ORCID Profile
0000-0002-9742-7937
Current Organisations
University of Oxford
,
Paul Scherrer Institute
Does something not look right? The information on this page has been harvested from data sources that may not be up to date. We continue to work with information providers to improve coverage and quality. To report an issue, use the Feedback Form.
Publisher: Springer Science and Business Media LLC
Date: 03-12-2021
DOI: 10.1038/S41467-021-27224-5
Abstract: Small ion-irradiation-induced defects can dramatically alter material properties and speed up degradation. Unfortunately, most of the defects irradiation creates are below the visibility limit of state-of-the-art microscopy. As such, our understanding of their impact is largely based on simulations with major unknowns. Here we present an x-ray crystalline microscopy approach, able to image with high sensitivity, nano-scale 3D resolution and extended field of view, the lattice strains and tilts in crystalline materials. Using this enhanced Bragg ptychography tool, we study the damage helium-ion-irradiation produces in tungsten, revealing a series of crystalline details in the 3D s le. Our results lead to the conclusions that few-atom-large ‘invisible’ defects are likely isotropic in orientation and homogeneously distributed. A partially defect-denuded region is observed close to a grain boundary. These findings open up exciting perspectives for the modelling of irradiation damage and the detailed analysis of crystalline properties in complex materials.
Publisher: Springer Science and Business Media LLC
Date: 06-04-2017
DOI: 10.1038/SREP45993
Abstract: Focussed Ion Beam (FIB) milling is a mainstay of nano-scale machining. By manipulating a tightly focussed beam of energetic ions, often gallium (Ga + ), FIB can sculpt nanostructures via localised sputtering. This ability to cut solid matter on the nano-scale revolutionised s le preparation across the life, earth and materials sciences. Despite its widespread usage, detailed understanding of the FIB-induced structural damage, intrinsic to the technique, remains elusive. Here we examine the defects caused by FIB in initially pristine objects. Using Bragg Coherent X-ray Diffraction Imaging (BCDI), we are able to spatially-resolve the full lattice strain tensor in FIB-milled gold nano-crystals. We find that every use of FIB causes large lattice distortions. Even very low ion doses, typical of FIB imaging and previously thought negligible, have a dramatic effect. Our results are consistent with a damage microstructure dominated by vacancies, highlighting the importance of free-surfaces in determining which defects are retained. At larger ion fluences, used during FIB-milling, we observe an extended dislocation network that causes stresses far beyond the bulk tensile strength of gold. These observations provide new fundamental insight into the nature of the damage created and the defects that lead to a surprisingly inhomogeneous morphology.
Publisher: The Optical Society
Date: 23-02-2015
DOI: 10.1364/OE.23.005438
Publisher: Proceedings of the National Academy of Sciences
Date: 09-02-2015
Abstract: X-ray fluorescence microscopy provides unparalleled sensitivity for measuring the distribution of trace elements in many-micrometer-thick specimens, whereas ptychography offers a path to the imaging of weakly fluorescing biological ultrastructure at beyond-focusing-optic resolution. We demonstrate here for the first time, to our knowledge, the combination of fluorescence and ptychography for imaging frozen-hydrated specimens at cryogenic temperatures, with excellent structural and chemical preservation. This combined approach will have significant impact on studies of the intracellular localization of nanocomposites with attached therapeutic or diagnostic agents, help elucidate the roles of trace metals in cell development, and further the study of diseases where trace metal misregulation is suspected (including neurodegenerative diseases).
Publisher: American Physical Society (APS)
Date: 15-09-2021
Publisher: International Union of Crystallography (IUCr)
Date: 11-08-2016
DOI: 10.1107/S1600577516011917
Abstract: Owing to its extreme sensitivity, quantitative mapping of elemental distributions via X-ray fluorescence microscopy (XFM) has become a key microanalytical technique. The recent realisation of scanning X-ray diffraction microscopy (SXDM) meanwhile provides an avenue for quantitative super-resolved ultra-structural visualization. The similarity of their experimental geometries indicates excellent prospects for simultaneous acquisition. Here, in both step- and fly-scanning modes, robust, simultaneous XFM-SXDM is demonstrated.
