Sci. Adv. 4, e1701373 (2018)

The fast-growing family of 2D materials span the entire range of electronic classes including insulators, semiconductors, magnets and superconductors. However, examples of stable and readily available 2D metals are still sparse. Now, Kochat and colleagues report an exfoliation method to obtain atomically thin metallic gallenene from the molten phase of bulk gallium.

In the so-called solid–melt exfoliation process, a liquid gallium droplet is brought into contact with a Si/SiO2 substrate that provides sufficient stabilization for the formation of gallenene. Structural analysis shows that the exfoliated 2D material can be stabilized on the substrate in two distinct crystallographic orientations and is four to six layers thick. Gallenene behaves as a metal with a low thermal conductivity and shows a strong chemical interaction with its substrate. The latter implies that its fundamental electronic properties can be readily tuned by changing the substrate material. In particular, the authors show that gallenene creates a good 2D contact with MoS2 by inducing the MoS2 to transform from a semiconductor to a metal. The solid–melt exfoliation technique is not limited to gallenene and could be used to exfoliate other 2D materials from low-melting pure metals and alloys.

https://doi.org/10.1126/sciadv.1701373