  Two-dimensional molybdenum disulphide on graphene grown by chemical vapour
deposition is a promising van der Waals system for applications in
optoelectronics and catalysis. To extend the fundamental understanding of
growth and intrinsic properties of molybdenum disulphide on graphene,
molybdenum disulphide on highly oriented pyrolytic graphite is a suitable model
system. Here we show, experimentally and by density-functional-theory
calculations, that molybdenum disulphide flakes grow in two orientations. One
of the orientations is energetically preferred, the other one is rotated by 30
degree. Because of a high energy barrier confirmed by our calculations both
orientations are stable at room temperature and their switching can only be
forced by external stimuli, i.e. by a scanning tunneling microscope tip.
Combined Kelvin probe microscopy and Raman spectroscopy measurements show that
the flakes with a typical size of a few hundred nanometers are less doped than
the often studied exfoliated molybdenum disulphide single layer.
