Peak Width Analysis Research Articles

Comprehensive peak-width analysis in matter-wave diffraction under grazing incidence conditions

Comprehensive peak-width analysis in matter-wave diffraction under grazing incidence conditions

An approach for identifying the deformation-induced strain from tensile tests and x-ray diffraction measurements

ABSTRACT Non-uniform plastic deformation and phase transformation introduce residual stress (RS) in a material. The present study focuses on the influence of tensile strain on RS development in 304L austenitic stainless steel, wherein strain-induced martensite (SIM) transformation influences deformation behaviour. Room temperature tensile tests were interrupted at various tensile strains between the material yield and ultimate tensile strength at 5.21 × 10−4 and 1.3 × 10−2 s−1 strain rates. Microstructural characterisation of as-received and deformed samples by electron backscatter diffraction provides evidence of SIM formation and shear bands. Analysis of tensile flow and work hardening behaviour is discussed in correlation to the microstructural and dislocation density variations. In addition, RS in the austenite and martensite phases was measured using the x-ray diffraction method, and the RS balance that occurs between the longitudinal and transverse components and the two phases after tensile deformation is presented. It is shown that a combined analysis of RS and x-ray diffraction peak width could be utilised to find the deformation level in tensile fractured, press brake bent, and roll bent samples.

Classification of laser modality for a self-mixing interferometric sensor.

Robust detection and classification of multimodal self-mixing (SM) signals emanating from the optical feedback-based SM interferometric laser sensor are necessary for accurate retrieval of sensing information. An abrupt shift in the modality of SM signals can occur due to different operating conditions; consequently, an unidentified modality shift can cause severe measurement errors. Therefore, it is necessary to detect and identify the type of multimodality so that relevant adjustments could then be made, either in the SM sensor setup or in the relevant signal processing, to avoid the errors caused by the shift in modality. In this work, SM modality identification and classification techniques based on the machine learning classifier algorithms of linear regression, XGB regressor, and decision tree regressor are proposed. The distinguishing feature values, which are used to train and test the classifiers, are extracted from the given SM signal by applying techniques such as principal component analysis, peak width, and linear discriminant analysis. Proposed methods are tested on an SM signal dataset containing a total of 45 unseen SM signals, acquired experimentally from the SM sensor. The identification and classification accuracy of the three classifiers of linear regression, XGB regressor, and decision tree regressor is 76%, 96%, and 100%, respectively.

Evolution of lattice distortions in 4H-SiC wafers with varying doping

Lattice distortions (LD) in 4H-silicon carbide (SiC) wafers were quantified using synchrotron X-ray rocking curve mapping (RCM), and were resolved into their two components of lattice strain (Δd/d) and lattice plane curvature (LPC) for 150 mm diameter wafers. The evolution of these LDs were investigated for three sequential substrates from the same boule, one of which was the substrate reference, and the other two had a 10 µm thick, 1 × 1017 and 4 × 1014 cm-3 n-type doped epitaxial layer. The lattice strain, Δd/d, was highest for the lowest doped wafer due to higher mismatch with the substrate wafer. After epitaxial layer growth, the LPC variation across the wafer increases by a factor of 2, irrespective of doping. The LPC maps indicate presence of a twist in the lattice planes that increases after epitaxial growth. The LPC component has higher influence on wafer shape change, which can reduce device yields. The lattice strain component predominantly affects the glide of basal plane dislocations (BPDs), thereby reducing device reliability. From analysis of peak widths, it was determined that threading dislocations in the top 6 microns of the wafer increase after epitaxial layer growth.

Understanding the Strengthening Effect of β1 Precipitates in Mg-Nd Using In Situ Synchrotron X-ray Diffraction

In situ synchrotron x-ray diffraction was carried out at beamline BL14B1 of Shanghai Synchrotron Radiation Facility (SSRF) to study the tensile deformation of an extruded Mg-2.2 wt.%Nd alloy before and after aging. The aged specimen that contained β1 (Mg3Nd) precipitates showed higher strength than the nonaged specimen, while the strain to failure of the two specimens was almost equal. Analysis of the lattice strain evolution in the aged specimen revealed a modest load-transfer effect from Mg to β1 after 2% strain. Peak width analysis indicated that a high level of microstrain developed in β1 immediately after material yielding. Ex situ transmission electron microscopy (TEM) showed strong interaction between basal dislocations and β1 precipitates. Based on these results, it is proposed that the extra strength in the aged specimen is caused by β1 impeding dislocation movement and eventually being sheared by dislocations.

