Diamond Concise Annual Review 2020/21

18 19 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 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 ofmaterials.The focus this year has beenon improving theuser interface andaccessibility 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 withtheusergroups,leadingtostrongercollaborationsandexceptionalresults.Ithascontinuedtobeabusyyearforbeamlinedevelopments 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. Recent studies from this group include pioneering approaches in the design and production of renewable solar fuels and organic solar cells and developing newmaterials for data storage in solid-state electronic devices. Discovering new catalysts for solar fuel production In our current era of climate change, intensive international efforts are ongoing to develop carbon neutral processes that exploit renewable resources. One of the most promising areas of research is the production of solar fuels that can be made from common substances such as water and carbon dioxide and then stored for later use. Different photocatalytic materials are currently being used in developing photo-electrochemical cells to perform water splitting (to produce hydrogen and oxygen) or carbon dioxide reduction (to produce hydrocarbons). However, these materials suffer from severe limitations related to charge carrier recombination phenomena and inefficient light harvesting, and the search is on for more sustainable and efficient photocatalysts. Spanish researchers are investigating the potential of metal-organic frameworks (MOFs) to act as photocatalysts. They used VerSoX (B07) at Diamond Light Source to provide detailed data on the charge dynamics processes and electrical properties in a new bismuth metal-organic-framework (MOF) to produce hydrogen. These studies, combined with spectroscopy, allowed the team to determine the structure of the photocatalyst and themechanismbehind the charge dynamic process and will allow further development of this exciting material. Garcia-Sanchez A. et al. DOI: 10.1021/jacs.9b10261 Designing new high-efficiency organic solar cells Organic solar cells are a type of photovoltaic cell that use a blend of carbon- based semi-conductor materials to produce electricity from sunlight. They offer the potential of cost-effective photovoltaics with low environmental impact when compared with inorganic cells such as silicon, but not all combinations of organic materials work efficiently, andmany have had lowefficiency, stability and strength. Researchers in China and the UK carried out X-ray scattering experiments on Diamond Light Source's beamline I07, combined with other techniques, to explore the device efficiency of a blend of three different organic semiconductors. This so- called‘ternary blend’has the potential to enhance optical absorption, but selection of materials has been challenging. These new measurements provide critical information on how adding a third component changes the molecular ordering of the blend. The research team were then able to correlate the thin film morphology with the electronic properties of the solar cell. Their results also allow predictions of whether a third component is likely to enhance device efficiency. Their work will help develop high-efficiency solar cells and is another step towards commercialisation of this technology. Li W. et al. DOI: 10.1063/1.5125438 Developing newmaterials for data storage PdCrO 2 is a magnetic oxide metal with remarkably high conductivity, which consists of an alternating stack of Pd (palladium) and CrO 2 (chromium dioxide) layers. An international group of researchers wanted to study the unusual electronic properties of this layered lattice material which could have a significant impact on the design of solid-state devices for data storage and transfer. They performed initial studies using Angle-Resolved Photoemission Spectroscopy (ARPES) on beamline I05 at Diamond Light Source and observed some unusual spectral signatures. Theoretical calculations suggested that correlations and interlayer interactions had a significant role in their generation. To understand the origin of these unusual spectral signatures, the team used the Surface and Interface X-ray Diffraction beamline (I09) to perform ARPES measurements. The combined nature of the study, with closely integrated work on the I09 and I05 beamlines applying different photoemission measurements, was crucial to the success of this work. This novel use of ARPES provides an approach to study materials that are incompatible with other, more conventional probes of spin-spin correlation functions. This potentially opens up new systems to experimental study, and an improved understanding of their magnetic properties will be important for real-world applications such as 2D spintronics. Sunko V. et al. DOI: 10.1126/sciadv.aaz0611