Silicene discovery: from massively parallel nano-ribbons to two-dimensional sheets
Guy Le Lay
CINaM-CNRS, Campus de Luminy, Case 913, F-13288 Marseille Cedex 09, France

Silicene [1], the alternative of graphene for silicon, has been theoretically conjectured recently [2]. Its synthesis has just been reported [3]: silicon deposition onto Ag(110) surfaces reveals the formation of silicon nano-ribbons (NRs) [4], in a massively parallel arrangement along the [-110] direction. Their atomic geometry was derived by high-resolution STM images showing a honeycomb arrangement, i.e., a silicene-like structure, further supported by theoretical calculations [5,6].
These one-dimensional (1D) silicene NR’s, showing quantized/edge states in STS imaging [7], self-assemble by lateral compaction to form a grating with a pitch of ~2 nm covering the entire substrate surface [8]. The band dispersion along the NRs direction reveals, as for graphene, massless Dirac fermions resulting from the 1D projection of π and π* Dirac cones [9].
This points to sp2 hybridization, which is further confirmed
1)by the incidence angle dependence of Electron Energy Loss Spectra near the silicon K absorption edge [10]: the measured anisotropy is very similar to that found for the carbon K edge of HOPG graphite [11],
2)by the strong resistance toward oxidation [12].
Recently, two-dimensional silicene-like sheets have been also obtained in Marseille upon Si deposition onto Ag(111) [13].
Finally, the implications of these novel results for new physics and applications will be discussed.

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[13] P. Vogt et al., in preparation