Unveiling the Penta-Silicene nature of perfectly aligned single and double strand Si-nanoribbons on Ag(110)

We reveal through extensive DFT calculations, confronted to key experimental facts, the hidden penta-silicene nature of single and double strand chiral Si nanoribbons perfectly aligned on Ag(110) surfaces, that were discovered in 2005, but whose structure remained elusive. We thus simultaneously demonstrate the existence of penta-silicene, a recently conjectured novel pentagonal silicon allotrope, which remained unveiled for 11 years, and which materializes a paradigmatic shift from normal hexagonal silicene.