A first-principles study of a real energetically stable MoN2 nanosheet and its tunable electronic structure

Abstract

Due to their extraordinary electronic and magnetic properties, transition-metal dinitrides (TMDNs) are the rising stars in two-dimensional (2D) layered materials. For MoN₂ nanosheets, the structural stabilities of MoS₂-type geometries are still controversial and all the known nanostructures are energetically unfavorable relative to the Mo bulk and N₂ molecules. In this work, we have computationally discovered a non-MoS₂-type bilayer hexagonal structure (BHS) for the MoN₂ nanosheets. It is found that such BHS-MoN₂ is the lowest-energy structure of the MoN₂ nanosheets, which possess robust dynamical, mechanical, and thermal stabilities. Moreover, it is more favorable than the elementary substances, which confirms that it is the real energetically stable structure. Different from the MoS₂-type MoN₂ nanosheets, the BHS-MoN₂ one is an indirect-band-gap semiconductor, for which the tensile strains would effectively reduce the gap size and cause an indirect-to-quasi-direct band gap transition and a semiconductor-to-metal transition. Tunable ferromagnetism will be induced by hole doping in the BHS-MoN₂ system, which is transformed into a robust half-metal against the strain. Our study demonstrates that the non-MoS₂-type structure will emerge in the TMDN systems, which possess robust structural stabilities and peculiar electronic properties for potential nano-electronics and device applications.