The SuperSTEM microscope at Daresbury Laboratory has been developed by scientists from the Universities of Liverpool and Cambridge. It is so powerful that it can make atoms visible. Atoms are the smallest indivisible part of matter, so small that a billion of them can fit into the width of a full stop.
SuperSTEM – the Scanning Transmission Electron Microscope - uses high-energy electrons to image atoms. It uses electrons as their wavelength is about 100 times smaller than the size of an atom; light has a wavelength about 1000 times larger than an atom which means the smallest details that can be seen with light is larger than an atom. Unfortunately, until recently defects in electron lenses limited their resolving power so that they were unable to image atoms. The challenge for scientists was to develop and install a corrector to overcome the defect known as spherical aberration, a defect common to all lenses.
“It’s similar to astigmatism in human eyes, where your eye isn’t perfectly round and this prevents you focusing properly,” explained Professor Alan Craven from the University of Glasgow, who is leading the SuperSTEM exhibition. “But in 1997, a UK group from Cambridge University managed to design and build something to correct this and bring everything into clear focus, creating the potential for the world's most powerful electron microscope. You say that what they did was make glasses for the electron microscope”.
“SuperSTEM is one of only four such microscopes in the world and its key advantage is its incredible stability. If the system is unstable, the image changes. Our system is so stable that any sample in the microscope would move no more than half a millimetre in 100 years. That's 2000 times slower than continental drift”, he added.
The major breakthrough at Daresbury is imaging atoms inside structures, so that the way that atoms interact at the interface between different materials can be seen. Imaging how atoms interact at interfaces is key to the development of the next generation of computer chips.
“Computing power continues to increase as transistor size decreases, but we are now reaching our technical limits. The key insulating layer of silica in these transistors has just five silicon atoms across it”, explained Alan. “Any thinner and the current leaking across this insulating layer will increase rapidly because of an effect known as quantum mechanical tunnelling, making the transistor unusable. Alternatives to silicon are currently being sought. With SuperSTEM we can see how the atoms in these alternatives behave at interfaces which determines their suitability as the next generation insulators”, he explained.
SuperSTEM also has applications in medicine and is being used to aid understanding of diseases such as haemochromatosis, where the liver becomes overloaded with iron. The tiny nanocrystals that hold iron within the body are being examined as their structure will shed light on how iron is transported, stored and released in the body.
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