Publisher: International Union of Crystallography (IUCr)
Date: 08-08-2017
DOI: 10.1107/S1600577517009183
Abstract: Multi-reflection Bragg coherent diffraction imaging has the potential to allow three-dimensional (3D) resolved measurements of the full lattice strain tensor in specific micro-crystals. Until now such measurements were h ered by the need for laborious, time-intensive alignment procedures. Here a different approach is demonstrated, using micro-beam Laue X-ray diffraction to first determine the lattice orientation of the micro-crystal. This information is then used to rapidly align coherent diffraction measurements of three or more reflections from the crystal. Based on these, 3D strain and stress fields in the crystal are successfully determined. This approach is demonstrated on a focused ion beam milled micro-crystal from which six reflections could be measured. Since information from more than three independent reflections is available, the reliability of the phases retrieved from the coherent diffraction data can be assessed. Our results show that rapid, reliable 3D coherent diffraction measurements of the full lattice strain tensor in specific micro-crystals are now feasible and can be successfully carried out even in heavily distorted s les.
Publisher: IOP Publishing
Date: 14-03-2016
Publisher: International Union of Crystallography (IUCr)
Date: 28-09-2017
DOI: 10.1107/S1600576717012663
Abstract: The recent availability of extremely intense, femtosecond X-ray free-electron laser (XFEL) sources has spurred the development of serial femtosecond nanocrystallography (SFX). Here, SFX is used to analyze nanoscale crystals of β-hematin, the synthetic form of hemozoin which is a waste by-product of the malaria parasite. This analysis reveals significant differences in β-hematin data collected during SFX and synchrotron crystallography experiments. To interpret these differences two possibilities are considered: structural differences between the nanocrystal and larger crystalline forms of β-hematin, and radiation damage. Simulation studies show that structural inhomogeneity appears at present to provide a better fit to the experimental data. If confirmed, these observations will have implications for designing compounds that inhibit hemozoin formation and suggest that, for some systems at least, additional information may be gained by comparing structures obtained from nanocrystals and macroscopic crystals of the same molecule.
Publisher: International Union of Crystallography (IUCr)
Date: 2017
DOI: 10.1107/S1600577516017525
Abstract: The proliferation of extremely intense synchrotron sources has enabled ever higher-resolution structures to be obtained using data collected from smaller and often more imperfect biological crystals (Helliwell, 1984). Synchrotron beamlines now exist that are capable of measuring data from single crystals that are just a few micrometres in size. This provides renewed motivation to study and understand the radiation damage behaviour of small protein crystals. Reciprocal-space mapping and Bragg coherent diffractive imaging experiments have been performed on cryo-cooled microcrystals of hen egg-white lysozyme as they undergo radiation damage. Several well established metrics, such as intensity-loss and lattice expansion, are applied to the diffraction data and the results are compared with several new metrics that can be extracted from the coherent imaging experiments. In idually some of these metrics are inconclusive. However, combining metrics, the results suggest that radiation damage behaviour in protein micro-crystals differs from that of larger protein crystals and may allow them to continue to diffract for longer. A possible mechanism to account for these observations is proposed.
Publisher: Walter de Gruyter GmbH
Date: 14-07-2014
DOI: 10.3139/146.111065
Abstract: The spatial resolution of diffractive imaging techniques depends upon the numerical aperture of the detected scatter rather than any image forming optics. Fresnel coherent diffractive imaging has been developed over the past decade as a means for examining regions of interest within continuous s les and for overcoming many of the stagnation issues traditionally associated with coherent diffractive imaging. Ptychography meanwhile has been developed independently as a method of reconstructing the transmission function of extended objects from diffraction data recorded using a sequence of multiple overlapping probes on the s le. The relatively recent combination of these two methods has been found to provide substantial benefits over either of the two techniques when applied separately. The experimental requirements and basic principles of ptychographic Fresnel diffraction tomography are reviewed in this paper.
