Yale engineers have created
a process that may revolutionize the manufacture of nano-devices from computer
memory to biomedical sensors by exploiting a novel type of metal. The material
can be molded like plastics to create features at the nano-scale and yet is
more durable and stronger than silicon or steel. The work is reported in the
February 12 issue of Nature.
 | | Various parts (nano-molds, nano-wires, gears, membrane, scalpels, and tweezers) fabricated by molding metallic glass over wide range of length scales -- from 13 nm to several millimeters. Credit: Kumar/Schroers(Yale) |
The search for a cost-effective and manageable process for higher-density computer
chip production at the nano-scale has been a challenge. One solution is making
nano-scale devices by simple stamping or molding, like the method used for fabricating
CDs or DVDs. This however requires stamps or master molds with nano-scale features.
While silicon-based molds produce relatively fine detail, they are not very
durable. Metals are stronger, but the grain size of their internal structure
does not allow nano-scale details to be imprinted on their surfaces.
Unlike most metals, “amorphous metals” known as bulk metallic glasses
(BMGs) do not form crystal structures when they are cooled rapidly after heating.
Although they seem solid, they are more like a very slow-flowing liquid that
has no structure beyond the atomic level — making them ideal for molding
fine details, said senior author Jan Schroers of the Yale School of Engineering
& Applied Science.
Researchers have been exploring the use of BMGs for about a decade, according
to Schroers. “We have finally been able to harness their unusual properties
to transform both the process of making molds and producing imprints,”
he said. “This process has the potential to replace several lithographic
steps in the production of computer chips.”
Schroers says BMGs have the pliability of plastics at moderately elevated temperatures,
but they are stronger and more resilient than steel or metals at normal working
temperatures.
“We now can make template molds that are far more reliable and lasting
than ones made of silicon and are not limited in their detail by the grain size
that most metals impose,” said Schroers.
To actually get detail at the nano-scale the researchers had to overcome an
issue faced in any molding process — how to get the material to cover
the finest detail, and then how to separate the material intact from the mold.
Surfaces of liquid metals exhibit high surface tension and capillary effects
that can interfere in the molding.
Postdoctoral fellow Golden Kumar found that by altering the mold-BMG combination
they could create surfaces so that the atoms take advantage of their favorable
interaction with the mold— to both fill the mold and then release the
product.
In this paper, Schroers’ team reports nano-patterning of details as small
as 13 nanometers— about one ten-thousandth the thickness of a human hair
— and the scientists expect that even finer detail will be possible since
the BMGs are only limited by the size of a single atom.
While ‘plastics!’ was the catchword of the 1960’s, Schroers
says, “We think ‘BMGs!’ will be the buzz-word for the coming
decade.”
Posted February 11th, 2009
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