Peak Broadenings Research Articles

Identification of different WO3 modifications in thin films for photocatalytic applications by peak shape analysis in high temperature XRD diffractometry

Until now, the structural analysis of WO3 films has been insufficient. The similar peak positions of the possible crystalline phases make a precise differentiation difficult or even impossible. In particular, the presence of possible mixed phases is difficult to determine. However, the exact determination of the crystalline phases would be important for use as a photocatalyst, as these phases and also their mixtures may have an effect on the photocatalytic properties.The identification of the monoclinic (P21/n), orthorhombic (Pbcn) and triclinic (P1¯) components at room temperature seems to be of particular interest. By heating WO3 films before cooling them to room temperature, a broadening of the diffraction peaks was observed, which can be associated with phase transformations. By following these peak broadenings, individual phases of WO3 could be identified and the progression of mixed phases could be visualized. By avoiding a delamination process, which can occur at high temperatures, and an adapted heating strategy, it should be possible to identify different crystalline phases of WO3 films at room temperature after calcination.

Correlations Between XRD Peak Broadening and Elastic and Plastic Deformation for Mild Steel Sheets Under Tensile Loading

The polycrystalline nature of steel sheets plays a fundamental role in their plastic behavior during forming, especially under complex stresses, such as the deep drawing process. Heterogeneous microstructures cause variable internal stress levels, which strongly impact the material’s macroscopic mechanical properties. X-ray diffraction (XRD) technique can be applied to determine microscopic internal stresses by peaks broadening analysis, which can be related to the degree of cold work at the microscopic level. As deep drawing is a complex deformation mode, an important motivating factor to perform such a study is to find the correlation between anisotropy and XRD peak broadening through tensile deformation tests. Therefore, the initial mechanical state and different deformed states were analysed by in-situ XRD peak broadening under tensile tests in various directions in the rolling plane of mild steel sheet, for both the elastic and plastic deformation domains. The results showed that the XRD peak broadening gives accurate estimations of deformation degrees. In the elastic domain, under realistic assumptions, a relation between the relative variation of peak broadening and the applied stress σ, like Hooke’s law, was obtained by exploiting the linearity between the peak broadening and the elongation measured by the strain gauge. This formula may be used to deduce The Young’s modulus. Interesting empirical relations between peak broadenings, macro deformations and hardness have been also established for the studied sheet in the plastic deformation region. Moreover, XRD peak broadenings were able to characterize the anisotropy of deformation in the rolling plane of the sheet. They are like the anisotropy coefficients in indicating the expected behavior under complex processes such as deep drawing by using ordinary tensile tests.

Phase-Incremented Steady-State Free Precession as an Alternate Route to High-Resolution NMR.

Pulsed Fourier transform nuclear magnetic resonance (FT-NMR) has reigned supreme in high-resolution, high-field spectroscopy─particularly when targeting complex liquid-state samples involving multiple sharp peaks spread over large spectral bandwidths. It is known, however, that if spectral resolution is not a must, the FT-based approach is not necessarily the optimal route for maximizing NMR sensitivity: if T2 ≈ T1, as often found in solutions, Carr's steady-state free-precession (SSFP) approach can in principle provide a superior signal-to-noise ratio per √(acquisition_time) (SNRt). A rapid train of pulses will then lead to a transverse component that reaches up to 50% of the thermal equilibrium magnetization, provided that pulses are applied at repetition times TR ≪ T2, T1, and that a single suitable offset is involved. It is generally assumed that having to deal with multiple chemical shifts deprives SSFP from its advantages. The present study revisits this assumption by introducing an approach whereby arbitrarily short SSFP-derived free induction decays (FIDs) can deliver high-resolution spectra, without suffering from peak broadenings or phase distortions. To achieve discrimination among nearby frequencies, signals arising from a series of regularly phase-increased excitation pulses are collected. Given SSFP's amplitude and phase sensitivity to the spins' offset, this enables the resolution of sites according to their chemical shift position. In addition, the extreme fold-over associated with SSFP acquisitions is dealt with by a customized discrete FT of the interpulse time-domain signal. Solution-state 13C NMR spectra which compare well with FT-NMR data in terms of sensitivity, bandwidth, and resolution can then be obtained.

