FILL a carbon nanotube with water and what do you get? Not just a wet carbon fibre, but an ultrafast switch for nanoelectronics. At least, that鈥檚 what some curious computer simulations are suggesting.
The idea comes from computer simulations run by Erik Jakobsson and colleagues at the University of Illinois in Urbana-Champaign. They were modelling the flow of water through carbon nanotubes with various diameters when they were surprised to find that water wouldn鈥檛 flow through tubes with a diameter of precisely 0.86 nanometres.
Investigations revealed that the simulated water molecules had arranged themselves into stacks of hexagonal molecules, similar to the structure of one form of ice. Somehow the nanotube鈥檚 dimensions force the water to solidify, even at room temperature. 鈥淚t鈥檚 a geometrically-induced freezing,鈥� says Jakobsson.
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If the effect occurs in real nanotubes, Jakobsson thinks it may help nanoelectronics designers. One problem with making components such as transistors ever tinier is that it becomes harder and harder to use electrons to carry a current that you can switch on and off cleanly in an instant. That鈥檚 because electrons can easily 鈥渙vershoot鈥� nanoscale distances when the current is switched off.
However, protons do not have the same problem, so a proton current could be switched off much more cleanly, says Jakobsson. Not only that, but protons are thought to travel far more freely in ice than in liquid water. So if you can create a water-filled nanotube whose diameter you can vary, you should effectively have a proton-current switch 鈥� 鈥渇reeze鈥� the water and it鈥檚 on, liquefy it and it鈥檚 off. This could be used to represent digital 1s and 0s.
Jakobssen believes that this could be done by embedding the walls of the nanotube with charged particles that can gently squeeze the tube when an external electric field is applied. However, the predicted freezing action has yet to be seen in real nanotubes.
