High-resolution X-ray Diffraction Techniques Research Articles

Solid and Liquid State Dewetting of Thin Silicon Films Sandwiched between Two Silicon Carbide Substrates

Silicon carbide (SiC) is a very promising material for power electronics thanks to its wide band gap and high thermal conductivity. Stacking of SiC substrates of different crystalline quality and/or doping levels through wafer bonding is of particular interest for applications. Although a direct SiC/SiC bonding may result in an unstable interface, a layer of intermediate material playing a role of a “glue” can be sandwiched between the SiC substrates to ensure their good attachment. However, the processing of the power electronics devices at a high temperature may degrade the properties of this material which evolution under high temperature annealing must be studied in advance.In this work, we exploited the possibility to use silicon (Si) as a bonding material. We studied the structure evolution of a nanometer-thick polycrystalline Si layer sandwiched between two monocrystalline SiC substrates with a high temperature annealing. We focused our attention on understanding the impact of as-bonded Si layer thickness and the temperature of annealing on the eventual Si layer morphology. Tests were conducted for Si films of as-bonded thickness of 8 nm, 20 nm and 40 nm at temperatures ranging from 950°C to 1400°C, i.e. below Si melting temperature of 1414°C, and above it up to 1700°C. The experiments were realized using transmission electron microscopy (TEM), scanning electron microscopy (SEM) and high-resolution X-ray diffraction techniques. Cross-sectional TEM images were used to describe the structure and morphology of the interface. SEM was used to observe the inner surface of one of the SiC substrates once the other was removed by a cleavage. X-ray measurements were carried out to determine Si film thickness and texture as well as the strain in Si and SiC.We show that annealing at temperatures ranging from 950°C to 1400°C results in pitting, i.e. creation of voids, at the Si/SiC interfaces which are observed for any studied as-bonded thickness of a Si layer. We attribute this effect to a solid state dewetting of Si from SiC. This dewetting effect evolves into complete piercing of the silicon film and formation of cylindrical voids within the Si layer which grow in diameter with annealing temperature. We also observe a thickening of the silicon layer. The driving force for a solid state dewetting will be discussed in terms of SiC/Si interface energy, vacancies precipitation and Si atoms diffusion.When annealed to relatively higher temperatures allowing for Si melting followed by its solidification, we put into evidence the formation of step bunching on the internal surfaces of both SiC substrates. Regarding Si, it is concentrated along the SiC steps. The mechanism of the reconstruction of SiC internal surfaces resulting in the creation of step bunching will be discussed in relation to Si liquid state dewetting, carbon atoms dissolution, recondensation and migration within liquid Si.The effect of as-bonded silicon film thickness on the Si dewetting process is not pronounced after annealing at 950°C: all samples contain pits of a similar size and density. When the annealing temperature is slightly increased above 1000°C, the pits in the Si films of a lower initial thickness transform into cylindrical voids piercing the layers. The thicker layers contain both pits and cylindrical voids. At a high enough temperature of 1400°C only cylindrical voids were observed in all samples. The thicker layers present the lowest densities of voids.For the annealing at temperatures higher than 1400°C, the as-bonded thickness of a Si layer had a direct impact on the height of the steps formed on the internal surfaces of the SiC substrates. The eventual steps were higher the thicker the Si layer was used for bonding.The role of the diffusion and interaction of Si and C atoms and vacancies during annealing will be discussed in relation to the dynamics of solid and liquid state Si dewetting, size and density of pits and cylindrical voids and eventual Si layer morphology.Figure 1, on the left, SEM images showing the evolution of Si solid state dewetting with annealing temperature, from pitting to the formation of cylindrical voids. On the right, SEM and cross-sectional TEM images showing the step bunching on the SiC internal surfaces and the Si accumulation at the steps obtained after Si liquid state dewetting. Figure 1

Core shell heterojunction interface in green synthesized Sm3+ ions doped ZnO nano-particles to promote the charge separation for efficient photocatalytic applications

