Electronics could be produced more cheaply and using less energy thanks to research pioneered by chemical engineers at the University of Sydney.
Dr Mohammad Ghasemian said his research involves producing two-dimensional materials – super-thin layers of metal that are mere atoms thick – and other nanostructures.
“They are very small but at the same time have very good performance,” Ghasemian, who is a Research Fellow in the School of Chemical and Biomolecular Engineering at the University of Sydney, explained.
“Unfortunately, the metals for synthesising or producing those kinds of materials are usually complicated and costly. Through our method, we can produce a large number of new materials.”
That method, called liquid metal touch printing, also permits him to control some physical properties of the materials he uses for the structures, such as thickness and dimensions.
“Also, we can induce new properties by doping and adjusting the chemical composition and atomic ratios,” Ghasemian added.
Melting moments
Ghasemian first developed the liquid metal touch printing technique with colleagues at Melbourne’s RMIT University, and he has since sought to refine the process by developing better materials.
His most recent breakthrough on this front is an alloy of tin, zirconium and hafnium with ferroelectric properties that can be used in memory devices, which require large amounts of energy to manufacture and use.
The alloy, crucially, has a much lower melting point than zirconium and hafnium – around 500 °C, rather than 1855 °C for zirconium and 2227 for hafnium.
“The advantage is that it works at low temperature,” Ghasemian explained. “For some metals that are very useful, the melting point is too high, and we cannot use those on the metals at room temperature – or at least at lab-scale temperature.”
The tin-zirconium-hafnium alloy could be melted using common lab equipment such as a hotplate, making it much easier to work with.
And while something like gallium, which has a melting point of 30 °C, would be even easier to work with, Ghasemian sought a tin alloy because it was more useful for electronic components.
“When they are melted, I can exfoliate or harvest 2D materials from the surface of the liquid metal – which has never been done before,” he said.
Just a touch
Ghasemian’s process of exfoliation requires first heating the solid alloy to its melting point.
“Then the surface of the metal oxidises immediately upon exposure with air,” he explained. “But the surface of liquid metal – that oxide layer – is atomically thin. Then, that surface can be harvested and be used as a suitable substrate.
“If, for example, we touch the surface of liquid metal – which is oxide – with another oxide substrate like silicon oxide, then the oxide layer from the surface of liquid metal transfers to the substrate.”
Developing the technology involved overcoming other challenges, such as limitations on size.
“For other methods [of producing nanostructures] – for example, for the chemical deposition method – they can easily adjust the dimension of the substrate and the nanostructure,” Ghasemian explained. “But, in our case, the maximum that we can use is the surface area of the liquid metal.
“At the lab scale, we use a very small – even smaller than one centimetre of liquid metal – which means that the 2D material that we harvest is not as large as an industrial one.”
To produce larger, industrial nanostructures would involve regenerating the substrate anew, something the researchers are yet to try.
These difficulties are worth dealing with, however, due to the simplicity of Ghasemian’s process.
“These drawbacks are really minor,” he said. “We do need very high-purity metals; we do not need … complex, complicated and costly procedures and machinery.”
Magnificent materials
Even beyond this most recent technological advance, Ghasemian told create he sees great possibility in the broader field of liquid metals.
“It’s not just about 2D materials or nanostructures; it’s about photocatalysis, it’s about sensing, it’s about composites,” he said. “I think that liquid metals are really extraordinary, and they have a large capacity and potential to be used in industry.
“And that’s what I try to do: to make industry in Australia familiar with liquid metal’s fantastic properties.”