I12-JEEP: Joint Engineering, Environmental and Processing
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Diamond Proposal Number(s):
[2933]
Abstract: Synchrotron white beam X-ray topography has been used to characterise bulk crystal defects of thick vapour grown CdZnTe crystals. Whole 50 mm diameter wafers with thicknesses in the range of 2–3 mm were sliced from boules grown by the multi-tube physical vapour transport method and analysed by diffraction topography in a transmission geometry. A variety of defects were observed including cracks, voids and grain boundaries. The largest quantity of defects observed were sub-grains appearing as localised increased intensity in the topographs. The periphery of the wafers showed the highest number of defects, whereas central regions where largely defect-free. We failed to observe any inclusions or precipitates within these crystals. Surface damage from wire-saw cutting was also observed on poorly processed wafers; these defects were otherwise invisible to standard characterisation methods. X-ray topography has proven to be a useful tool for non-destructively investigating bulk extended defects in CdZnTe crystals for radiation detector applications.
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Jan 2012
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I08-Scanning X-ray Microscopy beamline (SXM)
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Diamond Proposal Number(s):
[11282]
Abstract: Rivers are significant contributors of Fe to the ocean. However, the characteristics of chemically reactive Fe remain poorly constrained, especially in large Arctic rivers, which drain landscapes highly susceptible to climate change and carbon cycle alteration. The aim of this study was a detailed characterisation (size, mineralogy, and speciation) of riverine Fe-bearing particles (> 0.22 µm) and colloids (1 kDa – 0.22 µm) and their association with organic carbon (OC), in the Lena River and tributaries, which drain a catchment almost entirely underlain by permafrost. Samples from the main channel and tributaries representing watersheds that span a wide range in topography and lithology were taken after the spring flood in June 2013 and summer baseflow in July 2012. Fe-bearing particles were identified, using Transmission Electron Microscopy, as large (200 nm – 1 µm) aggregates of smaller (20 nm - 30 nm) spherical colloids of chemically-reactive ferrihydrite. In contrast, there were also large (500 nm – 1 µm) aggregates of clay (illite) particles and smaller (100 - 200 nm) iron oxide particles (dominantly hematite) that contain poorly reactive Fe. TEM imaging and Scanning Transmission X-ray microscopy (STXM) indicated that the ferrihydrite is present as discrete particles within networks of amorphous particulate organic carbon (POC) and attached to the surface of primary produced organic matter and clay particles. Together, these larger particles act as the main carriers of nanoscale ferrihydrite in the Lena River basin. The chemically reactive ferrihydrite accounts for on average 70 ± 15 % of the total suspended Fe in the Lena River and tributaries. These observations place important constraints on Fe and OC cycling in the Lena River catchment area and Fe-bearing particle transport to the Arctic Ocean.
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Jul 2017
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I08-Scanning X-ray Microscopy beamline (SXM)
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Qing
Wu
,
Karolina
Soppa
,
Nadim
Scherrer
,
Benjamin
Watts
,
Tadahiro
Yokosawa
,
Laetitia
Bernard
,
Tohru
Araki
,
Max
Döbeli
,
Markus
Meyer
,
Erdmann
Spiecker
,
Rainer H.
Fink
Diamond Proposal Number(s):
[15595]
Open Access
Abstract: Zwischgold is a two-sided metal foil made by adhering a gold leaf over a silver leaf to present a gold surface while using less gold than gold foils. Corroded Zwischgold surfaces appear dark, accompanied by gloss loss and possible mechanical stability issues. Zwischgold applied artefacts are commonly found in museums and churches across Europe and they currently face an uncertain future as conservators have little knowledge to base conservation treatments on. We present a comprehensive material analysis of Zwischgold models through advanced characterization techniques including focused ion beam coupled with scanning electron microscopy (FIB-SEM), transmission electron microscopy (TEM), scanning transmission X-ray microscopy (STXM), time-of-flight secondary ion mass spectrometry (TOF-SIMS)and Rutherford backscattering spectrometry (RBS). Complementary information on the foil thickness,sharpness of the gold-silver interface, gold purity, and the formation as well as distribution of corrosion products on Zwischgold models have been obtained, representing a starting point for understanding themorphology and the long-term chemistry of Zwischgold artefacts.
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Jan 2018
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I08-Scanning X-ray Microscopy beamline (SXM)
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Diamond Proposal Number(s):
[15854, 19779]
Open Access
Abstract: Altered metabolism of biometals in the brain is a key feature of Alzheimer’s disease, and biometal interactions
with amyloid-β are linked to amyloid plaque formation. Iron-rich aggregates, including evidence
for the mixed-valence iron oxide magnetite, are associated with amyloid plaques. To test the hypothesis
that increased chemical reduction of iron, as observed in vitro in the presence of aggregating amyloid-β,
may occur at sites of amyloid plaque formation in the human brain, the nanoscale distribution and
physicochemical states of biometals, particularly iron, were characterised in isolated amyloid plaque cores
from human Alzheimer’s disease cases using synchrotron X-ray spectromicroscopy. In situ X-ray magnetic
circular dichroism revealed the presence of magnetite: a finding supported by ptychographic observation
of an iron oxide crystal with the morphology of biogenic magnetite. The exceptional sensitivity and
specificity of X-ray spectromicroscopy, combining chemical and magnetic probes, allowed enhanced
differentiation of the iron oxides phases present. This facilitated the discovery and speciation of ferrousrich
phases and lower oxidation state phases resembling zero-valent iron as well as magnetite.
