Diamond Light Source - Annual Review 2022/23 - Concise Edition

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 2 / 2 3 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 2 / 2 3 22 23 Structures and Surfaces Group 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. The group continue to benefit frommany key developments during remote working restrictions, such as 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. This year’s studies include investigating the electronic properties in a stack of crystals, a new NEXAFS end-station at B07 and study of disorderly crystals. The electronic properties in a stack of crystals Traditional solid-state physics focuses on crystals with a well-defined periodicity. However, in recent years it has become increasingly clear that stacks of thin crystals with non-compatible periodicities can bring about new properties that are different from those of the constituent parent crystals. Researchers from Aarhus University in Denmark wanted to develop a better understanding of this phenomenon. The research team chose to investigate a so-called misfit compound. A misfit compound is a naturally occurring infinite stack of two-dimensional materials with incompatible. Their chosen misfit compound was a stack of square and hexagonal layers with no common periodicity. Using Diamond’s I05 nanoARPES branch allowed them to study the surface with a very high spatial resolution. This is necessary because the misfit crystal is a stack of two types of layers. It can have two terminations at the surface with either one or the other layer. Their results showed that the properties of each layer strongly resemble those expected for a free-standing version of that layer, without the influence of the other layer. However, there were some new properties arising in the form of one-dimensional electronic states. The findings provide a new way to create one-dimensional electronic states. Such states have interesting fundamental properties that could potentially be used for next-generation electronic devices in the future. Chikina, A. et al. DOI: 10.1103/ PhysRevMaterials.6.L092001 New NEXAFS beamline rapidly characterises bonds in noncrystalline materials Drugs are commonly manufactured in the form of tablets that contain other materials. The role of these additional ingredients is to ensure that drug release in the body is controlled, with just the right dose over a defined amount of time. There is a lot of interest in the idea of manufacturing the drug itself by crystallisation with a second ingredient, giving access to drug release profiles that cannot be achieved through tablet formulation. The products of crystallisation with a second component are typically held together by electrostatic bonds associated with the sharing of hydrogen atoms between the two components. Such bonds are called hydrogen bonds. Often, the hydrogen nucleus separates from its electron and forms an ionic bond, and the resulting product is called a salt. Clarity about which type of bonding occurs is essential for predictive modelling of properties as well as for regulatory approval and patenting of the resulting medicine. Diamond and the University of Leeds partnered to develop the new high throughput Near-Edge X-ray Absorption Fine-Structure (NEXAFS) spectroscopy end station at the B07 beamline. The team then used it to characterise three 2-component systems to examine whether the sensitivity of NEXAFS to the hydrogen position is sufficient to identify the nature of the intermolecular bond. The high-throughput NEXAFS capability of the new B07 beamline facilitates the characterisation of local bonding in organic crystal structures on timescales of minutes. The capability to identify these interactions quickly and correctly will be an invaluable aid in the development of new technologies and products. Edwards, PT. et al. DOI: 10.1021/acs.jpca.2c00439 Taming disorderly oxides Gallium oxide (Ga 2 O 3 ) is an interesting electronic material with potential applications in, for example, power electronics, solar-blind UV photodetectors, gas-sensing devices, and solar cells. It exists in a number of different crystal structures (polymorphs), known as alpha, beta, gamma, delta and epsilon. An international team of researchers wanted to understand how structure influences the electronic structure of one particular phase, γ-Ga 2 O 3 , which is highly disordered and, therefore, incredibly challenging for experiment and theory. They used both soft and hard X-ray Photoelectron Spectroscopy as well as X-ray Absorption Spectroscopy at beamline I09 at Diamond to investigate the electronic properties of γ-Ga 2 O 3 and how this relates to its crystal structure. Using the theoretical approach, they were able to identify a small number of possible structures γ-Ga 2 O 3 could realistically have. They then validated this by directly comparing theory with the photoelectron spectroscopy results. By using this combined approach, they could identify good descriptions of both structure and electronic structure of this complex material. Disordered systems are increasingly interesting for electronic and optical applications. Unlocking their full potential will involve engineering their structure through targeted synthesis in a way that enables finetuning of their electronic and optical behaviour and performance in a device. This is only possible if we have the fundamental knowledge about the relationships between these aspects and the tools to describe and probe them. Ratcliff, L, E. et al. DOI: 10.1002/adma.202204217