  The electronic structure of epitaxial single-layer MoS$_2$ on Au(111) is
investigated by angle-resolved photoemission spectroscopy, scanning tunnelling
spectroscopy, and first principles calculations. While the band dispersion of
the supported single-layer is close to a free-standing layer in the vicinity of
the valence band maximum at $\bar{K}$ and the calculated electronic band gap on
Au(111) is similar to that calculated for the free-standing layer, significant
modifications to the band structure are observed at other points of the
two-dimensional Brillouin zone: At $\bar{\Gamma}$, the valence band maximum has
a significantly higher binding energy than in the free MoS$_2$ layer and the
expected spin-degeneracy of the uppermost valence band at the $\bar{M}$ point
cannot be observed. These band structure changes are reproduced by the
calculations and can be explained by the detailed interaction of the
out-of-plane MoS$_2$ orbitals with the substrate.
