High-resolution X-ray Diffractometry Research Articles

Defect structure of high-resistance CdTe:Cl single crystals and MoOx/CdTe:Cl/MoOx heterostructures according to the data of high-resolution X-ray diffractometry

Clorine doped CdTe single crystals (CdTe:Cl) were grown by the traveling heater method. MoO x /CdTe:Cl/MoO x films were deposited using the reactive magnetron sputtering technique. The defect structure of the obtained single crystals and heterostructures was investigated using high-resolution X-ray diffractometry. The optimized models of dislocation systems in the CdTe:Cl single crystals were constructed based on the Thompson tetrahedron. The distribution of the intensity of diffracted X-rays as a function of reciprocal space coordinates and rocking curves was analyzed using the kinematic theory of X-ray scattering in real crystals. The experimental and theoretically predicted values of the helical dislocation densities in the CdTe:Cl and MoO x /CdTe:Cl crystals with perfect and mosaic structures were compared. Two-fold increase in the dislocation concentration in the MoO x /CdTe:Cl heterostructures as a result of compression deformations of the CdTe:Cl crystal lattice was found. The ~0.1 μm thick transition deformed layer at the boundary between the MoO x film and CdTe:Cl single crystal significantly affects the electrical and spectroscopic properties of the obtained systems as the materials for γ-radiation detection.

Rare Earth Nitrate Hybrid Double Perovskites [Me4N]2[MLn(NO3)6] (M = Na-Cs; Ln = La-Gd, ex. Pm).

An exploration of the synthetic and structural phase space of rare earth hybrid double perovskites A2B'BX6 (A = organocation, B' = M+, B = M3+, X = molecular bridging anion) that include X = NO3- and B' = alkali metal is reported, complementing earlier studies of the [Me4N]2[KB(NO3)6] (B = Am, Cm, La-Nd, Sm-Lu, Y) (Me4N = (CH3)4N+) compounds. In the present efforts, the synthetic phase space of these systems is explored by varying the identity of the alkali metal ion at the B'-site. Herein, we report three new series of the form [Me4N]2[B'B(NO3)6] (B = La-Nd, Sm-Gd; B' = Na, Rb, Cs). The early members of the Na-series crystallize in the trigonal space group R3̅ from La to Nd where a phase transition occurs in the phase between 273 and 300 K, going from R3̅ to the high-symmetry, cubic space group Fm3̅m. The preceding trigonal members of the Na-series also undergo phase transitions to cubic symmetry at temperatures above 300 K, establishing a decreasing trend in the phase-transition temperature. The remainder of the Na-series, as well as the Rb- and Cs-series, all crystallize in Fm3̅m at 300 K. The temperature-dependent phase behavior of the synthesized phases is studied via variable-temperature spectroscopic methods and high-resolution powder X-ray diffractometry. All phases were characterized via single-crystal and powder X-ray diffraction and Fourier transform infrared (FT-IR) and Raman spectroscopic methods. These results demonstrate the versatility of the perovskite structure type to include rare earth ions, nitrate ions, and a suite of alkali metal ions and serve as a foundation for the design of functional rare earth hybrid double perovskite materials such as those possessing useful multiferroic, optical, and magnetic properties.

Synthesis and DC Electrical Conductivity of Nanocomposites Based on Poly(1-vinyl-1,2,4-triazole) and Thermoelectric Tellurium Nanoparticles.

