Diamond Annual Review 2023/24

24 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 3 / 2 4 Structures and Surfaces Group Chris Nicklin, Science Group Leader (- December 2023) Cephise Cacho, Science Group Leader (Febuary 2024 -) T his 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 ofmaterials. The grouphas continued to develop its strategy, outlining the facilities thatwe 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 insertiondevice 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. Beamline I05 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. Beamline I07 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