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

Two-dimensional (2D) materials have wide applications towards electronic devices, energy storages, and catalysis, et al. So far, most of the pure element 2D materials are composed of group IIIA,IVA, and VA elements. Beyond the scope, the orbit hybrid configuration becomes a key fact to influence 2D structure stably. Here we show a sp2d3 hybridization in the outmost electrons with O-shell for Iodine and P-shell for astatine element, builds up triangle configuration (beta-type) to form 2D structures beta-iodiene and beta-astatiene. Each atom is connected by pi bonds, and surrounded by 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 beta-iodiene and beta-astatiene. Our discovery has paved a new way to construction of 2D materials.