In this work, we report core-shell heterojunction of Sm3+ ions doped ZnO nanoparticles (NPs) by green synthesis technique and their photocatalytic activity for rapid degradation of methyl green dye molecules under UV light irradiation. High-resolution X-ray diffraction and high-resolution transmission electron microscope characterization techniques were employed to investigate structural and morphological studies. It is found that, the crystallite size of NPs is decreased with increasing Sm3+ ions concentration in NPs since Sm3+ ions are inhibiting the further growth of NPs. In addition, Sm3+: ZnO NPs catalyst shows irregular core shell heterojunction ensuing in the augmentation of a charge partition. Following that, the elemental compositional studies of Sm3+: ZnO NPs were estimated by energy dispersive spectroscopy. XPS imaging is also done in this work to get chemical mapping and the results suggested that the peaks are related to the Sm3+ ions in the ZnO lattice, which confirms the appropriate incorporation of Sm3+ into the ZnO. The optical energy band gap of NPs was estimated using diffuse reflectance spectroscopy. Excitation spectrum of Sm3+: ZnO NPs tinted the typical f-f transitions of Sm3+ ions. Photoluminescence emission shows the e− /h+ pair recombination rate reduced with increasing wt% of dopant Sm3+ ions in NPs. 10 wt% Sm3+: ZnO NPs showed the optimum photodegradation efficiency towards methyl green dye under the irradiation of UV light for 50 min. The dye degradation rate of Sm3+: ZnO NPs was 91% which is 26% higher than that of pristine ZnO NPs. Furthermore, the catalyst retains its original efficiency after fifth cycle.

X-Rays Diffraction Study of InGaN/GaN Heterostructures Grown by MOCVD Technique at Different Temperatures

Indium gallium nitride / gallium nitride (InGaN/GaN) heterostructures were grown by using metal organic vapor deposition technique with four different growth temperatures (740 °C, 760 °C, 780 °C, and 800 °C). The structural properties and crystalline quality were investigated using high resolution X-ray diffraction (HRXRD) technique. XRD ω-2θ scan mode at GaN (002) diffraction plane was performed to assess the film’s quality. Through the simulation fitting, the indium composition and the thickness of the thin films were obtained. From the observation, an increase in the growth temperature resulted in higher intensity and smaller full-width at half maximum value of the InGaN (002) diffraction peak, which indicated improvement to the crystalline quality of the InGaN/GaN heterostructure. Moreover, the indium composition of the InGaN epilayer was found to decrease with an increase of the growth temperature due to the thermal decomposition of In-N bond and its re-evaporation from the growing surfaces.

Spatiotemporal Changes in Atomic and Molecular Architecture of Mineralized Bone under Pathogenic Conditions

Mechanisms responsible for spatiotemporal changes in the atomic-molecular architecture of the human femur in intact and osteoarthritis-affected areas were studied using high-resolution X-ray diffraction and spectroscopic techniques. Comparison of the experimental data demonstrates strong deviations of core electron-binding energies, lattice constants of hydroxyapatite crystal cells, linear sizes of crystallites, and degrees of crystallinity for both intact and osteoarthritic areas. The quantitative values of these characteristics and their standard deviations in each area are measured and presented. A systematic analysis of the site-dependent deviations was carried out within the framework of the 3D superlattice model. It is argued that the main mechanism responsible for the deviations arises primarily as a result of carbonization and catalytic reactions at the mineral-cartilage interface. The impact of the mechanism is enhanced in the vicinities of the area of sclerosed bone, but not inside the area where mechanical loads are maximum. Restoration of the atomic-molecular architecture of mineralized bone in the sclerosis area is revealed. Statistical aspects of the spatiotemporal changes in mineralized bone under pathogenic conditions are discussed.