Sequestered calcium was discovered in two distinct mineral forms suggesting a dynamic process of
amyloid plaque calcification in vivo. The range of iron oxidation states present and the direct observation
of biogenic magnetite provide unparalleled support for the hypothesis that chemical reduction of iron
arises in conjunction with the formation of amyloid plaques. These new findings raise challenging questions
about the relative impacts of amyloid-β aggregation, plaque formation, and disrupted metal homeostasis
on the oxidative burden observed in Alzheimer’s disease.
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Apr 2018
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B16-Test Beamline
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Diamond Proposal Number(s):
[13464]
Abstract: During 4H silicon carbide (4H-SiC) homoepitaxy and post-growth processes, the development of stress relaxation has been observed, in which interfacial dislocations (IDs) are formed at the epilayer/substrate interface, relaxing the misfit strain induced by the nitrogen doping concentration difference between the epilayer and substrate. It is widely believed that an interfacial dislocation is created by the glide of a mobile segment of a basal plane dislocation (BPD) in the substrate or epilayer towards the interface, leaving a trailing edge component right at the interface.
However, direct observation of such mechanisms has not been made in SiC before. In this work, we present an in situ study of the stress relaxation process, in which a specimen cut from a commercial
4H-SiC homoepitaxial wafer undergoes the stress relaxation process during a high-temperature heat treatment while sequential synchrotron white beam X-ray topographs were recorded simultaneously. Based on the dynamic observation of this process, it can be concluded that thermal stress plays a role in the relaxation process while the increased misfit strain at elevated temperature most likely drives the formation of an interfacial dislocation.
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Jun 2018
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B16-Test Beamline
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Diamond Proposal Number(s):
[13464]
Abstract: We present in-situ observations of the dynamical operation of multiple double-ended Frank-Read dislocation sources in a PVT-grown 4H-SiC wafer under thermal gradient stresses. The nucleation of these sources is facilitated by a specific configuration consisting of one basal plane dislocation (BPD) segment pinned by two threading edge dislocations (TEDs). This configuration is formed during PVT crystal growth by deflection of TEDs on to the basal planes by macrosteps and re-deflection of resulting BPDs back into TEDs. Under the influence of thermal gradient stresses induced by heating inside a double ellipsoidal mirror furnace, the pinned BPD segment glides and activates dislocation multiplication by the double Frank-Read source mechanism. A more intricate
mechanism of swapping of TED pinning points between Frank-Read sources lying on the same basal plane is identified, enabling one dislocation loop to effectively “pass through” the other dislocations on the same basal plane.
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Jun 2018
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B16-Test Beamline
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Diamond Proposal Number(s):
[13464]
Abstract: During 4H silicon carbide (4H-SiC) homoepitaxy and post-growth processes, the development of stress relaxation has been observed, in which interfacial dislocations (IDs) are formed at the epilayer/substrate interface, relaxing the misfit strain induced by the nitrogen doping concentration difference between the epilayer and substrate. It is widely believed that an interfacial dislocation is created by the glide of a mobile segment of a basal plane dislocation (BPD) in the substrate or epilayer towards the interface, leaving a trailing edge component right at the interface. However, direct observation of such mechanisms has not been made in SiC before. In this work, we present an in situ study of the stress relaxation process, in which a specimen cut from a commercial 4H-SiC homoepitaxial wafer undergoes the stress relaxation process during a high-temperature heat treatment while sequential synchrotron white beam X-ray topographs were recorded simultaneously. Based on the dynamic observation of this process, it can be concluded that thermal stress plays a role in the relaxation process while the increased misfit strain at elevated temperature most likely drives the formation of an interfacial dislocation.
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Sep 2018
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I08-Scanning X-ray Microscopy beamline (SXM)
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Daniela
Medas
,
Ilaria
Carlomagno
,
Carlo
Meneghini
,
Giuliana
Aquilanti
,
Tohru
Araki
,
Diana
Bedolla
,
Carla
Buosi
,
Maria Antonietta
Casu
,
Alessandra
Gianoncelli
,
Andrei C.