Determination of residual stresses in fibre laser welded AA2024-T3 T-joints by numerical simulation and neutron diffraction

This paper presents an experimental and numerical study of residual stress states and deformation in fillet welded AA2024-T3 T-joints produced using a high-power fibre laser. Welded sheets with one and three stiffeners were prepared, respectively, to determine changes in microstructure, residual stress, distortion and micro-hardness. 3D sequentially coupled thermo-mechanical finite element models were developed to analyse welding temperature fields, and accurately simulate welding residual stresses and deformation. The simulated results were calibrated using the experimental database on weld pool geometry obtained from optical metallography and temperature fields measured using thermocouples. Residual stress measurements were made using neutron diffraction techniques and sheet distortions were measured using a coordinate measuring machine. The influence of various mechanical boundary conditions on angular and cambering sheet distortions was examined to optimise the restraint parameters. The application of element death and rebirth and dummy element techniques were studied and compared to incorporate the effect of filler metal deposition during welding. The level of residual microstrain was evaluated by diffraction peak width analysis, which indicated the maximal values in the weld metal. The effect of grain growth with respect to strength was of minor importance, whereas, considerable softening in the weld metal was observed.

Study of age hardening in a Mg–2.2 wt%Nd alloy by in situ synchrotron X-ray diffraction and mechanical tests

Microstructure evolution of a supersaturated solid solution Mg–2.2wt%Nd alloy during aging at 240°C for 6h (stage I), at 295°C for 3h (stage II), and finally at 320°C for 1h (stage III) was studied by in situ synchrotron X-Ray diffraction. In stage I, diffraction from β1 (Mg3Nd, FCC) precipitates was observed after ~ 15min. Evolution of the volume, size, and aspect ratio of β1 with the aging time were estimated from peak intensity and peak width analysis. In stage II, diffraction from β (Mg12Nd, tetragonal) precipitates was observed after ~ 36min while β1 remained in the material. In stage III, the volume of β1 reduced substantially in relative to β. The identified precipitation sequence from the in situ aging experiment is supported by ex situ electron microscopy observations. β′, which had not been detected by synchrotron X-rays, was additionally found using transmission electron microscopy in the material by the end of aging stage I. Tension and hardness tests using specimens with different aging conditions were further performed to understand how different precipitates affect the strength and ductility of the Mg–Nd alloy.

Structural and Raman Spectroscopic Study of Antimony Doped Bi<SUB>0.5</SUB>Na<SUB>0.5</SUB>TiO<SUB>3</SUB> Electroceramic

Pure and Antimony (Sb, x = 0.01%, 0.02% and 0.03%) doped Bi0.5Na0.5TiO3 electro ceramics were successfully synthesized by a conventional solid state reaction route. X-ray diffraction analysis showed that a distinct 002/200 peak splitting appears when doping percentage changes from 0.02 to 0.03, referring to a hexagonal symmetry. The data show the Lorentzian deconvolution of the 002 and 200 peaks of the tetragonal phase and the 202 peak of the rhombohedral phase. There is no significant change in the Raman spectra for the prepared compositions while some additional peaks around 151, 281, 585 and 853 cm-1 compared to the peaks observed in BNT. It may be possible that a morphotrophic phase boundary (MPB) exists around x = 0.03. Analysis of peak positions, widths and intensities of Raman spectroscopy study also confirmed the existence of structural change around x = 0.03 composition.

Quantitative determination of a nano-object's atom density without atomic resolution

We outline a possibility to determine the adatom density of individual nano-objects via measurement of their electronic structure. For this aim, the nonlinear shift of image potential states measured on individual Cu nanoclusters on Ag(100) by low-temperature scanning tunneling spectroscopy is carefully analyzed. The quantitative analysis is confirmed by density-functional theory calculations. A peak width analysis furthermore reveals whether the clusters are purely metallic or alloyed.

