First-principles study of sulfur atom doping and adsorption on α–Fe₂O₃ (0001) film

Using the spin-polarized density functional theory (DFT) and the DFT+U method, the geometric and electronic properties of the hematite α–Fe₂O₃ (0001) film with the sulfur (S) atom doping and adsorption have been investigated systematically. The most stable hematite α–Fe₂O₃ (0001) film with an anti-ferromagnetic arrangement is identified. For the study of sulfur adsorption on the film, the S adatom prefers to bond with three O atoms, in the center of a triangle formed by the three O atoms. The S acts as a cation at this site. The sulfur adsorption has introduced two gap states, in addition to the unoccupied surface states. Furthermore, with the most stable S-adsorption configuration, the diffusion of the S adatom from the surface to the inside is searched and the transition state along the minimum-energy pathway is also evaluated. For S-doping in the film, it is found that S substitution of O in the top layer is energetically favored than that in the deeper layer. It shows that the value of the band gap is reduced to ∼1.26 eV from ∼1.43 eV of the clean film. The formation energy of S substitution of O in the film is also obtained.