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Every year, Diamond produces an Annual Review, covering the scientific, technical, computing and business updates from the facility. The feature that follows has been prepared for our latest review, and looks at work conducted between April 2023 to April 2024.
This year has been another busy year for the Structures and Surfaces group, with a full user programme and the experiments becoming ever more complex. In situ and operando studies continue to be a real focus for the group, whether it is straining a sample for electronic structure measurements, employing ‘realistic’ conditions to study catalytic processes or understanding the processes occurring under electrochemical control amongst many others. Many of these developments have been undertaken collaboratively with key groups, but with the resulting environments being made available to all users. Increasingly, developments are being undertaken across relevant beamlines to ensure consistent approaches that will benefit the user community; for example, a new electrochemistry special interest group has been set up to identify the opportunities for correlative studies and cell development.
The Structures and Surfaces Group includes 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). 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. The group has continued to develop its strategy, outlining the facilities that we plan to offer as part of the Diamond-II programme, including a significant upgrade to the Near Ambient Pressure X-ray Photoelectron Spectroscopy (NAP-XPS) branchline, converting it to be sourced by a variable polarisation insertion device and extending the energy range. The critical role that surfaces and interfaces play in broader research areas such as battery technology, photovoltaic structures, the discovery of novel quantum materials and catalytic/electrochemical systems under operando conditions are key drivers for these developments. Below we highlight some of the important developments on each instrument over the last year.
The ARPES beamline had a very productive year, delivering more than 25 user experiments on the High Resolution branch and 17 experiments on the nanoARPES branch. We have a consistent demand for investigations of topological materials and the electronic response of mechanically strained quantum materials, whilst with the microfocus capability (nanoARPES branch), we observe a growing demand to study 2D heterostructures including twistronics through small rotations in multilayer assemblies, charge transfer by gating control, and 2D magnetic systems. Another highly productive area is related to the systematic investigation of termination dependence for cleaved Van der Waals single crystals. The optimised balance between spatial resolution and flux at I05 also makes our current configuration ideal to explore charge density waves in multilayer structures.
After more than ten years of operation, some major maintenance has been undertaken. All the cooling seals of the plane grating monochromator have been replaced to recover the smooth operation over the full photon energy range of the beamline. The nano-positioning motor of the nanoARPES end-station has been replaced by a newer version to improve the reliability of the sample positioning. The cryostat connection with the sample holder has been improved to reach a world-leading temperature of 25 K on the nanoARPES branch.
An important development for the I05 beamline is to implement a new operando cryo-manipulator on the HR branch. It will allow the users to perform electronically gated experiments at low temperature (<10 K) with the best spectroscopic resolution possible. We have successfully developed a prototype with eight contacts that can be integrated in our standard manipulator design. The new manipulator body and cryostat are due to arrive this year and we expect full commissioning in early 2025. In collaboration with the University of Birmingham, we are developing a piezo driven strain cell for ARPES experiments. A first cell to host the piezo has been produced, and more design effort is ongoing to make the sample plate user friendly.
Diamond-II will be a higher energy machine (3.5 GeV), resulting in an increase in the heat load on the beamline optics, particularly in the low photon energy region. To mitigate this challenge for I05, the current APPLE-II undulator will be replaced by an APPLE-KNOT design, where most of the heat energy is off-axis therefore avoiding the beamline optics. The design of this new insertion device is complete, and various simulations have successfully shown the limited impact on the rest of the machine. In linear mode, the predicted flux for the beamline is similar to that currently available. Furthermore, this new ID technology will enable user experiments over a greater energy range from 10 eV to 250 eV further enhancing the world leading science programme.
The beamline has been extremely busy with the commissioning of new sample environments, improving beam stability and integrating additional functionalities. The recommissioning of the focusing system allowed significant improvements, removing vibration sources and reducing the vertical beam size by 20%. The possibility to perform energy scans during grazing incidence experiments has been successfully implemented. This has been used for combining diffraction and X-ray absorption methods, including X-ray Absorption Spectroscopy (in fluorescence) and Diffraction Absorption Fine Structure (DAFS) experiments providing a unique capability of gathering structural and chemical information from thin films and interfaces. On the software side, the development of the data analysis software is continuing and the possibility of reducing Nexus hdf5 format data sets to 1D, 2D and 3D reciprocal space maps for the different experimental configuration supported by the beamline is now complete. The aim is to integrate the system in the acquisition routine to provide an automatic data reduction pipeline.