Temperature-dependent photoluminescence of structurally-precise quantum-confined Au25(SC8H9)18 and Au38(SC12H25)24 metal nanoparticles.

Temperature-dependent photoluminescence of structurally precise Au25(SC8H9)18 and Au38(SC12H25)24 monolayer-protected cluster (MPC) nanoparticles were studied using energy-resolved, intensity-integrated, and time-resolved spectroscopy. Measurements were carried out at sample temperatures spanning the range from 4.5 to 200 K following electronic excitation using 3.1 eV pulsed lasers. The integrated PL intensity for Au25(SC8H9)18 increased sharply by 70% as the sample temperature was increased from 4.5 to 45 K. The PL intensity was statistically invariant for temperatures between 45 and 65 K but was quenched when the sample temperature was raised above 65 K. For both MPC samples, the global PL emission included several components. Each PL component exhibited an increase in emission energy when the sample temperature was increased from 4.5 to 40 K. This unexpected behavior may imply that MPCs in the 1 nm domain have negative expansion coefficients. Quantitative analysis of PL emission energies and peak widths obtained at sample temperatures greater than 45 K indicated MPC nonradiative relaxation dynamics are mediated by coupling to low-frequency vibrations associated with the ligand shell that passivated the nanoclusters, which accounted for the low emission yields at high sample temperatures. Contributions from two different vibrational modes were identified: Au(I)-S stretching (200 cm(-1)) and Au(0)-Au(I) stretching (90 cm(-1)). Analysis of each PL component revealed that the magnitude of electronic-vibration coupling was state-specific, and consistently larger for the high-energy portions of the PL spectra. The total integrated PL intensity of the Au25(SC8H9)18 MPC was correlated to the relative branching ratios of the emission components, which confirmed decreased emission for recombination channels associated with strong electron-vibration coupling and high emission yields for low emission energies at low temperature. The efficient low-energy emission was attributed to a charge-transfer PL transition. This conclusion was reached based on the strong correlation between temperature-dependent intensity-integrated and time-resolved emission measurements that revealed an ∼3.5-5.5 meV activation barrier to nonradiative decay. These findings suggest that nanoscale structure and composition can be modified to tailor the optical and mechanical properties and electronic relaxation dynamics of MPC nanostructures.

The Improved Electrochemistry of Single-Phase Layered Li-Mn-Ni-O Materials over That of Layered-Layered Nano-Composites

The Li-Mn-Ni-O system has received much attention for potential positive electrode materials in lithium ion batteries. In recent work [1-4], the entire phase diagram has been mapped out. Using the phase diagram as a guide, it is possible to select compositions near the boundary of the layered region. These materials can either be single phase layered if prepared by quenching from high temperature or layered-layered nano-composites if cooled more slowly. Work presented here will compare the electrochemistry of materials made under various synthesis conditions at such compositions.Here, two compositions near LiNi0.5Mn0.5O2are studied under various oxygen partial pressures and cooling rates. Figure 1 (top) shows the phase diagram with the two compositions studied, A and B (B is slightly lithium rich compared to A). XRD patterns and peak width analysis will be used to show that the materials made at B are single-phase while the only material made at A that was single-phase was made in 2% oxygen and quenched. The samples made in air showed peak broadening attributed to phase separation and the non-quenched sample in 2% oxygen showed the smallest signs of phase separation (high angle peak broadening only).Figure 1 (bottom) shows that the capacities of the single-phase materials are all higher than those that show phase separation and the cycling stability is comparable. The poor performance of the layered-layered composites is attributed to the compositions of the two phases: they are not Li2MnO3 and LiNi0.5Mn0.5O2 as promoted in the literature [5]. Instead, the end-members both contain some nickel and one contains a high proportion of nickel on the lithium layer (as high as 30% depending on synthesis conditions). Interestingly, the sample that showed the smallest sign of phase separation in the XRD (2% O2, RC) had the largest drop in capacity (140 to 100 mAh/g) compared to the quenched sample. The dramatic decrease in capacity in the sample showing the first signs of forming a layered-layered nano-composite suggests that layered-layered nano-composities should be avoided in the Li-Mn-Ni-O system. The approach often used in research experiments of adding a small amount of excess lithium then serves to help keep the material single phase which improves the electrochemistry.Figure 1: Top: a partial Li-Mn-Ni-O phase diagram showing how the upper layered boundary moves with temperature, synthesis condition (Q is quench, RC is regular cooling at a rate of 5°C/min) and atmosphere (air versus 2% O2). For all conditions, the lower layered boundary is the curved solid line joining Li2MnO3 to LiNiO2. The red lines indicate the a lattice parameter contour plots (the corresponding cones will be shown also) while the blue dotted line is a rocksalt to layered phase transition. Bottom: capacity vs. cycle number for materials made at compositions A and B in the top panel.