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.

Enhancing Chromatographic Performance of Immobilized Angiotensin II Type 1 Receptor by Strain-Promoted Alkyne Azide Cycloaddition through Genetically Encoded Unnatural Amino Acid.

During integration to the solid surface, the effects of tags introduced for bioorthogonal reactions on protein activity have received far less investigation. This represents the major challenge of improving the performance of the immobilized protein-based assays. Herein, the relationship between the fusion tags and their reaction efficiency in mediating the assay performance was realized by determining the chromatographic performance using genetically encoded azide-alkyne cycloaddition, and Halo- and SNAP-tagged bioorthogonal reactions for synthesizing immobilized angiotensin II type 1 receptor (AT1R). We demonstrated that immobilization with the incorporation of unnatural amino acid in the receptor minimizes the peak tailings and broadenings of irbesartan, fimasartan, losartan, and tasosartan, while attachment via large tags (SNAP and Halo) leads to serious asymmetry peaks. Upon the first immobilization, the association constants of the four drugs to AT1R appeared to be 1 order of magnitude greater than the other two attachments. Such enhancement is likely reasoned by the improved association rate constants and the relatively identical dissociation rates due to the small tag. While demonstrating improved chromatographic performance, the immobilized AT1R prepared by the genetically encoded azide-alkyne reaction was applied in analyzing Uncaria Schreber nom. cons. extract, which identified hynchophylline as a specific ligand binding to the receptor. As immobilized proteins move toward diverse assays, our findings provide an unprecedented insight into the relation between fusion tags and their reaction efficiency in mediating the assay performance, which is thus dedicated to the creation of a protein-functionalized surface for precisely determining the drug-protein interaction and discovering the specific partner of the protein.

Conversion of (NH4)2[ReF6] into ReO2 mixed phases: A thermal analysis study

The thermal behavior of (NH4)2[ReF6] was evaluated in an alumina crucible using simultaneous thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) in an argon atmosphere. The TGA of (NH4)2[ReF6] is characterized by a single step decomposition while the DSC exhibits two exothermic peaks. Powder X-ray diffraction (PXRD) analyses of the decomposition products show the presence of a mixed ReO2 phase. The formation of ReO2 is driven by the reaction of (NH4)2[ReF6] with Al2O3 at the grain boundary of the alumina crucible. XRD peak broadenings due to the combined effect of crystallite size and lattice strain were evaluated using both Scherrer and Williamson-Hall methods.

Straightforward route for terbium oxide powders: synthesis, morphology, and microstructural parameters

Abstract The goals of this study lie in the endeavour to synthesise terbium oxide powders, calculation of the average crystallite size, lattice parameter, lattice strain and dislocation density by using X-ray diffraction peak broadenings and, particularly, examination of the effects of precursor molarity on morphology, microstructural parameters and crystal imperfections. The X-ray diffraction patterns demonstrated that the powders had pure cubic bixbyite body-centred phase with high crystallinity. The crystallite size values varied between 21.05 and 31.45 nm depending on both precursor molarity and four different calculation methods, i.e. Debye–Scherrer, modified Debye–Scherrer, Williamson–Hall and Halder–Wagner methods. It was found that regardless of the calculation method, there was a positive relationship between the average crystallite size values and the precursor molarity, and it was concluded that the crystallinity was improved. The lattice strain values calculated by both the Williamson–Hall analysis integrated with the uniform deformation model and the Halder–Wagner methods showed that the tensile stress in the structure became more effective with increasing precursor molarity. The lattice strain values calculated using the Halder–Wagner method were approximately 10 times higher than those of the Williamson–Hall method because of reflections at low and mid angles in X-ray diffraction data. The dislocation density values calculated using the Williamson–Smallman method demonstrated that a decrease in crystal defects occurred with increasing molarity, that is, the crystallinity was enhanced. The presence of Tb–O bonds was proved by Fourier-transform infrared spectroscopy analysis showing that terbium carbonate powders were converted into terbium oxide by the calcination process. A nearly round morphology of produced terbium oxide powders were clearly shown in scanning electron microscopy and transmission electron microscopy images. Increasing positive tensile stress in the lattice increased the particle size and changed the powder morphology from agglomerated nearly round grains to rod-like bundles.

