New liquid-metal technique could create flexible, low-energy wearables

10 Jul 2020

Transmission electron microscope image of atomically thin (monolayer) tin-sulphide nanosheet. Image: Fleet

A new study has applied liquid-metal synthesis to piezoelectric materials, which could pave the way for future wearable electronics.

As researchers look at ways to advance the future of flexible, wearable electronics and biosensors, a new technique to synthesise certain materials could be the answer.

Materials such as atomically thin tin-monosulphide (SnS) are already predicted to exhibit inherent flexibility and strong piezoelectric properties, converting mechanical forces or movement into electrical energy. Piezoelectric devices can sense sudden changes in acceleration and are used to trigger vehicle air bags, while more sensitive devices can recognise orientation changes in mobile phones, or form the basis of sound and pressure sensors.

Even more sensitive piezoelectric materials can take advantage of the small voltages generated by extremely small mechanical displacement, vibration, bending or stretching to power miniaturised devices such as biosensors embedded in the human body, removing the need for an external power source.

These impressive properties make materials such as SnS likely candidates for flexible nanogenerators that could be used in wearable electronics or internal, self-powered biosensors. However, this potential use has been impinged by limitations in synthesising large, highly crystalline monolayer tin-monosulphide, with difficulties caused by strong interlayer coupling.

But a new collaborative study between RMIT University and UNSW Sydney published in Nature Communications appears to resolve this issue by applying a new liquid-metal technique developed at RMIT to synthesise the materials.

High durability and flexibility

The unprecedented technique of synthesis used involves the van der Waals exfoliation of a tin sulphide that forms on the surface of tin when it is melted, while exposed to the ambient of hydrogen sulphide gas. The gas breaks down on the interface and sulphurises the surface of the melt to form SnS.

This liquid-metal-based method allows scientists to extract homogenous and large-scale monolayers of SnS with minimal grain boundaries. Furthermore, measurements confirm that the material has exceptional peak values of generated voltage and loading power, as well as high durability and flexibility.

According to the study, the results are a step towards piezoelectric-based, flexible, energy-scavenging wearables, as the synthesised monolayer SnS can be commercially implemented into power-generating nanodevices or transducers harvesting mechanical human movements.

Jenny Darmody is the editor of Silicon Republic