Researchers in Japan have reported successfully producing a single layer of silicon atoms - or silicene - opening a debate about what silicene actually is.
Back in April, a group of researchers in Europe, led by Patrick Vogt, reported "compelling experimental evidence for… two dimensional silicon" in a paper published in Physical Review Letters, the first reported synthesis of the material.
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Silicene is the thinnest possible form of silicon, and if the material can be commercialised, it could mean even smaller electronics. It is the silicon equivalent of graphene, the two-dimensional carbon lattice that has gripped the world of materials science since it was isolated in 2004.
Graphene has a long list of astonishing properties: it has better intrinsic electron mobility than silicon, is so strong you can actually pick up a sheet of single atoms, and has a current density more than a million times that of copper, at room temperature.
Silicene vs graphene
But silicene is potentially even more exciting because it could be more easily compatible with existing silicon-based electronics, which means its benefits could be exploited quicker. Since carbon is right next to silicon on the periodic table, scientists began to wonder if a single layer of silicon atoms might be similarly revolutionary, and so the race to make some was on.
The European research team reported that their silicene behaved just like graphene in a key respect: its electrons behave in a very particular way. They are capable of moving like massless particles, travelling through the lattice at the speed of light, on a range of energy levels that are continuous, rather than discrete. When plotted, this energy continuum is known as a Dirac cone.
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However, the results from Japan, first published on 11 June, do not show the same behaviour. Paola De Padova, a physicist from the Italian National Research Council in Rome, who was involved in the original European study, says the absence of the Dirac cone leaves room for doubt, according to Cosmos Magazine.
Yukiko Yamada-Takamura, senior author of the study and materials scientist at the Japan Advanced Institute of Science and Technology, in Nomi, has cautioned against trying to define silicene too rigidly, too soon. The work is all at a very early stage, she notes.
Where graphene has no band gap, the sample of silicene (if that is what it is) produced in Japan, does. This makes it immediately more suitable for use in developing nano-scale transistors, for example.