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University is part of £4.5m consortium for new super microscope funding

14 Nov 2011

The University of Manchester has been awarded part of a £4.5m grant because of the quality of its microscopy research.

The grant, from the Engineering and Physical Sciences Research Council (EPSRC), has been given to the SuperSTEM consortium, consisting of the Universities of Glasgow, Liverpool, Manchester, Oxford and led by the University of Leeds.

This award reflects the internationally-leading research carried out under the existing smaller SuperSTEM consortium, notably the recent characterisation of graphene contributing to the Nobel Prize winning work of Andre Geim and Konstantin Novoselov at The University of Manchester, and the future capabilities of the widened SuperSTEM consortium that carried the bid forward.

Aberration-corrected scanning transmission electron microscopy (STEM) uses computer-controlled lens correctors to form a probe of electrons smaller than the width of an atom. This is used to image nanostructures in atomic projection and also analyse the type of atom and its chemical bonding. Aberration-corrected STEM is a prime tool for the characterisation of nanostructures and nanotechnological devices.

Access to an aberration-corrected STEM facility is a key requirement for many areas of physics, chemistry, biochemistry and materials science and the new EPSRC National Facility for aberration-corrected STEM will provide "free at point of use" access to cutting-edge instruments for EPSRC funded researchers within the UK, and also for non-EPSRC and commercial users within the utilisation limits of the facility.

In addition, by widening the consortium, users of the EPSRC National Facility will also have access to other specialised aberration-corrected instruments at both the consortium universities and external partner universities such as Cambridge, Sheffield and Warwick, where required. These will provide access to additional important capabilities for STEM users.

SuperSTEM1, established in 2001, was the first instrument of its kind in Europe to incorporate a special lens system to correct for lens aberrations. It was soon followed by SuperSTEM2 - an even further corrected instrument.

Both instruments are situated at the SuperSTEM core site at the STFC Daresbury Laboratories in a purpose-built low-vibration laboratory and allow for a range of atomic resolution imaging and analysis techniques at various incident electron beam energies.

The SuperSTEMs excel in a special imaging technique, so-called atomic resolution high angle dark field (HAADF) imaging, which enables direct depiction of a material’s atomic structure, almost like showing its ball-and-stick model, especially suited to investigations of nano-material structures.

In a unique combination with atomic resolution electron loss spectroscopy detection, identification and site specification of individualatoms can be achieved, thus enabling spotting of a single impurity atom.

At Manchester, researchers have applied this technique to investigations of a number of exciting new materials, such as novel functional ceramics (perovskites), nano-materials for green energies (shelled semiconductor nano-particles), materials for silicon-based integrated opto- electronics (rare-earth doped Si-nanocrystals), uniquely doped carbon nanotubes and, especially, graphene.

SuperSTEM has also played an important role in a 'detective story' about uncovering secrets of gem diamonds, in collaboration with the Diamond Trading Company, a DeBeers group.

The vast majority of mined diamonds are brown in colour and considered worthless to the gem trade. However, these diamonds can be rendered sparkling and colourless like their gem-quality counterparts through high pressure heat treatment, so they could be bought for next-to-nothing and sold for large amounts of money.

Although ultra-violet spectroscopy can give some indication of original brownness, in order to take fundamental measures against tampering and rogue trade, DeBeers researchers have tried for many years to find the origin of the brown colour.

This was to no avail, because in terms of impurities (chemical content) and microstructure (defects) brown and colourless diamonds are identical. It was only through electron microscopy that it first emerged that tiny bubbles (vacancy clusters) – so far undetectable – might cause the difference in optical absorption.

SuperSTEM experiments accompanied by HAADF image modelling showed for the first time without doubt that nano-scale bubbles really exist in brown diamonds - his could only be evidenced in HAADF at atomic resolution, where cavities comprising of 50 or so missing atoms are visible. In addition, after high high temperature treatment (at ~25000C) under high pressure the colour, together with the cavities, has disappeared, leaving a perfect atomic lattice.