Distribution Of Light Elements Research Articles

Seismic low-velocity equatorial torus in the Earth's outer core: Evidence from the late-coda correlation wavefield.

Thermochemical inhomogeneities in the Earth's outer core that enhance our understanding of the geodynamo have been elusive. Seismic constraints on such inhomogeneities would provide clues on the amount and distribution of light elements in the core apart from iron and nickel. Here, we present evidence for a low-velocity volume within the outer core via the global coda correlation wavefield. Several key correlogram features with a unique sensitivity to the liquid core show variations with wave paths remarkably slower in the equatorial than polar planes. We constrain a torus structure at low latitudes with ~2% lower velocity than the surrounding liquid outer core via waveform modeling. We propose a thermochemical origin for such a low-velocity torus, providing important constraints on the dynamical processes of the Earth's outer core.

Ultracompact mirror device for forming 20-nm achromatic soft-X-ray focus toward multimodal and multicolor nanoanalyses

Nanoscale soft-X-ray microscopy is a powerful analysis tool in biological, chemical, and physical sciences. To enhance its probe sensitivity and leverage multimodal soft-X-ray microscopy, precise achromatic focusing devices, which are challenging to fabricate, are essential. Here, we develop an ultracompact Kirkpatrick-Baez (ucKB) mirror, which is ideal for the high-performance nanofocusing of broadband-energy X-rays. We apply our advanced fabrication techniques and short-focal-length strategy to realize diffraction-limited focusing over the entire soft-X-ray range. We achieve a focus size of 20.4 nm at 2 keV, which represents a significant improvement in achromatic soft-X-ray focusing. The ucKB mirror extends soft-X-ray fluorescence microscopy by producing a bicolor nanoprobe with a 1- or 2-keV photon energy. We propose a subcellular chemical mapping method that allows a comprehensive analysis of specimen morphology and the distribution of light elements and metal elements. ucKB mirrors will improve soft-X-ray nanoanalyses by facilitating photon-hungry, multimodal, and polychromatic methods, even with table-top X-ray sources.

Single-Slice XRF Mapping of Light Elements in Frozen-Hydrated Allium schoenoprasum via a Self-Absorption-Corrected Hyperspectral Tomographic Reconstruction Approach.

3D and 2D-cross-sectional X-ray fluorescence analysis of biological material is a powerful tool to image the distribution of elements and to understand and quantify metal homeostasis and the distribution of anthropogenic metals and nanoparticles with minimal preparation artifacts. Using tomograms recorded on cryogenically prepared leaves of Allium schoenoprasum, the cross-sectional distribution of physiologically relevant elements like calcium, potassium, manganese, and zinc could be tomographically reconstructed by peak fitting followed by a conventional maximum-likelihood algorithm with self-absorption correction to reveal the quantitative cross-sectional element distribution. If light elements such as S and P are located deep in the sample compared to the escape depth of their characteristic X-ray fluorescence lines, the quantitative reconstruction becomes inaccurate. As a consequence, noise is amplified to a magnitude where it might be misinterpreted as actual concentration. We show that a tomographic MCA hyperspectral reconstruction in combination with a self-absorption correction allows for fitting of the XRF spectra directly in real space, which significantly improves the qualitative and quantitative analysis of the light elements compared to the conventional method as noise and artifacts in the tomographic reconstruction are reduced. This reconstruction approach can substantially improve the quantitative analysis of trace elements as it allows the fitting of summed voxel spectra in anatomical regions of interest. The presented method can be applied to XRF 2D single-slice tomography data and 3D tomograms and is particularly relevant for, but not limited to, biological material in order to help retrieve self-absorption corrected quantitative reconstructions of the spatial distribution of light elements and ultra-trace-elements.

Effect of mechanical surface treatments on the high temperature oxidation of pure titanium: the role of nitrogen

The mechanically treated high temperature (700°C) oxidation of commercially pure titanium was studied for long exposures (3000 h). The treatments studied here are the shot-peening and the laser-shock peening. The mass gain was measured by discontinued weighing. SEM and Raman imaging revealed strong differences between laser-shock peened, shot-peened and untreated oxidized samples. The laser treatment leads to thin compact and protective oxide layer while the shot-peened and untreated samples exhibit cracked oxide layers. The distribution of light elements like carbon, oxygen and nitrogen was revealed by Ion Beam Analysis. The presence of nitrogen located at the interface between the oxide scale and the metal was revealed on laser-shock peened samples. It is supposed the nitrogen slows-down the oxygen diffusion into the metal. The extent of the oxygen-enriched metal is also smaller on LSP samples, which improves the ductility of titanium.