Dopant mapping in highly p-doped silicon by micro-Raman spectroscopy at various injection levels

Micro-Raman spectroscopy has been used to investigate the acceptor distribution in highly p-doped silicon. As an example, the dopant distribution in crystalline thin-film layers, as developed for solar cells, was mapped. The method is based on the analysis of the Fano-type Raman peak shape which is caused by free charge carriers. For calibration of the Raman acceptor measurements (excitation at a wavelength of 532 nm), we used mono-crystalline reference samples whose acceptor concentration was determined by electrochemical capacitance voltage. We find a significant influence of light induced free charge carriers on the peak shape which results from typical Raman excitation. Thus, the selection of a suitable intensity is important to avoid a too low signal-to-noise ratio on the one hand and systematic errors due to light induced carriers on the other hand. Different evaluation methods, i.e., peak asymmetry versus peak width analysis, are compared in respect to interference caused by random noise of the spectra or else by internal stress in the sample. While the width analysis method is more robust to a low signal-to-noise ratio, the symmetry analysis is more reliable in case of high intrinsic stress.

Grain size effects on the compressibility and yield strength of copper

A comparative investigation on mechanical properties of micro- and nano-sized polycrystalline copper (Cu) under high pressure and temperature (high P–T) up to 9.1GPa and 1150K has been conducted in a single experimental run using in-situ synchrotron X-ray diffraction integrated with the high pressure technique. We derived the bulk moduli for both samples from the least-squares fitting of measured pressure-volume (P–V) data by a second-order Birch–Murnaghan equation of state (EOS). The results reveal that in the present study grain sizes negligibly affect the compressibility of Cu. Furthermore, we investigated the deformation of samples under high P–T conditions. At high pressure and room temperature, both local/micro and bulk/macro yielding points are observed in the elastic stage of nano-sized Cu. By contrast, micro-sized Cu demonstrates only a bulk yielding point over its entire elastic regime. At high temperature and fixed pressure, both samples exhibit stress relaxation, grain growth, and finally reach an identical status. Based on the peak-width analysis of diffraction profiles and subsequent graphic derivation, the yield strengths are determined to be 0.17±0.05GPa and 0.75±0.07GPa for micro- and nano-sized grains, respectively, which indicates a substantial enhancement of yield strength in Cu by nanocrystals.

In situ observations of particle size evolution during the hydrothermal crystallization of TiO2: A time-resolved synchrotron SAXS and WAXS study

