Free-standing electronic character of monolayer MoS2 in van der Waals epitaxy.

We have evaluated as-grown MoS2 crystals, epitaxially grown on a monocrystalline sapphire by chemical vapor deposition (CVD), with direct electronic band-structure measurements by energy-filtered k-space photoelectron emission microscopy performed with a conventional laboratory vacuum ultraviolet He I light source under off-normal illumination. The valence states of the epitaxial MoS2 were mapped in momentum space down to 7 eV below the Fermi level. Despite the high nucleation density within the imaged area, the CVD MoS2 possesses an electronic structure similar to the free-standing monolayer MoS2 single crystal, and it exhibits hole effective masses of 2.41±0.05m0, and 0.81±0.05m0, respectively, at Γ and K high-symmetry points that are consistent with the van der Waals epitaxial growth mechanism. This demonstrates the excellent ability of the MoS2 CVD on sapphire to yield a highly aligned growth of well-stitched grains through epitaxial registry with a strongly preferred crystallographic orientation. [ABSTRACT FROM AUTHOR]