In this work, the structural characteristics and DC electrical conductivity of firstly synthesized organic-inorganic nanocomposites of thermoelectric Te0 nanoparticles (1.4, 2.8, 4.3 wt%) and poly(1-vinyl-1,2,4-triazole) (PVT) were analyzed. The composites were characterized by high-resolution transmission electron microscopy, X-ray diffractometry, UV-Vis spectroscopy, and dynamic light scattering analysis. The study results showed that the nanocomposite nanoparticles distributed in the polymer matrix had a shape close to spherical and an average size of 4-18 nm. The average size of the nanoparticles was determined using the Brus model relation. The optical band gap applied in the model was determined on the basis of UV-Vis data by the Tauc method and the 10% absorption method. The values obtained varied between 2.9 and 5.1 nm. These values are in good agreement with the values of the nanoparticle size, which are typical for their fractions presented in the nanocomposite. The characteristic sizes of the nanoparticles in the fractions obtained from the Pesika size distribution data were 4.6, 4.9, and 5.0 nm for the nanocomposites with percentages of 1.4, 2.8, and 4.3%, respectively. The DC electrical conductivity of the nanocomposites was measured by a two-probe method in the temperature range of 25-80 °C. It was found that the formation of an inorganic nanophase in the PVT polymer as well as an increase in the average size of nanoparticles led to an increase in the DC conductivity over the entire temperature range. The results revealed that the DC electrical conductivity of nanocomposites with a Tellurium content of 2.8, 4.3 wt% at 80 °C becomes higher than the conventional boundary of 10-10 S/cm separating dielectrics and semiconductors.

Dislocation arrangements in 4H-SiC and their influence on the local crystal lattice properties.

Two wafers of one 4H-silicon carbide (4H-SiC) bulk crystal, one cut from a longitudinal position close to the crystal's seed and the other close to the cap, were characterized with synchrotron white-beam X-ray topography (SWXRT) in back-reflection and transmission geometry to investigate the dislocation formation and propagation during growth. For the first time, full wafer mappings were recorded in 00012 back-reflection geometry with a CCD camera system, providing an overview of the dislocation arrangement in terms of dislocation type, density and homogeneous distribution. Furthermore, by having similar resolution to conventional SWXRT photographic film, the method enables identification of individual dislocations, even single threading screw dislocations, which appear as white spots with a diameter in the range of 10 to 30 µm. Both investigated wafers showed a similar dislocation arrangement, suggesting a constant propagation of dislocations during crystal growth. A systematic investigation of crystal lattice strain and tilt at selected wafer areas with different dislocation arrangements was achieved with high-resolution X-ray diffractometry reciprocal-space map (RSM) measurements in the symmetric 0004 reflection. It was shown that the diffracted intensity distribution of the RSM for different dislocation arrangements depends on the locally predominant dislocation type and density. Moreover, the orientation of specific dislocation types along the RSM scanning direction has a strong influence on the local crystal lattice properties.

Lattice parameters of ScxAl1−xN layers grown on GaN(0001) by plasma-assisted molecular beam epitaxy

An accurate knowledge of lattice parameters of ScxAl1−xN is essential for understanding the elastic and piezoelectric properties of this compound as well as for the ability to engineer its strain state in heterostructures. Using high-resolution x-ray diffractometry, we determine the lattice parameters of 100-nm-thick undoped ScxAl1−xN layers grown on GaN(0001) templates by plasma-assisted molecular beam epitaxy. The Sc content x of the layers is measured independently by both x-ray photoelectron spectroscopy and energy-dispersive x-ray spectroscopy, and it ranges from 0 to 0.25. The in-plane lattice parameter of the layers linearly increases with increasing x, while their out-of-plane lattice parameter remains constant. Layers with x≈0.09 are found to be lattice matched to GaN, resulting in a smooth surface and a structural perfection equivalent to that of the GaN underlayer. In addition, a two-dimensional electron gas is induced at the ScxAl1−xN/GaN heterointerface, with the highest sheet electron density and mobility observed for lattice-matched conditions.

Dynamical theory of X-ray diffraction by crystals with different surface relief profiles.

A dynamical theory is developed of X-ray diffraction on a crystal with surface relief for the case of high-resolution triple-crystal X-ray diffractometry. Crystals with trapezoidal, sinusoidal and parabolic bar profile models are investigated in detail. Numerical simulations of the X-ray diffraction problem for concrete experimental conditions are performed. A simple new method to resolve the crystal relief reconstruction problem is proposed.

Surface Morphology and Spectroscopic Features of Homoepitaxial Diamond Films Prepared by MWPACVD at High CH4 Concentrations.

