US researchers have demonstrated a form of nanotube archival memory
that can store a memory bit for a billion years, and has a theoretical
trillion bits/square inch density.
The researchers at the U.S. Department of Energy's Lawrence Berkeley
National Laboratory (Berkeley Lab) and the University of California
(UC) Berkeley were led by physicist Alex Zettl. They built a prototype
device based on a nanoscale iron particle, about 1/50,000th the width
of a human hair, moving along a carbon nanotube like a shuttle.
By applying an electric current, the iron particle shuttle could be
made to move inside the nanotube either away from or towards the
current source. When the current was turned off the particle was, as it
were, frozen in position. By applying the current in a timed pulse the
particle could be made to move a fixed 3nm distance in steps. The speed
of movement could be altered by varying the applied bias voltage.
The researchers say that placing the shuttle either side of the
mid-point along the length of the nanotube can constitute a digital one
or zero. A transmission electron microscope showed the shuttle moving -
there is a video showing this accessible here.
In a practical device the shuttle position could be read via detecting
the axial electrical resistance of the nanotube by small voltage
pulses. This is sensitive to the physical location of the enclosed
nanoparticle shuttle and the pulses do not alter the state of the
shuttle.
Other calculations suggest a complete archival chip could store a
trillion bits in a square inch in this way. Fascinating stuff, but any
practical usage is still many, many years away.
http://www.theregister.co.uk/2009/06/08/shuttle_nanotube_memory/
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