B18 has been conceived as a versatile instrument and consequently has a wide and multidisciplinary research portfolio. The design proposal for B18 was supported by researchers coming from 26 different UK academic institutions, with research programs in Physics, Chemistry, Surface Science, Nanoscale Science, Biology and Environmental and Earth Sciences and whose scientific interests ranged from the fundamental to industrial applications. Here are some examples:
Semiconductor physics: The chemical selectivity of XAS techniques and ability to look at short range order makes them ideal to study the critical role of dopants in these materials. Semiconducting devices are often only a few nanometers thick and hence are measured in grazing incidence, a set-up available at B18.
Strongly correlated electrons systems: Small structural changes can have dramatic consequences in the electronic properties of these systems. XAS can track distortions with high accuracy thanks to its sensitivity to changes in the geometry of the atomic configuration. Of particular interest for these studies is the combined use of EXAFS and x-ray diffraction (XRD), possible at B18, in order to acquire simultaneously short and long range order structural information. In addition, XANES measurements allow us to distinguish between the electronic states of a chosen atomic species. The low temperature equipment available at B18 makes the beamline particularly suitable for this type of studies.
Chemistry and Materials
Ion conducting oxides, batteries and fuel cells: ion conducting oxides are often complex, multicomponent oxide ceramics with operating conditions in excess of 500 oC in various oxidizing or reducing gases. XAS measurements are ideal to study such processes, as changes in the short-range structure around specific atomic species are of the most importance. The combined use of XRD and XAS for the study of fuel cell electrocatalysts allows the investigation of complete working systems, through all stages of the life of the fuel cell. The time resolution offered by B18, with the possibility to perform EXAFS measurements with continuous scanning of the monochromator (QEXAFS), is particularly suited for this type of work.
Catalysis and microporous solids: XAS plays a pivotal role in understanding the relationship between structure and functionality in these of systems. Long-range order measurements are required to identify phases and determine the framework structure of these crystalline materials. However, the unique catalytic properties found in open framework solids (e.g. aluminosilicates, aluminophosphates and metal ion substituted variants) are due to a small and randomly distributed number of atoms. XAS is the ideal technique to obtain relevant local structural information about those active sites.
Combinatorial Chemistry: the optimization of chemical processed requires the testing of many formulations. The high throughput capabilities of B18 will enable an efficient characterisation of large numbers of samples. In addition, the flexibility of the experimental set-up allows users to carry out in-situ structural analysis of identified leads.
Hydrothermal reactions: the study of the genesis and transformation of multiphase materials, where a variety of length scales are relevant, is an area that benefits greatly from the combined use of XRD and XAS techniques. The flexible sample space at B18 allows the development of specialized sample environments in order to investigate, for example, microwave acceleration of reaction processes or the properties of laser heated levitated high temperature glasses and liquids.
Materials and chemistry relevant to industry: XAS has long been recognized by the chemical industry as an invaluable tool. The scope of studies driven by industry is broad, as it ranges from urgent questions about processes that will be applied immediately, to the investigation of developments that could be applied in the longer term. Examples of areas where XAS work has been relevant in recent years are the study of promoters and poisons in homogenous and heterogeneous catalysis, the study of scale inhibitors used in oil production or the development of novel inorganic pigments. B18 has a healthy contribution of industrial users to its user community.
Interfacial and surface science
The determination of the properties of interfaces and surfaces is key to a wide range of areas. Examples are the study of semiconducting and superconducting devices, artificially-grown layered materials with new electronic behaviour, corrosion processes, electro-deposition and biomineralisation. XAS offers the opportunity to probe the surfaces and interfaces in-situ and gives access to local structural information at the atomic level.
There is intense interest in the properties of materials with nano-sized dimensions. Most materials can now be prepared in nano-scale form: metals, oxides, semiconductors, polymers, etc. with applications in areas as diverse as nano-electronics, optics and catalysis. These often have complex phase structures (e.g. quantum dots in inert matrices, metal clusters inside porous structures). An important part of the characterisation of these materials is determining their structure, including interatomic distances and mean oxidation state of atoms in the nanoparticle. The combined use of XAS and XRD can provide this information.
Environmental and Earth Sciences
Waste management: Contamination to the environment remains an inevitable consequence of industrial and domestic processes. Consequently the containment and environmental impact of wastes is an important problem. XAS is proving an extremely important tool in identifying the nature of toxic metals causing contamination; it provides information about the speciation of the metals in both solid and liquid environments and the role of sorption on mineral surfaces in the cycling of metals. Within the scope of this technique are some of the most important contaminating elements contained in industrial waste: Cd, Hg, As, Pb, etc. There is also particular interest in radio-elements (e.g. U, Np, Pu), as there is a legacy of nuclear waste and the debate about the future use of nuclear energy has been revitalised. XAS is used in the study of both natural and model systems, as one of its main strengths is that it can provide information about both crystalline and non-crystalline phases on an equal footing.
Mineralogy: the element specific structural determination that can be carried out using XAS techniques allows mineralogist to study of the most chemically complex materials, including those with only short range order. One area where this has proven to be particularly relevant is the study of sorption/desorption processes in the cycling of metals. XAS can provide unique information on the structure and structural development of amorphous phases, known to form crucial reactive stages in the cycling of these elements. In combination with XRD, XAS has been crucial for the studies of solid solutions and the study of trace element substitutions. The structural information obtained has helped explain the properties (e.g. reactivity, magnetism and conductance) of bulk minerals.
XAS can provide important information for metalloproteins that are only partially ordered or for which the oxidation state is in doubt. It has the additional advantage of allowing the study of biomolecules in solution. B18 is particularly suited for those cases where proteins can be produced in reasonable quantities (as concentration is potentially a limiting factor). A typical application of XAS is the study of metal-based therapeutic agents (e.g. anti-cancer, anti-ulcer and anti-arthritic drugs). It will also possible to follow bio-inorganic transformations using combined XAS and XRD techniques in order to determine the evolution of short and long range order in-situ and in real time.
The chemical selectivity and non-destructive nature of X-ray absorption spectroscopy make this technique particularly useful for the study of objects of historical value. XAS measurements can provide key information for developing new conservation techniques, understanding the effect of earlier restorations on the object and also unravel details about how, when and where they were made originally. Examples of this type of work are the investigation of hydrophobic coatings as a method to preserve stonework, such as the York Minster cathedral, or how iron and sulphur compounds can affect the integrity of the wooden planks from the Henry VIII’s warship, the Mary Rose.
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