Stress-driven structural and bond reconstruction in 2D ferromagnetic semiconductor VSe2

Abstract

Two-dimensional (2D) semiconducting transition metal dichalcogenides can be used to make high-performance electronic, spintronic, and optoelectronic devices. Recently, room-temperature ferromagnetism and semiconduction in 2D VSe2 nanoflakes were attributed to the stable 2H-phase of VSe2 in the 2D limit. Here, our first-principles investigation shows that a metastable semiconducting H′ phase can be formed from the H VSe2 monolayer through uniaxial stress or uniaxial strain. The calculated phonon spectra indicate the dynamical stability of the metastable H′ VSe2 and the path of phase switching between the H and H′ VSe2 phases is calculated. For the uniaxial stress (or strain) scheme, the H′ phase can become lower in total energy than the H phase at a transition point. The H′ phase has stronger ferromagnetism and its Curier temperature can be enhanced by applying uniaxial stress or strain. Applying uniaxial stress or strain can substantially change spin-resolved electronic structures, energy band edges, and effective carrier masses for both of the H and H′ phases, and can cause some flat bands near the band edges in the strained H′ phase. Further analysis indicates that one of the Se–Se bonds in the H′ phase can be shortened by 19% and the related Se–V–Se bond angles are reduced by 23% with respect to those of the H phase, which is believed to increase the Se–Se covalence feature and reduce the valence of the nearby V atoms. Therefore, structural and bond reconstruction can be realized by applying uniaxial stress in such 2D ferromagnetic semiconductors for potential spintronic and optoelectronic applications.