Controlling the electronic and optical properties of HfS 2 mono-layers via lanthanide substitutional doping: a DFT+ U study.

Two dimensional HfS 2 is a material with potential applications in the field of photo-catalysis and advanced solid state devices. Density functional theory with the Hubbard U parameter (DFT+ U ) calculations were carried out to investigate the structural, electronic and optical properties of lanthanide dopant atoms (LN = La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) in the HfS 2 mono-layer. The calculated electronic band gap for a pristine HfS 2 mono-layer is 1.30 eV with a non-magnetic ground state. The dopant substitutional energies under both Hf-rich and S-rich conditions were evaluated, with the S-rich condition for the dopant atoms being negative. This implies that the incorporation of these LN dopant atoms in the HfS 2 is feasible and experimental realization possible. The introduction of LN dopant atoms in the HfS 2 mono-layer resulted in a significant change of the material properties. We found that the presence of LN dopant atoms in the HfS 2 mono-layer significantly alters its electronic ground states by introducing defect states as well as changes in the overall density of states profile resulting in a metallic ground state for the doped mono-layers. The doped mono-layers are all magnetic with the exception of La and Lu dopant atoms. We found that LN dopant atoms in the HfS 2 mono-layer influence the absorption and reflectivity spectra with the introduction of states in the lower frequency range (<1.30 eV). Furthermore, we showed that the applicability of doped HfS 2 mono-layers as photo-catalysts is very different compared with the pristine HfS 2 mono-layer.