Silicene: It could be the new graphene

Single-layer sheets of silicon might have electronic applications

The hottest celebrity in the world of nanomaterials may soon face a new rival. Inspired by the Nobel Prize-winning creation of the carbon material known as graphene, physicists have now created atom-thin sheets of carbon’s big brother, silicon.

ONE-ATOM LAYER Silicon atoms (bright spots) in a honeycomb pattern are a new type of material known as silicene. Bernard Aufray / CNRS, Hamid Oughaddou / University of Cergy Pontoise

THINK THIN Calculations reveal the structure of silicene nanoribbons, flat strips of silicon atoms (white) arranged in hexagons. A. Kara / University of Central Florida

Silicon shares many properties with carbon, which sits just above silicon on the periodic table. In 2007 Lok Lew Yan Voon and then-graduate student Gian Guzmán-Verri of Wright State University in Dayton, Ohio, proposed that silicon could exist in flat sheets similar to graphene, even though silicon doesn’t naturally form the kind of atomic bonds needed to accomplish this.

They coined the new term for this material: silicene.

“Silicon has the advantage of being more integratable in today’s electronics,” said Antoine Fleurence, a physicist at the Japan Advanced Institute of Science and Technology in Ishikawa. The semiconductor industry has spent decades building the infrastructure needed to manipulate silicon to create the chips that run modern electronics.

Speaking March 24 at a meeting in Dallas of the American Physical Society, Fleurence described a new recipe for making silicene. He and his Japanese colleagues grew a thin layer of silicon on top of the ceramic material zirconium diboride. X-rays shined on this thin layer of silicon revealed a honeycomb of hexagons similar to the structure of graphene.

This structure looks familiar to Guy Le Lay, a physicist at the University of Provence in Marseille, France. Last year, he created the first-ever silicene ribbons. Le Lay described these 1.6-nanometer wide stripes of honeycombed atoms, grown on top of silver, in the June 28 Applied Physics Letters.

“These ribbons can be more than a hundred nanometers long, perhaps micrometers,” Le Lay says.

New data from Le Lay’s group, also presented at the physical society meeting, suggests that silicene and graphene share not only a similar structure, but possibly similar electronic properties. Spectroscopic techniques provided evidence that silicene contains a Dirac cone — the entity that intrigues scientists because it allows electrons to move very quickly through graphene, which makes graphene a promising material for flexible electronics.

To prove silicene’s worth, though, Le Lay will need to grow it not on silver — which, as an electrical conductor can interfere with the movement of electrons in the single-layer silicon — but on an insulating material. On an insulating platform, physicists will be able to do direct tests of the material’s electronic properties and experiments to determine whether the same quantum effects that make graphene so remarkable are at work.

For silicene to compete with graphene in the long run, however, the process of creating it must be comparably simple, says Sankar Das Sarma, a physicist who studies graphene at the University of Maryland in College Park. “Graphene really took off in 2004 because it was so easy to make,” he says.

Competing with graphene in this regard won’t be easy: The Russian scientists who first made graphene in 2004 — and won the 2010 Nobel Prize in Physics for their efforts — did it using only a piece of Scotch tape and a chunk of graphite similar to pencil lead.

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