Diamond Annual Review 2020/21

46 47 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 0 / 2 1 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 0 / 2 1 Structures and Surfaces Group Chris Nicklin, Science Group Leader T he Structures and Surfaces Group at Diamond Light Source comprises four beamlines: 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). These offer a variety of techniques to examine the atomic scale structure, chemical nature and electronic state at buried interfaces or the surfaces of materials. The focus this year has been on improving the user interface and accessibility for control of experiments to ensure that as many experiments as possible could be carried out remotely by users with the support of the beamline teams on-site. The success of the majority of these studies has been enabled by the strong partnership of the Diamond scientists with the user groups, leading to stronger collaborations and exceptional results. It has continued to be a busy year for beamline developments (as detailed below) whilst also taking a strategic view for the future, in particular 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. Expanding the techniques to these communities remains a key aim for the group. On I05, the high resolution branch has continued with its upgrade programme to install new gratings and a new electron energy analyser. The team also took the opportunity to fully realign the beamline, leading to a reduced spot size and increased flux. Together, these developments will maintain the high resolution branch at the forefront of ARPES facilities and continue to enable its world leading research. The NanoARPES end station has delivered improved flux and reduced spot size through the incorporation of a capillary mirror, with further improvements possible with another capillary. The sample preparation and mounting facilities have also been enhanced through the recent installation of a glove box and micromanipulation system to enable precise alignment of crystals that are air sensitive.The group have ambitious plans for developing photoelectron spectroscopy at Diamond to complement the high resolution facilities available on I05, the arrival of a soft X-ray ARPES system (momentum microscope) this year on I09, the Hard X-ray (HAXPES) station also on I09 and the Near Ambient Pressure X-ray Photoelectron Spectroscopy (NAP- XPS) capability on B07. The surface and interface diffraction facilities on I07 continue to be upgraded to enhance the capabilities. Continuous scanning of the diffractometer will improve the data collection efficiency and automated fast attenuators will enable fast measurement of crystal truncation rods that cover many orders of magnitude changes in intensity. The new Excalibur detector is now in use, with updated software control to integrate fully with the continuous scanning capability and offering a high dynamic range. The diffractometer upgrade has been delayed due to lockdown restrictions, but the beamline team has commissioned the new hexapod to increase the reliability and speed of experiments. The ultrahigh vacuum experiment capabilities have been improved through the integration of the XPS system into the end station and a sample preparation chamber that incorporates a small integrated glove box for improved sample handling. A new optical layout of the beamline has been investigated with the Optics Group that would give much greater control and reduction of the beam size, whilst increasing the flux at the sample. Discussions are continuing about the optimal approach that will enable these developments to be realised. This year, the second branch of B07 (VerSoX) has opened to users, initially enabling NEXAFS studies using soft X-rays to study processes such as molecular adsorption or catalysis, using an end station built in partnership with Prof. Sven Schroeder at the University of Leeds. This will be complemented towards the end of the year by a high throughput XPS system that will allow chemical state analysis of many samples. It has been installed and is currently undergoing commissioning. The two branchlines work independently and this will therefore bring additional capability and supplement the techniques offered by the group. The 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 controlledmixtures of gases. Full scripting of this facility through the data acquisition systemwill enable complex studies to be semi-automated. Additional capability for nanoscale cluster studies is also being provided through a collaboration between Diamond and Prof. Richard Palmer from the University of Swansea, to house a vacuum cluster source close to B07 with vacuum suitcase transfer capabilities. This system is available for user experiments and its potential use should be discussed with the beamline team. Beamline I09 continues to maintain a very active user programme whilst also developing new capabilities. The Hard X-ray Photoelectron Spectroscopy (HAXPES) system is commissioned with X-rays and ready to host single sample experiments; new X-ray windows are being tested to allow emission-angle dependent studies and a multipurpose sample manipulator stick will be developed for high-throughput experiments. The delivery of the soft X-ray ARPES system (also known as a momentum microscope) was delayed by the COVID-19 pandemic. The end station has been designed and the construction is underway, with delivery of the bespoke analyser due in the summer of 2021. This challenging project, undertaken together with Prof. Gerd Schönhense from the University of Mainz and Prof. Ralph Claessen from the University of Wurzburg, will provideworld-leadingcapabilitiesforsuchsoftX-rayARPESstudies.Smaller scale upgrades are also underway including amodifiedmanipulator design that enables sample biasing and more accurate sample temperature control whilst still allowing sample transfer. Future developments include replacing the simple (three fixed-energy) monochromator with a fully tuneable version to enhance the HAXPES studies and an upgraded plane grating monochromator for the soft X-ray branch. The group is 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 Diamond Scientific Advisory Committee (SAC).This was delayed due to the lockdown restrictions but 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 range of science undertaken at the Structures and Surfaces beamlines continues to be a combination of detailed surface science characterisation through to application of the methods to novel samples, as outlined in the contributions from a selection of our users. These highlight a broad range of investigations from studies of materials in device structures to purely fundamental research. The report by the group of Tao Wang in collaboration with David Lidzey, highlighting work on I07, indicates how the addition of a third component into a blend of polymers used in organic photovoltaics (OPVs) could change the crystalline structure and increase the device efficiency. Work relating to energy materials is also the subject of the highlight report from B07, by Dr Victor A. de la Peña O’Shea, which focused on understanding the charge dynamics in metal-organic frameworks (MOFs) and how this is related to their photocatalytic behaviour. The long term aim is to use these types of material for fuel production via artificial photosynthesis. Some of the more fundamental studies are highlighted by the work of Dr Veronika Sunko in collaboration with Prof. Phil King, who have identified a method to investigate the magnetic behaviour of a material using a combination of energy dependent soft X-ray ARPES on I09 and lower energy ARPES on I05. The report from Dr Niels Schröter also focuses on the key parameters of a material system, showing how ARPES on I05 can be applied to complex chiral crystals to understand the origin of the topological charge in PdGa. 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 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. The focus this year has been on improving the user interface and accessibility for control of experiments to ensure that as many experiments as possible could be carried out remotely by users with the support of the beamline teams on-site.