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

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.

Single-Element 2D Materials beyond Graphene: Methods of Epitaxial Synthesis

“…Finally, quite recently, there was a report on the heteroepitaxial growth of the last single-element 2D-material of group IIIA, thallene [73]. As far as we know, as of early 2022, this work is the only article dedicated to thallene.…”

“…The last stage was the annealing of the system at the temperature of 375 • C for 5 min in order to leave 2/3 ML of thallium on the NiSi 2 surface. As a result, a Tl/NiSi 2 /Si(111) sample with a thallene monolayer was obtained [73].…”

“…The distance between boron atoms in the borophene structure is about 0.17 nm [2,59]. Borophene, aluminene, gallenene, indiene, and thallene-representatives of group IIIA transgraphenes-can have various modifications of the crystal lattice [59][60][61][62][63][64][65][66][67][68][69][70][71][72][73].…”

“…The last representative of group IIIA transgraphenes, thallene, was synthesized in 2020 on the NiSi 2 /Si(111) surface [73] in the form of a flat honeycomb structure similar to graphene (Figure 2a), with parameter l ≈ 0.38 nm. Density functional theory calculations predict for a free-standing thallene l = 0.3 nm (Table 2).…”

Rashba Effect and Raman Spectra of Tl$_2$O/PtS$_2$ Heterostructure

“…While 2D Tl 2 O still awaits experimental realization, a 2D thallene was recently fabricated on NiSi 2 /Si(111) substrate experiencing a strong tensile strain due to the large lattice mismatch. 35 It is therefore extremely critical to select an appropriate material capable to host Tl 2 O in its most stable form (without causing detrimental effects to its structure and properties) and permits usage in advanced applications.…”