Case Studies

The instruments at SuperSTEM offer imaging and analysis of unrivalled resolution allowing observers to see and identify single atoms and study their local chemical electronic environment. This precision is coupled with a sensitivity that allows delicate materials to be imaged without damage. The instruments thus provide state-of-the-art characterisation backed by world leading research and expertise.



Engineering the structures of thermoelectric oxides for power generation

Thermoelectric materials generate power from waste hear. Used in space missions for over 40 years, they are starting to be used in automotive and other industrial applications. A barrier to this wider uptake is the nature of traditional thermoelectric materials. They are metallic, and often based on increasingly rare and sometimes toxic elements. We need to develop materials with improved environmental sustainability and with a higher temperature capability. Oxide thermoelectrics offer a solution, but to be really competitive with the more traditional thermoeletrics, they require improvement of their thermoelectric performance.

To enhance the thermoelectric performance requires a simultaneous reduction in thermal conductivity and a reduction in thermal conductivity. This is challenging as the two properties are linked. Most strategies to control the electrical and thermal transport properties are based on engineering the material at the nanoscale. To evaluate the effectiveness of the different routes requires detailed knowledge of the chemistry and structure at the atomic scale. Professor Bob Freer and colleagues at the University of Manchester have been studying these oxides for years: "The SuperSTEM has been invaluable, providing detailed maps of the distribution of primary atoms. impurities and defects", says Prof. Freer.

For example, the figure on the left shows SuperSTEM data collected for a barium neodymium titanium oxide being explored as a possible thermoelectric material. The Manchester group wanted to understand the distribution of Ba, Nd and Ti, and their relationship to major structural features. By traditional imaging it is impossible to distinguish between the Ba and Nd columns (main image). However, using the chemical mapping capabilities of the SuperSTEM microscopes, the SuperSTEM chemical map (inset image) shows the distinct distributions of Ba and Nd, the shapes of the complex cavities in the atomic structure, while the nature of the low angle grain boundary are revealed. Bob Freer says "With this knowledge we were able to design routes to engineer the microstructure and chemistry to enhance the thermoelectric properties."


Catalysing Technology

Catalysts are a vital part of modern society and their production is itself a multi billion pound industry. The continuing improvement of exisiting catalysts and the development of new ones is important to solve the major energy and environmental challenges.Understanding how they work is critical.

Haldor Topsøe AS has used SuperSTEM to look at molybdenum disulphide, a catalyst used in oil refineries to remove harmful sulphlsur impurities from fossil fuels. They have imaged its constituent atoms one-by-one to gain a detailed understanding of its structure, in particular, single atom rearranged at the edge of the nanoscale MoS2 catalysts. With this insight they are able to see how additives, such as cobalt, alter its structures and thus boost its properties.

Dr Stig Helveg from Haldor Topsøe says "The images show exactly how the atoms are arranged. Knowing this helps to explain what makes a catalyst good or bad. The images are hard to obtain as we are working right at the edge of what is physically possible. We did this work anyway because other experimental tools gave in the past only some hints to the structure and no one had ever seen this type of industrial catalyst, atom-by-atom."


Iron: From SuperSTEM to the Clinic

Iron is a "trace" or minor dietary element, necessary for mammalian life. Uptake and loss of iron from the body is finely balanced and one significant storage pool of iron in the body is the molecule ferritin. Ferritin provides iron storage by temporarily mineralising the ferric iron in a nanoparticulate form at the core of the molecule. Researchers led by Dr Andy Brown, University of Leeds in collaboration with groups at King's College London and the Medical Research Council Human Nutrition Research Unit, Cambridge have used SuperSTEM to image and analyse the structure of this mineral core in liver-tissue sections and from the resulting images have established that the protein shell of the molecule acts as a template for the mineralisation of the iron. This work has been used for example, to monitor the biodegradation of iron oxide nanoparticles used for MRI contrast enhancement.

The structural insight provided by the SuperSTEM images of ferritin inspired the group at MRC Human Nutrition to develop a new oral iron supplement that uses nanotechnology to mimic the iron in ferritin. In collaboration with the group at Leeds the team have used SuperSTEM to guide and confirm the development of the appropriate particle structure for the supplement.

Dr Jonathan Powell, co-inventor of the supplement and head of the Biomineral Research Group at MRC HNR said: "Current forms of oral iron are either toxic or expensive, and in some cases both, and these are significant barriers to the implementation of effective oral iron therapy. Patients don't like side effects and health providers don't like expensive therapeutics. Our iron supplement is based upon understanding how dietary iron digestion works and all the evidence is that it is safe, side-effect-free, well absorbed and cheap to manufacture. These are exciting times."


The Colour of Diamonds

De Beers Technologies UK has supported research in collaboration with SuperSTEM for more than 10 years. Historically, the focus of the research work at the facility has been the analysis of brown colouration in natural diamonds. However, more recently this has been extended to investigate the origin of other colourations in synthetic gem-quality diamonds. In particular these studies have concentrated on establishing links between vacancy defects observed on an atomic scale and the occurrence of brown colour. While theoretical predictions and indirect experimental techniques have played an important part in establishing these links, they have been unable to provide a method of observing the defects directly. By comparison, scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS) are two complementary techniques that provide a means of imaging defects on an atomic scale and analysing their chemistry locally. These attributes ideally lend themselves to the investigation of nanometre sized crystallographic defects in diamond.

The advantages of the aberration corrected instruments at SuperSTEM over similar instruments are the high brightness electron source and unique aberration corrector optics. Together these characteristics provide a high current sub-nanometre size probe, which is a fundamental requirement for achieving high spatial resolution (< 0.1nm) and high energy resolution (0.3eV).

Commenting on the work, collaborators at De Beers who have supported the work of three students at SuperSTEM say that SuperSTEM "has improved our understanding of why some diamond is brown and what happens on an atomic scale when that brown colour is removed by heat treatment. This research has culminated in the imaging of facetted vacancy clusters with diameters of 3-4 nm in heat treated Chemical Vapour Deposition synthetic diamond. While theory and other techniques have suggested that small vacancy clusters play a role in causing brown colour in diamond, SuperSTEM research has provided the first direct evidence for the existence of vacancy clusters in diamond."