Carbon Partitioning Between the Earth's Inner and Outer Core

AbstractKnowledge of the abundance and distribution of light elements in the core is fundamental to the understanding of the Earth and other planetary systems. Recent studies (Li et al., 2018; Mashino et al., 2019) suggest the particular importance of carbon for explaining core properties, yet knowledge of carbon partitioning between the outer and inner core is unknown. By using the quasiharmonic approximation, ab initio molecular dynamics, and thermodynamic integration techniques, we have computed the chemical potential of carbon in liquid Fe and solid hcp‐Fe at core conditions. We find that substitutional carbon is more stable than interstitial carbon and other carbon defect cluster structures in solid Fe. Lattice strain and overcoordination effects lead to a high chemical potential of C in solid Fe compared to the liquid, and consequently carbon partitions almost completely into the liquid. We find that carbon can account for most of the density jump at the inner‐core boundary. This provides an alternative mechanism to the necessity of an oxygen‐rich outer core and may have significant implications for the composition and structure of the deep Earth.

Light element distribution in fresh and frozen-thawed human ovarian tissues: a preliminary study.

Does synchrotron X-ray fluorescence (XRF) provide novel chemical information for the evaluation of human ovarian tissue cryopreservation protocols? Tissues from five patients undergoing laparoscopic surgery for benign gynaecological conditions were fixed for microscopic analysis either immediately or after cryopreservation. After fixation, fresh and slowly frozen samples were selected by light microscopy and transmission electron microscopy, and subsequently analysed with synchrotron XRF microscopy at different incident energies. The distributions of elements detected at 7.3 keV (S, P, K, Cl, Fe, and Os) and 1.5 keV (Na and Mg) were related to the changes revealed by light microscopy and transmission electron microscopy analyses. The light elements showed highly informative findings. The S distribution was found to be an indicator of extracellular component changes in the stromal tissues of the freeze-stored samples, further revealed by the transmission electron microscopy analyses. Low-quality follicles, frequent in the freeze-thawed tissues, showed a high Na level in the ooplasm. On the contrary, good-quality follicles were detected by a homogeneous Cl distribution. The occurrence of vacuolated follicles increased after cryopreservation, and the XRF analyses showed that the vacuolar structures contained mainly Cl and Na. The study demonstrates that elemental imaging techniques, particularly revealing the distribution of light elements, could be useful in establishing new cryopreservation protocols.

NGC 6535: the lowest mass Milky Way globular cluster with a Na-O anti-correlation?

To understand globular clusters (GCs) we need to comprehend how their formation process was able to produce their abundance distribution of light elements. In particular, we seek to figure out which stars imprinted the peculiar chemical signature of GCs. One of the best ways is to study the light-element anti-correlations in a large sample of GCs that are analysed homogeneously. As part of our spectroscopic survey of GCs with FLAMES, we present here the results of our study of about 30 red giant member stars in the low-mass, low-metallicity Milky Way cluster NGC 6535. We measured the metallicity (finding [Fe/H]=-1.95, rms=0.04 dex in our homogeneous scale) and other elements of the cluster and, in particular, we concentrate here on O and Na abundances. These elements define the normal Na-O anti-correlation of classical GCs, making NGC 6535 perhaps the lowest mass cluster with a confirmed presence of multiple populations. We updated the census of Galactic and extragalactic GCs for which a statement on the presence or absence of multiple populations can be made on the basis of high-resolution spectroscopy preferentially, or photometry and low-resolution spectroscopy otherwise; we also discuss the importance of mass and age of the clusters as factors for multiple populations.

