X-ray Topographic Methods Research Articles

Investigation of the Spatial Distribution of Deformations in Quartz Piezo Elements by the X-Ray Topography Method

Investigation of the Spatial Distribution of Deformations in Quartz Piezo Elements by the X-Ray Topography Method

Defect structure of ZnGeP2 crystals grown in the furnaces with tube diameters of 70 and 130 mm

The crystal structures of two ZnGeP2 crystals grown by the Vertical Bridgman method in different furnaces were compared. The furnace tube diameter was 70 mm for the first crystal and 130 mm – for the second one. The diameter of both crystals was 30 mm. The radial temperature profiles of the furnaces show different curvatures in the growth zone. For the first crystal the profile was slightly concave, whereas, for the second one, it was flat. The structure was analyzed by X-ray diffractometry and topography methods. In the first crystal, the dislocation density changed from 102 cm−2 in the initial growth region of the sample to 104 cm−2 at the last-to-freeze end. Low-angle grain boundaries were observed. The second crystal contained only single dislocations. Both crystals showed growth striae. After thermal annealing (both crystals were treated under identical conditions), the second crystal showed a much better optical transparency than the first one.

In-operando x-ray topography analysis of SiC metal–oxide–semiconductor field-effect transistors to visualize stacking fault expansion motions dynamically during operations

We developed an in-operando x-ray topography method for dynamically visualizing single Shockley-type stacking fault (1SSF) expansion motions in silicon carbide (SiC) metal–oxide–semiconductor field-effect transistors (MOSFETs) during their operations and investigated the effect of the operating condition applied to the body diodes in SiC MOSFETs on dislocation glide velocity. In-operando x-ray topography observations were carried out in reflection geometry, and a high-resolution x-ray camera was used as a detector to record topographies dynamically. The sequence of 1SSF expansion motions in the SiC MOSFETs was observed at a high resolution of 1 s in x-ray topographies, which is sufficient to analyze the dislocation glide velocity of a 1SSF expansion. The observation results of changing the forward current density applied to the body diodes in SiC MOSFETs revealed that each triangular and bar-shaped 1SSF expands at different forward current densities. The 1SSF expansion timings also differed, even in the same chip under the same current density. The dislocation glide velocity of each expanded 1SSF in SiC MOSFETs was extracted, and it increased with the forward current density. Our method enables the dynamic visualization of bipolar degradation in SiC MOSFETs during their operations, and we can accurately obtain the information of when, where, and which 1SSF expands in a SiC MOSFET.

X-Ray Diffraction Topography Methods (Review)

Various X-ray topography methods for visualizing crystal lattice defects are described, issues of the formation of diffraction contrast are considered, and examples of the use of X-ray topography for studying various structural defects of the crystal lattice are given.

Double-Crystal X-Ray Diffractometry and Topography Methods in the Analysis of the Real Structure of Crystals

The high efficiency of double-crystal X-ray diffractometry and topography methods in the characterization of crystals during refinement of the crystal-growth technology is demonstrated for the example of diamond bulk crystals and films obtained by the high pressure, high temperature method and by chemical vapor deposition, respectively. Techniques and study schemes for analysis of the real crystal structure, assessment of the chemical composition and the period of the crystal lattice, and analysis of the distinctive features of the deformation and thickness of thin films are described. Major structural defects (dislocations, stacking defects, inclusions of a different phase, and others) that emerge during the production of synthetic diamond crystals are identified.

Mathematical Simulation of the Process of Growing a CdTe Single Crystal by the Obreimov–Shubnikov Method

For the first time, the process of growing a CdTe crystal by the modified Obreimov–Shubnikov method using the technique of self-nucleation from the initial cooling temperature (1100°C) to the time of reaching the stationary growth mode is simulated. The motion of the crystallization front during crystal growth is calculated. The results are confirmed by the X-ray topography method with use of synchrotron rad-iation.

Crystal growth and optical properties of Ca3TaGa3Si2O14 single crystals

Transparent yellowish Ca3TaGa3Si2O14 single crystals were grown in Ar+(0.5–3)% O2 along the Y-axis by the Czochralski technique. The structural perfection of Ca3TaGa3Si2O14 samples was studied by X-ray topography and rocking curve methods. Topograms and rocking curves along the surfaces of the Y- and Z-cuts were studied before and after surface treatments (polishing and etching). Transmittance spectra were measured in the wavelength range of 200–3300 nm. Optical anisotropy was studied along the X- and Z-axes, and dichroism along the X-axis. The dispersions of the refractive index No and specific rotation of the polarization plane were determined using spectrophotometric methods.

