▎ 摘　　要

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,thallenebuilt of atoms of the Group-III element, thallium (Tl). It is formed when 2/3 monolayer of mobile Tl atoms on a single-layer NiSi(2)atop Si(111) substrate crystallizes upon cooling below similar to 150 K into root 3 x root 3-R30 degrees 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.