2 July 2012
Japanese researchers have produced silicene, a one-atom-thick layer of silicon similar to graphene, that could work in microprocessor chips and could result in the ultimate miniaturisation of devices.
Graphene, a one-atom-thick mesh as well, but made of carbon, is the most conductive known material, and has been touted as the future of computing. It could be a critical component of better batteries, as well as lightweight, flexible devices.
Silicene, which was first reported in April by European researchers, is predicted to share some of the impressive properties of its carbon cousin, graphene. Importantly, however, silicene could be integrated with current silicon-based electronic devices, whereas graphene is incompatible.
Yukiko Yamada-Takamura, senior author of the study published in Physical Review Letters and materials scientist at the Japan Advanced Institute of Science and Technology, in Nomi, describes the material as a “sensation.”
Ultimate miniaturisation possible
“Silicene is the thinnest possible form of silicon, which is the unbeatable, dominant electronic material used in many devices around us. Ultimate miniaturisation of such devices should be achieved if silicene is made available for applications,” said Yamada-Takamura.
But she is also quick to point out that a lot of research questions remain outstanding. “This research is really in its infancy,” she said.
The latest study synthesised silicene with a buckled, bumpy appearance, with silicon atoms at three different heights. With this buckled structure, researchers observed a bandgap – a no-go zone for electrons.
Opens the way to nanoscale semiconductors
The band gap means that nanoscale semiconductors – which are at the heart of almost every electronic device – could be developed, with myriad applications including light emitting diodes and microprocessor chips. To date, researchers been unable to achieve such a bandgap with graphene.
The structure was a consequence of the structure of the substrate on which the researchers synthesised the silicene, the ceramic Zirconium diboride. Yamada-Takamura predicts a large family of silicene may be waiting to be discovered, each material having tunable electronic properties according to the substrate used.
The European researchers who produced silicene in April, however, point out that a key feature is missing. In both graphene and the European silicene, there was something called a ‘Dirac cone’, which allows electrons to behave like massless particles, enabling them to zip through materials at speeds close to the speed of light.
Controversy over claims of silicene
The Dirac cone occurs when the valence band of an atom overlaps with the conduction band of an atom.
The presence or lack of a Dirac cone is the source of some disagreement among researchers as to whether the Japanese study actually synthesised silicene in the first place.
“I think that this study is really nice, because this is the demonstration of the growth of honeycomb silicon on another substrate. However, since no Dirac cone was found one can doubt that this is really silicene,” said Paola De Padova, a physicist from the Italian National Research Council in Rome, who was involved in the original European study.
Yamada-Takamura argues that the definition of silicene should not be narrowed down at this early stage in the research of the material.
“The definition of silicene is not decided, yet. Our finding is particularly interesting in the sense that we demonstrated that the structure of silicene can be modified easily, and we can have an atom thick layer of silicon with different properties,” said Yamada-Takamura.
Hurdles to jump before industrial application
Shu-jen Han, a researcher at the IBM T.J. Watson Research Centre in New York State specialises in nanoelectronics. He’s pragmatic regarding the industrial application of silicene.
“Successful formation of silicene is a major step forward. However, before silicene can be grown or transferred on insulating substrates for electrical measurements, [and] thus be compared to graphene for their transport properties, we will hold our excitement,” said Han.
De Padova concurs there is still much to do, but also thinks there’s plenty to look forward to.
“The determination of the electronic and structural properties of silicene, the capability to growth this new allotrope silicon on several substrates and finally the hard task to isolate the silicene, will open the way forwards a research rich of new discovery,” said De Padova.