Unlike graphene, the hexagonal arrays of silicon atoms in silicene are slightly kinked, creating a slightly more complex surface.
Since the isolation of graphene, a carbon layer one atom thick, researchers have developed a number of other two-dimensional materials. (Yes, they really are three-dimensional; it’s just one of the dimensions that is only an atom thick and therefore negligible.) Knowledge of the periodic table would suggest that elements from the same column as carbon would have similar chemical properties, and therefore excellent are candidates for forming two-dimensional plates. So why hasn’t more been done with silicon, the next element in the column of carbon?
People to have actually made silicene, the silicon version of graphene. But they only managed to make small pieces of it on silver surfaces; under almost all other conditions it reacts quickly with the oxygen in the air and decomposes.
On Monday, however, researchers announced that they had succeeded in making the first device – a field-effect transistor – using silicene. Because interactions with silver protected the silicone sheet, the authors fabricated a large sheet on top of a thin silver surface. They then covered this with aluminum oxide, which also protected the silicene. At this point they can etch away some of the aluminum and use the remaining metal as source and drain contacts. By depositing the aluminum oxide on a silicon dioxide surface, the resulting device acted as a field-effect transistor.
This allowed them to examine the flow of electrons through the silicene, which turned out to be… disappointing. While theoretical predictions had suggested electron mobilities were consistent with what is seen in graphene, silicene’s device saw mobilities about ten times smaller than expected. The authors aren’t sure why this is – whether it’s silicene itself or just their manufacturing techniques isn’t clear.
But now that we know how to make some of them, it should be possible to study their properties more thoroughly. Because silicon has a larger and more complex electronic structure than carbon, silicene is thought to be easily manipulated through chemical reactions or simply placing other materials in close proximity. So it’s possible that further research could make silicene behave more in line with what researchers hoped for.
Nature Nanotechnology2014. DOI: 10.1038/NNANO.2014.325 (About DOIs).