Atomic force microscopy images of 2D gallium phosphate and piezoelectric measurements at varying applied voltages. Image: FLEET.
Atomic force microscopy images of 2D gallium phosphate and piezoelectric measurements at varying applied voltages. Image: FLEET.

Researchers in Australia have developed a revolutionary method for 'printing' large-scale sheets of a two-dimensional (2D) piezoelectric material, opening new opportunities for piezo-sensors and energy harvesting. Importantly, the inexpensive process, reported in a paper in Nature Communications, should allow the integration of piezoelectric components directly onto silicon chips.

Piezoelectric materials can convert applied mechanical force or strain into electrical energy. Such materials form the basis of sound and pressure sensors, embedded devices that are powered by vibration or bending, and even the simple 'piezo' lighter used for gas BBQs and stovetops.

Until now, however, no 2D piezoelectric material has been manufactured in large sheets, making it impossible to integrate into silicon chips or use in large-scale surface manufacturing. This limitation meant that piezo accelerometer devices – such as vehicle air bag triggers or the devices that recognize orientation changes in mobile phones – have required separate, expensive components to be embedded onto silicon substrates, adding significant manufacturing costs.

Now, researchers with the Australian Research Council’s Centre of Excellence in Future Low-Energy Electronics Technologies (FLEET), based at RMIT University in Melbourne, have demonstrated a method for producing large-scale 2D gallium phosphate (GaPO4) sheets. This method will allow 2D gallium phosphate, an important piezoelectric material commonly used in pressure sensors and microgram-scale mass measurement, to be formed at large scales in low-cost, low-temperature manufacturing processes onto silicon substrates, or any other surface.

The method involves exfoliating gallium oxide from the surface of liquid gallium, made possible by the lack of affinity between the oxide and the bulk of the liquid metal. The gallium oxide film is then ‘printed’ onto a substrate and transformed into 2D GaPO4 via exposure to phosphate vapor.

"As so often in science, this work builds on past successes," explains lead researcher Kourosh Kalantar-Zadeh. "We adopted the liquid-metal material deposition technique we developed recently to create 2D films of GaPO4 through an easy, two-step process." Kalantar-Zadeh, now professor of chemical engineering at the University of New South Wales, led the team that developed the new method while professor of electronic engineering at RMIT University.

The revolutionary new method allows easy, inexpensive growth of large-area (several centimeters), wide-bandgap, 2D GaPO4 nanosheets of unit cell thickness. It is the first demonstration of strong, out-of-plane piezoelectricity of the popular piezoelectric material.

This story is adapted from material from FLEET, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.