Diamond Annual Review 2021/22

38 39 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 2 1 / 2 2 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 2 1 / 2 2 Structures and Surfaces Group Chris Nicklin, Science Group Leader T he Structures and Surfaces Group includes four beamlines, each consisting of multiple end-stations that are optimised for a specific type of experiment: I05 (Angle Resolved Photoelectron Spectroscopy – ARPES), I07 (Surface and Interface X-ray Diffraction), B07 (Versatile Soft X-ray Scattering – VERSOX), and I09 (Atomic and Electronic Structure of Surfaces and Interfaces). They offer a variety of techniques to examine the atomic scale structure, chemical nature and electronic state at buried interfaces or the surfaces of materials. This year, the group has started to welcome users back for their experiments in-person, building on the strong partnerships that have developed during remote working restrictions. The group continue to benefit from many of the developments that have been realised during this period (for example enhanced automation) but recognise that many of the more complex studies rely on the expertise of the user groups, especially for sample preparation and experiment planning. It has also been a busy year for beamline upgrades (as detailed below) whilst also taking a strategic view for the future, with a focus on outlining the facilities that we plan to offer as part of the Diamond-II programme. The important role that surfaces and interfaces play in broader research areas such as battery technology, photovoltaic structures, and catalytic/electrochemical systems under operando conditions are key drivers for these developments. On beamline I05, the new electron energy analyser is now installed and in routine operation, offering exceptional quality data in terms of energy resolution. The future implementation of the ‘deflector mode’ will enable angle resolved measurements to be recorded without having to physically move the sample and will therefore increase the speed of data acquisition and maintain the photon beam in a consistent position on the sample. The NanoARPES branch-line continues to benefit from improved flux and reduced spot size through the incorporation of a capillary mirror, with a beam of four micrometres now achievable. Excellent data quality is achieved through the ability to focus the beam onto high quality areas of the sample, which in many newly produced crystals may only be a few micrometres in size. Understanding how sample heterogeneity influences the electronic structure is now a very active focus of research on the beamline. The sample preparation and mounting facilities also continue to benefit the user programme, with the glove box and micromanipulation system enabling precise mounting and alignment of crystals that are air sensitive. The team on I05 is looking to develop a new manipulator design to integrate electrical contacts that will enable direct biasing of the sample or control of a piezoelectric device to apply mechanical strain to a crystal. The surface and interface diffraction facilities on beamline I07 continue to be upgraded to enhance the capabilities. Continuous scanning of the diffractometer is now implemented for single axis scans while automated fast attenuators are currently being built and installed. This will enable fast measurement of crystal truncation rods that cover many orders of magnitude changes in intensity. The next stage will be to develop trajectory scanning in reciprocal space to enable rapid acquisition of crystal truncation rods or data in arbitrary hkl directions. The Large Area Detector positioning system has been upgraded to extend the range of sample-detector distances that can be achieved, improving the implementation for grazing incidence small (wide) angle X-ray scattering (GIS(W)AXS) investigations. A new CdTe Eiger 4M detector has been purchased for these experiments, which will improve the angular resolution of the measurements and the operating efficiency at higher energies. The diffractometer upgrade has been further delayed due to lockdown restrictions, but the beamline team have commissioned the new hexapod to increase the reliability and speed of experiments. There is an ambitious plan to upgrade the optical layout of the beamline, switching from mirror focusing to making use of compound refractive lenses to provide additional tunability in the beamdimensions as well as a smaller ultimate spot size. A concurrent upgrade to the double crystal deflector (DCD) system would improve the ease of operation and improve data quality for diffraction studies from liquid surfaces. The I07 team is also moving forward with improving the software provision, in particular for visualisation of reciprocal space maps and reduction/extraction of data for crystal truncation rod analysis. This year, the second branch (B07B) of theVERSOX beamline is scheduled to be fully open to users, with the second end-station for high-throughput X-ray photoelectron spectroscopy (XPS) studies, to enable chemical state analysis of many samples, having its first users in May 2022. The initial end-station for near edge X-ray absorption fine structure (NEXAFS) studies using soft X-rays to study processes such as molecular adsorption or catalysis has proven to be exceptionally productive. The near ambient pressure XPS (NAP-XPS) system