Single crystal diamond (SCD) is a promising material to satisfy emerging requirements of high-demand fields, such as microelectronics, beta batteries and wide-spectrum optical communication systems, due to its excellent optical characteristics, elevated breakdown voltage, high hardness and superior thermal conductivity. For such applications, it is essential to study the optically active defects in as-grown diamonds, namely three-dimensional defects (such as stacking faults and dislocations) and the inherent defects arising from the cultivation method. This paper reports the growth of SCD films on a commercial HPHT single-crystal diamond seed substrate using a 2.45 GHz microwave plasma-assisted chemical vapor deposition (MWPACVD) technique by varying the methane (CH4) gas concentration from 6 to 12%, keeping the other parameters constant. The influence of the CH4 concentration on the properties, such as structural quality, morphology and thickness, of the highly oriented SCD films in the crystalline plane (004) was investigated and compared with those on the diamond substrate surface. The SCD film thickness is dependent on the CH4 concentration, and a high growth rate of up to 27 µm/h can be reached. Raman spectroscopy, high-resolution X-ray diffractometry (HRXRD), scanning electron microscopy (SEM), surface profilometry and optical microscopic analyses showed that the produced homoepitaxial SCD films are of good quality with few macroscopic defects.

The Effect of Ne+ Ion Implantation on the Crystal, Magnetic, and Domain Structures of Yttrium Iron Garnet Films

The mechanism of the influence of crystal inhomogeneities on the magnetic and domain microstructures of functional materials based on yttrium iron garnet heterostructures is an important subject of investigation due to the aim to predict parameters for manufacturingpurposes. A study of the structural and magnetic characteristics of a set of yttrium iron garnet films grown on gadolinium–gallium garnet substrate is presented. High-resolution X-ray diffractometry, Mössbauer spectroscopy, MFM, as well as ion implantation simulation and X-ray diffraction simulation were used together to determine the features of the effect of Ne+ ion implantation with different dose rates on the samples. The simulation of ion implantation with E = 82 keV showed energy loss profiles of Ne ions with subsequent defect formation up to amorphization of near-surface layers at high doses. Implantation creates two magnetically non-equivalent types of tetrahedrally located Fe3+ ions, which leads to a rotation of the total magnetic moment relative to the film surface and a change in the width of the magnetic domain stripes.

Shape modulation due to sub-surface damage difference on N-type 4H–SiC wafer during lapping and polishing

The technology enhancement of obtaining 4H–SiC wafers with a concave Si face shape has improved the performance of GaN-on-SiC. For manufacturers, the wafer shape has a tremendous impact on the deposited films quality by increasing defects generation or causing undesirable strain. Therefore, it is crucial to control the wafer shape and explore the mechanism. This study recorded the wafer shape evolution by flatness tester during the machining process of lapping, mechanical polishing (MP), and chemical mechanical polishing (CMP). The varying shapes of SiC wafers are due to surface damage and intrinsic stress caused by the early lapping process, but the intrinsic stress is dominant. The measurement results show that double side MP and single side CMP make the wafer more convex and concave. It indicates that the residual surface stress is involved in shape formation. Perfect symmetrical shape between (0001) Si face and (000 1‾) C face suggests that there is indeed bending stress within the wafer. In this study, atomic force microscopy (AFM), high-resolution X-ray diffractometry (HRXRD), and scanning electron microscopy (SEM) was used to investigate the surface damage between SiC polar faces. According to the results, the damage to the Si face is more severe than that to the C face after double-sided mechanical polishing, leading to the wafer becoming more convex.