GaN/AlInN/AlN/Safir HEMT Yapılar için Mozaik Kusur ve AFM Çalışması

In this study, three samples of GaN/AlInN/AlN/Al2O3 high electron mobility (HEMT) structures are investigated with high resolution X-ray diffraction (HR-XRD) technique. Peak positions and peak broadenings are used in calculations, gained from rocking curves. Structural quality is determined from symmetric and asymmetric peak planes. Mosaic defects such as treadening dilocations (TDs), tilt and twist angles, lateral and vertical crystallite lengths are determined by using Williamson Hall (WH) method. In addition to these, surface morphology is also investigated by atomic force microscopy (AFM). It is noticed that crystal quality of epitaxial layers decrease in the order of samples C, B and A. Al compositions for samples A, B and C are found as %87.4, %86.6 and %86.4, respectively by using Vegard’s law.

Effect of Si-doped and undoped inter-layer transition time on the strain-compensated InGaAs/InAlAs QCL active region grown with MOVPE

In this study, we report the effect of the combination of Si-doped and undoped inter-layer transition time in the strain compensated In0.67Ga0.33As/In0.36Al0.64As quantum cascade laser (QCL) structure grown on InP substrate by Metal Organic Vapor Phase Epitaxy (MOVPE). In situ reflectance spectroscopy and high resolution X-ray diffraction (HRXRD) technique have been used for the analysis of growth steps and crystalline quality of QCL structures, respectively. In addition, since thickness accuracy is very important for QCLs, two different thickness calculation methods have been used in the Global Fit simulation program for detailed thickness accuracy of structures. As a result, optimum values for thickness accuracy have been obtained as 5 and 10 s between undoped and Si-doped layers, respectively, as verified by the two methods.

Performance Optimization of ZnO Nanorods ETL Based Hybrid Perovskite Solar Cells With Different Seed Layers

This article discusses the direct effect of the seed layers on the growth of the ZnO nanorods (ZNRs) and related photovoltaic parameters of the hybrid perovskite solar cell (PSC). Four different types of ZnO seed layer samples are prepared to analyze the growth of ZNRs over the respective seed layers. Various device parameters for the respective PSCs made of different seed layers are investigated. The ZnO quantum dot-based seed layer shows the well-aligned, vertical, and uniform distribution of ZNRs and improves SC parameters over the other three samples. The ZnO seed layer deposited via drop cast methods results in less density, random, and nonuniform distribution of the ZNRs. The surface morphology, optical absorption, transmission, and crystalline structure were analyzed with high resolution scanning electron microscopy (HRSEM), TEM, UV-visible absorption, and X-ray diffraction (XRD) techniques. 10.69&#x0025; of power conversion efficiency with improved open-circuit voltage (<inline-formula> <tex-math notation="LaTeX">${V}_{OC}$ </tex-math></inline-formula>) of 1.01 V is achieved for device structure, fluorine doped tin oxide (FTO)/ZnO QDs seed layer/ZNRs/perovskite/poly[bis(4-phenyl)(2,5,6-trimethylphenyl)amine (PTAA)/gold (Au).

V-pits formation in InGaN/GaN: influence of threading dislocations and indium content

Two sets of InGaN/GaN MOVPE-grown samples were studied by high-resolution x-ray diffraction techniques together with statistical analysis of atomic force microscope images in order to determine the impact of In concentration and threading dislocations (TDs) density on the V-pit formation. It was shown that in our samples, the density of V-pits in the epilayer matched the TD density with a screw component in the substrate. Pure edge TDs do not affect the V-pit density. The In concentration influences the size of the V-pits, but not their density.

The Effect of Si (111) Substrate Surface Cleaning on Growth Rate and Crystal Quality of MOVPE Grown AlN

In this work, the effect of Si (111) substrate surface cleaning by RCA (Radio Corporation of America) method on growth rate and crystalline quality of epitaxially grown AlN thin films by MOVPE (Metal Organic Vapor Phase Epitaxy) technique is investigated. In situ reflectance system and high resolution X-ray diffraction (HRXRD) technique are used for the analysis of growth rate and crystal quality of epitaxial AlN layers, respectively. Also, The Raman measurement is done to show the effect of the RCA cleaning procedure on the position of the peaks that occurred in the Raman spectra. The results have shown that the surface cleaning of Si (111) substrate by the RCA method removes the oxide layer formed on the surface, also helps to decrease the parasitic reactions and increases the adatom efficiency, results in an increased growth rate of the AlN layer. Besides, surface cleaning of Si (111) substrate by the RCA method has reduced the FWHM value ~5% for ω-2θ scan and ~60% for ω scan of AlN epilayer, indicating an improvement in crystal quality.