available on Branch C of the beamline continues to work well and has been enhanced by the addition of a bespoke gas panel to enable automated exposure to pure and well controlled mixtures of gases. Full scripting of this facility through the data acquisition system enables complex studies to be semi-automated. Beamline I09 continues to maintain a very active user programme whilst also developing new capabilities. The hard X-ray photoemission (HAXPES) system is commissioned and available for users. The end station for the soft X-ray ARPES system is now built and the momentum microscope was delivered in the early part of 2022. Integration is underway, with an extensive commissioning programme to be started in Summer 2022, that we expect to take several months due to this novel design. I09 is awaiting the delivery of a small spot ultraviolet photoelectron spectroscopy (UPS) system that will enable the commissioning to be developed whilst user experiments continue. The next stage of this project is to ensure that maintainable software is developed in collaboration with the detector manufacturer through an EPICS interface. Smaller scale hardware upgrades are also being developed, including a modified manipulator design that enables sample biasing, cooling and heating whilst still allowing sample transfer. The group are aiming to enhance the associated infrastructure available for surface science research including the design of a new offline ultrahigh vacuum system to characterise samples, a proposal that was well received by the Scientific Advisory Committee (SAC). Design work has started as this system continues to be a high priority that will position Diamond to be able to rapidly study new samples and enhance the link between laboratory and synchrotron based experiments. We aim for this capability to be at the core of many of the joint PhD studentships that we support. The group aim to develop its suite of instruments in a number of ways as part of the Diamond-II programme. A dedicated nanoARPES instrument to be built on a mid-straight section has been announced as one of the five flagship beamlines. An associated upgrade to I05 will ensure that the suite of ARPES facilities is optimised to deliver high energy resolution and high spatial resolution, including fast mapping capabilities. Beamline B07 is currently sourced by a bending magnet, but as part of the Diamond-II upgrade, branch C will be changed to an insertion device, increasing the flux and energy range available for the NAP-XPS experiments and opening up new science opportunities. We aim for I07 to be Diamond-II ready through the optics upgrade outlined above that will also enhance the beamline before the Diamond-II dark period. Beamline I09 requires some modest changes to its optics scheme due to a change in the source positions in the machine. We will take the opportunity to incorporate higher specification mirrors and other components that will improve the beam quality at the sample position. The science undertaken within the group continues to be a range of underpinning fundamental surface science investigations through to using the techniques to understand the relevance to real-world applications. The user highlights include how I05 has been used to identify the spin-polarised surface states in the magnetic topological insulators MnBi 4 Te 7 and MnBi 6 Te 10 and to really in understand the interplay between the magnetic order and the topological state in the absence of magnetic dopants, opening up potential developments inthefieldofmetrology.Thereport fromAnthoulaPapageorgiou, shows how beamline I09 has enabled X-ray Standing Wave measurements to reveal the detailed atomic structure of two similar Ru porphyrins and relate it to the catalytic activity relating to CO adsorption. Changes to the bonding height of the Ru atom caused by the CO binding are suggested as an important factor affecting the efficiency of the catalyst. Novel assembly methods for the creation of synthetic van der Waals heterostructures are the subject of the I07 highlight. The group of Prof. Feng used an on-water synthesis methods to create a 2d polymer-graphene structure where the detailed structure was investigated using GIWAXS. Beamline B07 has been used to understand key details of a catalyst used in hydrogenation/dehydrogenation reactions, by the group of Prof. Edman Tsang. They have identified the mechanism of hydrogen spillover through monitoring the ruthenium oxidation state in the catalyst and have been able to relate the pathway to oxidation of hydrogen to protons and an increase in the concentration of surface hydroxyl species. The members of the Structures and Surfaces group are committed to continue offering the best support to our users, to ensure the highest quality scientific output from the beamlines. The combination of strong interactions and collaborations, together with continuous improvements to the instrumentation, software and technique development is key to our success. Please contact us if you would like to discuss any of the possibilities that we offer and how such synchrotron based studies could help in your research. B07 Senior Beamline Scientist David Grinter with the high-throughput XPS end station. The I09 Soft X-ray ARPES end station awaiting installation of the momentummicroscope electron energy analyser. The recently installed glove box on beamline I05.