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
|
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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B16-Test Beamline
B18-Core EXAFS
I08-Scanning X-ray Microscopy beamline (SXM)
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Debi
Garai
,
Vladyslav
Solokha
,
Axel
Wilson
,
Ilaria
Carlomagno
,
Ajay
Gupta
,
Mukul
Gupta
,
V. R.
Reddy
,
Carlo
Meneghini
,
Francesco
Carla
,
Christian
Morawe
,
Jorg
Zegenhagen
Diamond Proposal Number(s):
[17145]
Open Access
Abstract: This work reports about a novel approach for investigating surface processes during the early stages of galvanic corrosion of stainless steel in situ by employing ultra-thin films and synchrotron X-radiation. Characterized by X-ray techniques and voltammetry, such films, sputter deposited from austenitic steel, were found representing useful replicas of the target material. Typical for stainless steel, the surface consists of a passivation layer of Fe- and Cr-oxides, a couple of nm thick, that is depleted of Ni. Films of ≈ 4 nm thickness were studied in situ in an electrochemical cell under potential control (-0.6 to +0.8 V vs Ag/AgCl) during exposure to 0.1 M KCl. Material transport was recorded with better than 1/10 monolayer sensitivity by X-ray spectroscopy. Leaching of Fe was observed in the cathodic range and the therefor necessary reduction of Fe-oxide appears to be accelerated by atomic hydrogen. Except for minor leaching, reduction of Ni, while expected from Pourbaix diagram, was not observed until at ≈ +0.8 V Cr-oxide was removed from the film. After couple of minutes exposure at +0.8 V, the current in the electrochemical cell revealed a rapid pitting event that was simultaneously monitored by X-ray spectroscopy. Continuous loss of Cr and Ni was observed during the induction time leading to the pitting, suggesting a causal connection with the event. Finally, a spectroscopic image of a pit was recorded ex situ with 50 nm lateral and 1 nm depth resolution by soft X-ray scanning absorption microscopy at the Fe L2,3-edges by using a 80 nm film on a SiN membrane, which is further demonstrating the usefulness of thin films for corrosion studies.
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Dec 2020
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B18-Core EXAFS
I08-Scanning X-ray Microscopy beamline (SXM)
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Diamond Proposal Number(s):
[20567, 20204]
Open Access
Abstract: Understanding the potential of nanomaterials (NMs) to cross the blood–brain barrier (BBB), as a function of their physicochemical properties and subsequent behavior, fate, and adverse effect beyond that point, is vital for evaluating the neurological effects arising from their unintentional entry into the brain, which is yet to be fully explored. This is not only due to the complex nature of the brain but also the existing analytical limitations for characterization and quantification of NMs in the complex brain environment. By using a fit-for-purpose analytical workflow and an in vitro BBB model, we show that the physiochemical properties of metallic NMs influence their biotransformation in biological matrices, which in turn modulates the transport form, efficiency, amounts, and pathways of NMs through the BBB and, consequently, their neurotoxicity. The data presented here will support in silico modeling and prediction of the neurotoxicity of NMs and facilitate the tailored design of safe NMs.
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Jul 2021
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B24-Cryo Soft X-ray Tomography
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Ilias
Kounatidis
,
Megan L.
Stanifer
,
Michael A.
Phillips
,
Perrine
Paul-Gilloteaux
,
Xavier
Heiligenstein
,
Hongchang
Wang
,
Chidinma
Okolo
,
Thomas M.
Fish
,
Matthew C.
Spink
,
David I.
Stuart
,
Ilan
Davis
,
Steeveh
Boulant
,
Jonathan M.
Grimes
,
Ian M.
Dobbie
,
Maria
Harkiolaki
Diamond Proposal Number(s):
[21046, 18314]
Open Access
Abstract: Imaging of biological matter across resolution scales entails the challenge of preserving the direct and unambiguous correlation of subject features from the macroscopic to the microscopic level. Here, we present a correlative imaging platform developed specifically for imaging cells in 3D under cryogenic conditions by using X-rays and visible light. Rapid cryo-preservation of biological specimens is the current gold standard in sample preparation for ultrastructural analysis in X-ray imaging. However, cryogenic fluorescence localization methods are, in their majority, diffraction-limited and fail to deliver matching resolution. We addressed this technological gap by developing an integrated, user-friendly platform for 3D correlative imaging of cells in vitreous ice by using super-resolution structured illumination microscopy in conjunction with soft X-ray tomography. The power of this approach is demonstrated by studying the process of reovirus release from intracellular vesicles during the early stages of infection and identifying intracellular virus-induced structures.
