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Delft University of Technology
discovers how to control nanowires
Delft, Netherlands, June 13: Jorden van Dam,
researcher at the Kavli Institute of Nanoscience Delft, has succeeded in largely
controlling the transportation of electrons in semiconductor nanowires. Van Dam
moreover discovered how to observe a divergent type of supercurrent in these
wires. Nanowires have superior electronic properties which in time could improve
the quality of our electronics. On Tuesday, June 13, Van Dam will receive his
PhD degree at Delft University of Technology based on this research.
During his PhD research, Jorden van Dam focused
on semiconductor nanowires. These are extremely thin wires (1-100 nanometers
thick) made of, for example, the material indiumarsenide, which has superior
electronic properties. The integration of these high quality nanowires with the
now commonly used silicium technology offers intriguing possibilities for
improving our electronics in future. According to Van Dam, in recent years many
possible applications for semiconductor nanowires have emerged, such as in
lasers, transistors, LEDs and bio-chemical sensors. Philips is one of the
companies that is conducting intensive research into the possibilities for
semiconductor nanowires in specific applications.
Van Dam - who during his PhD research co-authored
articles that were published in Nature and Science - was able to make a
so-called quantum dot in a semiconductor nanowire (this is done at extremely low
temperatures). These quantum dots can be regarded as artificial atoms and in the
distant future will serve as building blocks for super-fast quantum computers.
In a quantum dot, a number of electrons can be 'confined'. The magnificence of
Van Dam's research is the total control he has managed to gain over the number
of electrons that can be confined in a quantum dot. He can control this number
by means of an externally introduced charge. A crucial factor for the extreme
degree of control that Van Dam has achieved is the quality (for example the
purity) of the nanowires, which were supplied by Philips. It is above all the
quality of the material used (wires and electrodes) that was greatly improved
during Van Dam's research.
The research also produced new physical
observations. In the improved nanowires, Van Dam achieved for the first time the
realisation and observation of a (theoretically already predicted) divergent
type of supercurrent (a supercurrent is the current that occurs in
superconductivity). In a quantum dot, the electrons normally pass through one by
one. In superconductivity, the passage of electrons occurs in pairs. Van Dam,
with the help of superconductor electrodes, has now achieved a supercurrent in
the quantum dot, whereby the pairs of electrons pass through one by one.
Van Dam has also - under specific conditions -
achieved a reversal in the direction of the supercurrent. He is able to control
this reversal by varying the number of electrons confined in the quantum dot.
With this, the Delft University of Technology researcher has achieved a largely
controllable superconductor connection in semiconductor nanowires.
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