Coherent methods in the X-ray sciences

X-ray sources are developing rapidly and their coherent output is growing extremely rapidly. The increased coherent flux from modern X-ray sources is being matched with an associated rapid development in experimental methods. This article reviews the literature describing the ideas that utilise the increased brilliance from modern X-ray sources. It explores how ideas in coherent X-ray science are leading to developments in other areas, and vice versa. The article describes measurements of coherence properties and uses this discussion as a base from which to describe partially-coherent diffraction and X-ray phase contrast imaging, with its applications in materials science, engineering and medicine. Coherent diffraction imaging methods are reviewed along with associated experiments in materials science. Proposals for experiments to be performed with the new X-ray free-electron-lasers are briefly discussed. The literature on X-ray photon correlation spectroscopy is described and the features it has in common with other coherent X-ray methods are identified. Many of the ideas used in the coherent X-ray literature have their origins in the optical and electron communities and these connections are explored. A review of the areas in which ideas from coherent X-ray methods are contributing to methods for the neutron, electron and optical communities is presented.Comment: A review articel accepted by Advances in Physics. 158 pages, 29 figures, 3 table

Hybrid Semiconductor Detectors for High Spatial Resolution Phase-contrast X-ray Imaging

When conventional x-ray radiography presents inadequate absorption-contrast, higher sensitivity can be achieved using phase-contrast methods. The implementation of phase-contrast x-ray imaging using propagation-based techniques requires stringent spatial resolution requirements that necessitate lengthy propagation distances and thin (and hence low detection efficiency) scintillator-based detectors. Thus, imaging throughput is limited, and the absorbed dose in the sample can be unacceptable for radiation sensitive life science and biomedical applications. This work develops hybrid amorphous selenium and complementary metal-oxide-semiconductor detectors with a unique combination of high spatial resolution and detection efficiency for hard x-rays. A semiconductor fabrication process was developed for large-area compatible vertical detector integration by back-end processing. Characterization of signal and noise performance using Fourier-based methods was performed by modulation transfer function, noise power spectrum, and detective quantum efficiency experiments using radiography and microfocus x-ray sources. The measured spatial resolution at each stage of detector development was one of the highest, if not the highest reported for hard x-rays. In fact, charge carrier spreading from x-ray interactions with amorphous selenium was shown physically larger than the pixel pitch for the first time. A simultaneous factor of four improvement in detection efficiency compared to thin gadolinium oxysulfide-based scintillator detectors was also achieved, despite the detector being a relatively unoptimized prototype. Fast propagation-based phase-contrast x-ray imaging in compact geometries is demonstrated using a conventional microfocus source. This simple implementation of the phase-contrast technique was applied to imaging the mouse stifle joint. Using propagation-based edge-enhancement the articular cartilage was delineated, opening the possibility of studying diseases such as osteoarthritis using a compact, relatively simple laboratory setup. This research suggests that hybrid semiconductor technology offers the potential to fill the large performance deficit in high spatial resolution scintillator-based detectors for propagation-based phase-contrast x-ray imaging

X-ray Phase-Contrast Tomography: Underlying Physics and Developments for Breast Imaging

X-ray phase-contrast tomography is a powerful tool to dramatically increase the visibility of features exhibiting a faint attenuation contrast within bulk samples, as is generally the case of light (low-Z) materials. For this reason, the application to clinical tasks aiming at imaging soft tissues, as e.g., breast imaging, has always been a driving force in the development of this field. In this context, the SYRMA-3D project, which constitutes the framework of the present work, aims to develop and implement the first breast computed tomography system relying on the propagation-based phase-contrast technique at the Elettra synchrotron facility (Trieste, Italy). This thesis finds itself in the \u2018last mile\u2019 towards the in-vivo implementation, and the obtained results add some of the missing pieces in the realization of the project. The first part of the work introduces a homogeneous mathematical framework describing propagation-based phase contrast from the sample-induced X-ray refraction, to detection, processing and tomographic reconstruction. The original results reported in the following chapters include the implementation of a pre-processing procedure dedicated for a novel photon-counting CdTe detector; a study, supported by a rigorous theoretical model, on signal and noise dependence on physical parameters such as propagation distance and detector pixel size; hardware and software developments for improving signal-to-noise ratio and reducing the scan time; and, finally, a clinically-oriented study based on comparisons with clinical mammographic and histological images. The last part of the thesis attempts to widen the experimental horizon: first, a quantitative image comparison of the synchrotron-based setup and a clinically available breast-CT scanner is presented and then a practical laboratory implementation is detailed, introducing a monochromatic propagation-based micro-tomography setup making use on a high-power rotating anode source

Crystal Cartography: Mapping Nanostructure with Scanning Electron Diffraction

Nanostructure describes the network of defective and distorted atomic structure existing on the nanoscale within materials. This nanostructure bridges the gap between idealised crys- talline structure and real materials, playing a deterministic role in tailoring physico-chemical properties, as well as providing a basis for mechanistic understanding of complex processes such as mechanical deformation and phase transformation. Characterising nanostructure, to develop understanding of materials, requires experimental techniques capable of probing the structure with spatial resolution on the order of nanometres and across regions of interest up to micrometres. Recent developments in electron microscopy, enabling the acquisition of numerous diffraction patterns in a spatially resolved manner, combined with modern computational power, provides a route to meet this need as developed in this work. Scanning electron diffraction (SED) involves the acquisition of a two-dimensional elec- tron diffraction pattern at each probe position in a two-dimensional scan of a specimen. An information rich 4-dimensional (4D-SED) dataset is obtained that can be analysed extensively post-facto using a wide-range of computational methods. The acquisition of such 4D-SED data from the specimen at numerous orientations may also enable the reconstruction of nanostructure in three-dimensions via tomographic methods. In this work, methods for the acquisition and analysis of 4D-SED data are developed and applied to reveal nanostructure in two and three-dimensions. These methods are applied to various prototypical characterisation challenges in materials science, particularly: strain mapping in two and three dimensions, revealing inter-phase crystallographic relationships, mapping grains in two-dimensional materials, and probing nanostructure in polyethylene

