High-resolution Diffractometry Research Articles

In Ukrainian

The paper describes the method of obtaining the SiC/porous-Si/Si heterostructure and the study of its structural and morphological properties. The method of obtaining heterostructures consisted of several stages: electrochemical etching of single-crystal silicon p-Si (111), annealing of porous Si in a CO atmosphere. The fabricated structures were characterized using scanning electron microscopy, X-ray spectral microanalysis, X-ray phase analysis, high-resolution diffractometry, X-ray reflectometry, and photoluminescence. The method of high-resolution diffractometry made it possible to assess the state of the SiC/Si(001) system. On the 2Theta-omega diffractograms, in addition to the (111) reflection of the Si substrate in the region of 2 Theta = 35.67, the (111) reflection of the cubic SiC film is observed. This means that the formed SiC film is textured in the (111) growth direction of the silicon substrate. The classical technique of X-ray phase analysis showed the presence of a hexagonal phase in the SiC film. The concentration ratio of cubic to hexagonal phase is 80 % cubic and 20 % hexagonal. The RMS deformation of the lattice (ε) in such a structure is ε = 1∙10–2. The photoluminescence spectra of the SiC films of the experimental samples in most cases consist of narrow and broad bands and extend from the near ultraviolet to the entire visible spectrum. At the same time, in the range of wavelengths corresponding to the energy forbidden zones of hexagonal polytypes and cubic polytypes, a noticeable glow was observed in most of the samples. In some samples, luminescence in the area of hexagonal phases was predominant. In the photoluminescence spectra both at T = 77 K and at T = 300 K, a narrow line at a wavelength of ~ 371 nm is observed.

In situ synchrotron X-ray diffraction study of synthesis reactions in mechanically activated Ti + Al powder mixture under linear heating conditions

In the present work, we studied the features of phase formation in mechanically activated Ti + Al powder mixture at various heating rates for the first time. The study was carried out using high-resolution diffractometry method which made it possible to study the processes of phase formation in situ at any stage of heating. It was established that ignition of the activated mixture can be initiated in the solid phase with an extremely low content of reaction products formed at the preheating stage. An increase in the heating rate leads to a decrease in the average burning rate and an increase in the ignition temperature. At high heating rates, the ignition is initiated in the presence of a liquid phase when the ignition temperatures are close to the melting temperature of aluminum. In this case, the content of reaction products formed during preheating stage is relatively high. It was found that the all main compounds presented in the equilibrium diagram of Ti-Al system are synthesized in parallel. The content of phases in the reaction products depends on the heating rate.

Properties of the dispersive double bent crystal monochromator setting with a multicrystal sandwich at the place of the second axis

In this paper, some luminosity, focusing and resolution properties of a double-crystal (n,-m) dispersive setting which contains a bent perfect Si(111) crystal as a first one and a sandwich consisting of four different bent perfect crystals (BPC) Si(220), Si(400), Ge(111) and Ge(311) located at the second axis, is introduced with the aim of possible use in high-resolution diffractometry. The properties were investigated at a neutron wavelength of 0.162 nm. It was shown that a narrow and highly collimated and high-resolution monochromatic beam can be obtained. By using a standard polycrystalline pin of α-Fe, the resolution of the three-axis diffraction performance, namely, in the vicinity of the scattering angle 2 θ S = 90 ∘ was tested in detail. It has been found that the dispersive double-crystal (DC) setting represents a high-resolution monochromator alternative, e.g. in powder diffraction which could be used at high-flux neutron sources.

Influence of dislocation structure on electrical and spectroscopic properties of MoOx/p-CdTe/MoOx heterostructures

The defective structure of p-CdTe:Cl single crystals and MoOx/p-CdTe/MoOx heterostructures were investigated by high-resolution X-wave diffractometry methods. Different models of dislocation systems were used and the dislocation densities were estimated from the Williamson-Hall plot. It is noted that significant deformations of the mismatch in the transition layer negatively affect the current–voltage characteristics of heterostructures.

Observation of multiple Bragg reflections accompanying forbidden Si(002) reflection in bent-perfect Si crystal

Strong multiple Bragg reflections (MBRs) which can be realized in a bent-perfect-crystal (BPC) slab provide a monochromatic beam of excellent resolution parameters. For identifying MBR effects in the BPC Si crystal, we used the method of azimuthal rotation of the crystal lattice around the scattering vector of the primary forbidden Si(200) reflection for a fixed chosen wavelength. In this paper, several azimuthal scans searching strong MBR effects with the intention of a possible practical exploitation for very high-resolution diffractometry are presented.