There have been upgrades to several of the sample environments, the EH2 Ultrahigh Vacuum (UHV) system has been equipped with a precision temperature probe and new gas handling capabilities, which largely improves the flexibility and operability of the system, opening up the possibility of dosing toxic gases in the chamber. A high-pressure catalysis reactor, capable of operation up to 20 bar, has been commissioned and is now available to the user community.
Finally, the development of a new flight tube and slits for the EH1 diffractometer is ongoing, this will provide flexibility to the system allowing for more efficient background reduction and improved operation when incorporating large sample environments. The long-term plan for the refurbishment of the focusing optics is continuing, a new system for refractive optics (f-switch) to provide micro focusing capabilities in EH1 has been approved, while a set of Be lenses for the system is already available. The aim is to install the new optical system during the Diamond-II dark period. The user programme of the beamline continues to focus on a wide range of subjects, including electrochemistry (electrodeposition, corrosion, etc.), peroskvite solar cells, 2D materials and biomimetic membranes amongst many others.
Both branches of B07 have been in full operation, providing beamtime for 38 and 33 standard user experiments on Branch B and C, respectively. Concurrently, commissioning was carried out to integrate a silicon drift partial fluorescence yield detector and automated sample transfer in the UHV endstation (ES1) of Branch B whilst a new channel-cut crystal monochromator (CCM) was installed on Branch C. The latter is important for X-ray Photoelectron Spectroscopy (XPS) at high photon energies, as it provides significantly higher energy resolution than the standard Plane Grating Monochromator (PGM), but only offers three fixed energies, 2000, 2250, and 2500 eV. It is available for user operation.
The focus of new beamline developments has been to consolidate the existing ambient-pressure sample environments and to develop new cells for solid-liquid and high-pressure experiments. The beamline’s electrochemical flow cell, which was developed as part of the EU-funded project HySolChem, has proven to be very popular with users. It enables Total Electron Yield (TEY) and Total Fluorescence Yield (TFY) Near Edge Extended X-ray Absorption Fine Structure (NEXAFS) experiments on electrochemical interfaces in ES2 of Branch B using catalyst-coated SiNx windows, as well as operando XPS in Branch C using coated membranes in a water-vapour environment. In addition, a high-pressure cell, which was developed in collaboration with the group of Dr Paul Webb from the University of St Andrews, has been rolled out for standard user operation. Using SiNx windows, it enables TEY NEXAFS at pressures up to around 2 bar and temperatures up to 400° C on ES2 of Branch B. Furthermore, a new manipulator for the endstation of Branch C provides extended and more reproducible motion and thus contributed to a significantly improved productivity of user experiments.
The beamline’s cluster source, a collaboration with Prof. Richard Palmer’s group at the University of Swansea, has seen an upgrade that dramatically improved the size selectivity of clusters. It has been used in the last year by a small number of user groups who have been supplied with clusters for their experiments.
In 2023, Branch B became associated with the EPSRC-funded national facility Harwell XPS. As a consequence, rapid access to ES1 and ES2 is now managed through the Harwell XPS website.
VerSoX will undergo a major upgrade as part of the Diamond-II project. This will mostly affect Branch C, which will see an increase in flux by up to 100x and an expansion of its energy range to 125 – 4000 eV. This upgrade will enable measurements at higher pressures and with much improved time resolution compared to the current beamline. The Technical Design Report has been accepted and design work and procurement will start in 2024. Gratings for a novel multilayer PGM design, which is led by the Optics Group of Diamond, will be tested at the beamline already before the dark period to ensure as little downtime as possible.
