X-ray photoelectron spectroscopy(XPS) and extended X-ray absorption fine structure(EXAFS) were used to characterize the structure of the mixture of molybdenum oxide and anatase calcined at 723 K. The results indicate that molybdenum oxide can disperse onto the surface of anatase(TiO 2) and the dispersion threshold is 11.2 mg in per gram of MoO 3 or 4.8 Mo atoms/nm 2 TiO 2. When the content of MoO 3 is below the dispersion threshold, MoO 3 species is in highly dispersed state interacting strongly with TiO 2 support and in discrete tetrahedral coordination, [MoO 4], on the surface of TiO 2. When the MoO 3 loading is above this value, MoO 3 exists in both dispersed phase and crystalline phase. MoO 3 in dispersed phase is still a discrete [MoO 4] tetrahedron; MoO 3 in crystal phase is in octahedral coordination.
A flat and compact Al2O3 film of 20urn in thickness was prepared on the substrate of Si wafer by magnetic controlled sputtering Al reaction with O2 in Ar. A small amount of MoO3 was va- porized in vacuum and deposited onto a slot in a covering film on the surface of A12O3 film. The samples were heated in dry or wet N2, O2 and air respectively, characterized by TRSRF, AES, XPS, XRD and SEM to study the surface diffusion of MoO3 on the A12O3 film. The results show that MoO3 can diffuse on the surface of Al2O3 film by heating the samples at 573K or 673K. The diffusion rate increases with the heating temperature. moisture can accelerate the diffusion rate of MoO3 on the surface of Al2O3.
