Nanostructures in nanoseconds

CREDIT card embossing machines could be adapted to make gold nanostructures for mobile phone touch-screens in the blink of an eye.

A pressure-based coalescence method has been demonstrated to create nanorod, nanowire and nanosheet structures 9m times faster than typical chemical methods.

Gold nanostructures have the potential for a wide range of applications due to their unique electrical, conductive and optical properties. Nanowires, for example, underlie the surfaces of touch-screens for mobile phones, sensors, computers, and TVs, while other applications include biosensing, catalysis, imaging and therapeutics.

Chemical methods such as redox reactions are normally used to synthesise a variety of gold nanostructures by growing crystals. While fine control of size and shape can be achieved through techniques such as using organic ligands like alkanethiols to bind to the surface, such techniques can take hours to complete.

A new process called ‘stress-induced fabrication’, developed by researchers at Sandia National Laboratories, US, uses pressure instead of chemicals for synthesis. Through pressure, stress is applied to arrays of commercially-available nanoparticles, which are sandwiched between two flat plates such as silicon wafers or diamond anvils. Resulting components can either be organised during their formation or dispersed in solvents for later assembly.

Lead researcher Hongyou Fan, said: “Under manual or automatically-controlled electromagnetic compression, nanoparticle separation decreases until adjacent particles contact one another. They subsequently consolidate, forming new classes of chemically and mechanically stable 1–3D nanomaterials and nanocomposites that cannot be manufactured by current chemical synthesis methods.

“Precise and systematic tuning of interparticle separation distance is possible, allowing reversible manipulation at the angstrom level to adjust charge and energy coupling for a wide range of applications such as surface plasmon resonance-based sensors, stress sensors, and photovoltaics.”

Another researcher, Jack Wise, added: “The method is 9m times faster than any known chemical method when performed on Sandia’s Veloce pulsed-power machine, which generates pressures of the order of 100,000 atmospheres.”

Three patents have been issued for the technology, and Fan says that they are currently looking for partners to co-develop and license it. He believes that few modifications would be needed to convert embossing and imprinting machines commercially in use for high-throughput fabrication.

Fan said: “This new technology mimics imprint processes already used by manufacturers – only instead of embossing credit cards, we’re using the same type of process to fabricate nano-sized components at ultrashort time scales.”

There are also environmental benefits to using the technique, namely no chemical waste, and a potential materials saving, as only the exact amount needed is placed on a substrate.