surface stores data
Technology Research News
Cramming more data into a given storage
device is all about making bits that are extremely small and consistently
Using individual molecules to store bits would be a tremendous leap forward.
One molecule gaining researchers' attention is rotaxane, which contains
a ringed portion that can move along a long, thread-like portion of the
molecule. Moving the ring from one end of the thread to the other could
be a way to change a bit from a 1 to a 0.
Perfecting a method to make storage devices out of individual molecules
is a tall order. But it turns out that the rotaxane molecule's unique
shape could be used for data storage in a different way.
When researchers from universities in Italy and Edinburgh found that drawing
the tip of an atomic force microscope across a thin film of rotaxane molecules
resulted in perfectly-spaced strings of dots, they realized the phenomenon
could be used for storing data. "Once you have the capability to write
a dot and to fix its position... you immediately think about writing bits,"
said Fabio Biscarini, head scientist of nanotechnology of multifunction
materials research at the National Council of Research Institute for the
Study of Nanostructured Materials (CNR-ISMN) in Italy.
The method could allow for a super-capacity DVD-like media that could
be written to extremely quickly. It could also provide a different way
to form biochips, or labs-on-a chip that provide tiny channels to move
and mix biological substances.
The force imparted during repeated passes of the microscope tip along
a line works the rotaxane thin film into a series of bumps, much like
repeat passes of a truck causes washboard-like bumps to form in a dirt
road. "We discovered that we had the capability to write collectively
as many dots [as] we wanted by simply adjusting the length of the line
scan," said Biscarini.
The rotaxane dots are a few molecules high, 20 to 40 nanometers wide and
100 nanometers apart. A nanometer is one millionth of a millimeter, or
the span of 10 hydrogen atoms. The exact size of the dots depend on the
thickness of the film, and their spacing is consistent, said Biscarini.
The researchers found they could write parallel strings of dots spaced
closely enough to fit 100 billion of them per square inch of film. Today's
DVD's hold 4.7 gigabytes of information, which works out to 2.77 billion
bits, or gigabits per square inch. Today's highest-density magnetic disk
drives hold 50 gigabits, and lab prototypes have reached 100 gigabits
per square inch.
In theory, data could be written to the rotaxane film bits in parallel,
using a stamp or an array of probe tips. This would allow information
to be pressed extremely quickly into CD or DVD-like media that would hold
much more information. "Parallel writing would enable high-throughput
permanent information writing, as in CDs or DVD's, but with a considerably
larger area density," said Biscarini.
The key to the method is carefully controlled, gentle pressure on the
tip. "We had to control carefully the force acting between the tip and
the rotaxane film; the transformation into dots occurs only in a very
narrow range of forces," said Biscarini. "At smaller forces nothing happens;
at larger forces the film is scratched and destroyed," he said.
The structure of the molecules makes the change possible, said Biscarini.
The molecules' rings can rotate with relative ease even when they are
part of a solid, depending on the energy states of the hydrogen bonds
within and among the molecules. "This makes molecules quite mobile even
in [a] solid state, if appropriate energy is provided -- [this] molecular
mobility is the key ingredient for achieving a transformation in the solid
state," said Biscarini.
The scanning tip provides enough energy to the rotaxane molecules along
the line so that they form the nuclei of the dots, which then grow larger
as the energy diffuses to nearby molecules.
The researchers also found that the process could be stopped and started.
"The fascinating feature of the phenomenon is that... the film rupture
could be stopped simply by decreasing, and restarted by restoring the
caressing force," said Biscarini. "The evolution of the dots could be
slowed down at our convenience, and we could take a sequence of snapshots,"
The researchers are perfecting a method of writing data to the dots in
parallel, according to Biscarini. They are also working on a method to
erase data, he said.
The researchers are also working on ways to quickly retrieve information
stored in the rotaxane bits. "The big problem is a method to read information
fast on bits one nanometer high, a few nanometers wide, and less than
100 nanometers apart," said Biscarini. Current data-reading methods measure
differences in magnetic, electrical or optical properties on portions
of flat films rather than just a second raised structures. However, "it
is reasonable to think that the dots will have different properties with
respect to the unperturbed film", he said.
A method to write to ultra-high-density rotaxane thin film bits could
be ready in two years, said Biscarini. Perfecting readout and erasing
methods could easily take as long as five years, however, he said.
The method could also be used to form patterned surfaces that change their
structures at precise locations when stimulated, said Biscarini. "It could
then become a new way to make biochips, sensors [and] pressure transducers,"
Biscarini's research colleagues were Massimiliano Cavallini of CNR-ISMN,
Salvador León and Francesco Zerbetto of the University of Bologna in Italy,
and Giovanni Bottari and David A. Lee of the University of Edinburgh in
Scotland. They published the research in the January 24, 2003 issue of
Science. The research was funded by the European Union.
Timeline: 2-5 years
TRN Categories: Data Storage Technology; Materials Science
and Engineering; Chemistry
Story Type: News
Related Elements: Technical paper, "Information Storage
Using Supramolecular Surface Patterns," Science, January 24, 2003.
29/February 5, 2003
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