Saturday, August 31, 2013

3:32 AM
One of the biggest knocks against cellphones is they require small amounts of rare earth elements: gallium, indium and arsenic, for example, that are both scarce and expensive. But what if you could make a phone out of a more common element, like carbon?
Researchers are taking slow but sure steps toward building the innards of a cellphone out of carbon nanotubes, a structure that resembles a microscopic sheet of chicken wire rolled into a cylinder. These cylinders can be used to either conduct electricity or store energy.
CellAt the Technical University of Denmark, Jakob Wagner and colleagues have found a better way to build carbon nanotubes that could lead to their use as a semiconductor, a key component of all electronic circuit parts found in both cellphones and laptops. Carbon nanotubes have properties of both a metal and a semiconductor, depending on how they are rolled.
“The breakthrough here is that we are able to control the production of nanotubes whether they are metallic or semiconducting,” Wagner said. “That’s important because if you want to use them in cellphones, we have to make sure they are either one or the other. The prospect is to use semiconducting carbon nanotubes as a substitute for gallium.”
Warner published his work earlier this month in the Nature publication Scientific Reports.
The next step is to be able to produce large amounts of semiconducting carbon nanotubes that could be made into an electronic device, Wagner said.
“It will not be tomorrow, let’s say 10 years,” he said.
But at IBM, researchers like James Hannon are working to speed up that lab-to-prototype timescale. Hannon says that Wagner’s finding is an important step, but it needs to be replicated on larger-diameter carbon nanotubes.
"This is a nice scientific demonstration, but not in the range that would be used in a logic application," said Hannon, manager of IBM’s carbon electronics group in Yorktown Heights, N.Y. "I’d like to see if this technique could work for larger diameter tubes as well."
Last year, Hannon and his IBM colleagues announced they had built memory and microprocessing chips using carbon nanotubes. He said the tough thing is getting them to lie down in straight lines, but they overcame this obstacle by creating special grooves etched into the silicon chip surface and a bonding agent.
Hannon says the two challenges with carbon nanotubes is figuring out how to place them and how to separate the semiconducting ones from the metallic ones, which are thrown away. A separate team at North Carolina State University recently reported they were able to integrate carbon nanotubes into a flexible scaffold for a silicon-based battery that would last longer than existing lithium ion batteries.


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