Ancient goldbeating aids nanomanufacturing

A new solid-state process seeks to precisely compress colloidally synthesised gold nanocrystals for use in nanosensors.

Bridging the gap between ancient arts and modern technology, researchers from the University of South Florida, Clemson University and the University of Illinois at Urbana-Champaign, USA, have discovered that even nanoscopic gold ingots can be compressed into 2D leaf forms using uniaxial compressive stress, replicating the ancient process of goldbeating.

The colloidally synthesised nanoparticles in the form of nanospheres and nanorods are assembled on ultra-smooth and clean silicon substrates. and subsequently transformed into 2D leaf form using a custom-built, hard-contact, compression set-up.

It applies uniaxial compressive stress via direct contact between the top silicon wafer surface and the assembled nanoparticles on the bottom silicon substrate, reports the paper in Pnas Nexus.

To compress the gold, researcher Michael Cai Wang of the University of South Florida says, they have also 'applied atomistic molecular dynamics simulations to understand the precise deformation mechanisms during the compression process. Compared to conventional hydrostatic diamond anvil compression, this new method allows precise uniaxial compression, and is controllable over a much larger millimetre to centimetre scale, thus enabling 2D transformation of arbitrary nanoparticle assemblies'.

The structure and properties of the compressed 2D gold is dependent on the degree of compression, the nanoparticles’ original morphology, size and on-substrate arrangement, and surface/interface properties, etc.

'At such thinness, the crystallographic arrangement may also begin to deviate not only from their intrinsic bulk crystallinity, but also from more symmetric nanoscale geometries (such as nano-spheres and nano-cubes), which has significant ramifications for their multi-physical properties,' adds Wang.

He says this has been achieved because 'existing research on inducing anisotropic morphologies in nanoparticles has primarily centered on bottom-up, multi-step, solution-based chemical techniques. In comparison, our new top-down, solid-state method is based purely on mechanical deformation, and thus highly scalable and generalisable to all types of nanoparticles'.

Wang and his team reportedly came up with this idea by drawing inspiration from the age-old practice of manually flattening gold ingots into incredibly thin sheets and adapted this method to the extreme length scale. This technique allows versatile control to induce anisotropic deformation in a variety of nanoparticles and enables them to further explore their emergent properties.

Gold, especially at the nanoscale, has been instrumental in shaping modern technological innovations across microelectronics and nanomedicine.

Wang envisions that the additional degrees of freedoms afforded by this new solid-state process will enable them to study the emergent properties that accompany 2D transformation of many low-dimensional nanomaterials, such as nanocrystals (metallic, polymeric, or ceramic), with potential applications in optical metamaterials, quantum logic and storage devices, and biochemical sensors.