  We demonstrate the growth of thin films of molybdenum ditelluride and
molybdenum diselenide on sapphire substrates by molecular beam epitaxy. In-situ
structural and chemical analyses reveal stoichiometric layered film growth with
atomically smooth surface morphologies. Film growth along the (001) direction
is confirmed by X-ray diffraction, and the crystalline nature of growth in the
2H phase is evident from Raman spectroscopy. Transmission electron microscopy
is used to confirm the layered film structure and hexagonal arrangement of
surface atoms. Temperature dependent electrical measurements show an insulating
behavior which agrees well with a two-dimensional variable-range hopping model,
suggesting that transport in these films is dominated by localized
charge-carrier states.
