Making faster computers means making
smaller circuits in order to shorten the paths electrons follow. The
smallest transistor possible would let only one electron pass through at a
time, and could lead to computers that are much faster and require much
less power than today’s models.
Researchers in Sweden and Denmark
have found a way to use carbon nanotubes as electronic leads that connect
a circuit with a tiny particle of gold to form a single-electron
The researchers’ transistor is a first step towards
single-electron devices that would measure a mere 3 or 4 nanometers, or
about as wide as 30 to 40 hydrogen atoms end to end. Single-electron
transistors have to be this small in order to work at room temperature.
Manipulation of such tiny objects is a delicate process. The
researchers managed to position a carbon nanotube between two electrodes
using an atomic-force microscope (AFM) tip. Then they used the tip to cut
the nanotube -- a rolled-up sheet of carbon atoms -- into two sections,
"each section still in contact with its respective electrode," said Lars
Samuelson, a professor of Solid State Physics and Head of the Nanometer
Structure Consortium at Lund University. Next, the researchers made the
nanotube halves parallel, and deposited a 7-nanometer gold nanoparticle
The researchers then adjusted the temperature. They
found that cooling the device below 200 degrees Kelvin, or -73 degrees
Celsius, makes it an ideal single-electron transistor, said Samuelson.
The researchers next plan to use smaller nanoparticles to make a
device that will operate at room temperature, said Samuelson.
is good work, said Zhen Yao, an assistant professor of physics at the
University of Texas at Austin. "This approach opens up [ways] to
systematically study the electronic properties of individual nanoparticles
--metallic, semiconducting, magnetic, or superconducting -- as a function
of their sizes," he said.
This type of systematic study is crucial
to testing nanoparticles for various applications but has been lacking
mainly because it is difficult to address individual nanoparticles, Yao
said. "They are typically 2 to 10 nanometers in diameter, which is beyond
the resolution of standard electron-beam lithography" processes used to
make experimental computer chips.
The method is useful for basic
science but probably not for practical applications, said Hongkun Park, an
assistant professor of Chemistry at Harvard University. AFM manipulation
is not a practical strategy to make commercial devices, because it can
only be used to make one device at a time, which is far too slow for
manufacturing, he said.
Samuelson’s research colleagues were Claes
Thelander, Martin H. Magnusson, and Knut Deppert at Lund University in
Sweden, and Per Rugaard Poulsen, Jesper Nygard, and Jorn Borggreen at the
Niels Bohr Institute at the University of Copenhagen, Denmark. They
published the research in the September 24, 2001 issue of the journal
Applied Physics Letters. The research was funded by the Swedish Foundation
for Strategic Research (SFF), The Swedish Research Council for Natural
Sciences and for Engineering Sciences, and the European Union (EU).
TRN Categories: Nanotechnology;
Story Type: News
Elements: Technical paper, "Gold Nanoparticle Single-Electron
Transistor With Carbon Nanotube Leads," Applied Physics Letters, September