Quantitative Energy Dispersive X-ray Spectroscopy Research Articles

Influence of excess silicon on polytype selection during metal-mediated epitaxy of GaN nanowires

We have examined the origins of polytype selection during metal-mediated molecular-beam epitaxy of GaN nanowires (NWs). High-angle annular dark-field scanning transmission electron microscopy reveals [111]-oriented zinc blende (ZB) NWs and [0001]-oriented wurtzite (WZ) NWs, with SixNy at the interface between individual NWs and the Si (001) substrate. Quantitative energy dispersive x-ray spectroscopy reveals a notably higher Si concentration of 7.0% ± 2.3% in zinc blende (ZB) NWs than 2.3% ± 1.2% in wurtzite (WZ) NWs. Meanwhile, density functional theory calculations show that incorporation of 8 at. % Si on the Ga sublattice inverts the difference in formation energies between WZ and ZB GaN, such that the ZB polytype of GaN is stabilized. This identification of Si and other ZB polytype stabilizers will enable the development of polytype heterostructures in a wide variety of WZ-preferring compounds.

Quantifying the phase assemblage in the hydrated cement paste by an interpretable and automatic EDS image analysis framework

The Energy dispersive X-ray spectroscopy (EDS) data, characterized by high dimensionality, low resolution, and large scale, necessitates a robust characterization method that is both easy to understand and delicate to reveal the underlying information. Here, we present a practical and interpretable framework for quantitative EDS (QEDS) image analysis. To improve the quality of data, we employ sequential processing techniques including guided filter, linear enhancement, and super-pixel segmentation. For phase identification and classification, the dimensionality reduction algorithm Potential of heat-diffusion for affinity-based transition embedding (Phate) was integrated with cluster analysis algorithm Gaussian Mixture Model (GMM). This integration cleanly and clearly reveals typical data patterns such as linear progressions and local clusters, indicating the presence of phase evolution and representative phases. We expect that this QEDS image analysis offers an intuitive and visual way to quantify the phase assemblage in cementitious systems, thereby shifting the quantification process from expert knowledge-dominated “black boxes” into data structure-dominated “glass boxes”.

Synthesis under Normal Conditions and Morphology and Composition of AlF3 Nanowires.

AlF3 has interesting electrophysical properties, due to which the material is promising for applications in supercapacitors, UV coatings with low refractive index, excimer laser mirrors, and photolithography. The formation of AlF3-based nano- and micro-wires can bring new functionalities to AlF3 material. AlF3 nanowires are used, for example, in functionally modified microprobes for a scanning probe microscope. In this work, we investigate the AlF3 samples obtained by the reaction of initial aluminum with an aqueous hydrofluoric acid solution of different concentrations. The peculiarity of our work is that the presented method for the synthesis of AlF3 and one-dimensional structures based on AlF3 is simple to perform and does not require any additional precursors or costs related to the additional source materials. All the samples were obtained under normal conditions. The morphology of the nanowire samples is studied using scanning electron microscopy. We performed an intermediate atomic force microscope analysis of dissolved Al samples to analyze the reactions occurring on the metal surface. The surface of the obtained samples was analyzed using a scanning electron microscope. During the analysis, it was found that under the given conditions, whiskers were synthesized. The scale of one-dimensional structures varies depending on the given parameters in the system. Quantitative energy-dispersive x-ray spectroscopy spectra are obtained and analyzed with respect to the feedstock and each other.

