Effect of Cr-doping on the electronic structure and work function of α-Fe₂O₃ thin films

We investigate the effect of Cr-doping on the properties of α-Fe₂O₃(001) thin films with Fe termination using the local density approximation plus a Hubbard U correction. We find that both the doping site and concentration of Cr atoms dramatically affect the electronic structure and work function (W_F) of α-Fe₂O₃ films. The results demonstrate that it is most energetically favorable for Cr atoms to substitute the Fe atoms in the sub-surface of α-Fe₂O₃ thin films. The doping of Cr atoms in the sub-surface not only lowers the band gap of the film but also greatly enhances the work function by 0.9 eV with respect to the pure α-Fe₂O₃ film. The increase of W_F correlates with the reduction of occupied O p_x/p_y states at the top valence band which leads to a decrease of the Fermi energy. As the Cr concentration changes from 4.2% to 16.7%, the W_F firstly increases, and then drops. The W_F reaches a maximum of 6.61 eV for the Cr concentration of 8.3%. These results suggest that doping Cr atoms in a α-Fe₂O₃(001) thin film can increase the corrosion potential and benefits the protection of steel from corrosion.