  Transition Metal Dichalcogenides (TMD) are layered materials obtained by
stacking two-dimensional sheets weakly bonded by van der Waals interactions. In
bulk TMD, band dispersions are observed in the direction normal to the sheet
plane (z-direction) due to the hybridization of out-of-plane orbitals but no
kz-dispersion is expected at the single-layer limit. Using angle-resolved
photoemission spectroscopy, we precisely address the two-dimensional to
three-dimensional crossover of the electronic band structure of epitaxial
WSe$_2$ thin films. Increasing number of discrete electronic states appears in
given kz-ranges while increasing the number of layers. The continuous bulk
dispersion is nearly retrieved for 6-sheet films. These results are reproduced
by calculations going from a relatively simple tight-binding model to a
sophisticated KKR-Green's function calculation. This two-dimensional system is
hence used as a benchmark to compare different theoretical approaches.
