Substrate Effects on Growth of MoS2 Film by Laser Physical Vapor Deposition on Sapphire, Si and Graphene (on Cu)

Abstract

Molybdenum disulfide (MoS2) films were deposited on sapphire (0001), Si (001) and graphene on Cu by laser physical vapor deposition at 600°C for different time periods to achieve control of thickness. MoS2 film was found to grow on all the substrates in the (0002) orientation. Films are found to be S-deficient and a free Mo peak was observed in the x-ray diffraction. Raman spectroscopy showed the characteristic peaks of MoS2 film with decreasing separation between the A1g and E 2g 1 peaks for a shorter time of deposition or smaller thickness of the film. MoS2 films on sapphire substrate showed additional peaks due to MoO3 and Mo4O11 phases. Films on Si substrate and graphene on Cu contained only the characteristic peaks. MoS2 films on graphene suppressed the graphene peak as a result of large fluorescence background in the Raman spectrum. Interfacial effects and the presence of an oxygen impurity are considered responsible for the large fluorescence background in the Raman spectrum. X-ray photoelectron spectroscopy indicated substrate interaction with the films on sapphire and Si. Coverage of the film on the substrates is uniform with uniform distribution of the Mo and S as evidenced from the x-ray maps. Atomic force microscopy image revealed the surface of the film on sapphire to be very smooth. Electrical conductance measurements showed the MoS2 film on sapphire is semiconducting but with much lower activation energy compared to the bandgap. The presence of excess Mo in the film is considered responsible for the lower activation energy.