Investigation on synthesis, growth, Hirshfeld surface and third order nonlinear optical properties of Urea-Succinic Acid single crystal: A potential candidate for self-defocusing lasing application

A wide optical band gap Urea-Succinic Acid (USA) single crystal was grown by using slow evaporation solution growth techniques. The structural analysis of grown ingot has been assessed by single crystal X-ray diffraction and high resolution X-ray diffraction techniques respectively. The various types of intermolecular interaction for the grown single crystal were visualized by Hirshfeld surface analysis using Crystal Explorer software. The photoluminescence study of grown crystal suggests major emission occurs at 460 nm which corresponds to blue light in EM spectrum. From time resolved Photoluminescence, the bi-exponential curve of major emission photons shows a defect energy state in the band structure of the grown single crystal. The self-defocusing lasing action of the grown single crystal has been studied through Nd-YAG nanosecond laser with a 532 nm wavelength. The nonlinear optical variables like nonlinear refractive index (n2) and nonlinear absorption coefficient (β) of titled compound single crystal are evaluated from Z-scan measurement. The laser damage threshold of USA single crystal is found to be 1.69 GW/cm2 for a single shot.

Spatially Resolved Operando Synchrotron-Based X-Ray Diffraction Measurements of Ni-Rich Cathodes for Li-Ion Batteries

Understanding the performance of commercially relevant cathode materials for lithium-ion (Li-ion) batteries is vital to realize the potential of high-capacity materials for automotive applications. Of particular interest is the spatial variation of crystallographic behavior across (what can be) highly inhomogeneous electrodes. In this work, a high-resolution X-ray diffraction technique was used to obtain operando transmission measurements of Li-ion pouch cells to measure the spatial variances in the cell during electrochemical cycling. Through spatially resolved investigations of the crystallographic structures, the distribution of states of charge has been elucidated. A larger portion of the charging is accounted for by the central parts, with the edges and corners delithiating to a lesser extent for a given average electrode voltage. The cells were cycled to different upper cutoff voltages (4.2 and 4.3 V vs. graphite) and C-rates (0.5, 1, and 3C) to study the effect on the structure of the NMC811 cathode. By combining this rapid data collection method with a detailed Rietveld refinement of degraded NMC811, the spatial dependence of the degradation caused by long-term cycling (900 cycles) has also been shown. The variance shown in the pristine measurements is exaggerated in the aged cells with the edges and corners offering an even lower percentage of the charge. Measurements collected at the very edge of the cell have also highlighted the importance of electrode alignment, with a misalignment of less than 0.5 mm leading to significantly reduced electrochemical activity in that area.

Thermal effects on stability of hierarchical microstructure in medium- and high-entropy alloys

In this study, we explored the elevated-temperature stability of the medium- and high-entropy alloys for metallurgical processes and applications. Because the extraordinary mechanical properties of medium- and high-entropy alloys are strongly correlated with their distinct microstructural developments, we applied the latest in-situ high-resolution synchrotron X-ray diffraction technique to trace the real-time microstructural evolutions of these alloys during annealing and recrystallization processes. We resolved the convolution information for crystallite size, dislocation characteristics, and planar fault probabilities to examine the microstructural stability and differences between CrFeNi and CoCrFeMnNi alloys. The most significant difference is the grain coarsening of the two alloys subjected to heating from 600 °C to 800 °C. Specifically, the dominant dislocation type of medium- and high-entropy alloys switched from screw to mixed screw-edge after 700 °C. Meanwhile, the screening of dislocation-induced strain-fields of both alloys became stronger during annealing. Our major findings will be useful for the welding and additive manufacturing medium- and high-entropy alloys.