Quantifying the microstructure evolution and phase assemblage of solid waste as construction materials by EDS image analysis: A case study of carbonated basic oxygen furnace slag aggregates

The diversities of raw materials and manufacturing techniques lead to large fluctuations in the upcycling potential of solid waste as construction materials. A quantitative energy dispersive X-ray spectroscopy (EDS) image analysis methodology was developed to measure the microstructure evolution and phase assemblage of solid waste. Based on the proposed EDS image enhancement algorithm, the component complexity and structural heterogeneity of basic oxygen furnace slag (BOFS) can be fully revealed by the EDS images. Thereafter, the proportions of major phases (i.e., pores, reaction products, and unreacted components) and the specific composition information of involved phases can be determined. The spatial distributions of reaction products and unreacted components could be studied by the lineal-path distribution function and the phase assemblage of reaction products could be studied by the elemental ratios. The results showed that the effects of subsequent hydration on the microstructural and mineralogical alterations of carbonation products were more prominent than the consumption of unreacted components. The continuous dissolution of the Ca and Si ions upon the hydration significantly promoted the transformation of carbonation products and microstructure densification of BOFS aggregates, which was the main contributor to the development of mechanical performance.

Thermally controlled structural strain reduction in core shell magnetoelectric nanocomposite

In this research, we have presented detailed studies of the effect of temperature-controlled hydrothermal fabrication techniques on the morphology and structural strain in magnetoelectric core-shell nanocomposite having magnetic CoFe2O4 core coated with a piezoelectric BaTiO3 shell. We have presented the effect of controlled cooling rate during annealing process of synthesis on the structural integrity and structural strain of the core-shell hetero-nanostructure. Using temperature controlled hydrothermal method, it has been observed that controlling the cooling rate to 20 °C/min while annealing process leads to low structural strain on the deposited BaTiO3 shell. This also leads to high structural integrity of the fabricated heterostructure nanocomposite. To measure the strain distribution in the coated shell, geometric phase analysis was performed on the high-resolution transmission electron microscopic image of the fabricated core-shell nanostructure. Semi quantitative Energy-dispersive X-ray spectroscopy line scan elemental mapping have confirmed the elemental distribution throughout the nanostructure and formation of the core–shell structure. Moreover, through the geometric phase analysis, the core and the shell can be distinctively visualized which confirms the homogeneity of the coating of single crystalline BaTiO3 shell on the CoFe2O4 core.

Dilution of the magnetic lattice in the Kitaev candidate α−RuCl3 by Rh3+ doping

Magnetic dilution of a well-established Kitaev candidate system is realized in the substitutional ${\mathrm{Ru}}_{1\ensuremath{-}x}{\mathrm{Rh}}_{x}{\mathrm{Cl}}_{3}$ series $(x=0.02--0.6)$. Optimized syntheses protocols yield uniformly doped single crystals and polycrystalline powders that are isostructural to the parental $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{RuCl}}_{3}$ as per x-ray diffraction. The Rh content $x$ is accurately determined by the quantitative energy-dispersive x-ray spectroscopy technique with standards. We determine the magnetic phase diagram of ${\mathrm{Ru}}_{1\ensuremath{-}x}{\mathrm{Rh}}_{x}{\mathrm{Cl}}_{3}$ for in-plane magnetic fields from magnetization and specific-heat measurements as a function of $x$ and stacking periodicity and identify the suppression of the magnetic order at $x\ensuremath{\approx}0.2$ towards a disordered phase, which does not show any clear signature of freezing into a spin glass. Comparing with previous studies on the substitution series ${\mathrm{Ru}}_{1\ensuremath{-}x}{\mathrm{Ir}}_{x}{\mathrm{Cl}}_{3}$, we propose that chemical pressure would contribute to the suppression of magnetic order, especially in ${\mathrm{Ru}}_{1\ensuremath{-}x}{\mathrm{Ir}}_{x}{\mathrm{Cl}}_{3}$, and that the zigzag magnetic ground state appears to be relatively robust with respect to the dilution of the Kitaev-$\mathrm{\ensuremath{\Gamma}}$-Heisenberg magnetic lattice. We also discovered a slight dependence of the magnetic properties on thermal cycling, which would be due to an incomplete structural transition.