Optimization of the Growth Technology for Crystals with Garnet Structure Based on X-Ray Diffraction Data

High efficiency of the methods of double-crystal X-ray diffractometry (DCXRD) and topography for improving the growth technology of highly homogeneous crystals has been demonstrated on the example of gadolinium gallium garnet (GGG) single crystals. The main types of structural defects observed in Czochralski-grown GGG crystals are found to be macroscopic inhomogeneity of composition distribution, caused by the facet effect manifestation; microinhomogeneous distribution of impurity and main components of the composition in striations; dislocations; and second-phase inclusions. The relationship between the type and density of newly formed defects and the technological conditions for crystal growth are considered. Optimization of the composition of crystals and their growth technology made it possible to obtain high-quality dislocation-free crystals of GGG and complex-substituted garnets on its basis for magneto-optical and microwave devices, elements of solid-state lasers, and other applications.

X-Ray Topography: Yesterday, Today, and Prospects for the Future

X-ray topography is a set of X-ray diffraction techniques that make it possible to see images of defects, to determine their type and location in the volume of the crystal structure or on its surface, and to measure their main characteristics. The review discusses the possibilities, limitations, and prospects of X-ray topography methods.

Simulation of GaSb:Te Crystal Growth in Space Experiment

An application of X-ray topography methods allowed us to construct a two-dimensional map of the impurity distribution in a GaSb:Te crystal grown under microgravity conditions. This map served as a framework for the analysis of crystal growth features and of the impurity inhomogeneity in the crystal. The data on the impurity distribution in the sample became an experimental basis for the analysis of the crystallization parameters (the crystal growth rate and the maximum convection velocity) and an adequate application of theoretical models (analytical and numerical) to explaining the mechanisms of onset of impurity inhomogeneities in the crystal.

X-ray diffraction characterization of synthetic garnet, diamond and sapphire crystals

The structural features of synthetic garnet, diamond, and sapphire single crystals are investigated via the nondestructive methods of double-crystal X-ray diffractometry and topography. The conditions of diffraction studies into these crystals performed with the help of Ge monochromators are optimized. The main structural defects (dislocations, stacking faults, growth striations, second-phase inclusions, etc.) of crystals arising from their generation are revealed. It is demonstrated that the experimental techniques for studying the real structure turn out to be highly efficient in optimizing crystal-growth technology.

Estimation of quality of GaAs substrates used for constructing semiconductor power devices

X-ray topography and high-resolution diffractometry methods are used for testing GaAs wafers from different manufacturers, which are used as substrates for epitaxial growth in construction of power semiconductor devices. Typical features of such wafers are a distorted surface layer, bent, and growth dislocations with two types of distribution with a density of (1–2) × 104 cm−2. The best and worse substrates are determined from the finishing of the working surface, and the optimal combination of X-ray methods for estimating the quality of finishing of the working surface of the crystals with a high level of X-ray absorption is established.

New applications of sapphire crystals

Results of studies of sapphire as a prospective material for different modern applications are presented. An analysis of different growth techniques was performed and a crystalline surface treatment technique developed. Processes of high-temperature surface recrystallization have been studied and the structure of dislocations in the crystals examined. Some applications for sapphires are shown. The following techniques were applied: RHEED, AFM, HRTEM, X-ray scattering, topography, and tomography, using both x-ray tubes and synchrotron radiation sources. High-temperature annealing of super-smooth sapphire surfaces (RMS roughness < 0.2 nm) produces terrace-step structures on the surface. The influence of the miscut parameters and annealing conditions on the structures is analyzed. The substrates with such surface structures were used to form regular ensembles of gold nanoparticles and for the epitaxy processes of AIIBVI thin films. The availability of sapphires that are perfect from the X-ray optics point of view can overcome major limiting factors for meV resolved nuclear resonance scattering and other high energy-resolution X-ray spectroscopy techniques. The analysis made by different X-ray topographic methods shows that the presence of dislocations limits the size of useful reflective area of the crystal. It is shown, that only Kyropoulos-grown crystals demonstrate very low dislocation densities, as low as 100 cm^-2, and the most narrow backscattering spectral reflectivity band. This work is supported by the Russian Foundation for Basic Researches (Grants No. 13-02-01065a and 13-02-91325), Presidium of the Russian Academy of Sciences (Program No.24) and Helmholtz association of German Research Centers (HRJRG-402 project). We thank A. Danilewsky, J. Härtwig, A. Muslimov, I. Prokhorov, A. Vasilyev, V. Vlasov for their assistance as well as principal investigators of the project: A. Chumakov, H.-C. Wille, I. Sergueev, S. Stankov.

Brazing of hexagonal boron-nitride ceramics with VT1-0 titanium alloy using a rapidly quenched titanium-based brazing alloy

A brazing alloy was developed for the brazing of boron-nitride ceramics with VT1-0 alloy in the form of nanostructured rapidly quenched tapes. The wetting capacity of the boron-nitride ceramics by the brazing alloys of the Ti–Zr system is evaluated. The surface of the brazing alloy tape was investigated by X-ray diffraction and topographic methods and the brazed joints between theVT1-0 titanium alloy and boron-nitride ceramics were studied by examination of microstructure and mechanical properties.

