucible-free floating zone crystal growth process. In this works shapes and geometries of the applied melting inductors and the relative positions of these inductors to the seed axis were examined concerning the values of radial macroscopic and microscopic doping inhomogeneities in dependence on other growth parameters, for instance crystal rotation rate. The application of eccentric inductor-seed positions effects a decreasing “bending value” of the crystallization interface, that means an improvement of the macroscopic radial doping inhomogeneity with crystal rotation rate in the range between 4 and 8 min⁻¹.     

X-ray interferometric investigations of structural distortions in silicon crystals as a result of diffusion

The influence of boron diffusion on the X-ray Moiré pattern is investigated by means of X-ray interferometry. It is shown that at low boron concentrations in silicon, the Moiré patterns indicate the non-dislocative character of arising stresses. At higher concentrations the dislocations arise. Basing on the obtained topogram, the maximum local stress is evaluated, which at boron concentration of 2.5 · 10¹⁹ at/cm³ is 1.05 · 10⁸ N/m².     

Growth of Ni-doped MgF2 crystals in self-sealing graphite crucibles

Large Ni-doped MgF₂ single crystals of excellent optical quality have been grown in self-sealing graphite crucibles by a vertical gradient freeze technique. This relatively simple technique always yields single crystals having excellent optical quality and should be applicable to the melt growth of other crystals that are too volatile to permit the use of open systems.     

Method for estimating the morphological significance of simple forms of crystals from X-ray data

When developing V.I. Mikheev and I.I. Shafranovskiĭ’s method for estimating the morphological significance of faces of different simple forms from X-ray reflection intensities, a way to approximately evaluate the morphological significance of simple forms on crystals from the structure amplitudes of the corresponding atomic planes is proposed. The potential for this approach is demonstrated by the examples of marcasite and zircon.     

An X-ray topographic method for identifying the active slip systems in cubic crystals

An original technique based on the geometric characteristics of dislocations in planar pileups is suggested which allows the estimation of the local thermoelastic stresses and analysis of the influence of a number of growth parameters on the formation of dislocations in A ^III B ^V semiconductor crystals.