Elemental profiling of laser cladded multilayer coatings by laser induced breakdown spectroscopy and energy dispersive X-ray spectroscopy

Multilayer tungsten carbide wear resistant coatings were analyzed by laser induced breakdown spectroscopy (LIBS) and energy dispersive X-ray (EDX) spectroscopy. Coaxial laser cladding technique was utilized to produce tungsten carbide coating deposited on low alloy steel substrate with additional inconel 625 interlayer. EDX and LIBS techniques were used for elemental profiling of major components (Ni, W, C, Fe, etc.) in the coating. A good correlation between EDX and LIBS data was observed while LIBS provided additional information on light element distribution (carbon). A non-uniform distribution of tungsten carbide grains along coating depth was detected by both LIBS and EDX. In contrast, horizontal elemental profiling showed a uniform tungsten carbide particles distribution. Depth elemental profiling by layer-by-layer LIBS analysis was demonstrated to be an effective method for studying tungsten carbide grains distribution in wear resistant coating without any sample preparation.

Development of a microbeam PIXE system for additive light elements in structural materials

A new submicron scanning nuclear microprobe beam line was constructed in early 2016 at the accelerator facility of the University of Tsukuba, Japan. A microbeam scanning endstage (OM-2000, Oxford Microbeams, Oxford, UK) was installed at the end of this system. The distance from the object slit to the target position is 8730mm and the working distance is 180mm. This ion microbeam system will be used mainly for X-ray imaging of two-dimensional distributions of light elements in structural materials using particle-induced X-ray emission (PIXE). A silicon drift detector (SDD) with a thin window of Si3N4 was installed to detect characteristic X-rays emitted from light elements such as B, C, and N, which are common additive elements in structural materials. In addition, a superconducting tunnel junction (STJ) array detector is going to be installed to perform PIXE measurements more efficiently. By combining a microbeam scanning technology with the X-ray detectors, we plan to obtain two-dimensional maps of additive light elements in structural materials. Experiments for obtaining proton microbeams are ongoing, and a 6MeV proton beam with a diameter of between 12 and 20μm has been obtained to date.

MULTIPLE POPULATIONS IN THE OLD AND MASSIVE SMALL MAGELLANIC CLOUD GLOBULAR CLUSTER NGC 121*

ABSTRACT We used a combination of optical and near-UV Hubble Space Telescope photometry and FLAMES/ESO-VLT high-resolution spectroscopy to characterize the stellar content of the old and massive globular cluster (GC) NGC 121 in the Small Magellanic Cloud (SMC). We report on the detection of multiple stellar populations, the first case in the SMC stellar cluster system. This result enforces the emerging scenario in which the presence of multiple stellar populations is a distinctive-feature of old and massive GCs regardless of the environment, as far as the light-element distribution is concerned. We find that second-generation (SG) stars are more centrally concentrated than first-generation (FG) ones. More interestingly, at odds with what is typically observed in Galactic GCs, we find that NGC 121 is the only cluster so far to be dominated by FG stars that account for more than 65% of the total cluster mass. In the framework where GCs were born with 90%–95% of FG stars, this observational finding would suggest that either NGC 121 experienced a milder stellar mass-loss with respect to Galactic GCs or it formed a smaller fraction of SG stars.

Analytical Electron Microscopy of Carbon-Rich Mineral Aggregates in Solvent-Diluted Bitumen Products from Mined Alberta Oil Sands

Contaminant solids in solvent-diluted bitumen product obtained by solvent extraction and solids agglomeration (SESA) of Alberta oil sands are characterized using aberration-corrected scanning transmission electron microscopy (STEM). In particular, the distribution of carbon present in these contaminant solids is determined from spatially resolved spectroscopy. Three distinct types of carbon-rich particles are identified and consist of carbonate minerals, micrometer-sized particles of toluene-insoluble organic carbon, and clay aggregates containing toluene-insoluble organic carbon. Energy-dispersive X-ray spectroscopy (EDX) maps confirm the presence of carbonates, in addition to other minerals, whose abundances are determined by a recently developed quantitative phase analysis methodology. Carbonaceous micrometer-sized particles with detectable amounts of oxygen and sulfur also appear in the elemental maps and suggest the presence of bitumen-unrelated organic materials. Finally, EDX maps also suggest an intricate sub-micrometer association of carbon with clay minerals. To map the distribution of light elements and transition metals in these clay aggregates, electron energy-loss spectroscopy (EELS) analysis has been carried out at the nanometer scale. In addition to carbon-rich regions, sub-10-nm titanium and iron oxide particles are often found dispersed on the clay surfaces. By observing clay platelets in orientations both parallel and perpendicular to the electron beam, EELS maps confirm that the carbon is present on the surface of the clays, rather than intercalated between individual clay mineral layers within the crystal structure. Furthermore, the organic coating is not uniform, displaying carbon-rich features with dimension on the order of a few nanometers, while leaving some regions of the clay mineral surface exposed. Partial nanometer-scale organic coverage has been proposed to result in a biwettable character for clay platelets that will influence the bitumen extraction process, and such coverage has been shown here directly for the first time using spatially resolved spectroscopic microscopy observations.

