Dear Mr. Frederick AF, 

As per your information, you are facing problem with MoS2 Growth at ~800oC, the base Graphene layer is etched off by precursor and carrier inert gasses.

According to recently published article by Mrk C Hersam. et.al  the partial pressure at time of MoS2 growth should be constant as  45-50mTorr. To get damaged free CVD Graphene over Si/SiO2. It is preferred to synthesis over sputtered Cu(30-200nm) film over Si/SiO2 to get transfer-free high quality Few layer Graphene(FGL) film. The FGL/Si/SiO2 would be annealed at 170oC in vacuum to increase adhesiveness at interface. For MoS2 growth the carrier gas flow should be as low as 20 sccm (can be depend upon the diameter of CVD furnace) to save Graphene film from etching at 800 oC

Kindly check the article attached here:

"Rotationally Commensurate Growth of MoS2 on Epitaxial Graphene Xiaolong Liu , Itamar Balla , Hadallia Bergeron , Gavin P. Campbel , Michael J. Bedzyk , and Mark C. Hersam"

Thank you Mr Mohammad.  I will.read the attached paper and try your suggestion.