Slow Phase Transition-Induced Scan Rate Dependence of Spin Crossover in a Two-Dimensional Supramolecular Fe(III) Complex

Slow Phase Transition-Induced Scan Rate Dependence of Spin Crossover in a Two-Dimensional Supramolecular Fe(III) Complex

Strain-balanced InAs/GaSb superlattices used for the detection of VLWIR radiation

This work reports on the impact of defects on the parameters of type II InAs/GaSb superlattices (SLs) and photoconductors (PCs) from the very long wavelength infrared region. SLs were grown by means of molecular beam epitaxy and characterised using microscopes, high-resolution X-ray diffractometry (HRXRD) and low-temperature photoluminescence (LT-PL). PCs were investigated using Fourier-transform infrared spectroscopy and a current–voltage measurements. The basic technological parameters were optimised using 30-period SLs. Tests on the growth temperature showed that different defect types dominated in SL samples of different thicknesses. The diffuse scattering in reciprocal space maps (RSMs) taken for 200-period SLs was the mirror image of that for 30-period SLs. Scanning electron microscope (SEM) images of 200 period SLs revealed three types of defects: holes, slits and others not belonging to the first two groups. Slits were the predominant type. The diameter of the defects determined by SEM and HRXRD was about 2.5 μm. The cross section along the defects was made using focus-ion beam technique. The investigations using high-resolution transmission electron microscopy revealed the origins of the defects: holes were formed at the SL/buffer interface and propagated throughout entire SL, while slits were created in the volume of the SL without disturbing the surrounding crystal lattice. The lowest defect density was found for an SL grown at 425 °C. The highest overall crystal quality, measured using an HRXRD rocking curve, was obtained for an SL deposited at 405 °C, while the highest optical quality was determined for an SL at 445 °C by means of LT-PL. The best parameters were achieved for PCs grown at two lower temperatures. The difference in the effective bandgaps of the PCs made it difficult to determine the optimal value of the growth temperature. The effective bandgap for three PCs was determined based on the spectral dependences of the photoresponse measured at 20 K. Activation energies for high (150–300 K) and low (<50 K) temperature ranges were estimated from R(1000/T) dependence.

Structural Properties of Superlattices {LTG-GaAs/GaAs : Si} on GaAs (100) and (111)A Substrates

The proposed new structure for photoconductive antennas is a multilayer epitaxial film grown on a GaAs (111) A substrate and consisting of alternating layers of undoped GaAs grown at low temperature (LTG-GaAs) and GaAs layers formed in the standard high-temperature regime and doped with silicon (GaAs : Si). The ratio of As4 and Ga fluxes (γ) was chosen such that the GaAs : Si layers hadp-type conductivity. LTG-GaAs layers were grown at an increased γ value. A similar structure was grown on a (100) substrate as a reference sample. Phase composition was investigated using high-resolution X-ray diffractometry, surface relief — by mean of atomic force microscopy and distribution of Si impurity over thickness — using secondary ion mass spectrometry.

Influence of rapid thermal annealing on the distribution of nitrogen atoms in GaAsN/GaAs

The article investigates the effect of rapid thermal annealing of ternary GaAs1-xNx/GaAs solid solutions on the distribution of nitrogen atoms in the crystal lattice. The samples are studied by photoluminescence spectroscopy and high-resolution X-ray diffractometry. Due to the size and electronegativity mismatch of nitrogen and arsenic atoms, nitrogen is incorporated unevenly into the GaAs crystal lattice. Options of the nitrogen atoms arrangement in the GaAs crystal lattice before and after rapid thermal annealing are shown. Keywords: dilute nitrides, heterostructures, molecular-beam epitaxy, GaAs, nitrogen.

Application of High-Resolution X-ray Diffractometry in Measurements of Residual Stress and Strain Rate on Deformed Quartz from Malanjkhand Copper Deposit, India

Application of High-Resolution X-ray Diffractometry in Measurements of Residual Stress and Strain Rate on Deformed Quartz from Malanjkhand Copper Deposit, India

MICROBIAL SYNTHESIS OF SILVER NANOPARTICLES USING STREPTOMYCES SP. PG12 AND THEIR CHARACTERIZATION, ANTIMICROBIAL ACTIVITY AND CYTOTOXICITY ASSESSMENT AGAINST HUMAN LUNG (A549) AND BREAST (MCF-7) CANCER CELL LINES