Crystallinity and grain distributions of fiber-formed nanostructure on tungsten surface with helium plasma exposure

Growth mechanisms of complex tungsten (W) fuzzy nanostructure on helium-plasma-irradiated W surface have been extensively studied since the discovery of the phenomenon in 2006. However, the growth process of complicated W nano-fibers from the atomistic and crystal structure standpoints is not well understood. In this study, the X-ray diffraction (XRD) and transmission electron microscopy (TEM) were performed to investigate complexity of nano-fibers as well as their crystallinity. Small-angle-incident XRD on the substrate with fuzz and He-defected bulk surface was used to determine grain distribution among contributions of different crystal orientation families, showing the difference in grain distribution of surface fuzz layer and the basing W bulk surface with helium defects compared with the distribution of pristine powder metallurgy W (PM-W). Peak shifts and broadenings of X-ray diffracted spectra with respect to pristine PM-W substrate and TEM observations were discussed in terms of crystallinity and He-bubbles induced strain. It is speculated that the grain distribution of the He-defected W with nano-fibers would be very similar to that of bulk α-phase W globally. Moreover, the scraped-off fuzz aggregate without basing plate makes it possible to conduct XRD using a thin glass capillary tube. The grain distribution of pure fuzz aggregate was found to be very similar to natural α-phase W with intensification of high grain orientation modes. The process of such high modes may bring morphological complexity to nano-fibers because grain boundaries play a role of turning surfaces along nano-fibers.

Layer Rotation-Angle-Dependent Excitonic Absorption in van der Waals Heterostructures Revealed by Electron Energy Loss Spectroscopy.

Heterostructures comprising van der Waals (vdW) stacked transition metal dichalcogenide (TMDC) monolayers are a fascinating class of two-dimensional (2D) materials. The presence of interlayer excitons, where the electron and the hole remain spatially separated in the two layers due to ultrafast charge transfer, is an intriguing feature of these heterostructures. The optoelectronic functionality of 2D heterostructure devices is critically dependent on the relative rotation angle of the layers. However, the role of the relative rotation angle of the constituent layers on intralayer absorption is not clear yet. Here, we investigate MoS2/WSe2 vdW heterostructures using monochromated low-loss electron energy loss (EEL) spectroscopy combined with aberration-corrected scanning transmission electron microscopy and report that momentum conservation is a critical factor in the intralayer absorption of TMDC vdW heterostructures. The evolution of the intralayer excitonic low-loss EEL spectroscopy peak broadenings as a function of the rotation angle reveals that the interlayer charge transfer rate can be about an order of magnitude faster in the aligned (or anti-aligned) case than in the misaligned cases. These results provide a deeper insight into the role of momentum conservation, one of the fundamental principles governing charge transfer dynamics in 2D vdW heterostructures.

