Diamond Annual Review 2019/20
72 73 D I A M O N D L I G H T S O U R C E A N N U A L R E V I E W 2 0 1 9 / 2 0 D I A M O N D L I G H T S O U R C E A N N U A L R E V I E W 2 0 1 9 / 2 0 Spectroscopy Group Sofia Díaz-Moreno, Science Group Leader T he Diamond Spectroscopy Group consists of four beamlines; the Microfocus Spectroscopy beamline (I18), the Core EXAFS beamline (B18), and the two independently operating branches of the Versatile X-ray Absorption Spectroscopy beamline (I20- Scanning and I20-EDE). These four spectrometers are complementary in the energy ranges they cover, the size of their focussed beam spots delivered to the sample and the time resolutions they are able to reach. This complementarity means that they can support research across many different scientific disciplines, from chemistry and catalysis through to materials science, condensed matter physics, environmental and life science, energy materials and cultural heritage. Many technical developments have been implemented on the spectroscopy beamlines over the last year, aimed at improving the operational efficiency. Specific achievements include the integration of faster detectors and optimising the data collection and processing chains, and the implementation of automatic procedures to reduce experimental setup times. Additionally, new sample environment equipment for the study of energy materials has also been added to the beamline inventories, such as the multichannel potentiostat for B18. I18 update The Microfocus Spectroscopy beamline, I18, uses a finely focused X-ray beam to investigate heterogeneous materials on the micrometre scale using a variety of techniques, such as X-ray Fluorescence (XRF) mapping, X-ray Absorption Spectroscopy (XAS) and X-ray Diffraction (XRD). In recent years, new techniques that required the processing of large amounts of data, such as fluorescence and diffraction computed tomography (CT) have been added to the techniques offered at I18. This has been possible thanks to advances in beamline data collection, both in software and hardware, enabling faster and more efficient measurements.These improvements include the development and implementation of the Diamond mapping project, a development to ease the use of fly scanning for 2D data collection, as well as the procurement and integration of the fast Excalibur detector used for XRD. In addition, the procurement of a second Vortex ME-4 energy resolving detector fitted with Cube pre-amplifiers allowed even faster collection rates for XRF and XAS measurements, as it can be used side by side with the existing unit. These developments have been accompanied by improvements in the on- line data processing, so preliminary results can now be visualised within few minutes of the data collection. Currently it is possible to do full XRF and/or XRD CT reconstructions with a fully automated processing chain which starts immediately after the data is collected, and that requires no manual input. This makes the beamline ready for the future developments planned for 2020 that will further increase data collection speeds, such as the new sample stages. The stages have already been purchased and will become available in the second half of the year. B18 update The Core EXAFS beamline, B18, is optimised for the efficient collection of XAS data over all elements heavier than phosphorous. The focussing optics and the capability of the monochromator for continuous scanning, together with a flexible experimental space that supports a large range of sample environments, make this beamline ideal to perform experiments under in situ and operando conditions for catalysis and energy materials research. The latter science area has seen a substantial increase in the number of experiments performed in the last year. The intrinsic ability of XAS to provide element- specific, local and symmetry-selective information enables the elucidation of the mechanisms associated with mobile ion uptake and release during battery cycling. In response to this increased level of interest in this science area, a multi-channel potentiostat has been purchased for the beamline, and work is now progressing for the full integration of this systemwithin the beamline data acquisition system. It is expected that the instrument will become available for the spectroscopy users for the second part of 2020. The capabilities for fluorescence measurements in B18 have been enhanced by the upgrading of the von Hamos dispersive emission spectrometer to a four crystal cylindrical geometry from the initial one crystal prototype. The spectrometer is equipped with two interchangeable four-element Medipix position sensitive detectors and has been successfully used for three experiments during the last year, including a very demanding in situ catalysis study. Further efforts are being concentrated on making the systemmore user- friendly, including the data analysis pipeline. The last year has also seen the integration of additional techniques at B18 that are complementary to XAS, such as the implementation of back- reflection energy-dispersive X-ray diffraction (EDXRD) with soft/tender X-rays