Objective: Synthesis of silver nanoparticles using Streptomyces sp. PG12 and their characterization, antimicrobial activity and cytotoxicity against A549 and MCF-7 cancer cell lines. Methods: The silver nanoparticles were subjected to UV-Vis. spectroscopy, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM/EDS), high-resolution transmission electron microscopy (HR-TEM), zeta potential, and X-ray diffractometry (XRD) analyses. Further, the antimicrobial potential was determined by using the agar well diffusion method and cytotoxicity was determined with the help of cell viability (MTT) assay and reactive oxygen species (ROS) assay. Results: The initial indication of silver nanoparticles synthesis was noticed by the colour change in the reaction mixture and the absorption maximum at 421 nm in UV-Vis. analysis; whereas, the FTIR analysis displayed the biological functional groups responsible for the capping and stabilization of silver nanoparticles. SEM and TEM micrographs revealed the surface morphology, spherical shape, and smallest particle size as 18.91 nm. The EDS and XRD patterns confirmed the involvement of various elements during the synthesis of silver nanoparticles and the crystalline, face-centered cubic nature, respectively. The silver nanoparticles displayed considerable antimicrobial activity against human pathogens even at low MIC and MBC concentrations and exhibited increased anticancer activity against A549 and MCF-7 cell lines, where the ability of silver nanoparticles to significantly restrict the growth of tumour cells was observed at IC50 values of 69.04µg/ml and 138.30µg/ml, respectively. Conclusion: Streptomyces sp. PG12 synthesized silver nanoparticles show significant anticancer activity against A549 and MCF-7 cell lines.

The Domain and Microstructure of Resin-Bonded Magnets.

This paper presents domain and structure studies of bonded magnets made from nanocrystalline Nd-(Fe, Co)-B powder. The structure studies were investigated using scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), Mössbauer spectroscopy and X-ray diffractometry. On the basis of performed qualitative and quantitative phase composition studies, it was found that investigated alloy was mainly composed of Nd2(Fe-Co)14B hard magnetic phase (98 vol%) and a small amount of Nd1.1Fe4B4 paramagnetic phase (2 vol%). The best fit of grain size distribution was achieved for the lognormal function. The mean grain size determined from transmission electron microscopy (TEM) images on the basis of grain size distribution and diffraction pattern using the Bragg equation was about ≈130 nm. HRTEM images showed that over-stoichiometric Nd was mainly distributed on the grain boundaries as a thin amorphous border of 2 nm in width. The domain structure was investigated using a scanning electron microscope and metallographic light microscope, respectively, by Bitter and Kerr methods, and by magnetic force microscopy. Domain structure studies revealed that the observed domain structure had a labyrinth shape, which is typically observed in magnets, where strong exchange interactions between grains are present. The analysis of the domain structure in different states of magnetization revealed the dynamics of the reversal magnetization process.

Investigations on Crystalline Perfection, Raman Spectra and Optical Characteristics of Transition Metal (Ru) Co-Doped Mg:LiNbO3 Single Crystals.

Congruent lithium niobate single crystals with a Ru:Mg co-dopant have been successfully grown using the Czochralski technique from the melt containing 0.02 mol % Ru with Mg of two varied concentrations (4.0 and 6.0 mol %). The effects of Ru and Mg co-doping on the crystalline quality were determined by high-resolution X-ray diffractometry, which confirmed that the crystalline quality is good and that the dopants are statistically distributed in the crystal. The Raman scattering analysis shows no change in the lattice vibration except a slight change in the peak width and intensity due to more asymmetry in the molecular charge, which leads to enhancement of the polarizability. The optical transmission spectra indicate that both the crystals have high optical transparency in the visible region, with a shift of the absorption edge toward shorter wavelengths, as compared to un-doped LN. The weak absorption band observed below 400 nm is attributed to Ru ions. The influence of co-doping in the electronic band gap energies is calculated by the Tauc relation. The refractive index is measured by using a prism coupler at two wavelengths (532 and 1064 nm). The calculated absorption coefficients and direct and indirect band gap energies for both the samples are found to be nearly the same within experimental error. A decrease in the birefringence is observed for the Ru:Mg(6 mol %) doped sample. The observed slight reduction in refractive indices with Ru:Mg co-doping is consistent with a rise in band gap energy, which is related to the change in absorption edge to the lower wavelength. The second harmonic generation (SHG) efficiency is measured by the Kurtz and Perry powder method, and a decrease in SHG efficiency for Ru:Mg(6 mol %) is observed.