Hierarchical ZnO/CuO nanostructures for room temperature detection of carbon dioxide

Hierarchical ZnO/CuO nanorods were grown on RF sputtered ZnO seed layer via the hydrothermal method and their characteristics are analyzed by high resolution scanning electron microscope (HRSEM) and X-ray diffraction (XRD) techniques to confirm the elemental composition, crystal structure, and morphology of the sensing material. The sensing performance of the carbon dioxide sensor was evaluated at room temperature under the various concentration of carbon dioxide gas from 150 ppm to 1000 ppm. The result obtained shows that the sensor yields a high response of 9.7 % for 1000 ppm of carbon dioxide gas with fast response and recovery time varied in the range of 1–4 min. The above results indicate the accomplishment of room temperature sensing with good reversibility and repeatability compared to conventional previously reported high temperature carbon dioxide sensors.

Monomode Optical Waveguide Achieved by Lattice Damage in Yttria-Stabilized Zirconia Crystal Induced from Energetic Oxygen Irradiation

With valuable physicochemical properties, yttria-stabilized zirconia crystal has promising advantages in optical applications. In this paper, the waveguide effect is observed in yttria-stabilized zirconia crystal irradiated by energetic oxygen ions. The waveguide properties and the field intensity are analyzed using prism and end-face coupling method arrangements, and the results show that monomode is found in the near-surface region and the light beam can be well confined in the waveguide structure, which shows refractive index distribution of the barrier-wall and enhanced-well type. The lattice damage induced by irradiation is investigated by the Rutherford backscattering/channeling experiment and high-resolution X-ray diffraction techniques. The simulation results are in good agreement with the experimental data.

Mosaic Defects of AlN Buffer Layers in GaN/AlN/4H-SiC Epitaxial Structure

Structural properties of AlN buffer layers, grown by Metal Organic Chemical Vapor Deposition (MOCVD) on 4H-SiC substrate with thicknesses of 61.34, 116.88, 129.46 and 131.50 nm, are investigated by High Resolution X-Ray Diffraction (HR-XRD) technique. Interfacial roughness of AlN buffer layer was determined by XRR technique. The interface roughness value of 131.50 nm thick sample is determined as 0.50 nm. Mosaic defects, tilt angle, vertical and lateral coherence lengths are characterized by HR-XRD technique. The edge and screw dislocations of the 131.50 nm thick sample are found as 2.98x1010 and 8.86x108 cm-2 respectively. The results indicate that 131.50 nm thick AlN buffer layer should be used in order to gain high performance in optoelectronic terms in this study. Thus, optimization of AlN buffer layer thickness is extremely important in device performance.

Enhanced Photodetection in Glancing Angle Deposited One-Dimensional In₂O₃ Nanorod Array.

Glancing angle deposition (GLAD) oriented electron beam (e-beam) evaporation process has been employed to develop 1D In₂O₃ nanorod array over n-Si substrate. The morphology of as-deposited In₂O₃ thin film (∼70 nm) and GLAD 1D In₂O₃ nanorod array (∼400 nm) were explored using field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS) and high resolution transmission electron microscopy (HRTEM) analysis. The structural analysis were perceived by high-resolution X-ray diffraction (HRXRD) and atomic force microscopy (AFM) techniques. The clampdown of ∼4.4 fold photoluminescence (PL) emission intensity was observed for In₂O₃ nanorod array. Metallization were done to measure the current (I)-voltage (V) characteristics for n-Si/In₂O₃ thin film and n-Si/In₂O₃ nanorod devices. The In₂O₃ nanorod device displayed ∼2.2 fold enhancement in current conduction at -4.6 V and an averagely ∼1.1 fold augmentation in photosensitivity were also observed. The photoresponsivity of ∼28 μA/W, maximum specific detectivity of ∼9.9×107 Jones and low NEP of ∼4.5×10-12 W/√Hz was achieved for the In₂O₃ nanorod-based photodetectors. The maximum ∼2.5 fold high detectivity and ∼2.4 fold low noise equivalent power (NEP) were perceived for the 1D In₂O₃ nanorod array detector as compared to the bare In₂O₃ thin film detector.