Atomic-scale characterization of the oxidation state of Ti in meteoritic hibonite: Implications for early solar system thermodynamics

Abstract Calcium-aluminum-rich inclusions (CAIs) in chondritic meteorites are composed of refractory minerals thought to be the first solids to have formed in the solar nebula. Among them, hibonite, nominally CaAl12O19, holds particular interest because it can incorporate significant amounts of Ti into its crystal structure in both Ti3+ and Ti4+ oxidation states. The relative amounts of these cations that are incorporated reflect the redox conditions under which the grain formed or last equilibrated and their measurement can provide insight into the thermodynamic landscape of the early solar nebula. Here we develop a new method for the quantification of Ti oxidation states using electron energy-loss spectroscopy (EELS) in an aberration-corrected scanning transmission electron microscope (STEM) to apply it to hibonite. Using a series of Ti-bearing oxides, we find that the onset intensity of the Ti L2,3 edge decreases with increasing Ti-oxidation state, which is corroborated by simulated Ti-oxide spectra using first-principles density-functional theory. We test the relationship on a set of synthetic hibonite grains with known Ti4+/ΣTi values and apply the developed method on a hibonite grain from a compact type A inclusion in the Northwest Africa (NWA) 5028 CR2 carbonaceous chondrite. The STEM-EELS data show that the chondritic hibonite grain is zoned with a Ti4+/ΣTi ratio ranging from 0.78 ± 0.04 to 0.93 ± 0.04 over a scale of 100 nm between the core and edge of the grain, respectively. The Ti substitution sites are characterized by experimental and calculated high-angle annular-dark-field (HAADF) images and atomic-level EEL spectrum imaging. Simulated HAADF images reveal that Ti is distributed between the M2 and M4 sites while Mg sits on the M3 site. Quantitative energy-dispersive X-ray spectroscopy shows that this grain is also zoned in Al and Ti. The Mg distribution is not well correlated with that of Ti and Ti4+/ΣTi at the nanoscale. The spatial decoupling of the element composition and Ti-oxidation states suggests a multistage evolution for this hibonite grain. We hypothesize that Ti and Mg were incorporated into the structure during condensation at high temperature through multiple reactions. Transient heating, presumably in the solar nebula, adds complexity to the crystal chemistry and potentially redistributed Ti and Mg. Concurrently, the formation of oxygen vacancies as a result of a reducing gas, led to the reduction of Ti4+ to Ti3+. The multiple defect reactions occurring in this single hibonite crystal preclude a simple relationship between the Ti4+/ΣTi and the fO2 of formation. However, moving forward, these measurements are fundamental inputs for modeling of the thermodynamic conditions under which hibonite formed in the early solar nebula.

Reaching for atomic-scale quantitative energy dispersive X-ray spectroscopy

Reaching for atomic-scale quantitative energy dispersive X-ray spectroscopy

Influence of Sr deficiency on structural and electrical properties of SrTiO3 thin films grown by metal\u2013organic vapor phase epitaxy

Homoepitaxial growth of SrTiO3 thin films on 0.5 wt% niobium doped SrTiO3 (100) substrates with high structural perfection was developed using liquid-delivery spin metal–organic vapor phase epitaxy (MOVPE). Exploiting the advantage of adjusting the partial pressures of the individual constituents independently, we tuned the Sr/Ti ratio of the gas phase for realizing, stoichiometric, as well as Sr deficient layers. Quantitative energy dispersive X-ray spectroscopy in a scanning transmission electron microscope confirm Sr deficiency of up to 20% in nominally off-stoichiometrically grown films. Our MOVPE process allows to grow such layers in phase pure state and without extended defect formation. Indications for oxygen deficiency could not be identified. Sr deficient layers exhibit an increased permittivity of ɛr = 202 and a larger vertical lattice parameter. Current–voltage characteristics (IVCs) of metal–oxide–semiconductor (Pt/SrTiO3/SrTiO3:Nb) structures reveal that Sr deficient SrTiO3 films show an intrinsic resistive switching with on–off ratios of three orders of magnitude at RT and seven orders of magnitude at 10 K. There is strong evidence that a large deviation from stoichiometry pronounces the resistive switching behavior. IVCs conducted at 10 K indicate a defect-based mechanism instead of mass transport by ion diffusion. This is supported by in-situ STEM investigations that show filaments to form at significant higher voltages than those were resistive switching is observed in our samples.

