DISTORTED PHASE OF SINGLE LAYER JANUS MoSTe

Recently synthesized monolayer of Janus MoSSe structure has attracted great attention on those out-of-plane anisotropic materials. Here, we investigate the electronic, vibrational, elastic, and piezoelectric properties of two dynamically stable crystal phases of monolayer Janus MoSTe, namely 1H-MoSTe and 1T′-MoSTe. The 1H-MoSTe phase is found to be an indirect band-gap semiconductor while 1T′-MoSTe is predicted as small-gap semiconductor. The calculated Raman spectrum of each structure shows unique character enabling us to clearly distinguish the stable crystal phases via Raman measurements. The systematic piezoelectric stress and strain coefficient analysis reveals that out-of-plane piezoelectricity appears in 1H-MoSTe and the noncentral symmetric 1T′-MoSTe has large piezoelectric coefficients. Static total-energy calculations show clearly that the formation of 1T′-MoSTe is feasible by using 1T′−MoTe2 as a basis monolayer. Therefore, we propose that the Janus MoSTe structure can be fabricated in two dynamically stable phases which possess unique electronic, dynamical, and piezoelectric properties.