The structural, electronic, elastic, dielectric, dynamical, thermal and optical properties of Janus ZrOS monolayer: A first-principles investigation

Abstract

The geometrical and electronic structures, elastic constants, dielectric permittivities, phonon spectra, thermal properties and optical responses of Janus ZrOS monolayer have been investigated by first-principles calculations. The lattice constant a, Zr–O bond length dZr-O, Zr–S bond length dZr-S, band gap Eg, in-plane stiffness C and Poisson's ratio υ of the Janus ZrOS monolayer are 3.44 Å, 2.15 Å, 2.55 Å, 1.88 eV, 226.35 N/m and 0.26, respectively. A p-d hybridized ionic bond exists in Janus ZrOS monolayer, instead of sp2 hybridized covalent bond in graphene. The larger values of Born effective charges Z11∗(Zr)=Z22∗(Zr)=6.76, Z11∗(O)=Z22∗(O)=-3.58 and Z11∗(S)=Z22∗(S)=-3.18 in-plane than the nominal chemical valences of +4 for Zr and −2 for O and S, reflecting a strong dynamic charge transfer from Zr atom to O and S atoms. After taking into account the Born effective charge and dielectric constant, the three acoustic-active modes (one A1 and two Eu) are degenerated (zero frequency) at Γ point, while a LO-TO splitting is observed for either Raman-active mode Eg or IR-active mode Eu at Γ point. The large dielectric permittivity, mechanical stability and dynamical stability make Janus ZrOS monolayer a promising dielectric material in modern semiconductor industry. The high and sharp absorption peaks in visible and UV light region propose Janus ZrOS monolayer a visible and UV light sensor application.