Studies of hybrid pixel detectors for use in Transmission Electron Microscopy

Hybrid pixel detectors (HPDs) are a class of direct electron detectors that have been adopted for use in a wide variety of experimental modalities across all branches of electron microscopy. Nevertheless, this does not preclude the possibility of further improvement and optimisation of their performance for specific applications and increasing the range of experiments for which they are suitable. The aims of this thesis are two-fold. Firstly, to develop a more comprehensive understanding of the current generation HPDs using Si sensors, with a view to optimising their design. Secondly, to determine the advantages of alternative sensor materials that, in principle, should improve the performance of HPDs in transmission electron microscopy (TEM) due to their increased stopping power. The three chapters review the relevant theoretical background. This includes the physics underpinning the performance of semiconductor-based sensors in electron microscopy as well as the operation of detectors more generally and the theory underlying the metrics used to evaluate detector performance in Chapter 1. In Chapter 2, TEM as a key tool in the study of nano- and atomic scale systems is also introduced, along with an overview of the detector technologies used in TEM. Also presented as part of the background material in Chapter 3 is a description of the experimental methods and software packages used to acquire the results presented in the latter half of the thesis. Chapter 4, the first results chapter, presents a comparison of the performance of Medipix3 detectors with Si sensors with various combination of pixel pitch and sensor thickness for 60 keV and 200 keV electrons. In Chapter 5, simulations of the interactions of electrons with energies ranging from 30-300 keV with GaAs:Cr and CdTe/CZT, two of the most viable alternatives to Si for use in the sensors of HPDs, are compared with simulations of the interactions of electrons with Si. A comparative study of the performance of a Medipix3 device with GaAs:Cr sensor with that of a Si sensor of the same thickness and pixel pitch for electrons with energies ranging from 60-300 keV is presented in Chapter 6. Also included in this Chapter are the results of investigations into the defects present in the CaAs:Cr sensor material and how these affect device performance. These consist of confocal scanning transmission electron microscopy scans used to estimate the size and shape of individual pixels and how these relate to the linearity of pixels’ response, as well as studies of how the efficacy of a standard flat field depends on the incident electron flux. In the final results chapter, the focus shifts to preliminary measurements of the response of an integrating detector with GaAs:Cr sensor to electrons. These initial experimental measurements prompted further simulations investigating how the backside contact of GaAs:Cr sensors can be improved when using electrons

Microscopy Conference 2021 (MC 2021) - Proceedings

Das Dokument enthält die Kurzfassungen der Beiträge aller Teilnehmer an der Mikroskopiekonferenz "MC 2021"

Abstracts on Radio Direction Finding (1899 - 1995)

The files on this record represent the various databases that originally composed the CD-ROM issue of "Abstracts on Radio Direction Finding" database, which is now part of the Dudley Knox Library's Abstracts and Selected Full Text Documents on Radio Direction Finding (1899 - 1995) Collection. (See Calhoun record https://calhoun.nps.edu/handle/10945/57364 for further information on this collection and the bibliography). Due to issues of technological obsolescence preventing current and future audiences from accessing the bibliography, DKL exported and converted into the three files on this record the various databases contained in the CD-ROM. The contents of these files are: 1) RDFA_CompleteBibliography_xls.zip [RDFA_CompleteBibliography.xls: Metadata for the complete bibliography, in Excel 97-2003 Workbook format; RDFA_Glossary.xls: Glossary of terms, in Excel 97-2003 Workbookformat; RDFA_Biographies.xls: Biographies of leading figures, in Excel 97-2003 Workbook format]; 2) RDFA_CompleteBibliography_csv.zip [RDFA_CompleteBibliography.TXT: Metadata for the complete bibliography, in CSV format; RDFA_Glossary.TXT: Glossary of terms, in CSV format; RDFA_Biographies.TXT: Biographies of leading figures, in CSV format]; 3) RDFA_CompleteBibliography.pdf: A human readable display of the bibliographic data, as a means of double-checking any possible deviations due to conversion

National synchrotron light source. Activity report, October 1, 1994--September 30, 1995

This report discusses research conducted at the National Synchrotron Light Source in the following areas: atomic and molecular science; energy dispersive diffraction; lithography, microscopy, and tomography; nuclear physics; scattering and crystallography studies of biological materials; time resolved spectroscopy; UV photoemission and surface science; x-ray absorption spectroscopy; x-ray scattering and crystallography; x-ray topography; the 1995 NSLS annual users` meeting; 17th international free electron laser conference; micro bunches workshop; VUV machine; VUV storage ring parameters; beamline technical improvements; x-ray beamlines; x-ray storage ring parameters; the NSLS source development laboratory; the accelerator test facility (ATF); NSLS facility improvements; NSLS advisory committees; NSLS staff; VUV beamline guide; and x-ray beamline guide