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Abstract: The PERCIVAL detector is a CMOS imager designed for the soft X-ray regime at photon sources. Although still in its final development phase, it has recently seen its first user experiments: ptychography at a free-electron laser, holographic imaging at a storage ring and preliminary tests on X-ray photon correlation spectroscopy. The detector performed remarkably well in terms of spatial resolution achievable in the sample plane, owing to its small pixel size, large active area and very large dynamic range; but also in terms of its frame rate, which is significantly faster than traditional CCDs. In particular, it is the combination of these features which makes PERCIVAL an attractive option for soft X-ray science.

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Abstract: This note shows the evolution of detectors for crystallography at Diamond Light Source since it came into operation and how this evolution shaped the way the experiments are done. It is also highlighted the next detector challenges due to the increase in photon flux related to the planned upgrade of the machine.

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Abstract: This paper describes the development of the Tristan 10M detector for time resolved synchrotron experiments. Tristan 10M has an unprecedented time resolution (ns time scale) over long duration continuous acquisition (days). The detector is constructed from an array of 160 Timepix3 readout ASIC (about 10 million pixels) flip chip bonded to 10 monolithic silicon sensors which enable it to cover an area large enough to effectively carry out crystallography experiments. The large array of ASICs resulted in a number of severe technical challenges that had to be overcome during the development of the detector. The minimization of the dead area between sensors required the development of a very challenging mechanical and electronic packaging. Such a packaging had to be able to route the large number of data and power lines within the footprint of a sensor, had to effectively sink the heat generated by the ASICs, and had to be able to position the sensors accurately. In addition, the packaging of the detector was designed to be scalable in consideration of possible future larger versions of this detector which added a further challenge. The data driven nature of Timepix3 and the sheer data volume produced by the array of ASICs required us to devise a dedicated hardware, firmware, and software data acquisition architecture. This architecture proved very effective during the commissioning of Tristan10M when time resolved crystallography experiments were carried out.

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Abstract: A new type of transmissive pixel detector has been developed for synchrotron radiation diagnostics at Diamond Light Source. A thin single-crystal CVD diamond plate is used as the detector material, and a pulsed-laser technique has been used to write conductive graphitic electrodes inside the diamond plate. Instead of using traditional electrodes formed from a layer of surface metallisation, the graphitic electrodes are buried under the surface of the diamond and result in an all-carbon imaging detector. Within the instrument’s transmissive aperture there are no surface structures that could be damaged by exposure to radiation beams, and no surface metallization that could introduce unwanted absorption edges. The instrument has successfully been used to image the X-ray beam profile and measure the beam position to sub-micron accuracy at 100 Hz at Diamond Light Source. A novel modulation lock-in technique is used to read out all pixels simultaneously. Presented in this work are measurements of the detector’s beam position resolution and intensity resolution. Initial measurements of the instrument’s spread-function are also presented. Numerical simulations are used to identify potential improvements to the electrode geometry to improve the spatial resolution of similar future detectors. The instrument has applications in both synchrotron radiation instrumentation, where real-time monitoring of the beam profile is useful for beam diagnostics and fault-finding, and particle tracking at colliders, where the electrode geometries that buried graphitic tracks can provide increased the charge collection efficiency of the detector.

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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.