Beamline I09 has maintained strong user support for materials research. Due to the possibility of accessing both soft and hard X-rays, photoelectron spectroscopy has been exploited with variable probing depth to elucidate the degradation mechanism at the cathode-electrolyte interfaces in lithium-ion batteries. It was also employed to determine the band edge profiles across oxide/semiconductor interfaces and to unveil gap states near the oxide surfaces. Hard X-ray photoelectron spectroscopy (HAXPES) proved to be a unique technique for investigating bulk electronic properties of novel materials such as (layered, hexagonal carbides and nitrides) MAX phases and transition-metal dihydrides. Heterostructures of two-dimensional materials, either transferred flakes or UHV-prepared epitaxial layers, have attracted more interest in the I09 user community. In addition to measurements probing the chemical compositions and band alignments with the substrates, the X-ray standing wave (XSW) method was also used to extract key structural information closely linked to the electronic properties of the heterostructures. The upgrade of the sample manipulator enabled operando HAXPES analysis incorporating in situ sample biasing being applied reliably to improve studies of lithium plating/stripping in solid-state batteries and degradation of perovskite-based solar cells and light emitting diodes.
The continued commissioning of the newly installed soft X-ray ARPES end-station has been the main focus of the I09 team in the past 12 months. This new facility is equipped with a momentum microscope comprising entrance and exit optics, a single hemispherical analyser, a time-of-flight (ToF) analyser and a fast delay-line detector. A monochromatic UV lamp that delivered a sub-100 μm beam spot for the He I and He II energies was used to facilitate the initial commissioning. At 30 K, a gold Fermi edge was measured to be 10 meV wide using a 10 eV pass energy of the hemispherical analyser, and a Rashba splitting of the gold surface state was observed with an instrumental momentum resolution estimated to be 0.01 Å-1. Using the synchrotron light, stacks of constant binding energy (kx, ky) maps were recorded, each over a binding energy or photon energy (i.e., kz) range, from UHV-prepared and cleaved single crystals and epitaxial thin films. The sample manipulator is being modified to improve the temperature control, and the commissioning of the ToF to work with the hemispherical analyser is expected to take place in the second half of 2024. It is envisaged that limited commissioning experiments with users will commence towards the end of 2024.
Over the years , most of the studies at I09 have utilised the end-station in Experimental Hutch 2, where users can investigate the same spot on a sample with either soft or hard X-rays. To better control the sample environment, a new version of the in-house developed manipulator stick was installed during the October 2023 shutdown to improve surface preparation and X-ray measurements. This upgrade offered higher repeatability and reduced parasitic motions of the sample azimuth and polar rotations coupled with faster cooling and lower liquid He consumption. It also allowed the manipulator to accommodate more samples for in situ or operando biasing with more contacts and improved electrical isolation.
To better support offline sample surface preparation for beamtimes, a Diamond-developed UHV system is being assembled for the group. This facility consists of multiple chambers designed for surface preparation and characterisation. The characterisation chamber is fitted with a mass spectrometer and a variable-temperature sample manipulator (from below 70 K to above 800 K) to enable temperature programmed (TP) desorption experiments. The chamber is also equipped with an electron analyser and a non-monochromatic X-ray source for XPS and TP-XPS. The preparation chamber permits standard sputtering and annealing procedures and deposition of atomically thin layers from various sources. The vacuum commissioning of the system is expected to start in June 2024, and will be followed by the commissioning of the surface science instruments. The addition of an Aarhus scanning tunnelling microscope (STM) to this system is planned as a future upgrade.
In preparation for the Diamond-II upgrade, the Diamond insertion device team reviewed the specification of the two current I09 undulators and confirmed that the two devices would be able to cover the required energy ranges after the upgrade. This was made possible by ensuring that specific minimum gap values could be reached by the two devices with the new electron optics and narrow gap vessel in the I09 straight. The list of critical beamline components is also being finalised. It includes replacing the first mirror of the soft X-ray branch to account for the new source position and upgrading the second crystal cage of the hard X-ray monochromator to improve the stability and repeatability of the mechanics.
The Structures and Surfaces group continues to be a vibrant and innovative group, based on true collaborations across the team and with our growing user community. We aim to deliver the best possible instrumentation and support for all of the experiments and to continue developing the capabilities as we prepare for the Diamond-II upgrade. We are always keen to hear the views of our users, to explore novel techniques or to improve our delivery. Please contact any of the beamline teams to discuss your requirements and ideas.
I05: From Theory to Confidence: Building Trust in Twistronics Models
I07: Surface Secrets: Understanding Stainless Steel's Resistance to Hydrogen Embrittlement
I09: Laser-Induced Crystallisation Offers a Quicker Route to Smart Windows
B07-C: Understanding How the Structure of Boron Oxynitride Affects its Photocatalytic Properties
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