Electronic properties of transition metal disulfide MS2 (M = Ti, Zr and Hf) nanosheets from first-principles sulfur K and L2,3 edges studies

The energy loss near edge structure (ELNES) study of transition metal dichalcogenide nanosheets was performed for the first time. In the framework of full potential linearized augmented plane wave method, ELNES spectra of sulfur K and L-2,L-3 edges of the layered TiS2, ZrS2, and HfS2 have been calculated under magic angle conditions, and they have been compared with those of bulks and the existing experimental fine structures. Compared to the bulks, the main spectral features in the sulfur K and L-2,L-3 edges of nanosheets occur at the higher energies, and this can be attributed to the smaller bond lengths in the nanosheets. In addition, there occurs a decrease in the energy difference associated with the t(2g)-eg. splitting in the sulfur K edges of the nanosheets, and this can be used as a fingerprint of nanosheets. The band widths of d states in all nanosheets are larger than those in the bulks. Sulfur K edges in nanosheets include some main features originated from the electron transition to the p states hybridized with d-like states. This mixture indicates the strong covalent bonding between the transition metal and the sulfur atoms. From 10 eV beyond the onset, the spectral features can be attributed to the transition metal d states mixed with sp states.