Publisher: International Union of Crystallography (IUCr)
Date: 17-01-2022
DOI: 10.1107/S1600577521012856
Abstract: Over the last decade ptychography has progressed rapidly from a specialist ultramicroscopy technique into a mature method accessible to non-expert users. However, to improve scientific value ptychography data must reconstruct reliably, with high image quality and at no cost to other correlative methods. Presented here is the implementation of high-speed ptychography used at the Australian Synchrotron on the XFM beamline, which includes a free-run data collection mode where dead time is eliminated and the scan time is optimized. It is shown that free-run data collection is viable for fast and high-quality ptychography by demonstrating extremely high data rate acquisition covering areas up to 352 000 µm 2 at up to 140 µm 2 s −1 , with 13× spatial resolution enhancement compared with the beam size. With these improvements, ptychography at velocities up to 250 µm s −1 is approaching speeds compatible with fast-scanning X-ray fluorescence microscopy. The combination of these methods provides morphological context for elemental and chemical information, enabling unique scientific outcomes.
Publisher: Inderscience Publishers
Date: 2017
Publisher: Elsevier BV
Date: 2023
Publisher: International Union of Crystallography (IUCr)
Date: 06-09-2022
DOI: 10.1107/S1600576722007646
Abstract: Bragg coherent X-ray diffraction imaging (BCDI) allows the 3D measurement of lattice strain along the scattering vector for specific microcrystals. If at least three linearly independent reflections are measured, the 3D variation of the full lattice strain tensor within the microcrystal can be recovered. However, this requires knowledge of the crystal orientation, which is typically attained via estimates based on crystal geometry or synchrotron microbeam Laue diffraction measurements. Presented here is an alternative method to determine the crystal orientation for BCDI measurements using electron backscatter diffraction (EBSD) to align Fe–Ni and Co–Fe alloy microcrystals on three different substrates. The orientation matrix is calculated from EBSD Euler angles and compared with the orientation determined using microbeam Laue diffraction. The average angular mismatch between the orientation matrices is less than ∼6°, which is reasonable for the search for Bragg reflections. The use of an orientation matrix derived from EBSD is demonstrated to align and measure five reflections for a single Fe–Ni microcrystal via multi-reflection BCDI. Using this data set, a refined strain field computation based on the gradient of the complex exponential of the phase is developed. This approach is shown to increase accuracy, especially in the presence of dislocations. The results demonstrate the feasibility of using EBSD to pre-align BCDI s les and the application of more efficient approaches to determine the full lattice strain tensor with greater accuracy.
Publisher: Royal Society of Chemistry (RSC)
Date: 2019
DOI: 10.1039/C8CC09664C
Abstract: Accurately locating biologically relevant elements at high resolution: simultaneous ptychography and fluorescence imaging of large specimens comes of age.
Publisher: International Union of Crystallography (IUCr)
Date: 21-07-2022
DOI: 10.1107/S1600577522006968
Abstract: The acquisition speed and spatial resolution of X-ray nanotomography have continuously improved over the last decades. Coherent diffraction-based techniques breach the 10 nm resolution barrier frequently and thus pose stringent demands on s le positioning accuracy and stability. At the same time there is an increasing desire to accommodate in situ or operando measurements. Here, an environmental control system for X-ray nanotomography is introduced to regulate the temperature of a s le from room temperature up to 850°C in a controlled atmospheric composition. The system allows for a 360° s le rotation, permitting tomographic studies in situ or operando free of missing wedge constraints. The system is implemented and available at the flOMNI microscope at the Swiss Light Source. In addition to the environmental control system itself, the related modifications of flOMNI are described. Tomographic measurements of a nanoporous gold s le at 50°C and 600°C at a resolution of sub-20 nm demonstrate the performance of the device.
