Carbon nanotubes align and spread evenly on bubbles

Nanotubes on the surface of a bubble will align and spread evenly on the surface.

This finding fits in nicely with the concept of giant space bubbles that was reported on this site. If the two ideas can be combined then space bubbles made from carbon nanotubes would be possible. This would allow for stronger and lighter walls. It could also be a means of forming large carbon nanotube solar sails.

Bubbles of epoxy mixture containing nanowires or nanotubes line the materials up neatly, and can be caught on flat plates (Image: Nature)

Bubbles were produced by pouring the epoxy mixture over a metal plate with a gas inlet at the centre. Turning on the gas creates a bubble and a metal ring above the plate catches hold as it grows. As the bubble expands to more than 25cm wide and 50cm tall, portions of film are deposited on surrounding pieces of flat silicon or plastic.

The nanomaterials contained in the mixture were found to have aligned themselves vertically, towards the top of the bubble. Varying the concentration of tubes or wires in the mixture altered the density of nanomaterials but not their alignment.

Exactly why the tubes line up is not known, although the researchers suspect that stress generated on the surface of the bubble, as it expands, pulls the tubes and wires into line. They add that having a simple way to align nanowires and nanotubes with a particular density could help integrate such components into electronic and optical devices.

To prove this, the team created arrays of transistors using bubbles containing silicon nanowires. Electrodes and an additional layer of insulator were patterned onto a plate coated using the bubble technique to make many field effect transitors that exploit the semiconductor properties of the nanowires.