B16-Test Beamline
|
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.
|
Jun 2018
|
|
B16-Test Beamline
|
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.
|
Sep 2018
|
|
I08-Scanning X-ray Microscopy beamline (SXM)
|
Open Access
Abstract: This study explores the delivery of phosphorus to the upper atmospheres of Earth, Mars, and Venus via the ablation of cosmic dust particles. Micron-size meteoritic particles were flash heated to temperatures as high as 2900 K in a Meteor Ablation Simulator (MASI), and the ablation of PO and Ca recorded simultaneously by laser induced fluorescence. Apatite grains were also ablated as a reference. The speciation of P in anhydrous chondritic porous Interplanetary Dust Particles was made by K-edge X-ray absorption near edge structure (XANES) spectroscopy, demonstrating that P mainly occurs in phosphate-like domains. A thermodynamic model of P in a silicate melt was then developed for inclusion in the Leeds Chemical Ablation Model (CABMOD). A Regular Solution model used to describe the distribution of P between molten stainless steel and a multicomponent slag is shown to provide the most accurate solution for a chondritic-composition, and reproduces satisfactorily the PO ablation profiles observed in the MASI. Meteoritic P is moderately volatile and ablates before refractory metals such as Ca; its ablation efficiency in the upper atmosphere is similar to Ni and Fe. The speciation of evaporated P depends significantly on the oxygen fugacity, and P should mainly be injected into planetary upper atmospheres as PO2, which will then likely undergo dissociation to PO (and possibly P) through hyperthermal collisions with air molecules. The global P ablation rates are estimated to be 0.017 t d−1 (tonnes per Earth day), 1.15 × 10−3 t d−1 and 0.024 t d−1 for Earth, Mars and Venus, respectively.
|
Apr 2020
|
|
I08-Scanning X-ray Microscopy beamline (SXM)
|
Dawn M.
Buchanan
,
Laura
Newsome
,
Jonathan R.
Lloyd
,
Majid
Kazemian
,
Burkhard
Kaulich
,
Tohru
Araki
,
Heath
Bagshaw
,
John
Waters
,
Gerrit
Van Der Laan
,
Alpha
N’diaye
,
Victoria S.
Coker
Diamond Proposal Number(s):
[17626]
Open Access
Abstract: Cobalt is an essential element for life and plays a crucial role in supporting the drive to clean energy, due to its importance in rechargeable batteries. Co is often associated with Fe in the environment, but the fate of Co in Fe-rich biogeochemically-active environments is poorly understood. To address this, synchrotron-based scanning X-ray microscopy (SXM) was used investigate the behaviour of cobalt at the nanoscale in Co-Fe(III)-oxyhydroxides undergoing microbial reduction. SXM can assess spatial changes in metal speciation and organic compounds helping to elucidate the electron transfer processes occurring at the cell-mineral interface and inform on the fate of cobalt in redox horizons. G. sulfurreducens was used to reduce synthetic Co-ferrihydrite as an analogue of natural cobalt-iron-oxides. Magnetite [Fe(II)/Fe(III)3O4] production was confirmed by powder X-ray diffraction (XRD), SXM and X-ray magnetic circular dichroism (XMCD) data, where best fits of the latter suggested Co-bearing magnetite. Macro-scale XAS techniques suggested Co(III) reduction occurred and complementary SXM at the nanoscale, coupled with imaging, found localised biogenic Co(III) reduction at the cell-mineral interface via direct contact with outer membrane cytochromes. No discernible localised changes in Fe speciation were detected in the reordered cobalt-iron-oxides that were formed and at the end point of the experiment only 11% Co and 1.5% Fe had been solubilised. The solid phase retention, alongside the highly localised and preferential cobalt bioreduction observed at the nanoscale is consistent with retention of Co in redox zones. This work improves our fundamental molecular-scale understanding of the fate of Co in complex environmental systems and supports the development of biogenic Co-doped magnetite for industrial applications from drug delivery systems to magnetic recording media.
|
May 2022
|
|
I08-Scanning X-ray Microscopy beamline (SXM)
|
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.
|
Jan 2018
|
|
I08-Scanning X-ray Microscopy beamline (SXM)
I10-Beamline for Advanced Dichroism
|
Open Access
Abstract: Atypical low-oxidation-state iron phases in Alzheimer’s disease (AD) pathology are implicated in disease pathogenesis, as they may promote elevated redox activity and convey toxicity. However, the origin of low-oxidation-state iron and the pathways responsible for its formation and evolution remain unresolved. Here we investigate the interaction of the AD peptide β-amyloid (Aβ) with the iron storage protein ferritin, to establish whether interactions between these two species are a potential source of low-oxidation-state iron in AD. Using X-ray spectromicroscopy and electron microscopy we found that the co-aggregation of Aβ and ferritin resulted in the conversion of ferritin’s inert ferric core into more reactive low-oxidation-states. Such findings strongly implicate Aβ in the altered iron handling and increased oxidative stress observed in AD pathogenesis. These amyloid-associated iron phases have biomarker potential to assist with disease diagnosis and staging, and may act as targets for therapies designed to lower oxidative stress in AD tissue.
