Improving Sensing of Sulfur-Containing Gas Molecules with ZnO Monolayers by Implanting Dopants and Defects

Two-dimensional ZnO materials are proposed for use in nanosensors and their ability to adsorb and detect toxic H2S and SO2 gases are compared. Graphene-like, two-dimensional ZnO monolayer (ZnO-ML) materials are considered that are doped with B, C, N, or S atoms or have Zn or O vacancies. In its pristine form, a ZnO-ML binds the two gases weakly, with binding energies of −0.33 eV and −0.67 eV for H2S and SO2, respectively. However, the presence of defects or the substitution of a Zn or O atom with heteroatoms was found to result in significant increases in the adsorption energy, resulting in a binding energy of up to −3.67 for H2S on a ZnO-ML with a Zn vacancy and −5.15 eV for SO2 on a C-doped ZnO-ML. The H2S molecule is observed to undergo dissociative adsorption on these substituted monolayers, which makes the materials unsuitable as reusable H2S sensors. However, SO2 does not dissociate in any of the cases studied. On SO2 adsorption, significant changes in the conductivity of the ZnO-ML that has an O vacancy occurs, observed as a reduction in the band gap. We also find a reduction in the band gap for S-doped ZnO when SO2 is adsorbed. In both cases, this is coupled with a value of the adsorption energy of about −1 eV, making them suitable for a reusable sensor for SO2.