Characterization of the Inhomogeneous Distribution of Light Elements in Ferritic Heat-Resistant Steels by Secondary Ion Mass Spectrometry

The addition of a small amount of boron and nitrogen is known to improve the creep strength and life of ferritic heat-resistant steels. These light elements are thought to be distributed in the microstructures in a complicated manner during the heat treatment and creep of these steels. In order to understand the influence of the light elements on the mechanical properties of ferritic heat-resistant steels, a microscopic distribution analysis of the light elements is of importance. In this study, two types of secondary ion mass spectrometry (SIMS) methods were used to investigate the measurement conditions for analyzing secondary ions derived from boron and nitrogen in steels. In dynamic SIMS with a quadrupole analyzer, boron in the samples was effectively detected as BO2– ions under irradiation with primary O2+ ions. From the time-of-flight (ToF) SIMS using a focused primary Bi32+ ion beam coupled with the exposure of the sample to a low partial pressure of oxygen, it was suggested that boron is enriched in M23C6 carbides in the steels and it may be, more or less, segregated at prior austenite grain boundaries with a moderate amount of nitrogen during normalizing. It was also demonstrated that nitrogen is precipitated as boron nitride in steels containing an excess amount of boron and nitrogen. The characteristics of the distribution of boron and nitrogen in the steels are discussed on the basis of the thermodynamic properties of these elements in the steels.

Development of a high‐resolution confocal micro‐XRF instrument equipped with a vacuum chamber

A confocal micro‐X‐ray fluorescence (micro‐XRF) instrument equipped with a vacuum chamber was newly developed. The instrument is operated under a vacuum condition to reduce the absorption of XRF in the atmosphere. Thin metal layers were developed to evaluate the confocal volume, corresponding to depth resolution. A set of thin metal layers (Al, Ti, Cr, Fe, Ni, Cu, Zr, Mo, and Au) was prepared by a magnetron sputtering technique. The depth resolutions of the new instrument were varied from 56.0 to 10.9 µm for an energy range from 1.4 to 17.4 keV, respectively. The lower limit of detection (LLD) was estimated by comparison with a glass standard reference material NIST SRM 621). The LLDs obtained by a conventional micro‐XRF were compared with the LLDs obtained by a confocal micro‐XRF instrument. The LLDs were improved in the measurement under confocal configuration because of the reduction of background intensity. Finally, layered materials related to forensic investigation were measured. The confocal micro‐XRF instrument was able to nondestructively obtain the distribution of light elements that cannot be detected by measurement in air. Copyright © 2013 John Wiley & Sons, Ltd.

Li‐enrichment in red giant rapid rotators: Planet engulfment versus extra mixing

AbstractLow mass stars undergo dramatic changes during the post main sequence evolution as the nuclear energy source shifts from the stellar core to a thin shell of active hydrogen burning. The outer convection zones of these stars deepen, dredging up nuclear‐processed material and altering the stellar surface abundances. Some light elements, such as lithium, are easily destroyed in the stellar interior, and dredge‐up depletes the surface abundances of these elements. The red giant stars' expanding radii also pose a threat to the stability of close orbiting planets, which can be tidally engulfed by the star. Planet engulfment may be able to account for two of the well known classes of atypical red giant stars: the rapid rotators and Li‐rich red giants. Alternatively, internal Li regeneration combined with “extra‐mixing” in red giants may account for Li‐rich giants, but this mechanism may not be able to explain rapid rotation. We have recently completed an observational study of field red giant stars, targeting both slow and rapid rotators, to compare the light element distribution between these two classes of rotators. We find that the rapid rotators have enriched Li abundances compared to the slow rotators; however, both classes of stars have similar distributions of 12C/13C – a proxy for mixing. Lower 12C/13C ratios are expected in stars that have regenerated Li internally. The peculiar red giant stars in our sample (both Li‐rich and rapid rotators) are not easily explained with either planet engulfment or Li regeneration alone. Both processes are likely at work. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Depth profiling of NbxO/W multilayers: effect of primary ion beam species (O2+, Ar+ and Cs+)

