In a hot new paper published in today’s Nature entitled Nanomoulding with amorphous metals, Yale researchers Golden Kumar, Hong X. Tang and Jan Schroers “demonstrate direct nanopatterning of metallic glasses by hot embossing, generating feature sizes as small as 13 nm.” Here’s a short description of their work, in their own words:
Nanoimprinting promises low-cost fabrication of micro- and nano-devices by embossing features from a hard mould onto thermoplastic materials, typically polymers with low glass transition temperature1. The success and proliferation of such methods critically rely on the manufacturing of robust and durable master moulds2. Silicon-based moulds are brittle3 and have limited longevity4. Metal moulds are stronger than semiconductors, but patterning of metals on the nanometre scale is limited by their finite grain size. Amorphous metals (metallic glasses) exhibit superior mechanical properties and are intrinsically free from grain size limitations.
Here we demonstrate direct nanopatterning of metallic glasses by hot embossing, generating feature sizes as small as 13 nm. After subsequently crystallizing the as-formed metallic glass mould, we show that another amorphous sample of the same alloy can be formed on the crystallized mould. In addition, metallic glass replicas can also be used as moulds for polymers or other metallic glasses with lower softening temperatures. Using this ‘spawning’ process, we can massively replicate patterned surfaces through direct moulding without using conventional lithography. We anticipate that our findings will catalyse the development of micro- and nanoscale metallic glass applications that capitalize on the outstanding mechanical properties, microstructural homogeneity and isotropy, and ease of thermoplastic forming exhibited by these materials5, 6, 7.
The paper may be behind a paywall, but Yale has “issued a press release on the work of Kumar et al:
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.
I know quite a few readers of Materialia Indica working on bulk metallic glasses, their properties and applications, so I’ll wait for them to add their perspectives on this work. For the mement, let me leave you with a link to a video demonstration of unusual mechanical properties of bulk metallic glasses (vis a vis crystalline metals and alloys).