Scientists stamp individual carbon nanotubes

Researchers from the Kavli Institute of Nanoscience (Delft University of Technology) and the FOM Foundation have devised a new method for reading out the electron state in a carbon nanotube. They did this by 'stamping’ an individual nanotube on a chip. Then the electron state can be read out, as the nanotube remains very clean and controllable. Electrons in such a nanotube can acquire special quantum characteristics which make these structures interesting for future quantum computers. The readout of the electron states is a crucial step in this. The research team led by FOM workgroup leader professor Leo Kouwenhoven published the results in the October issue of Nature Nanotechnology.

Carbon nanotubes are cylindrical structures with a diameter of several nanometres. If several electrons are confined in a small segment of the nanotube, a so-called quantum dot, quantum mechanical characteristics occur. Scientists are very interested in these characteristics as quantum dots could form the basis for future quantum computers. They want to know how the current through the quantum dots – within the nanotube – is dependent on the electron state and how this state can be influenced.

Stamping
The first result from the researchers is that the current through the nanotube is dependent on both the spin and the valley angular momentum of the electrons in the quantum dots. The researchers achieved this result by developing a new technique that allows very clean nanotubes to grow on a chip. Subsequently one individual nanotube is transferred to another chip where the quantum dots can be formed. With this approach the nanotubes remain clean throughout the entire process, even after manufacturing. As a result of this the nanotubes can be more easily controlled. The manufacturing process is comparable to stamping ink on a piece of paper: the first chip is the stamp and the second chip is a piece of paper. Using an optical microscope the researchers could carry out the stamping with micrometre precision.

Bent nanotube
An added advantage is that the nanotubes bend during the stamping process. Scientists have been trying to manufacture clean bent nanotubes for a long time, as it has been predicted that you can then control the angular momentum of an electron using an electric field. Kouwenhoven’s group did indeed manage to detect electron spin flips in this manner. This second result is an important step towards the creation of a nanotube qubit, the alternative for current computer bits.

Reference
'Valley-spin blockade and spin resonance in carbon nanotubes' Fei Pei, Edward A. Laird, Gary A. Steele and Leo P. Kouwenhoven. Nature Nanotechnology 7, 630-634 (2012).
The article was published on 23 September 2012 as an Advance online publication on the website of Nature Nanotechnology.
doi:10.1038/nnano.2012.160

Further information
FeiPei