Certification of diamond HPHT-plates for their use as substrates for CVD-synthesis

Incoming control of substates and gases is very important part of technological chain. The properties of diamond layer on substrates with different misorientation angles may differ considerably, therefore, determining the deviation of diamond growth plane (100) from the direction [100] is important. Also, in order to select diamond substrates that are most suitable for synthesis of pure quality crystal, it is required to determine the content of impurities in them and the roughness of their surface. In this research, HPHT-plates of one lot were examined using Fourier transform infrared spectrometry, high-resolution diffractometry and scanning probe microscopy in order to classify them according to the studied parameters. Further the classified diamond substrates were used to synthesize diamond layers. Ardis 300 was used for deposition of monocrystalline diamond; synthesis was carried out from a methane-hydrogen plasma with 3% methane at a temperature of 1100 °C, a pressure of 26.7 kPa and a power of 3800 W. The studies have shown that certification of diamond HPHT-plates allows to select substrates for the synthesis of pure quality monocrystalline diamonds.

Hetero-epitaxy of ε-Ga2O3 layers by MOCVD and ALD

Growth of gallium oxide thin films was carried out by Metalorganic Chemical Vapor Deposition (MOCVD) at different temperatures. Pure ε-phase epilayers of Ga2O3, with good morphology and structural properties, were obtained, for the first time with this technique, on sapphire at the temperature of 650°C. XRD analysis performed by high-resolution diffractometry confirmed the good crystallographic quality of the grown layers. At temperatures higher than 700°C the usual stable β-Ga2O3 phase was obtained. The ε-films were successfully deposited also on (0001)-oriented GaN and (111)- and (001)-oriented 3C–SiC templates, provided that the appropriate temperature was chosen. This indicates that the temperature, rather than substrate structure, is the growth parameter which decides what phase actually forms. The growth proceeds via coalescence of hexagonal islands and is favored when a substrate with an in-plane hexagonal arrangement of the atoms is employed. By applying Atomic Layer Deposition (ALD), epitaxial growth of the ε-phase was achieved at lower temperature, while the overall uniformity resulted improved, even on large sapphire substrates.

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.

Double bent crystal dispersive arrangement for high resolution diffractometry

In this paper some properties of the dispersive double-bent-crystal setting are described. Thanks to an easy manipulation with focusing of the monochromatic beam, high reflection probability of both bent crystals and very narrow (1-3 mm) obtained monochromatic beam such an arrangement could be attractive for an employment. We tested the properties of the double-bent-crystal setting of the bent Si(111) + bent Si(220) slabs on the diffractometer at the neutron wavelength of 0.163 nm for various curvatures of the Si(220) slabs. By using a standard polycrystalline sample of Fe it has been found that besides an excellent resolution the neutron current is sufficient even for powder diffraction experiments.

Experimental studies of dispersive double reflections excited in cylindrically bent perfect-crystal slabs at a constant neutron wavelength

Multiple Bragg reflections (MBRs), which can be realized in a bent perfect crystal (BPC) slab and are mutually in dispersive diffraction geometry, provide a monochromatic beam of excellent resolution. After identifying many MBR effects in a BPC Si crystal by using the method of θ–2θDscanning, we have turned our attention to the study of selected effects using the method of azimuthal rotation of the crystal lattice around the scattering vector of the primary reflection for a fixed chosen wavelength. In this paper, several azimuthal scans with the intention of possible practical exploitation for very high resolution diffractometry are presented.

Influence of mechanical defects on the crystal lattice of silicon

AbstractTo examine the impact of mechanical defects on the crystal lattice of silicon, controlled damage was applied to silicon wafers by a nanoindendation method. With increasing loads of 1, 5 and 50 N, the area with micro‐cracks and strain around the indents increases. The damage is characterised by high resolution diffractometry using a conventional X‐ray tube. Spatially resolved rocking curves were recorded across the indents and analysed with respect to full width at half maximum. From reciprocal space maps the amount of strain and tilt around the indents is separated. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Characterization of top-quality type IIa synthetic diamonds for new X-ray optics

We have performed a complex analysis of top-quality synthetic diamond HPHT type IIa single crystals in view of their potential application as X-ray optics elements, namely as free electron laser mirrors. We have employed X-ray topography and high-resolution diffractometry along with optical spectroscopy techniques for characterization of our synthetic diamonds.

Note: Construction of x-ray scattering and x-ray absorption fine structure beamline at the Pohang Light Source

A new hard x-ray beamline, 10B KIST-PAL beamline (BL10B), has been designed and constructed at the Pohang Light Source (PLS) in Korea. The beamline, operated by Pohang Accelerator Laboratory-Korean Institute of Science and Technology consortium, is dedicated to x-ray scattering (XRS) and x-ray absorption fine structure (XAFS) experiments. X rays with photon energies from 4.0 to 16.0 keV are delivered to the experimental station passing a collimating mirror, a fixed-exit double-crystal Si(111) monochromator, and a toroidal mirror. Basic experimental equipment for XAFS measurement, a high resolution diffractometry, an image plate detector system, and a hot stage have been prepared for the station. From our initial commissioning and performance testing of the beamline, it is observed that BL10B beamline can perform XRS and XAFS measurements successfully.