Averaging the intensity of many-layered structures for accurate stacking-fault analysis using Rietveld refinement

Many technologically important synthetic and natural materials display stacking faults which lead to complex peak broadenings, asymmetries and shifts in their powder diffraction patterns. The patterns can be described using an enlarged unit cell (called a supercell) containing an explicit description of the layers. Since the supercell can contain hundreds of thousands of atoms with hundreds of thousands ofhklreflections, a Rietveld approach has been too computationally demanding for all but the simplest systems. This article describes the implementation of the speed-ups necessary to allow Rietveld refinement in the computer programTOPASVersion 6 (Bruker AXS, Karlsruhe, Germany). Techniques implemented include: a peaks buffer that allows hundreds of thousands ofhkl-dependent peak shapes to be automatically approximated by a few hundred peaks; an averaging process for hundreds of large supercells with minimum impact on computational time; a smoothing technique that allows for the use of small supercells which approximate supercells ten to 20 times larger; and efficient algorithms for stacking sequence generation. The result is Rietveld refinement of supercells operating at speeds several thousand times faster than traditional Rietveld refinements. This allows quantitative and simultaneous analysis of structure and microstructure in complex stacking-faulted samples.

Raman study of the quantum interference of multiple discrete states and a continuum of states in the phonon energy region of semiconductors: examples of p-type Ga0.5In0.5P films

Although the Fano quantum interference of one longitudinal optical (LO) phonon mode and one electronic continuum of states due to inter-valence band transition has been investigated by the Raman spectra, there is no observation of the interference of multiple phonon modes despite its potential for electromagnetically induced transparency in the far infrared region. In this study, p-type Ga0.5In0.5P films with two main LO modes in the same plane of atomic vibration and one more mode due to CuPt-type ordering are investigated. Asymmetric line profiles, peak energy shifts and peak broadenings in the Raman spectra are analyzed, and the destructive quantum interference of these LO-continuum systems are observed. Discussion with the reference data of p-type GaAs and Si for the one-LO mode system reveals that the asymmetry parameter features the derivatives of the density of the continuum of states in the vicinity of the LO phonon energies and the degree of the electric polarization. It is found experimentally that the interaction between the two main LO modes through the interactions with the continuum states takes place. A1(LO) mode due to the ordering affects the spectrum, however the interaction with the main two LO modes through the continuum is small. On the basis of the experimental result, the spectrum features for this alloy with greater hole density are estimated, where the various controls of the absorption spectrum in the phonon energy region are predicted.

Effect of Nano CeO2 Addition on the Microstructure and Properties of a Cu-Al-Ni Shape Memory Alloy

This article deals with the effect of adding nano CeO2 to act as a grain pinner/refiner to a known Cu-Al-Ni shape memory alloy. Elements were taken in a predefined ratio to prepare 300 g alloy per batch and melted in an induction furnace. Casting was followed by homogenization at 1173 K (900 °C) and rolling to make sheets of 0.5-mm thickness. Further, samples were characterized for microstructure using optical and electron microscope, hardness, and different phase studies by X-ray and transformation temperatures by differential scanning calorimetry. X-ray peak broadenings and changes were investigated to estimate the crystallite size, lattice strain, and phase changes due to different processing steps. A nearly uniform distribution of CeO2 and better martensitic structure were observed with increasing CeO2. The addition of CeO2 also shows a visible effect on the transformation temperature and phase formation.

Structural Anisotropy and Optical Properties of Nonpolar a-Plane GaN Epitaxial Layers.

In-plane structural anisotropy is characteristic of nonpolar (1120) a-plane GaN (a-GaN) films grown on r-plane sapphire substrates. The anisotropic peak broadenings of X-ray rocking curves (XRCs) are clearly observed with M- or W-shaped dependence on the azimuth angles. We investigated the optical properties of both M- and W-shaped a-GaN samples with room and low-temperature photoluminescence (PL) measurements. The W-shaped a-GaN film showed higher PL intensity and more compressive strain compared to the M-shaped a-GaN film, whereas the XRC peak widths of the M-shaped a-GaN film on the azimuth angles are lower than those of W-shaped specimens, indicating that better crystalline quality was obtained. We speculate that the PL intensity and strain state of a-GaN layers may be more influenced by the crystallinity of a specific crystal orientation or direction, especially along the m-axis as opposed to the c-axis. This occurrence is most likely due to anisotropic defect distributions, resulting from differences in dangling bond densities of (0001) and {1-100} facets.