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Jun 2020
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B24-Cryo Soft X-ray Tomography
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Diamond Proposal Number(s):
[18339, 19615]
Open Access
Abstract: The organoiridium complex Ir[(C,N)2(O,O)] (1) where C, N = 1-phenylisoquinoline and O,O = 2,2,6,6-tetramethyl-3,5-heptanedionate is a promising photosensitiser for Photo-Dynamic Therapy (PDT). 1 is not toxic to cells in the dark. However, irradiation of the compound with one-photon blue or two-photon red light generates high levels of singlet oxygen (1O2) (in Zhang et al. Angew Chem Int Ed Engl 56 (47):14898-14902 https://doi.org/10.1002/anie.201709082,2017), both within cell monolayers and in tumour models. Moreover, photo-excited 1 oxidises key proteins, causing metabolic alterations in cancer cells with potent antiproliferative activity. Here, the tomograms obtained by cryo-Soft X-ray Tomography (cryo-SXT) of human PC3 prostate cancer cells treated with 1, irradiated with blue light, and cryopreserved to maintain them in their native state, reveal that irradiation causes extensive and specific alterations to mitochondria, but not other cellular components. Such new insights into the effect of 1O2 generation during PDT using iridium photosensitisers on cells contribute to a detailed understanding of their cellular mode of action.
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Mar 2020
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B24-Cryo Soft X-ray Tomography
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Nina
Vyas
,
Nina
Perry
,
Chidinma A.
Okolo
,
Ilias
Kounatidis
,
Thomas M.
Fish
,
Kamal L.
Nahas
,
Archana
Jadhav
,
Mohamed A.
Koronfel
,
Johannes
Groen
,
Eva
Pereiro
,
Ian M.
Dobbie
,
Maria
Harkiolaki
Diamond Proposal Number(s):
[25512]
Open Access
Abstract: Three-dimensional (3D) structured illumination microscopy (SIM) allows imaging of fluorescently labelled cellular structures at higher resolution than conventional fluorescence microscopy. This super-resolution (SR) technique enables visualization of molecular processes in whole cells and has the potential to be used in conjunction with electron microscopy and X-ray tomography to correlate structural and functional information. A SIM microscope for cryogenically preserved samples (cryoSIM) has recently been commissioned at the correlative cryo-imaging beamline B24 at the UK synchrotron.
It was designed specifically for 3D imaging of biological samples at cryogenic temperatures in a manner compatible with subsequent imaging of the same samples by X-ray microscopy methods such as cryo-soft X-ray tomography. This video article provides detailed methods and protocols for successful imaging using the cryoSIM. In addition to instructions on the operation of the cryoSIM microscope, recommendations have been included regarding the choice of samples, fluorophores, and parameter settings. The protocol is demonstrated in U2OS cell samples whose mitochondria and tubulin have been fluorescently labelled.
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May 2021
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B24-Cryo Soft X-ray Tomography
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Diamond Proposal Number(s):
[21046, 18314]
Abstract: Researchers have developed a new technique for studying cells in their native state. The goal was to obtain high-quality imaging data from cells without the need for sectioning or chemical fixation. The new method avoids any treatment that would disturb cell structure, so that no artefacts (errors) are introduced into the images.
To demonstrate this novel correlative microscopy platform’s effectiveness, the team studied the early stages of cell infection by reoviruses. Although the specific viruses have been studied extensively, there is a debate regarding the method of infection. This research focused on the way that the virus escapes from vesicles, a required step for replication. At beamline B24, using a correlative imaging approach by combining soft X-ray tomography with super resolution microscopy in cryogenic conditions, the team tracked the infection mechanism. The results revealed that the virus had already escaped from the host vesicles two hours after infection, with the vesicles preserving their circular shape, suggesting a gentle, pore-based exit mechanism for the virus.
Reoviruses are valuable tools that could be engineered to express proteins and have the potential to be used in vaccines. Knowing the infection mechanism will facilitate their handling and manipulation for biomedical purposes. The new imaging platform has also been used to validate anticancer compounds, study cell structure during development and investigate clearance of human pathogenic microorganism by immune host cells. The work is the outcome of a collective effort between Diamond Light Source and research groups and facilities across Europe, including the University of Oxford, Heidelberg University Hospital, the Université de Nantes and CryoCapCell.
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Jul 2021
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B24-Cryo Soft X-ray Tomography
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Mohamed A.
Koronfel
,
Ilias
Kounatidis
,
Dennis M.
Mwangangi
,
Nina
Vyas
,
Chidinma
Okolo
,
Archana
Jadhav
,
Tom
Fish
,
Phatcharin
Chotchuang
,
Albert
Schulte
,
Robert
Robinson
,
Maria
Harkiolaki
Diamond Proposal Number(s):
[23033, 23073]
Open Access
Abstract: Imaging of actin filaments is crucial due to the integral role that they play in many cellular functions such as intracellular transport, membrane remodelling and cell motility. Visualizing actin filaments has so far relied on fluorescence microscopy and electron microscopy/tomography. The former lacks the capacity to capture the overall local ultrastructure, while the latter requires rigorous sample preparation that can lead to potential artefacts, and only delivers relatively small volumes of imaging data at the thinnest areas of a cell. In this work, a correlative approach utilizing in situ super-resolution fluorescence imaging and cryo X-ray tomography was used to image bundles of actin filaments deep inside cells under near-native conditions. In this case, fluorescence 3D imaging localized the actin bundles within the intracellular space, while X-ray tomograms of the same areas provided detailed views of the local ultrastructure. Using this new approach, actin trails connecting vesicles in the perinuclear area and hotspots of actin presence within and around multivesicular bodies were observed. The characteristic prevalence of filamentous actin in cytoplasmic extensions was also documented.
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Dec 2021
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