Researchers from Karlruhe (Sciencexpress, June 26, 2003) have developed a method to separate metallic from semiconducting single-walled carbon nanotubes (SWNTs). The technique uses the different relative dielectic constants of the two types of tube with respect to the solvent.

Researchers from Karlruhe (Sciencexpress, June 26, 2003) have developed a method to separate metallic from semiconducting single-walled carbon nanotubes (SWNTs). The technique uses the different relative dielectic constants of the two types of tube with respect to the solvent.

Using alternative current dielectrophoresis, the two types of tube move in opposite directions along the electric field gradient. The metallic tubes are attracted towards a microelectrode array leaving the semiconducting ones in the solvent.
The effectiveness of the separation was tested using Raman spectroscopy. It is estimated that 80% of the deposited tubes are metallic with a 5% error. The original suspension is assumed to contain 33% metallic tubes.

The scientists believe that in principle a complete separation is possible if all tubes in the suspension are present as individual tubes and not bundled as is often the case. A metallic tube in a bundle of semiconducting ones would be attracted to the electrodes. In fact, the team used a four-hour preparation technique to boost the number of individual tubes before using their ten-minute dielectrophoresis process.

The team estimates that some 100pg of metallic tubes are deposited out of roughly 100ng in the drop. This is too small to see a depletion of metallic tube in the suspension.
"However," the report concludes, "we are confident that the separation method can be substantially upscaled by the use of microfluidic dielectrophoretic separation cells as commonly used in biology."

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Thanks to the great diversity of the semiconductor industry, we are always chasing new markets and developing a range of exciting technologies.

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