Structural defects in MBE-grown CdTe-basing heterojunctions designed for photovoltaic applications

Structural defects in the p-ZnTe/i-CdTe/n-CdTe single-crystalline heterojunctions designed for photovoltaic applications have been investigated by transmission electron microscopy (TEM) and deep-level transient spectroscopy (DLTS). Lattice parameters and misfit strain in the undoped cadmium telluride (CdTe) absorber layers of the heterojunctions, grown by the molecular-beam epitaxy technique on two different substrates, GaAs and CdTe, have been determined with high-resolution x-ray diffractometry. A dense network of misfit dislocations at the lattice-mismatched CdTe/GaAs and ZnTe/CdTe interfaces and numerous threading dislocations and stacking faults have been shown by the cross-sectional TEM imaging of the heterojunctions. The DLTS measurements revealed five deep-level traps in the heterojunctions grown on GaAs and only three of them in the heterojunctions grown on CdTe. Four of the traps have been attributed to the electronic states of extended defects, presumably dislocations, on the grounds of their logarithmic capture kinetics of charge carriers. Two of these traps, displaying the largest values of their capture cross-section and the properties characteristic of bandlike electronic states, have been ascribed to the core states of dislocations. It is argued that they are most likely responsible for decreased lifetime of photo-excited carriers resulting in a low energy conversion efficiency of solar cells based on similarly grown heterojunctions.

Combined role of SiC whiskers and graphene nano-platelets on the microstructure of spark plasma sintered ZrB2 ceramics

This research explores the sintering behavior and microstructure of ZrB2-based materials containing graphene nano-platelets (GNPs) and SiC whiskers (SiCw). Spark plasma sintering (SPS) process at 1900 °C was implemented to sinter the specimen, leading to a composite with 100% relative density. High-resolution transmission electron microscopy (HRTEM), field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), field emission-electron probe microanalyzer (FE-EPMA), and high-resolution X-ray diffractometry (HRXRD) were employed to study the SPSed sample, along with the thermodynamics predictions. According to the HRXRD result and microstructural observations, the sintering process was non-reactive, which was endorsed with the XPS analysis. Furthermore, graphene presented a beneficial role for eradicating the oxide impurities in the sample during the sintering. Such oxide impurities were reduced to the original phases of SiC and ZrB2, contributing to porosity removal. Nanostructural investigations revealed the formation of ultrathin amorphous interfaces (~10 nm) between ZrB2/graphene phases, disordered atomic planes in graphene platelets, and dislocations in ZrB2 grains. One reason for generating crystalline defects in the microstructure was found out to be the mismatches amongst the elastic properties of the available compounds in the system.

Prepration and Properties of Blue Tungsten Oxide Nanopowders by High Energy Ball-Mill

The purpose of this study is to prepare WO3 nanopowders by high-energy milling in mixture gas (7 % H2+Ar) with various milling times (10, 30, and 60 min). The phase transformation, particle size and light absorption properties of WO3 nanopowders during reduction via high-energy milling are studied. It is found that the particle size of the WO3 decreases from about 30 μm to 20 nm, and the grain size of WO3 decreases rapidly with increasing milling time. Furthermore, the surface of the particles due to the pulverization process is observed to change to an amorphous structure. UV/Vis spectrophotometry shows that WO3 powder with increasing milling times (10, 30, 60 min) effectively extends the light absorption properties to the visible region. WO3 powder changes from yellow to gray and can be seen as a phenomenon in which the progress of the color changes to blue. The characterization of WO3 is performed by high resolution X-ray diffractometry, Field emission scanning electron microscopy, Transmission electron microscopy, UV/Vis spectrophotometry and Particle size analysis.