Calculating x-ray diffraction from multilayer lateral crystal structures with arbitrary shapes and composition profiles

A theory of x-ray diffraction in the vertical direction from a lateral crystal having an arbitrary shape and arbitrary depth-composition profile has been developed within the framework of the kinematic approximation. The results of a numerical simulation of diffraction patterns from such crystals in high-resolution triple-axis diffractometry scheme are presented.

Theory of X-ray diffraction on a lateral crystal with elastically bent lattice planes

A theory of X-ray diffraction on a lateral crystal with elastically bent lattice planes is developed within the framework of the kinematic approximation. Analytical solutions for coherent and diffuse scattering are obtained in application to high-resolution triple-axis diffractometry. The angular distribution of the intensity of coherent and diffuse scattering near a node of the reciprocal lattice are numerically simulated. It is shown that the pattern of X-ray diffraction from a crystal with a trapezoidal cross section and elastically bent lattice planes has a “butterfly” shape that was previously observed in experiment.

Effect of annealing under enhanced hydrostatic pressure on the microstructure of Cz–Si:H, He

The microstructure of Czochralski silicon (Cz–Si) co-implanted with H 2 + at E = 135 keV and He + at 75 keV to a total dose D H+He = 5 × 10 16 cm −2 (Si:H, He) and of reference Si:H prepared by H 2 + implantation to the same total dose ( E = 135 keV, D H = 5 × 10 16 cm −2), and annealed/treated at 723 and 923 K under hydrostatic argon pressure up to 1.1 GPa was investigated by X-ray high-resolution diffractometry and photoluminescence measurements. The treatment-induced effects depend both on the kind of implanted atoms (hydrogen + helium or hydrogen) and on the treatment parameters (temperature, pressure and treatment time). A qualitative explanation of the observed effects has been proposed.

Defect structure of InAlAs/InP layers

In x Al 1 − x As layers on InP substrate can be subjected to compressive as well as tensile strain due to lattice parameter differences induced by suitable alloy composition changes. The 2 μm thick In x Al 1 − x As (0.50 ≤ x ≤ 0.53) layers were grown on the (0 0 1) oriented InP substrates by molecular beam epitaxy (MBE). They were investigated using X-ray diffraction and chemical etching. X-ray studies were performed applying high-resolution diffractometry in the double (DAD) and triple (TAD) axis configuration. It was found that the In 0.53Al 0.47As/InP layer under compressive strain relaxes partially along two 〈1 1 0〉 directions. On the other hand, the In 0.50Al 0.50As/InP layers, being under tensile strain, consist of two sub-layers; the first one, adjacent to the substrate is pseudomorphic whereas the upper sub-layer is partially relaxed and the relaxation is anisotropic. The upper sub-layer is fully strained in the [1 1 0] direction while partially relaxed in the [−1 1 0] one.

Study of structural properties of InxGa1−x As/InyAl1−y As heterosystems on InP substrates

The structural properties of InxGa1−x As/InyAl1−y As samples on InP substrates are studied as functions of growth conditions by the method of high-resolution diffractometry. The results obtained and the photoluminescence spectroscopy data are used to optimize the technology of preparation of high-quality heterostructures with sharp interfaces. The parameters of the two-dimensional electron gas of such heterostructures measured at 77 and 300 K are comparable with the best world standards in this field, so these heterostructures may be used to manufacture transistors and integral amplifiers operating at the frequency 40 GHz and even higher.

Design and performance of a two-dimensional multi-wire neutron detector with a sensitive area of 50×50 cm 2 and a spatial resolution of ∼2×2 mm 2

One two-dimensional position-sensitive multi-wire gaseous detector for small-angle neutron scattering (SANS), reflectometry and high-resolution diffractometry has been developed at the GKSS research center in co-operation with DENEX GmbH. The counter with a sensitive area of 500×500 mm 2 has been designed to be used in the reflectometer REFSANS being built at the new high flux reactor FRM-II. Tests of the detector with an 55Fe-source, cold neutrons and γ-radiation are presented.

The effect of fluctuations in the lateral period of a multilayer grating on the scattering of hard synchrotron radiation

The effect of fluctuations in the lateral period of a nonideal multilayer grating on the scattering of hard synchrotron radiation (X-ray frequency range) was studied. Maps of the angular distribution of the coherent and diffuse scattering intensity in the reciprocal space are constructed. Theoretical diffraction curves calculated for a Ni/C multilayer grating are compared to the experimental data obtained by high-resolution triple-axis diffractometry. It is shown that good agreement between theory and experiment is observed for a fluctuation dispersion within 3% of the average lateral period of the grating.