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Unique Spectra detector is like 'playing billiards with atoms'

Published: 
6 July 2009
Illustration

Another milestone has been passed in the new Mountbatten Building clean rooms with the commissioning of the ‘Spectra’ detector on the Zeiss Orion beam instrument.

The detector is the first of its kind to be installed, and measures the energy of the helium ions which bounce off the sample. ‘We are playing billiards with atoms’ said Professor Harvey Rutt, Head of the School of Electronics and Computer Science, who has been instrumental in acquiring the Orion. ‘The helium ion we fire into the sample is the cue ball, the instrument itself is the cue which fires the helium atom at the sample, and inside the sample it hits an atom and bounces off. Now atoms don’t come in different colours like billiard balls, but they do come in different masses (atomic weights) and by measuring the energy of the ion which bounces off we can tell what type of atom it actually hit.’

The reason this is important is that modern nano devices use extremely thin layers of materials, and this turns out to be a very good way to measure the composition of such thin layers.

The bump on the right-hand side of the graph pictured shows helium ions bouncing off a layer of hafnium oxide just a few nano metres thick – a few millionths of a millimetre – on a silicon wafer, which would be almost undetectable by any other technique. Hafnium is a rare element, but its oxide has great promise for applications in next generation nano-electronic devices.

In fact this measurement technique has links to the first detection of the atomic nucleus by Ernest Rutherford in 1911. He used alpha particles – naturally produced high speed helium ions – and observed them being scattered by sitting in a dark room for hours and observing tiny flashes of light on a screen.

‘I’m sure Rutherford would be amazed by modern day instrumentation’ said Professor Rutt, ‘but fundamentally we are doing exactly what he did, almost a century later, to help develop the next generation of high speed, low power electronic devices. Actually it turns out that Rutherford himself didn’t do much of the sitting in darkened rooms; he left that to a PhD student, Ernest Marsden; there’s a moral in there somewhere!’

For further information contact Joyce Lewis; tel.+44(0)23 8059 5453

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