We have monitored the homogeneous crystallization of TiO2 phases from aqueous TiCl4 solutions at 100°C using both time-resolved small-angle X-ray scattering (TR-SAXS) and time-resolved wide-angle X-ray scattering (TR-WAXS). The WAXS data revealed that metastable anatase was the first phase to crystallize, but it began transforming to rutile within the first hour of reaction. Scherrer analysis of WAXS peak widths indicated that anatase particles grew to an average size near 7nm on a time scale of minutes, after which their size remained static, while rutile grew rapidly from <3nm to ∼10nm within 1h, followed by slower growth at a rate of ∼0.15nm/h.Using a novel sample cell designed to withstand temperatures up to 150°C and hydrothermal vapor pressure, we collected in situ SAXS data for the same conditions as the WAXS experiments. Fourier analyses of the SAXS images revealed the rapid emergence of a broad, Gaussian-type particle size distribution ranging in diameter from 1 to ∼20nm with a mean near 7nm, in excellent agreement with our WAXS analysis. At 0.5h, a second population of <3nm particles emerged, and these crystals grew to ∼9nm after 7.5h, which we interpret as the nucleation and growth of rutile (as was also observed in the WAXS patterns). In contrast to studies that presume a solid-state transformation from anatase to rutile during growth, our results suggest that anatase and rutile co-precipitate during the early stages of crystallization, but once anatase crystals grow to a critical size of 7nm, they dissolve and the solution species re-precipitate onto primary rutile nanocrystals.

Raman temperature dependence analysis of carbon-doped titanium dioxide nanoparticles synthesized by ultrasonic spray pyrolysis technique

Carbon-doped titanium dioxide nanoparticles were prepared by ultrasonic spray pyrolysis technique using titanium tetra-ethoxide as a precursor and glucose as a dopant. The as-synthesized nanoparticles were then characterized using high resolution transmission electron microscopy for the structural properties and temperature dependence Raman spectroscopy for the optical properties. High resolution transmission electron microscopy analysis shows that the ultrasonic synthesized carbon-doped titanium dioxide nanoparticles have an interplanar d-spacing of 0.352 nm, a value close to 0.374 nm of the pure undoped anatase titanium dioxide (bulk). The fast Fourier transform (FFT) of the selected electron diffraction images, of the selected areas, display the fact that only the main diffraction (reflection) plane of Miller indices (101) in titanium dioxide is responsible for diffraction pattern. Raman spectroscopy confirms the titanium dioxide polymorph to be anatase with the intense phonon frequency at 153 cm−1 blue-shifted from 141 cm−1 due to both carbon doping and particle size decrease. The temperature dependence analysis of the spectra shows an initial linear dependence of the Raman shift for the E g(1) mode at 152.7 cm−1 with increase in temperature up to a critical temperature 450 °C, after which we observe a decrease with increase in temperature. The other Raman modes [B 1g and E g(3)] exhibit a different temperature dependence in that the B 1g displays a somewhat sinusoidal behavior and the E g(3) mode shows a linear decrease of Raman shift with an increase in temperature. Temperature dependence analysis of peak width for the E g(1) indicates the peak width of the as prepared nanoparticle to be 20 cm−1 which is far much larger than that for single crystal of 7 cm−1 at room temperature.

Monitoring Protein Conformation along the Pathway of Chaperonin-Assisted Folding

The GroEL/GroES chaperonin system mediates protein folding in the bacterial cytosol. Newly synthesized proteins reach GroEL via transfer from upstream chaperones such as DnaK/DnaJ (Hsp70). Here we employed single molecule and ensemble FRET to monitor the conformational transitions of a model substrate as it proceeds along this chaperone pathway. We find that DnaK/DnaJ stabilizes the protein in collapsed states that fold exceedingly slowly. Transfer to GroEL results in unfolding, with a fraction of molecules reaching locally highly expanded conformations. ATP-induced domain movements in GroEL cause transient further unfolding and rapid mobilization of protein segments with moderate hydrophobicity, allowing partial compaction on the GroEL surface. The more hydrophobic regions are released upon subsequent protein encapsulation in the central GroEL cavity by GroES, completing compaction and allowing rapid folding. Segmental chain release and compaction may be important in avoiding misfolding by proteins that fail to fold efficiently through spontaneous hydrophobic collapse.