High performance X-band electromagnetic shields based on methyl-orange assisted polyaniline-silver core-shell nanocomposites

ABSTRACT Present communication explores the remarkably high shielding effectiveness of about 70 dB, exhibited by advanced core-shell-type polyaniline-silver nanosheets (PAg) in X-band (4–12 GHz), synthesized from methyl-orange assisted chemical oxidative polymerization route. The high-resolution tunneling microscope reveals the formation of PAg nanogranules and nanosheets with different silver nitrate concentrations (0.3 M and 0.6 M, respectively). The enhanced shielding effectiveness of nanosheets compared to other samples is attributed quite sensitively to its high conducting value, which is predominantly determined by the concentration of silver nitrate used during synthesis. The structural characterizations using high-resolution X-ray diffraction technique reveals the enhanced crystallinity of PAg samples, which significantly contributes to the enhancement of their conductivities. The dc charge transport study in temperature range 77 K-300 K reveals that the PAg samples exhibit metallic behavior, whereas the polyaniline samples show semi-conducting nature. This can be ascribed to the presence of silver content in nanocomposites, which results in higher conductivities of the PAg samples. This study opens a new window for shielding of electromagnetic pollution by advanced core-shell morphologies at commercial scale.

Very thin (111) NiO epitaxial films grown on c-sapphire substrates by pulsed laser deposition technique

(111) NiO epitaxial layers are grown on c-sapphire substrates by pulsed laser deposition technique. Structural and morphological properties of the films are studied using in-plane as well as out-of-plane high resolution x-ray diffraction and atomic force microscopy techniques as functions of growth temperature, oxygen pressure and the pulses count of the laser. The study shows that continuous epitaxial films of thickness as low as 3 nm with high crystalline quality, smooth surface and interface morphology can be grown by this technique. The study also reveals the co-existence of 60°-rotated (111) triangular domains of NiO in the film. The study also evidences the presence of a very low density of 60° dislocations in these films. Density of screw and edge dislocations are also estimated to be quite low. It has been found that growth-temperature, oxygen partial pressure and the film thickness can influence differently the density of various dislocation types. These parameters are also found to affect significantly the strain developed in the films.

Influence of the cooling rate below Ms on the martensitic transformation in a low alloy medium-carbon steel

The influence of cooling rate below the martensite start temperature, Ms, on the kinetics of martensitic transformation in a medium carbon low alloy steel was determined using high resolution dilatometry, optical microscopy and X-ray diffraction techniques. A two-stage transformation was observed for slow cooling rates while at higher cooling rates, martensitic transformation occured through a single stage process. It is shown that the Koistinen–Marburger equation cannot adequately describe the observed two-stage transformation. A new equation is proposed in order to model the evolution of martensitic transformation by considering the influence of post Ms cooling rate. The method considers contributions from both, the initial austenite and the carbon enriched austenite. The underlying mechanisms are discussed and validated with experimental findings.

Non Destructive Evaluation of AlGaN/GaN HEMT structure by cathodoluminescence spectroscopy

We have investigated radiative defects in various component layers in an AlGaN/GaN HEMT structure by measuring Cathodoluminescence (CL) spectrum as a function of accelerating voltage. Low electron beam accelerating voltages (below 1 kV) CL spectra are used to get information about defects in the cap layer and the barrier layer. Samples with good quality GaN cap layer showed surface quantum well (SQW) transition in the CL spectrum. The cap layer thickness and its quality can be determined from the SQW emission energy and its integrated intensity. We show that low intensity electron beam provides information about the defects in the cap layer as well as barrier layer through the intensity and energy of the yellow luminescence peak. The observed changes in the CL intensity of the barrier layer towards the surface have been correlated to the formation of aluminium oxide, giving rise to higher concentration of deep acceptor defects probably related to the adsorbed oxygen on the uncapped AlGaN barrier layer samples. The results are supported by X-ray photoelectron spectroscopy (XPS), High resolution X-ray diffraction (HRXRD) and Secondary ion mass spectrometry (SIMS) techniques.