Electronic Structure of Epitaxial Single-Layer MoS2

The electronic structure of epitaxial single-layer MoS2 on Au(111) is investigated by angle-resolved photoemission spectroscopy. Pristine and potassium-doped layers are studied in order to gain access to the conduction band. The potassium-doped layer is found to have a (1.39 +/- 0.05) eV direct band gap at (K) over bar with the valence band top at (Gamma) over bar having a significantly higher binding energy than at (K) over bar. The moire superstructure of the epitaxial system does not lead to the presence of observable replica bands or minigaps. The degeneracy of the upper valence band at (K) over bar is found to be lifted by the spin-orbit interaction, leading to a splitting of (145 +/- 4) meV. This splitting is anisotropic and in excellent agreement with recent calculations. Finally, it is shown that the potassium doping does not only give rise to a rigid shift of the band structure but also to a distortion, leading to the possibility of band structure engineering in single-layers of transition metal dichalcogenides.