3-D Raman spectroscopy measurements of the symmetry of residual stress fields in plastically deformed sapphire crystals

The development of methods to characterize materials in three dimensions, such as tomography by X-rays, focused ion beam and electrons, has led to progress in the understanding of materials properties. Recently, even stress and deformation tensors could be measured in three dimensions. Specifically the stress fields around indents in metals were studied by three-dimensional (3-D) X-ray stress microscopy. In this paper, we investigate the 3-D residual stress field around a microindent using confocal Raman microscopy with a lateral resolution of 300 nm and a depth resolution of 600 nm. The model system investigated was single crystalline sapphire, which was indented normal to its basal c(0 0 0 1) plane. A cross-section of the indent was studied by transmission electron microscopy to visualize the deformed microstructure. The major result is that the geometry of the indenter has no direct influence on the symmetry of the resulting residual stress field. Residual stresses directly depend on the crystal symmetry and the defect structures formed during indentation. Confocal Raman microscopy is a powerful method for analyzing 3-D stress fields and the corresponding defect structures (by peak width analysis) with a resolution in the submicron range.

Defect study on the indium-gallium alloy system of copper chalcopyrites performed on solar cell heterostructures

We report on defect spectroscopy on Cu(In,Ga)Se2 based solar cells with varying gallium content. Our investigations using deep level transient and admittance spectroscopy do not reveal a pronounced qualitative difference in the defect spectra for the case of absorbers containing indium and gallium. Therefore, we conclude that there exists no detrimental defect in the bulk material that generally prohibits one to achieve an increase in efficiency even for solar cells based on absorbers with a gallium to gallium plus indium ratio (GGI) larger than 0.3. The boundary compositions with CuInSe2 and CuGaSe2 absorbers (i.e., GGI=0 and GGI=1, respectively) show additional trap signals. Additionally, a peak width analysis was performed for two defect signals that occur for all absorber compositions. The relative peak width was found to be independent of GGI whereas the activation energies show some correlation with the gallium content of the absorber layer.

Magnetically driven filament probe

A radially movable probe has been developed for studies of filamentary transport in ASDEX Upgrade during edge localized modes (ELMs) by means of Langmuir tips and magnetic pickup coils. The probe is permanently installed at the low field side in the ASDEX Upgrade vacuum vessel and is not subject to limitations in probe size, as, for example, probes on a shared manipulator are. The probe is moved by a magnetic drive, which allows for easy installation in the vessel, and has moderate machine requirements, as it will only require an electric feedthrough and an external power supply. The drive gives a linear motion with a radial range of 5 cm within 50 ms, where range and velocity can be largely scaled according to experimental requirements. The probe has been installed in the outer midplane of the ASDEX Upgrade vessel, where ELM filaments are expected to have their maximum amplitude. Filaments are coherent substructures within an ELM, carrying a fraction of the ELM released energy towards the wall. The new probe allows to measure the structure of these filaments, in particular, parameters such as filament rotation (by time delay measurements) and size (by peak width analysis). Activating the drive moves the probe from a safe position behind the limiter to a position in front of the limiters, i.e., exposes the Langmuir pins to the scrape-off layer plasma.

Identification and Characterization of EX1 Kinetics in H/D Exchange Mass Spectrometry by Peak Width Analysis

Proteins that undergo cooperative unfolding events display EX1 kinetic signatures in hydrogen exchange mass spectra. The hallmark bimodal isotope pattern observed for EX1 kinetics is distinct from the binomial isotope pattern for uncorrelated exchange (EX2), the normal exchange regime for folded proteins. Detection and characterization of EX1 kinetics is simple when the cooperative unit is large enough that the isotopic envelopes in the bimodal pattern are resolved in the m/z scale but become complicated in cases where the unit is small or there is a mixture of EX1 and EX2 kinetics. Here we describe a data interpretation method involving peak width analysis that makes characterization of EX1 kinetics simple and rapid. The theoretical basis for EX1 and EX2 isotopic signatures and the effects each have on peak width are described. Modeling of EX2 widening and analysis of empirical data for proteins and peptides containing purely EX2 kinetics showed that the amount of widening attributable to stochastic forward- and back exchange in a typical experiment is small and can be quantified. Proteins and peptides with both obvious and less obvious EX1 kinetics were analyzed with the peak width method. Such analyses provide the half-life for the cooperative unfolding event and the relative number of residues involved. Automated analysis of peak width was performed with custom Excel macros and the DEX software package. Peak width analysis is robust, capable of automation, and provides quick interpretation of the key information contained in EX1 kinetic events.