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 ZnOML. 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 Sdoped 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.