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Flat gallium joins roster of new 2-D materials

Credit: Ajayan Research Group/Rice University

Scientists at Rice University and the Indian Institute of Science, Bangalore, have discovered a method to make atomically flat gallium that shows promise for nanoscale electronics.

Materials scientist Pulickel Ajayan and colleagues in India have been able to create two-dimensional gallenene, a thin film of conductive material that is to gallium what graphene is to carbon.

Extracted into a two-dimensional form, the material appears to have an affinity for binding with semiconductors like silicon and could, according to researchers, make an efficient metal contact in two-dimensional electronic devices.

With a low melting point gallium, unlike graphene and many other 2-D structures, cannot yet be grown with vapor phase deposition methods. Gallium also tends to oxidise quickly. And while early samples of graphene were removed from graphite with adhesive tape, the bonds between gallium layers are too strong for such a simple approach.

As a result the Rice team led by co-authors Vidya Kochat, a former postdoctoral researcher at Rice, and Atanu Samanta, a student at the Indian Institute of Science, used heat instead of force.

The researchers have worked their way down from bulk gallium by heating it to 29.70C, just below the element's melting point but hot enough to allow gallium to drip onto a glass slide. As a drop cooled, the researchers pressed a flat piece of silicon dioxide on top to lift just a few flat layers of gallenene.

They successfully exfoliated gallenene onto other substrates, including gallium nitride, gallium arsenide, silicone and nickel. That allowed them to confirm that particular gallenene-substrate combinations have different electronic properties and to suggest that these properties can be tuned for applications.

Gallenene's plasmonic and other properties are being investigated, according to Ajayan. "Near 2-D metals are difficult to extract, since these are mostly high-strength, nonlayered structures, so gallenene is an exception that could bridge the need for metals in the 2-D world," he said.

Image: Model of the side structure of gallenene after exfoliation from bulk gallium.

Neil Tyler

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