by Staff Writers
Groningen, Netherlands (SPX) Apr 06, 2017
Carbon nanotubes can be used to make very small electronic devices, but they are difficult to handle. 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. The results were published in the journal Advanced Materials on 5 April.
The results look deceptively simple: a self-assembled transistor with nearly 100 percent purity and very high electron mobility. But it took ten years to get there. 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.
'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.'
The production process is simple: metallic patterns are deposited on a carrier , which is then dipped into a solution of carbon nanotubes. The electrodes are spaced to achieve proper alignment: 'The tubes are some 500 nanometres long, and we placed the electrodes for the transistors at intervals of 300 nanometres. The next transistor is over 500 nanometres away.' The spacing limits the density of the transistors, but Loi is confident that this could be increased with clever engineering.
'Over the last years, we have created a library of polymers that select semiconducting nanotubes and developed a better understanding of how the structure and composition of the polymers influences which carbon nanotubes they select', says Loi. The result is a cheap and scalable production method for nanotube electronics. So what is the future for this technology? Loi: 'It is difficult to predict whether the industry will develop this idea, but we are working on improvements, and this will eventually bring the idea closer to the market.'
Vladimir Derenskyi, Widianta Gomulya, Wytse Talsma, Jorge Mario Salazar-Rios, Martin Fritsch, Peter Nirmalraj, Heike Riel, Sybille Allard, Ulrich Scherf, Maria A. Loi: On-chip chemical self-assembly of semiconducting Single-Walled Carbon Nanotubes (SWNTs): towards robust and scale invariant SWNTs transistors Advanced Materials, online 5 april 2017
Washington DC (SPX) Apr 04, 2017
Contrary to the tremendous success story of electronic integration, photonic integration is still in its infancy. One the most serious obstacles it faces is the need to use a variety of materials to achieve different functions - unlike electronic integration. To complicate matters further, many of the materials required for photonic integration aren't compatible with silicon integration technolo ... read more
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