Lattice distortion analysis of nonpolar a-plane $$(11\bar 20)$$ GaN films by using a grazing-incidence X-ray diffraction technique

This work examines the anisotropic microstructure and the lattice distortions of nonpolar a-plane \((11\bar 20)\) GaN (a-GaN) films by using the grazing-incidence X-ray diffraction technique. Faulted a-GaN films typically exhibit an in-plane anisotropy of the structural properties along the X-ray in-beam directions. For this reason, the anisotropic peak broadenings of the X-ray rocking curves (XRCs) were observed for various angle (phi) rotations for a-GaN films with and without SiNx interlayers. Analysis revealed the peak widths of the XRCs displayed an isotropic behavior for a nonpolar a-GaN bulk crystal. Thus, the in-plane anisotropy of the XRC peak widths for nonpolar a-GaN films apparently originates from the heteroepitaxial growth of the a-GaN layer on a foreign substrate. The lattice distortion analysis identified the presence of compressive strains in both the two in-plane directions (the c- and the m-axis), as well as a tensile strain along the normal growth direction. In addition, the observed frequency shifts in the Raman E2 (high) mode for the a-GaN films showed the existence of considerable in-plane compressive strain on both a-GaN films, as confirmed by the lattice distortion analysis performed using the grazing-incidence XRD method.

Effects of ion insertion on cycling performance of miniaturized electrochemical capacitor of carbon nanotubes array

Capacity degradation and ion insertion of a miniaturized electrochemical capacitor are studied using ionic liquid [EMI] [TFSI] as the electrolyte. This capacitor is featured with two comb-like electrodes of vertical carbon nanotubes, ∼70 μm in height and 20 μm in interelectrode gap. We quantify the levels of ion insertion damage with Raman spectroscopy after the electrode experiences 120 consecutive voltammetric cycles to various potential limits. Distinct structural damage emerges due to [EMI] when the negative potential reaches −1.7 V, and those due to [TFSI] arise when the positive potential reaches 1.7 V vs. RHE. Judging from the peak broadenings, [EMI] is more detrimental than [TFSI]. When the voltage window ΔU is set as less than or equal to 2.8 V, both electrode potentials are within the two intercalation limits, little or no decay is observed in 104 charge/discharge cycles. When ΔU is 3.4 V, the positive potential exceeds the upper limit, but the negative potential stays within the lower limit, the cell capacitance decreases moderately. When ΔU increases to 3.8 V, both electrodes suffer from damages because of exceeding the intercalation limits. And the cell capacitance decreases substantially, even leading to a premature failure.

Anisotropic microstructure of hydrothermally-grown non-polar a-plane ZnO on a-plane GaN film

Nonpolar a-plane ZnO (a-ZnO) films with good crystalline quality have been achieved by a hydrothermal growth method on nonpolar a-plane GaN (a-GaN) films without any nucleation steps. The X-ray diffraction θ–2θ scan of the a-ZnO film grown on a-GaN film showed that the film was uniformly a-plane 112¯0 oriented. The a-ZnO films exhibited anisotropic peak broadenings of the on-axis rocking curves with X-ray in-beam orientations. The full width at half maximum of the on-axis rocking curve of nonpolar a-ZnO film along the c-axis direction was measured to be 2092arcsec, which is almost two times larger than the one along the m-axis direction (1219arcsec). The Williamson–Hall plot analysis of the symmetric 112¯0 and 224¯0 Bragg reflections showed that the mosaic tilt values were 0.647° and 0.407° along the c-axis and m-axis directions, respectively. It clearly indicates that large mosaic tilt along the c-axis in a-ZnO film is mainly responsible for the anisotropic peak broadenings of the on-axis rocking curves with respect to X-ray in-beam orientations.

