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Abstract: Annular-dark field imaging is one of the most readily interpretable techniques in scanning transmission electron microscopy (STEM). The ADF detector integrates the intensity of incoherent, high-angle scattered electrons providing images with strong atomic number sensitivity that can be directly interpreted in terms of the sample’s atomic structure. The ADF contrast increases monotonically with the number of atoms in projection. This allows direct atomic counting to solve three-dimensional (3D) structures or determine composition at a given thickness. However, ADF STEM is not efficient for light elements detection because they scatter less strongly at high scattering angles. More suitable methods to image both light and heavy atoms are based on bright-field or phase-contrast techniques that collect low-angle scattered electrons. However, because these electrons scatter coherently, image quantification, in this case, is non-trivial. This talk will discuss quantification methods for two main (quasi-)coherent STEM imaging modes: annular- bright field (ABF) imaging and 4D STEM electron ptychography. In the case of ABF, image quantification is applied to the characterisation of the oxygen framework in lithium- rich Li1.2Ni0.2Mn0.6O2 (LNMO) layered cathodes. In this material, short-range oxygen sublattice distortions are evidence for oxygen participation in charge compensation mechanisms. These movements are of the order of picometres and, to be measured, require well-designed quantification methods. However, achieving picometre accuracy and precision is challenging in these materials because of the limited signal-to-noise ratio of the images imposed by the electron dose. The first part of this talk discusses how to achieve high-quality ABF quantification using a combination of experimental design and computational data processing including simultaneous ADF atom counting and multi-slice image simulations. The second part of the talk shows how these methods can be extended to the quantification of 4D STEM electron ptychography data using fast electron detectors. A four-dimensional dataset consist of a two- dimensional (2D) convergent beam electron diffraction pattern (CBED) recorded at every pixel of a 2D scan array. The exit wave resulting from the electron-specimen interaction can be restored from this dataset using electron ptychography. In analogy with the contrast in ADF, the exit wave phase is fully quantitative and is highly sensitive to the number of atoms in the sample and their position along the column. Here, phase and ADF quantification are used to count the number of light and heavy elements simultaneously. The technique is applied to determine the composition in a reduced CeO2-x nanoparticle by simultaneous counting the number of Ce and O atoms. Experimental design is fundamental for any quantification technique. The last part of this talk discusses design strategies for comparing ptychographic techniques at low dose and imaging of light biological materials. Also, it examines how to efficiently compare restored data based on the effect of the contrast transfer function for the recovered spatial frequencies.

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Abstract: At synchrotron facilities, many X-ray imaging and diffraction experiments require pixel detectors with minimal noise, high speed and reasonably small pixel size, all of which can be achieved with the Medipix ASIC family. So, ESRF, Diamond Light Source and DESY have developed detector systems based on Medipix. In this paper, we report on these developments, with an emphasis on the challenges involved building readout systems and the potential of the Medipix family ASICs in this field of research.

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Abstract: One of the major limitations of XAS experiment at synchrotron facilities is the performance of the detectors. In order to be able to measure more challenging samples and to cope with the very high photon flux of the current and future (diffraction limited) sources technological developments of detectors are necessary. This paper reports on the construction and characterization of a monolithic nineteen channel germanium detector demonstrator fitted with CMOS preamplifiers. The detector was characterized in the lab with radioactive sources and with the X-ray synchrotron beam. Characteristics such as energy resolution, linearity, counting rate capabilities, and stability of the detector were thoroughly evaluated. In addition, it was proved that by using an advanced pulse processor such as Xspress4 it was possible to improve the performance of the detector system by eliminating the cross talk among channels and by suppressing the charge shared events. This work could pave the way to enhanced germanium fluorescence detectors for high throughput X-ray spectroscopy.

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Abstract: In this work, the spectroscopic performances of new cadmium–zinc–telluride (CZT) pixel detectors recently developed at IMEM-CNR of Parma (Italy) are presented. Sub-millimetre arrays with pixel pitch less than 500 µm, based on boron oxide encapsulated vertical Bridgman grown CZT crystals, were fabricated. Excellent room-temperature performance characterizes the detectors even at high-bias-voltage operation (9000 V cm−1), with energy resolutions (FWHM) of 4% (0.9 keV), 1.7% (1 keV) and 1.3% (1.6 keV) at 22.1, 59.5 and 122.1 keV, respectively. Charge-sharing investigations were performed with both uncollimated and collimated synchrotron X-ray beams with particular attention to the mitigation of the charge losses at the inter-pixel gap region. High-rate measurements demonstrated the absence of high-flux radiation-induced polarization phenomena up to 2 × 106 photons mm−2 s−1. These activities are in the framework of an international collaboration on the development of energy-resolved photon-counting systems for high-flux energy-resolved X-ray imaging.

Open Access

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Abstract: The increasing data throughput of modern detectors is a growing challenge for back-end data acquisition systems. OdinData provides a scalable framework for data acquisition used by multiple beamlines at Diamond Light Source (DLS). While it can be implemented standalone, OdinControl is used to provide a convenient interface to OdinData. Eiger detectors at DLS were initially integrated into the Odin framework specifically for the data acquisition capability, but the addition of detector control provides a more coherent and easily deployable system. OdinControl provides a generic HTTP API as a single point of control for various devices and applications. Adapters can abstract the low-level control of a detector into a consistent API, making it easier for high-level applications to support different types of detector. This paper sets out the design and development of Odin as a control system agnostic interface to integrate Eiger detectors into EPICS beamline control systems at DLS, as well as the current status of operation.