|
Jun 2020
|
|
I08-Scanning X-ray Microscopy beamline (SXM)
I14-Hard X-ray Nanoprobe
|
Diamond Proposal Number(s):
[15230, 15854, 20809, 24526, 24531]
Open Access
Abstract: A hallmark of Parkinson’s disease is the death of neuromelanin‐pigmented neurons, but the role of neuromelanin is unclear. Lack of a neuromelanin‐specific marker was highlighted over 30 years ago, yet in‐situ characterization of neuromelanin remains dependent on detectable pigmentation, rather than direct quantification of neuromelanin. We show that direct, label‐free nanoscale visualization of neuromelanin and associated metal ions in human brain tissue can be achieved using synchrotron Scanning Transmission X‐ray Microscopy (STXM), via a characteristic feature in the neuromelanin x‐ray absorption spectrum at 287.4 eV that is also present in iron‐free and iron‐laden synthetic neuromelanin. This is confirmed in consecutive brain sections by correlating STXM neuromelanin imaging with silver nitrate‐stained neuromelanin. Analysis suggests that the 1s ‐ σ* (C‐S) transition in benzothiazine groups accounts for this feature. This advance in visualizing neuromelanin illustrates the wider potential of STXM as a label‐free spectromicroscopy technique applicable to both organic and inorganic materials.
|
Mar 2020
|
|
I08-Scanning X-ray Microscopy beamline (SXM)
|
Diamond Proposal Number(s):
[20839]
Open Access
Abstract: Minerals are widely proposed to protect organic carbon from degradation and thus promote the persistence of organic carbon in soils and sediments, yet a direct link between mineral adsorption and retardation of microbial remineralisation is often presumed and a mechanistic understanding of the protective preservation hypothesis is lacking. We find that methylamines, the major substrates for cryptic methane production in marine surface sediment, are strongly adsorbed by marine sediment clays, and that this adsorption significantly reduces their concentrations in the dissolved pool (up to 40.2 ± 0.2%). Moreover, the presence of clay minerals slows methane production and reduces final methane produced (up to 24.9 ± 0.3%) by a typical methylotrophic methanogen—Methanococcoides methylutens TMA-10. Near edge X-ray absorption fine structure spectroscopy shows that reversible adsorption and occlusive protection of methylamines in clay interlayers are responsible for the slow-down and reduction in methane production. Here we show that mineral-OC interactions strongly control methylotrophic methanogenesis and potentially cryptic methane cycling in marine surface sediments.
|
May 2022
|
|
I08-Scanning X-ray Microscopy beamline (SXM)
|
Diamond Proposal Number(s):
[23540]
Open Access
Abstract: Mineral-associated organic matter is an integral part of soil carbon pool. Biological processes contribute to the formation of such organo-mineral complexes when soil microbes, and in particular soil fungi, deposit a suite of extracellular metabolic compounds and their necromass on the mineral surfaces. While studied in bulk, micro- to nanoscale fungal–mineral interactions remain elusive. Of particular interest are the mutual effects at the interface between the fungal exometabolites and proximal mineral particles. In this work, we have grown saprotrophic and symbiotic fungi in contact with two soil minerals with contrasting properties: quartz and goethite, on top of X-ray transparent silicon nitride membrane windows and analyzed fungal hyphae by synchrotron-based scanning transmission X-ray microscopy in combination with near edge X-ray fine structure spectroscopy at C(K) and Fe(L) absorption edges. In the resultant chemical maps, we were able to visualize and differentiate organic compounds constituting the fungal cells, their extracellular metabolites, and the exometabolites adsorbing on the minerals. We found that the composition of the exometabolites differed between the fungal functional guilds, particularly, in their sugar to protein ratio and potassium concentration. In samples with quartz and goethite, we observed adsorption of the exometabolic compounds on the mineral surfaces with variations in their chemical composition around the particles. Although we did not observe clear alteration in the exometabolite chemistry upon mineral encounters, we show that fungal–mineral interaction result in reduction of Fe(III) in goethite. This process has been demonstrated for bulk systems, but, to our knowledge, this is the first observation on a single hypha scale offering insight into its underlying biological mechanisms. This demonstrates the link between processes initiated at the single-cell level to macroscale phenomena. Thus, spatially resolved chemical characterization of the microbial–mineral interfaces is crucial for an increased understanding of overall carbon cycling in soil.
|
Jun 2022
|
|
I08-Scanning X-ray Microscopy beamline (SXM)
|
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.
|
Apr 2018
|
|