Iron-rich intermetallics in high pressure die cast A383 aluminum alloys

This work describes the composition and crystal structure of Fe-rich intermetallics that form during the high pressure die casting (HPDC) process of alloy A383. Engine castings were produced using the HPDC process with A383 material with a nominal iron content of 1 wt %. Quantitative energy dispersive X-ray spectroscopy (EDS) was used to measure the chemical composition of Fe-rich intermetallics that formed during the process, and electron backscattered diffraction (EBSD) was used to identify their corresponding crystal structures and space groups. The results revealed that there were two types of Fe-rich intermetallics: sludge particles with a polygonal morphology and α-Fe with a Chinese-script shape. No needle-like β-Fe intermetallics were observed. Sludge and α-Fe had the same crystal structures, indexed as body-center cubic (bcc) with the same space group of Im3¯(No. 204). Sludge contained more Mn and Cr than α-Fe, whereas there was a larger concentration of Cu in α-Fe than sludge. ThermoCalc software was used to estimate the formation temperature of Fe-rich intermetallics, and the results suggested that α-Fe (Al8Fe2Si) with the bcc crystal structure and sludge were the same phase but formed at different temperatures during solidification process.

Phase diagrams of liquid-phase mixing in multi-component metal-organic framework glasses constructed by quantitative elemental nano-tomography

Several distinct mixing processes and resulting microstructures have recently been reported in multicomponent glasses prepared from multiple metal-organic frameworks. Here, two illustrative examples of multicomponent zeolitic imidazolate framework (ZIF) glasses, the (aTZIF-4-Co)0.5(agZIF-62)0.5 blend and the ag[(ZIF-67)0.2(ZIF-62)0.8] flux melted glass, are studied. These materials are characterized by quantitative X-ray energy dispersive spectroscopy in the scanning transmission electron microscope. By advancing a partial ionization cross section methodology using standards of arbitrary morphology, quantitative nanoscale elemental analysis throughout the glass volume is achieved. In turn, phase diagrams describing the mixing states are presented, offering mechanistic insight into the formation of the observed microstructures. Significant miscibility was observed in ag[(ZIF-67)0.2(ZIF-62)0.8]. These findings establish phase-segregation and interdiffusion as two processes in multicomponent glass formation, which explains the different outcomes observed in blending and flux melting.

Probing Nanoscale Phase Separation at Atomic Resolution within β-Type Ti-Mn Alloy: A Potential Candidate for Biomedical Implants.

Biocompatible β-type Ti alloys with high ultimate tensile strength (UTS) and yield strength are potential candidates for certain orthopedic and cardiovascular implants. Aiming for these applications, Ti alloy with 14 wt % Mn (Ti-14 Mn) as β-stabilizer was processed through thermomechanical treatment along with solutionizing and quenching, followed by 95% cold rolling, which resulted in ultrahigh UTS and yield strength. 3-[4,5-Dimethylthiazol-2-yl]-2,5-diphenyltetrazolimbromide assay with different cell lines suggests efficient cell growth on alloy surface without compromising biocompatibility. Cell adhesion and spreading assay show that cells are not only able to attach to the alloy surface but also able to spread and grow with normal morphology, which projects this material as a potential candidate for biomedical application. Previous studies on binary β-type Ti alloy systems treated with the above-mentioned processing route confirm the presence of nanoscale phase separation, which enhances its mechanical properties. To discover the same phenomena in the alloy of the present study, bright-field and high-resolution transmission electron microscopy (HRTEM) imaging experiments were performed and nanoscale contrast-modulated lamella regions were observed. Geometrical phase analysis on complex-valued exit wave, reconstructed using focal series HRTEM images, demonstrates that the lamella is a result of d-spacing modulation. Ab initio calculation indicates that d-spacing modulation with the same crystal structure occurs due to composition modulation and was proved by scanning transmission electron microscopy imaging coupled with quantitative energy-dispersive X-ray spectroscopy. Correlating contrast, strain, and composition modulation confirms nanoscale phase separation, which is the first report of this phenomenon in Ti-Mn alloy system.

