New technique shakes up nano-devices

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Take heed, Apple Inc.: The compact disc has yet to surrender its final breath to the almighty iPod.

Using a new metal that is stronger than steel but more malleable than plastic — called bulk metallic glass — Yale engineers have developed a process that will transform the manufacturing process of nano-devices — from computer memory to CDs and DVDs.

“This is a manufacturing technique that would work with incredibly small structures,” said Jack Harris, professor of physics and author on the study, “Structures that are only a few atoms in size.”

While pure metals have ordered, crystalline lattices, metallic glasses are amorphous combinations of different pure metals which are mixed through melting and then solidified via rapid cooling, said senior author Jan Schroers, associate professor of mechanical engineering. The homogenous nature of BMGs prevents their component atoms from coming together in an organized manner, creating a random internal structure that essentially makes the material behave like a liquid, Schroers said. This property — combined with their durability — makes BMGs ideal candidates to create molds that can shape “soft” materials such as CDs and DVDs, postdoctoral fellow Golden Kumar, a co-author on the study, said.

“They combine the good properties of polymers and metals,” he said. “They flow like polymers but they have the strength of metals.”

Normally, CDs and DVDs are able to encode information using a physical pattern of bumps and flat regions on their surface that corresponds to binary code. The physical properties of BMGs enable them to etch a much smaller physical pattern onto a disk surface than metals can, and the newfound materials are much more durable that either semiconductor or silicon devices.

For this reason, BMGs — which enable CDs to store up to 20 times the amount of information they are currently engineered to hold — may soon supplant these more traditional materials, Kumar said.

While scientists have been investigating the properties of BMGs for about a decade, only with this latest research have they been applied practically.

“We’ve finally been able to harness their unusual properties to transform both the process of making molds and producing imprints,” Schroers said.

But the researchers had to overcome an initial hurdle before being able to work with BMGs on the nanoscale. Surfaces of liquid metals like BMGs exhibit antiwetting — weak interactions with various materials to be imprinted, such as other metals or polymers, Kumar said.

A major stepping stone in the study was Kumar’s discovery that altering the ratio of different metallic components of BMGs could potentially improve surface interactions, enabling the researchers to apply their technology on a smaller scale.

Apart from their applications to the semiconductor and computing industries, Kumar said BMGs have potential to be used as metallic implants and stents in the medical field due to their high elasticity.

Looking forward, the researchers said they are working to continue reducing the size of these devices to 1 to 2 nanometers — potentially by utilizing carbon nanotubes rather than silicon molds to pattern and refine metallic glasses, Kumar said. The team is also working on getting BMGs on the market — specifically that of the computing industry, within the next five years, he added.

The study was published in the February 12th of Nature.

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