Stable halogen 2D materials: the case of iodine and astatine.

2020 
Two-dimensional (2D) materials have wide applications towards electronic devices, energy storages, and catalysis, et al. So far, most of elemental 2D materials are composed of group IIIA- VA elements. Out of the scope, the orbital hybridization becomes a key factor to determine 2D structure stability. Here we show a sp2d3 hybridization in the outmost electrons with O-shell for Iodine and P-shell for astatine, builds up triangle lattice (delta-type) to form 2D structures-delta-iodiene and delta-astatiene. Each atom is connected by sigma bonds with surrounded 6 atoms. The pi bonds become possible, and band gap approaches zero because of interaction of unpaired single electron to each atom, depending on reducing bond length. By applying compression strain or spin orbit coupling (SOC), the Dirac points or topological nontrivial points can be available in the delta-iodiene and delta-astatiene. Our discovery has paved a new way to construction of 2D materials.
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