An Investigation of the Effect of Sintering Conditions on the Mechanical Behavior of Electroplated Nickel Foams

This study investigates the effect of sintering temperature on the compression strength of nickel foams in an inert atmosphere. The nickel foams were produced by the electrodeposition technique on polyurethane foam substrate. As-plated Ni foams were sintered at 873 K, 1073 K, and 1273 K (600 °C, 800 °C, and 1000 °C) in order to eliminate polyurethane and to enhance ductility at a controlled atmosphere. A compression test was used to determine the mechanical behavior. The morphology of produced foams was analyzed by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) techniques. Quantitative EDS analysis implied that carbon diffuses into nickel structure during the polyurethane decomposition. The amount of carbon in nickel foam increases with heat treatment temperature. The results also reveal that the oxygen impurity arisen from polymer vapors can diffuse into the nickel structure at elevated sintering temperature [i.e., 1273 K (1000 °C)]. The compression curve of as-plated foam showed brittle behavior due to the electroplating condition. The sintering process in the neutral atmosphere could create ductile foams, although the strength of the foams decreases with an increase in the sintering temperature.

Numerical modeling of specimen geometry for quantitative energy dispersive X-ray spectroscopy

Transmission electron microscopy specimens typically exhibit local distortion at thin foil edges, which can influence the absorption of X-rays for quantitative energy dispersive X-ray spectroscopy (EDS). Here, we report a numerical, three-dimensional approach to model the geometry of general specimens and its influence on quantification when using single and multiple detector configurations. As a function of specimen tilt, we show that the model correctly predicts the asymmetric nature of X-ray counts and ratios. When using a single detector, we show that complex specimen geometries can introduce significant uncertainty in EDS quantification. Further, we show that this uncertainty can be largely negated by collection with multiple detectors placed symmetrically about the sample such as the FEI Super-X configuration. Based on guidance provided by the model, we propose methods to reduce quantification error introduced by the sample shape. The source code is available at https://github.com/subangstrom/superAngle.

Cu segregation on the interface between Al2O3 substrate and Al-1.4Cu alloy

High angle annular dark field scanning transmission electron microscope (HAADF-STEM) imaging and quantitative energy-dispersive X-ray spectroscopy (EDX) analysis was used to elucidate the Cu segregation on the interface between Al2O3 substrate and Al-1.4Cu alloy. A significant Cu segregation (about 2at%) was observed, which can be mainly attributed to the enhanced diffusion caused by the high strain between Al2O3 substrate and Al-1.4Cu alloy. This investigation highlights the importance of Cu segregation and subsequent eutectic reaction on the heterogeneous nucleation of Al on Al2O3 substrate.

Structural and magnetic properties of LaCrO3 half-doped with Al

Structural and magnetic properties of LaCrO3 half-doped with Al are reported in this work. Pure and half-doped samples were prepared by combustion synthesis using urea as fuel. The crystal structure was investigated by X-ray diffraction and Rietveld analysis. A structural phase transition caused by a decrease of the chemical pressure was observed. The scanning electron microscopy (SEM) images show the formation of porous samples with particles of irregular morphologies. A quantitative Energy-dispersive X-ray spectroscopy (EDS) analysis on the surface indicates the inclusion of the Al on the structure. However, a small deficiency of La and Al was observed. Magnetization measurements as a function of temperature reveal an antiferromagnetic order in both samples. A large decrease of TN (Néel temperature) and a reduction of the frustration factor is observed in the sample doped with Al. The magnetic isothermal at 5K shows a typical antiferromagnetic behavior with a slightly spin canting for the doped sample.

X-Ray Absorption Correction for Quantitative Scanning Transmission Electron Microscopic Energy-Dispersive X-Ray Spectroscopy of Spherical Nanoparticles.

