Shedding light: Engineering research at Diamond

Shedding light: Engineering research at Diamond
As a supplier to The Diamond Light Source we are proud to relate its progress and for those who are perhaps not so familiar with the project, give some background and detail of just what it‘s all about. We are therefore delighted, with kind permission of The Engineer magazine, to bring you the following article written by Stuart Nathan.The UK’s Diamond Light Source is enabling advances across a range of engineering sectors.Guiding light
Guiding light: The synchrotron generates bursts of energy at defined frequencies

One of the stars of British science and engineering research, the Diamond Light Source at the Science and Technology Facilities Council’s (STFC’s) Harwell campus, is the brightest lamp in the world. While its technological wonders have been explored, it is now fully operational and shedding light on a variety of engineering, scientific and medical enigmas that could benefit sectors as diverse as construction, mining, pharmaceuticals and cancer therapies.
Of course, calling the Diamond a lamp is a drastic oversimplification. The facility is a synchrotron – a device that generates bursts of energy at defined frequencies by accelerating electrons around a ring using magnets until they are travelling near the speed of light.

The Diamond produces light in the X-ray, ultraviolet and infrared ranges (going from higher to lower energy and lower to higher wavelengths respectively), at intensities up to 100 billion times as bright as the Sun. This light allows researchers to probe the properties of matter in new and sometimes unexpected ways. For example, historians have found that the Diamond’s beams allow them to read the contents of sealed documents and closed books.
However, it is on the much smaller scales that the Diamond is proving its worth to industry. Each of the types of radiation produced by the synchrotron has its characteristic application in the study of matter, based on how it interacts with the substance under study: X-rays give details on the structure of crystals and the arrangement of atoms; ultraviolet light shows how electrons move around within molecules, which is useful for studying large organic molecules such as dyes and compounds containing transition metals such as iron and copper; and infrared interacts with the bonds between atoms, providing information on molecular structures and the way organic molecules react with other chemicals.

Historians have found that the Diamond’s beams allow them to read the contents of sealed documents

Structural studies can help us to understand many properties of materials. For example, the search for new methods of storing data depends strongly on the structure of materials, down to the electronic level. Andrei Sapelkin of Queen Mary University is leading a project looking at spintronics – the idea that manipulating the ’spin’ of electrons can be used to encode binary numbers. This would allow the magnetic storage capabilities of a hard disc to be combined with the electronics of a microprocessor in a single chip and to remove the limits of memory speed that hampers current electronic memory chips.
Sapelkin is using the Diamond to investigate the properties of silicon that has been doped with manganese, which has promising magnetic properties that could lend themselves to spintronics. The question, he said, is what actually causes this magnetism: is it intrinsic to the material or is it caused by the manganese molecules bunching together during processing?
The team used a technique known as EXAFS (extended X-ray absorption fine structure), which is useful for showing how the doping atoms are distributed in the semiconducting silicon. This showed that the structure of the doped semiconductor didn’t change when the substance was annealed and that the magnetic properties are indeed intrinsic to the blend, rather than being imparted by clumps of manganese atoms. This suggests that manganese-doped silicon could well be useful for spintronics tasks.
Elsewhere at the facility, a team led by Prof Sandy Blake of Nottingham University is looking at metal-organic framework (MOF) structures and how they might be used to store hydrogen for fuel cells. Safe hydrogen storage is a major roadblock on the way to fuel-cell-powered vehicles.
The knowledge of these structures allows us to understand how the current generation of MOFs works and helps us to design the next,’ he said.

We anticipate that the more efficient and effective doping of lithium ions is possible
Prof Sandy Blake, University of Nottingham

MOFs can absorb hydrogen reversibly, but their structure is difficult to study, added Blake. The crystals are small, don’t diffract X-rays much and tend to contain solvents. The intensity of the Diamond’s beams gets around this problem.
Current MOFs need high temperatures and pressures to absorb hydrogen. Blake’s team is exploring a theory that introducing lithium into a MOF containing indium bound into a carbon framework could improve the hydrogen storage ability, allowing the crystals to absorb hydrogen at ambient conditions. The team used ion-exchange methods to place lithium ions into a MOF and used the Diamond’s X-rays to study where and how the metal was bound into the structure. Blake found that the lithium ions can form structures that act as ’pore gates’ within the MOF and that the way the ions bind into the lattice considerably changes the properties of the material.

’On this basis, we anticipate that the more efficient and effective doping of lithium ions is possible,’ he said. This means that MOFs capable of storing hydrogen at room temperature are a possibility. ’Without the Diamond, we could never have made such rapid progress,’ added Blake.
Moving up in scale, the growth of conductive nanowires is the subject of research headed by Prof Geoff Thornton of University College London.
His team has used vapour deposition of palladium to create long, thin wires. Although the team could see the shape of the structures using a scanning electron microscope, this couldn’t provide any information on the composition of the wire; the team couldn’t tell whether it was conductive.
The Diamond allowed Thornton to use a technique called X-ray photoemission electron microscopy to study the chemical state of nanoparticles in the wires. The team found that the levels of energy in the bonds between nanoparticles were consistent with them being comprised of metallic palladium, implying that they were indeed capable of conducting charge between minute electronic components.
From electronics to mechanics, the Diamond’s X-rays are also providing information on the behaviour of single-molecule-thick layers of liquids adsorbed onto a solid surface. This might sound abstract, said researcher Tej Bhinde of Cambridge University, but it underpins many processes, from washing your hands to the mechanics of lubrication. Information on how these systems work could be vital to improving products and processes, he added, but they are difficult to study. ’This is because there is not much material in a single monomolecular layer and it is “buried” between two much larger bulk phases,’ said Bhinde. Any technique used to study the system must be sensitive enough to look at the film while ignoring the bulk materials.
He is using the synchrotron X-rays with a position-sensitive detector, which can see the weak signals from the 2D film between two bulk materials because it collects X-rays from many angles simultaneously.
The system Bhinde is studying consists of a film of alkyl amide, adsorbed onto a graphite surface.’The high flux of X-rays at the Diamond has allowed us to probe the molecular arrangements in 2D hydrogen-bonded amides in great detail,’ he said.
The study showed that the amide molecules ’pair up’ with a strong bond, and these pairs then bind to other pairs with weaker bonds to form durable film. The understanding of its structure could allow its properties to be improved and tuned, creating more commercial opportunities.

Diamond details ring true
The Diamond’s electrons start out in a electron gun, from where they are shot into a linear accelerator that imparts an energy of 100MeV. This injects the particles into a ’booster synchrotron’, a ring that takes them up to 3GeV. This energy is carried into a ring with a 560m circumference.

Diamond

This ring is, in fact, a polygon composed of 24 straight sections. As the magnets that steer the electrons round the ring bring them to a corner, the electrons lose energy, emitting radiation. The straight sections also contain arrays of insertion devices, which force the electrons to ’wriggle’ along the section; this allows the energy to be tuned to a specific frequency.

The Diamond is currently operating 18 beamlines and aims to increase this to 22 by 2012; however, uncertainties over funding mean this might be delayed.

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