DU professor improves nanotubes
Nathan Fried
Issue date: 5/22/09 Section: News
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Carbon nanotubes are much smaller in diameter than a human hair, yet stronger than steel, diamond, or any material known to man.
His work involving single-walled carbon nanotubes, or SWNT for short, is a facet of nanoelectronics that has yet to be fully investigated. Current research only focuses on fabricating carbon nanotubes and distinguishing correctly oriented nanotubes which would work in a circuit from disordered nanotubes that would be non-functional.
However, an important yet difficult milestone would be the discovery of methods to create regular patterns along a carbon nanotube which could support sequential transistors. Before Li's breakthrough, all attempts to do this resulted in poorly repeating patterns.
"That's basically what we did, the creation of these patterns. This can serve as a template if you put a conducting material within these domains [along the carbon nanotube]. You can literally generate one transistor out of this single domain and therefore make multiple transistors along the nanotube. This will lead to an extreme miniaturization of devices," Li Said.
Each transistor, being sequentially placed along the nanotube, would have the potential of being 20 nanometers long, equivalent to just 60 individual nucelotides of DNA.
"The success we have seen is primarily due to the block co-polymer we used," Li Said.
Li's team used polyethylene-block-poly (ethylene oxide) to create this periodic pattern. Block co-polymers are polymer chains formed by the connection of two completely different polymer chains which are then covalently linked together. Acting almost like lipids, these two polymers will naturally separate. However, the covalent bond between them keeps them together and causes a self-assembling ordered-pattern of stripes. Because the poly(ethylene oxide) block of the copolymer has a strong tendency to crystallize on the carbon nanotube surface, this ordered pattern of stripes can then form along nanotubes and act as an anchor for transistors.
The process involves setting a SWNT solution onto a carbon-coated grid which causes the nanotubes to line up with one another. It can then be decorated with a solution containing the copolymers and analyzed using transmission electron microscopy. Varying the concentration of the copolymer solution can change the amount of stripes and in turn, the distance between them. The period of this pattern can be adjusted anywhere between 10 nm to 100 nm. This versatility will make the utilization of nanotubes in electronic circuits possible.
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