Depth profiling of NbxO/W multilayered samples was carried out using O2+, Cs+ or Ar+ beams of different energies (2 keV, 1 keV and 0.5 keV). The obtained depth profiles showed that sputtering with O2+ or Ar+ beams can reveal the distribution of light elements, while sputtering with Cs+ cannot show correctly their distribution if lower energy of 0.5 keV is applied. SRIM simulations show that changes in primary energy of sputter ions have much stronger effect on deposited energy incl. vacancy/ion and sputter yields than for oxygen and argon ion beam etching. It is suggested that O2+ or Ar+ sputter sources should be used when both light and heavy species are present in nano‐scale multilayered targets. Copyright © 2012 John Wiley & Sons, Ltd.

Microscopic Distributions of Light Elements and Their Precipitates in Multicrystalline Silicon for Solar Cells

The behaviors of carbon, nitrogen, and oxygen in multicrystalline silicon grown by the cast method were investigated using infrared absorption spectroscopy. A microscopic distribution map of the impurities and their precipitates was obtained with a spatial resolution of a few tens of µm. The distribution and bonding states depended on the impurity: nitrogen and oxygen precipitated as crystalline nitride (α-Si3N4) and amorphous oxide (SiO2), respectively, while carbon distributed homogeneously as isolated substitutional atoms. The nitrogen and oxygen precipitates remained independent, and thus, they might not have formed a compound oxynitride like Si2N2O.

A new mapping acquisition and processing system for simultaneous PIXE-RBS analysis with external beam

Abstract The combination of ion beam analysis techniques is particularly fruitful for the study of cultural heritage objects. For several years, the AGLAE facility of the Louvre laboratory has been implementing these techniques with an external beam. The recent set-up permits to carry out PIXE, PIGE and RBS simultaneously on the same analyzed spot with a particle beam of approximately 20 μm diameter. A new mapping system has been developed in order to provide elemental concentration maps from the PIXE and RBS spectra. This system combines the Genie2000 spectroscopy software with a homemade software that creates maps by handling acquisition with the object position. Each pixel of each PIXE and RBS maps contains the spectrum normalised by the dose. After analysing each pixel of the PIXE maps (low and high energy X-ray spectra) with the Gupixwin peak-fitting software, quantitative elemental concentrations are obtained for the major and trace elements. This paper presents the quantitative elemental maps extracted from the PIXE spectra and the development of RBS data processing for light element distribution and thin layer characterization. Examples on rock painting and lustrous ceramics will be presented.

Distribution of Light Elements in Multicrystalline Silicon for Solar Cells Grown by Directional Solidification

We investigated the relationship between the formation of small grains and the distribution of precipitates such as and SiON in a multicrystalline silicon ingot grown by the unidirectional solidification method. precipitates were mainly observed inside the small grain region, while SiON was mainly precipitated outside the small grain region. SiON started to precipitate before the formation of precipitates. Therefore, precipitation of SiON before precipitation of is a candidate in the formation of small grains.

Distributions of Light Elements and Their Precipitations Grown by Unidirectional Solidification Method in Multicrystalline Silicon for Solar Cells

We investigated the relationship between the formation of small grains and distribution of precipitates such as Si3N4 and SiON in a multicrystalline silicon ingot grown by the unidirectional solidification method. Si3N4 precipitate was mainly observed inside the small grain region, while SiON was mainly precipitated outside there. We found that SiON started to precipitate prior to formation of Si3N4 precipitates. Therefore, precipitation of SiON prior to precipitation of Si3N4 plays a key role in the formation of small grains.

Investigation of light element contents in subsurface layers of silicon

A special methodology for determination of light element concentrations in subsurface layers of solids is developed. The clue of this methodology is simultaneous application of Rutherford Backscattering Spectroscopy (RBS) and Elastic Recoil Detection (ERD). The first analytical technique is used as a tool enabling the precise measurement of the number of He ions irradiating the target whilst the second one is appropriate for an analysis of a target containing light elements. The measurements of atomic concentrations in amorphous hydrogenated silicon carbide (a-SiC x :H) and in amorphous hydrogenated carbon (a-C:H) were done applying the described method (results for a-SiC x :H only are presented in the paper). The possibility for high precision measurements of depth distributions of light elements is also discussed.