Carbon nanotubes enable tiny transistors to build themselves

April 06, 2017 // By Jean-Pierre Joosting
University of Groningen scientists, together with colleagues from the University of Wuppertal and IBM Zurich, have developed a method to select semiconducting nanotubes from a solution and make them self-assemble on a circuit of gold electrodes – alleviating the difficulty of using carbon nanotubes to make very small electronic devices.

The result of ten years of research, the method produces a self-assembled transistor with nearly 100 percent purity and very high electron mobility. University of Groningen Professor of Photophysics and Optoelectronics Maria Antonietta Loi designed polymers which wrap themselves around specific carbon nanotubes in a solution of mixed tubes. Thiol side chains on the polymer bind the tubes to the gold electrodes, creating the resultant transistor.

'In our previous work, we learned a lot about how polymers attach to specific carbon nanotubes', Loi explains. These nanotubes can be depicted as a rolled sheet of graphene, the two-dimensional form of carbon.

'Depending on the way the sheets are rolled up, they have properties ranging from semiconductor to semi-metallic to metallic.' Only the semiconductor tubes can be used to fabricate transistors, but the production process always results in a mixture.

'We had the idea of using polymers with thiol side chains some time ago', says Loi. The idea was that as sulphur binds to metals, it will direct polymer-wrapped nanotubes towards gold electrodes. While Loi was working on the problem, IBM even patented the concept.

'But there was a big problem in the IBM work: the polymers with thiols also attached to metallic nanotubes and included them in the transistors, which ruined them.'

This is an artist's impression of carbon nanotubes wrapped in polymers with thiol side chains (yellow spheres) and assembled on gold electrodes. Image courtesy of Arjen Kamp.