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A NEW way of storing digital data has been pioneered by researchers in the US
and China. Their feat is to have reversibly altered the conductivity of areas
little bigger than molecules in a thin film of material. This should eventually
allow data to be packed more densely than will ever be possible with optical or
magnetic media, they say.

The researchers, from Oak Ridge National Laboratory in Tennessee and the
Chinese Academy of Sciences in Beijing, made an insulating crystalline film just
20 nanometres thick by depositing a mix of 3-nitrobenzal malonitrile and
1,4-phenylenediamine on a glass plate. They then moved a scanning tunnelling
microscope, which has a tungsten tip the size of a single atom, close enough to
the surface for electrons to jump the gap. When the voltage exceeds 3.2 volts,
the carbon-based molecules under the tip cease to be crystalline, and become
conductive. Applying a reverse polarity of 4.5 volts returns the spot of organic
material to its crystalline, insulating state. This switching between conduction
and non-conduction could represent digital code, the researchers say.

The capacity of today’s optical discs is ultimately limited by the wavelength
of the light used to read them. Magnetic discs also have limited capacity
because the magnetic domains representing individual bits can’t retain their
magnetism when they become too small.

The spots on the new conducting recorder are of near-molecular size. This
could lead to storage densities up to a million times greater than those
possible with CDs. If the technique ever takes off, it will need a completely
new generation of recorders and players.