Scanning Probe Electron AnalyseR (SPEAR)

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In the movie Spiderman nanotechnology was a tool in the hands of the evil Green Goblin, but in the Thunderbirds movie the Tracy family used it too. So, like any technology, nanotechnology can be a tool for good or evil. Of course, both examples are science fiction. But the scanning tunnelling microscope (STM) - a sharp needle which scans over a surface as it measures the electrical current flowing between the surface and the tip of the needle - is an example of real-world nanotechnology (it was invented in 1982), a tool which can image and manipulate individual atoms. The problem with STM is that it can't tell what kind of atoms it is seeing. Now, 100 years ago Einstein explained the photoelectric effect - some of the electrons in a material can jump out when you shine UV light or X-rays on the surface. The energy spectrum of these electrons carries information about the composition of the material and its so-called electronic states . If we could collect the photoelectrons and measure their energy with the tip of a scanning tunnelling microscope, we could analyse the material on a very small scale and find out about the atoms. So this project is aiming to build a tiny electron analyser onto the tip (in fact, inside the tip itself) - we call it the Scanning Probe Electron AnalyseR, or SPEAR for short. It will scan over the surface while the light is shining, and so measure the photoelectron spectrum with a resolution down to about 10 nanometres. This is 1000 times smaller than the diameter of a human hair and the size of about 30 atoms. To build the analyser we have to make a special kind of STM tip, a type of tip which hasn't been made before, but with the right people and the advanced equipment we have we believe we can do it. The tip is made of lots of layers like an onion, but it's the shape of a needle - that's the key idea. We think that the same kind of microfabricated tip can also be used as an electron source(rather than an analyser), to make possible another type of nanoscale spectroscopy, where we measure the energy lost by the emitted electrons when they bounce back from the surface - this is called Scanning Probe Energy Loss Spectroscopy, or SPELS. Finally, we want to demonstrate the power of both these new techniques by measuring the quantum properties of small clusters of atoms, which behave in a very different way from the materials we handle everyday. In the future, we think that these tools may be taken up by companies to solve practical problems in materials engineering.