in collaboration with the University of Leicester.This technique takes advantage of thebroadenergyrangecoveredbythebeamline,andhassignificantadvantages in that it is a non-destructive technique and does not require any specific sample preparation. This makes the methodology ideal for applications in culture heritage, palaeontology and conservation science. The first experiments have shown the potential of this method, and regular access to B18 has now been granted for the next two years to develop the technique further. I20-Scanning update The Scanning branch of I20, I20-Scanning, exploits the high flux provided by the wiggler source through two different end stations. The XAS end station uses a 64 element monolithic germanium detector with the Xspress-4 read-out system to examine the structure of very low concentration samples. The X-ray Emission Spectroscopy (XES) end station uses a spectrometer based on a 1 m Rowland circle geometry to perform high-energy resolution studies of the electronic structure of samples. A new first crystal cage with a wider first crystal for the four-bounce monochromator was installed in March 2019. The larger crystal shows no strain effects from clamping and gives a better beam profile than the previous crystal cage. This has enabled the closure of the wiggler gap for higher energy experiments, increasing significantly the available monochromatic flux. This upgrade will enhance the beamlines’ capability in many scientific areas, such as the radionuclide research studies on novel uranium speciation under environmental conditions that is presented in this report. This last year several experiments at cryogenic temperatures have been performed in the XES end station, either because the experiments required measurements at variable temperature, or to slow down the radiation damage that the high intensity beam at I20-Scanning often causes in sensitive samples during data collection. Some of these experiments have used the low profile closed cycle cryostat available at the beamline and that is specifically designed to fit in the limited space available in the XES end station. The liquid helium cryostat available in I18 has also been used as samples can be loaded into it under cryogenic conditions and this enables studies of short-lived species isolated from solution reactions. I20-EDE update The Energy Dispersive EXAFS (EDE) branch of I20 uses a polychromator to perform XAS experiments in a dispersive geometry. It is designed for in situ and operando studies with time resolutions ranging from seconds down to milliseconds or even microseconds. Many different sample environments are available at the beamline as illustrated in the scientific highlight on multimodal studies presented in this report. The efficiency and usability of the beamline has been improved by several developments. The introduction of beampipes that can be moved in and out of the beam remotely to reduce air absorption when working at low energies is necessary when optimising the beamline optics and checking energy calibration. Eliminating the manual exchange of pipes has reduced beamline setup time substantially. In addition, an automatic filling system has been installed for the liquid nitrogen cooled XH detector, that has removed the need for manual intervention on a daily basis. Lastly, improvements in data quality have been made by developing a sample spinning system such that samples in a tube furnace can be spun in the beam path to present a more homogeneous sample to the beam. Community support and development Aside from supporting the beamlines and the operational science programme, the Spectroscopy Group has continued its efforts to support the development of the spectroscopy user community through running workshops covering best practice for the analysis of XRF and XAS data. A two-day workshop on X-ray Fluorescence Analysis was organised by the Spectroscopy Group for the first time in November 2019. This event focused on the use of PyMca, a versatile software package for the analysis of X-ray Fluorescence (XRF) data, and was delivered by A. Sole (ESRF), the main developer of the code. In March this year the group organised the annual three- day X-ray Absorption Spectroscopy workshop, covering a brief introduction to the spectroscopy beamlines at Diamond, as well as methods to process and analyse spectroscopy data. As was the case in previous years, the workshop was in high demand, with more than 150 applications. Diamond, through the Spectroscopy Group, together with Newcastle University, are the principal partners of the COllaborative NEtwork for X-ray Spectroscopy (CONEXS), an EPSRC funded network that aims to bring together experimentalists and theoreticians who are working in the area of X-ray spectroscopy to improve their ability to fully exploit and interpret experimental data. As part of the activities of the network, a Summer School was organised in September 2019, and an International Conference ‘CONEXS 2020: Emerging Trends in X-ray Spectroscopy’was held in February 2020. Both events were very well attended.
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