Publisher: Royal Society of Chemistry (RSC)
Date: 2022
DOI: 10.1039/D1CE01586A
Abstract: Morphology, 3D lattice strain, and dissolution of a Co–Fe microcrystal was monitored using in situ Bragg coherent X-ray diffraction imaging.
Publisher: SPIE
Date: 26-09-2013
DOI: 10.1117/12.2027211
Publisher: Elsevier BV
Date: 11-2014
DOI: 10.1016/J.BBAMEM.2014.08.005
Abstract: Lipid-mimetic metallosurfactant based luminophores are promising candidates for labeling phospholipid membranes without altering their biophysical characteristics. The metallosurfactants studied exhibit high structural and physicochemical similarity to phospholipid molecules, designed to incorporate into the membrane structure without the need for covalent attachment to a lipid molecule. In this work, two lipid-mimetic phosphorescent metal complexes are described: [Ru(bpy)2(dn-bpy)](2+) and [Ir(ppy)2(dn-bpy)](+) where bpy is 2,2'-bipyridine, dn-bpy is 4,4'-dinonyl-2,2'-bipyridine and ppy is 2-phenylpyridine. Apart from being lipid-mimetic in size, shape and physical properties, both complexes exhibit intense photoluminescence and enhanced photostability compared with conventional organic fluorophores, allowing for prolonged observation. Moreover, the large Stokes shift and long luminescence lifetime associated with these complexes make them more suitable for spectroscopic studies. The complexes are easily incorporated into dimyristoil-phosphatidyl-choline (DMPC) liposomes by mixing in the organic solvent phase. DLS reveals the labeled membranes form liposomes of similar size to that of neat DMPC membrane. Synchrotron Small-Angle X-ray Scattering (SAXS) measurements confirmed that up to 5% of either complex could be incorporated into DMPC membranes without producing any structural changes in the membrane. Fluorescence microscopy reveals that 0.5% label content is sufficient for imaging. Atomic Force Microscopic imaging confirms that liposomes of the labeled bilayers on a mica surface can fuse into a flat lamellar membrane that is morphologically identical to neat lipid membranes. These results demonstrate the potential of such lipid-mimetic luminescent metal complexes as a new class of labels for imaging lipid membranes.
Publisher: American Physical Society (APS)
Date: 24-11-2020
Publisher: AIP Publishing
Date: 29-04-2015
DOI: 10.1063/1.4919641
Abstract: For laboratory and synchrotron based X-ray sources, radiation damage has posed a significant barrier to obtaining high-resolution structural data from biological macromolecules. The problem is particularly acute for micron-sized crystals where the weaker signal often necessitates the use of higher intensity beams to obtain the relevant data. Here, we employ a combination of techniques, including Bragg coherent diffractive imaging to characterise the radiation induced damage in a micron-sized protein crystal over time. The approach we adopt here could help screen for potential protein crystal candidates for measurement at X-ray free election laser sources.
Publisher: IOP Publishing
Date: 05-09-2014
Publisher: Public Library of Science (PLoS)
Date: 29-08-2022
DOI: 10.1371/JOURNAL.PONE.0273315
Abstract: X-ray directional dark-field imaging is a recent technique that can reveal a s le’s small-scale structural properties which are otherwise invisible in a conventional imaging system. In particular, directional dark-field can detect and quantify the orientation of anisotropic structures. Here, we present an algorithm that allows for the extraction of a directional dark-field signal from X-ray speckle-based imaging data. The experimental setup is simple, as it requires only the addition of a diffuser to a full-field microscope setup. Sandpaper is an appropriate diffuser material in the hard x-ray regime. We propose an approach to extract the mean scattering width, directionality, and orientation from the recorded speckle images acquired with the technique. We demonstrate that our method can detect and quantify the orientation of fibres inside a carbon fibre reinforced polymer (CFRP) s le within one degree of accuracy and show how the accuracy depends on the number of included measurements. We show that the reconstruction parameters can be tuned to increase or decrease accuracy at the expense of spatial resolution.
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Nicholas Phillips.