A new method to perform X-ray absorption correction for spherical particles in quantitative energy-dispersive X-ray spectroscopy in the scanning transmission electron microscope is presented. An absorption correction factor is derived and simulated data is presented encompassing a range of X-ray absorption conditions. Theoretical calculations are compared with experimental data of X-ray counts from Au nanoparticles to verify the derived methodology. The effect of detector elevation angle is considered and a comparison with thin-film absorption correction is included.

Ion milling-induced micrometer-sized heterogeneities and partial crystallization in a TiZrCuFeBe bulk metallic glass

The Ti36.2Zr30.3Cu8.3Fe4Be21.2 (at.%) bulk metallic glass (BMG) exhibits a regular micrometer-sized pattern in the transmission electron microscope (TEM) after ion milling. Quantitative energy-dispersive X-ray spectroscopy (EDX) results show that the compositions in the bright and dark regions are distinctly different, and the compositions gradually change with the contrast of the pattern. In the intermediate regions (with grey contrast) preferential crystallization is observed and this confirms that microscale heterogeneities exist in the ion-milled TEM specimens. On the contrary, the specimens prepared by focused ion beam and by electrolytic thinning show featureless microstructures in the TEM. Moreover, EDX results and the secondary ion mass spectroscopy show that the constituent elements are homogeneously distributed. An ion milling-induced compositional fluctuation mechanism is proposed, and the partial devitrification can be explained based on this mechanism. The present findings may lead to a deeper understanding of the occurrence of micrometer-sized heterogeneities in BMGs induced by ion milling.

Atomically ordered (Mn,Ga)As crystallites on and within GaAs

Metal organic vapor phase epitaxy (MOVPE) of Mn-rich (Mn,Ga)As on (001) oriented GaAs wafers resulted in atomically ordered (Mn,Ga)As crystallites of two morphological kinds, partially embedded on the wafer surface and fully embedded within the single crystalline matrix. While the former were apparently free of defects (other than unavoidable point defects), the latter contained two domains separated by a grain boundary. Since atomic ordering can be modeled by space group symmetry descent considerations (Barnighausen trees) that start with the space group of the known crystallographic phases of random (Mn,Ga)As alloys with specified chemical compositions, reasonable structure hypotheses have been derived for two atomically ordered Mn0.75Ga0.25As phases that we call the trigonal α' and the monoclinic β' phases. The implications of these structure hypotheses are in agreement with the results of a range of scanning transmission electron microscopy (STEM) and parallel illumination electron diffraction (ED) studies that include quantitative energy dispersive X-ray spectroscopy, X-ray spectroscopic imaging, as well nanobeam diffraction and high angle precession ED. The coexistence of two domains within the fully embedded crystallites is predicted by the corresponding Barnighausen tree and observed experimentally for the fully embedded crystallites.

Stabilisation of Fe2O3-rich Perovskite Nanophase in Epitaxial Rare-earth Doped BiFeO3 Films.

Researchers have demonstrated that BiFeO3 exhibits ferroelectric hysteresis but none have shown a strong ferromagnetic response in either bulk or thin film without significant structural or compositional modification. When remanent magnetisations are observed in BiFeO3 based thin films, iron oxide second phases are often detected. Using aberration-corrected scanning transmission electron microscopy, atomic resolution electron energy loss spectrum-mapping and quantitative energy dispersive X-ray spectroscopy analysis, we reveal the existence of a new Fe2O3-rich perovskite nanophase, with an approximate formula (Fe0.6Bi0.25Nd0.15)3+ Fe3+O3, formed within epitaxial Ti and Nd doped BiFeO3 perovskite films grown by pulsed laser deposition. The incorporation of Nd and Bi ions on the A-site and coherent growth with the matrix stabilise the Fe2O3-rich perovskite phase and preliminary density functional theory calculations suggest that it should have a ferrimagnetic response. Perovskite-structured Fe2O3 has been reported previously but never conclusively proven when fabricated at high-pressure high-temperature. This work suggests the incorporation of large A-site species may help stabilise perovskite-structured Fe2O3. This finding is therefore significant not only to the thin film but also to the high-pressure community.