Most of the so-called flatlands, the universe of two-dimensional (2-D) materials, is reminiscent of the beds and bowls of porridge sampled by Goldilocks during her short stay at the home of the three bears. Some 2-D materials, like silicene, are unable to remain two-dimensional for very long. Others, like graphene or boron nitride, remain stable but can’t be pressed into service as anything other than metallic conductors or insulators. (Another group of materials tick the stability box and behave as semiconductors, but are not one-atom-thick.)
Now researchers at the University of Kentucky, in collaboration with scientists from Daimler in Germany and the Institute for Electronic Structure and Laser (IESL) in Greece, may have found a formulation that is just right: a 2-D material that is both stable at high temperatures and under mechanical stress and easily fashioned into a semiconductor.
In research described in the journal Physical Review B, Rapid Communications, the researchers discovered that a combination of silicon, boron and nitrogen—all of which are cheap and abundant elements—led to the formation of an extremely stable one-atom-thick material.
In a phone interview, Madhu Menon, the physicist at the University of Kentucky who led the research, said that the stability was created by the fact that silicon and nitrogen form strong double bonds in 2-D form. This stands in contrast to silicene, the two-dimensional form of silicon.
“Silicene is not stable because the silicon atoms do not like to stay as a two-dimensional system,” Menon told IEEE Spectrum. “Silicon likes to have more than three neighbors, so that is why the surface gets puckered. And if you wait long enough, it will go into its 3-D silicon form.”
He added: “This proposed material is quite unique. The double bond between the silicon and nitrogen that leads to its stability in 2-D form was quite a revelation for me. This is unusual for this to happen.”
In the video below, Menon describes the new material and its potential electronic applications.
This new material is like graphene in that it too is a metallic conductor and must be functionalized in order to behave as a semiconductor. However, because its surface is made up of silicon atoms, it’s possible to functionalize the surface to gain a band gap. But with graphene, you cannot easily dope the surface but only the edges—a more complicated and expensive process.
One of the more interesting properties of the proposed silicon-boron-nitrogen material, according to Menon, is that when it is made into nanotubes it always acts as a metallic conductor. Nanotubes made from graphene can be semiconductors or metallic conductors. The prospect of having a material that will consistently form microscopic one-dimensional conductors is very attractive for electronic applications that depend on the availability of conducting channels.
Menon and his colleagues are eager to make the material in the lab, but they will need additional funding to proceed with that work. In the meantime, Menon will continue to characterize the material in simulations, examining its thermal properties and figuring out whether it can form n-type or p-type semiconductors.