Thallene: graphene-like honeycomb lattice of Tl atoms frozen on single-layer NiSi2

Abstract

Abstract The post-graphene materials termed also as 2D-Xenes (X = Si, Ge, Sn, Pb, As, Sb or Bi) are atomic-layer sheets comprised of single-element atoms arranged in a honeycomb lattice on a suitable substrate. In the present report, we introduce a new member to the current 2D-Xene family, thallene built of atoms of the Group-III element, thallium (Tl). It is formed when 2/3 monolayer of mobile Tl atoms on a single-layer NiSi2 atop Si(111) substrate crystallizes upon cooling below ∼ 150 K into a 3 × 3 -R30° superstructure with a honeycomb geometry. As compared to the hypothetical free-standing thallene layer, the thallene on the NiSi2/Si(111) substrate experiences a strong tensile strain. It was recognized that though the substrate can virtually tune the thallene into the topological phase, in reality the intrinsic electronic properties of thallene are suppressed due to the hybridization with electrons of the NiSi2/Si(111) substrate.