Oxygen deficient α-MoO3 with enhanced adsorption and state-quenching of H2O for gas sensing: a DFT study

Abstract

Semiconducting oxides with reducible cations are ideal platforms for various functional applications in nanoelectronics and catalysts. Here we report an ultrathin monolayer α-MoO₃ in which tunable electronic properties and different gas adsorbing behaviors are achieved upon the introduction of oxygen vacancies (V_O). A unique property of α-MoO₃ is that it contains three different types of oxygen atoms occupying three Wyckoff sites that are absent in other low-dimensional oxides and provides rich electronic hybridized states. The presence of V_O triggers an intermediate state in the gap at ∼0.59 eV below the conduction band minimum and reduces the work function dramatically, together with new excitations at the near infrared. The realigned Fermi level associated with the dangling state of V_O reduces the neighboring Mo atoms and affects gas adsorption thereafter. The binding energy of H₂O molecules above V_O is 2.5 times, up to −0.75 eV compared with that of a perfect lattice site and trends for the transfer of electrons are also reversed. The latter is related to the shallow localized state in the band gap due to H₂O adsorbed above perfect MoO₃ which becomes quenched upon adsorbing at the V_O site. The rich in-gap defective states in oxygen deficient MoO₃, broadening the light absorption and promoting the uptake of water, are conducive to the application of α-MoO₃ for optoelectronics, photothermal therapy, and sensing of moisture.