Chemical reactivity at buried-interfaces: I. Iron on stoichiometric molybdenite

Abstract

Interfacial and surface reactions between stoichiometric single crystals of molybdenite and iron were studied as a function of iron overlayer thickness and annealing temperature. At room temperature, iron was deposited as a relatively contiguous film on the basal plane of molybdenite. Annealing in UHV caused (i) iron to agglomerate into discrete particles and (ii) sulfur to transfer from the molybdenite basal plane to the iron surface. Annealing above 923 K caused the adsorbed sulfur to desorb or transfer back to the molybdenite and permitted some iron to migrate within the MoS 2 crystal structure forming subsurface layers of FeMo 2S 4. The ĉ-axis of the FeMo 2S 4 was oriented parallel to th of MoS 2. Annealing to 1123 K did not increase the fraction of FeMo 2S 4 suggesting that a limited number of defects in the molybdenite crystal provided pathways for the diffusion and reaction of iron. The effects of higher defect densities and excess sulfur within the molybdenite are discussed in Part II of this study. The above noted findings have implications in the fields of tribology and catalysis where interactions between iron and molybdenite determine adhesion/wear characteristics and/or catalytic activity/selectivity, respectively.