When Gordon Moore made his observation in 1965 that the number
of transistors integrated on a single silicon chip is doubling
roughly every two years, the only logical end point for such a
trend would be a transistor made from a single atom. This point
has now been reached. Writing in Nature Nanotechnology, Michelle
Simmons from the University of New South Wales in Sydney and
colleagues report a single-atom transistor, the world’s
smallest, on a silicon chip. The transistor is based on current
flowing through a single atom of phosphorus embedded in a
silicon wafer. Phosphorus is a natural choice for such a
transistor, as it is relatively easy to integrate into silicon.
There it acts as an electron donor because it has an additional
electron compared to silicon. This additional charge can be used
for conventional electronic devices such transistor, but also
more complex schemes are possible. For example, the magnetic
property of this single excess electron, its spin, can be used
for new types of quantum comput