Paper 2D+EM+MI+MN+NS+SS+TF-ThA8
The Symmetry Dependent Band Structure of MoS₂

Thursday, November 13, 2014, 4:40 pm, Room 310

We will present results of density functional theory (DFT) based calculations of symmetry dependent band structures of single crystal MoS₂(0001) surface together with symmetry-polarized angle resolved photoemission spectroscopy (ARPES) derived experimental band structure. The good agreement of the DFT band structure with the experimentally derived bands with even and odd symmetries, attests to the reliability of the results. We performed ARPES at the Hiroshima Synchrotron, determining the MoS₂ band structure separately for both p-, and s-, polarized to distinguish even and odd symmetry, and the experimentally determined dispersion, in accordance with expectations and experimental confirmation of C_3v symmetry, argues in favor of an experimental band structure obtained from single domains. The comparison of theory and experiment provides strong indications that the bands at the top of the valence band are dominated by Mo 4d states. These states and indeed placement of the valence band can be perturbed by adsorbates. Indeed, we find that, under the effect of Na adsorption, the changing placement of the valence band structure of MoS₂ clearly indicate the Na atoms donate electrons to MoS₂ and that the Fermi energy level shifts as much as 0.5 eV with respect to the top of MoS₂’s valance band. Surprisingly, Na adsorption does not perturb the MoS₂ band dispersion significantly. We will discuss these results in the light of those obtained for single layer MoS₂ for insights and clarity.