Oxygen deficient α-MoO 3 with enhanced adsorption and state-quenching of H 2 O for gas sensing: a DFT study

Semiconducting oxides with reducible cations are ideal platforms for various functional applications in nanoelectronics and catalysts. Here we report an ultrathin monolayer α-MoO 3 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-MoO 3 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 H 2 O 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 H 2 O adsorbed above perfect MoO 3 which becomes quenched upon adsorbing at the V O site. The rich in-gap defective states in oxygen deficient MoO 3 , broadening the light absorption and promoting the uptake of water, are conducive to the application of α-MoO 3 for optoelectronics, photothermal therapy, and sensing of moisture.