Science

Carbon Nanotube Filtering Breakthrough

Yellow stick of butter with two lines - one drawn across the top to represent a semiconducting wire that has not melted through the butter and another that has sunk to the bottom of the butter representing a conducting wire. The example shows a way to purify - or sort - carbon nanotubes with different properties.

Carbon nanotubes, microscopically-thin wires of carbon atoms, can be produced in sufficient quantity but not sufficient quality for electronics. They often include a bundle of wires where some are conductive, like the power wires going from your computer to the wall outlet, and some are semiconducting — the kind needed for processing information. Science Daily reports on a carbon nanotube purification breakthrough by a research team at University of Illinois at Urbana–Champaign, lead by professor John Rogers. Efforts to purify or sort conducting from semiconducting nanotubes have been expensive and require many steps. The new method discovered can be explained easily.

Imaging you have a stick of butter and you lay two thin metal wires — one a standard metal wire and the other a semiconducting wire — over top of the butter then attach the positive and negative electrodes of a battery to each end of wire. After a few seconds what happens? The conductive metal wire heats up and sinks into the butter stick. The semiconducting wire does not heat up nearly as much due to restricting the electron flow — so it does not sink into the butter as deeply. Instead the semiconducting wire stays nearly on the surface of the butter. Once the process is complete you can easily separate the conductive and semiconducting wire since the conductive one is at the bottom of the butter stick. Image edited to show example:

Yellow stick of butter with two lines - one drawn across the top to represent a semiconducting wire that has not melted through the butter and another that has sunk to the bottom of the butter representing a conducting wire. The example shows a way to purify - or sort - carbon nanotubes with different properties.

WARNING: DO NOT try the experiment described above! It is dangerous and could lead to burns or even an explosion — the battery and wires will heat up and can remain hot and the battery may even explode!

This new method of using current-induced heat to separate nanotubes of different properties is easy to do and is compatible with current manufacturing methods.

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