Revealing the cyclic hardening mechanism of an austenitic stainless steel by real-time in situ neutron diffraction

Real-time in situ neutron diffraction was performed on an austenitic stainless steel under cyclic loading at room temperature. The evolutions of individual phase stresses during martensitic transformation were derived from the lattice parameters and volume fraction based on Rietveld refinements and Hooke’s law, while the phase-specific dislocation densities were elucidated by the single peak broadenings. Both results reveal that the increasing content of martensite phase, instead of individual phase strengthening, should be accounted for the remarkable secondary cyclic hardening.

Optimization of milling parameters, processing and characterization of nano-crystalline oxide dispersion strengthened ferritic steel

Ferritic steel powder was mechanically milled in a dual drive planetary ball mill, under different milling conditions to optimize the milling parameters. The resulted powder was characterized, using particle size analyzer, X-rays and electron microscope. X-ray peak broadenings were investigated to estimate crystallite size, lattice strain and deformation stress. Better Pearson's coefficient was observed for uniform stress deformation model (USDM) (0.988) in comparison to uniform deformation model (UDM) (0.64) which shows better estimation of lattice parameter. An increase in fineness was observed with an increase in ball to powder ratio as well as for an increase in rotational speed. At the optimized condition, ferritic steel powder, together with Y2O3, was milled in the dual drive mill to produce oxide dispersion strengthened ferritic steel powder, suitable to be used in nuclear applications. Convoluted morphology, desired for better alloying, was confirmed using an electron microscope. A significant increase in per unit surface area was noticed due to milling using BET surface area analysis. Negligible contamination was observed due to milling atmosphere and mill container. The steel powder produced, was sintered using spark plasma sintering and its density and hardness were measured. High hardness and lower crystallite size were recorded using spark plasma sintering. Addition of Y2O3 shows decreases in the thermal expansion coefficient. Effect of added titanium was studied and an adverse effect on oxide dispersion strengthened steel was noticed.

X-ray diffraction study of short-period AlN/GaN superlattices

The structure of short-period hexagonal GaN/AlN superlattices (SLs) has been investigated by X-ray diffraction. The samples have been grown by metalorganic vapor-phase epitaxy (MOVPE) in a horizontal reactor at a temperature of 1050°C on (0001)Al2O3 substrates using GaN and AlN buffer layers. The SL period changes from 2 to 6 nm, and the thickness of the structure varies in a range from 0.3 to 1 μm. The complex of X-ray diffraction techniques includes a measurement of θ-2θ rocking curves of symmetric Bragg reflection, the construction of intensity maps for asymmetric reflections, a measurement and analysis of peak broadenings in different diffraction geometries, a precise measurement of lattice parameters, and the determination of radii of curvature. The thickness and strain of separate SL layers are determined by measuring the θ-2θ rocking curves subsequent simulation. It is shown that most SL samples are completely relaxed as a whole. At the same time, relaxation is absent between sublayers, which is why strains in the AlN and GaN sublayers (on the order of 1.2 × 10−2) have different signs. An analysis of diffraction peak half-widths allows us to determine the densities of individual sets of dislocations and observe their change from buffer layers to SLs.

Particle size effect on catalytic activity of carbon-supported Pt nanoparticles for complete ethylene oxidation

Effect of Pt particle size on the catalytic activity of complete ethylene oxidation in the temperature range of 25–220°C in fuel-lean conditions is investigated. Carbon black is used as a support for platinum nanoparticles of well-defined average sizes between 1.5 and 6.3nm. The results demonstrate that ethylene oxidation on Pt/C is strongly size sensitive reaction. Thus, the smallest Pt/C-4 nanoparticles (1.5±0.5nm) exhibit much higher catalytic activity toward ethylene oxidation reaching 50% conversion at 88°C compared to 164°C for the largest Pt/C-1 (6.3±0.5nm) nanocatalysts. XPS shows that particle size decrease results in noticeable binding energy increase and Pt4f peak broadenings. This indicates that the electronic effect induced by small Pt nanoparticles might play a role in the observed increase in their activity toward C2H4 oxidation.