Kuncser
,
V. Adrian
Maraloiu
,
Giovanni
De Giudici
Diamond Proposal Number(s):
[16496]
Abstract: Zinc incorporation into marine bivalve shells belonging to different genera (Donax, Glycymeris, Lentidium, and Chamelea) grown in mine-polluted seabed sediments (Zn up to 1% w/w) was investigated using x-ray diffraction (XRD), chemical analysis, soft x-ray microscopy combined with low-energy x-ray fluorescence (XRF) mapping, x-ray absorption spectroscopy (XAS), and transmission electron microscopy (TEM). These bivalves grew their shells, producing aragonite as the main biomineral and they were able to incorporate up to 2.0–80 mg/kg of Zn, 5.4–60 mg/kg of Fe and 0.5–4.5 mg/kg of Mn. X-ray absorption near edge structure (XANES) analysis revealed that for all the investigated genera, Zn occurred as independent Zn mineral phases, i.e., it was not incorporated or adsorbed into the aragonitic lattice. Overall, our results indicated that Zn coordination environment depends on the amount of incorporated Zn. Zn phosphate was the most abundant species in Donax and Lentidium genera, whereas, Chamelea shells, characterized by the highest Zn concentrations, showed the prevalence of Zn-cysteine species (up to 56% of total speciation). Other Zn coordination species found in the investigated samples were Zn hydrate carbonate (hydrozincite) and Zn phosphate. On the basis of the coordination environments, it was deduced that bivalves have developed different biogeochemical mechanisms to regulate Zn content and its chemical speciation and that cysteine plays an important role as an active part of detoxification mechanism. This work represents a step forward for understanding bivalve biomineralization and its significance for environmental monitoring and paleoreconstruction.
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Oct 2018
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I08-Scanning X-ray Microscopy beamline (SXM)
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Diamond Proposal Number(s):
[14946]
Open Access
Abstract: Adsorption of prebiotic building blocks is proposed to have played a role in the emergence of life on Earth. The experimental and theoretical study of this phenomenon should be guided by our knowledge of the geochemistry of the habitable early Earth environments, which could have spanned a large range of settings. Adsorption being an interfacial phenomenon, experiments can be built around the minerals that probably exhibited the largest specific surface areas and were the most abundant, i.e., phyllosilicates. Our current work aims at understanding how nucleotides, the building blocks of RNA and DNA, might have interacted with phyllosilicates under various physico-chemical conditions. We carried out and refined batch adsorption studies to explore parameters such as temperature, pH, salinity, etc. We built a comprehensive, generalized model of the adsorption mechanisms of nucleotides onto phyllosilicate particles, mainly governed by phosphate reactivity. More recently, we used surface chemistry and geochemistry techniques, such as vibrational spectroscopy, low pressure gas adsorption, X-ray microscopy, and theoretical simulations, in order to acquire direct data on the adsorption configurations and localization of nucleotides on mineral surfaces. Although some of these techniques proved to be challenging, questioning our ability to easily detect biosignatures, they confirmed and complemented our pre-established model.
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Nov 2018
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I08-Scanning X-ray Microscopy beamline (SXM)
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Diamond Proposal Number(s):
[12738]
Open Access
Abstract: Iron (Fe) limits or co-limits primary productivity and nitrogen fixation in large regions of the world's oceans, and the supply of Fe from hydrothermal vents to the deep ocean is now known to be extensive. However, the mechanisms that control the amount of hydrothermal Fe that is stabilized in the deep ocean, and thus dictate the impact of hydrothermal Fe sources on surface ocean biogeochemistry, are unclear. To learn more, we have examined the dispersion of total dissolvable Fe (TDFe), dissolved Fe (dFe) and soluble Fe (sFe) in the buoyant and non-buoyant hydrothermal plume above the Beebe vent field, Caribbean Sea. We have also characterized plume particles using electron microscopy and synchrotron based spectromicroscopy.
We show that the majority of dFe in the Beebe hydrothermal plume was present as colloidal Fe (dFe − sFe = cFe). During ascent of the buoyant plume, a significant fraction of particulate Fe (pFe = TDFe − dFe) was lost to settling and exchange with colloids. Conversely, the opposite was observed in the non-buoyant plume, where pFe concentrations increased during non-buoyant plume dilution, cFe concentrations decreased apparently due to colloid aggregation. Elemental mapping of carbon, oxygen and iron in plume particles reveals their close association and indicates that exchanges of Fe between colloids and particles must include transformations of organic carbon and Fe oxyhydroxide minerals. Notably, sFe is largely conserved during plume dilution, and this is likely to be due to stabilization by organic ligands, in contrast to the more dynamic exchanges between pFe and cFe.
This study highlights that the size of the sFe stabilizing ligand pool, and the rate of iron-rich colloid aggregation will control the amount and physico-chemical composition of dFe supplied to the ocean interior from hydrothermal systems. Both the ligand pool, and the rate of cFe aggregation in hydrothermal plumes remain uncertain and determining these are important intermediate goals to more accurately assess the impact of hydrothermalism on the ocean's carbon cycle.
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Jan 2019
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