Diamond Concise Annual Review 2019/20

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 1 9 / 2 0 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 1 9 / 2 0 16 17 Structures and Surfaces Group T he Structures and Surfaces Group comprises four beamlines: I05, I07, B07, and I09 that offer a variety of techniques to examine the atomic-scale structure, chemical nature and electronic states at buried interfaces or the surfaces of materials, and in novel quantum materials. Studies are increasingly being able to be performed under operando conditions or during sample biasing, extending the range of scientific questions that can be explored. The Diamond II science case highlighted, in particular, the important role that surfaces and interfaces play in broader research areas such as battery technology, photovoltaic structures, electronic devices (e.g. transistors) and catalytic/electrochemical systems under operando conditions. Expanding the techniques to these communities remains a key aim for the group. Studies that took place last year included optimising the design of catalysts that use nickel nanoparticles, the discovery of a new subatomic particle whichmay have important electronics applications and designing new catalysts for the production of clean fuel. Improving nickel nanoparticles catalysts As described in the Soft Condensed Matter section, chiral molecules occur in two different enantiomeric (mirror image) forms which can have very different effects. Maximising the effectiveness of a drug and reducing side-effects requires synthesis only of the desired form. AUKresearchcollaborationstudiedthesynthesisofmethyl‐3‐hydroxybutyrate (MHB), an important intermediate step in the synthesis of a treatment for glaucoma, which uses a nickel (Ni) catalyst to ensure that the (R) -MHB form is selected.This study focused on the synthesis of Ni nanoparticles and how they were active in enantioselective catalysis. The team also studied the impact of synthesis conditions on the size, shape and electronic structure of the Ni nanoparticles on their catalytic performance. They used the B07-C beamline to perform surface sensitive X-ray photoelectron and absorption spectroscopy over the Ni samples, and electron microscopy at ePSIC to determine the size and shape of the nanoparticles. The results will aid design of Ni nanoparticle-based catalysts and other asymmetric hydrogenation reactions and will benefit academic and industrial scientific communities. Arrigo R et al. doi: 10.1002/cctc.201901955 Discovery of theWeyl fermion after 80 years Condensed matter systems, such as crystals, can serve as a platform for the study of phenomena in many fields of physics. In 1929 the existence of a massless chiral particle inWeyl semi-metals called theWeyl fermion was proposed but never proven. In 2011, it was predicted that a magnetic crystal can host Weyl fermions, and the unique electronic structures in a crystal withWeyl fermions could give rise to many valuable physical phenomena such as chiral magnetic effects. An international team of researchers used the Angle-resolved Photoemission Spectroscopy (ARPES) beamline (I05) at Diamond to investigate the electronic structures of a Kagomé crystal (Co 3 Sn 2 S 2 ). They successfully found both bulk Weyl fermions and the unique surface Fermi-arcs that connect them for the first time. The Weyl fermions discovered in this compound have many interesting and potentially useful properties. Their enormous electron mobility means that they could be used for fast electronic devices. A large magnetoresistance makes them a candidate for large density magnetic storage devices. With spin-polarised surface electrons, this compound could be used in spintronics devices, and the bulk-surface electron correlation may be useful for new optoelectronic applications.  Liu DF et al . doi: 10.1126/science.aav2873 Engineering new catalysts for clean fuel production The generation and storage of clean energy is one of the great challenges of our century. Water splitting, using sunlight to split water into hydrogen and oxygen, is a promising strategy for clean hydrogen generation. However, it requires the concerted action of absorption of photons, separation of excitons and charge diffusion to catalytic sites and catalysis of redox processes. A new generation of photocatalysts will be needed that employ hybrid systems, where different components perform light-harvesting, charge separation and catalysis in synergy. Chalcogenide materials contain one or more chalcogen elements (e.g. sulphur, selenium or tellurium). Quantum dots (QDs) are semiconductor particles just a few nanometres in size, which have different optical and electronic properties to larger particles of the same material. Chalcogenide QDs have high absorption coefficients that can be easily optimised in the visible spectrum for efficient light harvesting. However, they suffer from photo-corrosion due to the build-up of photo-generated holes. Researchers developing a new class of hybrid photocatalyst for hydrogen generation used Hard X-ray Photoelectron Spectroscopy (HAXPES) measurements at the Surface and Interface Structural Analysis beamline (I09) at Diamond. The high energy HAXPES enabled them to detect new states that were induced by intercalating post-transition metal ions in V 2 O 5 semiconductors nanorods interfaced to the QDs.The added ions allowed rapid, efficient hole transfer from the quantum dot to suppress photo-corrosion and enhance hydrogen generation. This represents a significant step forward in the development of systems to generate clean fuel in the future. Andrews JL et al . doi: 10.1021/jacs.8b09924