Pointy tip is just one atom wide
It doesn’t get any sharper than this: the finest point ever made, with just a single atom at its tip.
Robert Wolkow and his team at the National Institute of Nanotechnology at the University of Alberta, Canada, have devised a method of coating a tungsten point with a protective layer of nitrogen, which holds all of the metal atoms in place and maintains the tiniest point possible.
’This coating has the effect of binding the little pyramid of metal atoms in place,’ said Wolkow. ’Such a pointy pyramid would normally just smudge away spontaneously, like a pile of sand.’
That smudging can leave the tip with a rounded curvature, around 10 nanometres (billionths of a metre) across. Sharpening it with nitrogen makes the tips much more useful in techniques such as electron microscopy, where a current flows between the tip and the surface under scrutiny.
’The lenses in an electron microscope work more perfectly if the electron beam comes from a very small point,’ explains Wolkow. ’The finer the point of electron illumination, the higher the resolution of the microscope.’
Since the apex of their tip is just one atom wide, Wolkow hopes that it will be able to deliver the sharpest beam yet out of an electron microscope. ’If this works, we could instantly improve a conventional electron microscope by inserting one of our tips,’ he said. The invention was unveiled in the Journal of Chemical Physics.
Sharpness isn’t everything though. The electron beam emitter must be able to provide lots of current into a small angle, explained Martin Seah of the UK’s National Physical Laboratory, Teddington.
’Emitters also need to be serviceable and cost effective in order to be practical,’ he added. ’But if these new tips accomplish this and greatly improve resolution, I think they could be of huge benefit.’
Since the tips are stable up to 900 ?C, it’s likely they could be used under the harsh conditions imposed on an emitter. Wolkow predicts that with an improvement in the resolution of electron microscopes, the design and manufacture of nanoscale devices could be made much easier.
R Wolkow et al,J. Chem. Phys. 2006 (DOI:10.1063/1.2198536)