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Electrical conductivity of carbon nano-tubes

April 20, 2000

Pb. 2000/38
Delft, 19 april 2000
EMBARGO TOT 19 APRIL 2000, 20.00 UUR

Fundamentally new view on electrical conductivity of carbon nano-tubes described in Nature
Molecular electrical conductivity unexpectedly different at nano-level

The electric charge in a semi-conductive carbon nano-tube of minuscule dimensions (a diameter of one millionth of a millimetre) is not evenly distributed, but divided into separate charge 'islands.' This is the conclusion of physicists Dr. Sander Tans and Prof. Dr. Cees Dekker of the section Quantum Transport at TU Delft, which is published in the current issue of Nature (released 20 April). An unexpected discovery in a FOM financed research project. Dekker: "This insight is important if conductive nano-tubes are eventually to be used in electric circuits."

Nano-tubes are made up of a series of connected hexagonal constructions of carbon atoms. These molecular tubes have conductive properties, which makes them interesting for future use in all kinds of nano-electrical applications. Dekker: "We had already made a transistor from a single nano-tube, and now wanted to know how the charge changes over the length of the tube. Such a charge-profile could help us understand how the nano-tube transistor works."

Tans and Dekker sent an electrical charge through the tube, causing electrons to be transported through it. By measuring the charge field at several points on the tube with an Atomic Force Microscope, the two researchers from Delft discovered all kinds of local charge-differences. Dekker: "The charge seems to be concentrated in small islands at intervals of approximately 40 nm. We had not expected this. The electrons apparently jump from one point to another, and this provides the conductive capacities of the nano-tube."

According to Dekker we still have a long way to go before we have a real application, but the research in Delft is the first step in the clarification of the 'how and why' of the conductivity of nano-tubes. One of the problems on which the research group will shortly concentrate is the question why the charge is divided into groups at 40 nm intervals. Dekker: "Of course there are also many interesting questions for research in the long term. In the future we will research the effects of mechanical deformation, a kink for example, on the conductivity of the nano-tube. New technologies make it possible to bend the tubes controllably."

Delft University of Technology

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