Development of Nickel Based Superalloys for Advanced Turbine Engines

Superalloys have been developed for specific, dedicated properties and applications. One of the main application for this material is advanced, high-performance aircraft engines elements. Turbine engine creates harsh environments for materials due to the high operating temperature and stress level. Hence, as described in this article, many alloys used in the turbine section of these engines are very complex and highly optimized. This article provides an overview of structural changes that occur during the aging process of wrought and cast alloys and provides insight into the use of precipitated particles to achieve desired structures. Example will focus on alloy Inconel 718 and CMSX-4. Functional properties of these alloys can be achieved by choosing proper heat treatment parameters to obtain required rate between secondary phases. The paper also attempts to determine structural perfection and changes of crystallographic orientation along the axis of growth of single crystal nickel superalloys cast using X-ray topography and Laue diffraction method. Single crystal bars and turbine blades were manufactured in VIM furnace using the Bridgeman method. Withdrawing rates typical for CMSX-4 superalloy were used. It has been found that with increasing withdrawing rate the nature of distribution along the axis of growth of the angle of [001] direction deviation from the axis of single crystal blades growth had changed. The change of the withdrawing rate results also in the rotation of γ’ phase in the form of cubes against the axis of single crystal blades growth.

Characterization of dislocations and sub-grain boundaries in mixed rare earth orthovanadate of Yb:YxLu1−xVO4

Mixed crystal of Yb:YxLu1−xVO4 was grown by Czochralski method. Defects of dislocations and sub-grain boundaries in Yb:Y0.71Lu0.29VO4 single crystal were studied by using chemical etching and synchrotron X-ray topographic methods. Some of the three intersecting boundaries were revealed by chemical etching method in Yb:Y0.71Lu0.29VO4 crystal. The generalized Read–Shockley formula for intersecting boundaries was introduced to verify the one-to-one correspondence between etching pits along these sub-boundaries and edge dislocations with Burgers vectors of 〈100〉. Synchrotron X-ray topographic confirmed that the dominating imperfections in the studied Yb:Y0.71Lu0.29VO4 single crystal are a variously developed block structure and sub-grain boundaries.

Bulk growth of ninhydrin single crystals by solvent evaporation method and its characterization for SHG and THG applications

Ninhydrin is a well-known compound generally used in amino acid synthesis and also for detecting the latent fingerprints on porous surfaces. Single crystals can be grown by dissolving the compound in double distilled water at ambient temperature, and can be used as a potential material for second and third harmonic generation applications. The grown specimen was subjected to different characterization techniques in order to find out its suitability for device fabrication. Its lattice dimensions have been confirmed by X-ray powder diffraction and its crystalline quality has been assessed by high resolution X-ray diffraction and X-ray topography methods. The presence of functional groups was identified from HETCOR analysis and confirmed the absence of impurities during crystallization. Its optical properties have been examined by photoluminescence and birefringence analyses. Its thermal parameters such as thermal diffusivity, thermal conductivity and specific capacity have been carried out by following photopyroelectric method. Third order nonlinear optical measurements have been carried out using Z-scan technique and its nonlinear optical absorption coefficient has been determined.

Characterization of single-crystal sapphire substrates by X-ray methods and atomic force microscopy

The possibility of characterizing a number of practically important parameters of sapphire substrates by X-ray methods is substantiated. These parameters include wafer bending, traces of an incompletely removed damaged layer that formed as a result of mechanical treatment (scratches and marks), surface roughness, damaged layer thickness, and the specific features of the substrate real structure. The features of the real structure of single-crystal sapphire substrates were investigated by nondestructive methods of double-crystal X-ray diffraction and plane-wave X-ray topography. The surface relief of the substrates was investigated by atomic force microscopy and X-ray scattering. The use of supplementing analytical methods yields the most complete information about the structural inhomogeneities and state of crystal surface, which is extremely important for optimizing the technology of substrate preparation for epitaxy.

Defect Evaluation of SiC Crystal Grown by Solution Method: The Study by Synchrotron X-Ray Topography and Etching Method

We investigated dislocation behavior in the crystal grown on 6H-SiC (0001) by solution method using synchrotron X-ray topography and thermal chlorine etching. It was confirmed that basal plane dislocation was not newly formed in the grown layer. In addition, the positions of threading screw dislocations (TSDs) were displaced and some of them disappeared in the grown layer. This displacement was caused by the bending of the TSDs during growth.

On the nature of the direct image of defects in diffraction methods of X-ray topography

The regularities of X-ray scattering in the most distorted region of the crystal, where the local lattice misorientations associated with the deformation field of a defect reach a maximum, have been analyzed. The assumption is made that one of the possible mechanisms of the formation of a direct image is the wave field scattering at the pseudoboundary in the region of local misorientations, where the crystal comes out of the reflecting position near the defect axis, for example, the dislocation core. The formation of a direct image is demonstrated using numerical simulation of section topographs of model defects as an example. The model sample is a perfect single crystal containing a thin tube oriented in a certain crystallographic direction and filled by the same single-crystal material with the orientation different from that of the parent crystal. Therefore, if the model crystal is in a reflecting position, the Bragg conditions inside the tube are not satisfied. Numerical topographs show that the direct image is formed at the boundary of the tube of the model crystal.