News and opinions
Bulk metallic glasses break the mold Cordelia Sealy Amorphous metal or bulk metallic glass molds could revolutionize nanoimprinting techniques, according to researchers from Yale University [G. Kumar et al., Nature (2009), doi:10.1038/nature07718]. Nanoimprinting, which employs a mold or stamp to pattern polymers, holds great promise for easy, low-cost fabrication at the nanoscale. But the mold material is critical for the success of the technique. Si molds can be patterned with high levels of detail, but are brittle and not very durable. Conversely, metals — which are very durable — are limited by their grain structure when it comes to ﬁne detail. Bulk metallic glasses do not suffer from these limitations. They are free from grain size limitations and are much stronger than Si. Jan Schroers and his team used hot embossing to pattern metallic glass molds with features as small as 13 nm. The molds can be used to replicate the surface pattern on polymers or even other bulk metallic glasses with lower softening temperatures. ‘‘We have ﬁnally been able to harness the unusual properties [of bulk metallic glasses] to transform both the process of making molds and producing imprints,’’ says Schroers. The molding process in bulk metallic glasses is controlled by capillary forces, which can make the achievement of features less than 100 nm difﬁcult. But the researchers ﬁnd that speciﬁc properties of the metallic glass — namely partial wetting behavior, low viscosity, and a slow crystallization rate at the molding temperature — can get around the problem. The researchers demonstrate the ability to form highaspect-ratio nanostructures and believe the technique could
produce features smaller than 10 nm with the right mold. Lindsay Greer of the University of Cambridge believes that the results open up interesting possibilities for the extension of soft-lithographic techniques to the nanoscale and could represent a new application for metallic glasses. ‘‘This process has the potential to replace several lithographic steps in the production of computer chips,’’ says Schroers. ‘‘We think BMGs will be the buzz-word for the coming decade.’’ Cordelia Sealy has many years’ experience as a scientiﬁc journalist and editor in areas spanning nanotechnology, materials science and engineering, physics and chemistry. She has served as Editor of Materials Today and Nano Today, and more latterly as Managing Editor of both titles. She has also worked in academic publishing as a books acquisitions editor and in business-to-business publishing as a journalist on European Semiconductor. She has a First in Physical Sciences (BSc) from University College London and a DPhil in materials science from the University of Oxford, and is a Member of the Institute of Physics. Cordelia is currently a freelance science writer for her own company, Oxford Science Writing, and News and Opinions Editor for Nano Today.
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1748-0132/$ — see front matter doi: 10.1016/j.nantod.2009.02.003