In my point of view its quite possible.

Yes. Different materials with honeycomb structure may be stable.

The detailed analysis you may find at:

H. Sahin, S. Cahangirov, M. Topsakal, E. Bekaroglu, E. Akturk, R. T. Senger, and S. Ciraci, Monolayer honeycomb structures of group IV elements and III-V binary compounds, arXiv:0907.4350v1 [cond-mat.mtrl-sci] 2009

In my piont of view, it is nearly impossible.

To my point, it is very possible. Beyond many theoretical prediction, reserachers have obtained silicene nanoribbon on Ag (110) substrate (e.g. Appl. Phys. Lett. 96, 183102 (2010); Appl. Phys. Lett. 96, 261905 (2010)). However, obtaining suspend silicene or high quality silicene samples may be difficult for current technoques.

I consider that carbon crystal should be made clear for the first time, and then we might consider that whether or not the hybridization of Sp2 silicon is able to be considered such as carbon. If the issue is not discussed in term of my suggestion, I believe that the answer will not be sole.

Elena Sheka - Peoples' Friendship University of Russia

sp2-like nanosilicons (fullerenes, nanotubes, and graphene-silicene) cannot exist at ambient conditions since they all are multi-fold radicals. The latter is a direct consequence of a strong correlation of odd electrons of the species.

Experimental reports are full of appealing to silicene, however observed experimentally (Kara, A.; Léandri, C.; Davila, M.T.; de Padova, P.; Ealet, B.; Ougaddou, H.; Aufray, B.; Le Lay, G. arXiv:0811.2611v1 [cond-mat.mtrl-sci], 2008;

Kara, A.; Léandri, C.; Davila, M.T.; de Padova, P.; Ealet, B.; Ougaddou, H.; Aufray, B.; Le Lay, G. J. Supercond. Novel Magn. 2009, 22, 259; Aufray, B.; Kara, A.; Vizzini, S.; Oughaddou, H.; Léandri, C.; Ealet, B.; Le Lay,G. Appl. Phys. Lett. 2010, 96, 183102; Lalmi, B.; Oughaddou, H.; Enriquez, H.; Kara, A.; Vizzini, S.; Ealet, B.; Aufray, B. Appl. Phys. Lett. 2010, 97, 223109; De Padova, P.; Quaresima, C.; Ottaviani, C.; Sheverdyaeva, P. M.; Moras, P.; Carbone, C.; Topwal, D.; Olivieri, B.; Kara, A.; Oughaddou, H.; Aufray, B.; Le Lay, G. Appl. Phys. Lett. 2010, 96, 261905; Fleurence, A.; Friedlein, R.; Wang, Y.; Yamada-Takamura, Y. Symposium on Surface and Nano Science 2011 (SSNS'11)，Shizukuishi, Japan，2011,01,21), is not silicene but one-atom-thick sp3 layers of cubic silicon crystal stabilized by three-neighbor packing within the layer and one additional chemically bonded neighbor below the layer.

A detailed description of the reasons can be found in Sheka, E.F. "May silicene exist?" arXiv:0901.3663v1[cond-mat.mtrl-sci], 2009 and Sheka, E.F. "Why sp2-Like Nanosilicons Should Not Form: Insight from Quantum Chemistry" to be appeared soon in Int. Journ. Quant. Chem. DOI:10.1002/qua.24081.