Epitaxial silicene: can it be strongly strained?

The possibility to synthesize honeycomb silicene has recently been demonstrated upon providing compelling evidence through the combination of complementary experimental results and density functional theory calculations (Vogt et al 2012 Phys. Rev. Lett. 108 155501). In this case silicene is grown on Ag(1 1 1) substrates and shows a nearest neighbour distance of two Si atoms of similar to 0.23 nm in agreement with theoretical results for free-standing silicene. In another publication from another group of authors a different silicene arrangement has been claimed previously, where the silicene sheet is strongly compressed with a Si-Si distance amounting to only 0.19 nm (Lalmi et al 2010 Appl. Phys. Lett. 97 223109). This has led to the fundamental question whether silicene could support such a large compressive strain. We will show that the apparent contradictions in the literature can be explained based on a thorough analysis, which reveals that the pure Ag(1 1 1) surface can mimic a honeycomb structure, which could easily be misinterpreted as a strained silicene layer. Our discussion will show that there is no evidence for the existence of such strong compressively strained silicene layers.