Heat a carbon nanotube in a vacuum and the tube will glow, emitting light right across the visible spectrum. And even thought this nanolamp is only a few nanometres in diameter, you can see the light it emits with the naked eye.
Now Scott Singer at pals at the University of California, Los Angeles, say they can use this light to completely determine the shape of the nanotube.
Here’s how they do it. The light that any object emits, and in particular the polarisation of this light, depends on its electronic structure.
But at the nanometer scale, the electronic structure of an object is intimately related to its shape.
So Singer and buddies simply measure the polarisation of the photons emitted by the nanotube at each wavelength. They can then work out what shape emitted this light by constructing an electronic model capable of producing the same signature and seeing whether they match.
Their nanotube, it turns out, is of the double-walled variety.
That’s potentially useful. One of the significant outstanding problems in nanotechnology is understanding the optical properties of very small things. So having a way to relate practical measurements with theoretical models could be useful.
The question, of course, is whether the same technique can be usefully applied to more complex shapes. It’s easy to imagine that this problem becomes intractable when the symmetries that nanotubes posses are no longer present.
If it does work more broadly, though, we may begin to see more nanostructures engineered in a way that optimises their optical properties. It’s not hard to see how such nano-emitters and receivers could revolutionise everything from photovoltaics to communications to computing.
Ref: arxiv.org/abs/1102.3484: Polarized Light Emission From Individual Incandescent Carbon Nanotubes